Shc associates with an unphosphorylated form of the p21ras guanine nucleotide exchange factor mSOS.
Association of the p21ras guanine nucleotide exchange factor mSOS with tyrosine-phosphorylated Shc has been implicated in the activation of p21ras. In addition, after growth factor stimulation mSOS becomes phosphorylated as indicated by the appearance of a form of mSOS with reduced electrophoretic mobility. This phosphorylation is delayed with respect to Shc-Grb2-mSOS complex formation and activation of p21ras. To investigate the role of mSOS phosphorylation in further detail we have investigated the effect of phosphorylation on mSOS complex formation and p21ras activation. We found that Shc is associated with the unphosphorylated, faster migrating form of mSOS. Furthermore, although there is a correlation between the amount of complexes formed and the activation of p21ras, there is no such a correlation between mSOS phosphorylation and p21ras activation. In addition, inhibition of mSOS phosphorylation did not affect complex formation of mSOS with tyrosine phosphorylated Shc. Also, induction of mSOS phosphorylation prior to complex formation did not affect EGF-induced association of mSOS with Shc significantly, and Shc still associated predominantly with the faster migrating form of mSOS. From these results we conclude that the unphosphorylated form of mSOS is associated with Shc and that perhaps a phosphorylation-dephosphorylation step is part of the mSOS activation-inactivation cycle.
de Vries-Smits
A M
AM
Laboratory for Physiological Chemistry, Utrecht University, The Netherlands.
Pronk
G J
GJ
Medema
J P
JP
Burgering
B M
BM
Bos
J L
JL
D016475:3T3 Cells; D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D066246:ErbB Receptors / Q000378:metabolism; D051380:GRB2 Adaptor Protein; D020662:Guanine Nucleotide Exchange Factors; D051379:Mice; D010766:Phosphorylation; D011506:Proteins / Q000378:metabolism*; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism; D020663:ras Guanine Nucleotide Exchange Factors
D048868:Adaptor Proteins, Signal Transducing; D051380:GRB2 Adaptor Protein; C495949:Grb2 protein, mouse; D020662:Guanine Nucleotide Exchange Factors; D011506:Proteins; D020663:ras Guanine Nucleotide Exchange Factors; D014443:Tyrosine; D066246:ErbB Receptors; D016283:Proto-Oncogene Proteins p21(ras)