# Patent

## Title
Leukotriene receptor

## Abstract

The present invention provides an isolated mammalian leukotriene receptor, isolated or recombinant nucleic acids and recombinant vectors encoding the same, host cells comprising the nucleic acids and vectors, and methods of making the receptor using the host cells. This invention further provides antibodies and antigen binding fragments thereof which specifically bind to the receptor and are useful for treating medical conditions caused or mediated by leukotriene. Also provided are screening methods for identifying specific agonists and antagonists of the mammalian leukotriene receptor.

## Background
This is a division of application Ser. No. 09/400,622, filed Sep. 20, 1999 now U.S. Pat. No. 6,465,212 B1 which is herein incorporated by reference.


TECHNICAL FIELD
The present invention relates to mammalian leukotriene receptors. More particularly, it relates to human leukotriene receptors, isolated nucleic acids and recombinant vectors encoding the receptors, to methods of making the receptors, to methods of making fragments or fusion proteins of the receptors using recombinant DNA methodology or chemical synthesis, and to methods of using the receptors in screening systems to identify inhibitors and activators of the receptors useful for the treatment of various diseases.
BACKGROUND OF THE INVENTION
Leukotrienes are products of eicosanoid metabolism and are implicated in a number of medical conditions, including inflammation, asthma, allergy, glomerulonephritis, neuroendocrine dysfunctions, AIDS, arthritis, bowel disease, psoriasis, diabetes, obesity, atherosclerosis, bacterial infection, etc. There are multiple classes of leukotrienes, e.g. class A, class B, class C, class D, class E and class F. Leukotrienes regulate the intensity and duration of immune responses and are involved in cell-to-cell communication. Leukotrienes are also involved in leukocyte migration and branchovasoconstriction. As established by radioligand binding as well as physiological assays, it appears that there are different types of receptors for leukotrienes. The molecular characteristics of leukotriene receptors were unknown until recently, when a leukotriene B4 receptor was cloned (Yokomizo et al., Nature, 387:620-624 (1997)).
In view of the important role that leukotrienes play in many physiological processes and medical conditions, there is a need for materials and methods useful for the identification of agonists and antagonists of leukotriene receptors.
SUMMARY OF THE INVENTION
The present invention fills the foregoing need by providing such materials and methods. More particularly, this invention provides a novel mammalian leukotriene receptor, isolated nucleic acids or recombinant nucleic acids encoding the receptor, and recombinant vectors and host cells comprising such nucleic acids. The leukotriene receptor can be actively expressed in mammalian cells where it displays active ligand binding and positive intracellular signaling upon ligand activation. This novel receptor has high affinity for ligands such as leukotriene B4, leukotriene B5, 15(5)-OH-5z, 8z, 11z, 13e)-eicosatetraenoic acid, and lipoxin A4. This invention further provides methods for the discovery of selective agonists and antagonists of the receptor that may be useful in the treatment and management of a variety of diseases including, for example, inflammation, asthma, allergy, glomerulonephritis, neuroendocrine dysfunctions, alcoholic liver diseases, hepatitis, atropic liver regeneration, AIDS, arthritis, bowel disease, psoriasis, diabetes, obesity, atherosclerosis, and bacterial infection.
The isolated or recombinant nucleic acids of the present invention are selected from the group consisting of:
(a) A nucleic acid encoding a mammalian leukotriene receptor comprising an amino acid sequence defined by SEQ ID NO: 2 or a subsequence thereof;
(b) A nucleic acid that hybridizes under moderately stringent conditions to the nucleic acid of (a) and encodes a polypeptide that (i) binds leukotriene and (ii) is at least 80% identical to a receptor encoded by the nucleic acid of (a); and
(c) A nucleic acid that, due to the degeneracy of the genetic code, encodes a mammalian leukotriene receptor encoded by a nucleic acid of (a) or (b).
This invention further provides methods of making a polypeptide comprising culturing a host cell comprising a nucleic acid encoding a mammalian leukotriene receptor comprising an amino acid sequence defined by SEQ ID NO: 2 or a subsequence thereof, under conditions in which the nucleic acid is expressed. In some embodiments, the method further comprises isolation of the polypeptide from the culture.
This invention also provides a recombinant nucleic acid comprising a sequence having at least about 70% identity over a stretch of at least about 30 nucleotides to the nucleic acid sequence of SEQ ID NO: 1, useful, e.g., as a probe or PCR primer for a related gene. Another embodiment further includes a polypeptide comprising at least about 60% identity over a stretch of at least about 20 amino acids to the amino acid sequence of SEQ ID NO: 2.
This invention also provides polypeptides comprising a fragment of a polypeptide having an amino acid sequence corresponding to the sequence of at least about 8 contiguous residues of the amino acid sequence of SEQ ID NO: 2. Preferably, the polypeptides comprise at least about 12, more preferably at least about 20, and most preferably at least about 30 such residues.
Still further, this invention provides fusion proteins comprising a polypeptide defined by SEQ ID NO: 2 or a fragment therefrom covalently linked to a fusion partner.
The present invention also provides antibodies, both polyclonal and monoclonal, that specifically bind to one or more of the leukotriene receptors or to polypeptides therefrom, and anti-idiotypic antibodies, both monoclonal and polyclonal, which specifically bind to the foregoing antibodies.
This invention further provides a method for producing a mammalian leukotriene receptor comprising culturing a host cell comprising a nucleic acid encoding a mammalian leukotriene receptor comprising an amino acid sequence defined by SEQ ID NO: 2 or a subsequence thereof, under conditions in which the nucleic acid is expressed. In one embodiment the receptor is isolated from the culture.
The present invention also provides a method for identifying a leukotriene agonist or antagonist comprising:

    
    
        (a) Contacting a mammalian leukotriene receptor having an amino acid sequence defined by SEQ ID NO: 2 or a subsequence thereof, in the presence of a known amount of labeled leukotriene or surrogate with a sample to be tested for the presence of a leukotriene agonist or antagonist; and
        (b) Measuring the amount of labeled leukotriene specifically bound to the receptor;

whereby a leukotriene agonist or antagonist in the sample is identified by measuring substantially reduced binding of the labeled leukotriene to the leukotriene receptor, compared to what would be measured in the absence of such agonist or antagonist.

    
    


In a preferred embodiment, membranes isolated from mammalian cells comprising a nucleic acid encoding the leukotriene receptor are used as the source of the receptor.
The present invention also provides a method for identifying an agonist or antagonist of a mammalian leukotriene receptor comprising:
(a) contacting cells expressing a mammalian leukotriene receptor comprising an amino acid sequence defined by SEQ ID NO: 2 or a conservative or allelic variant thereof, in the presence of a known amount of leukotriene or surrogate thereof with a sample to be tested for the presence of a mammalian leukotriene agonist or antagonist; and
(b) measuring at least one cellular function modulated by the binding of a ligand to said receptor present in the cells;
whereby a mammalian leukotriene receptor agonist or antagonist in the sample is identified by measuring its effect on said cellular function compared to what would be measured in the absence of such agonist or antagonist.
Examples of cellular functions modulated by the binding of a ligand to a mammalian leukotriene receptor include: intracellular second messenger pathways activated via the leukotriene receptors (e.g., cyclicAMP, calcium, inositol phosphate and MAP kinase), changes in cell growth rate, secretion of hormones, receptor-stimulated Ca2++ mobilization, mitogenic effects etc.,
This invention still further provides a method for treating leukotriene-mediated medical conditions comprising administering to a mammal afflicted with a medical condition caused or mediated by leukotriene, an effective amount of an agonist or antagonist of the leukotriene receptor that specifically binds to a mammalian leukotriene receptor having an amino acid sequence defined by SEQ ID NO: 2, or a subsequence thereof, and pharmaceutical compositions comprising one or more of such agonist or antagonist and a pharmaceutically acceptable carrier. Preferably, the mammal is a human being.
This invention also provides anti-sense oligonucleotides capable of specifically hybridizing to mRNA encoding a mammalian leukotriene receptor having an amino acid sequence defined by SEQ ID NO: 2 or a subsequence thereof so as to prevent translation of the mRNA. Additionally, this invention provides anti-sense oligonucleotides capable of specifically hybridizing to the genomic DNA molecule encoding a mammalian leukotriene receptor having an amino acid sequence defined by SEQ ID NO: 2 or a subsequence thereof.
This invention further provides a pharmaceutical composition comprising:
(a) An amount of an oligonucleotide effective to reduce activity of human leukotriene receptor by passing through a cell membrane and binding specifically with DNA or mRNA encoding human leukotriene receptor in the cell so as to prevent its transcription or translation; and
(b) A pharmaceutically acceptable carrier capable of passing through a cell membrane. In an embodiment, the oligonucleotide is coupled to a substance that inactivates mRNA.
In another embodiment, the substance that inactivates mRNA is a ribozyme.


