Epigenetic Silencing of CHD5, a Novel Tumor-Suppressor Gene, Occurs in Early Colorectal Cancer Stages

BACKGROUNDChromodomain helicase DNA binding protein 5 (CHD5) is a family member of chromatin remodeling factors. The epigenetic silencing mechanisms of CHD5 in colorectal cancer have not been well studied. METHODSHere we analyzed CHD5 methylation and mRNA expression in vitro and in clinical samples from African American patients. DNA and RNA were isolated from formalin fixed paraffin embedded (FFPE) colon tissues. DNA was tested for methylation using methylation-specific polymerase chain reation (PCR) and bisulfite sequencing. RNA was used for mRNA quantification using qRT-PCR. The RKO cell line was treated with 5-Aza-dC and SAHA. RKO cells were also stably transfected with a CHD5-expressing vector. The transcriptional activity was studied in the 1 kb upstream region of the CHD5 promoter using the dual reporter assay. We performed cell proliferation, migration, and invasion assays using the RKO cell line. RESULTSIn most adenoma samples, CHD5 expression was not detected in contrast to normal tissues. In RKO cells, CHD5 silencing was associated with DNA methylation and repressive histone modifications. CHD5 expression was restored after treatment with 5-Aza-dC and SAHA. CHD5 reactivation reduced cell proliferation, migration, and invasion. The reporter assay indicated that the main regulatory region of the CHD5 promoter is encompassed in the -489 to -823 region with important transcriptional regulatory sites (TCF/LEF, SP1, and AP-2). CONCLUSIONSThe CHD5 gene is repressed in all types of adenomas, either epigenetically or by chromosomal deletion. CHD5 activity is regulated by DNA methylation and repressive histone modifications. CHD5 likely acts as a tumor-suppressor gene in early colorectal carcinogenesis. Cancer 2014;120:172-180. (c) 2013 American Cancer Society. Colorectal cancer develops through an adenoma-adenocarcinoma carcinogenesis process, and this sequential process is driven by 3 molecular pathways: chromosomal instability, microsatellite instability, and CpG island methylation. This study was conducted to explore whether the CHD5 gene acts as a tumor-suppressor or oncogene in colon cancer.