Adaptor Protein‐2 Interaction with Arrestin Regulates GPCR Recycling and Apoptosis

Abstract

G protein-coupled receptors (GPCRs) are integral to cellular function in nearly all physiologic and many pathologic processes. GPCR signaling represents an intricate balance between receptor activation, inactivation (desensitization, internalization and degradation) and resensitization (recycling and de novo synthesis). Complex formation between phosphorylated GPCRs, arrestins and an ever-increasing number of effector molecules is known to regulate cellular function. Previous studies have demonstrated that, although N-formyl peptide receptor (FPR) internalization occurs in the absence of arrestins, FPR recycling is arrestin-dependent. Furthermore, FPR stimulation in the absence of arrestins leads to receptor accumulation in perinuclear endosomes and apoptosis. In this study, we show that the interaction of GPCR-bound arrestin with adaptor protein-2 (AP-2) is a critical anti-apoptotic event. In addition, AP-2 associates with the receptor-arrestin complex in perinuclear endosomes and is required for proper post-endocytic GPCR trafficking. Finally, we observed that depletion of endogenous AP-2 results in the initiation of apoptosis upon stimulation of multiple GPCRs, including P2Y purinergic receptors and CXCR2, but not CXCR4. We propose a model in which the abnormal accumulation of internalized GPCR-arrestin complexes in recycling endosomes, resulting from defective arrestin-AP-2 interactions, leads to the specific initiation of aberrant signaling pathways and apoptosis.

Trans-Golgi Network (TGN) as a Regulatory Node for β1-Adrenergic Receptor (β1AR) Down-modulation and Recycling

“…These data suggest that arrestin-3 inhibits ␤1AR recycling through the TGN-associated mechanism. This finding is at odds with prior work, which has shown that arrestin-2 and -3 increase the recycling of the formyl peptide receptor (26,27), and may suggest that arrestins regulate the recycling of GPCRs in a receptor-specific fashion.…”

“…It is noteworthy that endocytosed CC chemokine receptor 5 was initially thought to accumulate in the perinuclear region (9), but the TGN was identified later as the perinuclear organelle where CC chemokine receptor 5 retrotranslocated (9). Interestingly, other GPCRs such as ␤2AR (19), CXCR2 (C-X-C chemokine receptor type 2 (24), somatostatin receptor 3 (25), N-formyl peptide receptor (26), and vasopressin 2A receptor (5) also accumulate in the perinuclear area after endocytosis. Thus, it is possible that these receptors might also return to the TGN after desensitization.…”

Regulation of Protease-activated Receptor 1 Signaling by the Adaptor Protein Complex 2 and R4 Subfamily of Regulator of G Protein Signaling Proteins

“…AP-2 has been shown to associate with the N-formyl peptide receptor, a GPCR, on perinuclear endosomes via ␤-arrestins to facilitate recycling (33). Intriguingly, however, depletion of endogenous AP-2 resulted in the initiation of apoptosis induced by multiple GPCR-specific ligands.…”

“…In addition, AP-2 modulates RGS protein recruitment to G q protein in response to PAR1 activation and, thereby, provides an additional mode by which GPCR signaling can be regulated. Future studies will be important to determine whether other GPCRs that associate with AP-2, such as the N-formyl peptide receptor or thromboxane A2 receptor TP␤, are regulated similarly (33,39). The precise mechanism by which AP-2 affects RGS protein recruitment to G proteins remains unclear and is an important future pursuit.…”

Contribution of a tyrosine-based motif to cellular trafficking of wild-type and truncated NPY Y1 receptors

“…This suggests that the YETI motif does play a role in the trafficking of internalized Y 1 receptors. It was recently shown that AP-2 association with the N-formyl peptide receptor (FRP)-arrestin complex in perinuclear endosomes is required for recycling of this receptor [33]. Further work is thus necessary to determine whether indeed there is a direct interaction between the AP-2 complex and the full-length activated Y 1 receptor and whether this interaction influences the route of the receptor once internalized.…”