title: Status of reduced expression and hypermethylation of the APC tumor suppressor gene in human oral squamous cell carcinoma.
abstract: The adenomatous polyposis coli gene (APC gene) originally was identified as a tumor suppressor gene in colon cancer. We reported previously that APC is mutated and/or deleted in primary oral squamous cell carcinoma (OSCC) tissues and suggested that loss of APC function contributes to carcinogenesis in the oral region. In this study, we examined 50 OSCC tissue samples, which had been fixed in 10% buffered formaldehyde solution and embedded in paraffin, and eight cell lines, which were derived from OSCC, to analyze the expression level of the APC gene. Significant down-regulation of APC was detected by immunohistochemistry in 15 (30.0%) of 50 tissue samples and by the reverse transcriptase-polymerase chain reaction in five (62.5%) of eight cell lines. We then investigated the status of APC gene promoter methylation and restoration of the APC gene mRNA. Hypermethylation of the APC promoter CpG island was detected in two of eight (25%) OSCC-derived cell lines, and APC gene mRNA was restored in all OSCC-derived cell lines showing down-regulation of gene expression (n=5) after treatment with 5-aza-2'-deoxycytidine, a DNA demethylating agent. Thus, the contribution of down-regulated APC expression to the development of human OSCC was about 30%, and hypermethylation of the gene promoter CpG island was confirmed to be a significant mechanism of inactivation of the APC gene in oral carcinogenesis.
authors.affiliation: Division of Dentistry and Oral-Maxillofacial Surgery, Chiba University Hospital, Chiba, Japan.
authors.forename: Hisako
authors.initials: H
authors.lastname: Uesugi
authors.forename: Katsuhiro
authors.initials: K
authors.lastname: Uzawa
authors.forename: Kenshi
authors.initials: K
authors.lastname: Kawasaki
authors.forename: Ken
authors.initials: K
authors.lastname: Shimada
authors.forename: Tetsuhiro
authors.initials: T
authors.lastname: Moriya
authors.forename: Akio
authors.initials: A
authors.lastname: Tada
authors.forename: Masashi
authors.initials: M
authors.lastname: Shiiba
authors.forename: Hideki
authors.initials: H
authors.lastname: Tanzawa
mesh_terms: D025601:Adenomatous Polyposis Coli Protein / Q000235:genetics* / Q000378:metabolism; D001374:Azacitidine; D002294:Carcinoma, Squamous Cell / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D019175:DNA Methylation; D015536:Down-Regulation; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D009062:Mouth Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D025601:Adenomatous Polyposis Coli Protein; D012333:RNA, Messenger; D001374:Azacitidine