DESCRIPTION OF THE INVENTION
All references cited herein are hereby incorporated herein in their entirety by reference.
Leukotriene Receptor Characterization
The nucleotide sequence of the complete open reading frame and the corresponding amino acid sequence of the novel human leukotriene receptor of this invention are defined by SEQ ID NO: 1 and SEQ ID NO: 2, respectively. The cloned receptor resembles a member of the G-protein coupled receptor super-family that contains a 7-transmembrane domain. Furthermore, this receptor shares high homology at both the nucleotide and amino acid sequence levels with the previously described leukotriene receptor (Yokomizo et al., Nature, 387:620-624 (1997)). The cloned receptor is able to bind ligands (for example, leukotriene B and lipoxin A), as demonstrated with radioligand saturation and competition assays. Leukotriene is also capable of activating the cloned receptor resulting in intracellular responses, as shown by measurement of intracellular Ca2+ flux.
As used herein, the term “ligand” is defined to mean any molecule capable of specifically binding to the mammalian leukotriene receptors of the invention. Thus leukotriene itself is a ligand, as are agonists and antagonists that may compete with leukotriene for specific binding to the receptors.
The modifications that occur in a polypeptide often will be a function of how it is made. For polypeptides made by expressing a cloned gene in a host, for instance, the nature and extent of the modifications in large part will be determined by the host cell's post-translational modification capacity and the modification signals present in the polypeptide amino acid sequence. For instance, as is well known, glycosylation often does not occur in bacterial hosts such as E. coli. Accordingly, when glycosylation is desired, a polypeptide should be expressed in a glycosylating host, generally a eukaryotic cell. Insect cells often carry out the same post-translational glycosylations as mammalian cells do and, for this reason, insect cell expression systems have been developed to express efficiently mammalian proteins having the native patterns of glycosylation, inter alia. Similar considerations apply to other modifications.
It will be appreciated that the same type of modification may be present in the same or varying degrees at several sites in a given polypeptide. Also, a given polypeptide may contain many types of modifications.
The term “polypeptide” encompasses all such modifications, particularly those that are present in polypeptides synthesized by expressing a polynucleotide in a host cell.
“Variant(s)”, as the term is used herein, are polynucleotides or polypeptides that differ from a reference polynucleotide or polypeptide respectively. Variants in this sense are described below and elsewhere in the present disclosure in greater detail. (1) A polynucleotide that differs in nucleotide sequence from another, reference polynucleotide. Changes in the nucleotide sequence of the variant may be silent, i.e. they may not alter the amino acids encoded by the polynucleotide. Where alterations are limited to silent changes of this type a variant will encode a polypeptide with the same amino acid sequence as the reference polypeptide. Changes in the nucleotide sequence of the variant may alter the amino acid sequence of a polypeptide encoded by the reference polynucleotide. Such nucleotide changes may result in amino acid substitutions, additions, deletions, fusions and truncations in the polypeptide encoded by the reference sequence, as discussed below. (2) A polypeptide that differs in amino acid sequence from another, reference polypeptide. Generally, differences are limited so that the sequences of the reference and the variant are closely similar overall and, in many regions, identical. A variant and reference polypeptide may differ in amino acid sequence by one or more substitutions, additions, deletions, fusions and truncations, which may be present in any combination. (3) A variant may also be a fragment of a polynucleotide or polypeptide of the invention that differs from a reference polynucleotide or polypeptide sequence by being shorter than the reference sequence, such as by a terminal or internal deletion. A variant of a polypeptide of the invention also includes a polypeptide which retains essentially the same biological function or activity as such polypeptide, e.g., pro-proteins which can be activated by cleavage of the pro-protein portion to produce an active mature polypeptide. (4) A variant may also be (i) one in which one or more of the amino acid residues are substituted with a conserved or non-conserved amino acid residue (preferably a conserved amino acid residue) and such substituted amino acid residue may or may not be encoded by the genetic code, or (ii) one in which one or more of the amino acid residues includes a substituent group, or (iii) one in which the mature polypeptide is fused with another compound, such as a compound to increase the half-life of the polypeptide (for example, polyethylene glycol), or (iv) one in which the additional amino acids are fused to the mature polypeptide, such as a leader or secretory sequence or a sequence which is employed for purification of the mature polypeptide or a pro-protein sequence. (5) A variant of the polynucleotide or polypeptide may be a naturally occurring variant such as a naturally occurring allelic variant, or it may be a variant that is not known to occur naturally. Such non-naturally occurring variants or the polynucleotide may be made by mutagenesis techniques, including those applied to polynucleotides, cells or organisms, or may be made by recombinant means. Among polynucleotide variants in this regard are variants that differ from the aforementioned polynucleotides by nucleotide substitutions, deletions or additions. The substitutions, deletions or additions may involve one or more nucleotides. The variants may be altered in coding or non-coding regions or both. Alterations in the coding regions may produce conservative or non-conservative amino acid substitutions, deletions or additions. All such variants defined above are deemed to be within the scope of those skilled in the art from the teachings herein and from the art.
The present invention also encompasses fragments, analogs and physical variants of the disclosed leukotriene receptor. As used herein, the term “polypeptide” or “peptide” means a fragment or segment, e.g., of a mammalian leukotriene receptor having an amino acid sequence defined by SEQ ID NO: 2 which comprises a subsequence of the complete amino acid sequence of the receptor containing at least about 8, preferably at least about 12, more preferably at least about 20, and most preferably at least about 30 or more contiguous amino acid residues, up to and including the total number of residues in the complete receptor.
The polypeptides of the invention can comprise any part of the complete sequence of such a receptor. Thus, although they could be produced by proteolytic cleavage of an intact receptor, they can also be made by chemical synthesis or by the application of recombinant DNA technology and are not limited to polypeptides delineated by proteolytic cleavage sites. The polypeptides, either alone or cross-linked or conjugated to a carrier molecule to render them more immunogenic, are useful as antigens to elicit the production of antibodies. The antibodies can be used, e.g., in immunoassays of the intact receptors, for immunoaffinity purification, etc.
The term “analog(s)” means a mammalian leukotriene receptor of the invention which has been modified by deletion, addition, modification or substitution of one or more amino acid residues in the wild-type receptor. It encompasses allelic and polymorphic variants, and also muteins and fusion proteins which comprise all or a significant part of such a mammalian leukotriene receptor, e.g., covalently linked via a side-chain group or terminal residue to a different protein, polypeptide or moiety (fusion partner).
Some amino acid substitutions are preferably “conservative”, with residues replaced with physically or chemically similar residues, such as Gly/Ala, Asp/Glu, Val/Ile/Leu, Lys/Arg, Asn/Gln and Phe/Trp/Tyr. Analogs having such conservative substitutions typically retain substantial leukotriene binding activity. Other analogs, which have non-conservative substitutions such as Asn/Glu, Val/Tyr and His/Glu, may substantially lack such activity. Nevertheless, such analogs are useful because they can be used as antigens to elicit production of antibodies in an immunologically competent host. Because these analogs retain many of the epitopes (antigenic determinants) of the wild-type receptors from which they are derived, many antibodies produced against them can also bind to the active-conformation or denatured wild-type receptors. Accordingly, such antibodies can also be used, e.g., for the immunopurification or immunoassay of the wild-type receptors.
Some analogs are truncated variants in which residues have been successively deleted from the amino- and/or carboxyl-termini, while substantially retaining the characteristic ligand binding activity.
Modifications of amino acid residues may include but are not limited to aliphatic esters or amides of the carboxyl terminus or of residues containing carboxyl side chains, O-acyl derivatives of hydroxyl group-containing residues, and N-acyl derivatives of the amino-terminal amino acid or amino-group containing residues, e.g., lysine or arginine.
Other analogs are mammalian leukotriene receptors containing modifications, such as incorporation of unnatural amino acid residues, or phosphorylated amino acid residues such as phosphotyrosine, phosphoserine or phosphothreonine residues. Other potential modifications include sulfonation, biotinylation, or the addition of other moieties, particularly those that have molecular shapes similar to phosphate groups.
Analogs of the mammalian leukotriene receptors can be prepared by chemical synthesis or by using site-directed mutagenesis [Gillman et al., Gene 8:81 (1979); Roberts et al., Nature, 328:731 (1987) or Innis (Ed.), 1990, PCR Protocols: A Guide to Methods and Applications, Academic Press, New York, N.Y.] or the polymerase chain reaction method [PCR; Saiki et al., Science 239:487 (1988)], as exemplified by Daugherty et al. [Nucleic Acids Res. 19:2471 (1991)] to modify nucleic acids encoding the complete receptors. Adding epitope tags for purification or detection of recombinant products is envisioned.
General techniques for nucleic acid manipulation and expression that can be used to make the analogs are described generally, e.g., in Sambrook, et al., Molecular Cloning: A Laboratory Manual (2d ed.), 1989, Vols. 1-3, Cold Spring Harbor Laboratory. Techniques for the synthesis of polypeptides are described, for example, in Merrifield, J. Amer. Chem. Soc. 85:2149 (1963); Merrifield, Science 232:341 (1986); and Atherton et al., Solid Phase Peptide Synthesis: A Practical Approach, 1989, IRL Press, Oxford.
Still other analogs are prepared by the use of agents known in the art for their usefulness in cross-linking proteins through reactive side groups. Preferred derivatization sites with cross-linking agents are free amino groups, carbohydrate moieties and cysteine residues.
Substantial retention of ligand binding activity by the foregoing analogs of the mammalian leukotriene receptors typically entails retention of at least about 50%, preferably at least about 75%, more preferably at least about 80%, and most preferably at least about 90% of the leukotriene binding activity and/or specificity of the corresponding wild-type receptor.
Nucleic Acids and Expression Vectors
As used herein, the term “isolated nucleic acid” means a nucleic acid such as an RNA or DNA molecule, or a mixed polymer, which is substantially separated from other components that are normally found in cells or in recombinant DNA expression systems. These components include but are not limited to ribosomes, polymerases, serum components, and flanking genomic sequences. The term thus embraces a nucleic acid that has been removed from its naturally occurring environment, and includes recombinant or cloned DNA isolates and chemically synthesized analogs or analogs biologically synthesized by heterologous systems. A substantially pure molecule includes isolated forms of the molecule.
An isolated nucleic acid will generally be a homogeneous composition of molecules but may, in some embodiments, contain minor heterogeneity. Such heterogeneity is typically found at the ends of nucleic acid coding sequences or in regions not critical to a desired biological function or activity.
A “recombinant nucleic acid” is defined either by its method of production or structure. Some recombinant nucleic acids are thus made by the use of recombinant DNA techniques which involve human intervention, either in manipulation or selection. Others are made by fusing two fragments that are not naturally contiguous to each other. Engineered vectors are encompassed, as well as nucleic acids comprising sequences derived using any synthetic oligonucleotide process.
For example, a wild-type codon may be replaced with a redundant codon encoding the same amino acid residue or a conservative substitution, while at the same time introducing or removing a nucleic acid sequence recognition site. Similarly, nucleic acid segments encoding desired functions may be fused to generate a single genetic entity encoding a desired combination of functions not found together in nature. Although restriction enzyme recognition sites are often the targets of such artificial manipulations, other site-specific targets, e.g., promoters, DNA replication sites, regulation sequences, control sequences, or other useful features may be incorporated by design. Sequences encoding epitope tags for detection or purification as described above may also be incorporated.
A nucleic acid “fragment” is defined herein as a nucleotide sequence comprising at least about 17, generally at least about 25, preferably at least about 35, more preferably at least about 45, and most preferably at least about 55 or more contiguous nucleotides.
This invention further encompasses recombinant DNA molecules and fragments having sequences that are identical or highly homologous to those described herein. The nucleic acids of the invention may be operably linked to DNA segments that control transcription, translation, and DNA replication.
“Identity”, as known in the art, is a relationship between two or more polypeptide sequences or two or more polynucleotide sequences, as determined by comparing the sequences. In the art, “identity” also means the degree of sequence relatedness between polypeptide or polynucleotide sequences, as the case may be, as determined by the match between strings of such sequences. “Similarity” between two polypeptides is determined by comparing the amino acid sequence and its conserved amino acid substitutes of one polypeptide to the sequence of a second polypeptide. “Identity” and “similarity” can be readily calculated by known methods, including but not limited to those described in (Computational Molecular Biology, Lesk, A. M., ed., Oxford University Press, New York, 1988; Biocomputing: Informatics and Genome Projects, Smith, D. W., ed., Academic Press, New York, 1993; Computer Analysis of Sequence Data, Part I, Griffin, A. M., and Griffin, H. G., eds., Humana Press, New Jersey, 1994; Sequence Analysis in Molecular Biology, von Heinje, G., Academic Press, 1987; and Sequence Analysis Primer, Gribskov, M. and Devereux, J., eds., M Stockton Press, New York, 1991; and Carillo, H., and Lipman, D., SIAM J. Applied Math., 48:1073 (1988). Preferred methods to determine identity are designed to give the largest match between the sequences tested. Methods to determine identity and similarity are codified in publicly available computer programs. Preferred computer program methods to determine identity and similarity between two sequences include, but are not limited to, the GCG program package (Devereux, J., et al., Nucleic Acids Research 12 (1):387 (1984)), BestFit, BLASTP, BLASTN, and FASTA (Altschul, S. F. et al., J. Mol. Biol. 215:403-410 (1990). The BLAST X program is publicly available from NCBI and other sources (BLAST Manual, Altschul, S., et al., NCBI NLM NIH Bethesda, Md. 20894; Altschul, S., et al., J. Mol. Biol. 215:403-410 (1990). The well-known Smith Waterman algorithm may also be used to determine identity.
Preferred parameters for polypeptide sequence comparison include the following:

