title: Promoter hypermethylation: an important epigenetic mechanism for hMLH1 gene inactivation in head and neck squamous cell carcinoma.
abstract: OBJECTIVE
  The hMLH1 gene is one of the mismatch DNA repair genes. Inactivation of the hMLH1 gene has been implicated in the tumorigenesis of many types of human cancers. In most sporadic forms of human cancers, promoter hypermethylation is responsible for hMLH1 gene inactivation. Lack of hMLH1 protein expression has been found in a subset of head and neck squamous cell carcinomas (HNSCCs). The purpose of this study was to investigate whether promoter hypermethylation causes hMLH1 gene inactivation in HNSCCs.
  
  
  METHODS
  hMLH1 protein expression was determined by immunohistochemical staining in 62 cases, whereas hMLH1 gene promoter methylation was analyzed by methylation-sensitive restriction enzyme digestion, followed by polymerase chain reaction, in 35 cases of HNSCCs.
  
  
  RESULTS
  Sixteen (26%) of 62 cases of HNSCCs showed near-complete loss of hMLH1 protein expression on immunohistochemical staining. Twelve (92%) of 13 cases that were negative for the hMLH1 protein displayed promoter hypermethylation, whereas 17 (77%) of 22 cases positive for the protein were free of promoter methylation.
  
  
  CONCLUSIONS
  Promoter hypermethylation may be an important mechanism for hMLH1 gene inactivation in a subset of HNSCCs.
authors.affiliation: Department of Pathology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA.
authors.forename: Kela
authors.initials: K
authors.lastname: Liu
authors.forename: Huaiyun
authors.initials: H
authors.lastname: Huang
authors.forename: Perkins
authors.initials: P
authors.lastname: Mukunyadzi
authors.forename: James Y
authors.initials: JY
authors.lastname: Suen
authors.forename: Ehab
authors.initials: E
authors.lastname: Hanna
authors.forename: Chun-Yang
authors.initials: CY
authors.lastname: Fan
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D002294:Carcinoma, Squamous Cell / Q000235:genetics* / Q000473:pathology; D002352:Carrier Proteins; D019175:DNA Methylation; D020868:Gene Silencing; D006258:Head and Neck Neoplasms / Q000235:genetics* / Q000473:pathology; D006801:Humans; D000070957:MutL Protein Homolog 1; D009363:Neoplasm Proteins / Q000235:genetics*; D009687:Nuclear Proteins; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic / Q000235:genetics*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; C501486:MLH1 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D000070957:MutL Protein Homolog 1