Androgen receptor primes prostate cancer cells to apoptosis through down-regulation of basal p21 expression

► Degradation of p21 proteins is required for UV-induced AR-mediated apoptosis. ► AR down-regulates basal p21 expression in a transcription independent manner. ► AR controls basal p21 expression through the PIRH2-p53-p21 axis. ► Down-regulation of basal p21 expression by AR reduces cell death threshold.