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 (*)
- From the (1)Cell Biology Laboratory and the
- (2)Laboratory of the Chief Senior Researcher, National Institute of Bioscience and Human Technology, 1-1 Higashi, Tsukuba, Ibaraki 305, Japan and the
- (3)Research and Development Department, TABAI ESPEC Corp., 3-5-6, Tenjinbashi, Kita-ku, Osaka 530, Japan
- § To whom correspondence should be addressed. Tel.: 81-298-54-6072; Fax: 81-298-54-6095.
Abstract
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 
I-FGF-1 binding demonstrated that high affinity FGF receptors were homogeneously distributed on the surface of all hepatocytes.
Cross-linking 
I-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.
Footnotes
-
↵* This work was supported by a grant for research and development projects for the elucidation of biological function (Agency of Industrial Science and Technology). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
-
↵1 The abbreviations used are:
- TGF-α
-
transforming growth factor-α
- EGF
-
epidermal growth factor
- HGF
-
hepatocyte growth factor
- FGF
-
heparin-binding fibroblast growth factor
- FGFR
-
FGF receptor
- FBS
-
fetal bovine serum
- PBS
-
phosphate-buffered saline
- PAGE
-
polyacrylamide gel electrophoresis
- RIPA
-
radioimmune precipitation assay
- KGF
-
keratinocyte growth factor.
-
↵2T. Tanahashi, M. Suzuki, T. Imamura, and Y. Mitsui, unpublished data.
-
↵3M. Suzuki, unpublished data.
-
- Received May 15, 1995.
- Revision received January 2, 1996.
- © 1996 by The American Society for Biochemistry and Molecular Biology, Inc.
