title: Identification of Claudin 1 Transcript Variants in Human Invasive Breast Cancer.
abstract: BACKGROUND
  The claudin 1 tight junction protein, solely responsible for the barrier function of epithelial cells, is frequently down regulated in invasive human breast cancer. The underlying mechanism is largely unknown, and no obvious mutations in the claudin 1 gene (CLDN1) have been identified to date in breast cancer. Since many genes have been shown to undergo deregulation through splicing and mis-splicing events in cancer, the current study was undertaken to investigate the occurrence of transcript variants for CLDN1 in human invasive breast cancer.
  
  
  METHODS
  RT-PCR analysis of CLDN1 transcripts was conducted on RNA isolated from 12 human invasive breast tumors. The PCR products from each tumor were resolved by agarose gel electrophoresis, cloned and sequenced. Genomic DNA was also isolated from each of the 12 tumors and amplified using PCR CLDN1 specific primers. Sanger sequencing and single nucleotide polymorphism (SNP) analyses were conducted.
  
  
  RESULTS
  A number of CLDN1 transcript variants were identified in these breast tumors. All variants were shorter than the classical CLDN1 transcript. Sequence analysis of the PCR products revealed several splice variants, primarily in exon 1 of CLDN1; resulting in truncated proteins. One variant, V1, resulted in a premature stop codon and thus likely led to nonsense mediated decay. Interestingly, another transcript variant, V2, was not detected in normal breast tissue samples. Further, sequence analysis of the tumor genomic DNA revealed SNPs in 3 of the 4 coding exons, including a rare missense SNP (rs140846629) in exon 2 which represents an Ala124Thr substitution. To our knowledge this is the first report of CLDN1 transcript variants in human invasive breast cancer. These studies suggest that alternate splicing may also be a mechanism by which claudin 1 is down regulated at both the mRNA and protein levels in invasive breast cancer and may provide novel insights into how CLDN1 is reduced or silenced in human breast cancer.
authors.affiliation: Department of Pathology, University of Manitoba, Winnipeg, Manitoba, Canada.|Department of Physiology and Pathophysiology, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: Anne A
authors.identifier: http://orcid.org/0000-0002-6752-6280
authors.initials: AA
authors.lastname: Blanchard
authors.affiliation: Department of Pediatrics and Child Health, University of Manitoba, Winnipeg, Manitoba, Canada.|Department of Biochemistry and Medical Genetics, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: Teresa
authors.initials: T
authors.lastname: Zelinski
authors.affiliation: Department of Physiology and Pathophysiology, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: Jiuyong
authors.initials: J
authors.lastname: Xie
authors.affiliation: Department of Pathology, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: Steven
authors.initials: S
authors.lastname: Cooper
authors.affiliation: Department of Pathology, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: Carla
authors.initials: C
authors.lastname: Penner
authors.affiliation: Department of Biochemistry and Medical Genetics, University of Manitoba, Winnipeg, Manitoba, Canada.|Manitoba Institute of Cell Biology, Winnipeg, Manitoba, Canada.
authors.forename: Etienne
authors.initials: E
authors.lastname: Leygue
authors.affiliation: Department of Pathology, University of Manitoba, Winnipeg, Manitoba, Canada.|Department of Physiology and Pathophysiology, University of Manitoba, Winnipeg, Manitoba, Canada.|Manitoba Institute of Cell Biology, Winnipeg, Manitoba, Canada.
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Myal
mesh_terms: D001940:Breast / Q000473:pathology; D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology; D062445:Claudin-1 / Q000235:genetics*; D004273:DNA, Neoplasm; D005091:Exons; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D020641:Polymorphism, Single Nucleotide
chemical_list: D062445:Claudin-1; D004273:DNA, Neoplasm