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 abili ty to inhibit interleukin-6 expression at the molecular level. In a se ries of co-transfection assays, we found that 5 alpha-dihydrotestoster one, through the androgen receptor, repressed activation of the interl eukin-6 promoter, in part, by inhibiting NF kappa B activity. It did n ot appear that 5 alpha-dihydrotestosterone inhibited NF kappa B by act ivating the androgen receptor to compete for the NF kappa B response e lement as we could not detect androgen receptor binding to the IL-6 pr omoter by DNase I footprinting assay. However, by electrophoretic mobi lity shift assay we found that 5 alpha-dihydrotestosterone repressed f ormation of NF kappa B . NF kappa B response element complex formation . In LNCaP prostate carcinoma cells, 5 alpha-dihydrotestosterone achie ved 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 alp ha 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 natur al androgen-regulated gene.