Activation of Overexpressed Receptors for Insulin and Epidermal Growth Factor Interferes in Mitogenic Signaling without Affecting the Activation of p21ras

Abstract

Activated receptors with a tyrosine kinase activity induce a variety of responses like changes in the differentiation and mitogenic status of cells. These responses are mediated in part by p2lras. Some of these activated receptors induce in certain cell types a pronounced, but transient, increase in RasOGTP. We have stimulated cells with insulin, epidermal growth factor (EGF), and fetal calf serum (FCS), and the mitogenic response, as reflected by stimulation of [ 3H] thymidine incorporation, was compared with the magnitude of the transient increase in RasOGTP levels. Cell lines were used that expressed both physiological and elevated numbers of p2lras and receptors for insulin and EGF, respectively. In all the examined cell lines 9% FCS did not induce a marked increase in Ras-GTP despite its high mitogenic potency. Pronounced increases in Ras-GTP levels were observed in insulin-stimulated C H O cells which overexpress insulin receptors whereas in the parental C H O cells only a small increase is seen. Insulin (1 pM The ras protooncogenes encode small guanine nucleotide binding proteins with molecular masses of approximately 2lkDa (Barbacid, 1987). P2lras is active when complexed to GTP. It has a slow intrinsic GTPase activity that converts Ras.GTP into inactive RasSGDP. This activity is enhanced by cellular proteins like pl20-GAP' and NF1-GAP (McCormick, 1992). Activation of p2lras requires exchange of bound GDP for GTP (Randazzo et al., 1992). A variety of proteins, regulating this exchange, have been identified (West et al., 1990;Downward et al., 1990b

Paracrine effects of hepatocyte growth factor/scatter factor on non-small-cell lung carcinoma cell lines

“…These include primary cultures of hepatocytes (Nakamura et al, 1987), mammary (Niranjan et al, 1995), biliary (Strain et al, 1995) and bronchial (Tsao et al, 1993) epithelia, keratinocytes (Matsumoto et al, 1991) and melanocytes (Halaban et al, 1992). It is worth noting that the activation of overexpressed tyrosine kinase receptors often leads to a suppression of cell proliferation, independent of the activation of the p21"-'s and MAP kinase (Osterop et al, 1994 (Fournier et al, 1996;Ponzetto et al, 1996). This would be consistent with our findings that the ability of HGF/SF to induce motogenic activity is not affected by the constitutive activation of the ras signal transduction pathway.…”

Roles of Insulin Receptor Substrate-1 and Shc on Insulin-Like Growth Factor I Receptor Signaling in Early Passages of Cultured Human Fibroblasts

“…9. The dose-response for EGF is also indicated in this figure, and the maximal response for EGF was obtained at the concentration of 0.1 nm, which was consistent with a report on rat-1 fibroblasts (29). Interestingly, IGF-I was the strongest in mitogenic potency and promoted DNA synthesis about 2-fold over basal (Fig.…”

Epidermal growth factor (EGF) suppresses staurosporine-induced apoptosis by inducing mcl-1 via the mitogen-activated protein kinase pathway

“…However, the antiapoptotic e ect reached a plateau at 30 ng/ml (5610 79 M). In EGF receptor-overexpressing Rat-1 cells (Osterop et al, 1994) and a human breast epithelial cell line MCF-10A (Basolo et al, 1992), a signi®cantly higher mitogenic e ect was seen after the addition of 10 710 M rather than 10 79 M EGF. Thus, EGF may utilize high a nity or low a nity receptors to transduce mitogenic or survival signals, respectively.…”