Abstract 17543: DMPK E Disrupts Sarcomere Structure by Inhibition of SRF Transcriptional Activity

Abstract

Background: Heart failure is associated with elongation of cardiomyocytes and loss of sarcomeres. Although the transcription factor myocyte enhancer factor-2 (MEF2) has an important role in this adverse remodeling, the mechanism underlying the structural changes of cardiomyocytes remains to be elucidated. In a screen for MEF2 target genes, we have recently identified myotonic dystrophy protein kinase (DMPK) as a potential mediator of adverse cardiomyocyte remodeling. However, it remains to be determined whether DMPK levels are increased in failing hearts and if DMPK is sufficient to induce structural remodeling of cardiomyocytes. Methods and Results: Since the DMPK gene is subject to extensive alternative splicing, we performed RT-PCR and QPCR analysis of known DMPK splice variants in hearts from mice subjected to transverse aortic constriction (TAC) or sham surgery. This demonstrated a 1.6 fold increase in the DMPK E isoform in failing mouse hearts compared to controls (P<0.05). To test the role of this specific splice isoform, we generated adenoviruses expressing DMPK E or a kinase dead mutant DMPK E. Overexpression of wildtype DMPK E, but not of the kinase dead mutant, in cardiomyocytes resulted in severe loss of sarcomeric structure. Moreover, QPCR analysis showed a decrease in mRNA levels for several sarcomeric genes after overexpression of DMPK E. Since these genes are known targets of the transcription factor serum response factor (SRF) and DMPK is known to phosphorylate SRF, we tested the effect of DMPK E on SRF activity. Luciferase experiments demonstrated that DMPK E is an inhibitor of SRF transcriptional activity. Finally, immunostaining revealed a translocation of SRF from the nucleus to the cytosol upon DMPK E overexpression. Conclusion: Our data indicate that the expression of DMPK E is increased in heart failure. Moreover, increased expression of this DMPK splice variant results in a decrease in sarcomeric gene expression by translocation and inhibition of SRF. Together, these results assign a novel function to DMPK in adverse cardiomyocyte remodeling during heart failure development.