PCNA and prostate cancer: In contrast with the above-mentioned studies indicating the tumor suppressor function of SIRT3 in prostate cancer, Singh et al. demonstrated that SIRT3 expression inhibits the cleavage of poly (ADP-ribose) polymerase [94], a known marker of apoptosis, and upregulates the expression of proliferating cell nuclear antigen, a known marker of cell proliferation, in DU145 and 22Rν1 prostate cancer cells.