Promoter methylation of cysteine dioxygenase type 1: gene silencing and tumorigenesis in hepatocellular carcinoma

BACKGROUNDS/AIMS: Cysteine dioxygenase type 1 (CDO1) acts as a tumor suppressor and is silenced by promoter methylation in various malignancies. The relationship between the CDO1 methylation status and hepatocellular carcinoma (HCC) tumorigenesis was evaluated. METHODS: Using a HCC cell line (SNU423), an in vitro demethylation study was performed to confirm whether promoter methylation causes CDO1 down-regulation. The SNU423 cells transfected with the CDO1 cell function was compared to that of naïve cells. An in vivo study using immunohistochemical staining of HCC specimens that were collected from patients who underwent curative liver resection was also performed. RESULTS: CDO1 was activated after demethylation treatment in the HCC specimens. Moreover, tumor cell proliferation, colony-forming, migration, and invasion activities significantly decreased after CDO1 transfection (p<0.05). The percentage of tumors that were larger than 5 cm was higher in patients who had a lower expression of CDO1 (p=0.030). Vascular invasion and histological grade were independent prognostic factors for poor overall and recurrence-free survival. The degree of CDO1 expression was not an independent prognostic factor in this study's population. CONCLUSIONS: These results suggested that methylation down-regulated CDO1 expression in the HCC cells. CDO1 methylation may be a potentially valuable diagnostic biomarker for HCC.