Phosphatidylserine exposure modulates adhesion GPCR BAI1 (ADGRB1) signaling activity

• Type of Material: Article
• Authors: Trisha Lala, Emory University; JulevaK Doan, Emory University; Hiroyuki Takatsu, Kyoto University; Criss H Hartzell, Emory University; Hye-Won Shin, Kyoto University; Randy Hall, Emory University
• Language: English
• Date: 2022-12-01
• Publisher: Elsevier Inc.
• Publication Version: Final Published Version
• Copyright Statement: © 2022 The Authors
• License: Creative Commons Attribution 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1016/j.jbc.2022.102685
• Title of Journal or Parent Work: Journal of Biological Chemistry
• Volume: 298
• Issue: 12
• Start Page: 102685
• End Page: 102685
• Grant/Funding Information: T. L. was supported by a T32 training grant in Integrative Biology; Neuroscience (grant no.: NS096050) and a T32 training grant in Translational Research in Neurology (grant no.: NS007480). These studies were supported by the National Institutes of Health grants R21-MH113166 (to R. A. H.) and R01-GM132598 (to H. C. H.). The content is solely the responsibility of the authors and does not necessarily reflect the official views of the National Institutes of Health.
• Keywords: signal transduction; Phosphatidylserines; cell culture; lipid-binding protein; dimerization; Receptors, G-Protein-Coupled; G protein–coupled receptor; synaptic; brain; engulfment; Humans; Signal Transduction; HEK293 Cells; externalization; multimerization; Thrombospondins
• Research Categories: Health Sciences, Pharmacology

Abstract

Brain-specific angiogenesis inhibitor 1 (BAI1; also called ADGRB1 or B1) is an adhesion G protein–coupled receptor known from studies on macrophages to bind to phosphatidylserine (PS) on apoptotic cells via its N-terminal thrombospondin repeats. A separate body of work has shown that B1 regulates postsynaptic function and dendritic spine morphology via signaling pathways involving Rac and Rho. However, it is unknown if PS binding by B1 has any effect on the receptor's signaling activity. To shed light on this subject, we studied G protein–dependent signaling by B1 in the absence and presence of coexpression with the PS flippase ATP11A in human embryonic kidney 293T cells. ATP11A expression reduced the amount of PS exposed extracellularly and also strikingly reduced the signaling activity of coexpressed full-length B1 but not a truncated version of the receptor lacking the thrombospondin repeats. Further experiments with an inactive mutant of ATP11A showed that the PS flippase function of ATP11A was required for modulation of B1 signaling. In coimmunoprecipitation experiments, we made the surprising finding that ATP11A not only modulates B1 signaling but also forms complexes with B1. Parallel studies in which PS in the outer leaflet was reduced by an independent method, deletion of the gene encoding the endogenous lipid scramblase anoctamin 6 (ANO6), revealed that this manipulation also markedly reduced B1 signaling. These findings demonstrate that B1 signaling is modulated by PS exposure and suggest a model in which B1 serves as a PS sensor at synapses and in other cellular contexts.