Expression of claudin-1 molecule in canine circumanal gland tumours Immunohistochemical study

The aim of the present study was to characterise the expression pattern of claudin-1 tight junction protein in canine intact circumanal, or hepatoid glands and in pathological proliferative lesions of the hepatoid gland, including nodular hyperplasia, adenoma, epithelioma, differentiated carcinoma and poorly differentiated carcinoma. The present study has evaluated the expression of claudin-1 in 10 intact and 67 hyperplastic and neoplastic lesions of the canine hepatoid gland. The studied lesions included nodular hyperplasias (n=10), adenomas (n=12), epitheliomas (n=15), differentiated carcinomas (n=15) and poorly differentiated carcinomas (n=15). There was diffuse, homogenous, intense expression of claudin-1 in intact canine hepatoid glands, hyperplasias, adenomas and differentiated carcinomas, detected as intense lateral membrane labelling of epithelial cells. The claudin-1 expression was weaker in epitheliomas. The poorly differentiated carcinoma cells never expressed claudin-1. The basal reserve cells of the intact gland, hyperplasia and adenoma showed intense membrane positivity for claudin-1. In epitheliomas the neoplastic basal cells never expressed this tight junction protein. In the epitheliomas some peripheral individual tumour cells showed non-junctional (cytoplasmatic) claudin-1 expressions. Claudin-1 molecule is an integral membrane protein of tight junction structures expressed by canine intact mature circumanal gland cells and peripheral basal reserve cells. Consequently, the authors hypothesize that claudin-1 plays a role in the carcinogenesis of canine circumanal glands. Low claudin-1 expression in epitheliomas and mislocalised claudin-1 expression from the cell membrane to the cytoplasm and the loss of claudin-1 protein in poorly differentiated carcinomas may be the molecular phenomenon of increasing cellular disorientation, motility, invasion, and metastasis of tumour cells.