Abstract

We have shown previously that activation of endogenously expressed, Gα_q/11-coupled P2Y₂ nucleotide receptors with UTP reveals an intracellular Ca²⁺ response to activation of recombinant, Gα_i-coupled CXC chemokine receptor 2 (CXCR2) in human embryonic kidney cells. Here, we characterize further this cross talk and demonstrate that phospholipase C (PLC) and inositol 1,4,5-trisphosphate [Ins(1,4,5)P₃]-dependent Ca²⁺ release underlies this potentiation. The putative Ins(1,4,5)P₃ receptor antagonist 2-aminoethoxydiphenyl borane reduced the response to CXCR2 activation by interleukin-8, as did sustained inhibition of phosphatidylinositol 4-kinase with wortmannin, suggesting the involvement of phosphoinositides in the potentiation. Against a Li⁺ block of inositol monophosphatase activity, costimulation of P2Y₂ nucleotide receptors and CXCR2 caused phosphoinositide accumulation that was significantly greater than that after activation of P2Y₂ nucleotide receptors or CXCR2 alone, and was more than additive. Thus, PLC activity, as well as Ca²⁺ release, was enhanced. In these cells, agonist-mediated Ca²⁺ release was incremental in nature, suggesting that a potentiation of Ins(1,4,5)P₃ generation in the presence of coactivation of P2Y₂ nucleotide receptors and CXCR2 would be sufficient for additional Ca²⁺ release. Potentiated Ca²⁺ signaling by CXCR2 was markedly attenuated by expression of either regulator of G protein signaling 2 or the Gβγ-scavenger Gα_t1 (transducin α subunit), indicating the involvement of Gα_q and Gβγ subunits, respectively.