Cell Adhesion Receptor GPR133 Couples to Gs Protein

Abstract

Adhesion G protein-coupled receptors (GPCR), with their very large and complex N termini, are thought to participate in cell-cell and cell-matrix interactions and appear to be highly relevant in several developmental processes. Their intracellular signaling is still poorly understood. Here we demonstrate that GPR133, a member of the adhesion GPCR subfamily, activates the G s protein/adenylyl cyclase pathway. The presence of the N terminus and the cleavage at the GPCR proteolysis site are not required for G protein signaling. G s protein coupling was verified by G␣ s knockdown with siRNA, overexpression of G␣ s , coexpression of the chimeric Gq s4 protein that routes GPR133 activity to the phospholipase C/inositol phosphate pathway, and missense mutation within the transmembrane domain that abolished receptor activity without changing cell surface expression. It is likely that not only GPR133 but also other adhesion GPCR signal via classical receptor/G protein-interaction.Adhesion receptors comprise the second largest subfamily of putatively G protein-coupled receptors (GPCR) 2 with more than 30 members in vertebrates (1, 2). Adhesion GPCR are characterized by long extracellular N termini, which are composed of multiple functional domains, a seven-transmembrane spanning (7TM) domain, and a cytoplasmic tail. Adhesion GPCR are believed to play a role in immune functions (3, 4), angiogenesis (5), cell polarity (6, 7), and development (8, 9). Mutations in some members of the protein family were identified as the cause of inherited developmental defects in humans such as Usher syndrome (VLGR1) (10) and bilateral frontoparietal polymicrogyria (GPR56) (11). Although there is consensus on the fact that this receptor class mediates essential cellcell and cell-matrix interactions (1, 12), the molecular mechanism of intracellular signal transduction of adhesion GPCR remains obscure.There are only a few studies on intracellular signaling mechanisms of adhesion GPCR. Latrophilin 1, the prototype of adhesion GPCR, induces intracellular Ca 2ϩ signaling upon interaction with the exogenous ligand ␣-latrotoxin (13, 14). GPR56 appears to activate the G 12/13 protein/Rho pathway after stimulation with an antibody against the ectodomain (15). BAI1 recognizes phosphatidylserine and can directly recruit a Racguanine nucleotide exchange factor (Rac-GEF) complex to mediate the uptake of apoptotic cells (16). The cytoplasmic domain of BAI2 interacts with GA-binding protein ␥, and GAbinding protein-␣/␥ or GA-binding protein-␣/␤ work as transcriptional repressors of VEGF (17). However, clear evidence of intracellular signaling for most adhesion GPCR via G proteins is still missing (12).Genetic variations in the GPR133 gene, also a member of the adhesion GPCR family, were associated with adult height (18) and the RR interval duration in electrocardiograms (19). GPR133 is expressed in CNS (20) and other tissues; its endogenous agonists and the signal transduction are unknown. Here we demonstrate that GPR133 is coupled to the G s protein/adeny...

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“…Interestingly, adhesion GPCRs frequently signal through Ga proteins. GPR56 has been reported to couple to Ga12/13 and Gaq/11 (25,27), GPR133 couples to Gas, and CD97 couples to Ga12/13 (28,47). Our study supports the idea that adhesion GPCRs also activate the classical receptor/G-protein signaling pathway.…”

Adhesion G Protein-Coupled Receptors: Signaling, Pharmacology, and Mechanisms of Activation

“…Moreover, GPR56 has been shown via coimmunoprecipitation to interact with G␣ q/11 (Little et al, 2004), which is consistent with work on other receptor types demonstrating that receptors coupling to G␣ 12/13 can also typically couple to G␣ q/11 (Takashima et al, 2008). In a similar vein, overexpression of GPR133 in various cell types has been shown to stimulate G␣ s and promote cAMP generation (Bohnekamp and Schöneberg, 2011;Gupte et al, 2012). Gpr126 has also been shown to exert actions on Schwann cells consistent with a cAMP-and G␣ s -dependent mechanism (Monk et al, 2009), and GPR114 has been shown to constitutively increase cAMP levels when overexpressed in HEK293 cells (Gupte et al, 2012).…”

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“…Without a known ligand, overexpression of an adhesion GPCR or its ␤-subunit constitutively activates specific signaling pathways that are normally stimulated by agonist activation (13,24,25). The constitutive activities of orphan receptors have been used to characterize their downstream signaling activities (26,27).…”