Role of sirtuin histone deacetylase SIRT1 in prostate cancer. A target for prostate cancer management via its inhibition?

Prostate cancer (PCa) is a major age-related malignancy, and according to estimates from the American Cancer Society, a man's chance of developing this cancer significantly increases with increasing age, from 1 in 10,149 by age 39 to 1 in 38 by age 59 to 1 in 7 by age 70. Therefore, it is important to identify the causal connection between mechanisms of aging and PCa. Employing in vitro and in vivo approaches, in this study, we tested the hypothesis that SIRT1, which belongs to the Sir2 (silent information regulator 2) family of sirtuin class III histone deacetylases, is overexpressed in PCa, and its inhibition will have antiproliferative effects in human PCa cells. Our data demonstrated that SIRT1 was significantly overexpressed in human PCa cells (DU145, LNCaP, 22Rnu1, and PC3) compared with normal prostate epithelial cells (PrEC) at protein, mRNA, and enzymatic activity levels. SIRT1 was also found to be overexpressed in human PCa tissues compared with adjacent normal prostate tissue. Interestingly, our data demonstrated that SIRT1 inhibition via nicotinamide and sirtinol (at the activity level) as well as via short hairpin RNA-mediated RNA interference (at the genetic level) resulted in a significant inhibition in the growth and viability of human PCa cells while having no effect on normal prostate epithelial cells. Further, we found that inhibition of SIRT1 caused an increase in FOXO1 acetylation and transcriptional activation in PCa cells. Our data suggested that SIRT1, via inhibiting FOXO1 activation, could contribute to the development of PCa. We suggest that SIRT1 could serve as a target toward developing novel strategies for PCa management.