Activation and inactivation of cAMP-response element-mediated gene transcription in cardiac myocytes

Objective: Chronic P-adrenergic stimulation of the cAMP-dependent signallin g pathway is implicated in functionally relevant expressional changes in co ngestive heart failure. We studied activation and inactivation of the cardi ac gene transcription mediated by the cAMP-response element (CRE) and the C RE-binding protein (CREB) as an important mechanism of a cAMP-dependent gen e regulation. Methods: We investigated the transcriptional activation by fo rskolin, an activator of the adenylyl cyclase, in chick embryonic cardiomyo cytes transfected with a CRE-controlled luciferase construct in comparison to the phosphorylation and expression of CREB determined on immunoblots. Re sults: Forskolin (10 mu mol/l; 8 h) increased CRE-mediated transcription an d phosphorylation of CREB 13- and 1.5-fold, respectively. The phosphorylati on was further elevated in combination with cantharidin, an inhibitor of ty pe 1+2A protein phosphatases. The transcriptional response to forskolin was desensitized by pretreatment with forskolin (1 mu mol/l; 24 h) while CREB phosphorylation was increased. In forskolin-pretreated cells, total CREB pr otein levels were decreased. Cantharidin did not restore the attenuated tra nscriptional response. Conclusions: In cardiomyocytes, there is an activati on of the CRE-mediated gene transcription by forskolin that is attenuated a fter prolonged stimulation, and this attenuation is not dependent from a de phosphorylation of CREB. We suggest that attenuation of the CRE-mediated tr anscription through chronic stimulation of the cAMP-pathway, e.g. by elevat ed catecholamines, contributes to the altered expressional regulation in co ngestive heart failure. (C) 2001 Elsevier Science B.V. All rights reserved.