SIRT1 and cancer: SIRT1 was found to be normally present in the cytoplasm in murine pancreatic islet cells and human embryonic kidney cells.89,90 Notably, SIRT1 was overexpressed predominantly in the cytosol of certain cancer cells, while normal epithelial cells showed nuclear localization.56,91 This phenomenon has been also observed in human colon and ovarian cancer specimens.51,56, Figure 2 illustrates differential expression of SIRT1 in human colon tumor and surrounding tissues.