Involvement of the integrin-linked Kinase pathway in hexachlorobenzene-induced gender-specific rat hepatocarcinogenesis

Abstract

Overexpression of the integrin-linked kinase (ILK) pathway disrupts cell-cell interactions, an epigenetic event leading to epithelial cell transformation. Female rats exposed to hexachlorobenzene (HCB) for 5 consecutive days and sampled 45 days later show a decrease in liver gap junctional intercellular communication. We hypothesized that HCB also alters E-cadherin expression and that this alteration is mediated by the ILK pathway. Hepatic ILK levels were markedly increased in HCB-treated female rats. Cytoplasmic/membrane levels of protein kinase B (Akt), a target of ILK, and its phosphorylated active form were decreased in treated female rats. Flow cytometric analysis showed a concomitant increase in nuclear Akt levels. Both ILK and Akt can phosphorylate glycogen synthetase kinase-3β (GSK3β), rendering it inactive. Phosphorylated-GSK3β levels were higher in treated females and resulted in a twofold decrease in the activity of GSK3β. The inactivation of GSK3β in HCB-treated female rats resulted in the nuclear translocation of β-catenin, as demonstrated by both immunocytochemistry and flow cytometric analyses. Western blot analysis showed an 84% decrease in E-cadherin levels in HCB-treated rats as compared to controls, and this decrease was not mediated by Snail activation. Mimicking the activation of ILK with specific GSK3β inhibitors resulted in downregulation of E-cadherin levels but had no effect on Cx32 expression in the MH1C1 cells. Overall, these results indicate that hepatic E-cadherin is downregulated as a result of an overexpression of the ILK pathway. The concomitant HCB-induced downregulation of intercellular communication does not occur as a result of either E-cadherin downregulation or GSK3β inactivation. © The Author 2005. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved.