title: Regulation of tetradecanoyl phorbol acetate-induced responses in NIH 3T3 cells by GAP, the GTPase-activating protein associated with p21c-ras.
abstract: Proteins of the ras family of oncogenes have been implicated in signal transduction pathways initiated by protein kinase C (PKC) and by tyrosine kinase oncogenes and receptors, but the role that ras plays in these diverse signalling systems is poorly defined. The activity of ras proteins has been shown to be controlled in part by a cellular protein, GAP (GTPase-activating protein), that negatively regulates p21c-ras by enhancing its intrinsic GTPase activity. Thus, overexpression of GAP provides a tool for determining the step(s) in signal transduction dependent on p21c-ras activity. In this paper, we report that overexpression of GAP blocks the phorbol ester (tetradecanoyl phorbol acetate [TPA])-induced activation of p42 mitogen-activated protein kinase (p42mapk), c-fos expression, and DNA synthesis. GAP overexpression did not block responses to serum or fluoroaluminate. Moreover, not all biochemical events elicited by TPA were affected by GAP overexpression, as increased glucose uptake and phosphorylation of MARCKS, a major PKC substrate, occurred normally. Reduction of GAP expression to near normal levels restored the ability of the cells to activate p42mapk in response to TPA. These findings suggest that ras and GAP together play a key role in a PKC-dependent signal transduction pathway which leads to p42mapk activation and cell proliferation.
authors.affiliation: Department of Microbiology, University of Virginia School of Medicine, Charlottesville 22908.
authors.forename: M
authors.initials: M
authors.lastname: Nori
authors.forename: G
authors.initials: G
authors.lastname: L'Allemain
authors.forename: M J
authors.initials: MJ
authors.lastname: Weber
mesh_terms: D016475:3T3 Cells; D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D002455:Cell Division / Q000187:drug effects; D004247:DNA / Q000096:biosynthesis; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D020690:GTPase-Activating Proteins; D005947:Glucose / Q000378:metabolism; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases; D011506:Proteins / Q000378:metabolism*; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism*; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D020703:ras GTPase-Activating Proteins
chemical_list: D020690:GTPase-Activating Proteins; D011506:Proteins; D016760:Proto-Oncogene Proteins c-fos; D020703:ras GTPase-Activating Proteins; D004247:DNA; D011494:Protein Kinases; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019950:Mitogen-Activated Protein Kinase 1; D016283:Proto-Oncogene Proteins p21(ras); D005947:Glucose; D013755:Tetradecanoylphorbol Acetate