P2Z/P2X7 receptor-dependent apoptosis of dendritic cells

Macrophages andthymocytes expressP_2Z/P2X₇nucleotide receptors that bind extracellular ATP. These receptors playa role in immune development and control of microbial infections, but their presence on dendritic cells has not been reported. Weinvestigated whether extracellular ATP could triggerP_2Z/P2X₇receptor-dependent apoptosis of dendritic cells. Apoptosis could beselectively triggered by tetrabasic ATP, since otherpurine/pyrimidine nucleotides were ineffective, and it wasmimicked by the P_2Z receptoragonist, benzoylbenzoyl ATP, and blocked by magnesium and theirreversible antagonist, oxidized ATP. RT-PCR analysis confirmed themRNA expression of theP_2Z/P2X₇receptor and the absence of P2X₁.Caspase inhibitors and cycloheximide had only a partial effect on theapoptosis, suggesting that a caspase-independent mechanism may also beoperative. Brief treatment with ATP led to an increase in theintracellular calcium concentration and permeabilization of the plasmamembrane to Lucifer yellow, which diffused throughout the dendriticcell cytosol. Other small extracellular molecules may thus attain a similar intracellular distribution, perhaps activating endogenous proteases that contribute to initiation of apoptosis.