INHIBITORS OF CELL-CYCLE PROGRESSION AND USES RELATED THERETO

Abstract: The present invention pertains to novel inhibitors of cyclin-dependent kinases (CDKs), particularly CDK/cyclin complexes, which inhibitors can be used to control proliferation and/or differentiation of cells in which the inhibitors are introduced.

Description: Inhibitors of Cell-Cycle Progression, and Uses Related Thereto Background of the Invention The cell division cycle is one of the most fundamental processes in biology which, in multicellular organisms, ensures the controlled generation of cells with specialized functions. Under normal growth conditions, cell proliferation is tightly regulated in response to diverse intra- and extracellular signals. This is achieved by a complex network of proto-oncogenes and tumor-suppressor genes that are components of various signal transduction pathways. Activation of a proto-oncogene(s) and/or a loss of a tumor suppressor gene(s) can lead to the unregulated activity of the cell cycle machinery. This, in turn, will lead to unregulated cell proliferation and to the accumulation of genetic errors which ultimately will result in the development of cancer (Pardee, Science 246:603-608, 1989). In the eukaryotic cell cycle a key role is played by the cyclin-dependent kinases (CDKs). Cdk complexes are formed via the association of a regulatory cyclin subunit and a catalytic kinase subunit. In mammalian cells, the combination of the kinase subunits (such as cdc2, CDK2, CDK4 or CDK6) with a variety of cyclin subunits (such as cyclin A, Bl, B2, DI, D2, D3 or E) results in the assembly of functionally distinct kinase complexes. The coordinated activation of these complexes drives the cells through the cell cycle and ensures the fidelity of the process (Draetta, Trends Biochem. Sci. 15:378-382, 1990; Sherr, Cell 73: 1059-1065, 1993). Each step in the cell cycle is regulated by a distinct and specific cyclin-dependent kinase. For example, complexes of Cdk4 and D-type cyclins govern the early Gl phase of the cell cycle, while the activity of the CDK2/cyclin E complex is rate limiting for the Gl to S-phase transition. The CDK2/cyclin A kinase is required for the progression through S-phase and the cdc2/cyclin B complex controls the entry into M-phase (Sherr, Cell 73:1059- 1065, 1993). The CDK complex activity is regulated by mechanisms such as stimulatory or inhibitory phosphorylations as well as the synthesis and degradation of the kinase and cyclin subunit themselves. Recently, a link has been established between the regulation of the activity of cyclin-dependent kinases and cancer by the discovery of a group of CDK inhibitors including the p27 κ 'Pl, p 2l Wafl/Ci P l an p i6ln 4/MTSl proteins. The activity of p21 Wafl ci P 1 is regulated transcriptionally by DNA damage through the induction of p53, senescence and quiescence (Harper et al., Cell 75:805- 816, 1993). The inhibitory activity of p27 Ki P ! is induced by the negative growth factor TGF-β and by contact inhibition (Polyak et al., Cell 78:66-69, 1994). These proteins, when bound to CDK complexes, inhibit their kinase activity, thereby inhibiting progression through the cell cycle. Although their precise mechanism of action is unknown, it is thought that binding of these inhibitors to the CDK/cyclin complex prevents its activation. Alternatively, these inhibitors may interfere with the interaction of the enzyme with its substrates or its cofactors. While p21 Wafl c 'P 1 and p27 κi P 1 inhibit all the CDK/cyclin complexes tested, pl6lnk4/MTSl 5 pi 5, pi 8 and ρl 9 block exclusively the activity of the CDK4/cyclin D and CDK6/cyclin D complexes in the early Gl phase (Serrano et al., Nature 366:704- 707, 1993), by either preventing the interaction of Cdk4 and Cyclin DI, or indirectly preventing catalysis. As mentioned above, the ρ21 Waf,/c 'P 1 is positively regulated by the tumor suppressor p53 which is mutated in approx. 50% of all human cancers. p2iWafl/Cipl ma y mediate the tumor suppressor activity of p53 at the level of cyclin- dependent kinase activity. pl6 Ink4 MTS 1 is the product of a tumor suppressor gene localized to the 9p21 locus, which is frequently mutated in human cancer cells. Of all the various kinases. the CDK4/cyclin D complexes are known to play an important role in regulating cell cycle progression in early Gl. These complexes function as integrators of various growth factor-induced extracellular signals and as a link between the different signal transduction pathways and other cyclin-dependent kinases. The expression of the cyclin DI positive regulatory subunit, is deregulated by gene translocations, retroviral insertions and amplifications in parathyroid adenomas, lymphomas, esophageal and breast carcinomas. The targeted overexpression of cyclin DI in the mammary epithelium of transgenic mice induces mammary adenomas and adenocarcinomas. This confirms that cyclin DI , when overexpressed, acts as an oncogene (Wang et al., Nature 369:669-671, 1994). These data supports the idea that the lack of functional pl6 Ink4 MTS 1 or the overexpression of cyclin DI leads to the deregulation of CDK4/cyclin DI kinase activity and thereby contribute to uncontrolled cell proliferation. The prominent role of CDK/cyclin kinase complexes, in particular, CDK4/cyclin D kinase complexes, in the induction of cell proliferation and their deregulation in tumors, makes them ideal targets for developing highly specific anti- proliferative agents. Summary of the Invention In one aspect, the present invention relates to a nucleic acid comprising a nucleotide sequence encoding a chimeric polypeptide having at least two CDK-binding motifs derived from different proteins which bind to cyclin dependent kinases (CDKs). The chimeric polypeptide binds to CDKs and inhibits cell-cycle progression. The chimeric polypeptide can be a fusion protein, or can be generated by chemically cross-linking the CDK-binding motifs. In preferred embodiments, at least one of the CDK-binding motifs is a CDK- binding motif of a CDK inhibitor protein, such as an INK4 protein, e.g., pi 5, pi 6, pi 8 and pl9, or a CIP protein, e.g., p21 CIP1 , p27 KIP1 , and p57 K1P2 . However, it will be understood that other CDK-binding motifs may be useful. Indeed, the CDK-binding motif of the INK4 proteins is characteristized by tandemly arranged ankyrin-like sequences, which sequences exist in other proteins and, for those which are able to bind a CDK, can be used to generate the subject chimeric proteins. Likewise, the CDK-binding motif can be a p21/p27 inhibitory domain of a protein which has some homology with the CIP protein family. Exemplary chimeric proteins of the present invention are designated by SEQ ID No. 2, 5 and 7, and are encoded by the CDS's designated in SEQ ID No. 1 , 4 and 6. In preferred embodiments, the CDK-binding motifs of the chimeric protein have different binding specificities, relative to one and other, for cyclin dependent kinases. For instance, the chimeric protein can be generated with a CDK-binding motif from a protein which binds to and inhibits a CDK involved in progression of the cell cycle in G 0 and/or Gi phase, and another CDK-binding motif from a protein which binds to and inhibits a CDK involved in progression of the cell cycle in S, G2 and/or M phase. That is, the chimeric protein will bind to and inhibit a plurality (two or more) of cyclin dependent kinases which are active in different phases of the cell- cycle. In most embodiments, the nucleic acid will further include a transcriptional regulatory sequence for controlling transcription of the nucleotide sequence encoding the chimeric polypeptide, e.g., the transcriptional regulatory sequence is operably linked to a chimeric gene encoding the chimeric polypeptide. For example, the present invention specifically contemplates recombinant transfection systems which include: (i) a gene construct including a nucleic acid encoding a chimeric polypeptide comprising CDK- binding motifs from two or more different proteins which bind to cyclin dependent kinases, and operably linked to a transcriptional regulatory sequence for causing expression of the chimeric polypeptide in eukaryotic cells, and (ii) a gene delivery composition for delivering the gene construct to a cell and causing the cell to be transfected with the gene construct. For example, the gene construct can be derived from a viral vector, such as an adenoviral vector, an adeno-associated viral vector or a retroviral vector. In such embodiments, the gene delivery composition comprises a recombinant viral particle. In other embodiments, the gene construct can be delivered by such means as a liposome or a poly-cationic nucleic acid binding agent. For in vivo delivery to a mammal, such as a human, the gene delivery composition will further include a pharmaceutically acceptable carrier for adminstration to an animal, and, as necessary, will be a sterile preparation and substantially free of pyrogenic agents. The present invention also pertains to preparations of such chimeric polypeptides. e.g., polypeptides which are generated from CDK-binding motifs from two or more different proteins which bind to cyclin dependent kinases. In preferred embodiments, the chimeric polypeptide is formulated in pharmaceutically acceptable carrier for delivery to a mammal. For example, the chimeric polypeptide can be formulated in liposomal preparations. Still another aspect of the present invention related to transgenic animals which have cells harboring a nucleic acid one of the subject fusion proteins. Yet another aspect of the present invention relates to recombinant transfection systems, comprising (i) a first gene construct comprising a coding sequence encoding a inhibitory polypeptide comprising at least one CDK-binding motif for binding and inhibiting activation of a cyclin dependent kinase (cdk), which coding sequence is operably linked to a transcriptional regulatory sequence for causing expression of the first polypeptide in eukaryotic cells, (ii) a second gene construct comprising a coding sequence encoding a endotheliazation polypeptide which promotes endothelialization, and (ii) a gene delivery composition for delivering the gene constructs to a cell and causing the cell to be transfected with the gene construct. In preferred embodiments, the CDK-binding motif is a CDK-binding motif of a CDK inhibitor protein, such as an INK4 protein (e.g., pl5, pl6, pl8 or pl9), or a CIP/KIP protein (e.g., p21 CIP1 , p27 KIP1 , and p57 KIP2 ). In other preferred embodiments, the CDK-binding motif comprises tandemly arranged ankyrin-like sequences, or a p21/p27 inhibitory domain. The inhibitory polypeptide can be a fusion protein comprising CDK-binding motifs from two or more different proteins which bind to cyclin dependent kinases. In preferred embodiments, the endothelization polypeptide stimulates endothelial cell proliferation and/or stimulates migration of endothelial cells to a wound site. For instance, the endothelization polypeptide is selected from the group consisting of angiogenic basic fibroblast growth factors (bFGF), acid fibroblast growth factor (aFGF), vascular endothelial growth factor (VEGF), platelet derived growth factor (PDGF), vascular permeability growth factor (VPF), and transforming growth factor beta (TGF-β). In preferred embodiments, the the first and second gene constructs are provided as part of a single vector, and can be provided as part of polycistronic message. Alternatively, the the fisrt and second gene constructs are provided on separate vectors. In certain embodiments, the gene construct comprises a viral vector, e.g., an adenoviral vector, an adeno-associated viral vector, or a retroviral vector. In other embodiments, the gene construct is provided in a delivery composition, e.g., selected from the group consisting of a liposome and a polycationic nucleic acid binding agent. The subject transfection systems can be used for treating an animal having a vascular wound characterized a breech of endothelial integrity and by excessive smooth muscle proliferation, by a method which includes administering the recombinant transfection system to the area of the vascular wound. In preferred embodiments, the subject transfection systems are used in the treatment of restenosis, and may be administered by catheter. Still another aspect of the present invention provides a gene construct encoding a fusion protein comprising a therapeutic polypeptide sequence from an intracellular protein which alter a biological process of a cell upon intracellular localization of the fusion protein, and a transcellular polypeptide sequence for promoting transcytosis of the fusion protein across a cell surface membrane and into a cell. In preferred embodiments, the trancellular fusion protein alters one or more such biological processes as proliferation, differentiation, cell death, gene expression, protein stability, calcium mobilzation, ion permability, phosphorylation of intracellular proteins, metabolism of inositol phosphates (IP3 and the like, diacyl glycerides, etc), and metabolism of nucleosides (such as cAMP). The transcellular fusion protein can, by virtue of its binding to a protein or nucleic acid in the targeted cell, alter (inhibit or potentiate) protein-protein interactions or protein-nucleic acid interactions between proteins and nucleic acids endogenous to the cell. In certain embodiments, the therapeutic polypeptide sequence can be dervied from a tumor suppressor, a transcription factor, a signal transduction protein, an antiviral protein or a metal chelating protein. For instance, the therapeutic polypeptide sequence can include a polypeptide sequence of a tumor supressor such as p53, Rb or an Rb-like protein, or a CKI protein. In other embodiments, the therapeutic polypeptide sequence includes a polypeptide sequence of a signal transduction protein, such as from tubby, a DOT protein, a Bel protein (bcl-2, bcl-x, etc), or an IκB protein. In a preferred embodiment, the fusion protein includes at least one CDK- binding motif for binding and inhibiting activation of a cyclin dependent kinase (cdk). For instance, the CDK-binding motif is a CDK-binding motif of a CDK inhibitor protein, such as an INK4 protein (e.g., pl5, pl6, pl8 or pl9), or a CIP/KIP protein (e.g., p21 CIP 1 , p27 KIP1 , and p57 κ,P2 ). In other preferred embodiments, the CDK- binding motif comprises tandemly arranged ankyrin-like sequences, or a p21/p27 inhibitory domain. In preferred embodiments, the polypeptide comprises CDK- binding motifs from two or more different proteins which bind to cyclin dependent kinases. The transcellular polypeptide sequence can be an internalizing peptide, such as may be derived from a polypeptide selected from the group consisting of antepennepedia protein, HIV transactivating (TAT) protein, mastoparan, melittin, bombolittin, delta hemolysin, pardaxin, Pseudomonas exotoxin A, clathrin, Diphtheria toxin and C9 complement protein. In other embodiments, the transcellular polypeptide sequence can be an accessory peptide sequence which enhances interaction of the fusion protein with a cell surface membrane, such as a peptide sequence that includes an RGD sequence. In preferred embodiments, the gene construct comprises a viral vector, e.g., an adenoviral vector, an adeno-associated viral vector, or a retroviral vector. In other embodiments, the gene construct is provided in a delivery composition, e.g., selected from the group consisting of a liposome and a polycationic nucleic acid binding agent. The invention also provides compositions of the fusion protein, e.g., such as may be formulated in pharmaceutical preparations. The gene construct and the fusion protein may each be used as part of a method for treating an animal for unwanted cell proliferation, by administering the chimeric gene or the fusion protein. The practice of the present invention will employ, unless otherwise indicated, conventional techniques of cell biology, cell culture, molecular biology, transgenic biology, microbiology, recombinant DNA, and immunology, which are within the skill of the art. Such techniques are explained fully in the literature. See, for example, Molecular Cloning A Laboratory Manual, 2nd Ed., ed. by Sambrook, Fritsch and Maniatis (Cold Spring Harbor Laboratory Press: 1989); DNA Cloning, Volumes I and II (D. N. Glover ed., 1985); Oligonucleotide Synthesis (M. J. Gait ed., 1984); Mullis et al. U.S. Patent No: 4,683,195; Nucleic Acid Hybridization (B. D. Hames & S. J. Higgins eds. 1984); Transcription And Translation (B. D. Hames & S. J. Higgins eds. 1984); Culture Of Animal Cells (R. I. Freshney, Alan R. Liss, Inc., 1987); Immobilized Cells And Enzymes (IRL Press, 1986); B. Perbal, A Practical Guide To Molecular Cloning (1984); the treatise, Methods In Enzymology (Academic Press, Inc., N.Y.); Gene Transfer Vectors For Mammalian Cells (J. H. Miller and M. P. Calos eds., 1987, Cold Spring Harbor Laboratory); Methods In Enzymology, Vols. 154 and 155 (Wu et al. eds.), Immunochemical Methods In Cell And Molecular Biology (Mayer and Walker, eds., Academic Press, London, 1987); Handbook Of Experimental Immunology, Volumes I-IV (D. M. Weir and C. C. Blackwell, eds., 1986); Manipulating the Mouse Embryo, (Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., 1986). Brief Description of the Drawings Figure 1 illustrates a construct for directing secretion of a p27 protein, and a gel indicating the secretion of the fusion protein into the media by COS cells expressing the construct. Figure 2 is a graph illustrating the inhibition of primary smooth muscle cell proliferation by various test polypeptides. Figure 3 is a gel illustrating the cellular uptake of tat/p27 fusion proteins. Figure 4 are fluorescence micrographs illustrating the cellular localization of various p27 fusion proteins. Figure 5 is a table of IC 50 values for inhibition various cdk2/cyclin complexes. Detailed Description of the Invention Progression of eukaryotic cells through the cell cycle is governed by the sequential formation, activation, and subsequent inactivation of a series of cyclin/cyclin dependent kinase complexes. The mechanisms underlying the expression of cyclins and the activation of the different cyclin-CDK complexes needed for progression through successive cell cycle transitions are now fairly well understood. In addition to positive regulation by the activation of cyclin-CDK complexes, negative regulation of the cell cycle occurs at checkpoints, many of which operate to control formation of cyclin/CDK complexes and/or activation of the complexes. Accordingly, these transitions are negatively regulated by signals that constrain the cell-cycle until specific conditions are fulfilled. Entry in to mitosis, for example, is inhibited by incompletely replicated DNA or DNA damage. These restriction on cell-cycle progression are essential for preserving the fidelity of the genetic information during cell division. The transition from G | to S phase, on the other hand, coordinates cell proliferation with environmental cues, after which the checks on the cell-cycle progression tend to be cell autonomous. Disruption of these signaling pathways can uncouple cellular responses from environmental controls and may lead to unrestrained cell proliferation or abherrent loss of differentiation. (i) Overview One aspect of the present invention pertains to novel inhibitors of cyclin- dependent kinases (CDKs), particularly CDK cyclin complexes, which inhibitors can be used to control proliferation and/or differentiation of cells in which the inhibitors are introduced. More specifically, the inhibitors of the invention are chimeric proteins which include CDK-binding motifs from two or more different proteins. Such chimeric proteins are refered to herein as "poly-CBM proteins". For example, as set forth in greater detail below, the subject chimeric proteins can be generated from the in-frame fusion of coding sequences from two different CDK inhibitor proteins (generically refered to herein as "CKI" proteins), such as may be derived from fusion of coding sequences for an INK4 protein and coding sequences for a CIP protein. Moreover, as the appended examples describe, chimeric proteins of the present invention have been observed to be more potent inhibitors of cyclin/CDK complexes than were either of the portions of the chimeric protein individually. For instance, p27-pl6 chimeric proteins inhibited a cyclin D1/CDK4 complex with an IC 5Q more than