Individual phosphorylation sites at the C-terminus of the apelin receptor play different roles in signal transduction

• Published in: Redox biology Vol. 36; p. 101629
• Main Authors: Chen, Jing, Chen, Xiaoyu, Li, Sheng, Jiang, Yunlu, Mao, Huiling, Zhang, Rumin, Ji, Bingyuan, Yan, Maocai, Cai, Xin, Wang, Chunmei
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01-09-2020; Elsevier
• Subjects: Apelin receptor (APJ); Bioluminescence resonance energy transfer (BRET); Internalization; Mass spectrometry; Phosphorylation; Research Paper; Signal transduction; Signal transduction; Phosphorylation; Bioluminescence resonance energy transfer (BRET); Apelin receptor (APJ); Mass spectrometry; Internalization
• ISSN: 2213-2317; 2213-2317
• DOI: 10.1016/j.redox.2020.101629

The apelin and Elabela proteins constitute a spatiotemporal double-ligand system that controls apelin receptor (APJ) signal transduction. Phosphorylation of multiple sites within the C-terminus of APJ is essential for the recruitment of β-arrestins. We sought to determine the precise mechanisms by which apelin and Elabela promote APJ phosphorylation, and to elucidate the influence of β-arrestin phosphorylation on G-protein-coupled receptor (GPCR)/β-arrestin-dependent signaling. We used techniques including mass spectrometry (MS), mutation analysis, and bioluminescence resonance energy transfer (BRET) to evaluate the role of phosphorylation sites in APJ-mediated G-protein-dependent and β-dependent signaling. Phosphorylation of APJ occurred at five serine residues in the C-terminal region (Ser335, Ser339, Ser345, Ser348 and Ser369). We also identified two phosphorylation sites in β-arrestin1 and three in β-arrestin2, including three previously identified residues (Ser412, Ser361, and Thr383) and two new sites, Tyr47 in β-arrestin1 and Tyr48 in β-arrestin2. APJ mutations did not affect the phosphorylation of β-arrestins, but it affects the β-arrestin signaling pathway, specifically Ser335 and Ser339. Mutation of Ser335 decreased the ability of the receptor to interact with β-arrestin1/2 and AP2, indicating that APJ affects the β-arrestin signaling pathway by stimulating Elabela. Mutation of Ser339 abolished the capability of the receptor to interact with GRK2 and β-arrestin1/2 upon stimulation with apelin-36, and disrupted receptor internalization and β-arrestin-dependent ERK1/2 activation. Five peptides act on distinct phosphorylation sites at the APJ C-terminus, differentially regulating APJ signal transduction and causing different biological effects. These findings may facilitate screening for drugs to treat cardiovascular and metabolic diseases.