Multi-input drug-controlled switches of mammalian gene expression based on engineered nuclear hormone receptors

Protein-based switches that respond to different inputs to regulate cellular outputs, such as gene expression, are central to synthetic biology. For increased controllability, multi-input switches that integrate several cooperating and competing signals for the regulation of a shared output are of particular interest. The nuclear hormone receptor (NHR) superfamily offers promising starting points for engineering multi-input-controlled responses to clinically approved drugs. Starting from the VgEcR/RXR pair, we demonstrate that novel (multi-)drug regulation can be achieved by exchange of the ecdysone receptor (EcR) ligand binding domain (LBD) for other human NHR-derived LBDs. For responses activated to saturation by an agonist for the first LBD, we show that outputs can be boosted by an agonist targeting the second LBD. In combination with an antagonist, output levels are tunable by up to three simultaneously present small-molecule drugs. Such high-level control validates NHRs as a versatile, engineerable platform for programming multi-drug-controlled responses. ### Competing Interest Statement The authors have declared no competing interest. * EcR : ecdysone receptor; RXR : retinoid x receptor; GR : glucocorticoid receptor; LBD : ligand binding domain; DBD : DNA binding domain; AD : activation domain; NHR : nuclear hormone receptor; FDA : U.S. Food and Drug Administration; PonA : ponasterone A; DEX : dexamethasone; PRED : prednisolone; BEX : bexarotene; E2 : 17β-estradiol; EE2 : 17α-Ethynylestradiol; 40HT : 4-hydroxytamoxifen; E/GRE : Ecdysone/Glucocorticoid response element; USP : Ultraspiracle