title: DNA methylation reactivates GAD1 expression in cancer by preventing CTCF-mediated polycomb repressive complex 2 recruitment.
abstract: Levels of γ-aminobutyric acid (GABA) and glutamic acid decarboxylase 1 (GAD1), the enzyme that synthesizes GABA, are significantly increased in neoplastic tissues. However, the mechanism underlying this increase remains elusive. Instead of silencing gene transcription, we showed that the GAD1 promoter was hypermethylated in both colon and liver cancer cells, leading to the production of high levels of GAD1. GAD1 is a target gene that is silenced by H3K27me3. The key locus responsible for GAD1 reactivation was mapped to a DNA methylation-sensitive CTCF-binding site (CTCF-BS3) within the third intron of GAD1. Chromosome configuration capture (3C) analysis indicated that an intrachromosomal loop was formed by CTCF self-dimerisation in normal cells (CTCF binds to both unmethylated CTCF-BS3 and CTCF-BS2). The CTCF dimer then interacted with suppressor of zeste 12 homologue (SUZ12), which is a domain of Polycomb repressive complex 2 (PRC2), promoting the methylation of H3K27 and the silencing of GAD1 expression. This silencing was shown to be inhibited by DNA methylation in cancer cells. These findings strongly suggest that GAD1 is reactivated by DNA methylation, which provided a model for DNA methylation and the active orchestration of oncogenic gene expression by CTCF in cancer cells.
authors.affiliation: Department of Laboratory Medicine, Changhai Hospital, The Second Military Medical University, Shanghai, China.
authors.forename: H
authors.initials: H
authors.lastname: Yan
authors.affiliation: Institute of Genetics, Second Military Medical University, Shanghai, China.
authors.forename: G
authors.initials: G
authors.lastname: Tang
authors.affiliation: Department of Colorectal Surgery, Changhai Hospital, Second Military Medical University, Shanghai, China.
authors.forename: H
authors.initials: H
authors.lastname: Wang
authors.affiliation: Department of Colorectal Surgery, Changhai Hospital, Second Military Medical University, Shanghai, China.
authors.forename: L
authors.initials: L
authors.lastname: Hao
authors.affiliation: Division of Hepatopancreatobiliary Surgery, Changhai Hospital, Second Military Medical University, Shanghai, China.
authors.forename: T
authors.initials: T
authors.lastname: He
authors.affiliation: Department of Laboratory Medicine, Changhai Hospital, The Second Military Medical University, Shanghai, China.
authors.forename: X
authors.initials: X
authors.lastname: Sun
authors.affiliation: Genomic Medicine Institute, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH, USA.
authors.forename: A H
authors.initials: AH
authors.lastname: Ting
authors.affiliation: Department of Laboratory Medicine, Changhai Hospital, The Second Military Medical University, Shanghai, China.
authors.forename: A
authors.initials: A
authors.lastname: Deng
authors.affiliation: Institute of Genetics, Second Military Medical University, Shanghai, China.
authors.forename: S
authors.initials: S
authors.lastname: Sun
mesh_terms: D000076246:CCCTC-Binding Factor; D045744:Cell Line, Tumor; D019175:DNA Methylation; D005968:Glutamate Decarboxylase / Q000235:genetics*; D006801:Humans; D009363:Neoplasm Proteins; D009369:Neoplasms / Q000378:metabolism* / Q000473:pathology; D063151:Polycomb Repressive Complex 2 / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000032:analysis; D012097:Repressor Proteins / Q000502:physiology*; D014157:Transcription Factors
chemical_list: D000076246:CCCTC-Binding Factor; C000619697:CTCF protein, human; D009363:Neoplasm Proteins; D012333:RNA, Messenger; D012097:Repressor Proteins; C430461:SUZ12 protein, human; D014157:Transcription Factors; D063151:Polycomb Repressive Complex 2; D005968:Glutamate Decarboxylase; C402565:glutamate decarboxylase 1