The pyrimidinergic P2Y 6 receptor mediates a novel release of proinflammatory cytokines and chemokines in monocytic cells stimulated with UDP

Abstract

The human P2Y 6 receptor (hP2Y 6) is a member of the G protein-coupled pyrimidinergic P2 receptor family that responds specifically to the extracellular nucleotide uridine diphosphate (UDP). Recently, the hP2Y 6 receptor has been reported to mediate monocyte IL-8 production in response to UDP or lipopolysaccharide (LPS), but the role of hP2Y 6 in regulating other pro-inflammatory cytokines or mediators is largely unknown. We demonstrate here that UDP specifically induces soluble TNF-α and IL-8 production in a promonocytic U937 cell line stably transfected with hP2Y 6. However, we did not detect IL-1α, IL-1β, IL-6, IL-10, IL-18, and PGE 2 in the conditioned media from the same cell line. These results distinguish UDP/P2Y 6 signaling from LPS signaling. Interestingly, UDP induces the production of IL-8, but not TNF-α, in human astrocytoma 1321N1 cell lines stably transfected with hP2Y 6. Therefore, the immune effect of UDP/P2Y 6 signaling on the production of proinflammatory cytokines is selective and dependent on cell types. We further identify that UDP can also induce the production of proinflammatory chemokines MCP-1 and IP-10 in hP2Y 6 transfected promonocytic U937 cell lines, but not astrocytoma 1321N1 cell lines stably transfected with hP2Y 6. From the Taqman analysis, UDP stimulation significantly upregulates the mRNA levels of IL-8, IP-10, and IL-1β, but not TNF-α. Taken together, these new findings expand the pro-inflammatory biology of UDP mediated by the P2Y 6 receptor.