Title

 

Authors

 E. Adinolfi ¹, A.L. Giuliani ¹, T. Ricco ¹, L. Raffaghello ², V. Pistoia ², F. Di Virgilio ¹
 
1 Dep. Experimental and Diagnostic Medicine Sec. General Pathology, University of Ferrara, Ferrara.
2 Laboratory of Oncology, G.Gaslini Paediatric Hospital, Genoa

 

Abstract

 P2X receptors for extracellular ATP are plasma membrane ion channels with important roles in many patho-physiological conditions comprising  pain, inflammation, cancer  and many others. The largest member of the family is P2X7 that is charachterized by its long C terminal tail (≈200 aa) , which is responsible for the opening of an unselective pore, permeable to solutes up to 900 Da. Membrane permeabilization to large molecules associates to P2X7-mediated cell death, IL1band ATP secretion. Moreover, P2X7 receptor mediates proliferation of different cell types, such as lymphocytes and microglia, and its expression is increased in several malignancies. Despite several reports link P2X7 expression to cancer there was no evidence of receptor involvement in tumor developmentin vivo. Here we show a tumorigenic activity of P2X7 receptor in HEK293. This cell line , which was selected because does not express any P2X subtype, was stably transfected with P2X7 (HEK293-P2X7). When subcutaneously injected into immune-compromised mice, HEK293 cells transfected with the empty vector (HEK293-mock) caused the formation of tumoral masses just in 50% of the animals; this percentage was increased to 90% for HEK293-P2X7cells. Furthermore, growth of HEK293-P2X7-derived tumours was significantly faster, causing the formation of larger tumoral masses. Accelerated growth was due to amplified proliferation, as shown by increased Ki67 labelling, but also to reduced apoptosis, as demonstrated by decreased TUNEL staining. Interestingly, P2X7 expression also increased tumour angiogenesis, causing the formation of blood vessels  in neoplasias. Moreover, the levels of  the calcium activated, proliferation factor NFATc1 were increased in P2X7 positive tumoral masses. These data confirms the importance of calcium signalling in P2X7-dependent tumoral transformation. To further support this hypothesis we also analysed the transforming ability of a human  P2X7 splice variant: P2X7B. This protein while loosing the pore forming activity, still retains the ability of forming an ion channel alsosharing the same agonist/antagonist profile of full length human receptor (P2X7A) (1). Moreover, P2X7B is widely expressed in human tissues often at a higher degree than P2X7A. Here we show that P2X7B causes ATP dependent cell proliferation activating the NFATc1 signalling pathway. Moreover, cells expressing P2X7B gain tumoral cells characteristics as they survive in serum starvation and also infiltrate a soft agar matrix. Even more interestingly, when co-expressed with P2X7A, P2X7B enhances all the full length receptor known activities comprising pore formation,  calcium permeability, cell proliferation and NFATc1 activation (2).
 
Reference List
 
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   2.   E. Adinolfiet al., FASEB J. 24, 3393 (2010).