Objective  To observe the effects of double-stranded small interfering RNA (siRNA) of the silent mating-type information regulation 2 homolog 1 (SIRT1) on the cell proliferation, cell cycle progression, and expression levels of the cell cycle negative regulators. These regulators include P21, P27, and phosphorylated retinoblastoma (PRb) proteins present in prostate cancer PC3 cells. This work further aims to explore the possible underlying mechanism for such effects.

  Methods  PC3 cells were cultured in vitro and then randomly divided into the mock group, scramble siRNA transfected group, and SIRT1 siRNA-transfected group. SIRT1 siRNA efficiency was examined through reverse transcription polymerase chain reaction and Western blot analysis. The inhibitory rate of PC3 cell growth was determined through a methyl thiazolyl tetrazolium assay, and the cell cycle was investigated with the use of flow cytometry. The P21 and P27 protein expression levels and PRb status were determined by Western blot assay.

  Results  Compared with those of the mock and scramble siRNA groups, the expression levels of SIRT1 mRNA and protein significantly decreased in SIRT1 siRNA-transfected cells. In addition, the inhibitory rate of PC3 cell growth was markedly increased, and the cell cycle of the PC3 cells was arrested at the G₁ stage. The expression levels of negative cell cycle regulators, including P21 and P27 protein levels increased, whereas Rb protein phosphorylation was inhibited in SIRT1 siRNA-transfected PC3 cells.

  Conclusion  SIRT1 RNA interference inhibits PC3 cell growth and arrests cell cycle progression through the upregulation of the P21 and P27 proteins and the inhibition of Rb protein phosphorylation.