CDKN1A and breast cancer: Expression of F-box only protein 22 (FBXO22) in HCC [130], UBR5 (ubiquitin protein ligase E3 component N-recognin 5) in colon cancer [131] and PSMD2 (26S proteasome non-ATPase regulatory subunit 2) in breast cancer [132] is upregulated; these genes regulate p21 stability by mediating ubiquitylation of p21.