The Role of SIRT1 in Breast Cancer Stem Cells

Abstract

Abstract : SIRT1 inhibitors cambinol and Ex527 are used for treatment in several breast cancer cell lines, including T47D, TB549, MDA-MB-231 and MDA-MB-468. Stem cell markers, SOX-2 and Nanog, are significantly decreased in SIRT1 inhibitor treated cancer cells by qRT-PCR and western blot in T47D cell line. The ALDH positive cells in MDA-MB-231 cell line are significant reduced from 29% to 3.2% with Adeflour assay, and the CD44 expression is significantly reduced in CD44/CD24 flow cytometry analysis. Using qRT-PCR, SIRT1 inhibitors significantly down regulate vimentin (-3.7 folds), N-cadherin and smooth muscle actin (-2.7 folds) and up regulate the gene of E-cadherin, indicating SIRT1 inhibitors can block the epithelial mesenchymal transformation (EMT) of breast cancer. SIRT1 inhibitors can completely block TGF-beta induced EMT. SIRT1 inhibitors can significantly (60-70%) block the cancer cell invasion and migration in several triple negative breast cancer cell lines. SIRT1 inhibitors can significantly reduce the mammosphere formation in T47D cells. Immunohistochemistry performed on breast cancer specimens shows the correlation between cancer stem cell markers and SIRT1 overexpression. SIRT1 inhibitors can inhibit cell proliferation on all tested breast cancer cell lines, and can induce significant cell apoptosis in T47D cells. Cell cycle analysis shows tumor cells are blocked at G1 to S phase. The molecular mechanism of SIRT1 inhibitors in blocking EMT and reducing cancer stem cells is likely associated with blocking the Wnt pathway. Several down stream target genes of Wnt pathway, such as cyclin D1, c-Myc and c-Jun, are significantly down regulated after using SIRT1 inhibitor cambinol, and the changes are more significant in TGF-beta stimulated cancer cells. Beta-catenin is significantly reduced including the active beta-catenin, and the decreasing beta-catenin protein may be related to the decreased Dvl proteins.