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Epigenetic silencing of CHD5 , a novel tumor‐suppressor gene, occurs in early colorectal cancer stages
Author(s) -
Fatemi Mehrnaz,
Paul Thomas A.,
Brodeur Garrett M.,
Shokrani Babak,
Brim Hassan,
Ashktorab Hassan
Publication year - 2013
Publication title -
cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.052
H-Index - 304
eISSN - 1097-0142
pISSN - 0008-543X
DOI - 10.1002/cncr.28316
Subject(s) - dna methylation , microbiology and biotechnology , epigenetics , biology , bisulfite sequencing , chromodomain , gene silencing , chromatin , cancer research , methylation , histone , gene expression , dna , rna , gene , genetics , helicase
BACKGROUND Chromodomain 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. METHODS Here 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. RESULTS In 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). CONCLUSIONS The 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 . © 2013 American Cancer Society .