Regulation of sex steroid formation by interleukin-4 and interleukin-6 in breast cancer cells

Sex steroids play a predominant role in the development and differentiation of normal mammary gland as well as in the regulation of hormone-sensitive breast cancer growth. There is evidence suggesting that local intracrine formation of sex steroids from inactive precursors secreted by the adrenals namely, dehydroepiandrosterone (DHEA) and 4-androstenedione (4-dione) play an important role in the regulation of growth and function of peripheral target tissues, including the breast. Moreover, human breast carcinomas are often infiltrated by stromal/immune cells secreting a wide spectra of cytokines. These might in turn regulate the activity of both immune and neoplastic cells. The present study was designed to examine the action of cytokines on 17 β -hydroxysteroid dehydrogenase (17 β -HSD) and 3 β -hydroxysteroid dehydrogenase/isomerase (3 β -HSD) activities in human breast cancer cells. The various types of human 17 β -HSD (five types) and 3 β -HSD (two types), because of their tissue- and cell-specific expression and substrate specificity, provide each cell with necessary mechanisms to control the level of intracellular active androgens and estrogens. We first investigated the effect of exposure to IL-4 and IL-6 on reductive and oxidative 17 β -HSD activities in both intact ZR-75-1 and T-47D human breast cancer cells. In ZR-75-1 cells, a 6 d exposure to IL-4 and IL-6 decreased E 2 -induced cell proliferation, the half maximal inhibitory effect being exerted at 88 and 26 pM, respectively. In parallel, incubation with IL-4 and IL-6 increased oxidative 17 β -HSD activity by 4.4- and 1.9-fold, respectively, this potent activity being observed at ec 50 values of 22.8 and 11.3 pM, respectively. Simultaneously, reductive 17 β -HSD activity leading to E 2 formation was decreased by 70 and 40% by IL-4 and IL-6, respectively. Moreover, IL-4 and IL-6 exerted the same regulatory effects on 17 β -HSD activities when testosterone and 4-dione were used as substrates, thus strongly suggesting the expression of the type 2 17 β -HSD ZR-75-1 cells. In contrast, in T-47D cells, IL-4 increased the formation of E 2 , whereas IL-6 exerts no effect on this parameter. However, we found that T-47D cells failed to convert testosterone efficiently into 4-DIONE, thus suggesting that there is little or no expression of type 2 17 β -HSD in this cell line. The present findings demonstrate that the potent regulatory effects of IL-4 and IL-6 on 17 β -HSD activities depend on the cell-specific gene expression of various types of 17 β -HSD enzymes. We have also studied the effect of cytokines on the regulation of the 3 β -HSD expression in both ZR-75-1 and T-47D human breast cancer cells. Under basal culture conditions, there is no 3 β -HSD activity detectable in these cells. However, exposure to IL-4 caused a rapid and potent induction of 3 β -HSD activity, whereas IL-6 failed to induce 3 β -HSD expression. Our data thus demonstrate that cytokines may play a crucial role in sex steroid biosynthesis from inactive adrenal precursors in human breast cancer cells.