title: Haplotype defined by the MLH1-93G/A polymorphism is associated with MLH1 promoter hypermethylation in sporadic colorectal cancers.
abstract: BACKGROUND
  Methylation of the MLH1 promoter region has been suggested to be a major mechanism of gene inactivation in sporadic microsatellite instability-positive (MSI-H) colorectal cancers (CRCs). Recently, single-nucleotide polymorphism (SNP) in the MLH1 promoter region (MLH1-93G/A; rs1800734) has been proposed to be associated with MLH1 promoter methylation, loss of MLH1 protein expression and MSI-H tumors. We examined the association of MLH1-93G/A and six other SNPs surrounding MLH1-93G/A with the methylation status in 210 consecutive sporadic CRCs in Japanese patients.
  
  
  METHODS
  Methylation of the MLH1 promoter region was evaluated by Na-bisulfite polymerase chain reaction (PCR)/single-strand conformation polymorphism (SSCP) analysis. The genotype frequencies of SNPs located in the 54-kb region surrounding the MLH1-93G/A SNP were examined by SSCP analysis.
  
  
  RESULTS
  Methylation of the MLH1 promoter region was observed in 28.6% (60/210) of sporadic CRCs. The proportions of MLH1-93G/A genotypes A/A, A/G and G/G were 26% (n=54), 51% (n=108) and 23% (n=48), respectively, and they were significantly associated with the methylation status (p=0.01). There were no significant associations between genotype frequency of the six other SNPs and methylation status. The A-allele of MLH1-93G/A was more common in cases with methylation than the G-allele (p=0.0094), especially in females (p=0.0067). In logistic regression, the A/A genotype of the MLH1-93G/A SNP was shown to be the most significant risk factor for methylation of the MLH1 promoter region (odds ratio 2.82, p=0.003). Furthermore, a haplotype of the A-allele of rs2276807 located -47 kb upstream from the MLH1-93G/A SNP and the A-allele of MLH1-93G/A SNP was significantly associated with MLH1 promoter methylation.
  
  
  CONCLUSIONS
  These results indicate that individuals, and particularly females, carrying the A-allele at the MLH1-93G/A SNP, especially in association with the A-allele of rs2276807, may harbor an increased risk of methylation of the MLH1 promoter region.
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Miyakura
authors.forename: Makiko
authors.initials: M
authors.lastname: Tahara
authors.forename: Alan T
authors.initials: AT
authors.lastname: Lefor
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Yasuda
authors.affiliation: Oncogene Research Unit/Cancer Prevention Unit, Tochigi Cancer Center Research Institute, 4-9-13, Yohnan, Utsunomiya, Tochigi 320-0834, Japan. ksugano@tcc.pref.tochigi.lg.jp.
authors.forename: Kokichi
authors.initials: K
authors.lastname: Sugano
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics*; D001483:Base Sequence; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000473:pathology; D019175:DNA Methylation / Q000235:genetics*; D024202:Electrophoretic Mobility Shift Assay; D005260:Female; D005787:Gene Frequency; D020022:Genetic Predisposition to Disease; D006239:Haplotypes / Q000235:genetics*; D006801:Humans; D008297:Male; D053842:Microsatellite Instability; D008969:Molecular Sequence Data; D015999:Multivariate Analysis; D000070957:MutL Protein Homolog 1; D009687:Nuclear Proteins / Q000235:genetics*; D016017:Odds Ratio; D016133:Polymerase Chain Reaction; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D011401:Promoter Regions, Genetic; D012307:Risk Factors
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C501486:MLH1 protein, human; D009687:Nuclear Proteins; D000070957:MutL Protein Homolog 1