Identification of HRK as a target of epigenetic inactivation in colorectal and gastric cancer

Toshiro Obata, Minoru Toyota, Ayumi Satoh, Yasushi Sasaki, Kazuhiro Ogi, Kimishige Akino, Hiromu Suzuki, Masafumi Murai, Takefumi Kikuchi, Hiroaki Mita, Fumio Itoh, Jean-Pierre J Issa, Takashi Tokino, Kohzoh Imai
Clinical Cancer Research 2003 December 15, 9 (17): 6410-8

PURPOSE: Aberrant methylation of CpG islands can be a good molecular marker for identifying genes inactivated in cancer. We found the proapoptotic gene HRK to be a target for hypermethylation in human cancers and examined the role of such methylation in silencing the gene's expression.

EXPERIMENTAL DESIGN: Methylation of HRK was evaluated by bisulfite-PCR and bisulfite sequencing in a group of colorectal and gastric cancer cell lines and primary cancers. Gene expression and histone acetylation were examined by reverse transcription-PCR and chromatin immunoprecipitation analyses, respectively. Apoptosis of cancer cells after treatment with a DNA methyltransferase inhibitor and/or histone deacetylase inhibitor was examined with fluorescence-activated cell-sorting analysis.

RESULTS: The region around the HRK transcription start site was methylated in 36% of colorectal and 32% of gastric cancer cell lines and was closely associated with loss of expression in those cell types. HRK expression was restored by treatment with a methyltransferase inhibitor, 5-aza-deoxycytidine, and enhanced further by addition of histone deacetylase inhibitor trichostatin A or depsipeptide. Such restoration of HRK expression was well correlated with induction of apoptosis and enhancement of Adriamycin-induced apoptosis. Expression of other proapoptotic genes, including BAX, BAD, BID, and PUMA, was unaffected by treatment with 5-aza-deoxycytidine. Aberrant methylation of HRK was also frequently detected in primary colorectal cancers that showed methylation of multiple genes, including p16INK4A and hMLH1, and was associated with wild-type p53.

CONCLUSION: HRK methylation can be a useful molecular target for cancer therapy in a subset of colorectal and gastric cancers.

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