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International audience; Expression of developmental genes Twist1 and Twist2 is reactivated in many human tumors. Among their oncogenic activities, induction of epithelial to mesenchymal transition is believed to increase cell motility and invasiveness and may be related to acquisition of cancer stem cell phenotype. In addition, Twist proteins promote malignant conversion by overriding two oncogene-induced failsafe programs: senescence and apoptosis. Reactive oxygen species (ROS) are also important mediators of apoptosis, senescence and motility and are tightly linked to disease, notably to cancer. We report here that Twist factors and ROS are functionally linked. In wild type cells both Twist1 and Twist2 exhibit antioxidant properties. We show that Twist-driven modulation of oncogene-induced apoptosis is linked to its effects on oxidative stress. Finally, we identify several targets that mediate Twist antioxidant activity. These findings unveil a new function of Twist factors that could be important in explaining their pleiotropic role during carcinogenesis.

International audience; BACKGROUND & AIMS: Apicobasal polarity, which is essential for epithelial structure and function, is targeted by several tumour-related pathogens and is generally perturbed in the course of carcinogenesis. Hepatitis C virus (HCV) infection is associated with a strong risk of hepatocellular carcinoma, typically preceded by dysplastic alterations of cell morphology. We investigated the molecular mechanisms and the functional consequences of HCV-driven perturbations of epithelial polarity. METHODS: We used biochemical, genetic, and cell biology approaches to assess the impact of hepatitis C viral protein NS5A on the polarity and function of hepatocytes and hepatic progenitors. Transgenic animals and xenograft models served for in vivo validation of the results obtained in cell culture. RESULTS: We found that expression of HCV-NS5A in primary hepatic precursors and in immortalized hepatocyte cell lines gave rise to profound modifications of cell polarity, leading to epithelial to mesenchymal transition (EMT). NS5A, either alone or in the context of the full complement of viral proteins in the course of infection, acted through activating Twist2, a transcriptional regulator of EMT. The effects of NS5A were additive to those of TGF-beta, a cytokine abundant in diseased liver and highly relevant to HCV-related pathology. Moreover, NS5A cooperates with oncogenic Ras, giving rise to transformed, invasive cells that are highly tumorigenic in vivo. CONCLUSIONS: Our data suggest that in the context of HCV infection, NS5A favors formation of preneoplastic lesions by disrupting cell polarity and additional oncogenic events cooperate with the viral protein to give rise to motile and invasive tumour cells.

Cellular differentiation relies on both physical and chemical environmental cues. The bipotential mouse embryonic liver (BMEL) cells are early progenitors of liver epithelial cells with an apparently infinite proliferative potential. These cells, which remain undifferentiated in a monolayer culture, differentiate upon release from geometrical constraints imposed by growth on a stiff plastic plate. In a complex three dimensional environment of a Matrigel extracellular matrix, BMEL cells form two types of polarized organoids of distinct morphologies: cyst-like structures suggesting cholangiocyte-type organization or complex organoids, reminiscent of liver parenchyma and associated with acquisition of hepatocyte-specific phenotypic markers. The choice of the in vitro differentiation lineage is governed by Transforming Growth Factor-beta (TGF-beta) signaling. Our results suggest that morphological cues initiate the differentiation of early hepatic precursors and confirm the inhibitory role of TGF-beta on hepatocytic lineage differentiation.