Hypermethylation of the RUNX3 gene in hepatocellular carcinoma

Methylation events play a critical role in various cellular processes including regulation of gene transcription and proliferation. Recently, RUNX3 gene, one of TGF-beta-Smads signaling transduction pathway genes, showed strong tumor-suppressor activity by regulation of epithelial proliferation and apoptosis. To elucidate the potential etiological role of the RUNX3 gene in the development of hepatocellular carcinoma (HCC), we have analyzed the methylation status of 5' CpG island of the RUNX3 gene in a series of 73 HCC tissues and 11 liver cell lines. Expectedly, promoter methylation of RUNX3 gene was found in 2 (2.7%) of 73 corresponding normal liver, whereas 30 (41.1%) of 73 HCCs and 4 (40%) of 10 liver cancer cell lines showed hypermethylation of the gene, respectively. There was no significant difference between promoter hypermethylaion and clinicopathologic parameters of primary HCC samples, including histologic grade, microvascular invasion, and clinical stage. Interestingly, demethylating agent 5-aza-2-deoxycytidine induced reactivation and more potent expression of RUNX3 gene in HCC cell lines. Our findings indicate that promoter hypermethylation of RUNX3 gene may occur as an early event in the development of HCC and that methylation may be a major mechanism for inactivation of RUNX3 gene in HCC.