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  • Title: Differential response of the Ras exchange factor, Ras-GRF to tyrosine kinase and G protein mediated signals.
    Author: Shou C, Wurmser A, Suen KL, Barbacid M, Feig LA, Ling K.
    Journal: Oncogene; 1995 May 18; 10(10):1887-93. PubMed ID: 7761090.
    Abstract:
    Ras-GRF, a guanine-nucleotide exchange factor that activates Ras p21, was tested for its ability to couple to either tyrosine kinase or heterotrimeric G protein signal transduction pathways. Ras-GRF failed to bind the SH2 and SH3 containing adaptor protein Grb2, either in vitro or in vivo. Furthermore, Ras-GRF did not form a stable complex with activated EGF receptor. However, as has been shown previously (Cen et al., 1994), the presence of Ras-GRF in NIH3T3 cells enhanced the activation of Ras induced by serum stimulation. A similar effect was not observed with PDGF stimulation. Moreover, serum stimulation lead to the hyperphosphorylation of Ras-GRF. Both the serum induced super-activation of Ras, and the hyperphosphorylation of Ras-GRF were blocked by pretreatment of cells with the Gi,o inhibitor pertussis toxin, but not by pretreatment with the tyrosine kinase inhibitor genistein. These results suggest that Ras-GRF has the capacity to mediate Ras activation initiated by signals using heterotrimeric G proteins.
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