Myofibril growth during cardiac hypertrophy is regulated through dual phosphorylation and acetylation of the actin capping protein CapZ

The mechanotransduction signaling pathways initiated in heart muscle by increased mechanical loading are known to lead to long-term transcriptional changes and hypertrophy, but the rapid events for adaptation at the sarcomeric level are not fully understood. The goal of this study was to test the hypothesis that actin filament assembly during cardiomyocyte growth is regulated by post-translational modifications (PTMs) of CapZ beta 1. In rapidly hypertrophying neonatal rat ventricular myocytes (NRVMs) stimulated by phenylephrine (PE), two-dimensional gel electrophoresis (2DGE) of CapZ beta 1 revealed a shift toward more negative charge. Consistent with this, mass spectrometry identified CapZ beta 1 phosphorylation on serine-204 and acetylation on lysine-199, two residues which are near the actin binding surface of CapZ beta 1. Ectopic expression of dominant negative PKC epsilon (dnPKC epsilon) in NRVMs blunted the PE-induced increase in CapZ dynamics, as evidenced by the kinetic constant (Kfrap) of fluorescence recovery after photobleaching (FRAP), and concomitantly reduced phosphorylation and acetylation of CapZ beta 1. Furthermore, inhibition of class I histone deacetylases (HDACs) increased lysine-199 acetylation on CapZ beta l, which increased Kfrap of CapZ and stimulated actin dynamics. Finally, we show that PE treatment of NRVMs results in decreased binding of HDAC3 to myofibrils, suggesting a signal-dependent mechanism for the regulation of sarcomere-associated CapZ beta 1 acetylation. Taken together, this dual regulation through phosphorylation and acetylation of CapZ beta 1 provides a novel model for the regulation of myofibril growth during cardiac hypertrophy. (C) 2016 Published by Elsevier Inc.