Aromatase activity in microsomal preparations of human genital skin fibroblasts: Influence of glucocorticoids

Skin is an important site of estrogen production in men. Although the aromatase complex in these cells appears to be similar to that of other human cells, the regulation of aromatase by glucocorticoids in cultured human skin fibroblasts is unique. We examined aromatase activity in microsomal-enriched fractions of cultured human skin fibroblasts in order to characterize better the factors that regulate the aromatase in these cells. The optimum pH for aromatase activity in microsomal preparations ranged between 7.0 and 7.5. When androstenedione was the substrate, the mean V_max was 0.58 pmol/mg protein/h (range: 0.09-1.26 pmol/mg protein/h) and the mean K_m was 27 nM (range: 9-50 nM). When aromatase activity was determined as a function of NADPH concentration, the mean V_max was 0.39 pmol/mg protein/h (range 0.11-0.82 pmol/mg protein/h) and the mean K_m., was 180 μM (range: 86-300 μM). For skin fibroblasts exposed to DEX, aromatase activity in isolated microsomes and intact cells was stimulated demonstrating a typical time course with peak levels at 14 h and a decline toward baseline with prolonged (48-60 h) exposure. Cytosol from DEX-stimulated cells did not stimulate the aromatase activity in microsomal-enriched preparations from untreated cells. In addition, cytosol from cells incubated with DEX for a prolonged period (60 h) did not inhibit the higher aromatase activity of microsomes from cells incubated with DEX for only 14 h. We previously demonstrated that skin fibroblasts incubated with DEX and CHX produced a superinduction phenomenon for aromatase activity. This superinduction of enzyme activity also occurred in the microsomal-enriched fraction and was unaffected by the cytosol of these cells. These studies exclude the possibility that the unique effects of DEX on the aromatase in human skin fibroblasts are due to the production of either inhibitory or stimulatory soluble factors within cytosol.