title: Mitogenic activation of the Ras guanine nucleotide exchange factor in NIH 3T3 cells involves protein tyrosine phosphorylation.
abstract: We report biochemical evidence that epidermal growth factor and platelet-derived growth factor stimulate the Ras guanine nucleotide exchange factor activity in quiescent NIH 3T3 cells. Moreover, the exchange activity is constitutively enhanced in NIH 3T3 cells transformed by Src and ErbB2 oncogenic tyrosine protein kinases (TPKs), whereas transformation by oncogenic Mos and Raf does not alter the activity. GTPase-activating protein activity was not affected under these conditions. Overexpression of pp60c-Src mutants containing activated and suppressor TPK mutations resulted in stimulation and inhibition of the exchange factor activity, respectively. A TPK inhibitor, genistein, prevented the activation of the exchange factor in epidermal growth factor/platelet-derived growth factor-treated cells and src-transformed cells. Furthermore, the exchange factor activity bound to an anti-phosphotyrosine antibody immunoaffinity column. These findings suggest that the guanine nucleotide exchange factor, but not GTPase-activating protein, plays a major role in the Ras activation in cell proliferation initiated by growth factor receptor TPKs and malignant transformation by oncogenic TPKs and that tyrosine phosphorylation of either the exchange factor or a tightly bound protein(s) may mediate the activation of the exchange factor by these TPKs.
authors.affiliation: Biological Carcinogenesis and Development Program, PRI/DynCorp, Frederick, MD 21702-1201.
authors.forename: B Q
authors.initials: BQ
authors.lastname: Li
authors.forename: M
authors.initials: M
authors.lastname: Subleski
authors.forename: D
authors.initials: D
authors.lastname: Shalloway
authors.forename: H F
authors.initials: HF
authors.lastname: Kung
authors.forename: T
authors.initials: T
authors.lastname: Kamata
mesh_terms: D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D002461:Cell Line, Transformed; D002471:Cell Transformation, Neoplastic; D002846:Chromatography, Affinity; D002852:Chromatography, Ion Exchange; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D066246:ErbB Receptors / Q000378:metabolism; D020690:GTPase-Activating Proteins; D016391:Genes, src; D019833:Genistein; D020662:Guanine Nucleotide Exchange Factors; D006153:Guanosine Diphosphate / Q000378:metabolism*; D007529:Isoflavones / Q000494:pharmacology; D051379:Mice; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D017354:Point Mutation; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism; D011506:Proteins / Q000302:isolation & purification / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000235:genetics; D011519:Proto-Oncogenes; D018719:Erb-b2 Receptor Tyrosine Kinases; D017479:Receptors, Platelet-Derived Growth Factor / Q000378:metabolism; D020703:ras GTPase-Activating Proteins; D020663:ras Guanine Nucleotide Exchange Factors
chemical_list: D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D020690:GTPase-Activating Proteins; D019833:Genistein; D020662:Guanine Nucleotide Exchange Factors; D006153:Guanosine Diphosphate; D007529:Isoflavones; D010982:Platelet-Derived Growth Factor; D011505:Protein-Tyrosine Kinases; D011506:Proteins; D011518:Proto-Oncogene Proteins; D018719:Erb-b2 Receptor Tyrosine Kinases; D017479:Receptors, Platelet-Derived Growth Factor; D020703:ras GTPase-Activating Proteins; D020663:ras Guanine Nucleotide Exchange Factors