bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tumorigenesis in transgenic mice: Identification and characterization of synergizing oncogenes
Authors: Berns Anton 
Published: May 2005

AbstractTransgenic mice carrying oncogenes present a useful model with which to assess the tissue‐specific action of oncogenes. These mice are usually predisposed to a specific type of neoplastic growth. The tumors that arise are usually monoclonal in origin and become only apparent after a variable latency period, suggesting that additional events are required for tumor formation. Identification of these additional events is highly relevant: it might give access to the genes that can synergize with a preselected oncogene in tumorigenesis and could facilitate the identification of the biochemical pathways in which these genes act. Retroviruses can be instrumental in identifying cooperating oncogenes. Proto‐oncogene activation or tumor suppressor gene inactivation by insertional mutagenesis is an important mechanism by which the non‐acute transforming retroviruses can induce tumors in several species. Owing to the sequence tag provided by the provirus, the relevant proto‐oncogene can be directly identified by cloning of the DNA flanking the proviral insertion site. We have exploited this potential of retroviruses by infecting Eμ‐pim‐1 and Eμ‐myc transgenic mice, which are predisposed to lymphomagenesis, with Moloney murine leukemia virus (MuLV). A strong acceleration of tumor induction ensued upon infection of these mice with MuLV. More importantly, it allowed us to identify a number of additional common insertion sites marking both previously known as well as new (putative) oncogenes. In a significant portion of the tumors more than one oncogene was found to be activated, indicating that within this system the synergistic effect of at least three genes can be established. Furthermore, the distribution of proviruses over these common insertion sites suggests that this methodology enables us to assign each of these genes to distinct complementation groups in tumorigenesis. To get insight into the function of these oncogenes, we have inactivated one of them, the pim‐1 oncogene, via homologous recombination in ES cells. We have shown that by using a pim‐1 targeting vector in which transcription and translation of the resistance marker was made dependent on the acquisition of both a promoter and an in‐frame translational initiation codon, the gene could be inactivated with high efficiency. Subsequently, we inactivated the second allele by using a different selectable marker. The absence of the pim‐1 gene product does not appear to have any detrimental effect on the growth of ES cells and hematopoietic cells derived from these ES cells in vitro, despite the fact that pim‐1 is highly expressed in wild‐type ES cells. More detailed analysis of pim‐1‐less cells and mice will be necessary to gain insight into the relevance of the highly conserved pim‐1 proto‐oncogene in development and maintenance of mammalian organisms.
Platelet‐derived endothelial cell growth factor
Authors: Heldin Carl‐Henrik , Usuki Kensuke , Miyazono Kohei 
Published: May 2005

AbstractPlatelet‐derived endothelial cell growth factor (PD‐ECGF) is a 45kDa single chain polypeptide which stimulates endothelial cell growth and chemotaxis in vitro and angiogenesis in vivo. Analysis of a full length PD‐ECGF cDNA revealed an open reading frame coding for 482 amino acids without homology to other known proteins. No signal sequence was observed, and analysis of the biosynthesis and processing of PD‐ECGF in a thyroid carcinoma cell line revealed that PD‐ECGF is released only very slowly. PD‐ECGF becomes covalently associated with nucleotide triphosphates (e.g., ATP) in vivo, as well as in vitro. The physiological significance of this posttranslational modification remains to be elucidated. The tissue distribution and target cell specificity of PD‐ECGF suggests roles in angiogenesis (e.g., during wound healing and in the developing placenta), as well as in the maintenance of the integrity of the endothelial cell lining of large vessels.
The vascular endothelial growth factor family of polypeptides
Authors: Ferrara Napoleone , Houck Keith A. , Jakeman Lyn B. , Winer Jane , Leung David W. 
Published: May 2005

