CDKN1A and primary biliary cholangitis: Moreover, the activity of Cyclin-dependent kinase inhibitor p21 (p21WAF1/Cip1) and Cyclin dependent kinase inhibitor 2A (p16INK4) and ataxia telangiectasia-mutated (ATM)/p53/p21WAF1/Cip1 signals in the liver may also induce the senescence of bile duct cells of PBC (48, 58–60).