two-fold less than p27 alone, and ten-fold less than pi 6 alone. Likewise, the p27- pl6 chimeric protein inhibited cyclin E/CDK2, cyclin A/CDK2 and cyclin B/CDK2 complexes with IC 50 's approximately two-fold less than p27 alone (pi 6 itself not having any significant inhibitory activity against any of the three complexes). Another aspect of the present invention pertains to chimeric polypeptides, particularly chimeric CKI polypeptides, which includes a heterologous peptide sequence which drives the translocation of an intracellular polypeptide across the cell membrane in order to facilitate localization of the polypeptide in the cellular cytoplasm and/or nucleoplasm to which the polypeptide is ectopically applied. Such chimeric polypeptides are referred to herein as "transcellular polypeptides". In general, such transcellular polypeptides includes a first peptide portion ("internalizing peptide") which by itself is capable of crossing the cellular membrane, e.g., by transcytosis, at a relatively high rate, or which facilitates such transcytosis. The internalizing peptide is conjugated to a polypeptide corresponding to a therapeutic polypeptide, e.g., having intracellular activity, such as the subject CKI polypeptides. The resulting chimeric polypeptide is transported into cells at a much higher rate than the therapeutic polypeptide alone would be, and thereby provide an effective means for introducing the therapeutic polypeptide into cells. The transcellular polypeptide can applied ectopically, or expressed and secreted by cells adjacent to the intended target cells. In the latter embodiment, the internalizing peptide facilitates the uptake of the therapeutic polypeptide by cells proximal to a cell which expresses the recombinant polypeptide. In this manner, the transcellular embodiment of the therapeutic polypeptide can be used to effectively treat cells which are, under the circumstances of treatment, e.g., inefficient or otherwise refractive to transfection with a gene contruct encoding the therapeutic polypeptide. In a preferred embodiment, the transcellular polypeptide is delivered by way of a gene therapy expression vector -e.g., expression of the chimeric polypeptide by a subset of treated cells can result in localization of the polypeptide, with concomitant mitotic inhibition, in neighboring cells. For embodiments of a transcellular CKI polypeptide, the polypeptide can include all or a fragment of a single CKI protein, or include the poly-CBM protein described above. In still another aspect, the present invention provides methods and compositions for enhancing endothelization of injured sites while concurrently inhibiting smooth muscle cell proliferation around the site. In these embodiments, a CKI polypeptide is co-delivered with a polypeptide (an "endothelization polypeptide") which stimulates (a) endothelial cell proliferation; (b) stimulates migration of endothelial cells to the wound site; (c) inhibits smooth muscle cell migration; and/or (d) inhibits proliferation of smooth muscle cells. In preferred embodiments, the CKI polypeptide and endothelization polypeptide are ultimately delivered in the form of a single expression vector encoding both polypeptides, though multiple transfection of cells with separate expression vectors is also contemplated. The CKI polypeptide can include all or a fragment of a single CKI protein, or can be the poly-CBM protein described above. The co-delivery of the CKI polypeptide and endothelization polypeptide can have beneficial effects in, e.g., the repair of cardiovascular damage, repair of arteriosclerotic lesions and endothelialization of synthetic vascular grafts. Other aspects of the present invention include: preparations of the subject polypeptides; expression constructs for recombinant production of the subject polypeptides, particularly for use as part of a gene therapy treatment; and methods for modulating cell proliferation and/or differentiation with the subject polypeptides. (ii) Definitions For convenience, certain terms employed in the specification, examples, and appended claims are collected here. The phrase "CDK-binding motif refers to that portion of a protein which interacts either directly or indirectly with a cyclin dependent kinase (CDK). The binding motif may be a sequential portion of the protein, i.e., a contiguous sequence of amino acids, or it may be conformational, i.e. a combination of non-contiguous sequences of amino acids which, when the protein is in its native folding state, forms a structure which interacts with a CDK. The term "CDK-binding motif explicitly includes any polypeptide which is identical, substantially homologous, or otherwise functionally or structurally equivalent to a portion of a CKI protein which binds directly or indirectly to a CDK or CDK complex. Other exemplary CDK-binding motifs can be provided from, for example, Rb and Rb-like proteins as well as cyclins. An "inhibitor of CDK activation" refers to a molecule able to interact with a CDK and prevent activation of a kinase activity of the CDK either by, for example, inhibiting formation of CDK complexes including regulatory subunits, inhibiting interaction of the CDK subunit with activating kinases or phosphatases, inhibiting substrate binding, inhibiting ATP binding, and/or inhibiting conformational changes required for enzymatic activity. Accordingly, such inhibition may be by a direct, competitive mechanism, or by an indirect, non- or uncompetitive mechanism. As used herein, the term "CKI protein" refers to a protein which can bind to and inhibit activation of a cyclin dependent kinase. Exemplary CKI proteins include members of the INK4 family, such as pl6 INK4A or pl5 INK4B , and members of the CIP family, such as p2lC i l, P 27Kl i, and p57Kl p 2. The term "INK4 protein" refers to a family of structurally related CDK inhibitors characterized by a fourfold repeated ankyrin-like sequence (Elledge et al. (1994) Curr. Opin. Cell Biol. 6:874-878), and the ability to bind to CDKs, especially CDK4 and CDK6. Exemplary members of this protein family include pi 6 (INK4A/MTS1; Serrano et al (1993) Nature 366:704-707); pl5 (INK4B; Hannon et al. (1994) Nature 371 :257-261); pl8 (Guan et al. (1994) Genes Dev. 8:2939-2952) and pl9 (Chan et al. (1995) Mol. Cell Biol. 15:2682-2688; and Hirai et al. (1995) Mol. Cell Biol. 15:2672-2681). Other proteins have been identified in the art as having tandemly arranged ankyrin-like sequences, such as the Pho81p protein (Ogawa et al. (1995) Mol. Cell Biol. 15:997-1004), and may provide CDK- binding motifs which are functionally equivalent to those of an INK4 protein. The term "CIP protein" refers to members of another CKI protein family which includes p21 CIP1 (WAF1/SDI1/CAP20; Xiong et al. (1993) Nature 366:701-704); p27 Klpl (Polyak et al. (1994) Cell 78:67-74); and p57 KIP2 (Lee et al. (1995) Genes Dev. 9:639-649; and Matsuoka et al. (1995) Genes Dev. 9:650-662). In addition to the functional characteristic of CDK inhibition, the CIP proteins each have a CDK inhibitory motif (a CDK-binding motif) of about 50 amino acids, referred to herein as a "p21/p27" inhibitory domain, which is conserved in members of the CIP family, as well as, for example, members of the Rb-like protein family. A "chimeric protein" refers to a protein which includes polypeptide sequences from at least two different and distinct proteins. A chimeric protein can be a fusion protein, or the different polypeptide sequences can be covalently linked by a non-peptide bond, e.g., a cross-linking agent. As used herein, the term "fusion protein" is art recognized and refer to a chimeric protein which is at least initially expressed as single chain protein comprised of amino acid sequences derived from two or more different proteins, e.g., the fusion protein is a gene product of a fusion gene. The art term "fusion gene" refers to a nucleic acid in which two or more genes are fused resulting in a single open reading frame for coding two or more proteins that as a result of this fusion are joined by one or more peptide bonds. As used herein, the term "nucleic acid" refers to polynucleotides such as deoxyribonucleic acid (DNA), and, where appropriate, ribonucleic acid (RNA). The term should also be understood to include, as equivalents, analogs of either RNA or DNA made from nucleotide analogs, and, as applicable to the embodiment being described, single- stranded (such as sense or antisense) and double-stranded polynucleotides. As used herein, the term "gene" or "recombinant gene" refers to a nucleic acid comprising an open reading frame encoding a fusion polypeptide of the present invention, including both exonic and (optionally) intronic sequences. An exemplary recombinant gene encoding a subject fusion protein is represented by SEQ. ID No: 1. As used herein, the term "transfection" means the introduction of a heterologous nucleic acid, e.g., an expression vector, into a recipient cell by nucleic acid-mediated gene transfer. "Transformation", as used herein with respect to transfected nucleic acid, refers to a process in which a cell's genotype is changed as a result of the cellular uptake of exogenous DNA or RNA, and, for example, the transformed cell expresses a recombinant form of a CDK-inhibitory fusion polypeptide of the present invention. "Expression vector" refers to a replicable DNA construct used to express DNA which encodes the desired protein and which includes a transcriptional unit comprising an assembly of (1) genetic element(s) having a regulatory role in gene expression, for example, promoters, operators, or enhancers, operatively linked to (2) a DNA sequence encoding a desired protein (in this case, a fusion protein of the present invention) which is transcribed into mRNA and translated into protein, and (3) appropriate transcription and translation initiation and termination sequences. The choice of promoter and other regulatory elements generally varies according to the intended host cell. In general, expression vectors of utility in recombinant DNA techniques are often in the form of "plasmids" which refer to circular double stranded DNA loops which, in their vector form are not bound to the chromosome. In the present specification, "plasmid" and "vector" are used interchangeably as the plasmid is the most commonly used form of vector. However, the invention is intended to include such other forms of expression vectors which serve equivalent functions and which become known in the art subsequently hereto. In the expression vectors, regulatory elements controlling transcription or translation can be generally derived from mammalian, microbial, viral or insect genes The ability to replicate in a host, usually conferred by an origin of replication, and a selection gene to facilitate recognition of transformants may additionally be incorporated. Vectors derived from viruses, such as retroviruses. adenoviruses, and the like, may be employed. "Transcriptional regulatory sequence" is a generic term used throughout the specification to refer to DNA sequences, such as initiation signals, enhancers, and promoters and the like which induce or control transcription of protein coding sequences with which they are operably linked. In preferred embodiments, transcription of the fusion gene is under the control of a promoter sequence (or other transcriptional regulatory sequence) which controls the expression of the recombinant gene in a cell-type in which expression is intended. It will also be understood that the recombinant gene can be under the control of transcriptional regulatory sequences which are the same or which are different from those sequences which control transcription of one of the naturally-occurring forms of a CDK inhibitor protein. As used herein, the term "tissue-specific promoter" means a DNA sequence that serves as a promoter, i.e., regulates expression of a selected DNA sequence operably linked to the promoter, and which effects expression of the selected DNA sequence in specific cells of a tissue, such as cells of a urogenital origin, e.g. renal cells, or cells of a neural origin, e.g. neuronal cells. The term also covers so-called "leaky" promoters, which regulate expression of a selected DNA primarily in one tissue, but cause expression in other tissues as well. "Operably linked" when describing the relationship between two DNA regions simply means that they are functionally related to each other. For example, a promoter or other transcriptional regulatory sequence is operably linked to a coding sequence if it controls the transcription of the coding sequence. "Recombinant host cells" refers to cells which have been transformed or transfected with vectors constructed using recombinant DNA techniques. As relevant to the present invention, recombinant host cells are those which produce CDK inhibitor fusion proteins by virtue of having been transformed with expression vectors encoding these proteins. As used herein, a "transgenic animal" is any animal, preferably a non-human mammal, a bird or an amphibian, in which one or more of the cells of the animal contain heterologous nucleic acid introduced by way of human intervention, such as by transgenic techniques well known in the art. The nucleic acid is introduced into the cell, directly or indirectly by introduction into a precursor of the cell, by way of deliberate genetic manipulation, such as by microinjection or by infection with a recombinant virus. The term genetic manipulation does not include classical cross-breeding, or in vitro fertilization, but rather is directed to the introduction of a recombinant DNA molecule. This molecule may be integrated within a chromosome, or it may be extrachromosomally replicating DNA. In the typical transgenic animals described herein, the transgene causes cells to express a recombinant form of a CDK inhibitory fusion protein. The term "chimeric animal" is used herein to refer to animals in which the recombinant gene is found, or in which the recombinant is expressed in some but not all cells of the animal. The term "tissue-specific chimeric animal" indicates that the recombinant gene is present and/or expressed in some tissues but not others. "Homology" refers to sequence similarity between two peptides or between two nucleic acid molecules. Homology can be determined by comparing a position in each sequence which may be aligned for purposes of comparison. When a position in the compared sequence is occupied by the same base or amino acid, then the molecules are homologous at that position. A degree of homology between sequences is a function of the number of matching or homologous positions shared by the sequences. (iii) Poly-CBM polypeptides One aspect of the invention pertains to chimeric proteins which include CDK- binding motifs from two or more different proteins. In one embodiment, the invention provides a nucleic acid having a nucleotide sequence encoding a chimeric CDK inhibitor protein, and/or equivalents of such nucleic acids. In general, the nucleic acid is derived by the in-frame fusion of coding sequences from two or more proteins which have CDK- inhibitory motifs, such motifs being preserved in the resultant chimeric protein. Accordingly, such chimeric proteins can be derived to include, for example, CKI protein sequences, such as from INK4 or CIP proteins. For instance, as described in the appended examples, a coding sequence providing the CDK-binding motif of an INK4 protein can be fused in frame to a coding sequence providing a CDK-binding motif of a CIP protein. Exemplary nucleic acid of the present invention encode fusion proteins which include at least a CDK-binding portion of an INK4 protein, such as pl5, pl6, pl8 or pl9. In preferred embodiments, the chimeric protein includes at least the two ankyrin-like sequence of the C-terminal portion of the INK4 protein, e.g. corresponding to the 3 rd request (residues 69-101) and 4 th repeat (residues 102-133) of pl6 INK4A (see Serrano et al. (1993) Nature 366:704-707). Similarly, preferred chimeric proteins of the present invention include at least the p21/27-related inhibitory domain of a CIP protein, e.g. from p21, p27 or p57. For example, the chimeric protein can include the CDK-inhibitory motif corresponding to residues 28-79 of p27, residues 17-68 of p21, and/or residues 31-82 of p57, though larger fragments may be used such as described in the appended examples. Moreover, CDK-binding motifs homologous to those occurring in either the INK4 or CIP protein families have been observed in other proteins. For example, the p21/p27- related inhibitory domain typical of the CIP protein family has been identified in such other proteins as the Rb-related protein pi 07 (Zhu et al. (1995) Genes Dev 9:1740-1752). Likewise, ankyrin-like repeats homologous with the INK4 proteins have been identified in such other proteins as the Phoδlp protein (Ogawa et al. (1995) Mol Cell Biol 15:997- 1004). Consequently, it will be apparent to one of ordinary skill in the art, based on the disclosure herein, that functional equivalents of the INK4 and CIP proteins, e.g. which are capable of binding to a CDK and inhibiting kinase activation, exist and can be provided in the subject chimeric proteins. Furthermore, it will be understood that the subject chimeric proteins can include CDK-binding motifs from proteins unrelated to either the INK4 family or CIP family. Moreover, such CDK-binding motifs, while inhibitory in and of themselves, can be derived from proteins which are otherwise activating in their full length form. To illustrate, the subject chimeric protein can be generated with a fragment of a cyclin which retains its CDK binding ability but not the CDK activating ability characteristic of the full length protein. In some instances it may be necessary to introduce an unstructured polypeptide linker region between portions of the chimeric protein derived from different proteins. This linker can facilitate enhanced flexibility of the chimeric protein allowing the CDK-binding motifs from each portion to freely and (optionally) simultaneously interact with a CDK by reducing steric hindrance between the two fragments, as well as allowing appropriate folding of each portion to occur. The linker can be of natural origin, such as a sequence determined to exist in random coil between two domains of a protein. Alternatively, the linker can be of synthetic origin. For instance, the sequence (Gly4Ser)3 can be used as a synthetic unstructured linker. Linkers of this type are described in Huston et al. (1988) PNAS 85:4879; and U.S. Patent Nos. 5,091,513 and 5,258,498. Naturally occurring unstructured linkers of human origin are preferred as they reduce the risk of immunogenicity. Techniques for making fusion genes are well known. Essentially, the joining of various DNA fragments coding for different polypeptide sequences is performed in accordance with conventional techniques, employing blunt-ended or stagger-ended termini for ligation, restriction enzyme digestion to provide for appropriate termini, filling-in of cohesive ends as appropriate, alkaline phosphatase treatment to avoid undesirable joining, and enzymatic ligation. In another embodiment, the fusion gene can be synthesized by conventional techniques including automated DNA synthesizers. Alternatively, PCR amplification of gene fragments can be carried out using anchor primers which give rise to complementary overhangs between two consecutive gene fragments which can subsequently be annealed to generate a fusion gene sequence (see, for example, Current Protocols in Molecular Biology, eds. Ausubel et al. John Wiley & Sons: 1992). The term nucleic acid as used herein is intended to include nucleotide sequences encoding functionally equivalent chimeric proteins which, for example, retain the ability to bind to a cyclin-dependent kinase. Equivalent nucleotide sequences will include sequences that differ by one or more nucleotide substitutions, additions or deletions, such as allelic variants; and will, therefore, include sequences that differ from the nucleotide sequence of, for example, an INK4 or CIP gene known in the art due to the degeneracy of the genetic code. Equivalents will also include nucleotide sequences that hybridize under stringent conditions (i.e., equivalent to about 20-27°C below the melting temperature (T m ) of the DNA duplex formed in about 1M salt) to the nucleotide sequence encoding a naturally- occurring CDK-binding motif. Furthermore, equivalent nucleic