Gastrin stimulates tyrosine phosphorylation of insulin receptor substrate 1 and its association with Grb2 and the phosphatidylinositol 3-kinase.
The growth-promoting effects of gastrin on normal and neoplastic gastrointestinal tissues have been shown to be mediated by the gastrin/CCKB receptor, which belongs to the family of G protein-coupled receptors. However, the downstream signaling pathways activated by gastrin are not well characterized. In the present study, we demonstrate that gastrin stimulates tyrosine phosphorylation of insulin receptor substrate 1 (IRS-1), the major cytoplasmic substrate of the insulin receptor. The gastrin-induced phosphorylation of IRS-1 was rapid and transient, occurring within 30 s of treatment and diminishing thereafter. IRS-1 binds several proteins containing Src homology 2 domains through its multiple tyrosine phosphorylation sites. Following gastrin stimulation, we observed a time- and dose-dependent association of IRS-1 with the p85 regulatory subunit of phosphatidylinositol 3-kinase (PI 3-kinase). In addition, activation of PI 3-kinase was detected in anti-IRS-1 immunoprecipitates from gastrin-treated cells, suggesting that tyrosine phosphorylation of IRS-1, which leads to the rapid recruitment of p85, might be one mechanism used by gastrin to activate PI 3-kinase. We have previously reported that tyrosine phosphorylation of Shc and its association with the Grb2-Sos complex may contribute to the activation of the mitogen-activated protein kinase pathway by gastrin. We report here that Grb2 also interacts with tyrosine-phosphorylated IRS-1 in response to gastrin. Taken together, our results suggest that IRS-1 may serve as a converging target in the signaling pathways stimulated by receptors that belong to different families, such as the gastrin/CCKB G protein-coupled receptor and the insulin receptor.
Kowalski-Chauvel
A
A
INSERM U.151, Groupe de Recherche de Biologie et Pathologie digestive, Institut Louis Bugnard, CHU Rangueil, 31054 Toulouse, France.
Pradayrol
L
L
Vaysse
N
N
Seva
C
C
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D004789:Enzyme Activation; D066246:ErbB Receptors / Q000378:metabolism*; D051380:GRB2 Adaptor Protein; D005755:Gastrins / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D010179:Pancreas / Q000187:drug effects / Q000201:enzymology; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; D051380:GRB2 Adaptor Protein; D005755:Gastrins; C495950:Grb2 protein, rat; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526296:Irs1 protein, rat; D010750:Phosphoproteins; D011506:Proteins; D014443:Tyrosine; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D066246:ErbB Receptors