Post-translational allosteric activation of the P2X(7) receptor through glycosaminoglycan chains of CD44 proteoglycans

Here, we present evidence for the positive allosteric modulation of the P2X(7) receptor through glycosaminoglycans (GAGs) in CHO (cell line derived from the ovary of the Chinese hamster) cells. The marked potentiation of P2X(7) activity through GAGs in the presence of non-saturating agonists concentrations was evident with the endogenous expression of the receptor in CHO cells. The presence of GAGs on the surface of CHO cells greatly increased the sensitivity to adenosine 5′-triphosphate and changed the main P2X(7) receptor kinetic parameters EC(50), Hill coefficient and E(max). GAGs decreased the allosteric inhibition of P2X(7) receptor through Mg(2+). GAGs activated P2X(7) receptor-mediated cytoplasmic Ca(2+) influx and pore formation. Consequently, wild-type CHO-K1 cells were 2.5-fold more sensitive to cell death induced through P2X(7) agonists than mutant CHO-745 cells defective in GAGs biosynthesis. In the present study, we provide the first evidence that the P2X(7) receptor interacts with CD44 on the CHO-K1 cell surface. Thus, these data demonstrated that GAGs positively modulate the P2X(7) receptor, and sCD44 is a part of a regulatory positive feedback loop linking P2X(7) receptor activation for the intracellular response mediated through P2X(7) receptor stimulation.