Ecdysteroids receptors

Martin D., Wang S.-F. and Raikhel A. S. (2001) The vitellogenin gene of the mosquito Aedes aegypti is a direct target of ecdysteroid receptor. Mol. Cell. Endocrin. 173, 75-86. 

Lin et al. [149] have recently reported the synthesis of 2-(4,5-dimethoxy-2-nitrobenzyl)-20-hydroxyecdysone (6-6), which itself has a very low affinity for ecdysteroid receptors expressed in mammalian 293T cells, but can be photolysed at 348 nm to release 20E, which then activates the receptor-regulated reporter gene. With this system, it will be possible not only to control the temporal activation of transfected genes, but also their spatial activation. The authors recognise that the effectiveness of this system can be considerably improved in future by derivatising an ecdysteroid (poA or muA) which is more active in ecdysteroid-responsive mammalian cells. 

Figure 9 Generalised scheme for an ecdysteroid-regulated gene switch system RXR = retinoid X receptor, EcR = ecdysteroid receptor, EcRE = ecdysteroid response element, MuA = muristerone A, PoA = ponasterone A.

The most informative analysis of ecdysteroid/receptor interaction would be by X-ray crystallography. Although it has been possible to crystallise the LBDs of several nuclear receptors and to determine their structures by X-ray crystallography (ER [208], PR [209], RAR [210], RXR [211], TR [212], USP [213] and VDR [214]), it has not yet been possible to do this for any EcR protein. This probably derives from the fact that EcR only binds ligand with high affinity when it is complexed with USP (RXR), necessitating the co-crystallisation of ligand + EcR LBD + USP LBD. Ultimately it should be possible to achieve this. In the meantime, two... 

Antagonists of vertebrate steroid receptors are proving experimentally and therapeutically very significant [220-222], It has been known that certain plants contain ecdysteroid receptor agonists (phytoecdysteroids) for over 30 years It seemed reasonable to assume that plants might also contain compounds which could antagonise the action of ecdysteroids. With the advent of simple, reliable bioassays, it became appropriate to search for such compounds. In the intervening years we have screened... 

The plant-insect chemical interactions concerning the stilbenoids have just been reviewed [509] (-i-)-Ampelopsin B (806) and ct-viniferin (635) antagonized the action of 20-hydroxyecdysone [510] cw-miyabenol A (735), kobophenol B and cw-miyabenol C (663) showed competitive binding to ecdysteroid receptors [337] resveratrol (1) and oligomers (suffruticosols A-C, 589-591) also exhibited ecdysteroid antagonistic activity [297]. 

The inhibition of uptake of [ HJpoA into Kc cells has also been used as a measure of the aflBnities of several ecdysteroids [190], More recently, a similar approach has been used for ecdysteroids and BAHs for the ecdysteroid receptors present in these cells [191] poA (IC50 = 1.3 x 10 ... 

The ecdysteroid receptor-containing Spodoptera frugiperda Sf-9 cell line has been used to compare the activities of ecdysteroids and BAHs in a cell uptake competition assay using [ H]poA [195]. The activities of the ecdysteroids tested were PoA (IC50 = 8.9 x lO M), 20E (1.7 x lO M),... 

Cell-free receptor assays have not been extensively used to investigate ligand specificity of ecdysteroid receptors. This is largely a consequence of the need to extract the receptor from a suitable biological source in adequate amounts to carry out assays with several analogues and the lability of the receptor. Two radiolabelled ecdysteroids ([ H]PoA and... 

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