CDKN1B and cancer: In many cancer cell types, 1,25-(OH)2D3 directly arrests the cell cycle in the G0/G1 phase by downregulating cyclin-dependent kinases (CDKs: CDK4, CDK6) and repressing the genes that encode cyclins D1 and C (CCND1, CCNC) and CDK inhibitors p21CIP1/WAF1 (CDKN1A), p27KIP1 (CDKN1B) and p19 (CDKN2D) [116,119].