Linkage of β1-adrenergic stimulation to apoptotic heart cell death through protein kinase A–independent activation of Ca2+/calmodulin kinase II

Abstract

β1-adrenergic receptor (β1AR) stimulation activates the classic cAMP/protein kinase A (PKA) pathway to regulate vital cellular processes from the change of gene expression to the control of metabolism, muscle contraction, and cell apoptosis. Here we show that sustained β1AR stimulation promotes cardiac myocyte apoptosis by activation of Ca2+/calmodulin kinase II (CaMKII), independently of PKA signaling. β1AR-induced apoptosis is resistant to inhibition of PKA by a specific peptide inhibitor, PKI14-22, or an inactive cAMP analogue, Rp-8-CPT-cAMPS. In contrast, the β1AR proapoptotic effect is associated with non–PKA-dependent increases in intracellular Ca2+ and CaMKII activity. Blocking the L-type Ca2+ channel, buffering intracellular Ca2+, or inhibiting CaMKII activity fully protects cardiac myocytes against β1AR-induced apoptosis, and overexpressing a cardiac CaMKII isoform, CaMKII-δC, markedly exaggerates the β1AR apoptotic effect. These findings indicate that CaMKII constitutes a novel PKA-independent linkage of β1AR stimulation to cardiomyocyte apoptosis that has been implicated in the overall process of chronic heart failure.