Insulin and insulin-like growth factor-I signal transduction requires p21ras.
We have investigated the role of cellular p21ras protein in insulin and insulin-like growth factor-I (IGF-I) signaling pathways. Insulin stimulation increased Ras-GTP formation in Rat-1 fibroblasts overexpressing normal human insulin receptors (HIRc-B), far greater than in parental Rat-1 fibroblasts, indicating that competent insulin receptors mediate this response. Cellular microinjection of a dominant-negative mutant p21ras protein (N17 ras) or anti-p21ras monoclonal antibody (Y13-259) into HIRc-B cells reduced insulin- and IGF-I-stimulated DNA synthesis by 75-90%. Insulin-induced c-fos protein expression was also inhibited by 74%. Microinjection of oncogenic p21ras (T-24 ras) into HIRc-B cells activated the mitogenic pathway, and coinjection of N17 ras and T-24 ras showed that oncogenic p21ras rescued the cells from the N17 ras blockade. This later finding indicates that T-24 ras acts downstream of N17 ras. In conclusion, 1) microinjection of a dominant interferring ras mutant into quiescent cells abrogated subsequent insulin and IGF-I mitogenic signaling; 2) oncogenic ras protein rescued cells from the N17 ras blockade, indicating that T24 ras action is downstream of the site of N17 inhibition; and 3) p21ras is an intermediate signaling molecule in the insulin/IGF-I signal transduction pathway and is required for gene expression and DNA synthesis.
Jhun
B H
BH
Division of Endocrinology and Metabolism, University of California at San Diego, La Jolla 92093.
Meinkoth
J L
JL
Leitner
J W
JW
Draznin
B
B
Olefsky
J M
JM
D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D002460:Cell Line; D004247:DNA / Q000096:biosynthesis; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008845:Microinjections; D015689:Oncogene Protein p21(ras) / Q000276:immunology / Q000502:physiology*; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis; D051381:Rats; D015398:Signal Transduction
D000906:Antibodies; D007328:Insulin; D016760:Proto-Oncogene Proteins c-fos; D007334:Insulin-Like Growth Factor I; D006160:Guanosine Triphosphate; D004247:DNA; D015689:Oncogene Protein p21(ras)