Pro‐apoptotic agents induce ATP release from leukemia/lymphoma tumor cells via pannexin‐1 dependent and pannexin‐1‐independent mechanism

Abstract

Extracellular ATP released from dying tumor cells treated with chemotherapeutic drugs plays a significant role in modulating antitumor immune responses. However, the mechanisms by which ATP is released from such tumor cells remain poorly defined. Physiological apoptosis induced by Fas signaling can elicit ATP release via pannexin 1 (panx1) channels gated by caspase 3/7 (casp3/7)‐mediated proteolytic cleavage of the panx1 C‐terminus. We used human Jurkat leukemia and murine EG7 lymphoma cells to test whether the pro‐apoptotic drugs doxorubicin (Dx) and staurosporine (STS) elicit the same casp3/7>; panx1>; ATP release pathway. Cells were treated with Dx or STS for 1–18 h in the presence or absence of the pan‐caspase inhibitor zVAD and then assayed for accumulation of extracellular adenine nucleotides (ANex). Apoptotic progression was monitored by accumulation of active casp3/7 and cleavage of PARP. Apoptotic progression in response to STS or Dx were characterized by similar kinetics and efficacies in both tumor cell models. STS and Dx‐induced ATP release from Jurkat cells was markedly suppressed by zVAD. In contrast, STS and Dx‐induced ATP release from EG7 cells was completely insensitive to zVAD despite very high expression of panx1 protein in this tumor model These findings indicate that the ability of pro‐apoptotic drugs to activate the casp3/7>; panx1>; ATP release pathway in hematopoietic cancer cells is tumor‐model specific and is not well‐correlated with panx1 protein expression. (Support: NIH‐R01‐GM3637).