Also, it is possible that like other transcription factors, p53 is able to bind to p53-responsive element (p53RE), and this union may mediate the transactivation of p21 [51], as well as acetylation of p53 that has been shown to be essential for p21 promoter transactivation and cell-cycle arrest in human cancer cell lines [53]. This evidence concerns the gene CDKN1A and cancer.