Abstract
UDP-glucose (UDPG), a glycosyl donor in the biosynthesis of carbohydrates, is an endogenous agonist of the G protein-coupled P2Y 14 receptor. RBL-2H3 mast cells endogenously express a P2Y 14 receptor at which UDPG mediates degranulation as indicated by β-hexosaminidase (HEX) release. Both UDPG and a more potent, selective 2-thio-modified UDPG analog, MRS2690 (diphosphoric acid 1-α- d-glucopyranosyl ester 2-[(2-thio)uridin-5″-yl] ester), caused a substantial calcium transient in RBL-2H3 cells, which was blocked by pertussis toxin, indicating the presence of the G i-coupled P2Y 14 receptor, supported also by quantitative detection of abundant mRNA. Expression of the closely related P2Y 6 receptor was over 100 times lower than the P2Y 14 receptor, and the P2Y 6 agonist 3-phenacyl-UDP was inactive in RBL-2H3 cells. P2Y 14 receptor agonists also induced [ 35S]GTPγS binding to RBL-2H3 cell membranes, and phosphorylation of ERK1/2, P38 and JNK. UDPG and MRS2690 concentration-dependently enhanced HEX release with EC 50 values of 1150 ± 320 and 103 ± 18 nM, respectively. The enhancement was completely blocked by pertussis toxin and significantly diminished by P2Y 14 receptor-specific siRNA. Thus, mast cells express an endogenous P2Y 14 receptor, which mediates G i-dependent degranulation and is therefore a potential novel therapeutic target for allergic conditions.
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