    1) Algorithm: Needleman and Wunsch, J. Mol. Biol. 48:443-453 (1970)

Comparison matrix: BLOSSUM62 from Hentikoff and Hentikoff, Proc. Natl. Acad. Sci. USA. 89:10915-10919 (1992)

Gap Penalty: 12

Gap Length Penalty: 4



A program useful with these parameters is publicly available as the “gap” program from Genetics Computer Group, located in Madison, Wis. The aforementioned parameters are the default parameters for peptide comparisons (along with no penalty for end gaps).
Preferred parameters for polynucleotide comparison include the following:

    1) Algorithm: Needleman and Wunsch, J. Mol. Biol. 48:443-453 (1970)

Comparison matrix: matches=+10, mismatch=0

Gap Penalty: 50

Gap Length Penalty: 3

Available as the Gap program from Genetics Computer Group, located in Madison, Wis. Given above are the default parameters for nucleic acid comparisons.



Preferred polynucleotide embodiments further include an isolated polynucleotide comprising a polynucleotide sequence having at least a 50, 60, 70, 80, 85, 90, 95, 97 or 100% identity to the reference sequence of SEQ ID NO: 1, wherein said polynucleotide sequence may be identical to the reference sequence of SEQ ID NO: 1 or may include up to a certain integer number of nucleotide alterations as compared to the reference sequence, wherein said alterations are selected from the group consisting of at least one nucleotide deletion, substitution, including transition and transversion, or insertion, and wherein said alterations may occur at the 5′ or 3′ terminal positions of the reference nucleotide sequence or anywhere between those terminal positions, interspersed either individually among the nucleotides in the reference sequence or in one or more contiguous groups within the reference sequence, and wherein said number of nucleotide alterations is determined by multiplying the total number of nucleotides in SEQ ID NO: 1 by the integer defining the percent identity divided by 100 and then subtracting that product from said total number of nucleotides in SEQ ID NO: 1, or: nn xn−(xn y), wherein nn is the number of nucleotide alterations, xn is the number of nucleotides in SEQ ID NO: 1, y is 0.50 for 50%, 0.60 for 60%, 0.70 for 70%, 0.80 for 80%, 0.85 for 85%, 0.90 for 90%, 0.95 for 95%, 0.97 for 97% or 1.00 for 100%, and is the symbol for the multiplication operator, and wherein any non-integer product of xn and y is rounded down to the nearest integer prior to subtracting it from xn. Alterations of a polynucleotide sequence encoding the polypeptide of SEQ ID NO: 2 may create nonsense, missense or frameshift mutations in this coding sequence and thereby alter the polypeptide encoded by the polynucleotide following such alterations.
By way of example, a polynucleotide sequence of the present invention may be identical to the reference sequence of SEQ ID NO: 2, that is it may be 100% identical, or it may include up to a certain integer number of amino acid alterations as compared to the reference sequence such that the percent identity is less than 100% identity. Such alterations are selected form the group consisting of at least one nucleic acid deletion, substitution, including transition and transversion, or insertion, and wherein said alterations may occur at the 5′ or 3′ terminal positions of the reference polynucleotide sequence or anywhere between those terminal positions, interspersed either individually among the nucleic acids in the reference sequence or in one or more contiguous groups within the reference sequence. The number of nucleic acid alterations for a given percent identity is determined by multiplying the total number of amino acids in SEQ ID NO: 2 by the integer defining the percent identity divided by 100 and then subtracting that product from said total number of amino acids in SEQ ID NO: 2, or nn=xn−(xn y), wherein nn is the number of amino acid alterations, xn is the total number of amino acids in SEQ ID NO: 2, y is, for instance 0.70 for 70%, 0.80 for 80%, 0.85 for 85% etc., is the symbol for the multiplication operator, and wherein any non-integer product of xn and y is rounded down to the nearest integer prior to subtracting it from xn.
Preferred polypeptide embodiments further include an isolated polypeptide comprising a polypeptide having at least a 50, 60, 70, 80, 85, 90, 95, 97 or 100% identity to a polypeptide reference sequence of SEQ ID NO: 2, wherein said polypeptide sequence may be identical to the reference sequence of SEQ ID NO: 2 or may include up to a certain integer number of amino acid alterations as compared to the reference sequence, wherein said alterations are selected from the group consisting of at least one amino acid deletion, substitution, including conservative and non-conservative substitution, or insertion, and wherein said alterations may occur at the amino-or carboxy-terminal positions of the reference polypeptide sequence or anywhere between those terminal positions, interspersed either individually among the amino acids in the reference sequence or in one or more contiguous groups within the reference sequence, and wherein said number of amino acid alterations is determined by multiplying the total number of amino acids in SEQ ID NO: 2 by the integer defining the percent identity divided by 100 and then subtraction that product from said total number of amino acids in SEQ ID NO: 2, or: na xa−(xa y), wherein na is the number of amino acid alterations, xa is the total number of amino acids in SEQ ID NO: 2, y is 0.50 for 50%, 0.60 for 60%, 0.70 for 70%, 0.80 for 80%, 0.85 for 85%, 0.90 for 90%, 0.95 for 95%, 0.97 for 97% or 1.00 for 100%, and is the symbol for the multiplication operator, and wherein any non-integer product of xa and y is rounded down to the nearest integer prior to subtracting it from xa.
By way of example, a polypeptide sequence of the present invention may be identical to the reference sequence of SEQ ID NO: 2, that is it may be 100% identical, or it may include up to a certain integer number of amino acid alterations as compared to the reference sequence such that the percent identity is less than 100% identity. Such alterations are selected from the group consisting of at least one amino acid deletion, substitution, including conservative and non-conservative substitution, or insertion, and wherein said alterations may occur at the amino-or carboxy-terminal positions of the reference polypeptide sequence or anywhere between those terminal positions, interspersed either individually among the amino acids in the reference sequence or in one or more contiguous groups within the reference sequence. The number of amino acid alterations for a given % identity is determined by multiplying the total number of amino acids in SEQ ID NO: 2 by the integer defining the percent identity divided by 100 and then subtracting that product from said total number of amino acids in SEQ ID NO: 2, or na=xa (xa y), wherein na is the number of amino acid alterations, xa is the total number of amino acids in SEQ ID NO: 2, y is, for instance 0.70 for 70%, 0.80 for 80%, 0.85 for 85% etc., and is the symbol for the multiplication operator, and wherein any non-integer product of xa and y is rounded down to the nearest integer prior to subtracting it from xa.
The term “homology”, as it is used herein, embraces both identity and similarity.
Some of the physical variants have substantial amino acid sequence homology with the amino acid sequences of the mammalian leukotriene receptors or polypeptides. In this invention, amino acid sequence homology, or sequence identity is determined by optimizing residue matches and, if necessary, by introducing gaps as required. Homologous amino acid sequences are typically intended to include natural allelic, polymorphic and interspecies variations in each respective sequence.
Typical homologous proteins or peptides will have from 25-100% homology (if gaps can be introduced) to 50-100% homology (if conservative substitutions are included), with the amino acid sequence of the leukotriene receptors. Primate species receptors are of particular interest.
Observed homologies will typically be at least about 35%, preferably at least about 50%, more preferably at least about 75%, and most preferably at least about 80% or more. See Needleham et al., J. Mol. Biol. 48:443-453 (1970); Sankoff et al. in Time Warps, String Edits, and Macromolecules: The Theory and Practice of Sequence Comparison, 1983, Addison-Wesley, Reading, Mass.; and software packages from IntelliGenetics, Mountain View, Calif., and the University of Wisconsin Genetics Computer Group, Madison, Wis.
Glycosylation variants include, e.g., analogs made by modifying glycosylation patterns during synthesis and processing in various alternative eukaryotic host expression systems, or during further processing steps. Particularly preferred methods for producing glycosylation modifications include exposing the mammalian leukotriene receptors to glycosylating enzymes derived from cells that normally carry out such processing, such as mammalian glycosylation enzymes. Alternatively, deglycosylation enzymes can be used to remove carbohydrates attached during production in eukaryotic expression systems.
“Homologous nucleic acid sequences” are those which when aligned and compared exhibit significant similarities. Standards for homology in nucleic acids are either measures for homology generally used in the art by sequence comparison or based upon hybridization conditions, which are described in greater detail below.
Substantial nucleotide sequence homology is observed when there is identity in nucleotide residues in two sequences (or in their complementary strands) when optimally aligned to account for nucleotide insertions or deletions, in at least about 50%, preferably in at least about 75%, more preferably in at least about 90%, and most preferably in at least about 95% of the aligned nucleotides.
Substantial homology also exists when one sequence will hybridize under selective hybridization conditions to another. Typically, selective hybridization will occur when there is at least about 55% homology over a stretch of at least about 30 nucleotides, preferably at least about 65% over a stretch of at least about 25 nucleotides, more preferably at least about 75%, and most preferably at least about 90% over about 20 nucleotides. See, e.g., Kanehisa, Nucleic Acids Res. 12:203 (1984).
The lengths of such homology comparisons may encompass longer stretches and in certain embodiments may cover a sequence of at least about 17, preferably at least about 25, more preferably at least about 50, and most preferably at least about 75 nucleotide residues.
Stringency of conditions employed in hybridizations to establish homology are dependent upon factors such as salt concentration, temperature, the presence of organic solvents, and other parameters. Stringent temperature conditions usually include temperatures in excess of about 30° C., often in excess of about 37° C., typically in excess of about 45° C., preferably in excess of about 55° C., more preferably in excess of about 65° C., and most preferably in excess of about 70° C. Stringent salt conditions will ordinarily be less than about 1000 mM, usually less than about 500 mM, more usually less than about 400 mM, preferably less than about 300 mM, more preferably less than about 200 mM, and most preferably less than about 150 mM. For example, salt concentrations of 100, 50 and 20 mM are used. The combination of the foregoing parameters, however, is more important than the measure of any single parameter. See, e.g., Wetmur et al., J. Mol. Biol. 31:349 (1968).
A further indication that two nucleic acid sequences of polypeptides are substantially identical is that the polypeptide encoded by the first nucleic acid is immunologically cross reactive with the polypeptide encoded by the second nucleic acid, as described below. Thus, a polypeptide is typically substantially identical to a second polypeptide, for example, where the two peptides differ only by conservative substitutions. Another indication that two nucleic acid sequences are substantially identical is that the two molecules hybridize to each other under stringent conditions, as described below.
The term “substantially pure” is defined herein to mean a mammalian leukotriene receptor, nucleic acid or other material that is free from other contaminating proteins, nucleic acids, and other biologicals derived from an original source organism or recombinant DNA expression system. Purity may be assayed by standard methods and will typically exceed at least about 50%, preferably at least about 75%, more preferably at least about 90%, and most preferably at least about 95% purity. Purity evaluation may be made on a mass or molar basis.
Nucleic acids encoding the leukotriene receptors or fragments thereof can be prepared by standard methods. For example, DNA can be chemically synthesized using, e.g., the phosphoramidite solid support method of Matteucci et al. [J. Am. Chem. Soc. 103:3185 (1981)], the method of Yoo et al. [J. Biol. Chem. 764:17078 (1989)], or other well known methods. This can be done by sequentially linking a series of oligonucleotide cassettes comprising pairs of synthetic oligonucleotides, as described below.
Of course, due to the degeneracy of the genetic code, many different nucleotide sequences can encode the leukotriene receptors. The codons can be selected for optimal expression in prokaryotic or eukaryotic systems. Such degenerate variants are of course also encompassed by this invention.
Moreover, nucleic acids encoding the leukotriene receptors can readily be modified by nucleotide substitutions, nucleotide deletions, nucleotide insertions, and inversions of nucleotide stretches. Such modifications result in novel DNA sequences that encode antigens having immunogenic or antigenic activity in common with the wild-type receptors. These modified sequences can be used to produce wild type or mutant receptors, or to enhance expression in a recombinant DNA system.
Insertion of the DNAs encoding the leukotriene receptors into a vector is easily accomplished when the termini of both the DNAs and the vector comprise compatible restriction sites. If this cannot be done, it may be necessary to modify the termini of the DNAs and/or vector by digesting back single-stranded DNA overhangs generated by restriction endonuclease cleavage to produce blunt ends, or to achieve the same result by filling in the single-stranded termini with an appropriate DNA polymerase.
Alternatively, desired sites may be produced, e.g., by ligating nucleotide sequences (linkers) onto the termini. Such linkers may comprise specific oligonucleotide sequences that define desired restriction sites. Restriction sites can also be generated by the use of the polymerase chain reaction (PCR). See, e.g., Saiki et al., Science 239:487 (1988). The cleaved vector and the DNA fragments may also be modified if required by homopolymeric tailing.
Recombinant expression vectors used in this invention are typically self-replicating DNA or RNA constructs comprising nucleic acids encoding one of the mammalian leukotriene receptors, usually operably linked to suitable genetic control elements that are capable of regulating expression of the nucleic acids in compatible host cells. Genetic control elements may include a prokaryotic promoter system or a eukaryotic promoter expression control system, and typically include a transcriptional promoter, an optional operator to control the onset of transcription, transcription enhancers to elevate the level of mRNA expression, a sequence that encodes a suitable ribosome binding site, and sequences that terminate transcription and translation. Expression vectors also may contain an origin of replication that allows the vector to replicate independently of the host cell.
Vectors that could be used in this invention include microbial plasmids, viruses, bacteriophage, integratable DNA fragments, and other vehicles that may facilitate integration of the nucleic acids into the genome of the host. Plasmids are the most commonly used form of vector but all other forms of vectors which serve an equivalent function and which are, or become, known in the art are suitable for use herein. See, e.g., Pouwels et al., Cloning Vectors: A Laboratory Manual, 1985 and Supplements, Elsevier, N.Y., and Rodriguez et al. (eds.), Vectors: A Survey of Molecular Cloning Vectors and Their Uses, 1988, Buttersworth, Boston, Mass.
Expression of nucleic acids encoding the leukotriene receptors of this invention can be carried out by conventional methods in either prokaryotic or eukaryotic cells. Although strains of E. coli are employed most frequently in prokaryotic systems, many other bacteria such as various strains of Pseudomonas and Bacillus are know in the art and can be used as well.
Prokaryotic expression control sequences typically used include promoters, including those derived from the β-lactamase and lactose promoter systems [Chang et al., Nature, 198:1056 (1977)], the tryptophan (trp) promoter system [Goeddel et al., Nucleic Acids Res. 8:4057 (1980)], the lambda PL promoter system [Shimatake et al., Nature, 292:128 (1981)] and the tac promoter [De Boer et al., Proc. Natl. Acad. Sci. USA 292:128 (1983)]. Numerous expression vectors containing such control sequences are known in the art and available commercially.
Suitable host cells for expressing nucleic acids encoding the mammalian leukotriene receptors include prokaryotes and higher eukaryotes. Prokaryotes include both gram negative and positive organisms, e.g., E. coli and B. subtilis. Higher eukaryotes include established tissue culture cell lines from animal cells, both of non-mammalian origin, e.g., insect cells, and birds, and of mammalian origin, e.g., human, primates, and rodents.
Prokaryotic host-vector systems include a wide variety of vectors for many different species. As used herein, E. coli and its vectors will be used generically to include equivalent vectors used in other prokaryotes. A representative vector for amplifying DNA is pBR322 or many of its derivatives. Vectors that can be used to express the mammalian leukotriene receptors include but are not limited to those containing the lac promoter (pUC-series); trp promoter (pBR322-trp); Ipp promoter (the pIN-series); lambda-pP or pR promoters (pOTS); or hybrid promoters such as ptac (pDR540). See Brosius et al., “Expression Vectors Employing Lambda-, trp-, lac-, and Ipp-derived Promoters”, in Rodriguez and Denhardt (eds.) Vectors: A Survey of Molecular Cloning Vectors and Their Uses, 1988, Buttersworth, Boston, pp. 205-236.
Higher eukaryotic tissue culture cells are preferred hosts for the recombinant production of the mammalian leukotriene receptors. Although any higher eukaryotic tissue culture cell line might be used, including insect baculovirus expression systems, mammalian cells are preferred. Transformation or transfection and propagation of such cells have become a routine procedure. Examples of useful cell lines include HeLa cells, Chinese hamster ovary (CHO) cell lines, baby rat kidney (BRK) cell lines, insect cell lines, bird cell lines, and monkey (COS) cell lines.
Expression vectors for such cell lines usually include an origin of replication, a promoter, a translation initiation site, RNA splice sites (if genomic DNA is used), a polyadenylation site, and a transcription termination site. These vectors also usually contain a selection gene or amplification gene. Suitable expression vectors may be plasmids, viruses, or retroviruses carrying promoters derived, e.g., from such sources as adenovirus, SV40, parvoviruses, vaccinia virus, or cytomegalovirus. Representative examples of suitable expression vectors include pCR®3.1, pCDNA1, pCD [Okayama et al., Mol. Cell Biol. 5:1136 (1985)], pMC1neo Poly-A [Thomas et al., Cell 51:503 (1987)], pUC19, pREP8, pSVSPORT and derivatives thereof, and baculovirus vectors such as pAC 373 or pAC 610.
Protein Purification
The proteins, polypeptides and antigenic fragments of this invention can be purified by standard methods, including but not limited to salt or alcohol precipitation, preparative disc-gel electrophoresis, isoelectric focusing, high pressure liquid chromatography (HPLC), reversed-phase HPLC, gel filtration, cation and anion exchange and partition chromatography, and countercurrent distribution. Such purification methods are well known in the art and are disclosed, e.g., in Guide to Protein Purification, Methods in Enzymology, Vol. 182, M. Deutscher, Ed., 1990, Academic Press, New York, N.Y. More specific methods applicable to purification of the leukotriene receptors are described below.
Purification steps can be followed by carrying out assays for ligand binding activity as described below. Particularly where a receptor is being isolated from a cellular or tissue source, it is preferable to include one or more inhibitors of proteolytic enzymes is the assay system, such as phenylmethanesulfonyl fluoride (PMSF).
Screening Systems and Methods
The invention allows the discovery of selective agonists and antagonists of the novel receptor that may be useful in treatment and management of a variety of diseases including inflammation, asthma, allergy, glomerulonephritis, neuroendocrine dysfunctions, AIDS, arthritis, bowel disease, psoriasis, diabetes, obesity, atherosclerosis, bacterial infection, encephalomyelitis, etc. Thus, the leukotriene receptor of this invention can be employed in screening systems to identify agonists or antagonists of the receptor. Essentially, these systems provide methods for bringing together a mammalian leukotriene receptor, an appropriate known ligand, including leukotriene itself, and a sample to be tested for the presence of a leukotriene agonist or antagonist.
Two basic types of screening systems can be used, a labeled-ligand binding assay and a “functional” assay. A labeled ligand for use in the binding assay can be obtained by labeling leukotriene or a known leukotriene agonist or antagonist with a measurable group as described above in connection with the labeling of antibodies. Various labeled forms of leukotriene are available commercially or can be generated using standard techniques. In an example below, 3H-leukotriene is used as the ligand.
Typically, a given amount of the leukotriene receptor of the invention is contacted with increasing amounts of a labeled ligand, such as labeled leukotriene itself, and the amount of the bound labeled ligand is measured after removing unbound labeled ligand by washing. As the amount of the labeled ligand is increased, a point is eventually reached at which all receptor binding sites are occupied or saturated. Specific receptor binding of the labeled ligand is abolished by a large excess of unlabeled ligand.
Preferably, an assay system is used in which non-specific binding of the labeled ligand to the receptor is minimal. Non-specific binding is typically less than 50%, preferably less than 15%, and more preferably less than 10% of the total binding of the labeled ligand.
As used herein, the term “leukotriene ligand” is defined to mean leukotriene itself or an analog of leukotriene, and extending up to the complete leukotriene molecule. For regulatory purposes it may be desirable to use leukotriene or an active fragment thereof as the leukotriene ligand in conjunction with the human receptor when screening for leukotriene agonists or antagonists for human therapeutic purposes.
In principle, a binding assay of the invention could be carried out using a soluble receptor of the invention, e.g., following production and refolding by standard methods from an E. coli expression system, and the resulting receptor-labeled ligand complex could be precipitated, e.g., using an antibody against the receptor. The precipitate could then be washed and the amount of the bound labeled ligand could be measured.
Preferably, however, a nucleic acid encoding one of the leukotriene receptors of the invention is transfected into an appropriate host cell, whereby the receptor will become incorporated into the membrane of the cell. A membrane fraction can then be isolated from the cell and used as a source of the receptor for assay. Preferably, specific binding of the labeled ligand to a membrane fraction from the untransfected host cell will be negligible.
The binding assays of this invention can be used to identify both leukotriene agonists and antagonists, because both will interfere with the binding of the labeled ligand to the receptor.
In the basic binding assay, the method for identifying a leukotriene agonist or antagonist comprises:

