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Somatic mutations in P2RY8 that promote B cell growth and migration are common in lymphomas. He et al. describe germline loss-of-function P2RY8 variants in SLE and uncover novel functions of P2RY8 in immunological tolerance through restraining plasma cell development and promoting B cell–negative selection., B cell self-tolerance is maintained through multiple checkpoints, including restraints on intracellular signaling and cell trafficking. P2RY8 is a receptor with established roles in germinal center (GC) B cell migration inhibition and growth regulation. Somatic P2RY8 variants are common in GC-derived B cell lymphomas. Here, we identify germline novel or rare P2RY8 missense variants in lupus kindreds or the related antiphospholipid syndrome, including a “de novo” variant in a child with severe nephritis. All variants decreased protein expression, F-actin abundance, and GPCR-RhoA signaling, and those with stronger effects increased AKT and ERK activity and cell migration. Remarkably, P2RY8 was reduced in B cell subsets from some SLE patients lacking P2RY8 gene variants. Low P2RY8 correlated with lupus nephritis and increased age-associated B cells and plasma cells. By contrast, P2RY8 overexpression in cells and mice restrained plasma cell development and reinforced negative selection of DNA-reactive developing B cells. These findings uncover a role of P2RY8 in immunological tolerance and lupus pathogenesis., Graphical Abstract

P2RY8 promotes the confinement and growth regulation of germinal center (GC) B cells, and loss of human P2RY8 is associated with B cell lymphomagenesis. The metabolite S-geranylgeranyl-l-glutathione (GGG) is a P2RY8 ligand. The mechanisms controlling GGG distribution are poorly understood. Here, we show that gamma-glutamyltransferase-5 (Ggt5) expression in stromal cells was required for GGG catabolism and confinement of P2RY8-expressing cells to GCs. We identified the ATP-binding cassette subfamily C member 1 (Abcc1) as a GGG transporter and showed that Abcc1 expression by hematopoietic cells was necessary for P2RY8-mediated GC confinement. Furthermore, we discovered that P2RY8 and GGG negatively regulated trafficking of B and T cells to the bone marrow (BM). P2RY8 loss-of-function human T cells increased their BM homing. By defining how GGG distribution was determined and identifying sites of P2RY8 activity, this work helps establish how disruptions in P2RY8 function contribute to lymphomagenesis and other disease states.

Germinal centres are important sites for antibody diversification and affinity maturation, and are also a common origin of B cell malignancies. Despite being made up of motile cells, germinal centres are tightly confined within B cell follicles. The cues that promote this confinement are incompletely understood. P2RY8 is a Gα13-coupled receptor that mediates the inhibition of migration and regulates the growth of B cells in lymphoid tissues1,2. P2RY8 is frequently mutated in germinal-centre B cell-like diffuse large B cell lymphoma (GCB-DLBCL) and Burkitt lymphoma1,3-6, and the ligand for this receptor has not yet been identified. Here we perform a search for P2RY8 ligands and find P2RY8 bioactivity in bile and in culture supernatants of several mouse and human cell lines. Using a seven-step biochemical fractionation procedure and a drop-out mass spectrometry approach, we show that a previously undescribed biomolecule, S-geranylgeranyl-L-glutathione (GGG), is a potent P2RY8 ligand that is detectable in lymphoid tissues at the nanomolar level. GGG inhibited the chemokine-mediated migration of human germinal-centre B cells and T follicular helper cells, and antagonized the induction of phosphorylated AKT in germinal-centre B cells. We also found that the enzyme gamma-glutamyltransferase-5 (GGT5), which was highly expressed by follicular dendritic cells, metabolized GGG to a form that did not activate the receptor. Overexpression of GGT5 disrupted the ability of P2RY8 to promote B cell confinement to germinal centres, which indicates that GGT5 establishes a GGG gradient in lymphoid tissues. This work defines GGG as an intercellular signalling molecule that is involved in organizing and controlling germinal-centre responses. As the P2RY8 locus is modified in several other types of cancer in addition to GCB-DLBCL and Burkitt lymphoma, we speculate that GGG might have organizing and growth-regulatory roles in multiple human tissues.

P2RY8 promotes the confinement and growth regulation of germinal center (GC) B cells, and loss of human P2RY8 is associated with B cell lymphomagenesis. The metabolite