Sirtuin 1 Expression in Canine Mammary Tumors: A Pilot Study

SIMPLE SUMMARY: Sirtuin family proteins (SIRTs) are intra-cellular enzymes that are found in mammals. They have a regulatory function in genomic transcription and are involved in a variety of physiologic mechanisms, such as aging and genome stability. Of these enzymes, SIRT1, the most investigated, may also be involved in cancerogenesis, although its possible dual role as an onco-suppressor and/or tumor promoter under a variety of biological conditions in humans and animals is still controversial. In normal or neoplastic canine mammary tissues, SIRT1 has not yet been investigated. We examined the cellular and subcellular distribution of SIRT1 in non-neoplastic (n = 5) and neoplastic (n = 45) mammary tissue samples of dogs using immunohistochemistry. In addition, we examined the expression and subcellular localization of SIRT1 in cultured canine mammary cancer cells by Western blot and immunofluorescence analyses. We found abundant and mainly nuclear expression in normal glandular cells; expression progressively weakened in mammary cancer cells in correlation with histologic features of increasing malignancy. In addition to weakening expression, a shift in the subcellular SIRT1 expression from predominantly nuclear to largely cytoplasmatic was also observable. In cultured canine cancer cells, subcellular localization was cytoplasmatic throughout. Our results suggest that SIRT1 may play a tumor0protecting role in canine mammary tumors, as deductible from the shifts in subcellular localization. ABSTRACT: Sirtuin 1 (SIRT1) is a protein involved in aging, cell protection, and energy metabolism in mammals. Recently, SIRT1 has been intensively studied in medical oncology, but the role of SIRT1 is still controversial, as it has been proposed as both an oncogene and a tumor suppressor. The aim of this study is to investigate the expression of SIRT1 by immunohistochemistry in canine mammary tissues, and by Western blot and immunofluorescence analysis in different canine mammary cell lines. Our results showed a decrease in SIRT1 expression from normal mammary gland tissue, and from benign and well-differentiated malignant tumors (G1) to less differentiated ones (G2–G3). Furthermore, a shift in the subcellular localization of SIRT1 from the nucleus to the cytoplasm was observed in less differentiated malignant tumors. However, further studies are needed to investigate the subcellular localization of SIRT1 in canine cancer cells and the role it may play in oncogenesis in animals.