Epigenetic silencing ofSFRP1andSFRP5by hepatitis B virus X protein enhances hepatoma cell tumorigenicity through Wnt signaling pathway

Abstract

Secreted frizzled-related proteins (SFRPs) are antagonists of the Wnt signaling pathway whose epigenetic downregulation have been shown to be involved in hepatocarcinogenesis. However, dysregulation of SFRPs induced by hepatitis B virus (HBV) X protein (HBx) has never been studied in HBV-related hepatocellular carcinoma (HBV-HCC). In this study, we sought to determine the clinical significance and underlying mechanism of HBx-induced SFRPs dysregulation in hepatoma cells and HBV-HCC patients. Our results showed that SFRP1 and SFRP5 expression were dramatically decreased by HBx in hepatoma cells. The repressed expression in hepatoma cells was partially rescued by a DNA methylation inhibitor and synergistically increased by a combination treatment with a histone deacetyltransferases inhibitor. In addition, we identified that SFRP1 and SFRP5 promoters were hypermethylated in both HBx-expressing hepatoma cells and HBV-HCC tissues. Downregulation of SFRP1 and SFRP5 in HBV-HCC tissues was significantly correlated with overexpression of DNA methyltransferase 1 (DNMT1) and poor tumor differentiation. HBx facilitated the binding of DNMT1 and DNMT3A to SFRP1 and SFRP5 promoters, and resulted in epigenetic silencing of SFRP1 and SFRP5. Moreover, overexpression of SFRP1, SFRP5 or RNA interference mediated silencing of DNMT1 inactivated the Wnt signaling pathway and decreased the expression levels of Wnt target genes c-Myc and CyclinD1, thus impeding HCC growth in vitro and in vivo, and regressing HBx-induced epithelial-mesenchymal transition (EMT). Our findings strongly suggest that epigenetic silencing of SFRP1 and SFRP5 by HBx allows constitutive activation of Wnt signaling pathway and hence contributes to hepatocarcinogenesis.Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related deaths worldwide. One of the high risk factors associated with HCC is chronic hepatitis B virus (HBV) infection.1 HBV X protein (HBx), a pleiotropic protein encoded by HBV, plays a vital role in hepatocellular carcinogenesis.2 As a multifunctional regulator, HBx is capable of trans-regulation of many cellular genes by interacting with nuclear transcription factors, such as CREB, AP-1 and NF- jB.3 Further, HBx is involved in the activation of several oncogenic signal transduction pathways, including the Wnt/ b-catenin, SAPK/JNK, NF-jB, Ras/MAPK and FAK pathways.3-5 Recent studies indicated that HBx is also involved in epigenetic regulation of several tumor suppressor genes in hepatocarcinogenesis. 6,7 The Wnt/b-catenin signaling pathway has been implicated in a wide range of biological processes, including cell

Methylation of the Glutathione-S-Transferase P1 Gene Promoter Is Associated with Oxidative Stress in Patients with Chronic Hepatitis B

“…In mammals, DNA methylation is mainly catalyzed by DNMT1, DNMT3a and DNMT3b. Several studies have reported that HBV could increase the expression of DNMT1 and DNMT3a, resulting in aberrant promoter methylation of E-cadherin, p16INK4A, SFRP1and SFRP5 (Lee et al 2005;Jung et al 2007;Xie et al 2014). Consistent with these studies, this study found that GSTP1 promoter methylation was positively correlated with DNMT1 mRNA, DNMT3a mRNA, TNF-α, MDA, HBeAg, ALT, AST and TBIL in patients with CHB.…”

Forced expression of Wnt antagonists sFRP1 and WIF1 sensitizes chronic myeloid leukemia cells to tyrosine kinase inhibitors

“…DNA methylation of CpG sites in the promoter region has been demonstrated to be responsible for the downregulation of sFRP genes in many forms of cancer and leukemia. 21,[32][33][34][35][36] Our data is in line with previous studies, showing that transcriptional silencing of sFRP1 correlates with therapy resistance and progressive disease. 29 We suggest a model of hematopoiesis in which Wnt antagonists sFRP1 and WIF1 normally play a central role in downregulating β-catenin in granulocyte-macrophage progenitors.…”

Epigenetic mechanisms in cancer: push and pull between kneaded erasers and fate writers

“…For example, expression of SFRP5 and SFRP1 was markedly reduced in HBx-infected cells. 28 In vitro analysis confirmed the presence of hypermethylated promoter regions of SFRP1 and SFRP5 genes in HBx-expressing hepatoma cells. Detailed assays provided evidence of HBx-directed binding of DNMT3A and DNMT1 to the promoter regions of SFRP5 and SFRP1.…”