title: Reappraisal of hMLH1 promoter methylation and protein expression status in the serrated neoplasia pathway.
abstract: OBJECTIVE
  The aim of this study was to determine whether human mutL homologue 1 (hMLH1) inactivation precedes the progression of sessile serrated lesion (SSL) into SSL with cytological dysplasia (SSL/D) and to define the histological stage at which promoter methylation and inactivation of hMLH1 occur.
  
  
  RESULTS
  Using the MassARRAY EpiTYPER assay and immunohistochemistry, we examined methylation levels and the protein expression status of hMLH1 in 33 SSL/Ds with conventional epithelial dysplasia and compared the results with those of control hyperplastic polyps (HPs) and SSLs. The methylation level of hMLH1 was higher in the dysplastic component than in the non-dysplastic component of SSL/Ds (P = 0.005), and differed significantly with regard to the degree of dysplasia (P = 0.002). The methylation levels of hMLH1 in the dysplastic component of SSL/Ds tended to be higher than those of control SSLs and HPs (P = 0.063 and P = 0.017, respectively). The loss of hMLH1 protein expression was identified in only 13 of 33 (39.39%) dysplastic components of SSL/Ds.
  
  
  CONCLUSIONS
  Promoter methylation and loss of protein expression of hMLH1 are not parallel processes that occur concurrently. hMLH1 methylation is an early molecular event which occurs even in HP. However, the loss of hMLH1 expression is a much later step, found in approximately 40% of SSL/Ds at various histological stages. Notably, the loss of hMLH1 protein expression does not necessarily precede the development of cytological dysplasia in SSL.
authors.affiliation: Department of Surgery, Daehang Hospital, Seoul, Korea.
authors.forename: Eun-Jung
authors.initials: EJ
authors.lastname: Lee
authors.affiliation: Department of Pathology, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea.
authors.forename: Sung-Min
authors.initials: SM
authors.lastname: Chun
authors.affiliation: Department of Pathology, Daehang Hospital, Seoul, Korea.
authors.forename: Mi-Jung
authors.initials: MJ
authors.lastname: Kim
authors.affiliation: Department of Pathology, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea.
authors.forename: Se-Jin
authors.initials: SJ
authors.lastname: Jang
authors.affiliation: Department of Surgery, Daehang Hospital, Seoul, Korea.
authors.forename: Do Sun
authors.initials: do S
authors.lastname: Kim
authors.affiliation: Department of Surgery, Daehang Hospital, Seoul, Korea.
authors.forename: Doo Han
authors.initials: DH
authors.lastname: Lee
authors.affiliation: Department of Surgery, Daehang Hospital, Seoul, Korea.
authors.forename: Eui Gon
authors.initials: EG
authors.lastname: Youk
mesh_terms: D000236:Adenoma / Q000175:diagnosis / Q000378:metabolism* / Q000473:pathology; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003111:Colonic Polyps / Q000175:diagnosis / Q000378:metabolism* / Q000473:pathology; D015179:Colorectal Neoplasms / Q000175:diagnosis / Q000378:metabolism* / Q000473:pathology; D019175:DNA Methylation; D005260:Female; D006801:Humans; D006965:Hyperplasia / Q000175:diagnosis / Q000378:metabolism* / Q000473:pathology; D007150:Immunohistochemistry; D008297:Male; D008875:Middle Aged; D000070957:MutL Protein Homolog 1 / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics*
chemical_list: C501486:MLH1 protein, human; D000070957:MutL Protein Homolog 1
keywords: colon; dysplasia; hMLH1; hyperplastic polyp; sessile serrated adenoma