Overexpression of c-src enhances beta-adrenergic-induced cAMP accumulation.
During our investigations into the physiological role of c-src tyrosine kinase in normal cells, we found that clonal transfectants of C3H10T1/2 murine fibroblasts overexpressing chicken c-src exhibited strikingly elevated levels of cAMP accumulation in response to adrenergic stimulation as compared to control cells. Enhanced cAMP accumulations were detected when cells were treated with the beta-agonists, epinephrine, isoproterenol, or terbutaline and were blocked by treatment with the beta-specific antagonist propranolol, indicating action through beta-adrenergic receptors. The hyperresponsiveness was not observed in cells overexpressing kinase-defective c-src. No differences in basal levels of cAMP, agonist concentration dependence, or kinetics of cAMP accumulation were detected between cells containing elevated levels of wild-type or kinase-defective c-src protein and control cells. To determine if the degree of c-src overexpression could influence the response, multiple clones, transfected with DNA encoding genes for wild-type or kinase-defective c-src plus neomycin resistance or neomycin resistance alone, were derived in parallel and assayed for the amounts of c-src protein produced and the levels of cAMP accumulated in response to epinephrine. Only clones with abundant wild-type c-src protein (greater than 10-fold above endogenous) exhibited enhanced cAMP accumulation, averaging 3.3-fold above control cells. We conclude, therefore, that the enhanced degree of cAMP accumulation in cells overexpressing c-src is dependent upon activation of beta-adrenergic receptors and upon a threshold level of pp60c-src that retains full tyrosine kinase activity.
Department of Microbiology, University of Virginia Health Sciences Center 22908.
W A
WA
Bushman
L K
LK
Wilson
D K
DK
Luttrell
J S
JS
Moyers
S J
SJ
Parsons
D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism*; D004837:Epinephrine / Q000494:pharmacology*; D015870:Gene Expression; D016391:Genes, src; D007545:Isoproterenol / Q000494:pharmacology*; D007700:Kinetics; D051379:Mice; D011433:Propranolol / Q000494:pharmacology*; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000502:physiology; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000235:genetics* / Q000502:physiology; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000502:physiology; D013726:Terbutaline / Q000494:pharmacology*; D014162:Transfection
D011943:Receptors, Adrenergic, beta; D011433:Propranolol; D000242:Cyclic AMP; D011505:Protein-Tyrosine Kinases; D016392:Proto-Oncogene Proteins pp60(c-src); D007545:Isoproterenol; D013726:Terbutaline; D004837:Epinephrine