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Novel recruitment of Shc, Grb2, and Sos by fibroblast growth factor receptor-1 in v-Src-transformed cells
M Curto1, P Frankel, A Carrero
1Department of Biological Sciences, Hunter College of the City University of New York, New York 10021, USA.
Abstract:
In response to fibroblast growth factor (FGF), FGF receptor-1 (FGFR-1) (flg) becomes tyrosine phosphorylated and associates with phospholipase C gamma (PLC gamma) and a 90 kDa protein. We report here that in cells transformed by v-Src, FGFR-1 becomes phosphorylated on tyrosine; however, neither PLC gamma nor p90 was found to be associated with tyrosine-phosphorylated FGFR-1. Instead, there was a strong constitutive association of FGFR-1 with the adaptor proteins Shc and Grb2 and the Ras guanine nucleotide exchange factor Sos. Association with Shc and Grb2 and Sos was not observed in response to FGF. Suramin did not prevent either tyrosine phosphorylation or Shc/Grb2/Sos association, indicating a non-autocrine mechanism. Thus, in cells transformed by v-Src, tyrosine phosphorylation of FGFR-1 results not in the expected association with PLC gamma and p90, but rather in the recruitment of the Ras activating Shc/Grb2/Sos complex. These data suggest a mechanism for Ras activation by v-Src involving phosphorylation of novel tyrosine(s) on FGFR-1.
Insights
Fibroblast growth factor receptor-1 (FGFR-1) phosphorylation by v-Src recruits Ras-activating proteins, not PLC gamma. This suggests v-Src activates Ras via novel FGFR-1 tyrosine phosphorylation.
Area of Science:
- Cellular signaling pathways
- Receptor tyrosine kinases
- Oncogene signaling
Background:
- Fibroblast growth factor receptor-1 (FGFR-1) normally associates with phospholipase C gamma (PLC gamma) upon tyrosine phosphorylation induced by fibroblast growth factor (FGF).
- The viral Src (v-Src) oncoprotein is known to induce tyrosine phosphorylation of various cellular proteins, including FGFR-1.
Purpose of the Study:
- To investigate the downstream signaling events following v-Src-induced tyrosine phosphorylation of FGFR-1.
- To determine if v-Src-transformed cells utilize the same FGFR-1 signaling pathway as FGF-stimulated cells.
Main Methods:
- Western blotting to detect tyrosine phosphorylation of FGFR-1.
- Co-immunoprecipitation assays to identify proteins associated with tyrosine-phosphorylated FGFR-1 in v-Src-transformed cells and FGF-stimulated cells.
- Treatment with suramin to investigate the mechanism of association.
Main Results:
- In v-Src-transformed cells, FGFR-1 undergoes tyrosine phosphorylation but does not associate with PLC gamma or p90.
- Instead, tyrosine-phosphorylated FGFR-1 constitutively associates with Shc, Grb2, and Sos, key components of the Ras signaling pathway.
- This Shc/Grb2/Sos complex association is not observed in response to FGF and is not inhibited by suramin, suggesting a non-autocrine mechanism.
Conclusions:
- v-Src transforms FGFR-1 signaling by recruiting the Ras-activating Shc/Grb2/Sos complex, distinct from the canonical FGF-induced PLC gamma pathway.
- These findings propose a novel mechanism for Ras activation by v-Src through the phosphorylation of previously unidentified tyrosine residues on FGFR-1.