The PDZ-binding motif of the β2-adrenoceptor is essential for physiologic signaling and trafficking in cardiac myocytes

beta(1)- and beta(2)-adrenergic receptors (AR) regulate cardiac myocyte function through distinct signaling pathways. In addition to regulating cardiac rate and contractility, beta(1)AR and beta(2)AR may play different roles in the pathogenesis of heart failure. Studies on neonatal cardiac myocytes from beta(1)AR and beta(2)AR knockout mice suggest that subtype-specific signaling is determined by subtype-specific membrane targeting and trafficking. Stimulation of beta(2)ARs has a biphasic effect on contraction rate, with an initial increase followed by a sustained G(i)-dependent decrease. Recent studies show that a PDZ domain-binding motif at the carboxyl terminus of human beta(2)AR interacts with ezrin-binding protein 50/sodiumhydrogen exchanger regulatory factor, a PDZ-domain-containing protein. The human beta(2)AR carboxyl terminus also binds to N-ethylmaleimide-sensitive factor, which does not contain a PDZ domain. We found that mutation of the three carboxyl-terminal amino acids in the mouse beta(2)AR (beta(2)AR-AAA) disrupts recycling of the receptor after agonist-induced internalization in cardiac myocytes. Nevertheless, stimulation of the beta(2)AR-AAA produced a greater contraction rate increase than that of the wild-type beta(2)AR. This enhanced stimulation of contraction rate can be attributed in part to the failure of the beta(2)AR-AAA to couple to G(i). We also observed that coupling of endogenous, wild-type beta(2)AR to Gi in beta(1)AR knockout myocytes is inhibited by treatment with a membrane-permeable peptide representing the beta(2)AR carboxyl terminus. These studies demonstrate that association of the carboxyl terminus of the beta(2)AR with ezrin-binding protein 50/sodiumhydrogen exchanger regulatory factor, N-ethylmaleimide-sensitive factor, or some related proteins dictates physiologic signaling specificity and trafficking in cardiac myocytes.