Fibroblast growth factor receptor gene expression and immunoreactivity are elevated in human glioblastoma multiforme

Glioblastomas were examined for abnormalities in fibroblast growth factor receptor (FGFR) expression by polymerase chain reaction and immunocytochemical analysis. Polymerase chain reaction analysis demonstrated that FGFR1 mRNA levels were significantly higher in glioblastomas than in normal brain adjacent to the tumor or in untransformed human brain. These results were consistent with immunocytochemical localization of FGFR1 protein in glioblastomas: glioblastoma cells exhibited intense FGFR1 immunoreactivity in frozen sections of tumor and low to undetectable FGFR1 immunoreactivity in adjacent normal brain or in normal white matter obtained from patients without neoplastic disease. Endothelial cells of capillaries and larger vessels within the tumor were devoid of FGFR1 immunoreactivity. All glioblastomas evaluated in the present study expressed FGFR1 mRNA and FGFR1 immunoreactivity. Examination of the FGFR1 gene by Southern blot analysis indicated that overexpression of FGFR1 mRNA in glioblastomas did not result from gene amplification. These results indicate that glioblastoma cells, in contrast to endothelial cells within the tumor, display increased levels of FGFR1. Therefore, FGFR1 signal transduction may be associated with increased autocrine growth activity of tumor cells and is probably not related to the increased endothelial cell proliferation associated with these tumors.

Stable and temperature-sensitive transformation of rat kidney epithelial cells suppresses expression of acidic fibroblast growth factor 1 but activates secretion of fibroblast growth factor 3 (int-2) and vascular endothelial growth factor

Rat kidney proximal tubule epithelial cells (RPTE) in primary culture express acidic fibroblast growth factor 1 (FGF-1). Transformation of RPTE by SV40 (SV-RPTE) suppressed FGF-1 expression but activated secretion of FGF-like factor(s). SV-RPTE conditioned medium contained growth-promoting activity for SV-RPTE and human umbilical vein endothelial cells, indicating that both autocrine and angiogenic factors were secreted. Reverse transcriptase-polymerase chain reaction and Northern analysis for various FGFs showed that only FGF-3, also known as int-2, mRNA was expressed in SV-RPTE. In addition, expression of mRNA for the heparin-binding angiogenic factor vascular endothelial growth factor (VEGF) increased dramatically in SV-RPTE. Physical characterization of the activity in the SV-RPTE conditioned medium suggested that FGF-3 and VEGF contributed the autocrine and angiogenic activities, respectively. We also investigated FGF-3 and VEGF secretion in temperature-sensitive (ts) SV40-transformed RPTE. tsSV-RPTE had transformed properties resembling those of SV-RPTE only at the permissive temperature (33 degrees C), e.g., increased growth potential and anchorage-independent growth. FGF-1 was expressed only at the nonpermissive temperature. VEGF mRNA levels and secretion of the human umbilical vein endothelial cell growth-promoting activity were reduced by switching tsSV-RPTE cells from 33 degrees to 39 degrees C. However, FGF-3 mRNA levels were not affected significantly by the temperature switch suggesting that activation of VEGF and FGF-3 occurs through different mechanisms. These results indicate that FGF-1 expression in RPTE is suppressed by SV40 transformation.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on the biological characterization and mitogenic interactions between hepatic stimulator substance and acidic fibroblast growth factor

During liver regeneration, hepatic stimulator substance (HSS) and acidic fibroblast growth factor (FGF-1) are produced in the liver. These growth factors may be involved in liver growth control but an understanding of their regulatory interactions is limited. To further characterize the mitogenic activity of HSS, we compared its effects with FGF-1 in cells of hepatocyte, non-parenchymal liver epithelial and non-hepatic lineages. Our studies with these cell types demonstrated differences in the mitogenic specificities of HSS and FGF-1. Whereas exposure of primary hepatocytes to epidermal growth factor and HSS synergistically increased DNA synthesis, simultaneous exposure to HSS and FGF-1 resulted in no such effect. Receptor-binding assays showed that HSS did not compete with FGF-1 in binding to FGF-1 receptors on rat primary hepatocytes. Additional immunoblot analysis demonstrated no cross-reactivity between FGF-1 antibodies and HSS. Distinct mitogenic and immunologic properties of HSS and FGF-1 should facilitate further analysis of liver regeneration and hepatic oncogenesis.

