Abstract
Steroid receptors are members of a large family of transcription factors whose activity is tightly regulated by the binding of their cognate steroid ligand. Mammalian steroid hormone receptors have been exploited to obtain the regulated expression of heterologous genes in mammalian cells. However, the utility of these systems in cultured cells and transgenic animals is limited by the presence of endogenous steroids and their receptors. We show that a Drosophila ecdysone receptor can function in cultured mammalian cells as an ecdysteroid-dependent transcription factor. The activity of the ecdysone receptor was not induced by any of the mammalian steroid hormones tested. The DNA-binding and transactivation activities of viral, mammalian, or bacterial proteins were rendered ecdysteroid-dependent when fused to the ligand-binding domain of the ecdysone receptor. The ecdysone receptor may prove useful in selectively regulating the expression of endogenous or heterologous genes in mammalian cells.
