Figure 1

4-Hydroxytamoxifen, dexamethasone, all-trans-retinoic acid and 9-cis-retinoic acid up-regulate expression of p27 in both estrogen receptor-positive and -negative human breast cancer cells in vitro. (a) Outline of how various anti-cancer agents specifically up-regulate expression of p27 and arrest the progression of cell cycle from G1 to S phase. (b) Schematic drawing of the luciferase reporter plasmid containing proximal 5'-upstream region (-1797) of the p27 gene (-1797 p27 (p27-Kpn I)). 4-Hydroxytamoxifen (but not tamoxifen), dexamethasone, all-trans-retinoic acid and 9-cis-retinoic acid up-regulated relative luciferase activity of p27 in (c) estrogen receptor (ER)-positive MCF7 and (d) estrogen receptor (ER)-negative MDA-MB-231 human breast cancer cells in vitro. (e) Western immunoblot analysis of the expression of p27 protein in estrogen receptor (ER)-negative MDA-MB-231 human breast cancer cells in vitro. In all experiments, the cells were exposed to 1 μM each of tamoxifen, 4-hydroxytamoxifen, dexamethasone, all-trans-retinoic acid or 9-cis-retinoic acid for 24 hours. All assays were performed in triplicates and repeated three times.