acids will include those with nucleotide sequences which differ from the natural sequence which encodes a CDK- binding motif because of degeneracy in the genetic code. For example, a number of amino acids are designated by more than one triplet. Codons that specify the same amino acid can, accordingly, be used to replace codons in the naturally-occurring sequence. This invention also provides expression vectors comprising a nucleotide sequence encoding a subject CDK inhibitor chimeric protein and operably linked to at least one regulatory sequence. Regulatory sequences are art-recognized and are selected to direct expression of the fusion protein. Accordingly, the term regulatory sequence includes promoters, enhancers and other expression control elements. Exemplary regulatory sequences are described in Goeddel; Gene Expression Technology: Methods in Enzymology 185, Academic Press, San Diego, CA (1990). For instance, any of a wide variety of expression control sequences-sequences that control the expression of a DNA sequence when operatively linked to it may be used in these vectors to express DNA sequences encoding the fusion proteins of this invention. Such useful expression control sequences, include, for example, the early and late promoters of SV40, adenovirus or cytomegalovirus immediate early promoter, the lac system, the tip system, the TAC or TRC system, T7 promoter whose expression is directed by T7 RNA polymerase, the major operator and promoter regions of phage lambda, the control regions for fd coat protein, the promoter for 3-phosphoglycerate kinase or other glycolytic enzymes, the promoters of acid phosphatase. e.g., Pho5, the promoters of the yeast α-mating factors, the polyhedron promoter of the baculovirus system and other sequences known to control the expression of genes of prokaryotic or eukaryotic cells or their viruses, and various combinations thereof. Of course, the transcriptional regulatory sequences can include those sequences which naturally control expression of one of the genes used to derive the fusion protein, such as 5' flanking sequences of an INK4 or CIP gene. It should be understood that the design of the expression vector may depend on such factors as the choice of the host cell to be transformed and/or the type of protein desired to be expressed. Moreover, the vector's copy number, the ability to control that copy number and the expression of any other proteins encoded by the vector, such as antibiotic markers, should also be considered. Expression vehicles for production of recombinant forms of the subject chimeric proteins include plasmids and other vectors. For instance, suitable vectors for expression of a fusion protein of the present invention include plasmids of the types: pBR322-derived plasmids, pEMBL-derived plasmids, pEX-derived plasmids, pBTac-derived plasmids and pUC-derived plasmids for expression in prokaryotic cells, such as E. coli. A number of vectors exist for the expression of recombinant proteins in yeast. For instance, YEP24, YIP5, YEP51, YEP52, pYES2, and YRP17 are cloning and expression vehicles useful in the introduction of genetic constructs into S. cerevisiae (see, for example, Broach et al. (1983) in Experimental Manipulation of Gene Expression, ed. M. Inouye Academic Press, p. 83). These vectors can replicate in E. coli due the presence of the pBR322 ori, and in S. cerevisiae due to the replication determinant of the yeast 2 micron plasmid. In addition, drug resistance markers such as ampicillin can be used. The preferred mammalian expression vectors (other than for gene therapy) contain both prokaryotic sequences to facilitate the propagation of the vector in bacteria, and one or more eukaryotic transcription units that are expressed in eukaryotic cells. The pcDNAI/amp, pcDNAI/neo, pRc/CMV, pSV2gpt, pSV2neo, pSV2-dhfr, pTk2, pRSVneo, pMSG, pSVT7, pko-neo and pHyg derived vectors are examples of mammalian expression vectors suitable for transfection of eukaryotic cells. Some of these vectors are modified with sequences from bacterial plasmids, such as pBR322, to facilitate replication and drug resistance selection in both prokaryotic and eukaryotic cells. Alternatively, derivatives of viruses such as the bovine papilloma virus (BPV-1), or Epstein-Barr virus (pHEBo, pREP- derived and p205) can be used for transient expression of proteins in eukaryotic cells. In some instances, it may be desirable to express the subject fusion protein by the use of a baculovirus expression system. Examples of such baculovirus expression systems include pVL-derived vectors (such as pVL1392, pVL1393 and pVL941), pAcUW-derived vectors (such as pAcUWl), and pBlueBac-derived vectors (such as the β-gal containing pBlueBac III). The various methods employed in the preparation of the plasmids and transformation of host organisms are well known in the art. For other suitable expression systems for both prokaryotic and eukaryotic cells, as well as general recombinant procedures, see Molecular Cloning: A Laboratory Manual, 2nd Ed., ed. by Sambrook, Fritsch and Maniatis (Cold Spring Harbor Laboratory Press: 1989) Chapters 16 and 17. Another aspect of the present invention concerns preparations of the subject chimeric proteins. In particular, purified and semi-purified preparations of the CDK inhibitors can be formulated according to specifications attendant the desired use of the chimeric protein. With respect to purifying the subject chimeric proteins, Applicant notes that it is widely appreciated that addition of certain heterologous sequences to a protein can facilitate the expression and purification of the proteins. For example, a fusion protein of the present invention can be generated to also include a glutathione-S-transferase (GST) polypeptide sequence. The GST portion of the recombinant proteins can enable easy purification of the protein, such as by the use of glutathione-derivativized matrices (see, for example, Current Protocols in Molecular Biology, eds. Ausabel et al. (N.Y.: John Wiley & Sons, 1991)). In another embodiment, the subject fusion protein can also include a purification leader sequence, such as a poly-(His)/enterokinase cleavage site sequence located at the N-terminus of the subject fusion protein. Such sequences facilitates purification of the poly(His)-expressed fusion protein by affinity chromatography using a Ni 2+ metal resin. The purification leader sequence can then be subsequently removed by treatment with enterokinase (e.g., see Hochuli et al. (1987) J. Chromatography 411:177; and Janknecht et al. PNAS 88:8972). The present invention further pertains to methods of producing the subject chimeric proteins. For example, a host cell transfected with a nucleic acid vector directing expression of a nucleotide sequence encoding one of the chimeric proteins of the present invention can be cultured under appropriate conditions to allow expression of the polypeptide to occur. The peptide may be secreted and isolated from a mixture of host cells and medium by inclusion of a signal secretion sequence. Alternatively, the peptide may be retained cytoplasmically and the cells harvested, lysed and the protein isolated. A cell culture includes host cells, media and other byproducts. Suitable media for cell culture are well known in the art. The recombinant chimeric protein can be isolated from cell culture medium, host cells, or both using techniques known in the art for purifying proteins including ion-exchange chromatography, gel filtration chromatography, ultrafiltration, electrophoresis, and immuno-affinity purification with antibodies specific for portions of the chimeric protein. This invention also pertains to a host cell transfected to recombinantly express one of the subject chimeric proteins. The host cell may be any prokaryotic or eukaryotic cell. Thus, a nucleic acid derived from the fusion of coding sequences for two or more CDK- binding motifs from different proteins can be used to produce a recombinant form of the chimeric protein via microbial or eukaryotic cellular processes. Ligating the polynucleotide sequence into a gene construct, such as an expression vector, and transforming or transfecting into hosts, either eukaryotic (yeast, avian, insect or mammalian) or prokaryotic (bacterial cells), are standard procedures used in producing other well-known proteins, e.g., pl6, p21, p27, p57, pl07, cyclins and the like. Similar procedures, or modifications thereof, can be employed to prepare recombinant chimeric proteins by microbial means or tissue-culture technology in accord with the subject invention. The chimeric molecules of the present invention can also be generated using well- known cross-linking reagents and protocols. For example, there are a large number of chemical cross-linking agents that are known to those skilled in the art and useful for crosslinking two heterologous polypeptide chains. For the present invention, the preferred cross-linking agents are heterobifiinctional cross-linkers, which can be used to link molecules in a stepwise manner. Heterobifiinctional cross-linkers provide the ability to design more specific coupling methods for conjugating proteins, thereby reducing the occurrences of unwanted side reactions such as homo-protein polymers. A wide variety of heterobifunctional cross-linkers are known in the art. These include: succinimidyl 4-(N- maleimidomethyl) cyclohexane- 1 -carboxylate (SMCC), m-Maleimidobenzoyl-N- hydroxysuccinimide ester (MBS); N-succinimidyl (4-iodoacetyl) aminobenzoate (SIAB), succinimidyl 4-(p-maleimidophenyl) butyrate (SMPB), l-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC); 4-succinimidyloxycarbonyl- a-methyl-a-(2- pyridyldithio)-tolune (SMPT), N-succinimidyl 3-(2-pyridyldithio) propionate (SPDP), succinimidyl 6-[3-(2-pyridyldithio) propionate] hexanoate (LC-SPDP). Those crosslinking agents having N-hydroxysuccinimide moieties can be obtained as the N- hydroxysulfosuccinimide analogs, which generally have greater water solubility. In addition, those cross-linking agents having disulfide bridges within the linking chain can be synthesized instead as the alkyl derivatives so as to reduce the amount of linker cleavage in vivo. In addition to the heterobifunctional cross-linkers, there exists a number of other cross-linking agents including homobifunctional and photoreactive cross-linkers. Disuccinimidyl suberate (DSS), bismaleimidohexane (BMH) and dimethylpimelimidate-2 HCl (DMP) are examples of useful homobifunctional cross-linking agents, and bis-[β-(4- azidosalicylamido)ethyl]disulfide (BASED) and N-succinimidyl-6(4'-azido-2'-nitrophenyl- amino)hexanoate (SANPAH) are examples of useful photoreactive cross-linkers for use in this invention. For a recent review of protein coupling techniques, see Means et al. (1990) Bioconiugate Chemistry 1 :2-12, incoφorated by reference herein. One particularly useful class of heterobifunctional cross-linkers, included above, contain the primary amine reactive group, N-hydroxysuccinimide (NHS), or its water soluble analog N-hydroxysulfosuccinimide (sulfo-NHS). Primary amines (lysine epsilon groups) at alkaline pH's are unprotonated and react by nucleophilic attack on NHS or sulfo- NHS esters. This reaction results in the formation of an amide bond, and release of NHS or sulfo-NHS as a by-product. Another reactive group useful as part of a heterobifunctional cross-linker is a thiol reactive group. Common thiol reactive groups include maleimides, halogens, and pyridyl disulfides. Maleimides react specifically with free sulfhydryls (cysteine residues) in minutes, under slightly acidic to neutral (pH 6.5-7.5) conditions. Halogens (iodoacetyl functions) react with -SH groups at physiological pH's. Both of these reactive groups result in the formation of stable thioether bonds. The third component of the heterobifunctional cross-linker is the spacer arm or bridge. The bridge is the structure that connects the two reactive ends. The most apparent attribute of the bridge is its effect on steric hindrance. In some instances, a longer bridge can more easily span the distance necessary to link two complex biomolecules. For instance, SMPB has a span of 14.5 angstroms. Preparing protein-conjugates using heterobifunctional reagents is a two-step process involving the amine reaction and the sulfhydryl reaction. For the first step, the amine reaction, the protein chosen should contain a primary amine. This can be lysine epsilon amines or a primary alpha amine found at the N-terminus of most proteins. The protein should not contain free sulfhydryl groups. In cases where both proteins to be conjugated contain free sulfhydryl groups, one protein can be modified so that all sulfhydryls are blocked using for instance, N-ethylmaleimide (see Partis et al. (1983) J. Pro. Chem. 2:263, incorporated by reference herein). Ellman's Reagent can be used to calculate the quantity of sulfhydryls in a particular protein (see for example Ellman et al. (1958) Arch. Biochem. Biophys. 74:443 and Riddles et al. (1979) Anal. Biochem. 94:75, incorporated by reference herein). The reaction buffer should be free of extraneous amines and sulfhydryls. The pH of the reaction buffer should be 7.0-7.5. This pH range prevents maleimide groups from reacting with amines, preserving the maleimide group for the second reaction with sulfhydryls. The NHS-ester containing cross-linkers have limited water solubility. They should be dissolved in a minimal amount of organic solvent (DMF or DMSO) before introducing the cross-linker into the reaction mixture. The cross-linker/solvent forms an emulsion which will allow the reaction to occur. The sulfo-NHS ester analogs are more water soluble, and can be added directly to the reaction buffer. Buffers of high ionic strength should be avoided, as they have a tendency to "salt out" the sulfo-NHS esters. To avoid loss of reactivity due to hydrolysis, the cross-linker is added to the reaction mixture immediately after dissolving the protein solution. The reactions can be more efficient in concentrated protein solutions. The more alkaline the pH of the reaction mixture, the faster the rate of reaction. The rate of hydrolysis of the NHS and sulfo-NHS esters will also increase with increasing pH. Higher temperatures will increase the reaction rates for both hydrolysis and acylation. Once the reaction is completed, the first protein is now activated, with a sulfhydryl reactive moiety. The activated protein may be isolated from the reaction mixture by simple gel filtration or dialysis. To carry out the second step of the cross-linking, the sulfhydryl reaction, the protein chosen for reaction with maleimides, activated halogens, or pyridyl disulfides must contain a free sulfhydryl, usually from a cysteine residue. Free sulfhydryls can be generated by reduction of protein disulfides. Alternatively, a primary amine may be modified with Traut's Reagent to add a sulfhydryl (Blattler et al. (1985) Biochem 24:1517, incorporated by reference herein). Again, Ellman's Reagent can be used to calculate the number of sulfhydryls available in protein. In all cases, the buffer should be degassed to prevent oxidation of sulfhydryl groups. EDTA may be added to chelate any oxidizing metals that may be present in the buffer. Buffers should be free of any sulfhydryl containing compounds. Maleimides react specifically with -SH groups at slightly acidic to neutral pH ranges (6.5-7.5). A neutral pH is sufficient for reactions involving halogens and pyridyl disulfides. Under these conditions, maleimides generally react with -SH groups within a matter of minutes. Longer reaction times are required for halogens and pyridyl disulfides. The first sulfhydryl reactive-protein prepared in the amine reaction step is mixed with the sulfhydryl-containing protein under the appropriate buffer conditions. The protein-protein conjugates can be isolated from the reaction mixture by methods such as gel filtration or by dialysis. (iv) Transcellular therapeutic polypeptides Another aspect of the present invention pertains to chimeric polypeptides which includes a heterologous peptide sequence ("internalizing peptide") which drives the translocation of an extracellular form of a thereapeutic polypeptide sequence across a cell membrane in order to facilitate intracellular localization of the thereapeutic polypeptide. In this regard, the therapeutic polypeptide sequence is one which is active intracellularly, such as a tumor suppressor polypeptide, transcription factor or the like. The internalizing peptide, by itself, is capable of crossing a cellular membrane by, e.g., transcytosis, at a relatively high rate. The internalizing peptide is conjugated, e.g., as a fusion protein, to a therapeutic polypeptide. The resulting chimeric polypeptide is transported into cells at a higher rate relative to the polypeptide alone to thereby provide an means for enhancing the introduction of inhibitory polypeptides into surrounding cells, e.g., to enhance gene therapy and/or topical applications of the therapeutic polypeptide. For convenience, the transcellular therapeutic polypeptides are described below as fusion proteins including CKI polypeptide sequences, though as also described below (section v), many other protein domains can be used in place of the CKI polypeptide. In one embodiment, the internalizing peptide is derived from the drosopholia antepennepedia protein, or homologs thereof. The 60 amino acid long long homeodomain of the homeo-protein antepennepedia has been demonstrated to translocate through biological membranes and can facilitate the translocation of heterologous polypeptides to which it is couples. See for example Derossi et al. (1994) J Biol Chem 269:10444-10450; and Perez et al. (1992) J Cell Sci 102:717-722. Recently, it has been demonstrated that fragments as small as 16 amino acids long of this protein are sufficient to drive intemalization. See Derossi et al. (1996) J Biol Chem 271 :18188-18193. The present invention contemplates a chimeric protein comprising at least one CDK binding motif and at least a portion of the antepennepedia protein (or homolog thereof) sufficient to increase the transmembrane transport of the chimeric protein, relative to the CDK binding motif alone, by a statistically significant amount. Another example of an internalizing peptide is the HIV transactivator (TAT) protein. This protein appears to be divided into four domains (Kuppuswamy et al. (1989) Nucl. Acids Res. 17:3551-3561 ). Purified TAT protein is taken up by cells in tissue culture (Frankel and Pabo, (1989) Cell 55: 1 189-1 193), and peptides, such as the fragment corresponding to residues 37 -62 of TAT, are rapidly taken up by cell in vitro (Green and Loewenstein, (1989) Cell 55: 1 179-1 188). The highly basic region mediates intemalization and targeting of the internalizing moiety to the nucleus (Ruben et al., (1989) J. Virol. 