Phosphoinositide 3-kinase regulates β2-adrenergic receptor endocytosis by AP-2 recruitment to the receptor/β-arrestin complex

Internalization of β-adrenergic receptors (βARs) occurs by the sequential binding of β-arrestin, the clathrin adaptor AP-2, and clathrin. D-3 phosphoinositides, generated by the action of phosphoinositide 3-kinase (PI3K) may regulate the endocytic process; however, the precise molecular mechanism is unknown. Here we demonstrate that βARKinase1 directly interacts with the PIK domain of PI3K to form a cytosolic complex. Overexpression of the PIK domain displaces endogenous PI3K from βARK1 and prevents βARK1-mediated translocation of PI3K to activated β2ARs. Furthermore, disruption of the βARK1/PI3K interaction inhibits agonist-stimulated AP-2 adaptor protein recruitment to the β2AR and receptor endocytosis without affecting the internalization of other clathrin dependent processes such as internalization of the transferrin receptor. In contrast, AP-2 recruitment is enhanced in the presence of D-3 phospholipids, and receptor internalization is blocked in presence of the specific phosphatidylinositol-3,4,5-trisphosphate lipid phosphatase PTEN. These findings provide a molecular mechanism for the agonist-dependent recruitment of PI3K to βARs, and support a role for the localized generation of D-3 phosphoinositides in regulating the recruitment of the receptor/cargo to clathrin-coated pits

Cardiac hypertrophy and altered {beta}-adrenergic signaling in transgenic mice expressing the amino terminus of {beta}ARK1

The G protein-coupled receptor (GPCR) kinase, {beta}-adrenergic receptor ({beta}AR) kinase ({beta}ARK1) is elevated in heart failure, however its role is not fully understood. {beta}ARK1 contains several domains capable of protein-protein interactions that may play critical roles in the regulation of GPCR signaling. In this study, we developed a novel line of transgenic mice that express an amino-terminal peptide of {beta}ARK1, comprised of amino acid residues 50-145 ({beta}ARKnt), in the heart, to determine if this domain has any functional significance in vivo. Surprisingly, the {beta}ARKnt transgenic mice presented with cardiac hypertrophy. Our data suggest that the phenotype was driven via an enhanced {beta}AR system, as {beta}ARKnt mice had elevated cardiac {beta}AR density. Moreover, administration of a {beta}AR antagonist reversed hypertrophy in these mice. Interestingly, signaling through the {beta}AR in response to agonist stimulation was not enhanced in these mice. Thus, the amino terminus of {beta}ARK1 appears critical for normal {beta}AR regulation in vivo, and further supports the hypothesis that {beta}ARK1 plays a key role in normal and compromised cardiac GPCR signaling

Intermittent pressure overload triggers hypertrophy-independent cardiac dysfunction and vascular rarefaction

For over a century, there has been intense debate as to the reason why some cardiac stresses are pathological and others are physiological. One long-standing theory is that physiological overloads such as exercise are intermittent, while pathological overloads such as hypertension are chronic. In this study, we hypothesized that the nature of the stress on the heart, rather than its duration, is the key determinant of the maladaptive phenotype. To test this, we applied intermittent pressure overload on the hearts of mice and tested the roles of duration and nature of the stress on the development of cardiac failure. Despite a mild hypertrophic response, preserved systolic function, and a favorable fetal gene expression profile, hearts exposed to intermittent pressure overload displayed pathological features. Importantly, intermittent pressure overload caused diastolic dysfunction, altered β-adrenergic receptor (βAR) function, and vascular rarefaction before the development of cardiac hypertrophy, which were largely normalized by preventing the recruitment of PI3K by βAR kinase 1 to ligand-activated receptors. Thus stress-induced activation of pathogenic signaling pathways, not the duration of stress or the hypertrophic growth per se, is the molecular trigger of cardiac dysfunction