Palli Subba R, Kapitskaya Mariana Z, Potter David W
Department of Entomology, University of Kentucky, Lexington, KY 40546, USA.
FEBS J. 2005 Dec;272(23):5979-90. doi: 10.1111/j.1742-4658.2005.05003.x.
A pair of nuclear receptors, ecdysone receptor (EcR) and ultraspiracle (USP), heterodimerize and transduce ecdysteroid signals. The EcR and its nonsteroidal ligands are being developed for regulation of transgene expression in humans, animals and plants. In mammalian cells, EcR:USP heterodimers can function in the absence of ligand, but EcR/retinoid X receptor (EcR:RXR) heterodimers require the presence of ligand for activation. The heterodimer partner of EcR can influence ligand sensitivity of EcR so that the EcR/Locusta migratoria RXR (EcR:LmRXR) heterodimers are activated at lower concentrations of ligand when compared with the concentrations of ligand required for the activation of EcR/Homo sapiens RXR (EcR:HsRXR) heterodimers. Analysis of chimeric RXRs containing regions of LmRXR and HsRXR and point mutants of HsRXR showed that the amino acid residues present in helix 9 and in the two loops on either end of helix 9 are responsible for improved activity of LmRXR. The EcR:Lm-HsRXR chimera heterodimer induced reporter genes with nanomolar concentration of ligand compared with the micromolar concentration of ligand required for activating the EcR:HsRXR heterodimer. The EcR:Lm-HsRXR chimera heterodimer, but not the EcR:HsRXR heterodimer, supported ligand-dependent induction of reporter gene in a C57BL/6 mouse model.
一对核受体，即蜕皮激素受体（EcR）和超气门蛋白（USP），形成异二聚体并转导蜕皮甾体信号。EcR及其非甾体配体正被开发用于调控人类、动物和植物中的转基因表达。在哺乳动物细胞中，EcR:USP异二聚体在没有配体的情况下也能发挥作用，但EcR/视黄酸X受体（EcR:RXR）异二聚体需要配体的存在才能被激活。EcR的异二聚体伙伴会影响EcR对配体的敏感性，因此与激活EcR/智人RXR（EcR:HsRXR）异二聚体所需的配体浓度相比，EcR/飞蝗RXR（EcR:LmRXR）异二聚体在较低浓度的配体下就能被激活。对包含LmRXR和HsRXR区域的嵌合RXR以及HsRXR的点突变体的分析表明，存在于螺旋9以及螺旋9两端两个环中的氨基酸残基是LmRXR活性提高的原因。与激活EcR:HsRXR异二聚体所需的微摩尔浓度的配体相比，EcR:Lm-HsRXR嵌合异二聚体在纳摩尔浓度的配体作用下就能诱导报告基因。在C57BL/6小鼠模型中，EcR:Lm-HsRXR嵌合异二聚体而非EcR:HsRXR异二聚体支持报告基因的配体依赖性诱导。
