The role of pannexins, a novel gap junction family, in glioma oncogenicity and neuronal differentiation

Gap junctions are unique intercellular channels assembled from the canonical gap junction family, connexins (Cxs). These channels connect the cytosols of adjacent cells, allowing direct passages of small ions and molecules for intercellular communication and homeostasis within tissues. A novel family of gap junction proteins, pannexins (Panxs), with low sequence similarity to the invertebrate gap junctions, innexins, was recently discovered in chordates. Similar to Cxs, Panxs are also capable of forming functional hemichannels as well as intercellular channels. Aberrations in gap junctions have been associated with abnormal CNS development and diseases including gliomas. The main purpose of this thesis was to determine if Panxs play a functional role under pathological and normal CNS conditions, each of which is represented by gliomas and neuronal differentiation, respectively. A loss of Panx expression was found in the C6 glioma cell line when compared to its normal counterparts, primary astrocytes. Restoring Panx1 and Panx2 expression in C6 glioma cells by stable transfection induced a dramatically flattened morphology, which is similar to the flat and polygonal shape of cultured astrocytes. Both Panx1 and Panx2 also significantly suppressed the neoplastic phenotype of C6 glioma cells, including in vitro monolayer growth, anchorage-independent growth, and in vivo tumorigenesis in immunodeficient mice. Interestingly, while Panx1 reduced cell motility in C6 glioma cells, Panx2 did not elicit a similar effect. Panx1 and Panx2 exhibited a distinct subcellular localization. Panx1 was detected at the plasma membrane and perinuclear regions, whereas Panx2 was only found in membrane-bound compartments within the cytosol, hence suggesting mechanistically different tumor-suppressive pathways employed by the two Panxs. Furthermore, it was determined that Panx1 and Panx3, but not Panx2, increased neurite numbers and further enhanced neurite outgrowth in PC12 cells during nerve growth factor-induced neuronal differentiation. In conclusion, findings from this thesis suggest a functional role of Panxs in normal and pathological conditions of the CNS, and merit critical future investigations to explore their underlying mechanisms and therapeutic implication in diseases.Medicine, Faculty ofGraduat