CDKN1A and cancer: In human cancer cells, Akt1 phosphorylates p21 at T145 and S146, thereby preventing its binding to PCNA (the processivity cofactor for DNA polymerases δ and ε), decreasing its inhibitory effect on cyclin CDK complexes, increasing p21 protein stability, localizing it to the cytoplasm, and protecting cells from apoptosis [5], [8], [39].