title: Activation of c-Src in cells bearing v-Crk and its suppression by Csk.
abstract: The protein product of the CT10 virus, p47gag-crk (v-Crk), which contains Src homology region 2 (SH2) and 3 (SH3) domains but lacks a kinase domain, is believed to cause an increase in cellular protein tyrosine phosphorylation. A candidate tyrosine kinase, Csk (C-terminal Src kinase), has been implicated in c-Src Tyr-527 phosphorylation, which negatively regulates the protein tyrosine kinase of pp60c-src (c-Src). To investigate how c-Src kinase activity is regulated in vivo, we first looked at whether v-Crk can activate c-Src kinase. We found that cooverexpression of v-Crk and c-Src caused elevation of c-Src kinase activity, resulting in an increase of tyrosine phosphorylation of cellular proteins and morphological transformation of rat 3Y1 fibroblasts. v-Crk and c-Src complexes were not detected, although v-Crk bound to a variety of tyrosine-phosphorylated proteins in cells overexpressing v-Crk and c-Src. Overexpression of Csk in these transformed cells caused reversion to normal phenotypes and also reduced the level of c-Src kinase activity. However, Csk did not cause reversion of cells transformed by v-Src or c-Src527F, in which Tyr-527 was changed to Phe. These results strongly suggest that Csk acts on Tyr-527 of c-Src and suppresses c-Src kinase activity in vivo. Because Csk can suppress transformation by cooverexpression of v-Crk and c-Src, we suggest that v-Crk causes activation of c-Src in vivo by altering the phosphorylation state of Tyr-527.
authors.affiliation: Laboratory of Molecular Oncology, Rockefeller University, New York, New York 10021-6399.
authors.forename: H
authors.initials: H
authors.lastname: Sabe
authors.forename: M
authors.initials: M
authors.lastname: Okada
authors.forename: H
authors.initials: H
authors.lastname: Nakagawa
authors.forename: H
authors.initials: H
authors.lastname: Hanafusa
mesh_terms: D000818:Animals; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D002522:Chlorocebus aethiops; D004789:Enzyme Activation; D050736:Oncogene Protein v-crk; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015682:Retroviridae Proteins, Oncogenic / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
chemical_list: D050736:Oncogene Protein v-crk; D015682:Retroviridae Proteins, Oncogenic; D011505:Protein-Tyrosine Kinases; D016392:Proto-Oncogene Proteins pp60(c-src)