Potential utility of HOP homeobox gene promoter methylation as a marker of tumor aggressiveness in gastric cancer

HOP homeobox (HOPX) is an unusual homeobox gene encoding three spliced transcript variants, among which the only HOPX-Β promoter harbors CpG islands. The characteristics of its promoter methylation was analyzed using bisulfite sequencing and quantitative-methylation-specific polymerase chain reaction (Q-MSP), and the effects of HOPX expression were also examined. HOPX-Β expression was silenced in all gastric cancer cell lines tested; its expression could be restored by treatment with demethylating agent. On Q-MSP, HOPX-Β hypermethylation (cut-off value of 3.55) was found in 84% (67 out of 80) of primary tumor tissues and 10% (8 out of 80) of the corresponding normal tissues and could discriminate normal from tumor tissues (P0.0001). The prognosis of the advanced cases with HOPX-Β hypermethylation was as poor as those with stage IV disease when cut-off value was set at 11.28. This finding was validated in an independent cohort of 90 advanced gastric cancers. The HOPX-Β hypermethylation was also an independent prognostic factor (P0.029) on multivariate analysis. Exogenous HOPX expression significantly inhibited cell proliferation, colony formation and invasion as well as enhanced apoptosis. Taken together, HOPX-Β promoter methylation is a frequent and cancer-specific event in gastric cancer. Quantitative assessment of HOPX-Β methylation has great clinical potential as a marker of tumor aggressiveness.