title: Regulation of MLH1 mRNA and protein expression by promoter methylation in primary colorectal cancer: a descriptive and prognostic cancer marker study.
abstract: BACKGROUND
  In colorectal cancer MLH1 deficiency causes microsatellite instability, which is relevant for the patient's prognosis and treatment, and its putative heredity. Dysfunction of MLH1 is caused by sporadic gene promoter hypermethylation or by hereditary mutations as seen in Lynch Syndrome. The aim of this study was to determine in detail how DNA methylation regulates MLH1 expression and impacts clinical management.
  
  
  METHODS
  Colorectal cancer samples were collected from 210 patients. The laboratory methods used to study these samples included methylation specific multiplex ligation-dependent probe amplification (MS-MLPA), real-time quantitative PCR (qPCR), and immunohistochemistry (IHC).
  
  
  RESULTS
  We found that the MLH1 mRNA and protein expression levels were highly related. MS-MLPA was successful in tumors from 195 patients. In these tumors, hypermethylation was observed in promoter regions A (n = 57), B (n = 30), C (n = 28), and D (n = 47), and in intron 1 (n = 25). The promoter region C and intron 1 methylation levels were found to be excellently suited for discriminating between low and high gene expression levels, whereas those of promoter regions A, B and D were less specific. Hypermethylation in any region (n = 77) served as an independent prognostic factor (hazard ratio 0.56, 95 % confidence interval 0.36-0.89, p = 0.01).
  
  
  CONCLUSIONS
  MLH1 inactivation through hypermethylation was found to be related to improved survival. Hypermethylation in promoter region C and intron 1 served as the most specific markers for this inactivation.
authors.affiliation: Danish Colorectal Cancer Group South, University of Southern Denmark and Vejle Hospital, Vejle, Denmark, lars.henrik.jensen@rsyd.dk.
authors.forename: Lars Henrik
authors.initials: LH
authors.lastname: Jensen
authors.forename: Anders Aamann
authors.initials: AA
authors.lastname: Rasmussen
authors.forename: Lene
authors.initials: L
authors.lastname: Byriel
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Kuramochi
authors.forename: Dorthe Gylling
authors.initials: DG
authors.lastname: Crüger
authors.forename: Jan
authors.initials: J
authors.lastname: Lindebjerg
authors.forename: Peter V
authors.initials: PV
authors.lastname: Danenberg
authors.forename: Anders
authors.initials: A
authors.lastname: Jakobsen
authors.forename: Kathleen
authors.initials: K
authors.lastname: Danenberg
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics* / Q000378:metabolism*; D000368:Aged; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D019175:DNA Methylation / Q000235:genetics*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D000070957:MutL Protein Homolog 1; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C501486:MLH1 protein, human; D009687:Nuclear Proteins; D012333:RNA, Messenger; D000070957:MutL Protein Homolog 1
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