The Effects of a 14-3-3 inhibitor peptide on cardiomyocyte hypertrophic gene expression

Abstract

Joel James Ellis, The Effects of a 14-3-3 inhibitor peptide on cardiomyocyte hypertrophic gene expression. Doctor of Philosophy (Biomedical Sciences), May 2006, 164 pp, 2 tables, 29 illustrations, references, 117 titles. The myocyte enhancer factor-2 (MEF2) family of transcription factors regulates transcription of muscle-dependent genes in skeletal, smooth and cardiac muscle types. MEF2 is activated by calcium/calmodulin (CaM)-dependent protein kinases I and IV and silenced by CaM kinase IlδC. MEF2 is held inactive in the nucleus by class I histone deacetylases (HDAC4&5) until phosphorylated by either CaM kinase I or IV. This phosphorylation results in HDAC transport out of the nucleus via a 14-3-3-dependent mechanism, thereby freeing MEF2 to drive transcription. 14-3-3 proteins exist as homodimers, which are modulated by the phosphorylation of serines 60 and 65 in the dimerization region. In this study, a HIV TAT protein transduction domain (PTD) fused 14-3-3 peptide inhibitor was generated that is designed to prevent the dimerization of 14-3-3 proteins. The data presented demonstrates that the 14-3-3 inhibitor peptide freely enters cardiomyocytes and is not cytotoxic under culture conditions. The presence of this 14-3-3 inhibitor promotes nuclear localization of class II HDACs in the presence of hypertrophic stimuli. Moreover, the 14-3-3 inhibitor prevented dimerization of wild type 14-3-3β in ventricular cardiomyocytes. Finally, increased MEF2-dependent transcriptional activity, due to CaMKI, CaMKIV and PE, was effectively silenced by this 14-3-3 inhibitor in cardiomyocytes. Atrial natriuretic peptide (ANP) transcriptional activity was also pressed in the presence of the 14-3-3 inhibitor under these same conditions. Taken together, these data suggest that the 14-3-3 inhibitor peptide is able to affect dimerization of 14-3-3, revealing a key regulatory point in the signaling of cardiac hypertrophy. Information from these results may provide a promising point of therapeutic intervention in the progression of heart disease due to cardiomyocyte hypertrophy.