N-Ethylmaleimide-Sensitive Factor Regulates β2 Adrenoceptor Trafficking and Signaling in Cardiomyocytes

Abstract

Recycling of G protein-coupled receptors determines the functional resensitization of receptors and is implicated in switching beta2 adrenoceptor (beta2AR) G protein specificity in cardiomyocytes. The human beta2AR carboxyl end binds to the N-ethylmaleimide-sensitive factor (NSF), an ATPase integral to membrane trafficking machinery. It is interesting that the human beta2AR (hbeta2AR) carboxyl end pulled down NSF from mouse heart lysates, whereas the murine one did not. Despite this difference, both beta2ARs exhibited substantial agonist-induced internalization, recycling, and Gi coupling in cardiomyocytes. The hbeta2AR, however, displayed faster rates of agonist-induced internalization and recycling compared with the murine beta2AR (mbeta2AR) and a more profound Gi component in its contraction response. Replacing the mbeta2AR proline (-1) with a leucine generated a gain-of-function mutation, mbeta2AR-P417L, with a rescued ability to bind NSF, faster internalization and recycling than the mbeta2AR, and a significant enhancement in Gi signaling, which mimics the hbeta2AR. Selective disruption of the mbeta2AR-P417L binding to NSF inhibited the receptor coupling to Gi. Mean-while, inhibiting NSF with N-ethylmaleimide blocked the mbeta2AR recycling after agonist-induced endocytosis. Expressing the NSF-E329Q mutant lacking ATPase activity inhibited the mbeta2AR coupling to Gi in cardiomyocytes. Our results revealed a dual regulation on hbeta2AR trafficking and signaling by NSF through direct binding to cargo receptor and its ATPase activity and uncovered an unprecedented role for the receptor binding to NSF in regulating G protein specificity that has diverged between mouse and human beta2ARs.