ABSTRACT: RATIONALE:Ca2+/calmodulin-dependent protein kinase (CaMK)II is a multifunctional kinase involved in vital cellular processes such as Ca(2+) handling and cell fate regulation. In mammalian heart, 2 primary CaMKII isoforms, deltaB and deltaC, localize in nuclear and cytosolic compartments, respectively. Although previous studies have established an essential role of CaMKII-deltaC in cardiomyocyte apoptosis, the functional role of the more abundant isoform, CaMKII-deltaB, remains elusive. OBJECTIVE:Here, we determined the potential role of CaMKII-deltaB in regulating cardiomyocyte viability and explored the underlying mechanism. METHODS AND RESULTS:In cultured neonatal rat cardiomyocytes, the expression of CaMKII-deltaB and CaMKII-deltaC was inversely regulated in response to H2O2-induced oxidative stress with a profound reduction of the former and an increase of the later. Similarly, in vivo ischemia/reperfusion (IR) led to an opposite regulation of these CaMKII isoforms in a rat myocardial IR model. Notably, overexpression of CaMKII-deltaB protected cardiomyocytes against oxidative stress-, hypoxia-, and angiotensin II-induced apoptosis, whereas overexpression of its cytosolic counterpart promoted apoptosis. Using cDNA microarray, real-time PCR and Western blotting, we demonstrated that overexpression of CaMKII-deltaB but not CaMKII-deltaC elevated expression of heat shock protein (HSP)70 family members, including inducible (i)HSP70 and its homolog (Hst70). Moreover, overexpression of CaMKII-deltaB led to phosphorylation and activation of heat shock factor (HSF)1, the primary transcription factor responsible for HSP70 gene regulation. Importantly, gene silencing of iHSP70, but not Hst70, abolished CaMKII-deltaB-mediated protective effect, indicating that only iHSP70 was required for CaMKII-deltaB elicited antiapoptotic signaling. CONCLUSIONS:We conclude that cardiac CaMKII-deltaB and CaMKII-deltaC were inversely regulated in response to oxidative stress and IR injury, and that in contrast to CaMKII-deltaC, CaMKII-deltaB serves as a potent suppressor of cardiomyocyte apoptosis triggered by multiple death-inducing stimuli via phosphorylation of HSF1 and subsequent induction of iHSP70, marking both CaMKII-delta isoforms as promising therapeutic targets for the treatment of ischemic heart disease.
