Adenylyl Cyclase Subtype–Specific Compartmentalization

Abstract

Rationale: Adenylyl cyclase (AC) represents one of the principal molecules in the β-adrenergic receptor signaling pathway, responsible for the conversion of ATP to the second messenger, cAMP. AC types 5 (AC V ) and 6 (AC VI ) are the 2 main isoforms in the heart. Although highly homologous in sequence, these 2 proteins play different roles during the development of heart failure. Caveolin-3 is a scaffolding protein, integrating many intracellular signaling molecules in specialized areas called caveolae. In cardiomyocytes, caveolin is located predominantly along invaginations of the cell membrane known as t-tubules. Objective: We take advantage of AC V and AC VI knockout mouse models to test the hypothesis that there is distinct compartmentalization of these isoforms in ventricular myocytes. Methods and Results: We demonstrate that AC V and AC VI isoforms exhibit distinct subcellular localization. The AC VI isoform is localized in the plasma membrane outside the t-tubular region and is responsible for β 1 -adrenergic receptor signaling–mediated enhancement of the L-type Ca 2+ current ( I Ca,L ) in ventricular myocytes. In contrast, the AC V isoform is localized mainly in the t-tubular region where its influence on I Ca,L is restricted by phosphodiesterase. We further demonstrate that the interaction between caveolin-3 with AC V and phosphodiesterase is responsible for the compartmentalization of AC V signaling. Conclusions: Our results provide new insights into the compartmentalization of the 2 AC isoforms in the regulation of I Ca,L in ventricular myocytes. Because caveolae are found in most mammalian cells, the mechanism of β- adrenergic receptor and AC compartmentalization may also be important for β-adrenergic receptor signaling in other cell types.