AbstractVascular endothelial growth factor (VEGF) was identified as a heparin‐binding polypeptide mitogen with a target cell specificity restricted to vascular endothelial cells. Molecular cloning reveals the existence of four species of VEGF having 121, 165, 189, and 206 amino acids. These have strikingly different secretion patterns, which suggests multiple physiological roles for this family of polypeptides. The two shorter forms are efficiently secreted, while the longer ones are mostly cell‐associated. Alternative splicing of mRNA, rather that transcription from different genes, is the mechanism for their generation. In situ hybridization reveals that the VEGF mRNA is widely distributed in most tissues and organs and expressed at particularly high levels in areas of active vascular proliferation, like the ovarian corpus luteum. Ligand autoradiography on rat tissue sections demonstrates that VEGF binding sites are associated with vascular endothelial cells of both fenestrated and non‐fenestrated capillaries and with the endothelium of large vessels, while no displaceable binding is evident on non‐endothelial cell types. These findings support the hypothesis that VEGF plays a highly specific role in the maintenance and in the induction of growth of vascular endothelial cells.
Endothelial cell regulation by transforming growth factor‐beta
Authors: RayChaudhury Amlan , D'Amore Patricia A. 
Published: May 2005

AbstractPronounced changes including growth inhibition, increased matrix deposition and suppression of cell‐associated proteolytic activity, take place in endothelial cells (EC) upon the application of TGF‐β. Interrelationships between these effects have shed some light on the mechanism of action of TGF‐β and on its role in regulating EC function vis‐a‐vis angiogenesis. For instance, preliminary evidence has indicated that increased levels of certain matrix components may be partly responsible for the antiproliferative action of TGF‐β. In addition, TGF‐β and bFGF have opposing effects on cellular proteolytic balance which may contribute to the antagonistic effect that TGF‐β has on bFGF‐induced EC growth and possibly to the anti‐angiogenic effect exerted by TGF‐β under certain circumstances. Of particular interest in this regard is the fact that physical contact between EC and vascular mural cells in EC:mural cell cocultures has been found to generate active TGF‐β, thus further implicating TGF‐β in the maintenance of the quiescent, differentiated aggreation of EC as found in vascular structures in vivo. While more information is needed to define what, if any, role TGF‐β plays in endothelial differentiation, it is to be noted that many of the cellular and biochemical processes affected by TGF‐β are linked to differentiation. It is therefore possible that the growth inhibition of EC by TGF‐β primes them for differentiation and/or is critical for the maintenance of a differentiated state.
Substrates and signalling complexes: The tortured path to insulin action
Authors: Roth Richard A. , Zhang Bei , Chin Janice E. , Kovacina Kristina 
Published: May 2005

AbstractIn the last few years several potential substrates of the insulin receptor tyrosine kinase have been identified, purified, and their cDNAs isolated. These putative substrates include: (1) pp15, a fatty acid‐binding protein; (2) pp120, a plasma membrane ecto‐ATPase; (3) pp42, a MAP serine/threonine kinase; (4) pp85, a subunit of the Type 1 phosphatidylinositol kinase; and (5) pp185, a phosphatidylinositol kinase binding protein. Although the tyrosine phosphorylation of several of these substrates correlates with the signalling capabilities of various mutant receptors, the role of these substrates in mediating any one of insulin's many biological responses is still unknown. In addition, recent data indicate that the tyrosine phosphorylation of pp42 may in fact be due to autophosphorylation, thereby removing it from the list of putative substrates of the insulin receptor kinase. Finally, the present review discusses the question of whether signalling occurs as a result of the tyrosine phosphorylation of substrates or via the formation of signalling complexes.
Modulation of collagen and fibronectin synthesis in fibroblasts by normal and malignant cells
Authors: Noel A. , Lambert C. A. , Nusgens B. , Lapiere C. M. , Munaut C. , Foidart J. M. , Boulvain A. , Calberg‐Bacq C. M. 
Published: May 2005