    
    
        (a) contacting a mammalian leukotriene receptor having an amino acid sequence defined by SEQ ID NO: 2 or a subsequence thereof, in the presence of a known amount of labeled leukotriene with a sample to be tested for the presence of a leukotriene agonist or antagonist; and
        (b) measuring the amount of labeled leukotriene bound to the receptor;
    
    


whereby a leukotriene agonist or antagonist in the sample is identified by measuring substantially reduced binding of the labeled leukotriene to the leukotriene receptor, compared to what would be measured in the absence of such agonist or antagonist.
Preferably, the leukotriene receptor used to identify a leukotriene agonist or antagonist for human therapeutic purposes has an amino acid sequence defined by SEQ ID NO: 2 or a subsequence thereof.
In one embodiment of the invention, the foregoing method further comprises:

    
    
        (c) Contacting a mammalian leukotriene receptor in the presence of a known amount of labeled leukotriene with a compound identified as a leukotriene agonist or antagonist in steps (a) and (b); and
        (d) Measuring the amount of labeled leukotriene bound to the receptor;

whereby a leukotriene agonist or antagonist specific for the leukotriene receptor is identified by measuring substantially undiminished binding of the labeled leukotriene to the receptor, compared to what would be measured in the absence of such agonist or antagonist.

    
    


