Cyclooxygenase-2 directly regulates gene expression of P450 Cyp19 aromatase promoter regions pII, pI.3 and pI.7 and estradiol production in human breast tumor cells

The present studies evaluated the direct effects of the presence of human cyclooxygenase-2 (Cox-2) on gene expression of specific promoter regions of the P450 Cyp19 enzyme aromatase enzyme and its product, estradiol, in Cox-2 null estrogen-dependent MCF-7 breast tumor cells and in a stable clone of MCF-7 cells containing transfected Cox-2 cDNA, designated as MCF-7/Cox-2 Clone 10. Clone 10 human breast tumor cells have significantly increased gene expression of total mRNA of the P450 Cyp19 enzyme aromatase, with high levels of gene expression of specific aromatase promoter (p) regions pII, pI.3, and pI.7, with no significant change in mRNA levels of pI.4. Clone 10 human breast tumor cells produced significantly increased amounts of both prostaglandin E-2 (PGE(2)) derived from Cox-2 enzyme activity and estradiol derived from aromatase enzyme activity (p < 0.01), compared to MCF-7/vector control cells. The greatest inhibition of PGE(2) or estradiol production was observed by the combination of the selective Cox-2 inhibitor celecoxib (25 mu M) and the aromatase inhibitor, formestane (10 nM) (p < 0.01). The greatest anti-proliferative effect in Cox-2 null MCF-7/vector control cells was observed with the combination of 25 mu M celecoxib and 10 nM formestane but not with 10 mu M celecoxib, suggesting that there are Cox-2-independent mechanisms involved in the anti-proliferative effect of this agent at doses greater than 10 mu M. Celecoxib (25 mu M) also significantly inhibited proliferation of MCF-7/Cox-2 Clone 10 human breast tumor cells, with no further anti-proliferative activity with the addition of 10 nM formestane observed at either 24 or 48 It of treatment. These studies demonstrate that Cox-2 directly regulates gene expression of specific aromatase promoter regions and regulates aromatase enzyme activity. Agents that inhibit Cox-2 or block the biological effects of PGE(2) may be useful in significantly limiting aromatase activity and proliferation of human breast tumor cells regardless of the presence of Cox-2. In addition, the unique human breast tumor cell model used in these studies may be a useful tool in identifying the spectrum of activities of agents that block the biological effects of PGE(2) and estradiol. (c) 2006 Elsevier Inc. All rights reserved.