Signal Transduction Pathway of Human Fibroblast Growth Factor Receptor 3

doi:10.1074/jbc.272.10.6621

Signal Transduction Pathway of Human Fibroblast Growth Factor Receptor 3

IDENTIFICATION OF A NOVEL 66-kDa PHOSPHOPROTEIN*

From the Gastrointestinal Unit and Center for the Study of Inflammatory Bowel Disease, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114

^‡ To whom correspondence should be addressed:
Gastrointestinal Unit, Massachusetts General Hospital, Fruit St., Boston, MA 02114.
Fax: 617-724-2136; E-mail: podolsky.daniel{at}mgh.harvard.edu

Abstract

Stimulation of fibroblast growth factor receptor 3 (FGFR3) results in a variety of functional effects, including regulation of epithelial cell growth and differentiation. In order to characterize the signaling pathway through which FGFR3 regulates cell growth, L6 cells lacking any endogenous FGFR were stably transfected with the two different human isoforms, FGFR3 IIIb and FGFR3 IIIc, that result from alternative splicing of exon III of the FGFR3 gene encoding the ligand binding domain. Expression of FGFR3 IIIc in stably transfected L6 cells conferred growth responses to several members of the FGF family including FGF-1, −2, −4, and −6, while FGFR3 IIIb-expressing cells responded only to FGF-1. Activation of FGFR3 upon ligand binding resulted in activation of mitogen-activated protein kinase pathway. FGFR3 utilizes two different pools of adapter protein GRB2 to link to Ras. Activated FGFR3 predominantly interacts with GRB2·Sos in complex with a previously identified 90-kDa protein and designated protein 80K-H. In addition, 80K-H·GRB2·Sos complex was found to contain a novel 66-kDa protein. Tyrosine phophorylation of the 66-kDa protein was dependent on ligand activation of FGFR3, suggesting that the 66-kDa protein may play an important role in FGFR3-specific signaling. In addition to this unique pathway, FGFR3 also links to GRB2·Sos complex via the adapter protein Shc. Furthermore, activated FGFR3 was not able to induce dissociation of GRB2·Sos complex following Sos phosphorylation. In summary, FGFR3 signaling pathway utilizes two GRB2-containing complexes; Shc·GRB2·Sos and 80K-H·pp66·GRB2·Sos; these two complexes may alternatively link FGFG3 to mitogen-activated protein kinase. Finally, activated FGFR3 was also found to result in phosphorylation of phospholipase C-γ but reduced phosphorylation of c-Src.

Footnotes

↵* This work was supported by grants from the Donaldson Trust and by National Institutes of Health Grants DK41557 and DK43351. The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

FGF

fibroblast growth factor

FGFR

fibroblast growth factor receptor

ERK

extracellular-signal regulated kinase

GST

glutathione S-transferase

GRB2

growth factor receptor-bound protein

MAP

mitogen-activated protein

MBP

myelin basic protein

MEK

MAP kinase kinase

PAGE

polyacrylamide gel electrophoresis

PLC-γ

phospholipase C-γ

PVDF

polyvinylidene difluoride

SH2

Src homology 2

Shc

Src homologous and collagen

Sos

Son of Sevenless

TBS

Tris-buffered saline.
- Received November 15, 1996.