63:1- 8). Peptides or analogs that include a sequence present in the highly basic region, such as CFITKALGISYGRKKRRQRRRPPQGS, are conjugated to CKI polypeptides (or CDK binding motifs thereof) to aid in intemalization and targeting those proteins to the intracellular milleau. Another exemplary transcellular CKI polypeptide can be generated to include a sufficient portion of mastoparan (T. Higashijima et al., (1990) J. Biol. Chem. 265:14176) to increase the transmembrane transport of the chimeric protein. While not wishing to be bound by any particular theory, it is noted that hydrophilic polypeptides may be also be physiologically transported across the membrane barriers by coupling or conjugating the polypeptide to a transportable peptide which is capable of crossing the membrane by receptor-mediated transcytosis. Suitable internalizing peptides of this type can be generated using all or a portion of, e.g., a histone, insulin, transferrin, basic albumin, prolactin and insulin-like growth factor I (IGF-I), insulin-like growth factor II (IGF-II) or other growth factors. For instance, it has been found that an insulin fragment, showing affinity for the insulin receptor on capillary cells, and being less effective than insulin in blood sugar reduction, is capable of transmembrane transport by receptor- mediated transcytosis and can therefor serve as an internalizing peptide for the subject transcellular CKI polypeptides. Preferred growth factor-derived internalizing peptides include EGF (epidermal growth factor)-derived peptides, such as CMHIESLDSYTC and CMYIEALDKYAC; TGF- beta (transforming growth factor beta )-derived peptides; peptides derived from PDGF (platelet-derived growth factor) or PDGF-2; peptides derived from IGF-I (insulin-like growth factor) or IGF-II; and FGF (fibroblast growth factor- derived peptides. Another class of translocating/internalizing peptides exhibits pH-dependent membrane binding. For an intemalizing peptide that assumes a helical conformation at an acidic pH, the intemalizing peptide acquires the property of amphiphilicity, e.g., it has both hydrophobic and hydrophilic interfaces. More specifically, within a pH range of approximately 5.0-5.5, an intemalizing peptide forms an alpha-helical, amphiphilic structure that facilitates insertion of the moiety into a target membrane. An alpha-helix- inducing acidic pH environment may be found, for example, in the low pH environment present within cellular endosomes. Such intemalizing peptides can be used to facilitate transport of CKI polypeptides, taken up by an endocytic mechanism, from endosomal compartments to the cytoplasm. A preferred pH-dependent membrane-binding intemalizing peptide includes a high percentage of helix-forming residues, such as glutamate, methionine, alanine and leucine. In addition, a preferred intemalizing peptide sequence includes ionizable residues having pKa's within the range of pH 5-7, so that a sufficient uncharged membrane-binding domain will be present within the peptide at pH 5 to allow insertion into the target cell membrane. A particularly preferred pH-dependent membrane-binding intemalizing peptide in this regard is aal-aa2-aa3-EAALA(EALA)4-EALEALAA-amide, which represents a modification of the peptide sequence of Subbarao et al. (Biochemistry 26:2964, 1987). Within this peptide sequence, the first amino acid residue (aal) is preferably a unique residue, such as cysteine or lysine, that facilitates chemical conjugation of the intemalizing peptide to a targeting protein conjugate. Amino acid residues 2-3 may be selected to modulate the affinity of the intemalizing peptide for different membranes. For instance, if both residues 2 and 3 are lys or arg, the intemalizing peptide will have the capacity to bind to membranes or patches of lipids having a negative surface charge. If residues 2-3 are neutral amino acids, the intemalizing peptide will insert into neutral membranes. Yet other preferred intemalizing peptides include peptides of apo-lipoprotein A-l and B; peptide toxins, such as melittin, bombolittin, delta hemolysin and the pardaxins; antibiotic peptides, such as alamethicin; peptide hormones, such as calcitonin, corticotrophin releasing factor, beta endorphin, glucagon, parathyroid hormone, pancreatic polypeptide; and peptides corresponding to signal sequences of numerous secreted proteins. In addition, exemplary intemalizing peptides may be modified through attachment of substituents that enhance the alpha-helical character of the intemalizing peptide at acidic pH. Yet another class of internalizing peptides suitable for use within the present invention include hydrophobic domains that are "hidden" at physiological pH, but are exposed in the low pH environment of the target cell endosome. Upon pH-induced unfolding and exposure of the hydrophobic domain, the moiety binds to lipid bilayers and effects translocation of the covalently linked CKI polypeptide into the cell cytoplasm. Such intemalizing peptides may be modeled after sequences identified in, e.g., Pseudomonas exotoxin A, clathrin, or Diphtheria toxin. Pore-forming proteins or peptides may also serve as intemalizing peptides herein. Pore forming proteins or peptides may be obtained or derived from, for example, C9 complement protein, cytolytic T-cell molecules or NK-cell molecules. These moieties are capable of forming ring-like structures in membranes, thereby allowing transport of attached CKI polypeptide through the membrane and into the cell interior. Mere membrane intercalation of an intemalizing peptide may be sufficient for translocation of the CKI polypeptide across cell membranes. However, translocation may be improved by attaching to the intemalizing peptide a substrate for intracellular enzymes (i.e., an "accessory peptide"). It is preferred that an accessory peptide be attached to a portion(s) of the intemalizing peptide that protmdes through the cell membrane to the cytoplasmic face. The accessory peptide may be advantageously attached to one terminus of a translocating/internalizing moiety or anchoring peptide. An accessory moiety of the present invention may contain one or more amino acid residues. In one embodiment, an accessory moiety may provide a substrate for cellular phosphorylation (for instance, the accessory peptide may contain a tyrosine residue). An exemplary accessory moiety in this regard would be a peptide substrate for N- myristoyl transferase, such as GNAAAARR (Eubanks et al., in Peptides. Chemistry and Biology, Garland Marshall (ed.), ESCOM, Leiden, 1988, pp. 566-69) In this constmct, an intemalizing, peptide would be attached to the C-terminus of the accessory peptide, since the N-terminal glycine is critical for the accessory moiety's activity. This hybrid peptide, upon attachment to a CKI polypeptide at its C-terminus, is N-myristylated and further anchored to the target cell membrane, e.g., it serves to increase the local concentration of the CKI polypeptide at the cell membrane. To further illustrate use of an accessory peptide, a phosphorylatable accessory peptide is first covalently attached to the C-terminus of an intemalizing peptide and then incoφorated into a fusion protein with a CKI polypeptide. The peptide component of the fusion protein intercalates into the target cell plasma membrane and, as a result, the accessory peptide is translocated across the membrane and protmdes into the cytoplasm of the target cell. On the cytoplasmic side of the plasma membrane, the accessory peptide is phosphorylated by cellular kinases at neutral pH. Once phosphorylated, the accessory peptide acts to irreversibly anchor the fusion protein into the membrane. Localization to the cell surface membrane can enhance the translocation of the CKI polypeptide into the cell cytoplasm. Suitable accessory peptides include peptides that are kinase substrates, peptides that possess a single positive charge, and peptides that contain sequences which are glycosylated by membrane-bound glycotransferases. Accessory peptides that are glycosylated by membrane-bound glycotransferases may include the sequence x-NLT-x, where "x" may be another peptide, an amino acid, coupling agent or hydrophobic molecule, for example. When this hydrophobic tripeptide is incubated with microsomal vesicles, it crosses vesicular membranes, is glycosylated on the luminal side, and is entrapped within the vesicles due to its hydrophilicity (C. Hirschberg et al., (1987) Ann. Rev. Biochem. 56:63-87). Accessory peptides that contain the sequence x-NLT-x thus will enhance target cell retention of corresponding CKI polypeptide. In another embodiment of this aspect of the invention, an accessory peptide can be used to enhance interaction of the CKI polypeptide with the target cell. Exemplary accessory peptides in this regard include peptides derived from cell adhesion proteins containing the sequence "RGD", or peptides derived from laminin containing the sequence CDPGYIGSRC. Extracellular matrix glycoproteins, such as fibronectin and laminin, bind to cell surfaces through receptor-mediated processes. A tripeptide sequence, RGD, has been identified as necessary for binding to cell surface receptors. This sequence is present in fibronectin, vitronectin, C3bi of complement, von-Willebrand factor, EGF receptor, transforming growth factor beta , collagen type I, lambda receptor of E. coli, fibrinogen and Sindbis coat protein (E. Ruoslahti, Ann. Rev. Biochem. 57:375-413, 1988). Cell surface receptors that recognize RGD sequences have been grouped into a superfamily of related proteins designated "integrins". Binding of "RGD peptides" to cell surface integrins will promote cell-surface retention, and ultimately translocation, of the CKI fusion protein. As described for the poly-CBM proteins above, the intemalizing and accessory peptides can each, independently, be added to a CKI polypeptide by either chemical cross- linking or in the form of a fusion protein. In the instance of fusion proteins, unstmctured polypeptide linkers can be included between each of the peptide moieties. The CKI polypeptide can consist of as little as a CDK-binding moitey of a CKI protein, or can include a full length CKI protein and/or poly-CBM protein. In general, the intemalization peptide will be sufficient to also direct export of the CKI polypeptide. However, where an accessory peptide is provided, such as an RGD sequence, it may be necessary to include a secretion signal sequence to direct export of the fusion protein from its host cell. In preferred embodiments, the secretion signal sequence is located at the extreme N-terminus, and is (optionally) flanked by a proteolytic site between the secretion signal and the rest of the fusion protein. In an exemplary embodiment, the CKI polypeptides is engineered to include an integrin-binding RGD peptide/SV40 nuclear localization signal (see, for example Hart SL et al., 1994; J. Biol. Chem.,269: 12468-12474), such as encoded by the nucleotide sequence provided in the Ndel -EcoRI fragment: catatgggtggctgccgtggcgatatgttcggttgcggtgctcctccaaaaaagaagagaaag-gtagctggattc, which encodes the RGD/SV40 nucleotide sequence: MGGCRGDMFGCGAPP-KKKRKVAGF. In another embodiment, the protein can be engineered with the HIV-1 tat(l-72) polypeptide, e.g., as provided by the Ndel -EcoRI fragmentxatatggagccagtagatcctagactagagccc- tggaagcatccaggaagtcagcctaaaactgcttgtaccaattgctattgtaaaaagtgttgctttcattgccaagtttgtttcataacaa aagcccttggcatctcctatggcaggaagaagcggagacagcgacgaagacctcctcaaggcagtcagactcatcaagtttctcta agtaagcaaggattc, which encodes the HIV-1 tat(l-72) peptide sequence: MEPVDPRLEPWKHPGSQPKT- ACTNCYCKKCCFHCQVCFITKALGISYGRKKRRQRRRPPQGSQTHQVSLSKQ. In still another embodiment, the fusion protein includes the HSV-1 VP22 polypeptide (Elliott G., O'Hare P (1997) Cell, 88:223-233) provided by the Ndel -EcoRI fragment: cat atg ace tct cgc cgc tec gtg aag teg ggt ccg egg gag gtt ccg cgc gat gag tac gag gat ctg tac tac ace ccg tct tea ggt atg gcg agt ccc gat agt ccg cct gac ace tec cgc cgt ggc gcc eta cag aca cgc teg cgc cag agg ggc gag gtc cgt ttc gtc cag tac gac gag teg gat tat gcc etc tac ggg ggc teg tea tec gaa gac gac gaa cac ccg gag gtc ccc egg acg egg cgt ccc gtt tec ggg gcg gtt ttg tec ggc ccg ggg cct gcg egg gcg cct ccg cca ccc get ggg tec gga ggg gcc gga cgc aca ccc ace ace gcc ccc egg gcc ccc cga ace cag egg gtg gcg act aag gcc ccc gcg gcc ccg gcg gcg gag ace ace cgc ggc agg aaa teg gcc cag cca gaa tec gcc gca etc cca gac gcc ccc gcg teg acg gcg cca ace cga tec aag aca ccc gcg cag ggg ctg gcc aga aag ctg cac ttt age ace gcc ccc cca aac ccc gac gcg cca tgg ace ccc egg gtg gcc ggc ttt aac aag cgc gtc ttc tgc gcc gcg gtc ggg cgc ctg gcg gcc atg cat gcc egg atg gcg gcg gtc cag etc tgg gac atg teg cgt ccg cgc aca gac gaa gac etc aac gaa etc ctt ggc ate ace ace ate cgc gtg acg gtc tgc gag ggc aaa aac ctg ctt cag cgc gcc aac gag ttg gtg aat cca gac gtg gtg cag gac gtc gac gcg gcc acg gcg act cga ggg cgt tct gcg gcg teg cgc ccc ace gag cga cct cga gcc cca gcc cgc tec get tct cgc ccc aga egg ccc gtc gag gaa ttc which encodes the HSV-1 VP22 peptide having the sequence: MTSRRSVKSGPREVPRDEYEDLYYTPSSGMASPDSPPDTSRRGALQTRSRQRGEVR FVQYDESDYALYGGSSSEDDEHPEVPRTRRPVSGAVLSGPGPARAPPPPAGSGGAG RTPTTAPRAPRTGRVATKAPAAPAAETTRGRKSAQPESAALPDAPASTAPTRSKTP AQGLARKLHFSTAPPNPDAPWTPRVAGFNKRVFCAAVGRLAAMHARMAAVQLW DMSRPRTDEDLNELLGITTIRVTVCEGKNLLQRANELVNPDVVQDVDAATATRGR SAASRPTERPRAPARSASRPRRPVE In still another embodiment, the fusion protein includes the C-terminal domain of the VP22 protein from, e.g., the nucleotide sequence (Ndel -EcoRI fragment): cat atg gac gtc gac gcg gcc acg gcg act cga ggg cgt tct gcg gcg teg cgc ccc ace gag cga cct cga gcc cca gcc cgc tec get tct cgc ccc aga egg ccc gtc gag gaa ttc which encodes the VP22 (C-terminal domain) peptide sequence: MDVDAATATRGRSAASRPTERPRAPARSASRPRRPVE (v) Transcellular polypeptides as General Gene Therapy Agents Another aspect of the present invention pertains generally to the use of intemalizing peptides as part of a strategy to deliver therapeutic proteins by gene therapy techniques. In addition to the subject CKI polypeptides, other therapeutic proteins such as various tumor suppressors, transcription factors, signal transduction proteins, antiviral polpeptides, and therapeutic peptides, e.g., which are otherwise localized intracellularly, can be engineered to include an intemalizing peptide which drives the translocation of the therapeutic polypeptide into surrounding cells. Thus, the transcytosis system can be used to increase the efficacy of gene therapy by delivering the therapeutic protein not only to cells actually transfected with the expression vector, but also to the surrounding cells. Such constmcts can be generated with other therapeutic polypeptides using such of the general teachings herein as applicable and the general knowledge in the art. In one illustrative embodiment, the therapeutic polypeptide sequence is derived from a tumor suppressor. In addition to the CKI proteins described above, exemplary tumor suppressors from which the subject transcellular proteins can be generated include the Rb protein (and related proteins) and the p53 protein. For instance, the subject constructs can be generated with a therapeutic polypeptide domain comprising at least a functional domain of Rb, pl07 or other Rb-like protein. Such tumor suppressor domainss have been mapped through both genetic and biochemical means. (Hu et al. (1990) EMBO J. 9:1147-1155; Ewen et al. (1991) Cell 66:1155-1164; Ewen et al. (1992) Science 255:85- 87). An approximately 400 amino acid fragment of Rb and pi 07, termed the Rb pocket, is responsible for association of these proteins with the DNA tumor vims oncoproteins and cellular ligands. Within this domain, are six regions of extensive sequence similarity between Rb and pi 07. (Ewen et al. (1991), supra). Another class of tumor suppressors which can be used to generate the subject transcellular proteins include the DOTs (also dpc-4 and MAD-like proteins in the literature). Exemplary members of the this protein family include GenBank accession numbers U76622, U59913, U59911, U68019, U65019, U68018, U68019, 1438077, U59913 and U59912. These proteins are involved in intracellular signal transduction events downstream of TGFβ (superfamily) receptors. For instance, it has been previously shown that Smad3 and Smad4 (the product of the tumor suppressor gene DPC-4) strongly synergize to induce strong ligand-independent TGF-β-like responses, and that inactive carboxy-terminally truncated mutants of either Smad act as dominant-negative inhibitors of the natural TGF -beta response. Zhang et al. (1997) Curr Biol 7:270-276. DPC-4 has been reported as a candidate tumour suppressor. Thus, agonist and antagonist (dominant negative) forms of the DOT proteins can be used to generate trancellular polypeptides which alter the response of a cell to TGFβ's. Another illustrative example of the subject transcellular proteins include fusion proteins generated with Bcl-2 or Bcl-x polypeptide sequences. The protein Bcl-2 plays a central role in the process of programmed cell death by blocking apoptosis. For example, when Bcl-2 levels in a cell are elevated, apoptosis is blocked. Conversely, when Bcl-2 levels in a cell are lowered, the rate of cell death is accelerated. The protein encoded by the bcl-2 proto-oncogene has been reported to be capable of inhibiting apoptosis in many hematopoietic cell systems. The bcl-2 protein is a 26 kD membrane-associated cytoplasmic protein (Tsujimoto et al. (1987) Oncogene 2: 3; USSN 5,202,429 and USSN 5,015,568; Hockenbery et al. (1991) PNAS 88:6961 ; Monaghan et al. (1992) J. Histochem. Cytochem. 40:1819; Nguyen et al. (1993) J. Biol. Chem. 268: 25265; and Nguyen et al. (1994) J. Biol. Chem. 269:16521). The capacity of bcl-2 to enhance cell survival is related to its ability to inhibit apoptosis initiated by several factors, such as cytokine deprivation, radiation exposure, glucocorticoid treatment, and administration of anti-CD-3 antibody. Thus, all or a portion of bcl-2 sufficient to inhibit apoptosis can be used to generate the subject transcellular proteins. Likewise, the transcellular protein can be generated using all or a portion of a protein which interacts with and/or is structurally related to the bcl-2 gene product have also been identified, such as for example bcl-x and bcl-x s [Boise et al. (1993) Cell 74: 597; Gonzalez-Garcia et al. (1994) Development 120: 3033; Gottschalk et al. (1994) PNAS 91 : 7350], Bax [Oltvai et al. (1993) Cell 74: 609], Mcl-1 [Kozopas et al. (1993) PNAS 90: 3516], and Al [Lin et al. (1993) J. Immunol. 151 : 179] An example of a signal transduction protein which can be used to generate the subject transcellular proteins is the product the mammalian tubby (tub) genes, e.g., which are involved in the control of mammalian body weight. See, for example, USSN 5,646,040. Tubby, an autosomal recessive mutation recently found to be the result of a splicing defect in the tubby gene. Thus, agonist and antagonist forms of tubby proteins can be used to control weight gain in animals. Moreover, these proteins are also excellent candidates for use in the treatment of ocular diseases as mutations in the tubby gene are known to lead to early progressive retinal degeneration. Still another family of proteins which can be used to generate a transcellular protein of the present invention are the IκB proteins. The nuclear factor-κB (NF-κB) is an inducible transcription factor which participates in the regulation of multiple cellular genes after treatment of cells with a variety of factors. These genes are involved in the immediate early processes of immune, acute phase, and inflammatory responses. NF-κB has also been implicated in the transcriptional activation of several viruses, most notably the type 1 human immunodeficiency vims (HIV-1) and cytomegalovirus (CMV) (Nabel et al. (1987) Nature 326:711; Kaufman et al. (1987) Mol. Cell. Biol. 7:3759; and Sambucetti et al. (1989) EMBO J 8:4251). Activation of the NF-κB transcription factor and various related forms can be initiated by a variety of agents, including TNF-cc, phorbol 12-myristate 13-acetate (PMA), interleukin-1 (IL-1) and interleukin-2 (IL-2). Activation proceeds through a post- translational event in which preformed cytoplasmic NF-κB in the Rel complex is released from a cytoplasmic inhibitory protein. A common feature of the regulation of transcription factors which belong to the Rel-family is their sequestration in the cytoplasm as inactive complexes with a class of inhibitory molecules known as IκBs (Baeuerle et al. (1988) Cell 53:211; Beg et al. (1993) Genes Dev. 7:2064; and Gilmore et al. (1993) Trends in Genetics 9:427). Treatment of cells with different inducers, e.g., IL-1, TNF-α, LPS, dsRNA or PMA, results in dissociation of the cytoplasmic complexes and translocation of free NF-κB to the nucleus (Grilli et al. (1993) International Rev. of Cytology 143:1-62; Baeuerle et al. (1994) Annu. Rev. Immunol. 