Critical Role of Nuclear Calcium/Calmodulin-dependent Protein Kinase IIδB in Cardiomyocyte Survival in Cardiomyopathy

Calcium/calmodulin-dependent protein kinase II (CaMKII) plays a central role in cardiac contractility and heart disease. However, the specific role of alternatively spliced variants of CaMKII in cardiac disease and apoptosis remains poorly explored. Here we report that the delta B subunit of CaMKII (CaMKII delta B), which is the predominant nuclear isoform of calcium/calmodulin- dependent protein kinases in heart muscle, acts as an anti-apoptotic factor and is a novel target of the antineoplastic and cardiomyopathic drug doxorubicin (Dox(adriamycin)). Hearts of rats that develop cardiomyopathy following chronic treatment with Dox also show down-regulation of CaMKII delta B mRNA, which correlates with decreased cardiac function in vivo, reduced expression of sarcomeric proteins, and increased tissue damage associated with Dox cardiotoxicity. Overexpression of CaMKII delta B in primary cardiac cells inhibits Dox-mediated apoptosis and prevents the loss of the antiapoptotic protein Bcl-2. Specific silencing of CaMKII delta B by small interfering RNA prevents the formation of organized sarcomeres and decreases the expression of Bcl-2, which all mimic the effect of Dox. CaMKII delta B is required for GATA-4-mediated co-activation and binding to the Bcl-2 promoter. These results reveal that CaMKII delta B plays an essential role in cardiomyocyte survival and provide a mechanism for the protective role of CaMKII delta B. These results suggest that selective targeting of CaMKII in the nuclear compartment might represent a strategy to regulate cardiac apoptosis and to reduce Dox-mediated cardiotoxicity.