Determination of whether a particular molecule inhibiting binding of the labeled ligand to the receptor is an antagonist or an agonist is then determined in a second, functional assay. The functionality of leukotriene agonists and antagonists identified in the binding assay can be determined in cellular and animal models.
Functional Assays for Antagonists/Agonists of Leukotriene Receptors
In cellular models, parameters for intracellular activities mediated by leukotriene receptors can be monitored for antagonistic and/or agonistic activities. Such parameters include but are not limited to intracellular second messenger pathways activated via the leukotriene receptors, changes in cell growth rate, secretion of hormones, etc., using published methods. Examples of such methods are, measurement of the effects of the ligands on receptor-mediated inhibition of forskolin-stimulated intracellular cAMP production [Parker et al., Mol. Brain Res. 34:179-189 (1995)], receptor-stimulated Ca2++ mobilization and mitogenic effects [Sethi et al., Cancer Res. 51:1674-1679 (1991)], and inositol phosphate production and MAP kinase induction (Wang et al., Biochemistry 37:6711-17 (1998). The FLIPR method described in this invention is also suitable for measuring intracellular release of calcium.
Agonists of leukotriene receptors may also be identified directly by using functional assays. An agonist may or may not directly inhibit leukotriene binding to leukotriene receptors.
In addition to the methods described above, activities of an antagonist may be measured in cellular models for altered intracellular cAMP or Ca2+ concentrations (Yokomizo et al. Nature, 1997, 387:620). Leukotriene-induced chemotaxis using cultured cells can also be utilized (Yokomizo et al. Nature, 1997, 387:620). Furthermore, models employing Xenopus laevis, pigment dispersion/aggregation in melanophores, and aequorin assay in mammalian cells are suitable for this purpose (Lynch et al., Nature, 1999, 399:790). Methods using animals or animal tissues for such activities can also be employed. Leukotriene-stimulated neutrophil chemotaxis (Palmer et al. Prostaglandins, 1980, 20:411-418), enhanced neutrophil-endothelial interaction (Hoover et al. Proc. Natl. Acad. Sci. U.S.A., 1984, 81:2191-2193), neutrophil activation leading to degranulation and release of mediators, enzymes and superoxides (Sha'afi et al. J. Cell Physiol. 1981, 108:401-408), inflammatory pain (Levine et al. Science, 1984, 225:743-745), and increased cytokine production (Brach et al. Eur. J. Immunol. 1992, 22:2705-2711) and transcription (Stanova, et al. Biochem. J. 1992, 282:625-629) are examples of such methods.
Other Mammalian Leukotriene Receptors
The present invention provides methods for cloning mammalian leukotriene receptors from other mammalian species. Briefly, Southern and Northern blot analysis can be carried out to identify cells from other species expressing genes encoding the leukotriene receptors. Complementary DNA (cDNA) libraries can be prepared by standard methods from mRNA isolated from such cells, and degenerate probes or PCR primers based on the nucleic acid and amino acid sequences provided herein can be used to identify clones encoding a leukotriene receptor.
Alternatively, expression cloning methodology can be used to identify particular clones encoding a leukotriene receptor. An antibody preparation which exhibits cross-reactivity with leukotriene receptors from a number of mammalian species may be useful in monitoring expression cloning.
However identified, clones encoding leukotriene receptors from various mammalian species can be isolated and sequenced, and the coding regions can be excised and inserted into an appropriate vector.
Other Related Genes
The present invention also provides compositions and methods for cloning other genes related to the gene encoding a polypeptide defined by SEQ ID NO: 2. Specifically, this invention provides a recombinant nucleic acid comprising a sequence having at least about 70% identity over a stretch of at least about 30 nucleotides to the nucleic acid sequence of SEQ ID NO: 1, useful, e.g., as a probe or PCR primer for a related gene.
Localization of mRNA encoding the polypeptide of SEQ ID NO: 2
The present invention also provides compositions and methods for localization of messenger RNA coding for the polypeptide defined by the amino acid sequence of SEQ ID NO: 2.
Specifically, human multiple tissue and cancer cell line blots containing approximately 2 μg of poly(A)+ RNA per lane, are purchased from Clontech (Palo Alto, Calif.). Probes are radiolabeled with [α-32P] dATP, e.g., using the Amersham Rediprime random primer labeling kit (RPN1633). Prehybridization and hybridizations are performed at 65° C. in 0.5M Na2HPO4, 7% SDS, 0.5M EDTA (pH 8.0). High stringency washes are conducted, e.g., at 65° C. with two initial washes in 2×SSC, 0.1% SDS for 40 min followed by a subsequent wash in 0.1×SSC, 0.1% SDS for 20min. Membranes are then exposed at −70° C. to X-Ray film (Kodak) in the presence of intensifying screens. More detailed studies by cDNA library Southerns are performed with selected clones of nucleic acids having the nucleotide sequence defined by SEQ ID NO: 1 to examine their expression in other cell subsets.
Two prediction algorithms that take advantage of the patterns of conservation and variation in multiply aligned sequences, (Rost and Sander (1994) Proteins 19:55-72) and DSC (King and Sternberg (1996) Protein Sci. 5:2298-2310), are used.
Alternatively, two appropriate primers are selected and RT-PCR is used on an appropriate mRNA sample selected for the presence of message to produce a cDNA, e.g., a sample which expresses the gene.
Full length clones may be isolated by hybridization of cDNA libraries from appropriate tissues pre-selected by PCR signal.
Message for genes encoding a polypeptide having the amino acid sequence of SEQ ID NO: 2 are assayed by appropriate technology, e.g., PCR, immunoassay, hybridization, or otherwise. Tissue and organ cDNA preparations are available, e.g., from Clontech, Mountain View, Calif.
Southern Analysis on cDNA libraries are performed as follows: DNA (5 μg) from a primary amplified cDNA library is digested with appropriate restriction enzymes to release the inserts, run on a 1% agarose gel and transferred to a nylon membrane (Schleicher and Schuell, Keene, N.H.).
Samples for human mRNA isolation may include, e.g.: peripheral blood mononuclear cells (monocytes, T cells, NK cells, granulocytes, B cells), resting (T100); peripheral blood mononuclear cells, activated with anti-CD3 for 2, 6, 12 h pooled (T101); T cell, TH0 clone Mot 72, resting (T102); T cell, TH0 clone Mot 72, activated with anti-CD28 and anti-CD3 for 3, 6, 12 h pooled (T103); T cell, TH0 clone Mot 72, anergic treated with specific peptide for 2, 7, 12 h pooled (T104); T cell, TH1 clone HY06, resting (T107); T cell, TH1 clone HY06, activated with anti-CD28 and anti-CD3 for 3, 6, 12 h pooled (T108); T cell, TH1 clone HY06, anergic treated with specific peptide for 2, 6, 12 h pooled (T109); T cell, TH2 clone HY935, resting (T110); T cell, TH2 clone HY935, activated with anti-CD28 and anti-CD3 for 2, 7, 12 h pooled (T111); T cells CD4+CD45RO- T cells polarized 27 days in anti-CD28, IL-4, and anti IFN-γ, TH2 polarized, activated with anti-CD3 and anti-CD28 4h (T116); T cell tumor lines Jurkat and Hut78, resting (T117); T cell clones, pooled AD130.2, Tc783.12, Tc783.13, Tc783.58, Tc782.69, resting (T118); T cell random γδT cell clones, resting (T119); Splenocytes, resting (B100); Splenocytes, activated with anti-CD40 and IL-4 (B 101); B cell EBV lines pooled WT49, RSB, JY, CVIR, 721.221, RM3, HSY, resting (B102); B cell line JY, activated with PMA and ionomycin for 1, 6 h pooled (B103); NK 20 clones pooled, resting (K100); NK 20 clones pooled, activated with PMA and ionomycin for 6 h (K101); NKL clone, derived from peripheral blood of LGL leukemia patient, IL-2 treated (K106); NK cytotoxic clone 640-A30-1, resting (K107); hematopoietic precursor line TF1, activated with PMA and ionomycin for 1, 6 h pooled (C100); U937 premonocytic line, resting (M100); U937 premonocytic line, activated with PMA and ionomycin for 1, 6 h pooled (M101); elutriated monocytes, activated with LPS, IFNγ, anti-IL-10 for 1, 2, 6, 12, 24 h pooled (M102); elutriated monocytes, activated with LPS, IFNγ, IL-10 for 1, 2, 6, 12, 24 h pooled (M103); elutriated monocytes, activated with LPS, IFNγ, anti-IL-10 for 4, 16 h pooled (M106); elutriated monocytes, activated with LPS, IFNγ, IL-10 for 4, 16 h pooled (M107); elutriated monocytes, activated LPS for 1 h (M108); elutriated monocytes, activated LPS for 6 h (M109); DC 70% CD1a+, from CD34+GM-CSF, TNFα 12 days, resting (D101); DC 70% CD1a+, from CD34+GM-CSF, TNFα 12 days, activated with PMA and ionomycin for 1 hr (D102); DC 70% CD1a+, from CD34+GM-CSF, TNFα 12 days, activated with PMA and ionomycin for 6 hr (D103); DC 95% CD1a+, from CD34+GM-CSF, TNFα 12 days FACS sorted, activated with PMA and ionomycin for 1, 6 h pooled (D104); DC 95% CD14+, ex CD34+GM-CSF, TNFα 12 days FACS sorted, activated with PMA and ionomycin 1, 6 hr pooled (D105); DC CD1a+CD86+, from CD34+GM-CSF, TNFα 12 days FACS sorted, activated with PMA and ionomycin for 1, 6 h pooled (D106); DC from monocytes GM-CSF, IL-4 5 days, resting (D107); DC from monocytes GM-CSF, IL-4 5 days, resting (D108); DC from monocytes GM-CSF, IL-4 5 days, activated LPS 4, 16 h pooled (D109); DC from monocytes GM-CSF, IL-4 5 days, activated TNFα, monocyte supernatant for 4, 16 h pooled (D110); leiomyoma L11 benign tumor (X101); normal myometrium M5 (O115); malignant leiomyosarcoma GS1 (X103); lung fibroblast sarcoma line MRC5, activated with PMA and ionomycin for 1, 6 h pooled (C101); kidney epithelial carcinoma cell line CHA, activated with PMA and ionomycin for 1, 6 h pooled (C102); kidney fetal 28 wk male (O100); lung fetal 28 wk male (O101); liver fetal 28 wk male (O102); heart fetal 28 wk male (O103); brain fetal 28 wk male (O104); gallbladder fetal 28 wk male (O106); small intestine fetal 28 wk male (O107); adipose tissue fetal 28 wk male (O108); ovary fetal 25 wk female (O109); uterus fetal 25 wk female (O110); testes fetal 28 wk male (O111); spleen fetal 28 wk male (O112); adult placenta 28 wk (O113); tonsil inflamed, from 12 year old (X100); psoriasis human skin sample; normal human skin sample; pool of rheumatoid arthritis human; Hashimoto's thyroiditis thyroid; normal human thyroid; ulcerative colitis human colon; normal human colon; normal weight monkey colon; pheumocystic carnii pneumonia lung; allergic lung; poll of three heavy smoker human lung; pool of two normal human lung; Ascaris-challenged monkey lung, 24 hr; Ascaris-challenged monkey lung, 4hr; and normal weight monkey lung.
Antibody Production
Antigenic (i.e., immunogenic) fragments of the mammalian leukotriene receptors of this invention, which may or may not have ligand binding activity, may be produced. Regardless of whether they bind leukotriene, such fragments, like the complete receptors, are useful as antigens for preparing antibodies by standard methods that can bind to the complete receptors. Shorter fragments can be concatenated or attached to a carrier. Because it is well known in the art that epitopes generally contain at least about five, preferably at least about 8, amino acid residues [Ohno et al., Proc. Natl. Acad. Sci. USA 82:2945 (1985)], fragments used for the production of antibodies will generally be at least that size. Preferably, they will contain even more residues, as described above. Whether a given fragment is immunogenic can readily be determined by routine experimentation.
