Abstract P191: Calpain-Generated Free PKCα Catalytic Domains Induce HDAC5 Nuclear Export and Regulate Cardiac Gene Transcription
Receptor-mediated activation of protein kinase (PK) C is a central pathway regulating cell growth, homeostasis, and programmed death. Recently, we showed that calpain-mediated proteolytic processing of PKC in ischemic myocardium activates PKC signaling in a receptor-independent manner by releasing a persistent and constitutively active free catalytic C-terminal fragment, PKCα-CT. This unregulated kinase provokes cardiomyopathy, but the mechanisms remain unclear. We examined hypothesis that PKCα-CT has transcriptional activity. Using immunoblot analysis and confocal microscopy, we found that PKCα-CT localized in part to nuclei and spontaneously induced cytosolic relocalization HDAC5 of the transcriptional regulator. Co- expression of calpain 1 with full length PKCα can generate PKCα-CT and produced the same HDAC5 cytosolic relocalization, whereas full length PKCα alone had no such effect. HDAC5 cytosolic relocalization induced by PKCα-CT was abolished by the protein kinase inhibitor GO6976, but not by PKD inhibitor CID 755673. The in vivo relevance of these findings was examined in transgenic mice expressing PKCα and PKCα-CT. To assess the consequence on gene expression, we performed global transcriptome profiling by Affymetrix microarrays and mRNA sequencing. The two techniques substantially agreed. Compared to control hearts, 621 mRNAs were regulated at least 1.3 fold in PKCα-CT hearts (P< 0.001), only 59 in full-length PKCα hearts. MEF2-dependent inflammatory pathway genes which are putative HDAC targets were upregulated in PKCα-CT heart: 15 MEF2 target mRNAs were upregulated in PKCα-CT hearts (p<0.001), only one in PKCα hearts. These results reveal that PKCα-CT is a potent regulator of pathological cardiac gene expression by localizing to nuclei and directly promoting nuclei-cytoplasmic shuttling of HDAC5. Receptor-independent effect of PKCα-CT and HDAC phosphorylation in ischemic hearts has broad ramifications for understanding and preventing the pathological transcriptional stress response.
- © 2011 by American Heart Association, Inc.