Transformation of Rat-1 fibroblasts with the v-src oncogene increases the tyrosine phosphorylation state and activity of the alpha subunit of Gq/G11.
Two major intermediaries in signal transduction pathways are pp60v-sre family tyrosine kinases and heterotrimeric guanine nucleotide-binding proteins. In Rat-1 fibroblasts transformed by the v-src oncogene, endothelin-1 (ET-1)-induced inositol 1,4,5-trisphosphate accumulation is increased 6-fold, without any increases in the numbers of ET-1 receptors or in the response to another agonist, thrombin. This ET-1 hyperresponse can be inhibited by an antibody directed against the carboxyl terminus of the Gq/G11 alpha subunit, suggesting that the Gq/G11 protein couples ET-1 receptors to phospholipase C (PLC). While v-src transformation did not increase the expression of the Gq/G11 alpha subunit, immunoblotting with anti-phosphotyrosine antibodies and phosphoamino acid analysis demonstrated that the Gq/G11 alpha subunit becomes phosphorylated on tyrosine residues in v-src-transformed cells. Moreover, when the Gq/G11 protein was extracted from control and transformed cell lines and reconstituted with exogenous PLC, AIF*4-stimulated Gq/G11 activity was markedly increased in extracts from v-src-transformed cells. Our results demonstrate that the process of v-src transformation can increase the tyrosine phosphorylation state of the Gq/G11 alpha-subunit in intact cells and that the process causes an increase in the Gq/G11 alpha-subunit's ability to stimulate PLC following activation with AIF-4.
Liu
W W
WW
Department of Pharmacology, School of Medicine, University of Virginia, Charlottesville 22908, USA.
Mattingly
R R
RR
Garrison
J C
JC
D000818:Animals; D002471:Cell Transformation, Neoplastic / Q000378:metabolism*; D002478:Cells, Cultured; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016391:Genes, src; D015688:Oncogene Protein pp60(v-src) / Q000378:metabolism*; D019000:Phosphotyrosine / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D051381:Rats; D044022:Receptor, Endothelin A; D017466:Receptors, Endothelin / Q000502:physiology*; D018179:Receptors, Thrombin / Q000502:physiology*; D015398:Signal Transduction; D010738:Type C Phospholipases / Q000378:metabolism
D044022:Receptor, Endothelin A; D017466:Receptors, Endothelin; D018179:Receptors, Thrombin; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases; D015688:Oncogene Protein pp60(v-src); D010738:Type C Phospholipases; D019204:GTP-Binding Proteins