The internalization of G protein-coupled receptors (GPCRs) is a key process limiting cell surface receptor activity, and possibly promoting their intracellular signaling. Dysregulation of this process has been implicated in various diseases. This process is known to result from the recruitment of β-arrestins (βarrs) to the active receptors, although some receptors do not require this for unclear reasons. Here, we clarify the importance of βarrs in the internalization of 60 different GPCRs. We show that βarrs are essential for agonist-induced internalization for only a third of the receptors, half of the GPCRs being partially dependent on βarrs or even independent for endocytosis. Furthermore, we develop several Förster resonance energy transfer (FRET)-based molecular interaction assays to elucidate the molecular mechanism of internalization of the glucagon-like peptide-1 receptor (GLP-1R). We show that GLP-1R internalizes mainly by a βarr-independent mechanism involving the direct binding of the clathrin adaptor protein complex-2 to the receptor. However, when this adaptor protein complex-2-dependent mechanism is affected, the GLP-1R internalization becomes βarr-dependent. It shows that multiple mechanisms regulate the internalization of a specific receptor. Our data highlight the various processes used to control cell surface GPCRs, and open novel possibilities to specifically control their signaling processes.
© 2025. The Author(s).

Internalization plays a crucial role in regulating the density of cell surface receptors and has been demonstrated to regulate intracellular signaling. Dysregulation of this process has been implicated in various diseases. The vast majority of GPCRs were considered to adopt one way for internalization. We challenged this conventional view by showing that multiple pathways converge to regulate the internalization of a specific receptor, based on an unparalleled characterization of 60 GPCR internalization profiles, both in the absence and presence of individual β-arrestins (βarrs). Furthermore, we revealed the internalization mechanism of the glucagon-like peptide-1 receptor (GLP-1R), a class B GPCR pivotal in promoting insulin secretion from pancreatic beta cells to maintain glucose homeostasis. GLP-1R can undergo agonist-induced internalization without βarrs, but can recruit and form stable complexes with βarrs. We found that GLP-1R recruits clathrin adaptor protein-2 for agonist-induced internalization in both βarr-dependent and -independent manners. These results provide a valuable resource for GPCR signaling and reveal the plasticity of different GPCRs to employ or not βarrs in the clathrin-mediated internalization.

Glioblastoma (GBM) is the most common and aggressive primary brain malignancy. Adhesion G protein-coupled receptors (aGPCRs) have attracted interest for their potential as treatment targets. Here, we show that CD97 (ADGRE5) is the most promising aGPCR target in GBM, by virtue of its de novo expression compared to healthy brain tissue. CD97 knockdown or knockout significantly reduces the tumor initiation capacity of patient-derived GBM cultures (PDGCs) in vitro and in vivo. We find that CD97 promotes glycolytic metabolism via the mitogen-activated protein kinase (MAPK) pathway, which depends on phosphorylation of its C terminus and recruitment of β-arrestin. We also demonstrate that THY1/CD90 is a likely CD97 ligand in GBM. Lastly, we show that an anti-CD97 antibody-drug conjugate selectively kills tumor cells in vitro. Our studies identify CD97 as a regulator of tumor metabolism, elucidate mechanisms of receptor activation and signaling, and provide strong scientific rationale for developing biologics to target it therapeutically in GBM.Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.

The selectivity of drugs for G protein-coupled receptor (GPCR) signaling pathways is crucial for their therapeutic efficacy. Different agonists can cause receptors to recruit effector proteins at varying levels, thus inducing different signaling responses, called signaling bias. Although several GPCR-biased drugs are currently being developed, only a limited number of biased ligands have been identified regarding their signaling bias for the M1 muscarinic acetylcholine receptor (M1mAChR), and the mechanism is not yet well understood. In this study, we utilized bioluminescence resonance energy transfer (BRET) assays to compare the efficacy of six agonists in inducing Gαq and β-arrestin2 binding to M1mAChR. Our findings reveal notable variations in agonist efficacy in the recruitment of Gαq and β-arrestin2. Pilocarpine preferentially promoted the recruitment of β-arrestin2 (∆∆RAi = -0.5), while McN-A-343 (∆∆RAi = 1.5), Xanomeline (∆∆RAi = 0.6), and Iperoxo (∆∆RAi = 0.3) exhibited a preference for the recruitment of Gαq. We also used commercial methods to verify the agonists and obtained consistent results. Molecular docking revealed that certain residues (e.g., Y404, located in TM7 of M1mAChR) could play crucial roles in Gαq signaling bias by interacting with McN-A-343, Xanomeline, and Iperoxo, whereas other residues (e.g., W378 and Y381, located in TM6) contributed to β-arrestin recruitment by interacting with Pilocarpine. The preference of activated M1mAChR for different effectors may be due to significant conformational changes induced by biased agonists. By characterizing bias towards Gαq and β-arrestin2 recruitment, our study provides insights into M1mAChR signaling bias.