SIRT1 against breast cancer through downregulating Bcl-2 protein.
34 Background: SIRT1, a member of the class III histone deacetylase (HDAC) family, is the mammalian orthologue of yeast Sir2. It has been reported to play a key role in a variety of physiological processes such as genomic stability, metabolism, neurogenesis and cell survival due to its ability to deacetylate both histone and numerous non-histone substrates. The deacetylase function of SIRT1 has been suggested as playing a role in prolonging the life of mammals. However, the suggested functions of SIRT1 as a potential tumor promoter have been challenged by observations of their respective down- and up-regulation in various cancers. The aim of the present study was to simultaneously evaluate the expression levels of SIRT1 and Ki67, the index of cellular proliferation, in normal and tumor tissues of the breast from 27 breast cancer patients and to determine the role of SIRT1 in breast tumorigenesis. Methods: A total of 27 breast cancer patients were included. Tumor tissues and matched normal breast tissues were immediately frozen after collection between 2007 and 2008. Immunohistochemistry and reverse transcription-polymerase chain reaction were applied for analyses of patients’ specimens. Cell proliferation assay, cell cycle analysis and Western blotting were used to investigate the effects of sirtinol on the human breast cancer lines MCF-7 and MDA-MB-231 cells. Results: Immunohistochemistry showed that there is a high correlation between SIRT1 and Ki67 expression. In addition, our results showed that inhibition of SIRT1 induces anti-cell growth in both MCF-7 (ER-positive, non-invasive) and MDA-MB-231 (ER-negative, invasive) breast cancer cell lines, especially in MDA-MB-231 cells. The levels of pro-survival protein Bcl-2 were dramatically decreased in both breast cell lines following sirtinol treatment. Conclusions: Our present study revealed that inhibition of SIRT1 activity may be a promising chemotherapeutic strategy against breast cancer.