Calcineurin B homologous protein 3 negatively regulates cardiomyocyte hypertrophy via inhibition of glycogen synthase kinase 3 phosphorylation

Cardiac hypertrophy is a leading cause of serious heart diseases. Although many signaling molecules are involved in hypertrophy, the functions of some proteins in this process are still unknown. Calcineurin B homologous protein 3 (CHP3)/tescalcin is an EF-hand Ca2+-binding protein that is abundantly expressed in the heart; however, the function of CHP3 is unclear. Here, we aimed to identify the cardiac functions of CHP3. CHP3 was expressed in hearts at a wide range of developmental stages and was specifically detected in neonatal rat ventricular myocytes (NRVMs) but not in cardiac fibroblasts in culture. Moreover, knockdown of CHP3 expression using adenoviral-based RNA interference in NRVMs resulted in enlargement of cardiomyocyte size, concomitant with increased expression of a pathological hypertrophy marker ANP. This same treatment elevated glycogen synthase kinase (GSK3 alpha/beta) phosphorylation, which is known to inhibit GSK3 function. In contrast, CHP3 overexpression blocked the insulin-induced phosphorylation of GSK3 alpha/beta without affecting the phosphorylation of Akt, which is an upstream kinase of GSK3 alpha/beta, in HEK293 cells, and it inhibited both IGF-1-induced phosphorylation of GSK3 beta and cardiomyocyte hypertrophy in NRVMs. Co-immunoprecipitation experiments revealed that GSK3 beta interacted with CHP3. However, a Ca2+-binding-defective mutation of CHP3 (CHP3-D123A) also interacted with GSK3 beta and had the same inhibitory effect on GSK3 alpha/beta phosphorylation, suggesting that the action of CHP3 was independent of Ca2+. These findings suggest that CHP3 functions as a novel negative regulator of cardiomyocyte hypertrophy via inhibition of GSK3 alpha/beta phosphorylation and subsequent enzymatic activation of GSK3 alpha/beta. (C) 2015 Elsevier Ltd. All rights reserved.