Inhibition of NF kappa B activity through maintenance of I kappa B alpha levels contributes to dihydrotestosterone-mediated repression of the interleukin-6 promoter

Androgens repress expression of many genes, yet the mechanism of this activity has remained elusive. The cytokine, interleukin-6, is active in a variety of biological systems, and its expression is repressed by androgens. Accordingly we dissected the mechanism of androgen's ability to inhibit interleukin-6 expression at the molecular level. In a series of co-transfection assays, we found that 5 alpha-dihydrotestosterone, through the androgen receptor, repressed activation of the interleukin-6 promoter, in part, by inhibiting NF kappa B activity. It did not appear that 5 alpha-dihydrotestosterone inhibited NF kappa B by activating the androgen receptor to compete for the NF kappa B response element as we could not detect androgen receptor binding to the IL-6 promoter by DNase I footprinting assay. However, by electrophoretic mobility shift assay we found that 5 alpha-dihydrotestosterone repressed formation of NF kappa B . NF kappa B response element complex formation. In LNCaP prostate carcinoma cells, 5 alpha-dihydrotestosterone achieved this effect through maintenance of I kappa B alpha protein levels in the face of phorbol ester, a stimulus that results in I kappa B alpha degradation. Finally, we confirmed that I kappa B alpha inhibits NF kappa B-mediated activation of the interleukin-6 promoter. These data suggest that maintenance of I kappa B alpha levels may represent the first identified mechanism for androgen-mediated repression of a natural androgen-regulated gene.