ATP in the tumour microenvironment drives expression of nfP2X7, a key mediator of cancer cell survival

The ATP-gated receptor P2X(7) is expressed in multiple malignant tumours including neuroblastoma, melanoma, prostate, lung and breast. P2X(7) has a significant role in mediating diverse cell responses, which upon dysregulation are associated with tumour initiation and development. The rapid, ATP-mediated activation of P2X(7) induces a fast-inward cation current in cells. However, prolonged ATP-mediated activation of P2X(7) leads to formation of a pore that increases membrane permeability and eventually causes cell death. This presents a potential paradox, as the tumour microenvironment contains extracellular ATP at levels sufficient to activate the P2X(7) pore and trigger cell death. However, P2X(7) expression is associated with enhanced cancer cell survival, proliferation and metastatic potential. At least one distinct conformational form of P2X(7), termed non-pore functional P2X(7) (nfP2X(7)), has been described, which is not able to form a functional pore. We demonstrate for the first time in this study that exposure to a high ATP concentration, equivalent to those measured in the tumour microenvironment, drives nfP2X(7) expression and also that nfP2X(7) is essential for tumour cell survival. We show that monoclonal antibodies raised against a P2X(7) amino acid sequence (200-216), whose conformation is distinct from that of wild-type (WT) P2X(7), bind specifically to nfP2X(7) expressed on the surface of tumour cells. We also show that nfP2X(7) is broadly expressed in patient-derived tumour sections from a wide range of cancers. Therefore, antibodies raised against E200 provide tools that can differentiate between forms of the P2X(7) receptor that have a key role in cancer.