Alcohol Induces RNA Polymerase III-dependent Transcription through c-Jun by Co-regulating TATA-binding Protein (TBP) and Brf1 Expression

Abstract

Chronic alcohol consumption is associated with steatohepatitis and cirrhosis, enhancing the risk for hepatocellular carcinoma. RNA polymerase (pol) III transcribes a variety of small, untranslated RNAs, including tRNAs and 5S rRNAs, which determine the biosynthetic capacity of cells. Increased RNA pol III-dependent transcription, observed in transformed cells and human tumors, is required for oncogenic transformation. Given that alcohol consumption increases risk for liver cancer, we examined whether alcohol regulates this class of genes. Ethanol induces RNA pol III-dependent transcription in both HepG2 cells and primary mouse hepatocytes in a manner that requires ethanol metabolism and the activation of JNK1. This regulatory event is mediated, at least in part, through the ability of ethanol to induce expression of the TFIIIB components, Brf1, and the TATA-binding protein (TBP). Induction of TBP, Brf1, and RNA pol III-dependent gene expression is driven by enhanced c-Jun expression. Ethanol promotes a marked increase in the direct recruitment of c-Jun to TBP, Brf1, and tRNA gene promoters. Chronic alcohol administration in mice leads to enhanced expression of TBP, Brf1, tRNA, and 5S rRNA gene transcription in the liver. These alcohol-dependent increases are more pronounced in transgenic animals that express the HCV NS5A protein that display increased incidence of liver tumors. Together, these results identify a new class of genes that are regulated by alcohol through the co-regulation of TFIIIB components and define a central role for c-Jun in this process.

Role of Brf1 interaction with ERα, and significance of its overexpression, in human breast cancer

“…Protein concentrations of the resultant lysates were measured by the Bradford method using a Fluostar Omega spectrometer (Cell Biology Core Laboratory of University of Southern California Research Center for Liver Diseases, P30 DK048522). Lysates (50 μg of protein) of tissues or cells were separated by SDS/PAGE and subjected to western blot analysis as previously described (Zhong et al ., 2011, 2013b). Membranes were probed with specific antibodies against Brf1, ERα, and β‐actin as indicated.…”

“…tRNA and 5S rRNA control the translational and growth capacity of cells (Goodfellow et al ., 2006; White, 2004). Studies have indicated that oncogenic proteins, such as c‐Myc, c‐Jun, c‐Fos, and Ras, increase Pol III gene transcription (Goodfellow et al ., 2006; Johnson et al ., 2008; Zhang et al ., 2011, 2013; Zhong and Johnson, 2007; Zhong and Johnson, 2009; Zhong et al ., 2011). In contrast, tumor suppressors, such as BRCA1, p53, PTEN, and pRB, decrease transcription of these genes (Johnson et al ., 2008; White, 2004; Woiwode et al ., 2008; Zhong et al ., 2015).…”

“…Our studies have demonstrated that upregulation of Pol III genes results in increases in cell growth, transformation, and tumor development (Zhang et al ., 2011, 2013; Zhong and Johnson, 2007, 2009; Zhong et al ., 2011). The products of the tRNA and 5S rRNA genes are elevated in both transformed cells and tumor cells and biopsies of human cancer, suggesting that they play a crucial role in tumorigenesis (Johnson et al ., 2008; Woiwode et al ., 2008; Zhang et al ., 2011, 2013; Zhong and Johnson, 2007, 2009; Zhong et al ., 2011).…”

“…The products of the tRNA and 5S rRNA genes are elevated in both transformed cells and tumor cells and biopsies of human cancer, suggesting that they play a crucial role in tumorigenesis (Johnson et al ., 2008; Woiwode et al ., 2008; Zhang et al ., 2011, 2013; Zhong and Johnson, 2007, 2009; Zhong et al ., 2011). A decrease in Brf1 expression reduces Pol III gene transcription and is sufficient for repressing cell transformation and xenograft tumor formation (Johnson et al ., 2008; Woiwode et al ., 2008; Zhong et al ., 2013a, 2015, 2016).…”

“…A decrease in Brf1 expression reduces Pol III gene transcription and is sufficient for repressing cell transformation and xenograft tumor formation (Johnson et al ., 2008; Woiwode et al ., 2008; Zhong et al ., 2013a, 2015, 2016). Alcohol increases Brf1 expression to upregulate Pol III gene transcription in vivo and in vitro (Zhang et al ., 2013; Zhong et al ., 2011). Studies have indicated that alcohol administration induces breast tumor formation of alcohol‐fed mice (Wang et al ., 2012; Wong et al ., 2012).…”