title: Negative feedback regulation and desensitization of insulin- and epidermal growth factor-stimulated p21ras activation.
abstract: Insulin and epidermal growth factor receptors transmit signals for cell proliferation and gene regulation through formation of active GTP-bound p21ras mediated by the guanine nucleotide exchange factor Sos. Sos is constitutively bound to the adaptor protein Grb2 and growth factor stimulation induces association of the Grb2/Sos complex with Shc and movement of Sos to the plasma membrane location of p21ras. Insulin or epidermal growth factor stimulation induces a rapid increase in p21ras levels, but after several minutes levels decline toward basal despite ongoing hormone stimulation. Here we show that deactivation of p21ras correlates closely with phosphorylation of Sos and dissociation of Sos from Grb2, and that inhibition of mitogen-activated protein (MAP) kinase kinase (also known as extracellular signal-related kinase (ERK) kinase, or MEK) blocks both events, resulting in prolonged p21ras activation. These data suggest that a negative feedback loop exists whereby activation of the Raf/MEK/MAP kinase cascade by p21ras causes Sos phosphorylation and, therefore, Sos/Grb2 dissociation, limiting the duration of p21ras activation by growth factors. A serine/threonine kinase downstream of MEK (probably MAP kinase) mediates this desensitization feedback pathway.
authors.affiliation: Department of Medicine, University of California, San Diego, La Jolla 92093, USA.
authors.forename: W J
authors.initials: WJ
authors.lastname: Langlois
authors.forename: T
authors.initials: T
authors.lastname: Sasaoka
authors.forename: A R
authors.initials: AR
authors.lastname: Saltiel
authors.forename: J M
authors.initials: JM
authors.lastname: Olefsky
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D015153:Blotting, Western; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D015536:Down-Regulation; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D051380:GRB2 Adaptor Protein; D020662:Guanine Nucleotide Exchange Factors; D006153:Guanosine Diphosphate / Q000032:analysis; D006160:Guanosine Triphosphate / Q000032:analysis; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D011233:Precipitin Tests; D011506:Proteins / Q000378:metabolism*; D016283:Proto-Oncogene Proteins p21(ras) / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D015398:Signal Transduction; D020663:ras Guanine Nucleotide Exchange Factors
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D051380:GRB2 Adaptor Protein; C495948:GRB2 protein, human; C495950:Grb2 protein, rat; D020662:Guanine Nucleotide Exchange Factors; D007328:Insulin; D011506:Proteins; D020663:ras Guanine Nucleotide Exchange Factors; D006153:Guanosine Diphosphate; D004815:Epidermal Growth Factor; D006160:Guanosine Triphosphate; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras)