title: Downregulation of ID4 by promoter hypermethylation in gastric adenocarcinoma.
abstract: Promoter hypermethylation has become apparent as a common mechanism of gene silencing in cancer. Based on our published microarray expression data, we noticed a prominent downregulation of ID4 in gastric adenocarcinoma. The dense 5' CpG island covering the previously mapped upstream promoter of ID4 has prompted us to relate its downregulation to promoter hypermethylation. ID proteins are distinct members in the helix-loop-helix family of transcriptional regulators, which modulate various key developmental processes. Emerging data have suggested the involvement of ID genes in tumorigenesis. In this study using bisulfite genomic sequencing, we have found hypermethylation of ID4 promoter in most gastric cancer cell lines and 30% of primary tumors. This correlated with decreased level of ID4 expression. Restoration of ID4 expression in various gastric cancer cell lines was achieved by treatment with the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine, which at times required the synergistic action of the histone deacetylase inhibitor trichostatin A, but not with trichostatin A alone. Re-expression was accompanied by the corresponding ID4 promoter demethylation. Furthermore, we have found significant association of ID4 promoter methylation with hMLH1 promoter methylation (P=0.008) and microsatellite instability (P=0.006). Overall, our results have shown that transcriptional silencing of ID4 is related to the aberrant methylation of its promoter in gastric cancer. The significant association of ID4 and hMLH1 promoter hypermethylation suggested that ID4 may also be among the genes being targeted in the CpG island methylator phenotype tumorigenic pathway.
authors.affiliation: Department of Pathology, The University of Hong Kong, Queen Mary Hospital, Hong Kong.
authors.forename: Agnes Sze Wah
authors.initials: AS
authors.lastname: Chan
authors.forename: Wai Yin
authors.initials: WY
authors.lastname: Tsui
authors.forename: Xin
authors.initials: X
authors.lastname: Chen
authors.forename: Kent Man
authors.initials: KM
authors.lastname: Chu
authors.forename: Tsun Leung
authors.initials: TL
authors.lastname: Chan
authors.forename: Annie Shuk Yee
authors.initials: AS
authors.lastname: Chan
authors.forename: Rui
authors.initials: R
authors.lastname: Li
authors.forename: Samuel
authors.initials: S
authors.lastname: So
authors.forename: Siu Tsan
authors.initials: ST
authors.lastname: Yuen
authors.forename: Suet Yi
authors.initials: SY
authors.lastname: Leung
mesh_terms: D000230:Adenocarcinoma / Q000235:genetics* / Q000378:metabolism; D001374:Azacitidine / Q000031:analogs & derivatives* / Q000627:therapeutic use; D002460:Cell Line; D019175:DNA Methylation; D015254:DNA Modification Methylases / Q000037:antagonists & inhibitors; D004268:DNA-Binding Proteins / Q000378:metabolism*; D000077209:Decitabine; D015536:Down-Regulation; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000627:therapeutic use; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D018257:Helix-Loop-Helix Motifs; D056572:Histone Deacetylase Inhibitors; D006801:Humans; D006877:Hydroxamic Acids / Q000627:therapeutic use; D051796:Inhibitor of Differentiation Proteins; D018895:Microsatellite Repeats / Q000235:genetics; D011401:Promoter Regions, Genetic; D013274:Stomach Neoplasms / Q000235:genetics* / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D056572:Histone Deacetylase Inhibitors; D006877:Hydroxamic Acids; C490128:ID4 protein, human; D051796:Inhibitor of Differentiation Proteins; D014157:Transcription Factors; C012589:trichostatin A; D000077209:Decitabine; D015254:DNA Modification Methylases; D001374:Azacitidine