Opposing roles of connexin43 in glioma progression.

Despite the tremendous amount of data over the last 40years, lack of gap junctional intercellular communication (GJIC) or altered expression of gap junction proteins is still a lesser known 'hallmark' of cancer. Expression of astrocytic gap junction protein, connexin43 (Cx43), is often reduced in astrocytomas, the most common neoplasia of the central nervous system (CNS) in adults. Supported by a number of evidences, the global decrease of Cx43 expression appears to be advantageous for the growth of glioma cells. Although the mechanisms by which Cx43 regulates the expression levels of proteins involved in cell growth is unclear, there are evidences to suggest that it might be independent of their channel forming properties. In this regard, the carboxyl tail of Cx43 may have the ability to control the translocation of transcription factor regulators into the nucleus. However, this putative tumor suppressor effect of Cx43 is counterbalanced by its capacity to enhance the migration of glioma cells out of the tumor core through mechanisms that seems to implicate its carboxyl tail, possibly by interacting with the actin cytoskeleton. This ambivalence between the tumor suppressor effect and promotion of cell migration may partly be explained by the heterogeneous expression of Cx43 in the glioma core especially at the malignant glioblastoma stage; some tumor cells would be expected to migrate (Cx43 expressing cells) and others to proliferate (non-expressing Cx43 cells). Moreover, the involvement of Cx43 in glioma progression seems to be more complex since, in addition, GJIC may increase their resistance to apoptosis and Cx43 may also affect cell homeostasis in a paracrine fashion via hemichannel action. In conclusion, Cx43 appears to be involved at different levels of the glioma progression by acting on cell growth regulation, promotion of cell migration and resistance to apoptosis. This article is part of a Special Issue entitled: The Communicating junctions, composition, structure and characteristics.