Speaker: Naoki Yamanaka, University of California, Riverside, Department of Entomology, Institute for Integrative Genome Biology

Title: A membrane transporter is required for steroid hormone update in Drosophila

Abstract: Steroid hormones regulate diverse biological processes through intracellular nuclear receptors. In insects, the primary steroid hormone ecdysone (more specifically, its active form 20-hydroxyecdysone or 20E and related ecdysteroids) enters target cells and binds to the nuclear receptor named ecdysone receptor (EcR) to direct transcription of diverse genes involved in molting and metamorphosis. Due to the widely-accepted notion that lipophilic steroid hormones can freely enter cells by simple diffusion, little is known about the mechanisms that regulate transport of steroids across lipid bilayers. To the best of our knowledge, however, the simple diffusion model of steroid hormone transport has not been critically tested in any in vivo model to date. Here we demonstrate in Drosophila that a membrane-bound solute carrier transporter encoded by Ecdysone Importer (EcI) is required for cellular uptake of ecdysone. EcI regulates ecdysone signaling in a cell-autonomous manner in vivo, and is both necessary and sufficient for inducing ecdysone-dependent gene expression in cultured cells that express EcR. Our results challenge the simple diffusion model and instead suggest a facilitated diffusion model for cellular uptake of steroid hormones.

Host: Hua Bai