Papel de Hakai durante la progresión tumoralimplicaciones sobre la plasticidad epitelial

Abstract

Cancer is a disease with a high mortality rate worldwide, and its incidence is increasing steadily. Carcinoma, the most common type of cancers, is the result of transformations in epithelial cells. During this transformation, cells acquire various phenotypic characteristics including increased cell proliferation, loss of cell-cell and cell-substrate adhesions, increasing motility and invasiveness. Ecadherin, the best characterized and prototype member of the adherens junctions, is expressed in epithelial cells. Loss of function or expression of Ecadherin protein is considered as a hallmark of epithelial-to-mesenchymal transition, favouring cell motility and invasiveness and being a poor prognosis predictor. In 2002, Hakai protein was identified as an E3 ubiquitin-ligase for Ecadherin substrate. Hakai induces E-cadherin ubiquitination and subsequent degradation, thus altering cell-cell junctions and increasing cell motility. In this context, firstly it was studied the possible role of a vinca alkaloid, vinflunine, on cell-cell contacts. Vinflunine is commonly used in patients with advanced stage metastatic bladder carcinoma that do not respond to cisplatin treatment. Vinflunine is an anti-microtubule agent, and since recent publications show a relationship between microtubule dynamics and adherens junctions, vinflunine effect on E-cadherin-dependent junctions and on Hakai was analyzed by in vitro studies. It was observed that vinflunine induces epithelial differentiation, Ecadherin dependent cell-cell contacts. Moreover, it regulates Hakai protein expression. On the other hand, the role of the Hakai protein was analyzed in vitro and in vivo. For this purpose, it was used Hakai overexpressing MDCK cells (Hakai-MDCK) and it was corroborated that Hakai induces epithelial-tomesenchymal transition, increases proliferation and cellular invasiveness, which is accompanied by a decrease in its specific substrates, E-cadherin and Cortactin. For the in vivo study, an athymic nude mouse model was used by injecting MDCK and Hakai-MDCK cells into the flanks. Hakai induces tumor formation, increases its tumour growth, and regulates the epithelial-tomesenchymal transition markers in vivo. Undifferentiated and highly aggressive tumors are formed and micrometastasis are detected in lung of Hakai-MDCK injected mice.