Evidence that a G-protein transduces signals initiated by the protein-tyrosine kinase v-Fps.
The protein-tyrosine kinase (PTK) v-Fps induces protein kinase C (PKC)-dependent expression of the transformation-related 9E3 gene in chicken embryo fibroblasts (Spangler, R., Joseph, C., Qureshi, S.A., Berg, K., and Foster, D.A. (1989) Proc. Natl. Acad. Sci. U.S.A. 86, 7017-7021). We present evidence here that a GTP-binding protein (G-protein) is a component of this PKC-dependent signaling pathway. 1) A GTP analogue that stimulates G-protein-mediated signals induced 9E3 gene expression. 2) A GDP analogue that inhibits signaling through G-proteins inhibited expression of 9E3 and phosphorylation of a 67-kDa PKC substrate induced by v-Fps. The GDP analogue had no effect on phosphorylation of the PKC substrate or the expression of 9E3 induced by direct activation of PKC with phorbol ester. 3) Increased v-Fps PTK activity led to increased GTP binding to a 50-kDa protein. The molecular weight of this GTP-binding protein is consistent with the molecular weight of alpha-subunits of G-proteins of the heterotrimeric class. The data suggest that a G-protein functions upstream from PKC in a signaling pathway that connects v-Fps PTK activity to increased 9E3 gene expression.
Alexandropoulos
K
K
Institute for Biomolecular Structure and Function, Hunter College, City University of New York, New York 10021.
Joseph
C K
CK
Spangler
R
R
Foster
D A
DA
D000818:Animals; D002642:Chick Embryo; D003432:Cross-Linking Reagents; D004790:Enzyme Induction; D015681:Fusion Proteins, gag-onc / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D015870:Gene Expression; D010766:Phosphorylation; D011493:Protein Kinase C / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D012313:RNA / Q000032:analysis; D015398:Signal Transduction; D013379:Substrate Specificity
D003432:Cross-Linking Reagents; D015681:Fusion Proteins, gag-onc; D012313:RNA; D011505:Protein-Tyrosine Kinases; C068415:v-fps oncogene protein, Fujinami sarcoma virus; D011493:Protein Kinase C; D019204:GTP-Binding Proteins