Overexpression of pp60c-src is associated with altered regulation of adenylyl cyclase.
The ability of activators of the beta-adrenergic receptor to elevate intracellular cAMP levels in murine fibroblasts is enhanced upon overexpression of avian c-src [Bushman et al. (1990) Proc. natn. Acad. Sci. U.S.A. 87, 7462-7466]. To investigate the molecular basis for this effect, we prepared particulate fractions from control and pp60c-src overexpressing C3H10T1/2 fibroblasts and assessed the relative abilities of several activators of the beta-adrenergic receptor-Gs-adenylyl cyclase (AC) signal transduction pathway to stimulate the enzymatic response. Two- to three-fold increases in both the sensitivity and maximum responsiveness of AC to the beta-adrenergic agonist isoproterenol were consistently observed in fractions prepared from the c-src overexpressing cells. Interestingly, the AC response to two agents believed to act directly at the level of the G protein were either enhanced (NaF) or unaffected (GTP gamma S) by c-src overexpression. Finally, overexpression of c-src was associated with a reduced ability of both Mn2+ and forskolin to activate AC directly. These results suggest that overexpression of wild type c-src may affect two distinct steps in the regulation of AC exerting a positive effect at the level of Gs activation and a negative effect on AC itself. As no differences in the relative number or affinity of beta-adrenergic receptors, or in the level of AC, Gs alpha or G beta, were detected between control cells and those overexpressing c-src, we propose that pp60c-src overexpression results in a modification of one or more components in this signal transduction pathway.
Luttrell
D K
DK
Glaxo Research Institute, Department of Cell Biology, Research Triangle Park, NC 27709.
Hausdorff
W P
WP
Moyers
J E
JE
Gilmer
T M
TM
Parsons
S J
SJ
Caron
M G
MG
Lefkowitz
R J
RJ
D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D000242:Cyclic AMP / Q000096:biosynthesis; D004789:Enzyme Activation / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000378:metabolism; D007545:Isoproterenol / Q000494:pharmacology; D051379:Mice; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism*; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology
D011943:Receptors, Adrenergic, beta; D000242:Cyclic AMP; D016392:Proto-Oncogene Proteins pp60(c-src); D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D007545:Isoproterenol