TY - JOUR
T1 - 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
AU - Kranenburg, Onno
AU - Verlaan, Ingrid
AU - Hordijk, Peter L.
AU - Moolenaar, Wouter H.
PY - 1997/6/2
Y1 - 1997/6/2
N2 - 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 Ca2+-dependent in COS cells, but undetectable in Rat-1 cells. Expression of dominant-negative Src or She 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.
AB - 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 Ca2+-dependent in COS cells, but undetectable in Rat-1 cells. Expression of dominant-negative Src or She 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.
KW - G protein-coupled receptors
KW - Grb2
KW - MAP kinase
KW - Shc
KW - Src
UR - http://www.scopus.com/inward/record.url?scp=0030924612&partnerID=8YFLogxK
U2 - https://doi.org/10.1093/emboj/16.11.3097
DO - https://doi.org/10.1093/emboj/16.11.3097
M3 - Article
C2 - 9214627
SN - 0261-4189
VL - 16
SP - 3097
EP - 3105
JO - EMBO Journal
JF - EMBO Journal
IS - 11
ER -