Although it is generally not necessary when complete mammalian leukotriene receptors are used as antigens to elicit antibody production in an immunologically competent host, smaller antigenic fragments are preferably first rendered more immunogenic by cross-linking or concatenation, or by coupling to an immunogenic carrier molecule (i.e., a macromolecule having the property of independently eliciting an immunological response in a host animal). Cross-linking or conjugation to a carrier molecule may be required because small polypeptide fragments sometimes act as haptens (molecules which are capable of specifically binding to an antibody but incapable of eliciting antibody production, i.e., they are not immunogenic). Conjugation of such fragments to an immunogenic carrier molecule renders them more immunogenic through what is commonly known as the “carrier effect”.
Suitable carrier molecules include, e.g., proteins and natural or synthetic polymeric compounds such as polypeptides, polysaccharides, lipopolysaccharides etc. Protein carrier molecules are especially preferred, including but not limited to keyhole limpet hemocyanin and mammalian serum proteins such as human or bovine gammaglobulin, human, bovine or rabbit serum albumin, or methylated or other derivatives of such proteins. Other protein carriers will be apparent to those skilled in the art. Preferably, but not necessarily, the protein carrier will be foreign to the host animal in which antibodies against the fragments are to be elicited.
Covalent coupling to the carrier molecule can be achieved using methods well known in the art, the exact choice of which will be dictated by the nature of the carrier molecule used. When the immunogenic carrier molecule is a protein, the fragments of the invention can be coupled, e.g., using water-soluble carbodiimides such as dicyclohexylcarbodiimide or glutaraldehyde.
Coupling agents such as these can also be used to cross-link the fragments to themselves without the use of a separate carrier molecule. Such cross-linking into aggregates can also increase immunogenicity. Immunogenicity can also be increased by the use of known adjuvants, alone or in combination with coupling or aggregation.
Suitable adjuvants for the vaccination of animals include but are not limited to Adjuvant 65 (containing peanut oil, mannide monooleate and aluminum monostearate); Freund's complete or incomplete adjuvant; mineral gels such as aluminum hydroxide, aluminum phosphate and alum; surfactants such as hexadecylamine, octadecylamine, lysolecithin, dimethyldioctadecylammonium bromide, N,N-dioctadecyl-N′,N′-bis(2-hydroxymethyl) propanediamine, methoxyhexadecylglycerol and pluronic polyols; polyanions such as pyran, dextran sulfate, poly IC, polyacrylic acid and carbopol; peptides such as muramyl dipeptide, dimethylglycine and tuftsin; and oil emulsions. The polypeptides could also be administered following incorporation into liposomes or other microcarriers.
Information concerning adjuvants and various aspects of immunoassays are disclosed, e.g., in the series by P. Tijssen, Practice and Theory of Enzyme Immunoassays, 3rd Edition, 1987, Elsevier, N.Y. Other useful references covering methods for preparing polyclonal antisera include Microbiology, 1969, Hoeber Medical Division, Harper and Row; Landsteiner, Specificity of Serological Reactions, 1962, Dover Publications, New York, and Williams, et al., Methods in Immunology and Immunochemistry, Vol. 1, 1967, Academic Press, New York.
Serum produced from animals immunized using standard methods can be used directly, or the IgG fraction can be separated from the serum using standard methods such as plasmaphoresis or adsorption chromatography with IgG-specific adsorbents such as immobilized Protein A. Alternatively, monoclonal antibodies can be prepared.
Hybridomas producing monoclonal antibodies against the leukotriene receptors of the invention or antigenic fragments thereof are produced by well-known techniques. Usually, the process involves the fusion of an immortalizing cell line with a B-lymphocyte that produces the desired antibody. Alternatively, non-fusion techniques for generating immortal antibody-producing cell lines can be used, e.g., virally-induced transformation [Casali et al., Science 234:476 (1986)]. Immortalizing cell lines are usually transformed mammalian cells, particularly myeloma cells of rodent, bovine, and human origin. Most frequently, rat or mouse myeloma cell lines are employed as a matter of convenience and availability.
Techniques for obtaining antibody-producing lymphocytes from mammals injected with antigens are well known. Generally, peripheral blood lymphocytes (PBLs) are used if cells of human origin are employed, or spleen or lymph node cells are used from non-human mammalian sources. A host animal is injected with repeated dosages of the purified antigen (human cells are sensitized in vitro), and the animal is permitted to generate the desired antibody-producing cells before they are harvested for fusion with the immortalizing cell line. Techniques for fusion are also well known in the art, and in general involve mixing the cells with a fusing agent, such as polyethylene glycol.
Hybridomas are selected by standard procedures, such as HAT (hypoxanthine-aminopterin-thymidine) selection. Those secreting the desired antibody are selected using standard immunoassays, such as Western blotting, ELISA (enzyme-linked immunosorbent assay), RIA (radioimmunoassay), or the like. Antibodies are recovered from the medium using standard protein purification techniques [Tijssen, Practice and Theory of Enzyme Immunoassays (Elsevier, Amsterdam, 1985)].
Many references are available to provide guidance in applying the above techniques [Kohler et al., Hybridoma Techniques (Cold Spring Harbor Laboratory, New York, 1980); Tijssen, Practice and Theory of Enzyme Immunoassays (Elsevier, Amsterdam, 1985); Campbell, Monoclonal Antibody Technology (Elsevier, Amsterdam, 1984); Hurrell, Monoclonal Hybridoma Antibodies: Techniques and Applications (CRC Press, Boca Raton, Fla., 1982)]. Monoclonal antibodies can also be produced using well-known phage library systems. See, e.g., Huse, et al., Science 246:1275 (1989); Ward, et al., Nature, 341:544 (1989).
Antibodies thus produced, whether polyclonal or monoclonal, can be used, e.g., in an immobilized form bound to a solid support by well known methods, to purify the receptors by immunoaffinity chromatography.
Antibodies against the antigenic fragments can also be used, unlabeled or labeled by standard methods, as the basis for immunoassays of the mammalian leukotriene receptors. The particular label used will depend upon the type of immunoassay. Examples of labels that can be used include but are not limited to radiolabels such as 32P, 125I, 3H and 14C; fluorescent labels such as fluorescein and its derivatives, rhodamine and its derivatives, dansyl and umbelliferone; chemiluminescers such as luciferia and 2,3-dihydrophthalazinediones; and enzymes such as horseradish peroxidase, alkaline phosphatase, lysozyme and glucose-6-phosphate dehydrogenase.
The antibodies can be tagged with such labels by known methods. For example, coupling agents such as aldehydes, carbodiimides, dimaleimide, imidates, succinimides, bisdiazotized benzadine and the like may be used to tag the antibodies with fluorescent, chemiluminescent or enzyme labels. The general methods involved are well known in the art and are described, e.g., in Immunoassay: A Practical Guide, 1987, Chan (Ed.), Academic Press, Inc., Orlando, Fla. Such immunoassays could be carried out, for example, on fractions obtained during purification of the receptors.
The antibodies of the present invention can also be used to identify particular cDNA clones expressing the leukotriene receptors in expression cloning systems.
Neutralizing antibodies specific for the ligand-binding site of a receptor can also be used as antagonists (inhibitors) to block leukotriene binding. Such neutralizing antibodies can readily be identified through routine experimentation, e.g., by using the radioligand binding assay described infra. Antagonism of leukotriene activity can be accomplished using complete antibody molecules, or well-known antigen binding fragments such as Fab, Fc, F(ab)2, and Fv fragments.
Definitions of such fragments can be found, e.g., in Klein, Immunology (John Wiley, New York, 1982); Parham, Chapter 14, in Weir, ed. Immunochemistry, 4th Ed. (Blackwell Scientific Publishers, Oxford, 1986). The use and generation of antibody fragments has also been described, e.g.: Fab fragments [Tijssen, Practice and Theory of Enzyme Immunoassays (Elsevier, Amsterdam, 1985)], Fv fragments [Hochman et al., Biochemistry 12:1130 (1973); Sharon et al., Biochemistry 15:1591 (1976); Ehrlich et al., U.S. Pat. No. 4,355,023] and antibody half molecules (Auditore-Hargreaves, U.S. Pat. No. 4,470,925). Methods for making recombinant Fv fragments based on known antibody heavy and light chain variable region sequences have further been described, e.g., by Moore et al. (U.S. Pat. No. 4,642,334) and by Plückthun [Bio/Technology 9:545 (1991)]. Alternatively, they can be chemically synthesized by standard methods.
Anti-idiotypic antibodies, both polyclonal and monoclonal, can also be produced using the antibodies elicited against the receptors as antigens. Such antibodies can be useful as they may mimic the receptors.
Pharmaceutical Compositions
The leukotriene receptor agonists and antagonists of this invention can be used therapeutically to stimulate or block the activity of leukotriene, and thereby to treat any medical condition caused or mediated by leukotriene. The dosage regimen involved in a therapeutic application will be determined by the attending physician, considering various factors which may modify the action of the therapeutic substance, e.g., the condition, body weight, sex and diet of the patient, the severity of any infection, time of administration, and other clinical factors.
Typical protocols for the therapeutic administration of such substances are well known in the art. Administration of the compositions of this invention is typically by parenteral, by intraperitoneal, intravenous, subcutaneous, or intramuscular injection, or by infusion or by any other acceptable systemic method. Often, treatment dosages are titrated upward from a low level to optimize safety and efficacy. Generally, daily dosages will fall within a range of about 0.01 to 20 mg protein per kilogram of body weight. Typically, the dosage range will be from about 0.1 to 5 mg per kilogram of body weight.
Dosages will be adjusted to account for the smaller molecular sizes and possibly decreased half-lives (clearance times) following administration. It will be appreciated by those skilled in the art, however, that the leukotriene antagonists of the invention encompass neutralizing antibodies or binding fragments thereof in addition to other types of inhibitors, including small organic molecules and inhibitory ligand analogs, which can be identified using the methods of the invention.
An “effective amount” of a composition of the invention is an amount that will ameliorate one or more of the well-known parameters that characterize medical conditions caused or mediated by leukotriene.
Although the compositions of this invention could be administered in simple solution, they are more typically used in combination with other materials such as carriers, preferably pharmaceutical carriers. Useful pharmaceutical carriers can be any compatible, non-toxic substances suitable for delivering the compositions of the invention to a patient. Sterile water, alcohol, fats, waxes, and inert solids may be included in a carrier. Pharmaceutically acceptable adjuvants (buffering agents, dispersing agents) may also be incorporated into the pharmaceutical composition. Generally, compositions useful for parenteral administration of such drugs are well known; e.g. Remington's Pharmaceutical Science, 17th Ed. (Mack Publishing Company, Easton, Pa., 1990). Alternatively, compositions of the invention may be introduced into a patient's body by implantable drug delivery systems [Urquhart et al., Ann. Rev. Pharmacol. Toxicol. 24:199 (1984)].
Therapeutic formulations may be administered in many conventional dosage formulation. Formulations typically comprise at least one active ingredient, together with one or more pharmaceutically acceptable carriers. Formulations may include those suitable for oral, rectal, nasal, or parenteral (including subcutaneous, intramuscular, intravenous and intradermal) administration.
