CDK20 and cancer: In glioblastoma cells CDK20 plays a role in cancer growth as a CDK-activating kinase (CAK), phosphorylating CDK2 and regulating the G1/S cell cycle transition.232 CDK20 knockdown by RNA interference (RNAi) reduces phosphorylated CDK2 (pCDK2) levels, causing G1 arrest and suppression of proliferation.430 Similarly, in colorectal cancer models, CDK20 downregulation inhibits cancer cell proliferation by inducing G0-G1 cell cycle arrest.