The HBx protein of hepatitis B virus regulates the expression, intracellular distribution and functions of ribosomal protein S27a

Abstract

The pleiotropic HBx protein of hepatitis B virus is linked functionally to the development of hepatocellular carcinoma (HCC) via effectors and signalling pathways of the host. To identify such effectors in a macrocarcinogenic environment, a PCR-based cDNA subtraction analysis was carried out in the X15-myc oncomouse model of HCC. Altogether, 19 categories of genes, mainly involved in protein biosynthesis and the electron-transport chain, were found to be upregulated in the liver of these mice. Ribosomal protein S27a (RPS27a), which is a natural fusion protein of N-terminal ubiquitin and C-terminal extension protein (CEP), topped the list of expressed genes, with .20-fold higher expression compared with its normal level. Sustained and elevated expression of RPS27a in the mouse liver and its moderate expression in cell culture in the presence of HBx suggested an indirect role of RPS27a in hepatocarcinogenesis. Nevertheless, a remarkable change in the intracellular distribution of ubiquitin from cytoplasm to late-endosomal lysosomes, and of CEP from nucleoli to the perinucleolar region/nuclear foci, was observed in the presence of HBx. RPS27a accelerated the progression of the cell cycle and cooperated with HBx in this process. Further, the knockdown of RPS27a expression by RNA interference in an HBx microenvironment led to retarded cell-cycle progression and reduced cell size. Thus, these results suggest strongly that RPS27a could be an effector of HBx-mediated hepatocarcinogenesis. INTRODUCTIONChronic infection by hepatitis B virus (HBV) is a major public-health threat worldwide because of its reported association with cirrhosis, and more ominously hepatocellular carcinoma (HCC) (McMahon, 2009;Yang & Roberts, 2010). The oncogenic mechanisms of HBV have now begun to be elucidated. Multiple direct and indirect processes are involved in establishing HBV-related HCC (Kremsdorf et al., 2006). Integration of the HBV genome may stimulate tumorigenesis through either the cisactivation of cellular genes, such as the myc family of genes in woodchucks (Fourel et al., 1990), or transactivation by the viral X protein or HBx (Caselmann, 1996). HBx has been studied extensively for its role in HCC. It is a pleiotropic trans-activator that can stimulate a wide range of viral and cellular promoters (reviewed by Benhenda et al., 2009;Kumar & Sarkar, 2004). The oncogenic potential of HBx is evident from its ability to modulate tumorigenic signalling pathways (reviewed by Benhenda et al., 2009;Bouchard & Schneider, 2004), upregulate the expression of cellular oncogenes such as c-myc and c-jun (Caselmann, 1996) and functionally inactivate the tumour-suppressor protein p53 (Ueda et al., 1995). Besides, HBx can transform immortalized cells in vitro (Höhne et al., 1990; Shirakata et al., 1989) and induce liver-specific tumours in transgenic mouse models (reviewed by Kumar, 2008). There is constitutive activation of selected signalling pathways that promote cell growth and survival (Chemin & Zoulim, 2009).Although HBx stimulates a number...

DNA damage stress induces the expression of Ribosomal Protein S27a gene in a p53-dependent manner

“…Interestingly, RPS27a is also overexpressed in renal, breast and colon carcinomas (Kanayama et al, 1991;Adams et al, 1992;Wong et al, 1993). Recently, we have also reported a dramatic increase in the expression of RPS27a gene in an oncomouse model of hepatocellular carcinoma (Fatima et al, 2012).…”

“…The development of expression vector for the human RPS27a is described elsewhere (Fatima et al, 2012). pIRES2-EGFP and pEGFP-N3 were procured from Clontech, (USA).…”

“…Reverse transcriptase-PCR (RT-PCR) was performed with M-MuLV reverse transcriptase (Fermentas) according to the manufacturer's guidelines. RT-qPCR was done using specific primers (Table S1) as described previously (Fatima et al, 2012). Results were analyzed by using the comparative ΔΔCt method (Schmittgen and Livak, 2008).…”

The role of ribosomal proteins in the regulation of cell proliferation, tumorigenesis, and genomic integrity

“…(Fatima et al, 2012;Ganger et al, 2001;Kim et al, 2004;Masuda et al, 2014;Song et al, 2011) Esophageal cancer p-S6, L15 Upregulation Downregulation of L14 occurs frequently in ESCC and is an early event in the tumorigenesis of the esophagus. Kim et al, 2013;Wang et al, 2001) L14 Downregulation…”

Nuclear shuttling of Y Box binding protein-1, its clinical relevance in cancer and as a therapeutic target

“…The higher expression of these proteins develops the liver cancer between 20 and 28 weeks in mice through modulating various signaling pathways. Transcriptomic profile of X15-myc transgenic mice were analyzed which clearly indicates that the transcriptomic level of YB-1 was increased and coupled with various proteins involved in cell cycle progression, apoptosis and other growth related genes (Lakhtakia et al, 2003;Fatima et al, 2012). A number of studies are available to cite akin relation between hepatocellular carcinoma and chronic inflammation (Parkin et al, 2005;.…”