ESR1 and breast cancer: To determine the core element for the activation of the proximal 5'-upstream region (-1797) of p27 gene, (P+) JB6 mouse epidermal cells or estrogen receptor (ER)-negative MDA-MB-231 human breast cancer cells were transfected with the following deletion mutants of -1797 p27 (Fig. 3a) and then treated with various nutritional and chemopreventive anti-cancer agents: -1797 p27 (p27-Kpn I) [4], -774 p27 (p27-Apa I) [4], -575 p27 (p27-5'UTR) [5,6], -435 p27 (p27-MB) [4], and -417 p27 (p27-IRES) [5,6].