A novel heparin-binding protein, HBp15, is identified as mammalian ribosomal protein L22

A 15kDa-protein (HBp15) was purified from mouse submandibular gland and bovine brain by virtue of its heparin-binding property. The amino acid sequences of mouse and bovine HBp15 showed a high degree of homology to a sea urchin protein encoded by gene called "development specific protein 217." Using reverse transcription-polymerase chain reaction methods, cDNA clones for HBp15 were isolated from submandibular gland mRNA of mouse, human and pig, and sequenced. Database search of HBp15 showed that HBp15 also resembles yeast ribosomal protein YL31 in addition to the 217 protein. Using specific antibodies against HBp15, HBp15 was identified as mammalian ribosomal protein L22, for which no sequence information is available.

Molecular cloning and expression of the gene for a major leucine-rich protein from human hepatoblastoma cells (HepG2)

The human hepatoblastoma cell line, HepG2, exhibits an array of stable properties in culture that have made it a popular cell culture model for studies on regulation of liver-specific gene expression and properties of hepatoma cells. In contrast to other hepatoma cell lines, HepG2 cells overexpress a characteristic detergent-extractable, wheat germ lectin-binding protein with apparent molecular mass of 130 kDa. Using an antibody to screen a phage expression library of HepG2 complementary DNA (cDNA), we identified and cloned a 4734 base pair cDNA which codes for a 130-kDa leucine-rich protein (lrp 130) when expressed in transfected cells. The deduced sequence of lrp130 exhibits sequences weakly homologous to the consensus sequence for the ATP binding site in ATP-dependent kinases and the protein kinase C phosphorylation site of the epidermal growth factor receptor. Consistent with the higher levels of expression of lrp130 antigen, Northern hybridization analysis indicated that HepG2 cells express high levels of the major 4.8 kilobase lrp130 mRNA relative to other hepatoma cells. Although currently of unknown function, lrp130 may be of utility as a marker for liver cell lineages represented by the HepG2 cell line.

Monoclonal antibodies against heparin-binding growth factor-1: neutralization of biological activity and recognition of specific amino acid sequence

A panel of three monoclonal antibodies against heparin-binding growth factor-1 (HBGF-1) was obtained. These antibodies, Ab-47 alpha, Ab-15, Ab-29, were able to recognize HBGF-1 but not HBGF-2. One of the antibodies, Ab-47 alpha, was identified as a HBGF-1 neutralizing antibody on the basis of its ability to inhibit the binding of [125I]HBGF-1 to receptors on HepG-2 cells and the proliferation of fetal bovine heart endothelial cells induced by HBGF-1. Ab-15 reacted with truncated HBGF-1(Mr = 16,000), intact HBGF-1(Mr = 18,000) and mutant HBGF-1U which lacks a putative nuclear translocation sequence (amino acid residues 21 to 27 of HBGF-1). Ab-29 reacted with only truncated HBGF-1 and was thought to recognize the putative nuclear translocation sequence of HBGF-1. The three monoclonal antibodies did not inhibit the binding of [125I]HBGF-1 to heparin. These data indicate that each monoclonal antibody recognizes a distinct epitope of HBGF-1 and identifies them as useful reagents for evaluating functional domains and biological roles of HBGF-1.

Exon switching and activation of stromal and embryonic fibroblast growth factor (FGF)-FGF receptor genes in prostate epithelial cells accompany stromal independence and malignancy