12:141). The dissociation of the cytoplasmic complexes is understood to be triggered by the phosphorylation and subsequent degradation of the IκB protein (Palombella et al. (1994) Cell 78:773; Ghosh et al. (1990) Nature 344:678). Thus, the IκB proteins provide a therapeutic target for being upregulated, such as be ectopic expression through gene therapy. Accordingly, the subject transcellular protein can be generated with an IκB polypeptide sufficient to bind to and prevent nuclear localization of NF-κB. In preferred embodiments, the IκB polypeptide has been altered, e.g., by point mutagenesis or truncation, to increase the intracellular half-life of the fusion protein. For instance, Lys-25 and Lys-26 of human IκBα can be mutated to remove the ability of the protein to be ubiquitinated. In still other embodiments, the trancellular protein can be generated with a transcription factor polypeptide, as well as with a transcription repressor polypeptide, e.g., to potentiate or inhibit the expression of a gene. In other embodiments, the therapeutic portion of the trancellular protein can be provided from a metal binding protein, e.g., for use in inhibiting the action of intracellular DNA damaging agents such as cisplatin. In yet other embodiments, the therapeutic polypeptide of the trancellular fusion protein can be derived from small peptides/polypeptides which are artificial in sequence, or which are tmncated forms of any of such proteins as described above. In an illustrative embodiment, the therapeutic polypeptide can be a peptide inhibitor of cyclin dependent kinases, such described in USSN 5,625,031. In general, the criteria for selecting the therapeutic polypeptide portion of the transcellular protein is reasonably straightforward. As with the CKI polypeptides, the therapeutic polypeptide sequence included in the fusion protein should from an intracellular protein which modulates a biological process in the cell, e.g., by either mimicing or antagonizing the wild-type form of the protein from which it is derived. The therapeutic polypeptide sequence included in the fusion protein preferably does not includes any membrane association sequences, such as transmembrane domains, myristolation sequences, etc. The therapeutic polypeptide sequence also preferably does not includes any disulfide bonds. It is preferably no larger than about lOOkD, and is even more preferably no larger than 75, 50 or even 30 kd. It is also preferably no smaller than about 20 amino acids residues. (vi) Co-delivery of CKI polypeptides and endothelialization polypeptides CKI polypeptides, including those chimeric CKI polypeptides described above, can be used to inhibit proliferation of smooth muscle cells, and can therefore be used as part of a therapeutic regimen in the treatment of a patient suffering from a condition which is characterized by excessive smooth muscle proliferation. The arterial wall is a complex multicellular structure and is important in the regulation of inflammation, coagulation, and regional blood flow. Vascular smooth muscle cells (SMCs) are located predominantely in the arterial tunica media and are important regulators of vascular tone and blood pressure. These cells are normally maintained in a nonproliferative state in vivo. Arterial injury results in the migration of SMCs into the intimallayer of the arterial wall, where they proliferate and synthesize extracellular matrix components. Arterial intimal thickening after injury is the result of the following series of events: 1) initiation of smooth muscle cell proliferation within hours of injury, 2) SMC migration to the intima, and 3) further SMC proliferation in the intima with deposition of matrix. Investigations of the pathogenesis of intimal thickening following arterial injury have shown that platelets, endothelial cells, macrophages and smooth muscle cells release paracrine and autocrine growth factors (such as platelet derived growth factor, PDGFα), epidermal growth factor, insulin-like growth factor, and transforming growth factor and cytokines that result in the smooth muscle cell proliferation and migration. T-cells and macrophages also migrate into the neotima. This cascade of events is not limited to arterial injury, but also occurs following injury to veins and arterioles. The overall disease process can be termed a hypeφroliferative vascular disease because of the etiology of the disease process. Vascular injury causing intimal thickening can be broadly categorized as being either biologically or mechanically induced. One of the most commonly occurring forms of biologically mediated vascular injury leading to stenosis is Atherosclerosis. The migration and proliferation of vascular smooth muscle plays a cmcial role in the pathogenesis of atherosclerosis. Atherosclerotic lesions include massive accumulation of lipid laden "foam cells" derived from monocyte/macrophage and smooth muscle cells. Formation of "foam cell" regions is associated with a breech of endothelial integrity and basal lamina destruction. Triggered by these events, restenosis is produced by a rapid and selective proliferation of vascular smooth muscle cells with increased new basal lamina (extracellular matrix) formation and results in eventual blocking of arterial pathways (Davies). Mechanical injuries leading to intimal thickening result following balloon angioplasty, vascular surgery, transplantation surgery, and other similar invasive processes that disrupt vascular integrity. Although balloon angioplasty can dilate arterial stenosis effectively, restenosis occurs in 30-40% of patients after 6 months. Intimal thickening following balloon catheter injury has been studied in animals as a model for arterial restenosis that occurs in human patients following balloon angioplasty. De- endothelialization with an intraarterial catheter, which dilates an artery, injures the innermost layers of medial smooth muscle and may even kill some of the innermost cells. Injury to the innermost layers of medial smooth muscle is followed by a proliferation of the medial smooth muscle cells, after which many of them migrate into the intima through fenestrae in the intemal elastic lamina and proliferate to form a neointimal lesion. Smooth muscle cell proliferation is a critical event in the pathogenesis of atherosclerosis and transplant arteriosclerosis as well as in the response to injury arising from all forms of vascular reconstruction such as angioplasty (Raines et al. (1993) Br. Heart J. 69 (Supplement), S 30; Clowes et al. (1991) Vase. Surg 13:885; and Isik et al. (1992) Am. J. Pathol. 141:1139). Invasive cardiovascular surgical procedures, such as percutaneous translumenal coronary angioplasty (PTCA, using a balloon catheter) and aorto-coronary bypass surgery (ACBS), that are currently employed in treating the coronary stenosis or occlusion caused by atherosclerosis represent a major therapeutic advance for managing coronary heart disease (CHD). However, the cellular proliferative response and associated intimal hypeφlasia that can follow the damage to blood vessels that occurs with these procedures leads to complications which cannot be effectively controlled by presently available drugs, and can be more detrimental than the original condition. The development of these complications, termed restenosis (in the case of PTCA) or stenosis (in the case of ACBS), has similarities to the development of atherosclerosis. However, reendothelialization of the injured area concurrent with smooth muscle cell proliferation is a major consideration for inhibiting restenosis (Casscells, W. Circulation 1992, 86, 722; Reidy, M. A.; Lidner, V. in endothelial Cell Dysfunctions, Simionescu, N. and Simionescu M., Ed. Plenum Press, NY N.Y., (1992), 31). Thus, any successful approach to inhibiting SMC proliferation should not interfere with endothelial cell repair or the normal function of other cell types (Weissberg, P. L.; Grainger, D. J.; Shanahan C. M.; Metcalfe, J. C. Cardiovascular Res. 1993, 27, 1191). Accordingly, the present invention provides compositions and methods for treating patients suffering from disorders marked by unwanted proliferation of smooth muscle cells where endothelization is a desired goal in addition to inhibiting proliferation of SMCs. In one aspect, the method of the present invention arranges for simultaneous delivery of a CKI polypeptide along with a second polypeptide (an "endothelization polypeptide") which (a) stimulates endothelial cell proliferation; (b) stimulates migration of endothelial cells to the wound site; and/or (c) inhibits smooth muscle cell migration. For instance, in an attempt to prevent restenosis or reduced intimal smooth muscle cell proliferation following angioplasty, the present compositions can be employed clinically, concurrent with or following angioplasty. Exemplary endothelization polypeptides which can be do-delivered with a CKI polypeptide include angiogenic basic fibroblast growth factors (bFGF), acid fibroblast growth factor (aFGF), vascular endothelial growth factor (VEGF), platelet derived growth factor (PDGF), vascular permeability growth factor (VPF), transforming growth factor beta (TGF-β) and various cytokines. Related molecules which operate in a similar fashion may also be used. Other endothelization polypeptides include those which may stimulate re- endothelial growth by, e.g., stimulating VEGF production by vascular smooth muscle cells, or inhibit smooth muscle cell migration by, e.g., down-regulating or antagonizing vascular smooth muscle cell PDGF receptors. In a preferred embodiment, the endothelization polypeptide is derived from basic FGF, such as a human bFGF. Basic FGF is an effective mitogen for vascular smooth muscle cells in the medial layer of the artery wall. For instance, a human bFGF molecule that was purified from placenta ("placental bFGF") was shown to (a) stimulate capillary endothelial cell proliferation, (b) to stimulate chemotaxis in capillary endothelial cells and (c) to stimulate these same cells to produce plasminogen activator and latent collagenase. Another exemplary polypeptide that can be co-delivered with the subject CKIs is acidic fibroblast growth factor (aFGF). It has been demonstrated that intravenous administration of aFGF promotes vascular repair in the rat carotid artery model of restenosis, and therefore may be efficacious in the prevention of restenosis (Bjomsson et al., (1991) /W .S 88: 8651-8655). In yet another preferred embodiment, the endothelialization polypeptide is derived from a vascular endothelial growth factor, particular a human VEGF. As is clear from the context above, also included within the scope of the term "endothelialization polypeptide" are biologically active fragments thereof, as well as N- terminally or C-terminally extended versions thereof or analogs thereof substituting and/or deleting or inserting one or more amino acid residues which retain qualitatively the biological activities of the protein described herein. For instance, preferred homologs include those in which one or more cysteine residues not required for biological activity are substituted by a different amino acid residue, preferably serine. Substitution of one or more cysteine residues reduces the opportunity for intermolecular and intramolecular disulfide bond formation, thereby rendering the molecule more stable. There are nine cysteine residues that are present in human VEGF121, bovine VEGF 120, human VEGF 165 and bovine VEGF 164. Of these, eight are conserved with PDGF. Accordingly, the most preferred analog is one in which the ninth cysteine residue is substituted by serine. This cysteine residue is present at position 160 of hVEGF165 and position 1 16 of hVEGF121 and the corresponding positions in the bovine forms. Amino acid substitutions can be accomplished by site specific mutagenesis of the DNA sequences described herein using well known techniques (see, e.g., Zoller, M. J. and Smith, M., Nucleic Acids Research (1982) 10:6487-6500). While the native form of the bovine vascular endothelial cell growth factor is apparently glycosylated, there is currently no evidence that glycosylation is essential for biological activity. Accordingly, biologically active non-glycosylated or partially glycosylated forms, which can be produced by prokaryotic host cells or by mutation of glycosylation sites in the protei, are included within the scope of VEGF and the other endothelialization polypeptides. In another embodiment, the endothelialization polypeptide comprises an epidermal growth factor (EGF) polypeptide coupled with hyaluronic acid (HA). HA/EGF formulations have been demonstrated to stimulate reendothelialization in the anterior chamber of the eye. Hyaluronic acid (HA) is one of the mucopolysaccharides having a straight chain structure consisting of the repetition of a disaccharide unit of N- acetylglucosamine and glucuronic acid. HA is found in nature, in microorganisms and in the skin and connective tissue of humans and other animals. Moreover, the glycosaminoglycans (GAGs) heparin and heparan sulfate (HS) are endogenous inhibitors of SMC proliferation, yet are able to promote endothelial cell growth (Castellot (1987) Seminars in Thrombosis and Hemostasis 13:489; and Wight, T. N. (1989) Arteriosclerosis 9:1). The endothelization polypeptide can be derived from a protein which naturally includes HS GAG chains, or which has been engineered to artificially include HS GAG chains. See, for example, U.S. Patent 5,486,599. There are a variety of assays available for rapidly accessing the suitability of a potential endothelialization polypeptide. For instance, mitogenic activity for vascular endothelial cells can be determined by an assay which uses, as target cells, adrenal cortex- derived capillary endothelial cells (ACE cells). This assay is carried out essentially as described in Gospodarowicz et al., (1986) J. Cell Physiol. 127:121-136). Generally, stock cultures of ACE cells are maintained in the presence of Dulbecco's modified Eagle's medium (DMEM-21) supplemented with 10% calf semm. The antibiotics penicillin (50 IU/ml), streptomycin (50 mu g/ml), gentamycin (50 mu g/ml), and Fungizone (0.25 mu g/ml) and 2 mM L-glutamine can also be added to the medium. Cells are passaged weekly on tissue culture dishes at a split ratio of between 1 :40 and 1 :200 (the preferred split ratio is that which gives 2.5 x 10 5 cells in 15 ml of medium in T75 flasks). For the mitogenic assay, cells are seeded in 12 well cluster plates at a density of 5 x 10 3 cells per well in 1 ml Dulbecco's modified Eagle's medium supplemented with 10% calf semm and antibiotics as described in Gospodarowicz et al., (1988) Europ. J. Cell. Biol. 46:144-151. Alternatively, the ACE cells are plated in 35 mm dishes or 6 well cluster plates at a density of 5-10 x 10 3 cells per dish or well in 2 ml of medium as described in Gospodarowicz et al., (1986), supra. Ten-microliter aliquots of appropriate dilutions of each sample are then added to duplicate or triplicate wells in the dishes on days 0 and 2. After 4 or 5 days in culture, the plates are trypsinized and cell densities determined in a Coulter counter. For puφoses of description herein, a factor is considered to have mitogenic activity for vascular endothelial cells if the cell density at the end of this assay is at least 1.5 times and preferably at least 3 times the cell density of control wells receiving no factor additions. The CKI polypeptide and endothelialization polypeptide can be co-delivered as, for example, purified protein mixtures. The proteins can be admixed prior to administration, or administered separately but in close temporal proximity to one and other. Alternatively, one or both of the polypeptides can be delivered by a gene therapy vector. Where both are delivered by expression vectors, the coding sequences for each polypeptide can be present on the same expression constmct, or can be provided by two separate constructs, the latter requiring co-transfection with both constructs. In the instance of the former, the coding sequences for each polypeptide can be under the control of the same promoter, and may even provide for a polycistronic message (see, for example, U.S. Patent 4,713,339); alternatively, the two coding sequences, while present on the same expression vector can be under the control of two separate promotes. The CKI polypeptide can consist of as little as a CDK-binding moitey of a CKI protein, or can include a full length CKI protein and/or be a poly-CBM protein. (vii) Exemplary Pharmaceutical Preparations For certain of the therapeutic uses of the subject chimeric proteins, particularly cutaneous uses such as for the control of keratinocyte proliferation, direct administration of the protein will be appropriate (rather than use of a gene therapy constmct). Accordingly, the subject CKI polypeptide formulations may be conveniently formulated for administration with a biologically acceptable medium, such as water, buffered saline, polyol (for example, glycerol, propylene glycol, liquid polyethylene glycol and the like) or suitable mixtures thereof. In preferred embodiments, the chimeric protein is dispersed in lipid formulations, such as miscelles, which closely resemble the lipid composition of natural cell membranes to which the chimeric protein is to be delivered. The optimum concentration of the active ingredient(s) in the chosen medium can be determined empirically, according to procedures well known to medicinal chemists. As used herein, "biologically acceptable medium" includes any and all solvents, dispersion media, and the like which may be appropriate for the desired route of administration of the pharmaceutical preparation. The use of such media for pharmaceutically active substances is known in the art. Except insofar as any conventional media or agent is incompatible with the activity of the CKI polypeptide (or intemalization peptide or endothelialization polypeptide as the case may be), its use in the pharmaceutical preparation of the invention is contemplated. Suitable vehicles and their formulation inclusive of other proteins are described, for example, in the book Remington's Pharmaceutical Sciences (Remington's Pharmaceutical Sciences. Mack Publishing Company, Easton, Pa., USA 1985). In an exemplary embodiment, the subject CKI protein mixture is provided for transmucosal or transdermal delivery. For such administration, penetrants appropriate to the barrier to be permeated are used in the formulation with the polypeptide. Such penetrants are generally known in the art, and include, for example, for transmucosal administration bile salts and fusidic acid derivatives. In addition, detergents may be used to facilitate permeation. Transmucosal administration may be through nasal sprays or using suppositories. For topical administration, the proteins of the invention are formulated into ointments, salves, gels, or creams as generally known in the art. In accordance with the subject method, expression constructs of the subject CKI polypeptides (and endothelialization polypeptide as appropriate) may be administered in any biologically effective carrier, e.g. any formulation or composition capable of effectively transfecting cells in vivo with a recombinant fusion gene. Approaches include insertion of the subject fusion gene in viral vectors including recombinant retroviruses, adenovirus, adeno-associated vims, and heφes simplex virus- 1, or recombinant bacterial or eukaryotic plasmids. Viral vectors can be used to transfect cells directly; plasmid DNA can be delivered with the help of, for example, cationic liposomes (lipofectin) or derivatized (e.g. antibody conjugated), polylysine conjugates, gramacidin S, artificial viral envelopes or other such intracellular carriers, as well as direct injection of the gene constmct or CaPO4 precipitation carried out in vivo. It will be appreciated that because transduction of appropriate target cells represents the critical first step in gene therapy, choice of the particular gene delivery system will depend on such factors as the phenotype of the intended target and the route of administration, e.g. locally or systemically. A preferred approach for in vivo introduction of nucleic acid encoding one of the subject CKI polypeptides into a cell is by use of a viral vector containing nucleic acid, e.g. a cDNA, encoding the gene product. Infection of cells with a viral vector has the advantage that a large proportion of the targeted cells can receive the nucleic acid. Additionally, molecules encoded within the viral vector, e.g., by a cDNA contained in the viral vector, are expressed efficiently in cells which have taken up viral vector nucleic acid. Retrovims vectors and adeno-associated vims vectors are generally understood to be the recombinant gene delivery system of choice for the transfer of exogenous genes in vivo, particularly into humans. These vectors provide efficient delivery of genes into cells, and the transferred nucleic acids are stably integrated into the chromosomal DNA of the host. A major prerequisite for the use of retroviruses is to ensure the safety of their use, particularly with regard to the possibility of the spread of wild-type vims in the cell population. The development of specialized cell lines (termed "packaging cells") which produce only replication-defective retroviruses has increased the utility of retroviruses for gene therapy, and defective retrovimses are well characterized for use in gene transfer for gene therapy puφoses (for a review see Miller, A.D. (1990) Blood 76:271). Thus, recombinant retrovims can be constructed in which part of the retroviral coding sequence (gag, pol, env) has been replaced by nucleic acid encoding a CKI polypeptide, rendering the retrovims replication defective. The replication defective retrovims is then packaged into virions which can be used to infect a target cell through the use of a helper virus by standard techniques. Protocols for producing recombinant retrovimses and for infecting cells in vitro or in vivo with such vi ses can be found in Current Protocols in Molecular Biology, Ausubel, F.M. et al. (eds.) Greene Publishing Associates, (1989), Sections 9.10-9.14 and other standard laboratory manuals. Examples of suitable retrovimses include pLJ, pZIP, pWE and pEM which are well known to those skilled in the art. Examples of suitable packaging vims lines for preparing both ecotropic and amphotropic retroviral systems include ψCrip, ψCre, ψ2 and ψAm. Retrovimses have been used to introduce a variety of genes into many different cell types, including neural cells, epithelial cells, endothelial cells, lymphocytes, myoblasts, hepatocytes, bone marrow cells, in vitro and/or in vivo (see for example Eglitis, et al. (1985) Science 230:1395-1398; Danos and Mulligan (1988) Proc. Natl. Acad. Sci. USA 85:6460-6464; Wilson et al. (1988) Proc. Natl. Acad. Sci. USA 85:3014-3018; Armentano et al. (1990) Proc. Natl. Acad. Sci. USA 87:6141-6145; Huber et al. (1991) Proc. Natl. Acad. Sci. USA 88:8039- 8043; Ferry et al. (1991) Proc. Natl. Acad. Sci. USA 88:8377-8381; Chowdhury et al. (1991) Science 254:1802-1805; van Beusechem et al. (1992) Proc. Natl. Acad. Sci. USA 89:7640-7644; Kay et al. (1992) Human Gene Therapy 3:641-647; Dai et al. (1992) Proc. Natl. Acad. Sci. USA 89:10892-10895; Hwu et al. (1993) J. Immunol. 