To determine the core activation elements in the proximal 5'-upstream region (-1797) of p27 gene, ER-negative MDA-MB-231 human breast cancer cells were transfected with the following deletion mutants of -1797 p27 (Figure 3a): namely -1797 p27 (p27-Kpn I) [32], -774 p27 (p27-Apa I) [32] and -575 p27 (p27-5'-UTR) [11,34]. Here, CDKN1B is linked to breast carcinoma.