Stroma and the heparin-binding fibroblast growth factor (FGF) family influence normal epithelial cell growth and differentiation in embryonic and adult tissues. The role of stromal cells and the expression of isoforms of the FGF ligand and receptor family were examined during malignant progression of epithelial cells from a differentiated, slowly growing, nonmalignant model rat prostate tumor. In syngeneic hosts, a mixture of stromal and epithelial cells resulted in nonmalignant tumors which were differentiated and slowly growing. In the absence of the stromal cells, epithelial cells progressed to malignant tumors which were independent of the stroma and undifferentiated. The independence of the malignant epithelial cells from stromal cells was accompanied by a switch from exclusive expression of exon IIIb to exclusive expression of exon IIIc in the FGF receptor 2 (FGF-R2) gene. The FGF-R2(IIIb) isoform displays high affinity for stromal cell-derived FGF-7, whereas the FGF-R2(IIIc) isoform does not recognize FGF-7 but has high affinity for the FGF-2 member of the FGF ligand family. The switch from expression of exclusively exon IIIb to exclusively exon IIIc in the resident FGF-R2 gene was followed by activation of the FGF-2 ligand gene, the normally stromal cell FGF-R1 gene, and embryonic FGF-3 and FGF-5 ligand genes in malignant epithelial cells. Multiple autocrine and potentially intracrine ligand-receptor loops resulting from these alterations within the FGF-FGF-R family may underlie the autonomy of malignant tumor cells.

Exon skipping causes alteration of the COOH-terminus and deletion of the phospholipase C gamma 1 interaction site in the FGF receptor 2 kinase in normal prostate epithelial cells

Polymerase chain reaction analysis revealed an mRNA in rat prostate that results from alternate splicing of exon 16 in the heparin-binding fibroblast growth factor receptor kinase type 2 gene (FGFR2). The absence of exon 16 and the shift in reading frame at the exon 15-17 junction predicts an expression product (FGFR2-2) with a unique COOH-terminus that does not exhibit the major autophosphorylation site (tyrosine 789) required for interaction of phospholipase C gamma 1 with the full-length FGFR2-1 isoform. Nuclease protection analysis revealed that the FGFR-2 splice variant is expressed in quantities equal to or greater than the FGFR2-1 isoform in normal prostate tissue. When combined with the same FGFR2 extracellular domain, co-expression of the two COOH-terminal variants may mediate effect of the same FGF ligand on different signal transduction pathways.

Control of fibroblast growth factor receptor kinase signal transduction by heterodimerization of combinatorial splice variants

A differentiated liver cell (HepG2), which exhibits a dose-dependent growth-stimulatory and growth-inhibitory response to heparin-binding fibroblast growth factor type 1 (FGF-1), displays high- and low-affinity receptor phenotypes and expresses specific combinatorial splice variants alpha 1, beta 1, and alpha 2 of the FGF receptor (FGF-R) gene (flg). The extracellular domains of the alpha and beta variants consist of three and two immunoglobulin loops, respectively, while the intracellular variants consist of a tyrosine kinase (type 1) isoform and a kinase-defective (type 2) isoform. The type 2 isoform is also devoid of the two major intracellular tyrosine autophosphorylation sites (Tyr-653 and Tyr-766) in the type 1 kinase. An analysis of ligand affinity, dimerization, autophosphorylation, and interaction with src homology region 2 (SH2) substrates of the recombinant alpha 1, beta 1, and alpha 2 isoforms was carried out to determine whether dimerization of the combinatorial splice variants might explain the dose-dependent opposite mitogenic effects of FGF. Scatchard analysis indicated that the alpha and beta isoforms exhibit low and high affinity for ligand, respectively. The three combinatorial splice variants dimerized in all combinations. FGF enhanced dimerization and kinase activity, as assessed by receptor autophosphorylation. Phosphopeptide analysis revealed that phosphorylation of Tyr-653 was reduced relative to phosphorylation of Tyr-766 in the type 1 kinase component of heterodimers of the type 1 and type 2 isoforms. The SH2 domain substrate, phospholipase C gamma 1 (PLC gamma 1), associated with the phosphorylated type 1-type 2 heterodimers but was phosphorylated only in preparations containing the type 1 kinase homodimer. The results suggest that phosphorylation of Tyr-653 within the kinase catalytic domain, but not Tyr-766 in the COOH-terminal domain, may be stringently dependent on a trans intermolecular mechanism within FGF-R kinase homodimers. Although phosphotyrosine 766 is sufficient for interaction of PLC gamma 1 and other SH2 substrates with the FGF-R kinase, phosphorylation and presumably activation of substrates require the kinase homodimer and phosphorylation of Tyr-653. We propose that complexes of phosphotyrosine 766 kinase monomers and SH2 domain signal transducers may constitute unactivated presignal complexes whose active or inactive fate depends on homodimerization with a kinase or heterodimerization with a kinase-defective monomer, respectively. The results suggest a mechanism for control of signal transduction by different concentrations of ligand through heterodimerization of combinatorial splice variants from the same receptor gene.

