Cutting off the power: inhibition of leukemia cell growth by pausing basal ATP release and P2X receptor signaling?

Abstract

T cells respond to antigen stimulation with the rapid release of cellular ATP, which stimulates an autocrine feedback mechanism that regulates calcium influx through P2X receptors. This autocrine purinergic feedback mechanism plays an essential role in the activation of T cells resulting in cell proliferation and clonal expansion. We recently reported that increases in mitochondrial ATP production drive this stimulation-induced purinergic signaling mechanism but that low-level mitochondrial ATP production fuels basal T cell functions required to maintain vigilance of unstimulated T cells. Here we studied whether defects in these purinergic signaling mechanisms are involved in the unwanted proliferation of leukemia T cells. We found that acute leukemia T cells (Jurkat) possess a larger number and more active mitochondria than their healthy counterparts. Jurkat cells have higher intracellular ATP concentrations and generat more extracellular ATP than unstimulated T cells from healthy donors. As a result, increased purinergic signaling through P2X1 and P2X7 receptors elevates baseline levels of cytosolic Ca 2+ in Jurkat cells. We found that pharmacological inhibition of this basal purinergic signaling mechanism decreases mitochondrial activity, Ca 2+ signaling, and cell proliferation. Similar results were seen in the leukemic cell lines THP-1, U-937, and HL-60. Combined treatment with inhibitors of P2X1 or P2X7 receptors and the chemotherapeutic agent 6-mercaptopurine completely blocked Jurkat cell proliferation. Our results demonstrate that increased mitochondrial metabolism promotes autocrine purinergic signaling and uncontrolled proliferation of leukemia cells. These findings suggest that deranged purinergic signaling can result in T cell malignancy and that therapeutic targeting aimed at purinergic signaling is a potential strategy to combat T cell leukemia.

Identification of a subset of immunosuppressive P2RX1-negative neutrophils in pancreatic cancer liver metastasis

“…We noticed that autocrine-induced P2RX1 activation was reported to promote CD4+ T cells activation and the mechanism seemed to be associated with upregulated mitochondrial activity 52,53 . Using P2RX1 antagonist to treat CD4+ T cells for 20 min, the authors observed that P2RX1-evoked cytosolic Ca 2+ response, and mitochondrial Ca 2+ uptake were significantly reduced.…”

Autocrine stimulation of P2Y1 receptors is part of the purinergic signaling mechanism that regulates T cell activation

“…We showed that the released ATP binds primarily to P2X1 and P2X4 receptors that accumulate at the immune synapse where ATP facilitates localized Ca 2+ influx that promotes T cell activation [6]. However, CD4 T cells also express ectonucleotidases including ectonucleoside triphosphate diphosphohydrolases (ENTPD) 1 and ENTPD2, also known as CD39 and CD39L1, respectively, which convert extracellular ATP to ADP and AMP [12,16,17]. In the current study, we used HPLC analysis to study the kinetics of the release of ATP from stimulated T cells and of the conversion of released ATP to ADP, AMP, and adenosine.…”

6-mercaptopurine promotes energetic failure in proliferating T cells

“…In addition, this finding underscores the critical role of ATP production in proliferating T cells, including the Jurkat T cell line [38]. Jurkat cells have high intracellular ATP concentration and generate more extracellular ATP than resting T cells.…”