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G i ‐mediated activation of the Ras/MAP kinase pathway involves a 100 kDa tyrosine‐phosphorylated Grb2 SH3 binding protein, but not Src nor Shc
Author(s) -
Kranenburg Onno,
Verlaan Ingrid,
Hordijk Peter L.,
Moolenaar Wouter H.
Publication year - 1997
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/16.11.3097
Subject(s) - proto oncogene tyrosine protein kinase src , biology , sh3 domain , map kinase kinase kinase , grb2 , mitogen activated protein kinase kinase , tyrosine phosphorylation , receptor tyrosine kinase , tyrosine kinase , map2k7 , mapk14 , microbiology and biotechnology , cyclin dependent kinase 9 , ask1 , mapk7 , sh2 domain , cyclin dependent kinase 2 , phosphorylation , signal transduction , protein kinase a
Mitogenic G protein‐coupled receptors, such as those for lysophosphatidic acid (LPA) and thrombin, activate the Ras/MAP kinase pathway via pertussis toxin (PTX)‐sensitive G i , tyrosine kinase activity and recruitment of Grb2, which targets guanine nucleotide exchange activity to Ras. Little is known about the tyrosine phosphorylations involved, although Src activation and Shc phosphorylation are thought to be critical. We find that agonist‐induced Src activation in Rat‐1 cells is not mediated by G i and shows no correlation with Ras/MAP kinase activation. Furthermore, LPA‐induced tyrosine phosphorylation of Shc is PTX‐insensitive and Ca 2+ ‐dependent in COS cells, but undetectable in Rat‐1 cells. Expression of dominant‐negative Src or Shc does not affect MAP kinase activation by LPA. Thus, G i ‐mediated Ras/MAP kinase activation in fibroblasts and COS cells involves neither Src nor Shc. Instead, we detect a 100 kDa tyrosine‐phosphorylated protein (p100) that binds to the C‐terminal SH3 domain of Grb2 in a strictly G i ‐ and agonist‐dependent manner. Tyrosine kinase inhibitors and wortmannin, a phosphatidylinositol (PI) 3‐kinase inhibitor, prevent p100–Grb2 complex formation and MAP kinase activation by LPA. Our results suggest that the p100–Grb2 complex, together with an upstream non‐Src tyrosine kinase and PI 3‐kinase, couples G i to Ras/MAP kinase activation, while Src and Shc act in a different pathway.