The role of P2X7 receptor in ATP-mediated human leukemia cell death: calcium influx-independent

Abstract

Activation of the P2X7 receptor leads to a rapid, bidirectional flux of cations, causing broad range of biological responses including cytotoxicity. However, the mechanism of P2X7-mediated cytotoxicity remains largely unexplored. In our previous study, the lack of P2X7-mediated calcium response under normal conditions was found in P2X7(+) hematopoietic cell lines. In this study, the P2X7-mediated cytotoxicity in different type of cells (P2X7(-), P2X7(+) with calcium response, and P2X7(+) without calcium response) was investigated. Our results showed that P2X7 agonists, adenosine 5'-triphosphate (ATP) or 2',3'-O-(4 benzoylbenzoyl)-ATP, dose-dependently reduced the cell viability in all P2X7(+) cells tested, including J6-1, LCL, and Namalva cells which are negative for P2X7-mediated calcium response, although these effects were lower than those observed in KG1a cells which has normal P2X7 functions. The cytotoxic effect could be blocked by P2X7 antagonists, oxidized ATP and 1-[N,O-bis(5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-phenylpiperazine. In addition, externalization of phosphatidylserine could be detected in a time-dependent manner and apoptotic morphological changes could be observed after the activation of P2X7 receptor in J6-1 cells. Furthermore, P2X7-mediated pore formation could be detected in KG1a and J6-1 cells under low-ionic conditions, but not under low-divalent conditions. These effects could not be observed in P2X7(-) Ramos cells. These results suggested that P2X7 receptor-mediated cytotoxic effects may occur independent of calcium response.

Purinergic signalling and cancer

“…P2X7 receptor expression was significantly higher (relative to bone marrow mononuclear cells) in cells from patients with lymphoblastic leukaemia (as well as acute and chronic myelogenous leukaemia) [467]. It has been claimed that the P2X7 receptor-mediated cytotoxic effects on KGla and J6-1 leukaemia cell lines may occur independently of the calcium response [468]. In paediatric acute leukaemia, RT-PCR and Western blots showed that P2X1, P2X4, P2X5 and P2X7 receptors were upregulated, while P2X2, P2X3 and P2X6 receptors were absent or marginally expressed and the highest expression of P2X7 receptors was found in relapsed patients [469].…”

Targeting Ion Channels in Leukemias: A New Challenge for Treatment

“…P 2X receptors exert widespread physiological roles in tissues such as the adult and developing nervous system, the respiratory, gastrointestinal, cardiovascular and genitourinary systems [45]. Abnormally high expression of P 2X7 was observed in solid tumors [46,47], as well as in hematologic malignancies, such as B-cell CLL [48], acute leukemia and myelodisplastic syndromes [49,50]. Moreover, a series of P 2X7 polymorphisms have been discovered, whose impact on P 2X7 functions, mechanisms and relationship with diseases were studied in a number of variants.…”

The impact of commercially available purinergic ligands on purinergic signalling research

“…MRS1754 has reinforced the important role of adenosine in suppressing the inflammatory response and has indicated that A 2B receptors are essential in these anti-inflammatory actions [52,65]. As with many other A 2B receptor antagonists, MRS1754 has again reinforced the suggestion that targeting the A 2B receptor may prove therapeutically useful [23].…”

“…In addition to having been implicated in areas such as pain and neurological diseases, the P2X 7 receptor has also been shown to be essential in other physiological areas and has notably been associated with cell proliferation and apoptosis [52]. KN-62, in addition to being a reversible and selective inhibitor of Cam Kinase II, is a potent, noncompetitive antagonist at the P2X 7 receptor (IC 50 value= 25 nM) [14].…”

“…There are currently few P2X 7 receptor blockers, however, KN-62 is considered to be one of the most potent. By blocking the P2X 7 receptor KN-62 inhibits reduction in cell viability by preventing a bidirectional flux of cations which triggers depolarisation [52]. This has revealed that the P2X 7 receptor is essential to cell cytotoxicity and crucially, has shown that P2X 7 receptor activation can both stimulate cell proliferation and cause cell death [52].…”