CD39-associated high ATPase activity contribute to the loss of P2X7-mediated calcium response in LCL cells

The P2X7 nucleotide receptor is an adenosine 5′-triphosphate (ATP)-gated ion channel, which induces cation channel opening imparting significant permeability to Ca2+, and is widely expressed in cells of hematopoietic origin. Our previous report showed that P2X7-mediated calcium response was absent in three Epstein-Barr virus (EBV)-positive and P2X7 positive cell lines. In this report, we detected the cell surface ATPase activity, which contributes to the hydrolysis of extracellular ATP, and the expression of CD39, which is the main source of ATPase on hematopoietic cells, in these cell lines. Then, we tried to restore the P2X7-mediated calcium response in LCL-H and J6-1 cells by either increasing the concentration of agonist or suppressing the ATPase activity by βγMeATP, a synthetic poorly metabolizable ATP analogue. The results showed that LCL-H and J6-1 cells had higher levels of ATPase activity and CD39 expression. The treatment of 300 μM βγMeATP efficiently inhibited the ATPase activity on LCL-H and J6-1 cells. Both elevation of agonist concentration (10 mM ATP or 1 mM BzATP) and pretreatment with 300 μM βγMeATP followed by stimulation with normal concentration of agonists (1 mM ATP or 0.1 mM BzATP) could cause P2X7-mediated calcium response in LCL-H but neither in J6-1 cells. These results suggested that multiple mechanisms contributed to the loss of the P2X7-mediated calcium response. CD39-associated high ATPase activity contributed to the loss of the P2X7-mediated calcium response in LCL-H cells, while additional mechanism(s) existed in J6-1 cells.