The formulations may conveniently be presented in unit dosage form and may be prepared by any methods well known in the art of pharmacy. See, e.g., Gilman et al. (eds.) (1990), The Pharmacological Bases of Therapeutics, 8th Ed., Pergamon Press; and Remington's Pharmaceutical Sciences, supra, Easton, Pa.; Avis et al. (eds.) (1993) Pharmaceutical Dosage Forms: Parenteral Medications Dekker, New York; Lieberman et al. (eds.) (1990) Pharmaceutical Dosage Forms: Tablets Dekker, New York; and Lieberman et al. (eds.) (1990), Pharmaceutical Dosage Forms: Disperse Systems Dekker, New York.
The present invention also encompasses anti-idiotypic antibodies, both polyclonal and monoclonal, which are produced using the above-described antibodies as antigens. These antibodies are useful because they may mimic the structures of the receptors.
Anti-sense Molecules
The present invention also encompasses anti-sense oligonucleotides capable of specifically hybridizing to mRNA encoding a mammalian leukotriene receptor having an amino acid sequence defined by SEQ ID NO: 2 or a subsequence thereof so as to prevent translation of the mRNA. Additionally, this invention contemplates anti-sense oligonucleotides capable of specifically hybridizing to the genomic DNA molecule encoding a mammalian leukotriene receptor having an amino acid sequence defined by SEQ ID NO: 2 or a subsequence thereof.
This invention further provides pharmaceutical compositions comprising (a) an amount of an oligonucleotide effective to reduce activity of human leukotriene receptor by passing through a cell membrane and binding specifically with mRNA encoding human leukotriene receptor in the cell so as to prevent its translation and (b) a pharmaceutically acceptable carrier capable of passing through a cell membrane. In an embodiment, the oligonucleotide is coupled to a substance that inactivates mRNA. In another embodiment, the substance that inactivates mRNA is a ribozyme.
EXAMPLES
The present invention can be illustrated by the following examples. Unless otherwise indicated, percentages given below for solids in solid mixtures, liquids in liquids, and solids in liquids are on a wt/wt, vol/vol and wt/vol basis, respectively. Sterile conditions were generally maintained during cell culture.
Materials and General Methods
Human marathon-ready cDNAs and RACE kit were from Clontech. Oligonucleotides were custom-synthesized by Gibco Life Technologies. 293-EBNA cell line was obtained from Invitrogen. Leukotrienes and other ligands were purchased from Sigma Chemicals. Radioligands were from NEN.
Standard methods were used, as described, e.g., in Maniatis et al., Molecular Cloning: A Laboratory Manual, 1982, Cold Spring Harbor Laboratory, Cold Spring Harbor Press; Sambrook et al., Molecular Cloning: A Laboratory Manual, (2d ed.), Vols 1-3, 1989, Cold Spring Harbor Press, N.Y.; Ausubel et al., Biology, Greene Publishing Associates, Brooklyn, N.Y.; or Ausubel, et al. (1987 and Supplements), Current Protocols in Molecular Biology, Greene/Wiley, New York; Innis et al. (eds.) PCR Protocols: A Guide to Methods and Applications, 1990, Academic Press, N.Y.
Example 1
Cloning and Characterization of the Human Leukotriene Receptor
The amino acid sequences of known G-protein coupled receptors were used to conduct a BLAST search of EST databases. The search identified a 397 bp EST as being a putative G-protein coupled receptor fragment. A phylogenetic analysis (Wisconsin Package, Genetics Computer Group, Madison, Wis.) of this EST suggested that the sequence could be a fragment of a leukotriene receptor cDNA. The complete coding region of the cDNA was assembled by combining contiguous sequences from DNA databases and RACE PCR.
To clone the full length cDNA(referred to hereinafter as SP9030), a PCR primer pair (oligo 358 and oligo 359) was designed, based on the assembled sequences, to amplify in a PCR using Clontech marathon-ready cDNA from liver as template. The PCR product containing the full length cDNA (1.1-kb) was cloned into expression vector pCR3.1 (Invitrogen) to form an expression construct pCR3.1-SP9030. PCR conditions for this PCR was 94° C. for 30 sec; 35 cycles at 94° C. for 30sec, 65° C. for 30 sec, 72° C. for 2 min; and 72° C. for 7 min. The sequences of this pair of PCR primers are: Oligo 358, gccgccaccatgtcggtctgctaccgtcc (SEQ ID NO: 3) and Oligo 359, gcaggttgtagggtctgctgtca (SEQ ID NO: 4). Sequencing analysis identified an open reading frame of 1077 bp (SEQ ID NO: 1) that encodes a protein of 358 amino acids (aa) (SEQ ID NO: 2).
Hydrophobicity analysis of the 358aa protein suggests that there are seven transmembrane spanning regions within the protein, a feature that is shared by the G-protein coupled receptor super-family. BLAST analysis with the amino acids of SP9030 against the Genbank database revealed high homology to three known receptors, i.e. the human leukotriene B4 receptor (Yokomizo et al., Nature, 387:620 (1997)), the human CRTH12 (Nagata et al., J. Immunol., 162:1278-1286 (1999)), and the human somatostatin receptor SSTR4 (Rohrer et al., Proc. Natl. Acad. Sci. USA., 90(9):4196-4200 (1993)). Sequence alignment analysis of the protein sequences using the J. Hein method (Guide to Protein Purification, Methods in Enzymology, 183:626-645 (1990), M. Deutscher, Ed., 1990, Academic Press, New York, N.Y.) showed highest homology of SP9030 to leukotriene B4 receptor (42%), followed by CRTH12 (32%) and SSTR4 (27%). These analyses suggest that the protein encoded by SP9030 ORF may be a leukotriene receptor.
In addition to the high homology of SP9030 to leukotriene B4 receptor (Yokomizo et al., Nature, 387:620-624 (1997)) (accession #D89079), physical linkage was observed between the two genes. The 5′ untranslated region of leukotriene B4 receptor (accession #D89079) is identical to the coding region at the 3′ end of the ORF and the immediate down stream 3′ untranslated sequence. This analysis indicates that the two receptors can exist on a single messenger RNA and thus be co-expressed in the cell.
Example 2
Agonist/antagonist Screening Assay
Transfection of Cells and Membrane Preparations
COS-7 cells, grown in DMEM/10% FCS until 80-90% confluence, were transfected with SuperFect agent (Giagene) at 20 μg DNA/150 mm plate. Forty eight hours after transfection, medium was changed to Opti-MEM or DMEM/Opti-MEM(1:1)/5% FCS. Cells were harvested 72 hours after transfection and membranes from the cells were prepared as follows. The cells were washed with 20 ml PBS without Ca2+/Mg2+ and incubated with 10 ml 10 nM Hepes pH 7.4, 0.5 mM PMSF, 20 μg/ml aprotinin. The cells were scraped off the plate and vortexed. The cell suspension was then centrifuged at 13,000 g at 4° C. for 15 min. The pellets were re-suspended in 1.8 ml 50 mM Tris-Cl, pH 7.5 and vortexed. The membranes were homogenized with a 23-gauge needle. The protein concentration of the membrane preparations was determined with the BCA agents (Pierce).
Radioligand Binding Assay
Radioligand binding assays were performed to test the ability of SP9030, when expressed in cultured cells, to bind 3H-labeled leukotriene. The ORF of SP9030 was cloned in the expression vector pCR3.1 (pCR3.1-SP9030). COS-7 cells were transfected with pCR3.1-SP9030 or pCR3.1 alone (mock transfection). Two days after transfection, the normal growth medium DMEM/10% FCS was replaced by either Opti-MEM or DMEM-Opti-MEM/5% FCS. The cells were allowed to grow one more day and then membranes were prepared for use in binding assay. Unlabeled LTB4 at 1 μM was used to determine non-specific binding. After a total of three days from transfection, membranes were prepared from the transfectant cells and specific binding to 3H-LTB4 observed.
For saturation binding, 150 μl binding assay buffer (30 mM Hepes, pH 7.4, 10 mM CaCl2, 10 mM MgCl2, 0.05% fatty acid-free BSA (w/v), kept cold on ice) containing 24 μg of membranes were mixed with 50 μl of binding assay buffer containing 2% (v/v) DMSO cold leukotriene (1 μM). 3H-LTB4/ethanol (NEN, 50 nM) was added to the assays at increasing concentrations. The reactions were incubated for 1 hour at 4° C. while rotated slowly. Multiscreen FB filters (Millipore) pre-soaked with 50 μl binding assay buffer for 1 hour at room temperature were used to filter the binding assays and the filters were washed twice with 100 μl 50 mM TrisCl, pH 7.5 (ice cold). Fifty microliters of scintillation fluid was added to the filters and counted to detect the bound radioligands. For radioligand competition assays, 160 μl binding assay buffer containing appropriate membranes were mixed with 20 μl of binding assay buffer containing 6% DMSO (v/v) and various concentrations of competing compounds. A final 20 μl of binding assay buffer containing 6% (v/v) DMSO and 1 μl of 3H-LTB4/ethanol (NEN, 50 nM) was added to start the binding reaction. The final concentration of radioligand was 0.25 nM. Incubation conditions were the same as that used for the above described saturation assays.
Saturation radioligand binding assays yielded a KD of 0.17±0.07 nM and Bmax of 70±8 fmol/mg (n=3). Radioligand competition assays using 3H-LTB4 as the label was employed to test the affinities of 13 unlabeled leukotriene and lipoxin compounds. COS-7 cells transfected with SP9030 cDNA were harvested three days after transfection and membrane prepared from cells used for binding assays. An unlabeled leukotriene or lipoxin at increasing concentration was used to compete with 3H-leukotriene B4 (0.25 nM). Ki values are calculated for individual compound by using Ki=EC50/(1+[3H-LTB4]/Kd), where [3H-LTB4] is the concentration of the radioligand used in the assay (0.25 nM), KD is the affinity of the radioligand for the receptor (0.17 nM) and EC50 is determined by non-linear regression analysis. High affinity for LTB4, LTB5 and lipoxin A4 were revealed (Ki=2.0±1.2, 8.6±5.3 and 112±40 nM, respectively). The other compounds displayed substantially weaker or no affinities for SP9030 (Ki>1 μM). These results indicate that the receptor encoded by SP9030 is structurally selective for certain ligands.
Intracellular Ca2+ concentration measurement
293-EBNA cells, grown in DMEM containing 10% FCS until 80-90% confluence, were transfected with SuperFect transfection agent. The next day, cells were trypsinized off culture plates and washed with PBS lacking Ca2+/Mg2+. The cells were then seeded at a density of 35,000 cells per 100 μl medium) into 96-well plates that were pre-coated with poly-D-lysine (Becton Dickinson). The third day following transfection, medium was removed from cells and 100 μl Hank's balanced salt solution (lacking phenol red) containing 4 μM of Fluo-3, AM (Molecular Probes), 20 mM Hepes, pH 7.4, 0.1% (w/v) BSA and 250 mM probenecid added and subsequently incubated at 37° C., 5% CO2 for 1 hour. The cells were then washed three times with 150 μl wash buffer containing HANK's BSS, 40 mM Hepes, pH 7.4 and 250 mM probenecid. One hundred μl of the wash buffer was added after the final wash and Ca2+ flux was measured after addition of 40 μl of wash buffer containing appropriate concentration of ligands. The FLIPR instrument (Molecular Device) was used in the measurement of Ca2+ flux.
Intracellular function that the SP9030 receptor may mediate through activation by its ligand was examined in measurements of intracellular Ca2+ flux. Interaction of SP9030 expressed in 293-EBNA cells with LTB4 activated cellular Ca2+ release, suggesting SP9030 is able to stimulate cellular functions by coupling to G protein(s) in the cell. Cells that were mock transfected without SP9030 cDNA did not respond to incubation with LTB4.
Many modifications and variations of this invention can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. The specific embodiments described herein are offered by way of example only, and the invention is to be limited only by the terms of the appended claims, together with the full scope of equivalents to which such claims are entitled.

