Differential response of the Ras exchange factor, Ras-GRF to tyrosine kinase and G protein mediated signals.
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.
Shou
C
C
Department of Biochemistry, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.
Wurmser
A
A
Suen
K L
KL
Barbacid
M
M
Feig
L A
LA
Ling
K
K
D016475:3T3 Cells; D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D018797:Cell Cycle Proteins / Q000378:metabolism; D066246:ErbB Receptors / Q000378:metabolism*; D051380:GRB2 Adaptor Protein; D019204:GTP-Binding Proteins / Q000378:metabolism*; D020690:GTPase-Activating Proteins; D020662:Guanine Nucleotide Exchange Factors; D051379:Mice; D037342:Pertussis Toxin; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D011506:Proteins / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D020703:ras GTPase-Activating Proteins; D020663:ras Guanine Nucleotide Exchange Factors; D020666:ras-GRF1
D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; D051380:GRB2 Adaptor Protein; D020690:GTPase-Activating Proteins; C495949:Grb2 protein, mouse; D020662:Guanine Nucleotide Exchange Factors; D011506:Proteins; D010566:Virulence Factors, Bordetella; D020703:ras GTPase-Activating Proteins; D020663:ras Guanine Nucleotide Exchange Factors; D020666:ras-GRF1; D037342:Pertussis Toxin; D066246:ErbB Receptors; D010749:Phosphoprotein Phosphatases; D019204:GTP-Binding Proteins