Abstract
Sirtuins (SIRTs), NAD+-dependent class III histone deacetylases (HDACs), play an important role in the regulation of cell division, survival, and senescence. Although several effective SIRT inhibitors have been developed, little is known about the specific mechanisms of their anti-cancer activity. Here, we investigate the anti-cancer effects of Sirtinol, a SIRT inhibitor, on human breast cancer MCF-7 cells. In the present study, apoptotic and autophagic cell death were measured. Sirtinol significantly inhibited the proliferation of MCF-7 cells in a concentration-dependent manner. The IC50 values of Sirtinol were 48.6 µM (24 h) and 43.5 µM (48 h) in MCF-7 cells. As expected, Sirtinol significantly increased acetylation of p53, which has been reported to be a target of SIRT1/2. Flow cytometry analysis revealed that Sirtinol significantly increased the G1 phase of the cell cycle. Up-regulation of Bax, down-regulation of Bcl-2, and cytochrome c release into the cytoplasm were observed in MCF-7 cells, these are involved in the mechanism of apoptotic cell death. The annexin V-FITC assay was used to confirm Sirtinol-induced apoptotic cell death. Furthermore, expression of LC3-II, an autophagy-related molecule, was significantly increased in MCF-7 cells after Sirtinol treatment. Autophagic cell deaths were confirmed by acridine orange and dansylcadaverine (MDC) staining. Interestingly, pretreatment of 3-methyladenine (3-MA) increased the Sirtinol-induced MCF-7 cells cytotoxicity, which is associated with blocking autophagic cell death and increasing apoptotic cell death. Based on our results, down-regulation of SIRT1/2 expression may play an important role in the regulation of breast cancer cell death; thus SIRT1/2 could be a novel molecular target for cancer therapy and these finding provide a molecular basis for targeting SIRT1/2 for future cancer therapy.
