title: 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.
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.
authors.affiliation: Unidad de Biología Molecular, Hospital Universitario de la Princesa, 28006 Madrid, Spain.
authors.forename: Francisca
authors.initials: F
authors.lastname: Molina-Jiménez
authors.forename: Ignacio
authors.initials: I
authors.lastname: Benedicto
authors.forename: Miki
authors.initials: M
authors.lastname: Murata
authors.forename: Samuel
authors.initials: S
authors.lastname: Martín-Vílchez
authors.forename: Toshihito
authors.initials: T
authors.lastname: Seki
authors.forename: José
authors.initials: J
authors.lastname: Antonio Pintor-Toro
authors.forename: María
authors.initials: M
authors.lastname: Tortolero
authors.forename: Ricardo
authors.initials: R
authors.lastname: Moreno-Otero
authors.forename: Kazuichi
authors.initials: K
authors.lastname: Okazaki
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Koike
authors.forename: José Luchi
authors.initials: JL
authors.lastname: Barbero
authors.forename: Koichi
authors.initials: K
authors.lastname: Matsuzaki
authors.forename: Pedro L
authors.initials: PL
authors.lastname: Majano
authors.forename: Manuel
authors.initials: M
authors.lastname: López-Cabrera
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000502:physiology*; D000818:Animals; D002478:Cells, Cultured; D019694:Hepatitis B, Chronic / Q000378:metabolism*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins / Q000096:biosynthesis* / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D054875:Ubiquitination
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D047908:Intracellular Signaling Peptides and Proteins; C110719:LAMTOR5 protein, human; D008565:Membrane Proteins; C112633:PTTG1IP protein, human