Beschreibung:
Heart failure (HF) is the number one killer disease in the western world and new and innovative treatments are needed. Sarco(endo)plasmic reticulum Ca 2+ -ATPase (SERCA)-2a is a crucial, for contractile function, calcium-handling protein expressed in the mammalian myocardium and its downregulation is one of the molecular hallmarks of chronic HF. Its activation is part of the signaling mechanism by which the β 1 -adrenergic receptors (ARs) increase cardiac contractility. Agonist-bound β 1 ARs however, like most G protein-coupled receptors (GPCRs), undergo functional desensitization/internalization due to the actions of βarrestin1 or -2. These two arrestins are universal GPCR adapter proteins, mediating G protein-independent signaling via multi-protein scaffolding, and, among the cellular processes they can regulate, is protein SUMO (small ubiquitin-like modifier)-ylation, which generally increases protein stability/levels. In the heart, βarrestin1 appears detrimental, whereas βarrestin2 beneficial, for structure and function post-myocardial infarction (MI). Post-MI βarrestin1 knockout mice also display elevated SERCA2a activity and better contractility than post-MI wild type mice. In addition, reduced cardiac SERCA2a SUMOylation is known to underlie its downregulation in HF, decreasing cardiac contractility. Thus, in the present study, we sought to investigate a potential involvement of cardiac β 1 AR-activated βarrestins in regulation of SERCA2a SUMOylation and activity. By studying individual βarrestin knockout heart extracts, we found that βarrestin2, but not βarrestin1, interacts with SERCA2a in the mouse heart in vivo, promoting the latter`s SUMOylation and activity. This interaction is direct, as indicated by pull-down and FRET experiments. Finally, via in vitro studies in the cardiomyocyte-like cell line H9c2, we found that this interaction is both β 1 AR-, and beta-agonist-specific, and leads to increased Ubc9-dependent SERCA2a SUMOylation, which, in turn, acutely enhances SERCA2a activity in H9c2 cells. These results suggest that βarrestin2, presumed to also decrease cardiac function by desensitizing βARs, may actually (directly) enhance cardiac contractility, thereby opposing βarrestin1 in that regard.