MUTUAL TRANSCRIPTIONAL INTERFERENCE BETWEEN RELA AND ANDROGEN RECEPTOR

Cross-modulation between androgen receptor (AR) and NF-kappa B/Rel pro teins was studied using various androgen- and NF-KB-regulated reporter genes under transient transfection conditions. In COS-1 cells, elevat ed expression of RelA (p65) repressed AR-mediated transactivation in a dose-dependent manner, whereas NF kappa B1 (p50), another major membe r of the NF-kappa B family, did not influence transactivation. The rep ression of AR appeared to involve the N-terminal region of the protein between residue 297 and the DNA-binding domain. ReLA-mediated transre pression could not be over come by increasing the amount of AR. Transc riptional interference between RelA and AR was mutual in that cotransf ected AR was able to attenuate transactivation by RelA in a dose- and steroid-dependent fashion. An excess of RelA was able to rescue the re pression to some extent. Immunological analyses of RelA and AR protein levels indicated that transrepression was not due to reciprocal decre ase in their amounts. Neither did AR increase the concentration of I k appa B alpha, which can sequester and inactivate RelA. Electrophoretic mobility shift assays using extracts from cotransfected cells and pur ified recombinant proteins showed that AR and RelA did not significant ly influence each other's DNA binding activity. Nevertheless, protein- protein interaction experiments demonstrated a weak association betwee n AR and RelA. Collectively, these data suggest that the mutual repres sion in intact cells is due to formation of AR-RelA complexes that are held together by another partner or to competition for a coactivator required for transcription.