STEROID REQUIREMENT FOR ANDROGEN RECEPTOR DIMERIZATION AND DNA-BINDING - MODULATION BY INTRAMOLECULAR INTERACTIONS BETWEEN THE NH2-TERMINALAND STEROID-BINDING DOMAINS

Infection of Spodoptera frugiperda Sf9 insect cells with recombinant h uman androgen receptor (AR) baculovirus results in expression of a 118 -kDa phosphoprotein that displays high affinity androgen binding and a ndrogen-dependent targeting to the nucleus. Using the DNA mobility shi ft assay, specific in vitro binding of full-length AR to androgen resp onse element DNA (ARE) requires intracellular hormone exposure. The ab ility of a variety of steroids to induce ARE binding paralleled their transcriptional potential. Certain antihormones, cyproterone acetate a nd RU486, promote ARE binding, but a pure antiandrogen, hydroxyflutami de, inhibits AR binding to ARE DNA. AR dimerization requires incubatio n 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 t o an ARE half-site, it appears that, unlike the glucocorticoid recepto r, AR binds DNA primarily as a dimer. Thus, full-length baculovirus-ex pressed AR requires intracellular hormone exposure for dimerization an d ARE binding to overcome inhibition imposed by the AR NH2-terminal do main. Antihormones with agonist activity promote dimerization and ARE binding, while a pure antiandrogen blocks AR DNA binding. It is conclu ded that intramolecular interactions between the NH2-terminal and ster oid-binding domains are regulated by the specificity of hormone bindin g and modulate receptor dimerization and DNA binding.