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Cell Death Dis. 2014 Jul 17;5:e1326. doi: 10.1038/cddis.2014.294.

Caveolin-1 is required for TGF-β-induced transactivation of the EGF receptor pathway in hepatocytes through the activation of the metalloprotease TACE/ADAM17.

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Bellvitge Biomedical Research Institute (IDIBELL), Barcelona, Spain.
Department of Cell Biology, Immunology and Neuroscience, School of Medicine IDIBAPS-University of Barcelona, Barcelona, Spain.
1] Department of Medicine, University of California, San Diego, La Jolla, CA, USA [2] Networked Biomedical Research Center on Hepatic and Digestive Diseases (CIBERehd), Madrid, Spain.
1] Networked Biomedical Research Center on Hepatic and Digestive Diseases (CIBERehd), Madrid, Spain [2] Alberto Sols Biomedical Research Institute, CSIC-UAM, Madrid, Spain.
Integrin Signaling Laboratory, National Center for Cardiovascular Research (CNIC), Madrid, Spain.
Molecular Hepatology section, Department of Medicine II, Medical Faculty Mannheim, University of Heidelberg, Mannheim, Germany.
1] Bellvitge Biomedical Research Institute (IDIBELL), Barcelona, Spain [2] Department of Physiological Sciences II, University of Barcelona, Barcelona, Spain.


Transforming growth factor-beta (TGF-β) plays a dual role in hepatocytes, inducing both pro- and anti-apoptotic responses, whose balance decides cell fate. Survival signals are mediated by the epidermal growth factor receptor (EGFR) pathway, which is activated by TGF-β in these cells. Caveolin-1 (Cav1) is a structural protein of caveolae linked to TGF-β receptors trafficking and signaling. Previous results have indicated that in hepatocytes, Cav1 is required for TGF-β-induced anti-apoptotic signals, but the molecular mechanism is not fully understood yet. In this work, we show that immortalized Cav1(-/-) hepatocytes were more sensitive to the pro-apoptotic effects induced by TGF-β, showing a higher activation of caspase-3, higher decrease in cell viability and prolonged increase through time of intracellular reactive oxygen species (ROS). These results were coincident with attenuation of TGF-β-induced survival signals in Cav1(-/-) hepatocytes, such as AKT and ERK1/2 phosphorylation and NFκ-B activation. Transactivation of the EGFR pathway by TGF-β was impaired in Cav1(-/-) hepatocytes, which correlated with lack of activation of TACE/ADAM17, the metalloprotease responsible for the shedding of EGFR ligands. Reconstitution of Cav1 in Cav1(-/-) hepatocytes rescued wild-type phenotype features, both in terms of EGFR transactivation and TACE/ADAM17 activation. TACE/ADAM17 was localized in detergent-resistant membrane (DRM) fractions in Cav1(+/+) cells, which was not the case in Cav1(-/-) cells. Disorganization of lipid rafts after treatment with cholesterol-binding agents caused loss of TACE/ADAM17 activation after TGF-β treatment. In conclusion, in hepatocytes, Cav1 is required for TGF-β-mediated activation of the metalloprotease TACE/ADAM17 that is responsible for shedding of EGFR ligands and activation of the EGFR pathway, which counteracts the TGF-β pro-apoptotic effects. Therefore, Cav1 contributes to the pro-tumorigenic effects of TGF-β in liver cancer cells.

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