150:4104-4115; U.S. Patent No. 4,868,116; U.S. Patent No. 4,980,286; PCT Application WO 89/07136; PCT Application WO 89/02468; PCT Application WO 89/05345; and PCT Application WO 92/07573). In choosing retroviral vectors as a gene delivery system for the subject fusion proteins, it is important to note that a prerequisite for the successful infection of target cells by most retrovimses, and therefore of stable introduction of the recombinant gene, is that the target cells must be dividing. In general, this requirement will not be a hindrance to use of retroviral vectors to deliver the subject fusion gene constructs. In fact, such limitation on infection can be beneficial in circumstances where the tissue (e.g. nontransformed cells) surrounding the target cells does not undergo extensive cell division and is therefore refractory to infection with retroviral vectors. Furthermore, it has been shown that it is possible to limit the infection spectrum of retrovimses and consequently of retroviral-based vectors, by modifying the viral packaging proteins on the surface of the viral particle (see, for example PCT publications WO93/25234, WO94/06920, and WO94/11524). For instance, strategies for the modification of the infection spectmm of retroviral vectors include: coupling antibodies specific for cell surface antigens to the viral env protein (Roux et al. (1989) PNAS 86:9079-9083; Julan et al. (1992) J. Gen Virol 73:3251-3255; and Goud et al. (1983) Virology 163:251-254); or coupling cell surface ligands to the viral env proteins (Neda et al. (1991) J Biol Chem 266:14143-14146). Coupling can be in the form of the chemical cross-linking with a protein or other variety (e.g. lactose to convert the env protein to an asialoglycoprotein), as well as by generating fusion proteins (e.g. single-chain antibody/env fusion proteins). This technique, while useful to limit or otherwise direct the infection to certain tissue types, and can also be used to convert an ecotropic vector in to an amphotropic vector. Moreover, use of retroviral gene delivery can be further enhanced by the use of tissue- or cell-specific transcriptional regulatory sequences which control expression of the fusion gene of the retroviral vector. Another viral gene delivery system useful in the present invention utilitizes adenovims-derived vectors. The genome of an adenovims can be manipulated such that it encodes a gene product of interest, but is inactivate in terms of its ability to replicate in a normal lytic viral life cycle (see, for example, Berkner et al. (1988) BioTechniques 6:616; Rosenfeld et al. (1991) Science 252:431-434; and Rosenfeld et al. (1992) Cell 68:143-155). Suitable adenoviral vectors derived from the adenovims strain Ad type 5 dl324 or other strains of adenovims (e.g., Ad2, Ad3, Ad7 etc.) are well known to those skilled in the art. Recombinant adenovimses can be advantageous in certain circumstances in that they are not capable of infecting nondividing cells and can be used to infect a wide variety of cell types, including endothelial cells (Lemarchand et al. (1992) Proc. Natl. Acad. Sci. USA 89:6482-6486), and smooth muscle cells (Quantin et al. (1992) Proc. Natl. Acad. Sci. USA 89:2581-2584). Furthermore, the virus particle is relatively stable and amenable to purification and concentration, and as above, can be modified so as to affect the spectrum of infectivity . Additionally, introduced adenoviral DNA (and foreign DNA contained therein) is not integrated into the genome of a host cell but remains episomal, thereby avoiding potential problems that can occur as a result of insertional mutagenesis in situations where introduced DNA becomes integrated into the host genome (e.g., retroviral DNA). Moreover, the carrying capacity of the adenoviral genome for foreign DNA is large (up to 8 kilobases) relative to other gene delivery vectors (Berkner et al., supra; Haj-Ahmand and Graham (1986) J. Virol. 57:267). Most replication-defective adenoviral vectors currently in use and therefore favored by the present invention are deleted for all or parts of the viral El and E3 genes but retain as much as 80% of the adenoviral genetic material (see, e.g., Jones et al. (1979) Cell 16:683; Berkner et al., supra; and Graham et al. in Methods in Molecular Biology. E.J. Murray, Ed. (Humana, Clifton, NJ, 1991) vol. 7. pp. 109-127). Expression of the inserted fusion gene can be under control of, for example, the El A promoter, the major late promoter (MLP) and associated leader sequences, the E3 promoter, or exogenously added promoter sequences. Yet another viral vector system useful for delivery of the subject CKI polypeptides is the adeno-associated vims (AAV). Adeno-associated vims is a naturally occurring defective vims that requires another vims, such as an adenovims or a heφes vims, as a helper vims for efficient replication and a productive life cycle. (For a review see Muzyczka et al. Curr. Topics in Micro, and Immunol. (1992) 158:97- 129). It is also one of the few vimses that may integrate its DNA into non-dividing cells, and exhibits a high frequency of stable integration (see for example Flotte et al. (1992) Am. J. Respir. Cell. Mol. Biol. 7:349-356; Samulski et al. (1989) J. Virol. 63:3822-3828; and McLaughlin et al. (1989) J. Virol. 62:1963-1973). Vectors containing as little as 300 base pairs of AAV can be packaged and can integrate. Space for exogenous DNA is limited to about 4.5 kb. An AAV vector such as that described in Tratschin et al. (1985) Mol. Cell. Biol. 5:3251-3260 can be used to introduce DNA into cells. A variety of nucleic acids have been introduced into different cell types using AAV vectors (see for example Hermonat et al. (1984) Proc. Natl. Acad. Sci. USA 81 :6466-6470; Tratschin et al. (1985) Mol. Cell. Biol. 4:2072- 2081; Wondisford et al. (1988) Mol. Endocrinol. 2:32-39; Tratschin et al. (1984) J. Virol. 51 :611-619; and Flotte et al. (1993) J. Biol. Chem. 268:3781-3790). Other viral vector systems that may have application in gene therapy have been derived from heφes vims, vaccinia vims, and several RNA vimses. In particular, heφes vims vectors may provide a unique strategy for persistent expression of the subject fusion proteins in cells of the central nervous system and ocular tissue (Pepose et al. (1994) Invest Ophthalmol Vis Sci 35:2662-2666) In addition to viral transfer methods, such as those illustrated above, non-viral methods can also be employed to cause expression of a the subject proteins in the tissue of an animal. Most nonviral methods of gene transfer rely on normal mechanisms used by mammalian cells for the uptake and intracellular transport of macromolecules. In preferred embodiments, non-viral gene delivery systems of the present invention rely on endocytic pathways for the uptake of the gene by the targeted cell. Exemplary gene delivery systems of this type include liposomal derived systems, poly-lysine conjugates, and artificial viral envelopes. In a representative embodiment, a gene encoding one of the subject proteins can be entrapped in liposomes bearing positive charges on their surface (e.g., lipofectins) and (optionally) which are tagged with antibodies against cell surface antigens of the target tissue (Mizuno et al. (1992) No Shinkei Geka 20:547-551 ; PCT publication WO91/06309; Japanese patent application 1047381 ; and European patent publication EP-A-43075). For example, lipofection of neuroglioma cells can be carried out using liposomes tagged with monoclonal antibodies against glioma- associated antigen (Mizuno et al. (1992) Neurol. Med. Chir. 32:873-876). In yet another illustrative embodiment, the gene delivery system comprises an antibody or cell surface ligand which is cross-linked with a gene binding agent such as poly-lysine (see, for example, PCT publications WO93/04701 , WO92/22635, WO92/20316, WO92/19749, and WO92/06180). For example, the subject gene constmct can be used to transfect hepatocytic cells in vivo using a soluble polynucleotide carrier comprising an asialoglycoprotein conjugated to a polycation, e.g. poly-lysine (see U.S. Patent 5,166,320). It will also be appreciated that effective delivery of the subject nucleic acid constmcts via receptor-mediated endocytosis can be improved using agents which enhance escape of the gene from the endosomal stmctures. For instance, whole adenovims or fusogenic peptides of the influenza HA gene product can be used as part of the delivery system to induce efficient disruption of DNA-containing endosomes (Mulligan et al. (1993) Science 260-926; Wagner et al. (1992) PNAS 89:7934; and Christiano et al. (1993) PNAS 90:2122). In clinical settings, the gene delivery systems can be introduced into a patient by any of a number of methods, each of which is familiar in the art. For instance, a pharmaceutical preparation of the gene delivery system can be introduced systemically, e.g. by intravenous injection, and specific transduction of the target cells occurs predominantly from specificity of transfection provided by the gene delivery vehicle, cell-type or tissue-type expression due to the transcriptional regulatory sequences controlling expression of the gene, or a combination thereof. In other embodiments, initial delivery of the recombinant gene is more limited with introduction into the animal being quite localized. For example, the gene delivery vehicle can be introduced by catheter (see U.S. Patent 5,328,470) or by stereotactic injection (e.g. Chen et al. (1994) PNAS 91 : 3054-3057). Moreover, the pharmaceutical preparation can consist essentially of the gene delivery system in an acceptable diluent, or can comprise a slow release matrix in which the gene delivery vehicle is imbedded. Alternatively, where the complete gene delivery system can be produced in tact from recombinant cells, e.g. retroviral packages, the pharmaceutical preparation can comprise one or more cells which produce the gene delivery system. In the case of the latter, methods of introducing the viral packaging cells may be provided by, for example, rechargeable or biodegradable devices. Various slow release polymeric devices have been developed and tested in vivo in recent years for the controlled delivery of dmgs, including proteinacious biopharmaceuticals, and can be adapted for release of viral particles through the manipulation of the polymer composition and form. A variety of biocompatible polymers (including hydrogels), including both biodegradable and non-degradable polymers, can be used to form an implant for the sustained release of an the viral particles by cells implanted at a particular target site. Such embodiments of the present invention can be used for the delivery of an exogenously purified virus, which has been incoφorated in the polymeric device, or for the delivery of viral particles produced by a cell encapsulated in the polymeric device. By choice of monomer composition or polymerization technique, the amount of water, porosity and consequent permeability characteristics can be controlled. The selection of the shape, size, polymer, and method for implantation can be determined on an individual basis according to the disorder to be treated and the individual patient response. The generation of such implants is generally known in the art. See, for example, Concise Encyclopedia of Medical & Dental Materials, ed. by David Williams (MIT Press: Cambridge, MA, 1990); and the Sabel et al. U.S. Patent No. 4,883,666. In another embodiment of an implant, a source of cells producing the recombinant vims is encapsulated in implantable hollow fibers. Such fibers can be pre-spun and subsequently loaded with the viral source (Aebischer et al. U.S. Patent No. 4,892,538; Aebischer et al. U.S. Patent No. 5,106,627; Hoffman et al. (1990) Expt. Neurobiol. 110:39-44; Jaeger et al. (1990) Prog. Brain Res. 82:41-46; and Aebischer et al. (1991) J. Biomech. Eng. 1 13:178-183), or can be co-extmded with a polymer which acts to form a polymeric coat about the viral packaging cells (Lim U.S. Patent No. 4,391,909; Sefton U.S. Patent No. 4,353,888; Sugamori et al. (1989) Trans. Am. Artif. Intern. Organs 35:791-799; Sefton et al. (1987) Biotechnol. Bioeng. 29:1135-1143; and Aebischer et al. (1991) Biomaterials 12:50-55). Again, manipulation of the polymer can be carried out to provide for optimal release of viral particles. (viii) Exemplary Uses for the subject antiproliferative formulations The subject fusion proteins can be used in the treatment of hypeφroliferative vascular disorders, e.g. smooth muscle hypeφlasia (such as atherosclerosis) or restinosis, as well as other disorders characterized by fibrosis, e.g. rheumatoid arthritis, insulin dependent diabetes mellitus, glomerulonephritis, cirrhosis, and scleroderma, particularly proliferative disorders in which loss of TGF-β autocrine or paracrine signaling, and accordingly loss of pi 5 function, is implicated. For example, restinosis continues to limit the efficacy of coronary angioplasty despite various mechanical and pharmaceutical interventions that have been employed. An important mechanism involved in normal control of intimal proliferation of smooth muscle cells appears to be the induction of autocrine and paracrine TGF-β inhibitory loops in the smooth muscle cells (Scott-Burden et al. (1994) Tex Heart Inst J 21 :91-97; Graiger et al. (1993) Cardiovasc Res 27:2238-2247; and Grainger et al. (1993) Biochem J 294:109-112). Loss of sensitivity to TGF-β, or alternatively, the overriding of this inhibitory stimulus such as by PDGF autostimulation, can be a contributory factor to abnormal smooth muscle proliferation in restinosis. It may therefore be possible to treat or prevent restinosis by the use of gene therapy with CDK inhibitor fusion protein of the present invention. The fusion gene construct can be delivered, for example, by percutaneous transluminal gene transfer (Mazur et al. (1994) Tex Heart Inst J 21 :104-11 1) using viral or liposomal delivery compositions. An exemplary adenovirus-mediated gene transfer technique and compositions for treatment of cardiac or vascular smooth muscle is provided in PCT publication WO 94/1 1506. In one embodiment, the co-delivery of a CKI polypeptide with an endothelization polypeptide can be used in the treatment of disorders/injury marked by unwanted smooth muscle cell proliferation and deepithelialization. For example, the co-administration approach can be used as a post-operative wound healing agent in balloon angioplasty, a procedure in which vascular endothelial cells are removed or damaged, together with compression of atherosclerotic plaques. The two polypeptides can be co-delivered to inner vascular surfaces by systemic or local intravenous application either as intravenous bolus injection or infusions of polypeptides, expression constructs, or a mixture thereof. If desired, the endothelialization polypeptide can be administered over time using a micrometering pump, while the CKI polypeptide is ultimately delivered by gene therapy. Suitable compositions for intravenous administration comprise the endothelization polypeptide in an amount effective to promote endothelial cell growth and a parenteral carrier material. The endothelization polypeptide can be present in the composition over a wide range of concentration, administered once or in dosing regimens that allow for multiple applications. Any of the known parenteral carrier vehicles can be used, such as normal saline or 5-10% dextrose. The co-delivery embodiment of the subject method can also be used to inhibit SMC proliferation yet promote endothelialization in vascular graft surgery. In the case of vascular grafts using either transplanted vessels or synthetic material, for example, the endothelization polypeptide can be applied to the surfaces of the graft and/or at the junctions of the graft and the existing vasculature in order to promote the growth of vascular endothelial cells. For such applications, the endothelization polypeptide can be applied intravenously as described above for balloon angioplasty or it can be applied directly to the surfaces of the graft and/or the existing vasculature either before or during surgery. Transforming growth factor-β is also understood to play a significant role in local glomerular and interstitial sites in human kidney development and disease. Consequently, the subject method provides a method of treating or inhibiting glomerulopathies and other renal proliferative disorders comprising the in vivo delivery and recombinant expression of the subject fusion proteins, e.g., the poly-CBM and/or transcellular CKI polypeptides, in kidney tissue. In other embodiments, therapeutic application of a CDK inhibitor fusion protein, e.g., by gene therapy, can be used in the treatment of a neuroglioma. Gliomas account for 40-50% of intracranial tumors at all ages of life. Despite the increasing use of radiotherapy, chemotherapy, and sometimes immunotherapy after surgery for malignant glioma, the mortality and morbidity rates have not substantially improved. However, there is increasing experimental and clinical evidence that for a significant number of gliomas, loss of TGF-β responsiveness is an important event in the loss of growth control. Irrespective of the cause of decreased responsiveness, e.g. the loss of function of pi 5 or the loss of other TGF-β signal transduction proteins, exogenous expression of, for example, an INK4 fusion protein such as pl5/p27 fusion protein in the cell can used effectively to inhibit cell proliferation. Yet another aspect of the invention pertains to methods of treating proliferative and/or differentiative disorders which arise from cells which, despite aberrant growth control, still require one or more CDKs (e.g., CDK4 or CDK6) for cell growth. There are a wide variety of pathological cell proliferative conditions for which the fusion gene constmcts of the present invention can provide therapeutic benefits, with the general strategy being the inhibition of an anomalous cell proliferation. For instance, the gene constmcts of the present invention can be used as a part of a gene therapy protocol in a cell in which a cell-cycle regulatory protein (such as an INK4 or CIP protein) is misexpressed or in which signal transduction pathways upstream of the protein are dysfunctional. To illustrate, cell types which exhibit pathological or abnormal growth presumably dependent at least in part on a function of a, INK4 or CIP protein include various cancers and leukemias, psoriasis, bone diseases, fibroproliferative disorders such as involving connective tissues, atherosclerosis and other smooth muscle proliferative disorders, as well as chronic inflammation. In addition to proliferative disorders, the treatment of differentiative disorders which result from, for example, de-differentiation