AbstractThe influence of various normal and malignant human cells on the level of collagen synthesis by human fibroblasts was tested in coculture. As revealed by immunoperoxidase staining, in cocultures with breast adenocarcinoma cells (MCF7, SA52, T47D) fibroblasts synthesized collagen while tumor cells did not. Fibroblasts displayed increased collagen production without change in the overall protein synthesis. Several other types of cells derived from normal human tissues (keratinocytes, normal mammary cells) or from fibrosarcoma, melanoma, cervical carcinoma, choriocarcinoma, or other breast adenocarcinoma (SW613, MDA, BT20) did not affect collagen synthesis of fibroblasts. Although to a lesser extent, this stimulating effect was reproduced by using the conditioned medium (CM) of the active cells but not with CM of the other cell types. A slight stimulation was also obtained when tumoral MCF7 cells and fibroblasts shared the same medium but were physically separated, suggesting that close contact was required for optimal stimulation of collagen synthesis. The collagen synthesis stimulating activity was not related to a modification of fibroblast proliferation rate. The production of collagen types I, III, and VI and fibronectin were increased in cocultures of fibroblasts with MCF7 cells. The increased synthesis of collagen types I and III and fibronectin was paralleled by similar changes in the steady‐state level of their mRNAs. On the contrary, the increased production of collagen type VI appeared regulated at a post‐transcriptional level.
Comparison between avian and human prolyl 4‐hydroxylases: Studies on the holomeric enzymes and their constituent subunits
Authors: Guzman Norberto A. , Ascari William Q. , Cutroneo Kenneth R. , Desnick Robert J. 
Published: May 2005

AbstractProlyl 4‐hydroxylase, a key enzyme in collagen biosynthesis, catalyzes the conversion of selected prolyl residues to trans‐hydroxyproline in nascent or completed pro‐α chains of procollagen. The enzyme is a tetramer composed of two nonidentical subunits, designated α and β. To compare the enzyme and its subunits from different sources, the chick embryo and human placental prolyl 4‐hydroxylases were purified to homogeneity and their physicochemical and immunological properties were determined. Both enzymes were glycoproteins with estimated apparent molecular weights ranging between 400 and 600 kDa. Amino acid and carbohydrate analyses showed slight differences between the two holomeric enzymes, consistent with their deduced amino acid sequences from their respective cDNAs. Human placental prolyl 4‐hydroxylase contained more tightly bound iron than the chick embryo enzyme. Immunodiffusion of the human placental enzyme with antibodies raised against the purified chick embryo prolyl 4‐hydroxylase demonstrated partial identity, indicating different antigenic determinants in their tertiary structures. The enzymes could be separated by high‐resolution capillary electrophoresis, indicating differential charge densities for the native chick embryo and human placental proteins.Electrophoretic studies revealed that the human prolyl 4‐hydroxylase is a tetrameric enzyme containing two nonidentical subunits of about 64 and 62 kDa, in a ratio of approximately 1 to 2, designated α and β, respectively. In contrast, the chick embryo α and β subunit ratio was 1 to 1. Notably, the human α subunit was partially degraded when subjected to electrophoresis under denaturing conditions. Analogously, when the chick embryo enzyme was subjected to limited proteolysis, selective degradation of the α subunit was observed. Finally, only the α subunit was bound to Concanavalin A demonstrating that the α subunits of prolyl 4‐hydroxylase in both species were glycosylated. Using biochemical techniques, these results demonstrated that the 4‐trans‐hydroxy‐L‐proline residues in human placental collagens are synthesized by an enzyme whose primary structure and immunological properties differ from those of the previously well‐characterized chick embryo enzyme, consistent with their recently deduced primary structures from cDNA sequences.
Expression of heat shock genes during differentiation of mammalian osteoblasts and promyelocytic leukemia cells
Authors: Shakoori Abdul Rauf , Oberdorf Annette M. , Owen Thomas A. , Weber Lee A. , Hickey Eileen , Stein Janet L. , Lian Jane B. , Stein Gary S. 
Published: May 2005