A widely expressed transmembrane serine/threonine kinase that does not bind activin, inhibin, transforming growth factor beta, or bone morphogenic factor

Molecular cloning of complementary DNAs (cDNA) whose expression products bind activin and transforming growth factor beta (TGF-beta 1 and -beta 2) suggests that transmembrane serine/threonine kinases constitute a new class of signaling molecules. A human liver cell cDNA which codes for a new serine/threonine kinase receptor (SKR1) was identified using degenerate oligonucleotide primers complementary to coding sequence for mouse activin and Caenorhabditis elegans daf-1 serine/threonine receptor kinase subdomains VI and VIII in the polymerase chain reaction. The deduced 509-amino acid product consisted of a cysteine-rich extracellular domain and a cytoplasmic serine/threonine kinase domain which are 10-20 and 40% homologous to the respective domains in the activin and transforming growth factor beta receptor kinases. Cells overexpressing SKR1 exhibited no increase in binding of activin, inhibin, TGF-beta 1, TGF-beta 2, or bone morphogenic factor type 2B. Except for its absence in bone and spleen, SKR1 exhibits a tissue expression pattern similar to the TGF-beta receptor II gene. Similarly, SKR1 is expressed in normal parenchymal cells, endothelial cells, fibroblasts, and tumor-derived epithelial cells. The expression pattern and lack of binding to prototypic members of the TGF-beta 1-5 branch of the TGF-beta superfamily suggests that SKR1 is potentially a receptor for a new member of the TGF-beta branch of the ligand superfamily.

An essential heparin-binding domain in the fibroblast growth factor receptor kinase

Heparin or heparin-like heparan sulfate proteoglycans are obligatory for activity of the heparin-binding fibroblast growth factor (FGF) family. Heparin interacts independently of FGF ligand with a specific sequence (K18K) in one of the immunoglobulin-like loops in the extracellular domain of the FGF receptor tyrosine kinase transmembrane glycoprotein. A synthetic peptide corresponding to K18K inhibited heparin and heparin-dependent FGF binding to the receptor. K18K and an antibody to K18K were antagonists of FGF-stimulated cell growth. Point mutations of lysine residues in the K18K sequence abrogated both heparin- and ligand-binding activities of the receptor kinase. The results indicate that the FGF receptor is a ternary complex of heparan sulfate proteoglycan, tyrosine kinase transmembrane glycoprotein, and ligand.

Heparin-binding fibroblast growth factors and prostate cancer

Studies of model rat prostate tissue and derived cells indicate the insulin-like (IGF), epidermal growth factor (EGF), transforming growth factor beta (TGF-beta) and heparin-binding fibroblast growth factor (HBGF) families and their receptors may play important roles in regulation of normal prostate cell growth. Tumor cells at different levels in the progression from slow-growing, hormone-dependence to fast-growing, hormone-independence exhibit distinct alterations in expression of specific growth factors and their receptor phenotype. Distinct IGF-I and HBGF mRNAs are constitutively expressed in the mesenchymal cells of slow-tumors, but alteration in HBGF receptor phenotype occurs in the epithelial cells. Fast-tumors exhibit even higher constitutive expression of multiple HBGFs. Splice variants in cDNA for the HBGF receptor in fast-tumors suggest constitutive expression of an intracellular receptor, that together with intracellular HBGFs, may constitute an intracellular autocrine system that is independent of exogenous hormones and growth factors.