of tissue which may (optionally) be accompanied by abortive reeentry into mitosis. Such degenerative disorders include chronic neurodegenerative diseases of the nervous system, including Alzheimer's disease, Parkinson's disease, Huntington's chorea, amylotrophic lateral sclerosis and the like, as well as spinocerebellar degenerations. Other differentiative disorders include, for example, disorders associated with connective tissue, such as may occur due to de-differentiation of chondrocytes or osteocytes, as well as vascular disorders which involve de-differentiation of endothelial tissue and smooth muscle cells, gastric ulcers characterized by degenerative changes in glandular cells, and renal conditions marked by failure to differentiate, e.g. Wilm's tumors. It will also be apparent that, by transient use of gene therapy constructs of the subject fusion proteins, in vivo reformation of tissue can be accomplished, e.g. in the development and maintenance of organs. By controlling the proliferative and differentiative potential for different cells, the subject gene constructs can be used to reform injured tissue, or to improve grafting and moφhology of transplanted tissue. For example, the subject CDK inhibitors can be employed therapeutically as part of a regimen to regulate organs after physical, chemical or pathological insult. Furthermore, as described in the art, transformation of a cell can be due in part to a loss-of-function mutation to a particular INK4 gene, e.g., ranging from a point mutation to gross deletion of the gene. Additionally, other data suggests that certain disorders may arise because cells have lost the ability to induce expression of an INK4 gene. Normal cell proliferation, for instance, is generally marked by responsiveness to negative autocrine or paracrine growth regulators, such as members of the TGF-β family, e.g. TGF-β 1, TGF-β2 or TGF-β3, and related polypeptide growth inhibitors. Ordinarily, control of cellular proliferation by such growth regulators, particularly in epithelial and hemopoietic cells, is in the form of growth inhibition. Moreover, as described in Hannon and Beach (1995) Nature 371 :257-261, TGF-β inhibits cell proliferation by inducing expressions of pi 5, which in turn inhibits activation of CDK4 or CDK6 complexes. It has been observed that a significant percentage of human cancers derived from cells types ordinarily inhibited by TGF-β display a reduced responsiveness to this growth regulator. For instance, some tumors of colorectal, liver epithelial, and epidermal origin show reduced sensitivity and resistance to the growth-inhibitory effects of TGF-β as compared to their normal counteφarts. In this context, a noteworthy characteristic of several retinoblastoma cell lines is the absence of detectable TGF-β receptors. Treatment of such tumors with the subject fusion proteins provides an opportunity to mimic the TGF-β inhibitory signal. Moreover, it will be appreciated that the subject method can be used generally to inhibit proliferation of cells which, in general, are still reliant on cyclin dependent kinases. It has been demonstrated that gene therapy can be used to target glioma cells for expression of recombinant proteins (Miyao et al. (1993) J. Neurosci. Res. 36:472- 479; Chen et al. (1994) PNAS 91 :3054-3057; and Takamiya et al. (1993) J. Neurosurg. 79:104-110). Thus, a gene construct for expressing the subject fusion protein can be delivered to the tumor, preferably by sterotactic-dependent means. In preferred embodiments, the gene delivery system is a retroviral vector. Since rapidly growing normal cells are rare in the adult CNS, glioma cells can be specifically transduced with a recombinant retrovims. For example, the retroviral particle can be delivered into the tumor cavity through an Ommaya tube after surgery, or alternatively, packaging fibroblasts encapsulated in retrievable immunoisolatory vehicles can be introduced into the tumor cavity. In order to increase the effectiveness and decrease the side effects of the retrovims-mediated gene therapy, glioma-specific promoters can be used to regulate expression of the therapeutic gene. For example, the promoter regions of glial fibrillary acidic protein (GFAP) and myelin basis protein (MBP) can operably linked to the fusion gene in order to direct glial cell-specific expression of the fusion protein. In another embodiment, gene therapy can be used in conjunction with the subject fusion proteins in the treatment of various carcinomas. In a representative embodiment, a gene therapy system comprising the subject fusion gene is used to treat certain breast cancers. In preferred embodiments, expression of the subject fusion protein is controlled at least in part by a mammary-specific promoter, a number of which are available (for review, see Hennighausen (1990) Protein Expression and Purification 1 :3-8; and Gunzberg et al. (1992) Biochem J 283:625-632). In similar fashion, gene therapy protocols involving delivery of the subject fusion protein can be used in the treatment of malignant melanoma, which also serves as a model for progressive TGF-β resistance in transformation. In preferred embodiments, gene therapy protocols for treatment of melanomas include, in addition to the delivery of the fusion gene constmct, the delivery of a pharmaceutical preparation of the gene by direct injection. For instance, U.S. patent no. 5,318,514 describes an applicator for the electroporation of genes into epidermal cells and can be used in accordance with the present invention. The subject method can also be used to treat retinoblastomas in which the retinoblastoma gene (RB) is not itself impaired, e.g. the effective impairment of the RB checkpoint is the result of a failure to control CDK4 phosphorylation of RB. Thus, one of the subject fusion proteins can be expressed in a retinoblastoma cell, thereby causing inhibition of CDK4 activation and down-regulating RB phosphorylation. To illustrate, a recombinant retrovims can be constructed to facilitate expression of a fusion protein including an INK4 protein, e.g., derived from pl6 or pl5, and a CIP protein, e.g., derived from p21, p27 or p57. Infectivity of retinoblastoma cells can be enhanced by derivatizing the env protein with antibodies specific for retinoblastoma cells, e.g. antibodies to retinal S-antigen (Doroso et al. (1985) Invest Opthalmol Vis Sci 26:560-572; see also Liao et al. (1981) Eur J Immunol 11 :450-454; and U.S. Patent No. 4,444,744). In yet another embodiment, the subject gene is delivered to a sarcoma, e.g. an osteosarcoma or Kaposi's sarcoma. In a representative embodiment, the gene is provided in a viral vector and delivered by way of a viral particle which has been derivatized with antibodies immunoselective for an osteosarcoma cell (see, for example, U.S. Patents 4,564,517 and 4,444,744; and Singh et al. (1976) Cancer Res 36:4130-4136). Given the role of CDK activation in various epithelial cell proliferative disorders, it will be evident that the subject fusion proteins will find ready application for the treatment or prophylaxis of, for example, psoriasis; keratosis; acne; comedogenic lesions; vermcous lesions such as verruca plana, plantar warts, verruca acuminata, and other verruciform lesions marked by proliferation of epithelial cells; folliculitis and pseudofolliculitis; keratoacanthoma; callosities; Darier's disease; ichthyosis; lichen planus; molluscous contagiosum; melasma; Fordyce disease; and keloids or hypertrophic scars. Yet another aspect of the present invention relates to the use of the subject fusion proteins to control hair growth. The growth of hard keratin fibers such as wool and hair is dependent on the proliferation of dermal sheath cells. Hair follicle stem cells of the sheath are highly active, and give rise to hair fibers through rapid proliferation and complex differentiation. The hair cycle involves three distinct phases: anagen (growing), catagen (regressing), and telogen (resting). The epidermal stem cells of the hair follicle are activated by dermal papilla during late telogen. This is termed "bulge activation". Moreover, such stem cells are thought to be pluripotent stem cells, giving rise not only to hair and hair follicle stmctures, but also the sebaceous gland and epidermis. The subject method provides a means for altering the dynamics of the hair growth cycle to induce quiescence of proliferation of hair follicle cells, particularly stem cells of the hair follicle, inhibiting CDK activation. For instance, gene therapy treatments or, alternatively, topical administration of a fusion protein preparation, can be employed as a way of reducing the growth of human hair as opposed to its conventional removal by cutting, shaving, or depilation. For instance, the present method can be used in the treatment of trichosis characterized by abnormally rapid or dense growth of hair, e.g. hypertrichosis. In an exemplary embodiment, the subject fusion proteins can be used to manage hirsutism, a disorder marked by abnormal hairiness. Application of the CDK inhibitors of the present invention can also provide a process for extending the duration of depilation. Moreover, because the CDK inhibitor fusion proteins are likely to be cytostatic to epithelial cells, rather than cytotoxic, these proteins can be used to protect hair follicle cells from cytotoxic agents which require progression into S-phase of the cell- cycle for efficacy, e.g. radiation-induced death. Treatment with a CDK inhibitor of the present invention provides protection by causing the hair follicle cells to become quiescent, e.g., by inhibiting the cells from entering S phase, and thereby preventing the follicle cells from undergoing mitotic catastrophe or programmed cell death. For instance, such treatments can be used for patients undergoing chemo- or radiation- therapies which ordinarily result in hair loss. The subject method can also be used in the treatment of folliculitis, such as folliculitis decalvans, folliculitis ulerythematosa reticulata or keloid folliculitis. For example, a cosmetic prepration of an CDK inhibitory fusion protein can be applied topically in the treatment of pseudofolliculitis, a chronic disorder occurring most often in the submandibular region of the neck and associated with shaving, the characteristic lesions of which are erythematous papules and pustules containing buried hairs. In similar fashion, such preparations can be used in the treatment of granulomas, e.g. tumor-like mass or nodule of granulation tissue, which may include epithelial tissue derived from cutaneous or mucosal sources. In another aspect of the invention, the subject method can be used in conjunction with various periodontal procedures in which inhibition of epithelial cell proliferation in and around periodontal tissue is desired. For example, preparations of the present invention can find application in the treatment of peridontal disease. It is estimated that in the United States alone, there are in excess of 125 million adults with periodontal disease in varying forms. Periodontal disease starts as inflammatory lesions because of specific bacteria localizing in the area where the gingiva attaches to the tooth. Usually first to occur is a vascular change in the underlying connective tissue. Inflammation in the connective tissue stimulates the following changes in the epithelial lining of the sulcus and in the epithelial attachment: increased mitotic activity in the basal epithelial layer; increased producing of keratin with desquamation; cellular desquamation adjacent to the tooth surface tends to deepen the pocket; epithelial cells of the basal layer at the bottom of the sulcus and in the area of attachment proliferate into the connective tissue and break up of the gingival fibers begins to occur, wherein dissolution of the connective tissue results in the formation of an open lesion. The application of CDK inhibitor preparations to the periodontium can be used to inhibit proliferation of epithelial tissue and thus prevent further periodontoclastic development. In yet another embodiment of the present invention, the subject CDK inhibitors can be used to inhibit spermatogenesis or oogenesis by inhibiting progression through mitotic or meiotic cell-cycle stages. The anti-mitotic and/or anti-meiotic activity of the fusion proteins identified in the present invention may accordingly be used, for example, in birth control methods by disrupting oogenic pathways in order to prevent the development of either the egg or sperm, or by preventing mitotic progression of a fertilized egg. In a still further embodiment, the subject fusion protein is recombinantly expressed in tissue which is characterized by unwanted de-differentiation and which may also be undergoing unwanted apoptosis. For instance, many neurological disorders are associated with degeneration of discrete populations of neuronal elements. For example, Alzheimer's disease is associated with deficits in several neurotransmitter systems, both those that project to the neocortex and those that reside with the cortex. For instance, the nucleus basalis in patients with Alzheimer's disease were observed to have a profound (75%) loss of neurons compared to age-matched controls. Although Alzheimer's disease is by far the most common form of dementia, several other disorders can produce dementia. Many are age-related, occurring in far greater incidence in older people than in younger. Several of these are degenerative diseases characterized by the death of neurons in various parts of the central nervous system, especially the cerebral cortex. However, some forms of dementia are associated with degeneration of the thalamus or the white matter underlying the cerebral cortex. Here, the cognitive dysfunction results from the isolation of cortical areas by the degeneration of efferents and afferents. Huntington's disease involves the degeneration of intrastriatal and cortical cholinergic neurons and GABAergic neurons. Pick's disease is a severe neuronal degeneration in the neocortex of the frontal and anterior temporal lobes, sometimes accompanied by death of neurons in the striatum. Accordingly, the subject fusion proteins can be delivered to the effected tissue by gene therapy techniques. It is noted that numerous advances have been made in the constmction of expression vectors, cellular and viral transgene carriers, and the characterization of target cells for neuronal gene therapy, and can be readily adapted for delivery of the subject genes (see, for example, Suhr et al. (1993) Arch Neurol 50:1252-1268; Jiao et al. (1993) Nature 362:450-453; Friedmann (1992) Ann Med 24:41 1-417; and Freese et al. (1991) Nuc Acid Res 19:7219-7223) In addition to degenerative-induced dementias, the subject gene therapy systems can be applied opportunely in the treatment of neurodegenerative disorders which have manifestations of tremors and involuntary movements. Parkinson's disease, for example, primarily affects subcortical structures and is characterized by degeneration of the nigrostriatal pathway, raphe nuclei, locus cereleus, and the motor nucleus of vagus. Ballism is typically associated with damage to the subthalmic nucleus, often due to acute vascular accident. Also included are neurogenic and myopathic diseases which ultimately affect the somatic division of the peripheral nervous system and are manifest as neuromuscular disorders. Examples include chronic atrophies such as amyotrophic lateral sclerosis, Guillain-Barre syndrome and chronic peripheral neuropathy, as well as other diseases which can be manifest as progressive bulbar palsies or spinal muscular atrophies. Moreover, the use of the subject fusion gene therapy constmcts is amenable to the treatment of disorders of the cerebellum which result in hypotonia or ataxia, such as those lesions in the cerebellum which produce disorders in the limbs ipsilateral to the lesion. For instance, pl6/p27 fusion gene constmcts can used to treat a restricted form of cerebellar cortical degeneration involving the anterior lobes (vermis and leg areas) such as is common in alcoholic patients. Furthermore, the subject fusion proteins can also be used in the treatment of autonomic disorders of the peripheral nervous system, which include disorders affecting the innervation of smooth muscle and endocrine tissue (such as glandular tissue). For instance, recombinant fusion protein of the present invention can be expressed by gene therapy and used to treat tachycardia or atrial cardiac arrythmias which may arise from a degenerative condition of the nerves innervating the striated muscle of the heart. As will be apparent, the subject gene constructs can be used to cause expression of the fusion polypeptides in cells propagated in culture, e.g. to produce proteins or polypeptides, including fusion proteins or polypeptides, for purification. In addition, recombinant expression of the subject fusion polypeptides in cultured cells can be useful for controlling differentiation states of cells in vitro, for instance, by controlling the level of activation of a CDK. To illustrate, in vitro neuronal culture systems have proved to be fundamental and indispensable tools for the study of neural development, as well as the identification of neurotrophic factors. Once a neuronal cell has become terminally-differentiated, it typically will not change to another terminally differentiated cell-type. However, neuronal cells can nevertheless readily lose their differentiated state. This is commonly observed when they are grown in culture from adult tissue, and when they form a blastema during regeneration. By preventing the activation of one or more CDKs, particularly in Go or Gj certain of the subject fusion proteins can prevent mitotic progression and hence provide a means for ensuring an adequately restrictive environment in order to maintain neuronal cells at various stages of differentiation, and can be employed, for instance, in cell cultures designed to test the specific activities of trophic factors. Other tissue culture systems which require maintenance of differentiation will be readily apparent to those skilled in the art. In this respect, each of the subject antagonist of CDK4 activation can be used for ex vivo tissue generation, as for example, to enhance the generation of prosthetic tissue devices for implantation. That is, by inhibiting the activation of a CDK with one of the subject fusion proteins, cultured cells can be guided along certain differentiative pathways. Exemplification The invention now being generally described, it will be more readily understood by reference to the following examples which are included merely for puφoses of illustration of certain aspects and embodiments of the present invention, and are not intended to limit the invention. Example 1 : p27/p!6 fusion proteins Prototype embodiments of the CDK inhibitory fusion protein described above were derived from the fusion of the coding sequences from the human p27 and pi 6 cDNAs. The nucleotide sequence for the fusion gene encoding the p27-pl6 protein is provided in SEQ ID No. 1, with the corresponding amino acid sequence being designated by SEQ ID No. 2. The construct includes a poly(His) leader for purification, along with a hinge region including a (G^Ser linker to permit proper folding and breathing of each of the p27 and pi 6 portions of the resulting protein. The sequences for both human p27 and human pi 6 have been described in the art. Briefly, the p27-pl6 fusion protein was constmcted as follow. The expression vector is pT7-7 from US Biocehmical. To constmct the p27- pl6 fusion, first we PCR amplified the p27 coding sequence using the following primers: N-terminal primer: (SEQ ID No. 3) 5'-GCGGCCGGTCATATGCACCACCATCACCATCACTCAAACG- TGCGAGTGTCT-3' This primer carries an Ndel site and 6 histidine codons that are inserted between the ATG and the second amino acid of p27. C-terminal primer: (SEQ ID No. 4) 5'-GCCGCCGGCGTCGACTCGGCCGAATTCGGATCCACCCCCGCCGGAACC- GCCACCCCCGCTGCCCCCGCCACCCGTTTGACGTCTTCTGAGGCCAGG-3' This primer carries the (Gly 4 Ser) 3 repeat and EcoRI , Sail and Hind3 restriction sites and eliminates the stop codon of p27. The p27 PCR product was cut with Ndel and Hind3 and inserted into pT7-7 cut with Ndel and Hind3. The resulted construct was cut with EcoRI and Sail and a full length pi 6 PCR product was inserted as an EcoRI -Xhol fragment. The position of the EcoRI site allows the in-frame insertion of pi 6. The rest of the