Oncogenic activation of the Wnt/b-catenin signaling pathway is common in hepatocellular carcinoma (HCC). Our recent studies have demonstrated that SRY (sex determining region Y)-box 1 (SOX1) and secreted frizzled-related proteins are concomitantly promoter-hypermethylated, and this might lead to abnormal activation of the Wnt signaling pathway in HCC. SOX1 encodes a transcription factor involved in the regulation of embryonic development and cell fate determination. However, the expression and functional role of SOX1 in HCC remains unclear. In this study, we confirmed via quantitative methylation-specific polymerase chain reaction that SOX1 was frequently downregulated through promoter hypermethylation in HCC cells and tissues. Overexpression of SOX1 by a constitutive or inducible approach could suppress cell proliferation, colony formation, and invasion ability in HCC cell lines, as well as tumor growth in nonobese diabetic/severe combined immunodeficiency mice. Conversely, knockdown of SOX1 by withdrawal of doxycycline could partially restore cell proliferation and colony formation in HCC cells. We used a T cell factor (TCF)-responsive luciferase reporter assay and western blot analysis to prove that SOX1 could regulate TCF-responsive transcriptional activity and inhibit the expression of Wnt downstream genes. Furthermore, we used glutathione S-transferase pull-down, co-immunoprecipitation, and confocal microscopy to demonstrate that SOX1 could interact with b-catenin but not with the b-catenin/TCF complex. Moreover, restoration of the expression of SOX1 induces significant cellular senescence in Hep3B cells. Conclusion: Our data show that a developmental gene, SOX1, may function as a tumor suppressor by interfering with Wnt/b-catenin signaling in the development of HCC. (HEPATOLOGY 2012;56:2277-2287 T he incidence and mortality of hepatocellular carcinoma (HCC) have been increasing rapidly worldwide in recent decades.1 The risk factors associated with hepatocarcinogenesis are numerous and include chronic hepatitis B or C viral infection, alcohol, aflatoxin B1, and others. However, the molecular mechanisms involved in the development of HCC remain unclear. Recent studies have demonstrated that inactivation of tumor suppressor genes (TSGs) through promoter hypermethylation plays an essential role in carcinogenesis.2,3 Furthermore, methylation profiles have been used as potential biomarkers for early diagnosis, prognostic prediction, and screening in HCC. 4 Therefore, exploring the molecular mechanisms of the inactivation of TSGs involved in HCC development could improve the treatment of HCC in the future.

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Concomitant epigenetic silencing of SOX1 and SFRPs through promoter hypermethylation is frequent in HCCs, and this might contribute to abnormal activation of canonical Wnt signal pathway.

Promoter methylation of ZNF177, COL14A1, HOXA9, DPYSL4, and TMEFF2 genes is a frequent epigenetic event in EC. Furthermore, the epigenetic hypermethylation of TMEFF2 may be a valuable marker for identifying undetected EC within endometrial hyperplasia.

Oncogenic activation of the Wnt/β-catenin signaling pathway is common in hepatocellular carcinoma (HCC). The secreted frizzled-related proteins (SFRPs) function as negative regulators of Wnt signaling and have important implications for carcinogenesis. Recently, we have shown that SFRPs are frequently downregulated through promoter hypermethylation in HCC cell lines and clinical HCC tissues. Furthermore, we have demonstrated that restoration of SFRPs could attenuate Wnt signaling in HCC cells with β-catenin point mutation, decrease abnormal accumulation of free β-catenin in the nucleus, and then suppress cell growth. Sox1 encodes a transcription factor involved in the regulation of embryonic development and cell fate determination. Structurally related to TCF/LEFs, several members of the Sox family, including Sox17, Sox3, Sox7, and Sox9, have also been implicated in repressing β-catenin activity by a mechanism that is not well understood. In this study, we found that the Sox1 was severely down-regulated by quantitative reverse transcription polymerase chain reaction (QRT-PCR). Next, we employed bisulfite modification and methylation-specific PCR (MS-PCR) to analyze the feature of Sox1 promoter methylation in the HCC cell lines and found that the majority of the tested cell lines exhibited hypermethylation. Meanwhile, we also examined sixty primary HCC surgical samples and adjacent nonturmorous liver tissues from Taiwan Liver Cancer Network (TLCN). These results showed that aberrant promoter methylation of SOX1 were found in 32 of 60 HCCs (53.3%), in 13 of 50 cirrhotic livers (26%), and in one of 30 normal control tissues (3.3%). Concomitantly, SFRPs was epigenetically inactivated in HCC cell lines and most of all the tumors with methylated SOX1. A significant correlation between the methylation of both genes was found (p >0.05). Furthermore, overexpression of SOX-1 in HCC cells could suppress TCF-dependent transcriptional activity and suppress colony formation. Taken together, our data suggest that SOX1 is a negative modulator of Wnt/β-catenin signaling, and that SOX1 silencing due to promoter hypermethylation is an early event during tumorigenesis and may contribute to aberrant activation of Wnt signaling in HCC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 173.

Oncogenic activation of the Wnt/β-catenin signaling pathway is common in hepatocellular carcinoma (HCC). Aberrant hypermethylation of tumor suppressor genes in their promoter regions is frequently found in human cancers. Our previous works have demonstrated that SOX1 gene was hypermethylated in HCCs as well as cervical and ovarian cancers. A growing number of papers suggest that SOX family proteins, such as SOX9, SOX17, SOX4 and SOX2, serve as either tumor suppressors or oncoproteins through manipulating Wnt signaling pathway in different types of cancer. However the molecular mechanism is not well understood. In this study, we established an inducible system to overexpress SOX1 in HCC cell lines and checked whether SOX1 have tumor suppressor function in vitro and in vivo. We found that overexpression of SOX1 could inhibit cell proliferation and colony formation in HCC cells and suppress tumor growth in xenograft mice. Next we used GST pull-down, co-immunoprecipitation (co-IP), immunocytochemistry and luciferase reporter assay to study whether SOX1 could interact with β-catenin to regulate Wnt/β-catenin signaling. Our data showed that SOX1 is physically associated with β-catenin/ TCF complex and could inhibit the TCF-dependent transcriptional activity. Furthermore, SOX1 was co-localized with β-catenin in nucleus by confocal microscopy. These results suggest that SOX1 functions as a tumor suppressor through interfering Wnt/β-catenin signaling in HCC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2199. doi:10.1158/1538-7445.AM2011-2199