Modulation of 11 beta-hydroxysteroid dehydrogenase type 2 activity in Ishikawa cells is associated with changes in cellular proliferation.

An important determinant of the potency of steroid hormones is the presence of activating and inactivating enzymes in target cells. The 11 beta-hydroxysteroid dehydrogenase type 1 and type 2 enzymes (11 beta HSD1 and 11 beta HSD2) modulate glucocorticoid action and may be important in regulating cellular growth. In the present study we examined 11 beta-hydroxysteroid dehydrogenase in Ishikawa endometrial cancer cells to see if modulation of enzyme activity could potentiate the antiproliferative effects of glucocorticoids. Ishikawa cells contain an NAD dependent enzyme migrating at 41 kDa on Western blots, consistent with the presence of the glucocorticoid-inactivating enzyme 11 beta HSD2, while the NADP dependent 11 beta HSD1 is barely detectable. Given that glucocorticoids decrease cellular proliferation we asked whether inhibition of 11 beta HSD2 could further enhance this effect. Cultivation of cells in the presence of 1 microM cortisol resulted in an elevation of 11 beta HSD2 and this was associated with a decrease in cell number. Enzyme activity and cell proliferation showed a biphasic response to the synthetic anti-progestin and anti-glucocorticoid RU38486, with < or =10 nM exerting agonistic effects and > or =100 nM producing antagonist effects in the presence of 1 microM cortisol. Inhibition of 11 beta HSD2 activity by glycyrrhetinic acid did not enhance the anti-proliferative effects of 1 microM cortisol, but the inhibitor showed significant antiproliferative activity in the absence of added glucocorticoid, consistent with protection of the low levels of glucocorticoids present in culture medium. Interestingly, the commonly used 11 beta HSD inhibitor, Carbenoxolone, did not block 11 beta HSD2 activity in whole Ishikawa cells, and there was no effect on cell proliferation, however, complete inhibition of 11 beta HSD2 was achieved in cellular homogenates suggesting that a barrier exists to entry of the inhibitor into intact cells. This study suggests that inhibition of 11 beta HSD2 activity can enhance the antiproliferative effects of low, but not high concentrations of glucocorticoids, and that beneficial effects may be attained in vivo at the nadir of diurnal glucocorticoid levels.