Identification of a 79-kDa heparin-binding fibroblast growth factor (FGF) receptor in rat hepatocytes and its correlation with the different growth responses to FGF-1 between hepatocyte subpopulations.
We reported previously that the potency of heparin-binding fibroblast growth factor-1 (FGF-1) as a mitogen for rat hepatocytes in primary culture is as high as that of epidermal growth factor (EGF) and hepatocyte growth factor. To gain insight into the pathophysiological significance of FGF-1 in hepatocyte growth, we analyzed the cooperative mitogenicity of FGF-1 and EGF. Results from a nuclear labeling assay using [3H]thymidine suggest that most hepatocytes in primary culture consist of two cell populations that differ in response to FGF-1; one is an FGF-1-responsive cell population, and the other is an EGF-responsive (but not FGF-1-responsive) cell population. On the other hand, autoradiographic analysis of 125I-FGF-1 binding demonstrated that high affinity FGF receptors were homogeneously distributed on the surface of all hepatocytes. Cross-linking 125I-FGF-1 to the nonstimulated hepatocyte surface indicated that the high affinity FGF receptors comprise two FGF receptors that differ in molecular mass (128 and 79 kDa). Furthermore, the 79-kDa receptor was preferentially down-regulated when the hepatocytes were stimulated with EGF or hepatocyte growth factor. These data suggest that the abundant expression of the 79-kDa FGF receptor on some populations of hepatocytes is involved in their lack of response to FGF-1. The 128- and 79-kDa FGF receptors were assigned as FGFR2 using an antibody specific to the ectodomain of FGFR2, whereas the 79-kDa receptor was not reactive to the antibody against the carboxyl terminus of FGFR2. This 79-kDa FGF receptor was not tyrosine-phosphorylated in response to FGF-1 stimulation, while the 128-kDa FGF receptor was recognized by anti-phosphotyrosine antibody under the same conditions. Also, the heterodimer of 79- and 128-kDa FGF receptors was less tyrosine-phosphorylated than the homodimer of 128-kDa FGF receptors. These data suggest that the 79-kDa FGF receptor inhibits the function of the 128-kDa FGF receptor through their heterodimerization. Thus, we surmise that the difference in response to FGF-1 between the cell populations of normal rat hepatocytes was caused by the different levels of the 79-kDa FGF receptor in each cell population.
Tanahashi
T
T
Cell Biology Laboratory and the Laboratory of the Chief Senior Researcher, National Institute of Bioscience and Human Technology, 1-1 Higashi, Tsukuba, Ibaraki 305, Japan.
Suzuki
M
M
Imamura
T
T
Mitsui
Y
Y
D000818:Animals; D002455:Cell Division; D002478:Cells, Cultured; D003432:Cross-Linking Reagents; D004357:Drug Synergism; D004815:Epidermal Growth Factor / Q000008:administration & dosage; D016220:Fibroblast Growth Factor 1 / Q000494:pharmacology*; D006493:Heparin / Q000378:metabolism; D017228:Hepatocyte Growth Factor / Q000008:administration & dosage; D008099:Liver / Q000166:cytology* / Q000378:metabolism; D008970:Molecular Weight; D011233:Precipitin Tests; D051381:Rats; D017468:Receptors, Fibroblast Growth Factor / Q000737:chemistry / Q000378:metabolism*
D003432:Cross-Linking Reagents; D017468:Receptors, Fibroblast Growth Factor; D016220:Fibroblast Growth Factor 1; D004815:Epidermal Growth Factor; D017228:Hepatocyte Growth Factor; D006493:Heparin