ADP is the endogenous agonist for both P2Y(1) and P2Y(12) receptors, which are important therapeutic targets. It was previously demonstrated that
ADP and a synthetic agonist,
2-methylthioadenosine 5'-diphosphate (
2MeSADP), can induce apoptosis by activating the human P2Y(1) receptor heterologously expressed in
astrocytoma cells. However, it was not known whether the P2Y(12) receptor behaved similarly. We demonstrated here that, unlike with the G(q)-coupled P2Y(1) receptor, activation of the G(i)-coupled P2Y(12) receptor does not induce apoptosis. Furthermore, activation of the P2Y(12) receptor by either
ADP or
2MeSADP significantly attenuates the
tumor necrosis factor alpha (
TNFalpha)-induced apoptosis in 1321N1 human
astrocytoma cells. This protective effect was blocked by the P2Y(12) receptor antagonist 2-methylthioAMP and by inhibitors of
phospholipase C (
U73122) and
protein kinase C (chelerythrin), but not by the P2Y(1) receptor antagonist
MRS2179. Toward a greater mechanistic understanding, we showed that hP2Y(12) receptor activation by 10nM
2MeSADP, activates Erk1/2, Akt, and JNK by phosphorylation. However, at a lower protective concentration of 100pM
2MeSADP, activation of the hP2Y(12) receptor involves only phosphorylated Erk1/2, but not Akt or JNK. This activation is hypothesized as the major mechanism for the protective effect induced by P2Y(12) receptor activation.
Apyrase did not affect the ability of
TNFalpha to induce apoptosis in hP2Y(12)-1321N1 cells, suggesting that the endogenous
nucleotides are not involved. These results may have important implications for understanding the signaling cascades that follow activation of P2Y(1) and P2Y(12) receptors and their opposing effects on cell death pathways.