title: Promoter hypermethylation of KLF4 inactivates its tumor suppressor function in cervical carcinogenesis.
abstract: OBJECTIVE
  The KLF4 gene has been shown to be inactivated in cervical carcinogenesis as a tumor suppressor. However, the mechanism of KLF4 silencing in cervical carcinomas has not yet been identified. DNA methylation plays a key role in stable suppression of gene expression.
  
  
  METHODS
  The methylation status of the KLF4 promoter CpG islands was analyzed by bisulfite sequencing (BSQ) in tissues of normal cervix and cervical cancer. KLF4 gene expression was detected by RT-PCR, immunohistochemistry and western blot. KLF4 promoter methylation in cervical cancer cell line was determined by BSQ and methylation-specific polymerase chain reaction (MS-PCR). Cell proliferation ability was detected by cell growth curve and MTT assay.
  
  
  RESULTS
  The methylated allele was found in 41.90% of 24 cervical cancer tissues but only in 11.11% of 11 normal cervix tissues (P<0.005). KLF4 mRNA levels were significantly reduced in cervical cancer tissues compared with normal cervix tissues (P<0.01) and KLF4 mRNA expression showed a significant negative correlation with the promoter hypermethylation (r = -0.486, P = 0.003). Cervical cancer cell lines also showed a significant negative correlation between KLF4 expression and hypermethylation. After treatment with the demethylating agent 5-Azacytidine (5-Aza), the expression of KLF4 in the cervical cancer cell lines at both mRNA and protein levels was drastically increased, the cell proliferation ability was inhibited and the chemosensitivity for cisplatin was significantly increased.
  
  
  CONCLUSIONS
  KLF4 gene is inactivated by methylation-induced silencing mechanisms in a large subset of cervical carcinomas and KLF4 promoter hypermethylation inactivates the gene's function as a tumor suppressor in cervical carcinogenesis.
authors.affiliation: Department of Reproductive Medicine, First Affiliated Hospital Medical School of Xi'an Jiaotong University, Xi'an, The People's Republic of China ; Department of Biochemistry and Molecular Biology, Medical School of Xi'an Jiaotong University, Xi'an, The People's Republic of China.
authors.forename: Wen-Ting
authors.initials: WT
authors.lastname: Yang
authors.affiliation: Department of Reproductive Medicine, First Affiliated Hospital Medical School of Xi'an Jiaotong University, Xi'an, The People's Republic of China ; Department of Biochemistry and Molecular Biology, Medical School of Xi'an Jiaotong University, Xi'an, The People's Republic of China ; Section of Cancer Stem Cell Research, Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education of People's Republic of China, Xi'an, The People's Republic of China.
authors.forename: Peng-Sheng
authors.initials: PS
authors.lastname: Zheng
mesh_terms: D001374:Azacitidine / Q000494:pharmacology; D063646:Carcinogenesis / Q000187:drug effects / Q000235:genetics* / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002945:Cisplatin / Q000494:pharmacology; D019175:DNA Methylation / Q000187:drug effects / Q000235:genetics*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D000090062:Kruppel-Like Factor 4; D051741:Kruppel-Like Transcription Factors / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D014176:Protein Biosynthesis / Q000187:drug effects / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*; D002583:Uterine Cervical Neoplasms / Q000235:genetics* / Q000473:pathology
chemical_list: C000715467:KLF4 protein, human; D000090062:Kruppel-Like Factor 4; D051741:Kruppel-Like Transcription Factors; D025521:Tumor Suppressor Proteins; D001374:Azacitidine; D002945:Cisplatin