S-geranylgeranyl-L-glutathione is a ligand for human B-cell confinement receptor P2RY8

Germinal centers (GCs) are important sites for antibody diversification and affinity maturation and are also a common origin of B-cell malignancies. Although made up of motile cells, GCs are tightly confined within B-cell follicles. The cues promoting GC B-cell confinement are incompletely understood. P2RY8 is a Gα13-coupled receptor that mediates migration inhibition and growth regulation of B cells in lymphoid tissues(4,6). P2RY8 is frequently mutated in GC-derived diffuse large B-cell lymphoma (DLBCL) and Burkitt lymphoma (BL)(1–5), and the ligand for this receptor has been undefined. In a search for P2RY8 ligands, we found P2RY8 bioactivity in bile and in culture supernatants of several cell lines. Using a seven-step biochemical fractionation procedure and a drop-out mass spectrometry approach, we identified a previously undescribed biomolecule, S-geranylgeranyl-L-glutathione (Ggg) as a potent P2RY8 ligand. Ggg was detectable in lymphoid tissues in the nanomolar range. Ggg inhibited chemokine-mediated migration of human GC B cells and follicular helper T cells and antagonized induction of pAkt in GC B cells. We found that gamma-glutamyltransferase-5 (Ggt5) metabolized Ggg to a form inactive on the receptor. Ggt5 was highly expressed by follicular dendritic cells (FDCs). Over-expression of this enzyme disrupted the ability of P2RY8 to promote B-cell confinement to GCs, indicating that it establishes a Ggg gradient in lymphoid tissues. This work defines Ggg as an intercellular signaling molecule involved in organizing and controlling GC responses. As well as DLBCL and BL the P2RY8 locus is modified in several other cancers and we speculate that Ggg has organizing and growth regulatory activities in multiple human tissues.