Hepatitis B virus X protein upregulates HSP90alpha expression via activation of c-Myc in human hepatocarcinoma cell line, HepG2

Abstract

BackgroundThe Hepatitis B Virus X protein (HBx) plays a major role in hepatocellular carcinoma (HCC) development, however, its contribution to tumor invasion and metastasis has not been established so far. Heat shock protein 90 alpha (HSP90alpha) isoform is an ATP-dependent molecular chaperone that maintains the active conformation of client oncoproteins in cancer cells, which is abundantly expressed in HCC, especially in hepatitis B virus (HBV)-related tumors, might be involved in tumor progression.MethodsThe levels of HSP90alpha, extracellular signal-regulated kinase 1/2 (ERK1/2), phosphorylated ERK1/2 (p-ERK1/2) and c-Myc in HBx-transfected HepG2 cells were determined by western blots analysis. The endogenous ERKs activity was demonstrated by ELISA assay. The regulation of c-Myc-mediated HSP90 alpha promoter transactivation by HBx was evaluated through electrophoretic mobility shift analysis (EMSA). The c-Myc-mediated HSP90alpha transcription was analysed by promoter assay. The HBx-expressing cells were transfected with specific small interference RNA (siRNA) against c-Myc. The in vitro invasion potentials of cells were evaluated by Transwell cell invasion assay.ResultsHBx induces HSP90alpha expression at the transcription level. The induction effect of HBx was inhibited after treatment with c-Myc inhibitor, 10058-F4. In addition, the luciferase activity of the HSP90alpha promoter analysis revealed that the HBx is directly involved in the c-Myc-mediated transcriptional activation of HSP90alpha. Furthermore, HBx induces c-Myc expression by activation of Ras/Raf/ERK1/2 cascades, which in turn results in activation of the c-Myc-mediated HSP90alpha promoter and subsequently up-regulation of the HSP90alpha expression. Overexpression of HSP90alpha in HBx-transfected cells enhances tumor cells invasion. siRNA-mediated c-Myc knockdown in HBx-transfected cells significantly suppressed HSP90alpha expression and cells invasion in vitro.ConclusionThese results demonstrate the ability of HBx to promote tumor cells invasion by a mechanism involving the up-regulation of HSP90alpha and provide new insights into the mechanism of action of HBx and its involvement in tumor metastasis and recurrence of HCC.

Deletion and Functional Analysis of Hepatitis B Virus X Protein: Evidence for an Effect on Cell Cycle Regulators

“…Lee [41]. As HBx is known to induce c-Myc expression [42], the observed downregulation of p53 in the present study might be due to increased binding of Myc to the p53 promoter. HBx has a controversial role in modulation of apoptosis: some studies have showed proapoptotic effects [43][44][45][46][47], while others have assigned an anti-apoptotic effect with a role in HCC [48][49][50][51][52].…”

Dietary mycotoxins, co-exposure, and carcinogenesis in humans: Short review

“…Association of HBV with liver cancer is well established, estimated to cause over a million deaths annually (Anzola 2004). HBV integrates its DNA within hepatocytes, enabling production of an oncogenic protein, HBx (Li et al 2010). The mechanisms by which this protein promotes carcinogenesis are manifold, with HBx described as a multifunctional factor able to inhibit a range of DNA repair and apoptotic mechanisms while upregulating growth factors (Zhang et al 2006).…”

Hepatitis B virus X gene and hepatocarcinogenesis

“…Firstly, several studies have uncovered various pathways which may be implicated in the increased motility of tumor cells, such as changes in the expression of proteins that may be involved in cell migration and decreased focal adhesion (e.g., upregulation of proteins such as MACF1, HMGB1, and Annexin A2 and downregulation of others such as Lamin A/C); activation of Rho GTPases and Rac1, with mutations at the sites of the proline-rich domain located in HBx; and upregulation of the expression of heat shock protein 90alpha (HSP90alpha) and c-met protein, as well as that of TANK-binding kinase-1 (TBK1), which induces the phosphorylation of NF-kappaB p65 at serine 536, at the transcriptional level [52,[76][77][78][79]. Secondly, the upregulation of inflammatory mediators by HBx is another pathway of interest.…”