CDKN1A and breast carcinoma: To investigate whether p53, a transcriptional activator, is required for the dsP21-322-mediated activation of p21, we selected three different p53-null human cell lines, including the human osteosarcoma cell line SaOS2, the human breast cancer cell line MDA-MB-157 and the human non-small cell lung cancer cell line NCI-H1299, to examine the activity of dsP21-322.