AbstractThe progressive differentiation of both normal rat osteoblasts and HL‐60 promyelocytic leukemia cells involves the sequential expression of specific genes encoding proteins that are characteristic of their respective developing cellular phenotypes. In addition to the selective expression of various phenotype marker genes, several members of the heat shock gene family exhibit differential expression throughout the developmental sequence of these two cell types. As determined by steady state mRNA levels, in both osteoblasts and HL‐60 cells expression of hsp27, hsp60, hsp70, hsp89α, and hsp89β may be associated with the modifications in gene expression and cellular architecture that occur during differentiation.In both differentiation systems, the expression of hsp27 mRNA shows a 2.5‐fold increase with the down‐regulation of proliferation while hsp60 mRNA levels are maximal during active proliferation and subsequently decline post‐proliferatively. mRNA expression of two members of the hsp90 family decreases with the shutdown of proliferation, with a parallel relationship between hsp89α mRNA levels and proliferation in osteoblasts and a delay in down‐regulation of hsp89α mRNA levels in HL‐60 cells and of hsp89β mRNA in both systems. Hsp70 mRNA rapidly increases, almost twofold, as proliferation decreases in HL‐60 cells but during osteoblast growth and differentiation was only minimally detectable and showed no significant changes. Although the presence of the various hsp mRNA species is maintained at some level throughout the developmental sequence of both osteoblasts and HL‐60 cells, changes in the extent to which the heat shock genes are expressed occur primarily in association with the decline of proliferative activity. The observed differences in patterns of expression for the various heat shock genes are consistent with involvement in mediating a series of regulatory events functionally related to the control of both cell growth and differentiation.
Biochemical and morphological differentiation of the human colonic epithelial cell line SW620 in the presence of dimethylsulfoxide
Authors: Omary M. Bishr , de Grandpre Louise , McCaffrey Michael , Kagnoff Martin F. 
Published: May 2005

AbstractIn vitro models of intestinal cell differentiation provide an important adjunct for studying normal and abnormal intestinal epithelial cell diffrentiation. The studies reported herein describe morphologic and biochemical changes in the colonic epithelial cell line SW620 following dimethylsulfoxide (DMSO) incubation. Cells cultured in the presence of DMSO showed striking changes in morphology characterized by enlargement, elongation, and formation of process‐like structures by light microscopy and a propensity to form microvillus‐like structures by electron microscopy. These changes were accompanied by significant differences in the expression of the cell surface markers CD4 (HIV gp120 receptor), CD44 (hyaluronate receptor), and KS1 (adenocarcinoma/epithelial specific antigen). There was a marked decrease in CD4 expression (38% to 2%), an increase in CD44 expression (4% to 50%) and a decrease in KS1 expression (98% to 66%) as detected by flow cytometry following incubation of SW620 cells in DMSO. Parallel changes in the expression of these markers were seen by metabolic and surface labeling studies. Although SW620 cells were infected by HIV‐1, DMSO‐treated SW620 cells could not be infected. DMSO‐induced changes in surface expression of CD4, CD44, and KS‐1 were reversible over time upon removal of DMSO from the culture medium. Secretory component, sucrase, neuron‐specific enolase, chromogranin‐A and mucin were not detectable in SW620 cells with or without DMSO treatment. SW620 cells provide a useful model for studying specific biochemical and molecular events involved in intestinal epithelial cell differentiation and function.
The inhibition of ATP‐dependent shape change of human erythrocyte ghosts correlates with an inhibition of Mg2+‐ATPase activity by fluoride and aluminofluoride complexes
Authors: Morris Michael B. , Monteith Gregory , Roufogalis Basil D. 
Published: May 2005

AbstractThe vanadate‐sensitive Mg2+‐dependent ATPase activity of the human erythrocyte ghost is believed to be involved in the shape change events that convert echinocytic ghosts to smoothed forms (biconcave discs and stomatocytes). At physiological salt concentration, pH 7.4, 2 mMATP, 5 mM Mg2+ and 1 mM EGTA, the Mg2+‐ATPase activity of ghosts was inhibited strongly by millimolar concentrations of sodium fluoride: I50 = 1.31 ± 0.2, mM (mean ± S.D., n = 12). The addition of aluminium chloride to 15 μM reduced the concentration of NaF required for 50% inhibition to 0.76 ± 0.21 mM (n = 10). Aluminium alone had only a small inhibitory effect of the ATPase activity (13 ± 9 %; n = 10). Desferrioxamine, a strong chalator of tervalent aluminium ion, failed to reverse the inbibition by fluoride and reversed the inhibition in the presence of aluminium and fluoride back to those values obtained with fluoride alone. Of several metal salts tested only beryllium sulfate was able to replace aluminium as an effective inhibitor in the presence of fluoride.Inhibition of the Mg2+‐ATPase activity by fluoride and the aluminofluoride complexes correlated with an inhibition of the rate of MgATP‐dependent change in red cell ghost shape from echinocytes to smoothed forms. All gross morphological changes of the smoothing process were affected, including the production of discocytes, stomatocytes and endocyctic vesicles.
Growth regulation of the mammalian ocular lens by vitreous humor
Authors: Banerjee Amit , Parafina Julian , Bagchi Mihir 
Published: May 2005

