Role of the P2X7 nucleotide receptor in intestinal epithelial cell proliferation and differentiation

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Stimulation of P2X ligand-gated ion channels by extracellular nucleotides is linked to multiple physiological effects ranging from cellular proliferation and differentiation, protein synthesis, regulation of cell secretion and absorption as well as modulation of apoptosis. The intestinal crypt-villus axis is a dynamic self-renewal system that is regulated by different cellular and molecular mechanisms involved in cell proliferation, differentiation and apoptosis. Our hypothesis is that P2 receptors could play an important role in the homeostasis of these physiological process. Immunohistochemistry studies showed a differential pattern of P2X receptors expression along the crypt-villus axis, suggesting that different P2X receptors play different role in the maturation of intestinal epithelial cells (IEC). The P2X7 receptor (P2X7R) is a unique member of the P2X family. It forms a pore in response to ligand stimulation leading to membrane depolarization and apoptosis.   We and others have shown that transient P2X7R stimulation lead to MAP kinases activation. In lights of those data, we hypothese, that P2X7R should not only be viewed as a "suicidal receptor" but also has a receptor regulating cell maturation. In that context, this research program will focus to unravel the functional molecular and cellular mechanisms dependant on P2X7R activity during intestinal epithelial cells (IEC) maturation. First, we propose to characterize the P2X7R signal transduction pathways associated with IEC maturation.  This will be investigated with the use of diverse cellular and molecular approaches, including interference RNA (siRNA), Western blotting and in vitro kinase assays. In a second aim, we will identify the P2X7R promoter regulatory elements and associated transcription factors important in sustaining receptor expression in maturating cells. Validation of the importance of the identified transcription factors will be assayed in vitro by siRNA and by chromatin immunoprecipitation assays (ChIP). This research program will define the molecular and cellular mechanisms governing the regulation of P2X7R expression and its putative role in IEC differentiation.