ARF regulates p16 protein levels in human cancer cells. (A) Inverse expression of ARF and p16 in human cancer cells. Western blot analyses of showing the expression levels of ARF and p16 proteins in the indicated human cancer cell lines, in which the CDNK2A gene is either deleted, methylated, or intact, as indicated. (B) Association of ARF and p16 expression with clinical outcome in bladder and prostate cancer. Representative images and categorical results of ARF and p16 immunostaining of tissue microarrays of human bladder and prostate cancer. Kaplan-Meier analyses show disease-specific survival of bladder cancer patients, and biochemical relapse (BCR)-free survival of prostate cancer patients. (C) Consequences of ARF knock-down for expression of p16 protein in J82 and DU145 cells using two independent ARF siRNA (or a scrambled siRNA as a control). (D) Consequences of expressing exogenous ARF in HeLa and TCCSUP cells following transfection with an ARF cDNA (or the empty vector as a control). In C and D the relative expression levels of p16 are indicated as determined using ImageJ software.