Expression of pituitary tumor–transforming gene 1 (PTTG1)/securin in hepatitis B virus (HBV)-associated liver diseases: Evidence for an HBV X protein–mediated inhibition of PTTG1 ubiquitination and degradation

Authors

  • Francisca Molina-Jiménez,

    1. Unidad de Biología Molecular, Hospital Universitario de la Princesa, Madrid, Spain
    2. Centro de Investigación Biomédica en Red de enfermedades hepáticas y digestivas (CIBERehd), Instituto de Salud Carlos III (ISCIII), Madrid, Spain
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  • Ignacio Benedicto,

    1. Unidad de Biología Molecular, Hospital Universitario de la Princesa, Madrid, Spain
    2. Centro de Investigación Biomédica en Red de enfermedades hepáticas y digestivas (CIBERehd), Instituto de Salud Carlos III (ISCIII), Madrid, Spain
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  • Miki Murata,

    1. Depdatamaticsf Gastroenterology and Hepatogips Kansai Medical University, Osaka, Japan
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  • Samuel Martín-Vílchez,

    1. Centro de Investigación Biomédica en Red de enfermedades hepáticas y digestivas (CIBERehd), Instituto de Salud Carlos III (ISCIII), Madrid, Spain
    2. Unidad de Hepatología, Hospital Universitario de la Princesa, Madrid, Spain
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  • Toshihito Seki,

    1. Depdatamaticsf Gastroenterology and Hepatogips Kansai Medical University, Osaka, Japan
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  • José Antonio Pintor-Toro,

    1. Centro Andaluz de Biología Molecular y Medicina Regenerativa, Sevilla, Spain
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  • María Tortolero,

    1. Departamento de Microbiología, Facultad de Biología, Universidad de Sevilla, Sevilla, Spain
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  • Ricardo Moreno-Otero,

    1. Centro de Investigación Biomédica en Red de enfermedades hepáticas y digestivas (CIBERehd), Instituto de Salud Carlos III (ISCIII), Madrid, Spain
    2. Unidad de Hepatología, Hospital Universitario de la Princesa, Madrid, Spain
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  • Kazuichi Okazaki,

    1. Depdatamaticsf Gastroenterology and Hepatogips Kansai Medical University, Osaka, Japan
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  • Kazuhiko Koike,

    1. Department of Infectious Diseases, Internal Medicine, Graduate School of Medicine, University of Tokyo, Tokyo, Japan
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  • José Luchi Barbero,

    1. Departamento de Biología Celular y del Desarrollo, Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas (CSIC), Madrid, Spain
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  • Koichi Matsuzaki,

    1. Depdatamaticsf Gastroenterology and Hepatogips Kansai Medical University, Osaka, Japan
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  • Pedro L. Majano,

    1. Unidad de Biología Molecular, Hospital Universitario de la Princesa, Madrid, Spain
    2. Centro de Investigación Biomédica en Red de enfermedades hepáticas y digestivas (CIBERehd), Instituto de Salud Carlos III (ISCIII), Madrid, Spain
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    • These authors contributed equally to this work.

  • Manuel López-Cabrera

    Corresponding author
    1. Unidad de Biología Molecular, Hospital Universitario de la Princesa, Madrid, Spain
    2. Centro de Investigación Biomédica en Red de enfermedades hepáticas y digestivas (CIBERehd), Instituto de Salud Carlos III (ISCIII), Madrid, Spain
    3. Centro de Biología Molecular Severo Ochoa (CBMSO), CSIC-UAM, Madrid, Spain
    • Unidad de Biología Molecular, Hospital Universitario de La Princesa, C/Diego de León 62, 28006 Madrid, Spain
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    • These authors contributed equally to this work.

    • fax: (34)-91-3093911


  • Potential conflict of interest: Nothing to report.

Abstract

Chronic infection with hepatitis B virus (HBV) is strongly associated with hepatocellular carcinoma (HCC), and the viral HBx protein plays a crucial role in the pathogenesis of liver tumors. Because the protooncogene pituitary tumor–transforming gene 1 (PTTG1) is overexpressed in HCC, we investigated the regulation of this protein by HBx. We analyzed PTTG1 expression levels in liver biopsies from patients chronically infected with HBV, presenting different disease stages, and from HBx transgenic mice. PTTG1 was undetectable in biopsies from chronic hepatitis B patients or from normal mouse livers. In contrast, hyperplastic livers from transgenic mice and biopsies from patients with cirrhosis, presented PTTG1 expression which was found mainly in HBx-expressing hepatocytes. PTTG1 staining was further increased in HCC specimens. Experiments in vitro revealed that HBx induced a marked accumulation of PTTG1 protein without affecting its messenger RNA levels. HBx expression promoted the inhibition of PTTG1 ubiquitination, which in turn impaired its degradation by the proteasome. Glutathione S-transferase pull-down and co-immunoprecipitation experiments demonstrated that the interaction between PTTG1 and the Skp1–Cul1–F-box ubiquitin ligase complex (SCF) was partially disrupted, possibly through a mechanism involving protein–protein interactions of HBx with PTTG1 and/or SCF. Furthermore, confocal analysis revealed that HBx colocalized with PTTG1 and Cul1. We propose that HBx promotes an abnormal accumulation of PTTG1, which may provide new insights into the molecular mechanisms of HBV-related pathogenesis of progressive liver disease leading to HCC development. (HEPATOLOGY 2010;51:777–787.)

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