CCAR2 and breast cancer: A major intracellular regulator of sirt1-dependent function recently described breast cancer cells but also in hepatocytes and other metabolic tissues is the protein Deleted in Breast Cancer 1 (DBC1) (11, 48, 49, 88, 89) DBC1 has been shown to directly bind SIRT1 and negatively regulate its activity as well as suppress sirt1 expression (47).