Paracrine Stimulation of P2x7 Receptor by Atp Activates a Proliferative Pathway in Ovarian Carcinoma Cells

Abstract

P2X7 is a purinergic receptor-channel; its activation by ATP elicits a broad set of cellular actions, from apoptosis to signals for survival. Here, P2X7 expression and function was studied in human ovarian carcinoma (OCA) cells, and biopsies from non-cancerous and cancer patients were analyzed by immunohistochemistry. Ovarian surface epithelium in healthy tissue expressed P2X7 at a high level that was maintained throughout the cancer. The cell lines SKOV-3 and CAOV-3 were used to investigate P2X7 functions in OCA. In SKOV-3 cells, selective stimulation of P2X7 by 2'(3')-O-(4-benzoylbenzoyl) adenosine-5'-triphosphate (BzATP) induced a dose-dependent increase of intracellular Ca(2+) concentration ([Ca(2+)](i)) but not cell death. Instead, BzATP increased the levels of phosphorylated ERK and AKT (pERK and pAKT), with an EC(50) of 44 ± 2 and 1.27 ± 0.5 μM, respectively; 10 μM BzATP evoked a maximum effect within 15 min that lasted for 120 min. Interestingly, basal levels of pERK and pAKT were decreased in the presence of apyrase in the medium, strongly suggesting an endogenous, ATP-mediated phenomenon. Accordingly: (i) mechanically stimulated cells generated a [Ca(2+)](i) increase that was abolished by apyrase; (ii) apyrase induced a decrease in culture viability, as measured by the MTS assay for mitochondrial activity; and (iii) incubation with 10 μM AZ10606120, a specific P2X7 antagonist and transfection with the dominant negative P2X7 mutant E496A, both reduced cell viability to 70.1 ± 8.9% and to 76.5 ± 5%, respectively, of control cultures. These observations suggested that P2X7 activity was auto-induced through ATP efflux; this increased pERK and pAKT levels that generated a positive feedback on cell viability.

Targeting of the P2X7 receptor in pancreatic cancer and stellate cells

“…These conclusions were supported by experiments with siRNA. Similar effect of P2X7R on cell survival and effects of the allosteric inhibition of P2X7R were also shown on mouse pancreatic stellate cells, 25 ovarian carcinoma cells 38 and in vivo on melanoma cancer model. 20 An important characteristic that makes PDAC aggressive is the ability of tumour cells to migrate and invade the surrounding or distant tissues.…”

P2×7 targeting inhibits growth of human mesothelioma

“…We and others have shown that basal expression or low level stimulation of the P2×7R, as opposed to sustained pharmacological stimulation, drives cell growth, and accordingly P2×7R silencing or pharmacological blockade inhibits proliferation [15, 13, 26, 27]. Growth-stimulating effect of P2×7R is enhanced in low nutrient culture conditions [16, 17].…”

“…P2YRs have been traditionally credited with growth-promoting activity, as they are G- protein-coupled, and thus linked to phosphoinositide hydrolysis, Ca 2+ mobilization from intracellular stores and activation of the MAPK pathway. More recent studies showed that the P2×7R also supports cell proliferation [13, 26, 29]. This was unanticipated due to the well-known cytotoxic effect due to activation of the P2×7R-associated large conductance pore [30, 31].…”

Nucleotides and nucleoside signaling in the regulation of the epithelium to mesenchymal transition (EMT)

“…Tumors induced by the implant of HEK-293 cells heterologously expressing P2X7 receptors in immunodeficient mice showed elevated growth rate, an anaplastic phenotype, and high production of VEGF a well-known EMT inductor [67]. In cell lines derived from neuroblastoma or ovarian carcinoma, P2X7 receptor activity is correlated with high tumoral growth and metastatic induction, effects that involve PI3K/ AKT pathway activity [67][68][69][70]. Moreover, in pancreatic ductal adenocarcinoma cell lines, P2X7 receptor activity regulates migration and invasion, responses associated with EMT induction [71].…”