AbstractExperiments were performed in our laboratory to study the effects of a mammalian 8 kD vitreous humor (VH) factor on the DNA synthesis and mitosis of the epithelial cells of organ cultured rabbit lens. The 8 kD polypeptide factor was purified from mature rabbit vitreous humor by liquid chromatography. Proliferative activities of the epithelial cells of organ cultured lenses were stimulated by 3% rabbit serum. The data from our experiments depicted that the 8 kD VH factor effectively inhibits DNA synthesis and mitosis by the epithelial cells of the organ cultured lens. Our experiments also showed that this 8 kD VH factor can maintain its growth inhibitory activity even when heated for 3 min at 95°C. The growth inhibitory effect of the 8 kD VH factor was dose dependent. Using iodinated vitreal proteins it was demonstrated that the VH proteins are able to enter or bind to lens epithelial cells. The growth inhibitory effect of the 8 kD VH factor was also tested on tissue cultured lens epithelial cells. These experiments showed that the 8 kD VH factor has no growth inhibitory effect on the tissue cultured lens epithelial cells. This experiment has been repeated many times using different concentrations of the factor. These observations suggest that the 8 kD VH factor may have receptors in the lens capsular material (extracellular matrix) and the factor‐receptor binding is essential for the growth inhibitory effect.
Wild‐type murine p53 represses transcription from the murine c‐myc promoter in a human glial cell line
Authors: Moberg Kenneth H. , Tyndall W. Andrew , Hall David J. 
Published: May 2005

AbstractHere we analyzed the effect of the suppressor proto‐oncogene p53 on transcription from the P2 promoter of the murien c‐myc gene. c‐myc promoter constructs were coupled to the chloramphenical acetyl‐transferase (CAT) gene and were transiently transfected into a human glial cell line along with plasmids overexpressing wild‐type or mutant p53. It was found that significant repression of c‐myc transcription took place following cotransfection with wild‐type but not mutant p53. However wild‐type p53 did not suppress transcription from the SV40 early promoter or from the MHC promoter. Promoter‐CAT constructs containing only the ME1a2 or E2F elements, from the P2 promoter, were repressed by p53, indicating that p53 may exert its effect at these two sites within the P2 promoter. Finally, when the SV40 T antigen and wild‐type p53 were expressed together in glial cells the repressive effect of p53 was abolished.
Identification of a fat cell enhancer: Analysis of requirements for adipose tissue‐specific gene expression
Authors: Graves Reed A. , Tontonoz Peter , Platt Kenneth A. , Ross Susan R. , Spiegelman Bruce M. 
Published: May 2005

AbstractThe molecular basis for adipose‐specific gene expression is not known. To approach the problem of adipocyte gene expression, we have analyzed in detail the capacity of the 5′‐flanking region of the adipocyte P2 (aP2) gene to direct cell‐type specific gene expression. Although the proximal promoter containing AP‐1 and C/EBP binding sites is capable of directing differentiation‐dependent gene expression in cultured adipocytes, these constructs are essentially inactive in the tissues of transgenic mice. We found that −5.4 kb of the 5‐flanking region were required to direct heterologous gene (chloramphenicol acetyl transferase; CAT) expression to the adipose tissue of transgenic mice. By deletion analysis, we identified a 520 bp enhancer at −5.4 kb of the aP2 gene. We show that this enhancer can direct high levels of gene expression specifically to the adipose tissue of transgenic mice. This enhancer also functions in a differentiation‐dependent manner in cultured adipocytes and cannot be transactivated in preadipocytes by C/EBP. Molecular analysis indicates that several cis‐ and transacting acting elements, though not C/EBP, contribute to the specificity and potency of this enhancer.