DNA methylation and histone deacetylation associated with silencing DAP kinase gene expression in colorectal and gastric cancers

Death-associated protein kinase is a positive regulator of programmed cell death induced by interferon γ. To investigate the role of epigenetic inactivation of death-associated protein kinase in gastrointestinal cancer, we examined the methylation status of the 5′ CpG island of the death-associated protein kinase gene. Methylation of the 5′ CpG island was detected in 3 of 9 colorectal and 3 of 17 gastric cancer cell lines, while among primary tumours, it was detected in 4 of 28 (14%) colorectal and 4 of 27 (15%) gastric cancers. By contrast, methylation of the edge of the CpG island was detected in virtually every sample examined. Death-associated protein kinase expression was diminished in four cell lines that showed dense methylation of the 5′ CpG island, and treatment with 5-aza-2′-deoxycitidine, a methyltransferase inhibitor, restored gene expression. Acetylation of histones H3 and H4 in the 5′ region of the gene was assessed by chromatin immunoprecipitation and was found to correlate directly with gene expression and inversely with DNA methylation. Thus, aberrant DNA methylation and histone deacetylation of the 5′ CpG island, but not the edge of the CpG island, appears to play a key role in silencing death-associated protein kinase expression in gastrointestinal malignancies.