Niller H.H.,University of Regensburg |
Ay E.,National Center for Epidemiology |
Banati F.,Europe Nonprofit Research Center |
Demcsak A.,University of Szeged |
And 2 more authors.
Reviews in Medical Virology | Year: 2016
Hepatitis B virus (HBV) is one of the causative agents of hepatocellular carcinoma. The molecular mechanisms of tumorigenesis are complex. One of the host factors involved is apparently the long-lasting inflammatory reaction which accompanies chronic HBV infection. Although HBV lacks a typical viral oncogene, the HBx gene encoding a pleiotropic regulatory protein emerged as a major player in liver carcinogenesis. Here we review the tumorigenic functions of HBx with an emphasis on wild type and truncated HBx variants, and their role in the transcriptional dysregulation and epigenetic reprogramming of the host cell genome. We suggest that HBx acquired by the HBV genome during evolution acts like a cellular proto-onc gene that is activated by deletion during hepatocarcinogenesis. The resulting viral oncogene (v-onc gene) codes for a truncated HBx protein that facilitates tumor progression. © 2016 John Wiley & Sons, Ltd.
Szenthe K.,Microbiological Research Group |
Szenthe K.,Europe Nonprofit Research Center |
Koroknai A.,Microbiological Research Group |
Banati F.,Microbiological Research Group |
And 10 more authors.
Biochemical and Biophysical Research Communications | Year: 2013
Although the microRNA miR-146a is an important regulator of immunological processes and contributes to the pathogenesis of certain B cell lymphoma types, in B cells the epigenetic regulation of miR-146a expresion has not been studied yet. To elucidate the mechanisms controlling miR-146a expression in B lymphoid cells we analysed epigenetic marks, including CpG methylation and histone modifications, at the miR-146a promoter in well characterized Epstein-Barr virus (EBV) positive and EBV negative B cell lines. In addition, EBV positive epithelial cell lines were also studied as controls. In cells with a silent miR-146a promoter the 5' regulatory sequences comprising a CpG island were devoid of activating histone modifications, independently of the methylation pattern of the regulatory region. The regulatory sequences flanking the inactive miR-146 promoter were hypermethylated at CpG dinucleotides in the EBV positive Burkitt's lymphoma (BL) cell lines of memory B cell phenotype (Rael and Akata), partially methylated in the mammary carcinoma cell lines C2G6 and C4A3, and completely unmethylated in the nasopharyngeal carcinoma cell line C666-1. In contrast, in EBV positive cell lines of activated B cell phenotype, and EBV negative BL cell lines the invariably unmethylated 5' regulatory sequences of active miR-146a promoters were enriched in the euchromatic histone modification marks acetylated histone H3, acetylated histone H4, and histone H3 dimethylated at lysine 4. The euchromatic histone modification marks extended over the immediate vicinity of the transcriptional initiation site to the 3' intron, too. We concluded that similarly to the promoters of protein coding genes, both DNA methylation and histone modifications contribute to the host cell dependent expression of miR-146a. © 2013 Elsevier Inc.