Steroid requirement for androgen receptor dimerization and DNA binding. Modulation by intramolecular interactions...

Infection of Spodoptera frugiperda Sf9 insect cells with recombinant human androgen receptor (AR) baculovirus results in expression of a 118-kDa phosphoprotein that displays high affinity androgen binding and androgen-dependent targeting to the nucleus. Using the DNA mobility shift assay, specific in vitro binding of full-length AR to androgen response element DNA (ARE) requires intracellular hormone exposure. The ability of a variety of steroids to induce ARE binding paralleled their transcriptional potential. Certain antihormones, cyproterone acetate and RU486, promote ARE binding, but a pure antiandrogen, hydroxyflutamide, inhibits AR binding to ARE DNA. AR dimerization requires incubation of recombinant baculovirus-infected insect cells with androgen, but only when one or both components of the dimer contain the NH2-terminal domain. Based on the intensities of ARE binding and lack of binding to an ARE half-site, it appears that, unlike the glucocorticoid receptor, AR binds DNA primarily as a dimer. Thus, full-length baculovirus-expressed AR requires intracellular hormone exposure for dimerization and ARE binding to overcome inhibition imposed by the AR NH2-terminal domain. Antihormones with agonist activity promote dimerization and ARE binding, while a pure antiandrogen blocks AR DNA binding. It is concluded that intramolecular interactions between the NH2-terminal and steroid-binding domains are regulated by the specificity of hormone binding and modulate receptor dimerization and DNA binding.