Inorganic arsenic trioxide induces gap junction loss in association with the downregulation of connexin43 and E-cadherin in rat hepatic “stem-like” cells

Abstract

Chronic exposure to inorganic arsenic trioxide causes tumors of the skin, urinary bladder, lung, and liver. Several cancer initiators and promoters have been shown to alter cell–cell signaling by interference with gap junction intercellular communication (GJIC) and/or modulation of cell adhesion molecules, such as connexin43 (Cx43), E-cadherin, and β-catenin. The aim of this study was to determine whether the disruption of cell–cell interactions occurs in liver epithelial cells after exposure to arsenic trioxide. WB-F344 cells were treated with arsenic trioxide (6.25–50 μM) for up to 8 hours, and gap junction function was analyzed using the scrape-load/dye transfer assay. In addition, the changes in mRNA and protein levels of Cx43, E-cadherin, and β-catenin were determined. A significant dose- and time-dependent decrease in GJIC was observed when WB-F344 cells were exposed to arsenic trioxide (p < 0.05). Consistent with the inhibition of GJIC, cells' exposure to arsenic trioxide resulted in dose- and time-dependent decreases in Cx43 and E-cadherin mRNA expression and protein levels. However, arsenic trioxide did not alter the mRNA or protein levels of β-catenin. In an immunofluorescence study, nuclei were heavily stained with anti-β-catenin antibody, indicating significant nuclear translocation. In this study, we also demonstrated that arsenic trioxide-induced GJIC loss was a reversible process. Taken together, these data support the hypothesis that disruption of cell–cell communication may contribute to the tumor-promoting effect of inorganic arsenic trioxide.