P2X7 is a bifunctional receptor (P2X7R) for extracellular ATP that, depending on the level of activation, forms a cation-selective channel or a large conductance nonselective pore. The P2X7R has a strong proapoptotic activity but can also support growth. Here, we describe the mechanism involved in growth stimulation. Transfection of P2X7R increases resting mitochondrial potential (delta psi(mt)), basal mitochondrial Ca2+ ([Ca2+]mt), intracellular ATP content, and confers ability to grow in the absence of serum. These changes require a full pore-forming function, because they are abolished in cells transfected with a mutated P2X7R that retains channel activity but cannot form the nonselective pore, and depend on an autocrine/paracrine tonic stimulation by secreted ATP. On the other hand, sustained stimulation of P2X7R causes a delta psi(mt) drop, a large increase in [Ca2+]mt, mitochondrial fragmentation, and cell death. These findings reveal a hitherto undescribed mechanism for growth stimulation by a plasma membrane pore.

P2X7 is the largest member of the P2X subfamily of purinergic receptors. A typical feature is the carboxyl tail, which allows formation of a large pore. Recently a naturally occurring truncated P2X7 splice variant, isoform B (P2X7B), has been identified. Here we show that P2X7B expression in HEK293 cells, a cell type lacking endogenous P2X receptors, mediated ATP-stimulated channel activity but not plasma membrane permeabilization, raised endoplasmic reticulum Ca(2+) content, activated the transcription factor NFATc1, increased the cellular ATP content, and stimulated growth. In addition, P2X7B-transfected HEK293 cells (HEK293-P2X7B), like most tumor cells, showed strong soft agar-infiltrating ability. When coexpressed with full-length P2X7 (P2X7A), P2X7B coassembled with P2X7A into a heterotrimer and potentiated all known responses mediated by this latter receptor. P2X7B mRNA was found to be widely distributed in human tissues, especially in the immune and nervous systems, and to a much higher level than P2X7A. Finally, P2X7B expression was increased on mitogenic stimulation of peripheral blood lymphocyte. Altogether, these data show that P2X7B is widely expressed in several human tissues, modulates P2X7A functions, participates in the control of cell growth, and may help understand the role of the P2X7 receptor in the control of normal and cancer cell proliferation.

The P2X 7 receptor is known for the cytotoxic activity because of its ability to cause opening of non-selective pores in the plasma membrane and activate apoptotic caspases. A key factor of P2X 7 -dependent cytotoxicity is the massive intracellular Ca 2؉ increase triggered by its activation. Here we show that P2X 7 transfection increased the ability of the endoplasmic reticulum to accumulate, store, and release Ca 2؉ . This caused a larger agonist-stimulated increase in cytosol and mitochondrial Ca 2؉ in P2X 7 transfectants than in mock transfected cells. P2X 7 transfectants survived and even proliferated in serum-free conditions and were resistant to apoptosis triggered by ceramide, staurosporin, or intracellular Zn 2؉ chelation. Finally, the nuclear factor of activated T cells complex 1 (NFATc1) was strongly activated in the P2X 7 transfectants. These observations support our previous finding that the P2X 7 receptor under tonic conditions of stimulation, i.e. those observed in response to basal ATP release, has an anti-apoptotic or even growth promoting rather than cytotoxic activity.Cell responses to extracellular ATP are mediated by P2 receptors: ionotropic P2X and metabotropic P2Y (1). The P2X 7 receptor (P2X 7 R) 4 subtype stands out in the P2X subfamily for its ability to trigger a host of physiologic or pathologic responses: plasma membrane blebbing (2, 3), rapid release of interleukin-1␤ via microvesicle shedding (2, 4), cell fusion (5), lymphoid cell proliferation (6), cell death (7,8), and bone formation/ resorption (9). This receptor is characterized by low affinity for ATP and by two states of permeability (10, 11). At high micromolar ATP concentrations, P2X 7 behaves as a cation-selective channel, whereas a prolonged exposure to nearly millimolar concentrations triggers the transition to a nonselective pore that admits hydrophilic solutes of molecular mass up to 900 Da (12-14). A common feature of both conductance states is a strong elevation of free cytoplasmic calcium levels ([Ca 2ϩ ] i ), a response critical for the biological role of this receptor.Recent evidence from our group shows that basal levels of ATP, naturally present in the extracellular milieu, cause a tonic activation of the P2X 7 R, which in turn triggers [Ca 2ϩ ] i increase and Ca 2ϩ entry into the mitochondria. The increased intramitochondrial Ca 2ϩ concentration ([Ca 2ϩ ] mt ) then enhances mitochondrial potential, increases ATP synthesis, and promotes survival and proliferation in the absence of serum (15). Increased mitochondrial potential and ability to grow under serum-free conditions are hallmark of tumor transformation (16). Furthermore, overexpression of the P2X 7 R is associated with several cancers or growth disturbances such as chronic lymphocytic leukemia (17), prostate (18)

Nucleotides are increasingly recognized as nonredundant extracellular signals for chemotaxis, cell growth, and cytokine release. Effects of extracellular nucleotides are mediated by P2 receptors, among which the P2X(7) subtype is attracting increasing attention for its involvement in apoptosis, cell growth, and cytokine release. Recent studies showed that P2X(7) is overexpressed in chronic lymphocytic leukemia and breast and prostate cancer. The aim of the present study was to better understand the clinical significance of P2X(7) receptor expression in normal and cancer human thyroid tissues. P2X(7) receptor message and protein expression and functional activity were tested in two cell lines (FB1 and FB2) established from either anaplastic or papillary primary thyroid cancer and in several histological samples of human papillary cancer. We show here that human thyroid papillary carcinoma, whether of the classical or follicular variant, expresses the P2X(7) receptor (P2X(7)R) to a much higher level than normal thyroid tissue. The P2X(7)R was similarly up-regulated in FB1 and FB2 cell lines. In contrast to normal thyroid cells, both cell lines responded to extracellular nucleotide stimulation with a large increase in intracellular Ca(2+) and secretion of IL-6. Ca(2+) increase was attenuated and release of IL-6 was fully blocked by P2X(7)R inhibitors. Finally, the thyroid carcinoma cell lines had at least a 3-fold higher intracellular ATP concentration and maintained at least a 3-fold higher extracellular ATP level, compared with control cells. These data suggest that an enhanced P2X(7)R function might be a feature of human thyroid cancer.

Introduction Pulmonary artery sarcoma (PAS) is a rare tumor, whose therapeutic approach is mainly based on surgery, either pneumonectomy or pulmonary endarterectomy (PEA). The prognosis reported in published series is very poor, with survival of 1.5 months without any kind of treatment. Patients and Methods From January 2010 to January 2016, 1027 patients were referred to our hospital for symptoms of acute or chronic pulmonary thromboembolic disease. Twelve patients having a confirmed diagnosis of PAS underwent PEA. Median age was 64.5 years. Most patients had a long history of symptoms, having a median time of 7.5 months from onset of symptoms to surgery. Results Following PEA and cardiopulmonary rehabilitation, 10 patients received conventional chemotherapy with doxorubicin and ifosfamide, starting at a median of 42 days from surgery. Four patients also received radiotherapy. Four patients have died due to disease progression, while 7 are still alive, with 5 being disease-free at 4–55+ months from diagnosis. Conclusions In patients with PAS, a multimodal approach including PEA, CT, and RT is feasible but it should be evaluated individually, according to the tumor extension and the patient's clinical condition. Apart from improving quality of life mainly by reducing or delaying symptoms due to PH, it may improve life expectancy.