Identification of tyrosines 154 and 307 in the extracellular domain and 653 and 766 in the intracellular domain as phosphorylation sites in the heparin-binding fibroblast growth factor receptor tyrosine kinase (flg)

Four tyrosine residues have been identified as phosphorylation sites in the tyrosine kinase isoform of the heparin-binding fibroblast growth factor receptor flg (FGF-R1). Baculoviral-insect cell-derived recombinant FGF-R1 was phosphorylated and fragmented with trypsin while immobilized on heparin-agarose beads. Phosphotyrosine peptides were purified by chromatography on immobilized anti-phosphotyrosine antibody and analyzed by Edman degradation and electrospray tandem mass spectrometry. Tyrosine residue 653, which is in a homologous spatial position to major autophosphorylation sites in the catalytic domain of the src and insulin receptor kinases, is the major intracellular FGF-R1 phosphorylation site. Residue 766 in the COOH-terminus outside the kinase domain is a secondary site. Tyrosine residues 154 and 307, which are in the extracellular domain of transmembrane receptor isoforms and are in an unusual sequence context for tyrosine phosphorylation, were also phosphorylated.

Heparin-binding keratinocyte growth factor is a candidate stromal-to-epithelial-cell andromedin

The growth of isolated epithelial and stromal cells from both androgen-dependent normal rat prostate and an androgen-responsive model rat prostate tumor is androgen-independent. When added to co-cultures of epithelial and stromal cells separated by a semipermeable membrane, androgen stimulated epithelial cell growth without an effect on stromal cell growth. Northern blot and nuclease protection analysis of mRNA revealed that stromal cells specifically expressed an androgen-sensitive secreted member of the heparin-binding fibroblast growth factor family [keratinocyte growth factor (KGF)/fibroblast growth factor-7]. KGF was mitogenic for epithelial cells, but not for stromal cells. Epithelial cells expressed specifically a splice variant of the bek receptor gene that specifically binds KGF. Expression of the bek receptor gene in stromal cells was undetectable by Northern blot and nuclease protection analyses. The results suggest that stromal cell-derived KGF has the properties of an andromedin, which mediates the indirect control of epithelial cell proliferation by androgen through a directional stromal-to-epithelial cell paracrine mechanism.

Expression and immunochemical analysis of rat and human fibroblast growth factor receptor (flg) isoforms

Potentially 96 splice variants among four genes that code for the human heparin-binding fibroblast growth factor receptor family complicate study of structure, metabolism, and function of single isoforms in mammalian cells. As an alternative, we expressed structural subdomains and isoforms of the flg receptor gene in bacteria and baculoviral-infected insect cells. We developed and characterized a panel of 16 isoform and domain-specific polyclonal and monoclonal antibodies. The panel of antibodies was used to distinguish mature glycosylated ligand-binding and kinase-active and -inactive recombinant isoforms in baculoviral insect cells and transfected mammalian cells and natural isoforms in rat prostate and human liver cells. The results revealed a cell type-specific expression of the flg gene and isoforms that result from combinations of splice variations. Reactive epitopes of monoclonal antibodies against both the three (alpha) and two (beta) immunoglobulin-like disulfide loop extracellular domain isoforms were mapped by cross-reactivity with synthetic polypeptide sequences and deletion mutants expressed in bacteria. The native alpha and beta receptor isoforms differed in display of shared epitopes and suggested that the NH2-terminal Loop I and COOH-terminal Loops II and III of the alpha isoform are interactive. Although the common Loops II and III appear qualitatively sufficient for ligand binding, the results suggest that tertiary relationships among loops in the three and two loop isoforms are distinct and, therefore, the two isoforms may have distinct activities. Spatial models for arrangement of immunoglobulin-like loops in the extracellular domain of the two isoforms are presented.

Substitution of putative half-cystine residues in heparin-binding fibroblast growth factor receptors. Loss of binding activity in both two and three loop isoforms

