Int.J.Curr.Microbiol.App.Sci (2018) 7(5): 1548-1553

International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 7 Number 05 (2018) Journal homepage: http://www.ijcmas.com

Review Article https://doi.org/10.20546/ijcmas.2018.705.183

Ecdysone Present in is a Novel Target for

Gagan Rani1*, Neha Gupta1, Neeru Singh Redhu2 and Sudhir Kumar2

1Department of Chemistry, 2Department of MBB & B, CCSHAU Hisar, Haryana, India

*Corresponding author

ABSTRACT

K e yw or ds

Ecdys one receptor, Insects occupy more than 70% of entire animal kingdom and are the most Novel target for successful group of organism living on earth. They are usually divided into insecti cide, Insects three groups i.e., harmless, injurious and beneficial. A group of injurious

Article Info insects referred as pests, annually destroy between 6-30% of agricultural harvest in developing countries. These losses become even more significant

Accepted: for stored cereal products than pre-harvest losses, because post-harvest 12 April 2018 Available Online: costs are much higher than the cost of production. 10 May 2018

Introduction hemimetabolous (incomplete metamorphosis) and holometabolous (complete Lepidopteran insects are among the major metamorphosis). pests of several economically important crops and their control requires a multi-pronged metamorphosis intervention. While have been used in several IPM (Insect pest management) Metamorphosis is the characteristic feature of programmes, pheromone traps have been majority of the insects, including frequently used to capture and kill insect pests holometabola during the postembryonic in the field. The capacity of novel chemicals development i.e., the ontogeny accomplished to disturb the mating and molting processes of after hatching. Metamorphosis is marked by insects has been capitalized for pest control. abrupt changes in the form and structure Insects on the basis of their ability to undergo during the postembryonic development. The metamorphosis are broadly classified into larval forms are the juveniles of holometabola ametabolous (no metamorphosis), that lack the external rudiments of wings and

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Int.J.Curr.Microbiol.App.Sci (2018) 7(5): 1548-1553 genitalia but possess imaginal discs. The Chemistry of ecdysteroids larvae are voracious feeders and have different habitat and niche from the adult stage. The Ecdysteroid is a well-defined term for all non-feeding pupal stages are usually hidden or compounds structurally related to . somehow protected stage. The tissue Further it includes true ecdysteroid and degeneration and rebuilding mainly occurs at ecdysteroid related compounds. The the pupal stage, which also possesses the biologically active ecdysteroid refers to the external rudiments of wings and genitalia. molting . Chemically ecdysone is the trivial name of a specific compound (22R)-2β, The adult stage of holometabolous insect is 3β, 14α, 22, 25-pentahydroxy-5β-cholest-7- morphologically very different from the en-6-one, a derivative of cholesterol. 20- previous stages and they are usually prolific Hydroxyecdysone (20E) is the active form, breeders (Sehnal et al., 1996; Truman and which is a result of ecdysone 20- Riddiford, 1999, 2002; Buszczak and monoxygenase catalyzed hydroxylation Segraves, 2000; Tissot and Stocker, 2000). (Grieneisen, 1994; Rees, 1995). The two Ecdysterone or 20E is responsible for insects molting ecdysone and 20E were development, Molting and metamorphosis. originally designated as α and β ecdysone The molting hormone, 20-Hydroxyecdysone respectively (Horn and Bergamasco, 1985). In (ecdysterone or 20E), is a naturally occurring , 20E is one of the most ecdysteroid hormone that controls the molting ubiquitously distributed ecdysteroid utilized of arthropods (Thummel, 1995, 1996). During by the molt cycle and is also associated with insect development, it binds to the ecdysone various physiological events (Gilbert et al., receptor, a -activated 2002). factor found in the nuclei of insect cells Regulation of ecdysteroid biosynthesis (Riddiford, 2000). This in turn leads to the activation of many other genes, as evidenced The regulation of ecdysteroidogenesis has by chromosomal puffing at over a hundred been studied continuously for the past several sites. Ultimately the activation cascade causes decades and recent discoveries using physiological changes that result in molting Drosophila molecular genetics have advanced (Henrich, 2005). our knowledge further.

Ecdysone Biosynthesis The availability of genome sequences, the ease of genetic manipulation and the large PTTH acts on the prothoracic glands (PGL) collection of mutants all make Drosophila an and stimulates ecdysteroid synthesis (Gilbert attractive system for understanding the et al., 1988). Thus 3-dehydroecdysone is mechanisms regulating steroidogenesis. released into the haemolymph where it is Regulation of ecdysteroid synthesis is reduced by a ketoreductase to ecdysone. The complex, and is under the control of peptide prohormone ecdysone is converted to the hormones as well as the JH. principal molting hormone 20- hydroxyecdysone (20E) in the mitochondria It has been known for some 85 years that a and microsomes of peripheral tissues such as factor from the insect brain can stimulate the haemocytes, fat body, Malpighian tubules and PGLs of both diptera and . PTTH epidermal cells (Riddiford et al., 2001). 20E stimulated ecdysteroid production in PGLs finally exerts its effect and causes apolysis and occurs via a cascade of events which is yet to secretion of larval, pupal or adult cuticle be elucidated completely. (Gilbert, 1989). 1549

Int.J.Curr.Microbiol.App.Sci (2018) 7(5): 1548-1553

Ecdysteroids mode of action on the nucleus. According to this model, the ecdysone upon binding to its specific receptor The isolation and purification of ecdysone and directly regulates two classes of genes, a small 20E by Butenandt and Karlson (1954) class of early regulatory genes and a large revolutionized the field of insect class of late genes. The products of the endocrinology. The pioneering research of early genes in turn repress their own Clever and Karlson (1960) revealed puffing expression and induce the much larger set of patterns of the Chironomous tentans salivary late genes that play a more direct role in gland polytene by ecdysteroid. controlling the biological response of This observation of puff regulation was later hormone. Extensive studies based on this confirmed in genetic model organism, the fruit model have provided insights into the Drosophila melanogaster by several other molecular mechanism of 20E action (Henrich groups (Ashburner et al., 1974; Ashburner and and Brown, 1995; Thummel, 1996; Henrich et Richards, 1976). al., 1999; Riddiford et al., 2001).

