The Nuclear δB Isoform of Ca2+/Calmodulin-dependent Protein Kinase II Regulates Atrial Natriuretic Factor Gene Expression in Ventricular Myocytes

Abstract

Cultured neonatal ventricular myocytes display features of myocardial hypertrophy including increased cell size, myofilament organization, and reexpression of the embryonic gene for atrial natriuretic factor (ANF). KN-93, an inhibitor of multifunctional Ca2+/calmodulin-dependent protein kinase (CaM kinase II), blocked the induction of these responses by the alpha1-adrenergic receptor agonist phenylephrine, whereas its inactive analog KN-92 did not. To directly determine whether CaM kinase II could regulate ANF gene expression, we transiently expressed each of three isoforms of CaM kinase II (alpha, deltaB, and deltaC) along with an ANF promoter/luciferase reporter gene. The deltaB isoform markedly increased luciferase gene expression, whereas comparable levels of the deltaC and alpha isoforms were ineffective. Expression of deltaB-CaM kinase II also potentiated phenylephrine-mediated ANF gene expression, and this effect was blocked by KN-93 but not by KN-92. The ability of deltaB-CaM kinase II to transactivate a truncated ANF promoter, containing a serum response element (SRE) required for phenylephrine-inducible gene expression, was lost when this SRE was mutated. The deltaB isoform of CaM kinase II has been shown to exhibit nuclear localization. Coexpression of the non-nuclear deltaC or alpha isoforms, which can form multimers with the deltaB isoform, prevented the nuclear localization of deltaB-CaM kinase II and also blocked its effects on ANF reporter gene and protein expression. In addition, a chimeric alpha-CaM kinase II which contains the nuclear localization signal of the deltaB isoform was able to induce ANF reporter gene expression, albeit to a lesser extent than deltaB-CaM kinase II. These data are the first to assign a function to the deltaB isoform of CaM kinase II and to link its nuclear localization to subsequent activation of cardiac gene expression.