Expression of cyclo-oxygenase-2 in naturally occurring squamous cell carcinomas in dogs

Squamous cell carcinoma is one of the most common cancers in humans and is also a frequently diagnosed neoplasm in dogs. Induction of cyclo-oxygenase-2 (COX-2), a key rate-limiting enzyme in prostaglandin biosynthesis, has been implicated in the oncogenesis of Various cancers in humans, including squamous cell carcinomas. However, expression of COX-2 has not been reported in spontaneous squamous cell carcinomas of nonhuman species. Canine squamous cell carcinomas share several similarities with the human disease. Therefore, the objective of this study was to determine whether COX isoenzymes were expressed in naturally occurring cases of squamous cell carcinomas in dogs. Canine normal skin (n=4) and squamous cell carcinomas (n=40) were studied by immunohistochemistry and immunoblotting analysis using polyclonal antibodies selective for COX-1 or COX-2. COX-2 was strongly expressed by neoplastic keratinocytes in all cases of squamous cell carcinomas, whereas no COX-2 was detected in normal skin and in the non-neoplastic skin and oral mucosa included in the tumor tissue samples (p <0.01). Immunoblotting analysis confirmed the restricted expression of COX-2 (72,000-74,000 molecular weight doublet) in squamous cell carcinomas only. In contrast, faint COX-1 staining was found in normal skin and in squamous cell carcinomas. This study demonstrates for the first time that COX-2 is induced in canine squamous cell carcinomas, and provides a new model to investigate the role and regulation of COX-2 gene expression in naturally occurring squamous cell carcinomas.