Growth factor-mediated regulation of aromatase activity in human skin fibroblasts

We investigated the effects of various hormones and growth factors on aromatase activity in cultured human skin fibroblasts. Several potential trophic factors were tested for their ability to modify basal aromatase activity or the response to dibutyryladenosine 3',5'-cyclic monophosphate and dexamethasone because (i) no endogenous ligand has been identified that is responsible for stimulating aromatase activity in the periphery, and (ii) dexamethasone and cAMP analogs can increase this enzyme's activity in fibroblasts. The effect of insulin and insulin-like growth factors were examined in closer detail because of the clinical association between insulin and hyperandrogenism. Pituitary hormones and hypothalamic releasing factors, such as human ACTH (10 nM), beta-endorphin (10 nM), beta-lipotropin (10 nM), alpha-MSH (10 nM), gamma 3-MSH (10 nM), ovine luteinizing hormone (10 ng/ml), ovine follicle-stimulating hormone (10 ng/ml), ovine thyroid-stimulating hormone (10 ng/ml), rat growth hormone (10 ng/ml), rat prolactin (10 ng/ml), rat corticotropin-releasing factor (10 nM), luteinizing hormone-releasing factor (10 nM), thyrotropin-releasing factor (10 nM), human growth hormone-releasing factor (10 nM), and somatostatin (10 nM), have no significant effects on aromatase activity. Porcine inhibin A (10 ng/ml) and porcine activin AB (10 ng/ml), two ovarian hormones with structural transforming homology to transforming growth factor-beta, also have no effect on aromatase activity. Although basic fibroblast growth factor (1-100 ng/ml), acidic fibroblast growth factor (1 ng/ml), epidermal growth factor (1 ng/ml), platelet-derived growth factor (1 ng/ml), tumor necrosis factor (1 ng/ml), and transforming growth factor-beta 1 (1 ng/ml) have no effect on basal aromatase activity in human skin fibroblasts, all of these growth factors inhibited the ability of dibutyryladenosine 3',5'-cyclic monophosphate to stimulate aromatase activity. In contrast, both insulin (100 pg/ml-10 ng/ml) and insulin-like growth factor-1 (1-100 ng/ml) had no effect on cAMP-stimulated aromatase but potentiated the action of dexamethasone (100 nM). Thus, there is a clear distinction between the effects of dexamethasone and cAMP on peripheral aromatase. On the basis of the results presented here, it is interesting to speculate that the hyperandrogenism that is often associated with insulin resistance may be due to a combination of growth factor-mediated inhibition of aromatase activity and the failure of peripheral tissues to respond to insulin and metabolize androgens to estrogens.