Agonist-induced association of the p21ras GTPase-activating protein with phosphatidylinositol 3-kinase.
The signal transduction properties of the 21-kDa GTP-binding proteins, encoded by the ras genes, are only partly known. In a recent report, we demonstrated that the signaling pathway of p21ras, like that of several growth factors, is closely associated with phosphatidylinositol 3-kinase (PtdIns 3-kinase) activity. We showed that insulin-like growth factor-1 (IGF-1) and insulin increased the phosphatidylinositol 3-kinase activity in immunoprecipitates obtained with anti-phosphotyrosine and anti-ras antibodies in Ha-ras-transformed epithelial cells. Several findings in this previous study suggested that an additional protein was likely to be associated with the PtdIns 3-kinase. The suggestion that p21ras GTPase-activating protein (GAP) acts not only as a regulator of p21ras activity but also as a direct downstream target in the signaling pathway of p21ras led us to investigate the possible association of PtdIns 3-kinase with GAP. The stimulation of Ha-ras-transformed epithelial cells with IGF-1 caused an increased association of PtdIns 3-kinase activity with GAP, as seen by immunoprecipitation with anti-p21ras and anti-GAP antibodies. The 85-kDa regulatory subunit of PtdIns 3-kinase was present in immunoprecipitates obtained with antibodies against GAP and p21ras of IGF-1 stimulated cells. These data suggest that GAP acts as a downstream target for p21ras via its association with PtdIns 3-kinase.
Sjölander
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A
Department of Cell Biology, Faculty of Health Sciences, University Hospital, Linköping, Sweden.
Lapetina
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EG
D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D004848:Epithelium; D020690:GTPase-Activating Proteins; D011905:Genes, ras; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007700:Kinetics; D008099:Liver; D019869:Phosphatidylinositol 3-Kinases; D010770:Phosphotransferases / Q000302:isolation & purification / Q000378:metabolism*; D011485:Protein Binding; D011506:Proteins / Q000302:isolation & purification / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344; D020703:ras GTPase-Activating Proteins
D020690:GTPase-Activating Proteins; D011506:Proteins; D020703:ras GTPase-Activating Proteins; D007334:Insulin-Like Growth Factor I; D010770:Phosphotransferases; D019869:Phosphatidylinositol 3-Kinases