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(Background) Tumor suppressor genes (TSG) play a critical role in cancer progression, and epigenetic aberrations including promoter hypermethylation and histone hypoacetylation lead to transcriptional inactivation of many TSG. A comprehensive survey of commonly inactivated tumor suppressor genes in major epithelial tumors has remained elusive. (Materials and Methods) We performed comprehensive identification of TSG in esophageal squamous cell carcinoma (ESCC) based on functional reactivation of epigenetically silenced TSGs by 5-aza-2’-deoxycytidine and trichostatin A using microarrays containing 12599 genes in ESCC cell lines. (Results) Among genes identified, the following 2 genes are of particular interest from clinical point of view (PGP9.5 and HOP). (1) PGP9.5 is frequently methylated (42%) in primary ESCC tissues by COBRA and TaqMan MSP. Methylation of gene PGP9.5 is significantly correlated with lymph node metastasis (p=0.03) and patient prognosis for 5-year survival (p=0.01). Multivariate analysis showed that gene X is an independent prognostic factor (p=0.03). (2) We identified gene HOP likely to be a master gate keeper of tumorigenesis in SCC. HOP α transcript is always silenced in primary ESCC tissues, while β transcript is silenced in half cases of the ESCC. α transcript is not associated with epigenetic state, while β transcript is likely controlled by epigenetics in primary ESCC tissues (70%), suggesting that β transcript shut-down could be a gatekeeping event. Forced expression of gene HOP into 4 SCC cells completely suppressed tumorigenesis in soft agar, and conversely RNA interference knock-down of this gene restored oncogenic properties. In this report, we proposed the novel gatekeeping event tightly associated with tumorigenesis of SCC, and the novel target for actual therapy against SCC. (Conclusion) DNA promoter methylation could be applicable and promising for actual clinics.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]