Activation of the integrin-linked kinase pathway downregulates hepatic connexin32 via nuclear Akt

Abstract

Gap junctions mediate intercellular communication through channels composed of proteins termed connexins (Cxs). We have shown that Cx32 is downregulated in the liver of female rats exposed to hexachlorobenzene (HCB), an epigenetic environmental carcinogen. This is concomitant with the activation of the integrin-linked kinase (ILK) pathway, leading to the activation and nuclear translocation of Akt and the inactivation of glycogen synthase kinase-3beta (GSK3beta). E-cadherin, an adhering junction protein, is also downregulated in the liver of these female rats, owing to the inactivation of GSK3beta. Using an in vitro model, the aim of this study was to determine the role of the ILK pathway in the regulation of Cx32. In order to mimic the activation of the ILK pathway, a well-differentiated rat hepatoma cell line, MH1C1, was transiently transfected with an expression vector for ILK (ILK+ cells). ILK+ cells displayed significantly lower Cx32 mRNA levels and Akt was also activated and translocated into the nucleus. Using a constitutively active Akt expression vector, we showed that Akt transfected cells had lower Cx32 mRNA levels, indicating a role for Akt in Cx32 regulation. Finally, using an Akt-NES vector, a nuclear-active form of Akt, we showed that Cx32 protein levels were reduced in transfected cells as compared with cell transfected with the wild-type inactive Akt vector, suggesting that the nuclear form of Akt is responsible for the downregulation of Cx32. Overall, these data indicate that Cx32 is downregulated by the ILK pathway activation in rat hepatocytes and that this is mediated via the activation and nuclear translocation of Akt.