title: Correlation between the single-site CpG methylation and expression silencing of the XAF1 gene in human gastric and colon cancers.
abstract: OBJECTIVE
  X-linked inhibitor of apoptosis protein (XIAP)-associated factor 1 (XAF1) antagonizes the anti-caspase activity of XIAP. XAF1 messenger RNA is present in normal tissues but undetectable in various cancers and thus poses a potential tumor suppressor gene. The aim of this study was to examine the novel pattern of methylation of XAF1 in gastric and colon cancers and locate the important CpG sites for transcriptional regulation and tumor progression.
  
  
  METHODS
  XAF1 expression was detected by reverse-transcription polymerase chain reaction (PCR) and Western blot analysis. Four different fragments around the transcription start site of XAF1 were cloned and examined putative promoter activities by luciferase reporter assay. Each CpG site in fragment F291 was mutated by site-directed mutagenesis technique, and the change of promoter activity of this fragment was detected by luciferase reporter assay. Methylation status of XAF1 was determined by methylation-specific PCR (MSP) and bisulfite DNA sequencing PCR analysis.
  
  
  RESULTS
  Down-regulation of XAF1 in association with hypermethylation was detected in 3 of 4 human gastric cancer cell lines and 6 of 8 colon cancer cell lines. Of the 4 promoter fragments, F291 showed the highest promoter activity, which could be down-regulated obviously by the mutation of particular CpG sites. Moreover, aberrant hypermethylation of these important CpG sites was strongly associated with the development of gastric and colon cancers.
  
  
  CONCLUSIONS
  A cluster of methylated CpG sites instead of CpG islands located in the promoter area resulted in gene silencing of XAF1, and CpGs at -2nd, -1st, and +3rd positions are functionally more important in its transcriptional regulation.
authors.affiliation: Department of Gastroenterology, Rui-jin Hospital, Shanghai Jiao Tong University, Shanghai, China.
authors.forename: Bing
authors.initials: B
authors.lastname: Zou
authors.forename: Chor Sang
authors.initials: CS
authors.lastname: Chim
authors.forename: Hui
authors.initials: H
authors.lastname: Zeng
authors.forename: Suet Yi
authors.initials: SY
authors.lastname: Leung
authors.forename: Yi
authors.initials: Y
authors.lastname: Yang
authors.forename: Shui Ping
authors.initials: SP
authors.lastname: Tu
authors.forename: Marie C M
authors.initials: MC
authors.lastname: Lin
authors.forename: Jide
authors.initials: J
authors.lastname: Wang
authors.forename: Hua
authors.initials: H
authors.lastname: He
authors.forename: Shi Hu
authors.initials: SH
authors.lastname: Jiang
authors.forename: Yun Wei
authors.initials: YW
authors.lastname: Sun
authors.forename: Li Fen
authors.initials: LF
authors.lastname: Yu
authors.forename: Siu Tsan
authors.initials: ST
authors.lastname: Yuen
authors.forename: Hsiang Fu
authors.initials: HF
authors.lastname: Kung
authors.forename: Benjamin C Y
authors.initials: BC
authors.lastname: Wong
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology; D051017:Apoptosis Regulatory Proteins; D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000235:genetics* / Q000378:metabolism; D018899:CpG Islands; D019175:DNA Methylation; D004273:DNA, Neoplasm / Q000235:genetics*; D000077209:Decitabine; D015536:Down-Regulation / Q000187:drug effects; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D020868:Gene Silencing; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D008875:Middle Aged; D009363:Neoplasm Proteins / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013274:Stomach Neoplasms / Q000235:genetics* / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000964:Antimetabolites, Antineoplastic; D051017:Apoptosis Regulatory Proteins; D004273:DNA, Neoplasm; D006877:Hydroxamic Acids; D047908:Intracellular Signaling Peptides and Proteins; D009363:Neoplasm Proteins; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; C417551:XAF1 protein, human; C012589:trichostatin A; D000077209:Decitabine; D001374:Azacitidine