Abstract 119: The Scaffolding Protein Enh1 is Essential for the Protein Kinase C or Protein Kinase D-dependent Activation of the Transcription Factor Camp-response Element Binding Protein in Cardiomyocytes

Abstract

PDZ-LIM proteins form a family of the scaffolding protein essential for both embryonic and post-natal development. ENH1 (PDLIM5) is a PDZ-LIM protein, composed of an N-terminal PDZ domain and 3 LIM domains at the C-terminal end. The enh gene encodes for several splice variants that have opposite functions. ENH1 promotes the cardiomyocytes hypertrophy whereas ENH splice variants lacking LIM domains prevents it. At the molecular level, ENH1 interacts with Protein kinase C (PKC) and Protein Kinase D1 (PKD1) both kinases playing a pivotal role in the pathological remodeling of the heart. In addition, the binding of ENH1’s LIM domains to PKC is sufficient to activate the kinase without any stimulation. However, the downstream events of the ENH1-PKC/PKD1 complex remain unknown. PKC and PKD1 are known to phosphorylate the transcription factor cAMP-response element binding protein (CREB) in cardiomyocytes. We therefore hypothesized that ENH1 could be a play a role in the PKC/PKD1-dependent activation of CREB. We first found that ENH1 expression is necessary to induce the phosphorylation of CREB at Ser133 in neonatal rat ventricular cardiomyocytes. On the contrary, the overexpression of ENH3, a LIM-less cardiac-specific splice variant, inhibited the phosphorylation of CREB-Ser133. Concomitantly, both real-time qPCR and promoter assay showed that the overexpression of ENH1 enhanced but ENH3 prevented the transcriptional activation of a CREB-target gene, the immediately early gene c-fos. Finally, we found that ENH1 regulated the translocation of phosphorylated CREB to the nucleus. Taken all together, our results suggest that ENH1 plays an essential role in CREB’s activation and dependent transcription in cardiomyocytes. At the opposite, ENH3 splice variant inhibited the CREB activity in cardiomyocytes. In conclusion, our work describes a new molecular mechanism involving ENH splice variants with opposing functions.