title: The claudin gene family: expression in normal and neoplastic tissues.
abstract: BACKGROUND
  The claudin (CLDN) genes encode a family of proteins important in tight junction formation and function. Recently, it has become apparent that CLDN gene expression is frequently altered in several human cancers. However, the exact patterns of CLDN expression in various cancers is unknown, as only a limited number of CLDN genes have been investigated in a few tumors.
  
  
  METHODS
  We identified all the human CLDN genes from Genbank and we used the large public SAGE database to ascertain the gene expression of all 21 CLDN in 266 normal and neoplastic tissues. Using real-time RT-PCR, we also surveyed a subset of 13 CLDN genes in 24 normal and 24 neoplastic tissues.
  
  
  RESULTS
  We show that claudins represent a family of highly related proteins, with claudin-16, and -23 being the most different from the others. From in silico analysis and RT-PCR data, we find that most claudin genes appear decreased in cancer, while CLDN3, CLDN4, and CLDN7 are elevated in several malignancies such as those originating from the pancreas, bladder, thyroid, fallopian tubes, ovary, stomach, colon, breast, uterus, and the prostate. Interestingly, CLDN5 is highly expressed in vascular endothelial cells, providing a possible target for antiangiogenic therapy. CLDN18 might represent a biomarker for gastric cancer.
  
  
  CONCLUSIONS
  Our study confirms previously known CLDN gene expression patterns and identifies new ones, which may have applications in the detection, prognosis and therapy of several human cancers. In particular we identify several malignancies that express CLDN3 and CLDN4. These cancers may represent ideal candidates for a novel therapy being developed based on CPE, a toxin that specifically binds claudin-3 and claudin-4.
authors.affiliation: Laboratory of Cellular and Molecular Biology, National Institute on Aging, Baltimore, MD 21224, USA. Hewittkyl@grc.nia.nih.gov
authors.forename: Kyle J
authors.initials: KJ
authors.lastname: Hewitt
authors.forename: Rachana
authors.initials: R
authors.lastname: Agarwal
authors.forename: Patrice J
authors.initials: PJ
authors.lastname: Morin
mesh_terms: D000595:Amino Acid Sequence; D062445:Claudin-1; D016000:Cluster Analysis; D003199:Computer Systems; D020869:Gene Expression Profiling; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D005810:Multigene Family; D009369:Neoplasms / Q000378:metabolism*; D010802:Phylogeny; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid
chemical_list: C568108:CLDN1 protein, human; D062445:Claudin-1; D008565:Membrane Proteins