title: Protein-tyrosine kinases regulate the phosphorylation, protein interactions, subcellular distribution, and activity of p21ras GTPase-activating protein.
abstract: The p21ras GTPase-activating protein (GAP) down-regulates p21ras by stimulating its intrinsic GTPase activity. GAP is found predominantly as a monomer in the cytosol of normal cells. However, in cells expressing an activated cytoplasmic protein-tyrosine kinase, p60v-src, or stimulated with epidermal growth factor, GAP becomes phosphorylated on tyrosine and serine and forms distinct complexes with two phosphoproteins of 62 and 190 kDa (p62 and p190). In v-src-transformed Rat-2 cells, a minor fraction of GAP associates with the highly tyrosine phosphorylated p62 to form a complex that is localized at the plasma membrane and in the cytosol. In contrast, the majority of GAP enters a distinct complex with p190 that is exclusively cytosolic and contains predominantly phosphoserine. Epidermal growth factor stimulation also induces a marked conversion of monomeric GAP to higher-molecular-weight species in rat fibroblasts. The GAP-p190 complex is dependent on phosphorylation and shows reduced GAP activity. These results indicate that protein-tyrosine kinases induce GAP to form multiple heteromeric complexes, which are strong candidates for regulators or targets of p21ras.
authors.affiliation: Department of Molecular and Medical Genetics, University of Toronto, Ontario, Canada.
authors.forename: M F
authors.initials: MF
authors.lastname: Moran
authors.forename: P
authors.initials: P
authors.lastname: Polakis
authors.forename: F
authors.initials: F
authors.lastname: McCormick
authors.forename: T
authors.initials: T
authors.lastname: Pawson
authors.forename: C
authors.initials: C
authors.lastname: Ellis
mesh_terms: D000818:Animals; D002460:Cell Line; D002461:Cell Line, Transformed; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D066246:ErbB Receptors / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D020690:GTPase-Activating Proteins; D015688:Oncogene Protein pp60(v-src) / Q000378:metabolism; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D013379:Substrate Specificity
chemical_list: D020690:GTPase-Activating Proteins; D011506:Proteins; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases; D015688:Oncogene Protein pp60(v-src); D020558:GTP Phosphohydrolases