Abstract 235: GJA1-11k Localizes to the Nucleus and Inhibits Cell Cycle Progression

Abstract

Gap Junction (GJ) channels, including the most common Connexin 43 (Cx43), are involved in the exchange of ions and small molecules to maintain homeostasis and also have fundamental roles in excitable tissues by facilitating rapid transmission of action potentials between adjacent cells. For instance, synchronization during each heartbeat is regulated by these ion channels at the cardiomyocyte cell-cell border. Numerous studies have found that Cx43 (predominantly the C-domain) is associated with control of cell proliferation, yet it is unclear how Cx43-based membrane channels effect these processes. We recently identified the existence of six endogenous Cx43 isoforms which are produced from the same full-length mRNA molecule in human cells by means of alternative translation and many of the known non-canonical roles of Cx43 can be attributed to these recently identified isoforms. Here we report that the smaller, non-channel related, alternatively translated isoform of Cx43 can directly affect cell growth. We found that 11KDa isoform (GJA1-11k) is localized in the nucleus of HEK293FT cells. GJA1-11k is a more potent growth suppressor than the wild type and full length isoform GJA1-43k. GJA1-11k-mediated growth suppression was achieved by limiting cell cycle progression from G0/G1 to S phase, in part, through regulation of internal translation of GJA1-11k. Nuclear localization experiments indicate that the cell growth-suppressive properties of GJA1-11k is linked to nuclear activity. RNA-seq based genome-wide mRNA transcriptome analysis revealed that the heat shock protein HSPA6, which is normally upregulated in certain cancer cells, was significantly downregulated in GJA1-11k overexpressing cells compared to cells overexpressing the full length isoform, suggesting a potential mechanism and/or new binding protein for the Cx43 C-terminal domain. In general, further understanding of the role of small Cx43 isoforms will provide a way not only to understand the mechanism controlling myocyte proliferation to improve the repair of the myocardium, but also to understand the pathobiology of cell growth associated with tumor suppressive properties of Cx43. It may be possible to develop new therapeutics by regulating alternative translation of Cx43.