Alternate use of an exon coding for an 89-residue NH2 terminal immunoglobulin-like disulfide loop results in isoforms of the heparin-binding fibroblast growth factor receptor (FGF-R) with three (FGF-R alpha) and two (FGF-R beta) Ig-like loops in the extracellular domain. Both FGF-R alpha and FGF-R beta isoforms exhibit qualitatively similar ligand-binding activities. In this report, we show by site-directed mutagenesis and analysis of ligand-binding activity in transfected cells that substitution of a cysteine that potentially forms an intra-loop disulfide in either juxtamembrane Loop II or III disrupted maturation and formation of the ligand-binding site in both FGF-R alpha and FGF-R beta isoforms. Neither three loop FGF-R alpha constructions coding for intact Loops I and II adjacent to defective Loop III nor intact Loops I and III separated by defective Loop II exhibited ligand-binding activity. In addition, a two-loop molecule of tandem Loops I and III was inactive. The results suggest that single Loops I, II, or III of FGF-R are insufficient to form a ligand-binding site. Loop I does not form an independent ligand-binding site with either Loop II or III, but interacts with a common ligand-binding site formed by Loops II and III (Xu, J., Nakahara, M., Crabb, J. W., Shi, E., Matuo, Y., Fraser, M., Kan, M., Hou, J., and McKeehan, W. L. (1992) J. Biol. Chem. 267, 17792-17803, 1992).

Expression and transforming activity of a variant of the heparin-binding fibroblast growth factor receptor (flg) gene resulting from splicing of the alpha exon at an alternate 3'-acceptor site

Splicing at an alternate 3'-acceptor site results in deletion of a CCCAG in the 5'-sequence of the exon coding for the NH2-terminal immunoglobulin-like disulfide loop of the heparin-binding fibroblast growth factor receptor (flg) alpha isoform. The result is an in-frame stop codon 138 base pairs after the first flg consensus translational initiation site. The next more favorable site predicts the same two loop intracellular receptor isoform, gamma, which was predicted from two different human cDNAs that arise by alternate use of two exons at the same site. Although expressed in normal tissue, the gamma mRNA is increased in rat prostate tumors and confers ability of anchorage-dependent cells expressing non-secreted heparin-binding fibroblast growth factors to grow in soft agar.

Potential role of HBGF (FGF) and TGF-beta on prostate growth

We review in this paper the role of heparin-binding growth factor (HBGF*) or fibroblast growth factor (FGF*), rat prostate cancer cells produce TGF-beta, IGF-II* and OGF*. Of these growth factors, TGF-beta and unknown labile factor with 19 kDa are the most probable candidates responsible for osteoblastic bony metastasis of prostate cancer. In vitro experiments suggest that TGF-beta modulates cell detachment of prostate cancer cells together with nutritional factors. HBGF-dependent growth of the prostate tumor epithelial cells is free from inhibition by TGF-beta, whereas normal prostate epithelial cells are sensitive to TGF-beta inhibition. Transfection experiments suggest that HBGF-2 (basic FGF) might be closely related to the malignant growth of prostate cancer, in addition to tumor angiogenesis.

When is intervention warranted?

A chemoprevention trial in prostate cancer would be a formidable but potentially rewarding study. The current status of knowledge of drug interactions with, biomarkers of, and even the natural history of prostate cancer is insufficient to study all levels of men at risk. Currently, the most promising group to study is group I--those men with a high probability of developing prostate cancer but who do not currently have evidence of the disease. This could be a placebo-controlled, prospective and randomized study with the endpoint being clinically-detected prostate cancer. In addition, much may be gained from short-term pilot studies of "chemo-active" agents on morphologic and other biomarkers of prostate cancer initiated immediately before surgical removal. It is hoped that such studies may provide rationale for future efforts directed at preventing progression of premalignant or early prostate cancer lesions.

16-kilodalton heparin binding (fibroblast) growth factor type one appears in a stable 40-kilodalton complex after receptor-dependent internalization

Incubation of 16-kDa 125I-labeled heparin binding (acidic fibroblast) growth factor type one (HBGF-1) with human hepatoma cells and normal rat hepatocytes resulted in the appearance of a stable 125I-labeled complex with an apparent molecular mass of 40 kDa. The complex could be isolated with specific antibodies against HBGF-1. In contrast to membrane receptor-bound 125I-HBGF-1, the complex was resistant to dissociation by detergents, acid, heat, and reducing or denaturing agents. Formation of a stable complex did not require treatment with cross-linking agents. Appearance of the 40-kDa complex was dependent on time, temperature, and enriched culture medium. Conditions that enhanced or reduced display of specific HBGF-1 membrane receptor sites enhanced or reduced the appearance of the 40-kDa complex. Dansylcadaverine, chloroquine, and staurosporine blocked the appearance of the 40-kDa complex concurrent with the blockage of internalization of the receptor-bound HBGF-1. Two-dimensional gel electrophoretic analysis, metabolic labeling with L-[35S]cysteine, and recovery of 16-kDa HBGF-1 from the 40-kDa complex after base treatment suggest involvement of a 24-kDa cellular protein in the complex formation. These results suggest a potentially novel receptor-dependent pathway for metabolism of HBGF-1.

