Swevers L, Cherbas L, Cherbas P, Iatrou K
Department of Medical Biochemistry, University of Calgary, Canada.
Insect Biochem Mol Biol. 1996 Mar;26(3):217-21. doi: 10.1016/0965-1748(95)00097-6.
The Drosophila ecdysone receptor (DmEcR) is a member of the nuclear receptor superfamily; it functions as an obligate heterodimer with another nuclear receptor, DmUSP. EcR homologs have now been cloned from several other insects. We report here that one such homolog, BmEcR from the commercial silkmoth, Bombyx mori, is a functional ecdysone receptor. Upon dimerization with BmCF1, the silkmoth homology of DmUSP, BmEcR binds the radiolabeled steroid ligand 125I-iodoponasterone A with Kd = 1.1 nM, indistinguishable from that exhibited by DmEcR/DmUSP. BmEcR/BmCF1 forms a specific complex with an ecdysone response element (EcRE) derived from the heat shock protein 27 (hsp27) gene promoter of Drosophila; and, as with DmEcR/DmUSP, formation of this complex is stimulated by the presence of 20-hydroxyecdysone. Finally, BmEcR can substitute for DmEcR in an EcR-deficient Drosophila tissue culture line, stimulating trans-activation of an ecdysone-inducible reporter gene construct. Thus, BmEcR and BmCF1 are the functional counterparts of DmEcR and DmUSP, respectively and, despite considerable sequence divergence between the Drosophila and Bombyx proteins, the counterparts are--at least qualitatively--functionally equivalent.
果蝇蜕皮激素受体（DmEcR）是核受体超家族的成员；它与另一种核受体DmUSP形成必需的异源二聚体发挥作用。现在已经从其他几种昆虫中克隆出了EcR同源物。我们在此报告，一种这样的同源物，即来自商业家蚕Bombyx mori的BmEcR，是一种功能性蜕皮激素受体。与DmUSP的家蚕同源物BmCF1二聚化后，BmEcR与放射性标记的类固醇配体125I-碘泼那睾酮A结合，解离常数Kd = 1.1 nM，与DmEcR/DmUSP表现出的解离常数无法区分。BmEcR/BmCF1与源自果蝇热休克蛋白27（hsp27）基因启动子的蜕皮激素反应元件（EcRE）形成特异性复合物；并且，与DmEcR/DmUSP一样，20-羟基蜕皮激素的存在会刺激该复合物的形成。最后，在缺乏EcR的果蝇组织培养细胞系中，BmEcR可以替代DmEcR，刺激蜕皮激素诱导型报告基因构建体的反式激活。因此，BmEcR和BmCF1分别是DmEcR和DmUSP的功能对应物，并且，尽管果蝇和家蚕蛋白质之间存在相当大的序列差异，但这些对应物至少在定性上功能等同。
