Pro-phagocytic function and structural basis of GPR84 signaling

Abstract

GPR84 is a unique orphan G protein-coupled receptor (GPCR) that can be activated by endogenous medium-chain fatty acids (MCFAs). The signaling of GPR84 is largely pro-inflammatory, which can augment inflammatory response, and GPR84 also functions as a pro-phagocytic receptor to enhance the phagocytic activities of macrophages. In this study, we first showed that the activation of GPR84 by the synthetic agonist 6-OAU could synergize with the blockade of CD47 on cancer cells to induce phagocytosis of cancer cells by macrophages. Then, we determined a high-resolution structure of the GPR84-Gi signaling complex with 6-OAU. This structure revealed a completely occluded binding pocket for 6-OAU, the molecular basis of receptor activation involving non-conserved structural motifs of GPR84, and an unusual Gi-coupling interface. Together with computational docking and simulations studies, our structure also suggested the mechanism for the high selectivity of GPR84 for MCFAs and the potential routes of ligand binding and dissociation. Our results provide a framework for understanding GPR84 signaling and developing new drugs targeting GPR84.

Signal regulatory protein beta 2 is a novel positive regulator of innate anticancer immunity

“…Another example of a pro-phagocytic receptor is the G protein-coupled receptor (GPCR), specifically GPR84. GPR84 is found to be upregulated in AML leukemic stem cells and expression of this GPR member is correlated with significantly overall survival of patients diagnosed with acute myeloid leukemia (AML) ( 14 , 15 ). In this context it is worthwhile to note that several of the other much less researched SIRP family members may also be of therapeutic interest.…”

Editorial for GPR84 pharmacology

“…However, GPR84 has a significantly broader expression pattern, including in brown adipocytes where it seems to play an important role in mitochondrial function (Sun et al, 2023). Moreover, in addition to the potential use of antagonists of GPR84 in the treatment of inflammatory conditions, such as ulcerative colitis and in liver, lung and kidney fibrosis, activators of GPR84 have been suggested to be useful agents to promote cancer cell phagocytosis (Kamber et al, 2021; Zhang et al, 2023). Since the symposium was held, perhaps the most important advances in understanding the pharmacology of GPR84 have been the publication of atomic level cryo‐Electron Microscopy structures of GPR84 bound by the synthetic agonists 6‐n‐octylaminouracil (6‐OAU; Zhang et al, 2023) and 6‐nonylpyridine‐2,4‐diol (LY‐237; Liu et al, 2023) or the MCFA 3‐hydroxylauric acid (Liu et al, 2023).…”

“…Moreover, in addition to the potential use of antagonists of GPR84 in the treatment of inflammatory conditions, such as ulcerative colitis and in liver, lung and kidney fibrosis, activators of GPR84 have been suggested to be useful agents to promote cancer cell phagocytosis (Kamber et al, 2021; Zhang et al, 2023). Since the symposium was held, perhaps the most important advances in understanding the pharmacology of GPR84 have been the publication of atomic level cryo‐Electron Microscopy structures of GPR84 bound by the synthetic agonists 6‐n‐octylaminouracil (6‐OAU; Zhang et al, 2023) and 6‐nonylpyridine‐2,4‐diol (LY‐237; Liu et al, 2023) or the MCFA 3‐hydroxylauric acid (Liu et al, 2023). These clearly show the molecular basis for the limit of the alkyl chain length of fatty acids that can bind to and activate GPR84, as well as the basis for the interaction with the receptor of the carboxylate of MCFAs and the bioisosteric head‐groups found in most synthetic GPR84 activators (Liu et al, 2023; Zhang et al, 2023).…”

“…It should be anticipated that other highly G protein‐biased GPR84 activators will also be poorly effective in promoting receptor desensitisation and it is known that the GPR84 allosteric activator PSB‐16671 (di(5,7‐difluoro‐1H‐indole‐3‐yl)methane) also fails to promote phosphorylation of residues Thr 263 and Thr 264 (Marsango & Milligan, 2024). Although DL‐175 binds within the same orthosteric pocket as 6‐n‐octylaminouracil, for which a cryoEM structure is available (Zhang et al, 2023), function of DL‐175 is not blocked by mutation of Arg 172 of the receptor to Ala, which is the case for 6‐n‐octylaminouracil and other GPR84 agonists with carboxylate bioisosteric head groups. The significance of this for the generation of signalling bias remains to be established.…”