## Claims

1. An isolated polypeptide comprising at least 12 contiguous residues of the amino acid sequence of SEQ ID NO: 2.

2. The polypeptide of claim 1 comprising at least 20 contiguous residues of the amino acid sequence of SEQ ID NO: 2.

3. The polypeptide of claim 1 comprising at least 30 contiguous residues of the amino acid sequence of SEQ ID NO: 2.

4. An isolated polypeptide comprising the amino acid sequence of SEQ ID NO: 2.

5. The polypeptide of claim 4 which is bound to leukotriene B4.

6. The polypeptide of claim 5 wherein the leukotriene B4 is labeled with 3H.

7. A method for identifying an agonist or antagonist of a mammalian leukotriene receptor, comprising:
(a) contacting a polypeptide of claim 4 in the presence of a known amount of labeled leukotriene with a sample to be tested for the presence of a leukotriene agonist or antagonist; and 
(b) measuring the amount of labeled leukotriene specifically bound to the polypeptide; 
whereby a leukotriene agonist or antagonist in the sample is identified by measuring substantially reduced binding of the labeled leukotriene to the polypeptide, compared to what would be measured in the absence of such agonist or antagonist.

8. The method of claim 7 in which membranes isolated from mammalian cells comprising a nucleic acid encoding the polypeptide are used as the source of said polypeptide.