Activated Gq-alpha potentiates platelet-derived growth factor-stimulated mitogenesis in confluent cell cultures.
We studied the effects of activation of the Gq-alpha signaling pathway on mitogenesis by expressing a mutant (Q209L), activated alpha-subunit of Gq (alpha q*) in NIH-3T3 cells. A clonal NIH-3T3 cell line expressing alpha q* in an inducible manner was isolated. Expression of alpha q* is induced with dexamethasone, allowing the use of non-induced cells as controls for the effects of alpha q* expression. We found that, by itself, expression of alpha q* did not increase either DNA synthesis or mitogen-activated protein (MAP) kinase activity in serum-starved cells. Because alpha q* transforms cells grown in the presence of serum (De Vivo M., Chen, J., Codina, J., and Iyengar, R. (1992) J. Biol. Chem. 267, 18263-18266), we tested whether growth factor-stimulated signaling and mitogenesis were affected by expression of alpha q*. Platelet-derived growth factor (PDGF) stimulated thymidine incorporation modestly (50%) in contact-inhibited, confluent cell cultures. In cells expressing alpha q*, PDGF stimulated DNA synthesis up to 3-fold over basal. Concomitant with the potentiation of PDGF-stimulated DNA synthesis, expression of alpha q* potentiated PDGF-stimulated p44 MAP kinase activity. PDGF was much more effective in stimulating both DNA synthesis and p44 MAP kinase activity in subconfluent cell cultures and expression of alpha q* exerted little or no effect on PDGF-stimulated effects in subconfluent cells. These data show that cooperation between signaling pathways may occur in a cell state-specific fashion. Such cooperation in part may be responsible for the triggering of complex cellular responses such as cell transformation.
De Vivo
M
M
Department of Pharmacology, Mount Sinai School of Medicine, City University of New York, New York 10029.
Iyengar
R
R
D016475:3T3 Cells; D000818:Animals; D002455:Cell Division / Q000187:drug effects; D016895:Culture Media, Serum-Free; D004247:DNA / Q000096:biosynthesis; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1; D010982:Platelet-Derived Growth Factor / Q000378:metabolism / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism; D015398:Signal Transduction
D016895:Culture Media, Serum-Free; D010982:Platelet-Derived Growth Factor; D004247:DNA; D011505:Protein-Tyrosine Kinases; D020794:Receptor Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019950:Mitogen-Activated Protein Kinase 1; D019204:GTP-Binding Proteins