hinge region between the p27 and pi 6 coding sequences derives from the 5' end of the pl6 cDNA. The pT7p27-pl6 expression plasmid was transformed into BL21 cells. For fusion protein expression, cells were grown in LB + 50μg/ml ampicillin at 37C to ODgoo = 0.8 and protein expression was induced by IPTG (final; cone: 20mM) for 4 hours as 37C. Cells were collected and the pellet was frozen at -80C. The preparation of the cell lysate and binding to a Ni^+ charged sepharose resin (Invitrogen catalog no. R801) was done according to the manufacturer's instruction (Invitrogen; see also Hochuli et al. (1987) J. Chromatography 41 1 :177-184; and Janknecht et al. (1991) PNAS 88:8972-8976). The bound proteins were eluted with 50mM, 200mM, 350mM, and 500mM imidazol and the fractions were analyzed on SDS/PAGE. The 200mM, 350mM, and 500mM imidazol fractions were collected, dialised against lxPBS(lmM KH 2 PO 4 , lOmM Na 2 HPO 4 , 137mM NaCl, 2.7mM KCl, pH=7.4) + 10% glycerol and stored at -80C in aliquots. -25% of the prep was the fusion protein. The purity of the p27-pl6, p27, and pi 6 preperationss were normalized using pi 6 and p27 specific antibodies. The kinase inhibitory activity of the p27-pl6 fusion protein was determined using an in vitro kinase assay in which the kinase activity of a particular cyclin/CDK complex was measured for varying concentrations of fusion protein. Briefly, the assay employs Sf9 cell extracts that were made from cells that were coinfected with the proper CDK and cyclin expression constmcts. Typically, 44μg of Sf9 extract in 50μl of 50mM Tris/Cl pH=7.6, lOmM MgCl 2 , ImM DTT, 25μM ATP, lOμCi 32 P-γ-ATP was used in the absence of the presnce of the particular inhibitor (inhibitor concentration was between 25nM to lμM). The reaction was carried out at 30°C for 30 minutes using 2μg of Gst-Rb as a substrate. Gst-Rb was recaptured using GSH- agaraose, separated on 10% SDS/PAGE and stained with Comassie blue. After autoradiography the GST-Rb bands were cut out and 32 P incoφoration was measured. The concentration of p27-pl6 fusion protein at which 50% of the kinase activity was blocked (IC50) was calculated for various cyclin/CDK pairs. The results are indicated in Table I. Table I Inhibition of cyclin dependent kinase complexes by p27-pl6 fusion protein inhibitor CD 4/ CD 2/ CDK2/ cdc2/ cyclin DI cyclin E cyclin A cyclin B nm=nanomolar Moreover, the inhibition constant, K j for the inhibition of CDK4/cyclin DI by p27-pl6 fusion protein was determined to be 23 nm, compared to a Kj of 75 nm for pi 6 inhibition of the same CDK4 complex. Other exemplary fusion proteins were derived as follows: (i) a "pl6(GS)p27" fusion protein was generated to include, N to C terminal, the entire coding sequence of pi 6, fused in frame with a (Gly4Ser) 3 linker and then the full coding sequence of p27. The nucleotide sequence for the fusion gene encoding the pl6(GS)p27 protein is provided in SEQ ID No. 4, with the corresponding amino acid sequence being designated by SEQ ID No. 5; and (ii) a "pl6p27" fusion protein was generated to include, N to C terminal, the entire coding sequence of pi 6, fused in frame the full coding sequence of p27 (no (Gly 4 Ser)3 linker). The nucleotide sequence for the fusion gene encoding the pl6p27 protein is provided in SEQ ID No. 6, with the corresponding amino acid sequence being designated by SEQ ID No. 7. (iii) a "p27pl6" fusion protein was generated to include, N to C terminal, the entire coding sequence of p27, fused in frame the full coding sequence of pi 6 (no (Gly4Ser) 3 linker). The construct includes a 5' EcoRI site, along with the coding sequence for an N-terminal HA tag, and a 3' NotI site. The nucleotide sequence for the fusion gene encoding the pl6p27 protein is provided in SEQ ID No. 29, with the corresponding amino acid sequence being designated by SEQ ID No. 30. In other embodiments, we have constructed fusion inhibitors that contain smaller portions of p27. In these p27 derivatives we have deleted sequences that may play a role in p27 degradation. The idea here that we may increase in vivo efficacy by increasing potency and stability, e.g., by rendering the fusion resistant to ubiquitin-mediated degradation. The truncated p27 protein (12aa-177aa) is shown in SEQ ID No. 16, which provides a polypeptide of the formula EcoRI -ATG-HA epitope-p27(12aa-177aa)-Stop- Notl. Still another truncated variant of p27 is provided in SEQ ID No. 18, and encodes a polypeptide of the formula EcoRI -ATG-HA epitope-p27(25aa-97aa)-STOP-Notl Utilizing these p27 fragments, we have constmcted p27/pl6 fusion proteins of the formula EcoRI -ATG-HA epitope-p27(12aa-177aa)-pl6(2aa-155aa)-STOP-Notl, which is shown in SEQ ID No. 20, and of the formula EcoRl-ATG-HA epitope-p27(12aa-177aa)- (Gly 4 Ser) 3 hinge-pl6((2aa-155aa)-STOP-Notl, shown in SEQ ID No. 22. Still other p27/pl6 fusion with the tmncated p27 is EcoRI -ATG-HA epitope- p27(25aa-93aa)-p!6(2aa-155aa)-STOP-Notl, shown in SEQ ID No. 24, and EcoRI -ATG- HA epitope-p27(25aa-93aa)-(Gly 4 Ser), hinge-pl6(2aa-155aa)-STOP-Notl, shown in SEQ ID No. 26. Example 2: Tat-derived CDK inhibitors To ascertain the ability of CDK inhibitor proteins to be exported from cell, we tested the ability of COS cells to secrete a fusion protein consisting of an IgH secretion signal and the human p27. Briefly, COS-7 cells were transfected with pIC400 negative control plasmid and with pAM7 and pAM8 plasmids, which encode an IgH secretion signal-p27 fusion protein. The IgH secretion signal sequence efficiently directed the normally intracellular p27 into the cell media. 20 ul aliquots of media were collected on days 1, 2, 3 and 5 following transfection, separated by SDS-PAGE and immunoblotted with anti-p27 antibody. As indicated by Figure 1, the level of secreted protein in the media increased over the time of the experiment for both pAM7 and pAM8, although there is considerably more p27 produced by the pAM7 vector design. No p27 is detected with pIC400 negative control. Purified p27 is included as a size marker. To test certain transcytosis embodiments, we derived fusion proteins including portions of the HIV tat protein and human p27. The HIV-1 tat derived delivery tags were as follows HIV-1 tat(47-72) nucleotide seqence: tat ggc agg aag aag egg aga cag cga cga aga cct cct caa ggc agt cag act cat caa gtt tct eta agt aag caa HIV-1 tat(47-72) protein seqence: YGRKKRRQRRRPPQGSQTHQVSLSKQ HIV-1 tat(48-60) nucleotide seqence: ggc agg aag aag egg aga cag cga cga aga cct cct caa HIV-1 tat(48-60) protein seqence: GRKKRRQRRRPPQ HIV-1 tat(47-58) nucleotide seqence: tat ggc agg aag aag egg aga cag cga cga aga cct HIV-1 tat(47-58) protein seqence: YGRKKRRQRRRP Figure 5 is table indicating the relative IC50 values for the various tat fusion constmcts for inhibition of various cdk/cyclin complexes. Proliferation Assay protocol: Low passage, asynchronous coronary artery smooth muscle cells (CASMC) were plated in 24 well dishes (7 X 10^ cells/ 2.0 cm 2 ) in smooth muscle cell medium supplemented with 5% FBS, 0.5 μg/ml hEGF, 5 μg/ml insulin, 1 μg/ml hFGF, 50 mg/ml gentamicin and 50 ng/ml amphotericin-B and allowed to recover overnight. Cells were then rendered quiescent by incubation for 48 h in low semm medium (O.05% FBS). As indicated by Figure 2, purified tat-fusion proteins were added in 1 ml complete medium at final concentration of 1 μM. The protein was left on the cells for 24 h. The cells were stimulated to reenter cycle by addition of 100% FBS to a final concentration of 5% FBS and allowed to grow for 72 h. Proliferation was monitored using the CyQUANT proliferation assay kit® (Molecular Probes). Fluorescence measurements were made using a microplate reader with excitation at 485 nm and emission detection at 530 nm. Intemalization Protocol Figure 3 is a gel illustrating the cellular uptake of tat/p27 fusion proteins. Asynchronous WI38 fibroblasts were plated in 6 well tissue cultures plates (1.7 X 10 4 cells/9.2 cm 2 ) in DMEM/ 10% FBS supplemented with pen/strep and glutamine (complete medium) and grown overnight at 37°, 5% CO 2 . Purified tat- fusion proteins were in 2 ml complete medium at final concentration of 10 μM. The protein was left on the cells for 72 h. Cells were harvested by extensive trypsinization (i.e.: >10 min) and cell pellets were lysed in 25 μl 2X SDS sample buffer, boiled 3', and spun down to pellet debris. The proteins were separated on a 4-20% SDS-PAGE gel, transferred to nitrocellulose and probed with monoclonal antibodies specific for HIV tat and/or human p27. Immunofluorescence protocol: Figure 4 are fluorescence micrographs illustrating the cellular localization of various p27 fusion proteins. Asynchronous WI38 fibroblasts were plated on cover slips in 6 well tissue cultures plates (5 X 10 4 cells/9.2 cm 2 ) in DMEM/ 10% FBS supplemented with pen/strep and glutamine and grown overnight at 37°, 5% CO2. Purified tat-fusion proteins were in 2 ml complete medium at final concentration of 1 μM. The protein was left on the cells for 24 h. The cells were fixed by incubation with 3.7% formaldehyde, permeabilized with 0.25% Triton X-100, and blocked 5% horse semm in PBS. Samples were then incubated with primary antibody (either anti- ET RULE 26 tat or anti-p27) followed by incubation with a FITC label secondary antibody and counter stained for DNA with Hoechst. All of the above-cited references and publications are hereby incoφorated by reference. Equivalents Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following claims.

Claims: We Claim: 1. A recombinant transfection system, comprising (i) a first gene constmct comprising a coding sequence encoding a inhibitory polypeptide comprising at least one CDK-binding motif for binding and inhibiting activation of a cyclin dependent kinase (cdk), which coding sequence is operably linked to a transcriptional regulatory sequence for causing expression of the first polypeptide in eukaryotic cells, (ii) a second gene constmct comprising a coding sequence encoding a endotheliazation polypeptide which promotes endothelialization, and (ii) a gene delivery composition for delivering the gene constmcts to a cell and causing the cell to be transfected with the gene constmct. 2. The transfection system of claim 1, wherein the CDK-binding motif is a CDK- binding motif of a CDK inhibitor protein. 3. The transfection system of claim 2, wherein the CDK inhibitor protein is an INK4 protein. 4. The transfection system of claim 3, wherein the INK4 protein is selected from the group consisting of pi 5, pi 6, pi 8 and pi 9. 5. The transfection system of claim 2, wherein the CDK inhibitor protein is a CIP protein. 6. The transfection system of claim 5, wherein the CIP protein is selected from the group consisting of p21 CIP1 , p27 KIP1 , and p57 KIP2 . 7. The transfection system of claim 1 , wherein the CDK-binding motif comprises tandemly arranged ankyrin-like sequences. 8. The transfection system of claim 1, wherein the CDK-binding motif comprises a p21/p27 inhibitory domain. 9. The transfection system of claim 1, wherein the inhibitory polypeptide is a fusion protein comprising CDK-binding motifs from two or more different proteins which bind to cyclin dependent kinases. 10. The transfection system of claim 1, wherein the endothelization polypeptide stimulates endothelial cell proliferation. 11. The transfection system of claim 1 , wherein the endothelization polypeptide stimulates migration of endothelial cells to a wound site. 12. The transfection system of claim 1, wherein the endothelization polypeptide is selected from the group consisting of angiogenic basic fibroblast growth factors (bFGF), acid fibroblast growth factor (aFGF), vascular endothelial growth factor (VEGF), platelet derived growth factor (PDGF), vascular permeability growth factor (VPF), and transforming growth factor beta (TGF-β). 13. The transfection system of claim 1, wherein the fisrt and second gene constmcts are provided as part of a single vector. 14. The transfection system of claim 1, wherein the fisrt and second gene constmcts are provided as part of polycistronic message. 15. The transfection system of claim 1, wherein the fisrt and second gene constmcts are provided on separate vectors. 16. The recombinant transfection system of claim 1, wherein the gene constmct comprises a viral vector. 17. The recombinant transfection system of claim 16, wherein the viral vector is an adenoviral vector. 18. The recombinant transfection system of claim 16, wherein the viral vector is an adeno-associated viral vector. 19. The recombinant transfection system of claim 16, wherein the viral vector is a retroviral vector. 20. The recombinant transfection system of claim 1, wherein the gene delivery composition comprises a recombinant viral particle. 21. The recombinant transfection system of claim 1, wherein the gene delivery composition is selected from the group consisting of a liposome and a polycationic nucleic acid binding agent. 22. The recombinant transfection system of claim 1, wherein the gene delivery composition further comprises a pharmaceutically acceptable carrier for adminstration to an animal. 23. A method for treating an animal having a vascular wound characterized a breech of endothelial integrity and by excessive smooth muscle proliferation, comprising administering the recombinant transfection system of claim 1 to the area of the vascular wound. 24. The method of claim 23, wherein the vascular wound is restenosis. 25. The method of claim 23, wherein the recombinant transfection system is administered by catheter. 26. A nucleic acid encoding a fusion protein comprising a therapeutic polypeptide sequence from an intracellular protein which alter a biological process of a cell upon intracellular localization of the fusion protein, and a transcellular polypeptide sequence for promoting transcytosis of the fusion protein across a ceil surface membrane and into a cell. 27. The transfection system of claim 26, wherein the therapeutic polypeptide sequence includes a CDK-binding motif. 28. The transfection system of claim 27, wherein the CDK-binding motif is a CDK- binding motif of a CDK inhibitor protein. 29. The transfection system of claim 28, wherein the CDK inhibitor protein is an INK4 protein. 30. The transfection system of claim 29, wherein the INK4 protein is selected from the group consisting of pl5, pl6, pl8 and pl9. 31. The transfection system of claim 28, wherein the CDK inhibitor protein is a CIP protein. 32. The transfection system of claim 31 , wherein the CIP protein is selected from the group consisting of p21 CIP 1 , p27 KIP1 , and p57 KIP2 . 33. The transfection system of claim 27, wherein the CDK-binding motif comprises tandemly arranged ankyrin-like sequences. 34. The transfection system of claim 27, wherein the CDK-binding motif comprises a p21/p27 inhibitory domain. 35. The transfection system of claim 27, wherein the inhibitory polypeptide is a fusion protein comprising CDK-binding motifs from two or more different proteins which bind to cyclin dependent kinases. 36. The transfection system of claim 26, wherein the therapeutic polypeptide sequence is from a tumor suppressor, a transcription factor, a signal transduction protein, an antiviral protein or a metal chelating protein. 37. The transfection system of claim 36, wherein the therapeutic polypeptide sequence includes a polypeptide sequence of a tumor supressor selected from the group consisting of p53, Rb and Rb-like proteins. 38. The transfection system of claim 36, wherein the therapeutic polypeptide sequence includes a polypeptide sequence of a signal transduction protein selected from the group consisting of tubby, a DOT protein, a Bel protein, and an IκB protein. 39. The transfection system of claim 38, wherein the Bel protein is Bcl-2 or Bcl-x. 40. The transfection system of claim 26, wherein the biological process is selected from the group consisting of proliferation, differentiation, cell death, gene expression, protein stability, calcium mobilzation, ion permability, phosphorylation of intracellular proteins, metabolism of inositol phosphates, and metabolism of nucleosides. 41. The transfection system of claim 26, wherein the fusion protein inhibits protein-protein interactions or protein-nucleic acid interactions between proteins and nucleic acids endogenous to the cell. 42. The transfection system of claim 26, wherein the transcellular polypeptide sequence is an intemalizing peptide. 43. The transfection system of claim 42, wherein the intemalizing peptide is derived from a polypeptide selected from the group consisting of antepennepedia protein, HIV transactivating (TAT) protein, mastoparan, melittin, bombolittin, delta hemolysin, pardaxin, Pseudomonas exotoxin A, clathrin, Diphtheria toxin and C9 complement protein. 44. The transfection system of claim 42, wherein the intemalizing peptide is derived from antepennepedia protein. 45. The transfection system of claim 42, wherein the intemalizing peptide is derived from HIV transactivating (TAT) protein. 46. The transfection system of claim 26, wherein the transcellular polypeptide sequence is an accessory peptide sequence which enhances interaction of the fusion protein with a cell surface membrane. 47. The transfection system of claim 42, wherein the accessory peptide includes an RGD sequence. 48. The recombinant transfection system of claim 26, wherein the gene constmct comprises a viral vector. 49. The recombinant transfection system of claim 48, wherein the viral vector is an adenoviral vector. 50. The recombinant transfection system of claim 48, wherein the viral vector is an adeno-associated viral vector. 51. The recombinant transfection system of claim 48, wherein the viral vector is a retroviral vector. 52. The recombinant transfection system of claim 26, wherein the gene delivery composition comprises a recombinant viral particle. 53. The recombinant transfection system of claim 26, wherein the gene delivery composition is selected from the group consisting of a liposome and a polycationic nucleic acid binding agent. 54. The recombinant transfection system of claim 26, wherein the gene delivery composition further comprises a pharmaceutically acceptable carrier for adminstration to an animal. 55. A fusion protein comprising at least one CDK-binding motif for binding and inhibiting activation of a cyclin dependent kinase (cdk), and a transcellular polypeptide sequence for promoting transcytosis of the fusion protein across a cell surface membrane and into a cell. 56. A method for treating an animal for unwanted cell proliferation, comprising administering to the animal the recombinant transfection system of claim 26 or the fusion protein of claim 55. 57. A nucleic acid encoding a fusion protein comprising a first polypeptide sequence having therapeutic activity, and a transcellular polypeptide sequence for promoting transcytosis of the fusion protein across a cell surface membrane and into a cell. 58. A fusion protein encoded by the nucleic acid of claim 57. 59. A nucleic acid comprising a nucleotide sequence encoding a chimeric polypeptide comprising CDK-binding motifs from two or more different proteins which bind to cyclin dependent kinases. 60. The nucleic acid of claim 59, which nucleic acid comprises the coding sequence designated in one of SEQ ID No. 1 , 4, 6, 16, 18, 20 , 22, 24 and 26. 61. A recombinant transfection system, comprising (i) a gene constmct including a nucleic acid encoding a chimeric polypeptide comprising CDK-binding motifs from two or more different proteins which bind to cyclin dependent kinases, and operably linked to a transcriptional regulatory sequence for causing expression of the chimeric polypeptide in eukaryotic cells, and (ii) a gene delivery composition for delivering the gene constmct to a cell and causing the cell to be transfected with the gene constmct. 62. A chimeric polypeptide comprising CDK-binding motifs from two or more different proteins which bind to cyclin dependent kinases. 56. The chimeric polypeptide of claim 55, which chimeric polypeptide comprises the fusion sequence designated in SEQ ID No. 2, 5, 7, 17, 19, 21, 23, 25 and 27.

Inventors: BEACH DAVID H, GYURIS JENO, LAMPHERE LOU, BEACH, DAVID, H., GYURIS, JENO, LAMPHERE, LOU
Applicants: BEACH DAVID H, GYURIS JENO, LAMPHERE LOU, MITOTIX INC, BEACH, DAVID, H., GYURIS, JENO, LAMPHERE, LOU, MITOTIX, INC.
Application year: 1998
Main classification: C12N15
IPC codes: A61K35, A61K38, A61K48, A61P35, C07K14, C07K19, C12N9, C12N15