title: p53-paralog DNp73 oncogene is repressed by IFNα/STAT2 through the recruitment of the Ezh2 polycomb group transcriptional repressor.
abstract: The DNp73 proteins act as trans-repressors of p53 and p73-dependent transcription and exert both anti-apoptotic activity and pro-proliferative activity. DNp73s are frequently up-regulated in a variety of human cancers, including human hepatocellular carcinomas (HCCs). Increased levels of DNp73 proteins confer to HCC cells resistance to apoptosis and, irrespective to p53 status, a chemoresistant phenotype. Here, we show that interferon (IFN)α down-regulates DNp73 expression in primary human hepatocytes (PHHs) and HCC cell lines. IFNα has been used as pro-apoptotic agent in the treatment of malignancies and there is increasing evidence of IFNα effectiveness in HCC treatment and prevention of recurrence. The precise mechanisms by which class I IFNs exert their anti-proliferative and anti-tumor activity remain unclear. IFNα binding to its receptor activates multiple intracellular signaling cascades regulating the transcription of numerous direct target genes through the recruitment of a complex comprising of STAT1, STAT2 and IFN regulatory factor (IRF)9 to their promoters. We found that, in response to IFNα, the P2p73 promoter undergoes substantial chromatin remodeling. Histone deacetylases (HDACs) replace histone acetyl transferases. STAT2 is recruited onto the endogenous P2p73 promoter together with the polycomb group protein Ezh2, leading to increased H3K27 methylation and transcriptional repression. The reduction of DNp73 levels by IFNα is paralleled by an increased susceptibility to IFNα-triggered apoptosis of Huh7 hepatoma cells. Our results show, for the first time, that IFN-stimulated gene factor 3 recruitment may serve both in activating and repressing gene expression and identify the down-regulation of DNp73 as an additional mechanism to counteract the chemoresistance of liver cancer cells.
authors.affiliation: Laboratory of Gene Expression, Fondazione A. Cesalpino, Rome, Italy. barbara.testoni@uniroma1.it
authors.forename: B
authors.initials: B
authors.lastname: Testoni
authors.forename: V
authors.initials: V
authors.lastname: Schinzari
authors.forename: F
authors.initials: F
authors.lastname: Guerrieri
authors.forename: S
authors.initials: S
authors.lastname: Gerbal-Chaloin
authors.forename: G
authors.initials: G
authors.lastname: Blandino
authors.forename: M
authors.initials: M
authors.lastname: Levrero
mesh_terms: D001665:Binding Sites / Q000235:genetics; D015153:Blotting, Western; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D047369:Chromatin Immunoprecipitation; D003110:Colonic Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D000071221:Enhancer of Zeste Homolog 2 Protein; D005260:Female; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D006657:Histones / Q000378:metabolism; D006801:Humans; D050834:Interferon-Stimulated Gene Factor 3, gamma Subunit / Q000235:genetics / Q000378:metabolism; D016898:Interferon-alpha / Q000378:metabolism / Q000494:pharmacology*; D008745:Methylation / Q000187:drug effects; D008875:Middle Aged; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D063151:Polycomb Repressive Complex 2; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding / Q000187:drug effects; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050794:STAT1 Transcription Factor / Q000235:genetics / Q000378:metabolism; D050795:STAT2 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D000072160:Tumor Protein p73; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; D006657:Histones; C494227:IRF9 protein, human; D050834:Interferon-Stimulated Gene Factor 3, gamma Subunit; D016898:Interferon-alpha; D009687:Nuclear Proteins; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050795:STAT2 Transcription Factor; C000606460:TP73 protein, human; D014157:Transcription Factors; D000072160:Tumor Protein p73; D025521:Tumor Suppressor Proteins; C498409:EZH2 protein, human; D000071221:Enhancer of Zeste Homolog 2 Protein; D063151:Polycomb Repressive Complex 2