title: Low expression of claudin-4 is associated with poor prognosis in esophageal squamous cell carcinoma.
abstract: BACKGROUND
  Claudins are 22-27 kDa sized adhesion molecules that constitute tight junctions. Their expression levels are often tissue-specific, and their altered degrees of expression have been reported in a variety of cancers. In addition, the prognostic significance of claudin expression has been implicated in various human cancers. However, the prognostic significance of claudin-4 expression in esophageal squamous cell carcinoma (ESCC) remains to be clarified.
  
  
  METHODS
  We investigated the prognostic significance of claudin-4 expression in 164 cases of ESCC using immunohistochemisty. We also evaluated claudin-4 mRNA expression levels using quantitative real-time reverse transcription polymerase chain reaction (RT-PCR) and analyzed its specific promoter methylation status using quantitative methylation-specific PCR.
  
  
  RESULTS
  According to clinicopathological parameters, low claudin-4 expression was found to be significantly associated with histological differentiation (P = 0.003), invasion depth (P = 0.002), and lymph node metastasis (P = 0.024). Low claudin-4 expression showed unfavorable influences on disease-free survival (P = 0.0115) and overall survival (OS) (P = 0.0009). In multivariate analysis, low claudin-4 expression was an independent predictor of poor OS (P = 0.007). Claudin-4 mRNA levels assessed using real-time RT-PCR were consistent with the protein levels determined using immunohistochemistry. Furthermore, this study demonstrates that loss of claudin-4 is associated with promoter hypermethylation.
  
  
  CONCLUSIONS
  Our study indicates that claudin-4 expression is deregulated in ESCC, implying its potential use as a prognostic biomarker in ESCC.
authors.affiliation: Department of Pathology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
authors.forename: Chang Ohk
authors.initials: CO
authors.lastname: Sung
authors.forename: Song Yiang
authors.initials: SY
authors.lastname: Han
authors.forename: Seok-Hyung
authors.initials: SH
authors.lastname: Kim
mesh_terms: D000368:Aged; D014408:Biomarkers, Tumor / Q000235:genetics* / Q000378:metabolism; D002294:Carcinoma, Squamous Cell / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D062506:Claudin-4; D019175:DNA Methylation; D004273:DNA, Neoplasm / Q000235:genetics; D004938:Esophageal Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D004947:Esophagus / Q000378:metabolism* / Q000473:pathology; D005260:Female; D006801:Humans; D007124:Immunoenzyme Techniques; D008207:Lymphatic Metastasis; D008297:Male; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D042282:Microdissection; D009361:Neoplasm Invasiveness; D009367:Neoplasm Staging; D011379:Prognosis; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015996:Survival Rate; D046888:Tissue Array Analysis
chemical_list: D014408:Biomarkers, Tumor; C568157:CLDN4 protein, human; D062506:Claudin-4; D004273:DNA, Neoplasm; D008565:Membrane Proteins; D012333:RNA, Messenger