Differential expression of genes encoding tight junction proteins in colorectal cancer: frequent dysregulation of claudin-1, -8 and -12
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Background and aims
As integral membrane proteins, claudins form tight junctions together with occludin. Several claudins were shown to be up-regulated in various cancer types. We performed an expression analysis of genes encoding tight junction proteins to display differential gene expression on RNA and protein level and to identify and validate potential targets for colorectal cancer (CRC) therapy.
Patients and methods
Amplified and biotinylated cRNA from 30 microdissected CRC specimen and corresponding normal tissues was hybridized to Affymetrix U133set GeneChips. Quantification of differential protein expression of claudin-1, -8 and -12 between normal and corresponding tumour tissues was performed by Western blot analyses. Paraffin-embedded CRC tissue samples, colon cancer cell lines and normal tissue microarray were analysed for protein expression of claudin-1 by immunohistochemistry (IHC).
Claudin-1 (CLDN1) and -12 (CLDN12) are frequently overexpressed in CRC, whereas claudin-8 (CLDN8) shows down-regulation in tumour tissue on RNA level. Quantification of proteins confirmed the overexpression of claudin-1 in tumour tissues, whereas changes of claudin-8 and -12 were not significantly detectable on protein level. IHC confirmed the markedly elevated expression level of claudin-1 in the majority of CRC, showing membranous and intracellular vesicular staining.
Differential expression of genes encoding claudins in CRC suggests that these tight junction proteins may be associated to and involved in tumorigenesis. CLDN1 is frequently up-regulated in large proportion of CRC and may represent potential target molecule for blocking studies in CRC.
KeywordsClaudin-1 Claudin-8 Tight junction Gene expression Colorectal cancer
The presented study originated from the collaboration of the Department of General, Vascular and Thoracic Surgery, Campus Benjamin Franklin, Charité, Berlin, with metaGen, Pharmaceuticals GmbH, Berlin, Germany. We thank Prof. Dr. Med. Fischer, Institute of Pathology, Städtische Kliniken gGmbH Wilhelmshaven, Germany, for providing paraffin-embedded colorectal tissues used for validation studies and Sonja Dullat for Western blot analyses.
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