SIRT1 and colorectal cancer: On the other hand, decreased SIRT1 activity due to NAD depletion causes acetylation and activation of pro-apoptotic factors such as p53, FOXO and poly(ADP-ribose) polymerase 1 (PARP1) (Menssen et al., 2012[19]; Abdolvahabi et al., 2019[1]) Consistently, Zhang et al. reported that miR-26b causes cell death and serves as a tumor suppressor in colorectal cancer cells and concluded that this effect is mediated through the inhibitory effect of this microRNA on NAMPT expression (Chen et al., 2013[8]).