Claudin 1 and Claudin 7 Gene Polymorphisms and Protein Derangement are Unrelated to the Growth Pattern and Tumor Volume of Colon Carcinoma

Abstract

Tight junctions together with adherens junctions are important for preserving tissue integrity. In tumors the normal tissue structure is lost which results in a disorganization and change of phenotype. In this study we assessed the complexity of the invasive front of colon carcinoma using an objective morphometrical technique based on the estimation of fractal dimension and number of free tumor cell clusters. The complexity of the invasive front was correlated to Claudin 1 and Claudin 7 protein expression as well as genetic polymorphisms of their genes. Thirty-three colon carcinomas were used. Images from the invasive front of the tumors were captured and used to calculate a complexity index of the invasive front. The tight junction proteins Claudin 1 and Claudin 7 were stained immunohistochemically in the tumor and in the surrounding normal mucosa. Screening of their genes was performed using DNA sequencing. A significant aberration of protein expression was seen for both Claudin 1 and Claudin 7 compared to normal mucosa. Both homozygous and heterozygous polymorphisms in exon 2 of claudin 1 were found. In claudin 7 a homozygous polymorphism was seen in exon 4. All individuals with tumors that showed either of these polymorphisms also showed the same polymorphism in the adjacent normal mucosa. A significant correlation was found between polymorphisms in CLDN 7 and tumor differentiation p<0.02. However no correlations were found to Complexity Index, tumor size, localization or tumor stage (pT and pN). The results show that there is a perturbed expression of claudin 1 and claudin 7 proteins in colon tumors compared to normal mucosa. A high incidence of polymorphisms was found in normal tissue and tumors. It remains to be shown if these polymorphisms are coupled to the occurrence of colon carcinomas.

Keywords: celladhesion; claudin; colon carcinoma; complexity index; polymorphism tight junction; tumor growth.

Figure 1

Photomicrographs of normal colon mucosa (a and c) and colon carcinoma (b and d) stained immunohistochemically for Claudin 1 (a and b) and Claudin 7 (c and d). An intense staining of the membrane and cytoplasm is seen in the normal mucosa while a weaker staining is seen in tumor cells.

Figure 2

Chromatogram of DNA sequencing of the CLDN1 gene (a) showing a heterozygous SNP in exon 2 and CLDN7 (b) showing a homozygous SNP in exon 4.