Attenuation of p53R2 decreased p21 expression and increased cyclin D1 in cancer cells. A, q-RT-PCR analysis validated that p53R2 mRNA expression was significantly decreased by at least ~92% in KB (p53 wild-type), PC3 (p53-trucated), MCF-7 (p53 wild-type) and MDA-MB-231 (p53-mutated) cells at 48 hour post-transfection with p53R2 siRNA. B, q-RT-PCR and C, Western blot analysis showed that p21 expression was significantly decreased by at least ~50% and cyclin D1 expression was moderately increased in the cancer cells after attenuation of p53R2 (Control: scramble siRNA transfected, p53R2: p53R2 siRNA transfected KB). D, quantitative levels of p21 protein and cyclin D1 in cancer cells transfected with p53R2 siRNA were determined by measuring the density of the band of p21/cyclin D1 and normalized to that of GAPDH. Data were presented as the ratio to control and were the mean ± SD of three experiments, *P < 0.05, **P < 0.01, compared with control cells.