P9 CYCLIC-AMP DOWN REGULATES EPAC TRANSCRIPTION IN CARDIAC FIBROBLASTS VIA INHIBITION OF YAP-TEAD ACTIVITY. A NOVEL NEGATIVE FEEDBACK LOOP CONTROLLING CAMP SIGNALLING

Exchange Protein Activated by cAMP-1 (EPAC1) is implicated in numerous physiological processes, including cell proliferation, migration, adhesion and inflammation. Changes in EPAC expression are implicated in several diseases including cardiac fibrosis and hypertrophy. Elevated cAMP increases EPAC activity but little is known about how EPAC levels are regulated. Here we investigate regulation of EPAC expression by cAMP.

Forskolin, db-cAMP or adenosine A2B-receptor agonist (BAY 60-6583) significantly reduced EPAC mRNA levels in cardiac fibroblasts. PKA and EPAC selective agonists acted additively to repress EPAC mRNA levels. Pre-splice EPAC RNA and activity of an EPAC-promoter reporter vector was similarly reduced in response to all of these stimuli, suggesting transcriptional repression of EPAC by cAMP. Phalloidin staining of F-actin demonstrated a rapid disruption of actin polymerisation in response to elevated cAMP. Furthermore, inhibition of actin polymerisation with latrunculin-B, cytochalasin-D or Y-27632 (ROCK inhibitor) significantly reduced EPAC mRNA. Analysis of the EPAC promoter identified a consensus TEAD binding element. Stimulation with Forskolin or Latrunculin B significantly inhibited TEAD-luciferase activity. Over expression of the TEAD co-factor YAP, completely reversed forskolin mediated inhibition of TEAD-LUC and EPAC promoter activity.

Taken together, these data demonstrate that cAMP reduces EPAC gene transcription. Our data demonstrates that this is mediated, at least in part, by cAMP mediated disruption of the actin cytoskeleton and inhibition of YAP-TEAD activity. These mechanisms represent a novel negative feedback loop controlling cAMP signalling, dysregulation of which may contribute towards the altered EPAC levels that have been observed during disease.