Basal p21 protein levels are controlled by the PIRH2-p53 pathway. (A) 104-R cells were transfected with either control siRNA (siCtrl) or two different PIRH2 siRNAs (siPIRH2 #1 and #2) for 48 h. Expression levels of p21, p53, and actin were analyzed by immunoblotting using corresponding antibodies. (B) 104-R cells were transfected with siCtrl, siPIRH2, or p53 siRNA (siP53). Expression levels of p21 and p53 were analyzed by immunoblotting, as described in (A).