Fibroblast growth factor receptors from liver vary in three structural domains

Changes in heparin-binding fibroblast growth factor gene expression and receptor phenotype occur during liver regeneration and in hepatoma cells. The nucleotide sequence of complementary DNA predicts that three amino-terminal domain motifs, two juxtamembrane motifs, and two intracellular carboxyl-terminal domain motifs combine to form a minimum of 6 and potentially 12 homologous polypeptides that constitute the growth factor receptor family in a single human liver cell population. Amino-terminal variants consisted of two transmembrane molecules that contained three and two immunoglobulin-like disulfide loops, as well as a potential intracellular form of the receptor. The two intracellular juxtamembrane motifs differed in a potential serine-threonine kinase phosphorylation site. One carboxyl-terminal motif was a putative tyrosine kinase that contained potential tyrosine phosphorylation sites. The second carboxyl-terminal motif was probably not a tyrosine kinase and did not exhibit the same candidate carboxyl-terminal tyrosine phosphorylation sites.

Hepatocyte growth factor/hepatopoietin A stimulates the growth of rat kidney proximal tubule epithelial cells (RPTE), rat nonparenchymal liver cells, human melanoma cells, mouse keratinocytes and stimulates anchorage-independent growth of SV-40 transformed RPTE

Hepatocyte growth factor/hepatopoietin A is a mitogen for primary hepatocytes and may mediate regeneration after liver damage. To date, the activity of this novel factor has been restricted to hepatocytes. We now show that the factor is also a mitogen for a number of primary epithelial cells but is inactive with human foreskin fibroblasts, human endothelial cells and HEP3B cells. The factor also substitutes for HBGF-2 (basic FGF) in stimulating the anchorage-independent growth of SV-40 transformed rat kidney epithelial cells. Therefore, hepatocyte growth factor/hepatopoietin A appears to act on a variety of epithelial, but not mesenchymal, cells which respond to HBGFs.

Stimulation of human arterial smooth muscle cell chondroitin sulfate proteoglycan synthesis by transforming growth factor-beta

Human platelet-derived transforming growth factor-beta (TGF-beta) is a cell-type specific promotor of proteoglycan synthesis in human adult arterial cells. Cultured human adult arterial smooth muscle cells synthesized chondroitin sulfate, dermatan sulfate, and heparan sulfate proteoglycans, and the percent composition of these three proteoglycan subclasses varied to some extent from cell strain to cell strain. However, TGF-beta consistently stimulated the synthesis of chondroitin sulfate proteoglycan. Both chondroitin 4- and chondroitin 6-sulfate were stimulated by TGF-beta to the same extent. TGF-beta had no stimulatory effect on either class of [35S]sulfate-labeled proteoglycans which appeared in an approximately 1:1 and 2:1 ratio of heparan sulfate to dermatan sulfate of the medium and cell layers, respectively, of arterial endothelial cells. Human adult arterial endothelial cells synthesized little or no chondroitin sulfate proteoglycan. Pulsechase labeling revealed that the appearance of smooth muscle cell proteoglycans into the medium over a 36-h period equaled the disappearance of labeled proteoglycans from the cell layer, independent of TGF-beta. Inhibitors of RNA synthesis blocked TGF-beta-stimulated proteoglycan synthesis in the smooth muscle cells. The incorporation of [35S]methionine into chondroitin sulfate proteoglycan core proteins was stimulated by TGF-beta. Taken together, the results presented indicate that TGF-beta stimulates chondroitin sulfate proteoglycan synthesis in human adult arterial smooth muscle cells by promoting the core protein synthesis.