Altered expression of claudin-1 is related with malignancy in canine thyroid tumors.

BACKGROUND/AIM Claudins (CLDNs) are crucial structural and functional components of tight junctions playing an important role in maintaining cell polarity, controlling paracellular diffusion and regulating cell growth and differentiation of epithelial cells. CLDNs are differentially expressed in neoplastic lesions compared to the corresponding healthy tissues; therefore, they are thought to play a role in tumorigenesis and tumor progression. Reduced expression of CLDN-1 has been observed in several types of human cancers, including thyroid tumors. There are no reports of CLDN-1 immunoexpression in normal and neoplastic canine thyroid tissues. MATERIAL AND METHODS CLDN-1 immunoexpression was investigated in normal canine thyroid gland (n=2), benign (n=1) and malignant (n=10) tumors, as well as neoplastic emboli (n=6). RESULTS CLDN-1 was constitutively expressed in normal canine follicular epithelium. Ninety percent of the malignant canine thyroid lesions showed absence or reduced CLDN-1 expression compared to that of normal thyroid gland. Additionally, a cytoplasmic subcellular location of CLDN-1 was recorded in the malignant epithelial cells and neoplastic emboli. CONCLUSION These findings link altered expression of CLDN-1 to neoplastic transformation and suggest that CLDN-1 expression is associated with malignant canine thyroid tumors and their vascular invasion.