The antisteroid RU486: its cellular and molecular mode of action.

RU486 is a very powerful antisteroid hormone compound, with antiprogestin and antiglucocorticosteroid clinical applications. High-affinity binding to the receptor ligand-binding domain results in essentially antagonistic function; however, some agonistlike effects have been observed. This review discusses the implications of recent discoveries concerning hsp90 (heat-shock protein M(r) approximately 90,000)-receptor interaction, receptor-DNA binding, and the involvement of transcription factors in the mechanism of action of RU486.