Based on these observations as well as Ecdysone receptor in insects through a series of detailed and elegant studies, Ashburner and group (1974, 1976) The ecdysone receptor is a noncovalent proposed a model for the regulation of gene heterodimer of two the EcR protein expression by 20E. Since then this model and ultraspiracle protein (USP). These nuclear became the basis of the knowledge of hormone receptor proteins are the insect mechanism of steroid hormone action, which orthologs of the mammalian farnesoid X suggests that ecdysteroid could initiate a receptor (FXR) and cascade of by directly acting proteins (RXR) receptively.

Fig.1 LBD of EcR in a) H. armegira and b) S. litura

Indeed, based on sequence nuclear hormone receptors, namely an N considerations, some researchers reserve the terminal transcriptional activation domain term USP for the EcR partner from (A/B domain), a DNA-binding domain (C lepidopteran and dipteran insects, and use domain, highly conserved between receptors), RXR in all other instances. EcR and USP a linker region (D region), a ligand-binding share multidomain architecture common to all domain (E domain, moderately conserved)

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Int.J.Curr.Microbiol.App.Sci (2018) 7(5): 1548-1553 and in some cases a distinct C-terminal regulates defensive secretions and controls extension (F-domain) (Koelle et al., 1991) choriogenesis (Gilbert et al., 1996). The The DNA-binding domains of EcR and USP ecdysteroid also initiates the breakdown of recognise specific short sequences in DNA, larval structures during metamorphosis. As it and mediate the binding of the hetero dimer to is clear, there exists a vast amount of these ecdysone response elements (EREs) in information regarding the regulation of the promoters of ecdysone responsive genes. ecdysteroids at the synthesis as well as at its titre level. However, knowledge regarding the The ecdysteroid binding pocket is located in mechanism of regulation of ecdysteroid the ligand-binding domain of the EcR subunit, dependent actions is not very clear and the but EcR must be dimerised with a USP (or field remains largely unexplored. In majority with an RXR) for high affinity ligand binding of holometabolous insects including to occur. In such circumstances, the binding lepidopterans, the 20E action is regulated to of an ligand triggers a conformational induce transition from the juvenile to adult change in the C terminal part of the EcR forms. ligand-binding domain that leads to transcriptional activation of genes under Ecdysone receptor as a Target by ECRE control. There is also a ligand-binding insecticides pocket in the corresponding domain of USP. Its natural ligand remains uncertain, and USPs Lepidopteran insects are among the major appears to be locked permanently in an pests of several economically important crops inactive conformation (Clayton et al., 2001) and their control requires a multi-pronged intervention. The molting hormone, 20- Regulation of ecdysteroids action Hydroxyecdysone (ecdysterone or 20E), is a naturally occurring ecdysteroid hormone that A major area with regard to understanding the controls the molting of arthropods (Thummel, regulation of 20E action is that of tissue 1995, 1996). During insect development, it specificity. The diversity in function of the binds to the ecdysone receptor, a ligand- hormone to some extent could be due to the activated found in the variation of responses among types that nuclei of insect cells (Riddiford, 2000). This typifies the action of 20E. The 20E also in turn leads to the activation of many other shows differential effects on same tissue at genes, as evidenced by chromosomal puffing different developmental stages (Riddiford et at over a hundred sites. Ultimately the al., 2001). Thus studies directed towards the activation cascade causes physiological molecular basis of differentiation during the changes that result in molting (Henrich, development and the built in regulatory 2005). In recent years research is focused on mechanisms at the tissue level largely aid in targeting the ecdysone receptor with the aim the understanding of 20E actions. In contrast to disrupt the molting process of insects and to vertebrate systems, ecdysteroids perform a facilitate insect control. Insect growth wide variety of functions in the entire insect regulators control insect population, by class. Hence, it is often referred that almost primarily regulating molting, metamorphosis the entire insect is target of ecdysteroids and many other physiological and (Gilbert et al., 1996). It stimulates the growth developmental processes (Williams, 1956). and development of imaginal discs, promotes Nonsteroidal di benzoyl hydrazines such as the deposition of cuticle by epidermis, RH5849 and RH5992 exert their insecticidal regulates the growth of motor neurons, effect by binding to the 20-hydroxyecdysone

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Int.J.Curr.Microbiol.App.Sci (2018) 7(5): 1548-1553 binding site and activating the ecdysteroid hormone-binding residues are conserved receptors permanently. Their comprehensive (Figure 1). Specifically, Phe-397/Phe-329 effects and high selectivity as well as lower (EcR/LXR) and Met- 380/Met-312 have toxicity to non-target animals and the hydrophobic interactions with the centre of environment provide new tools for integrated the hormone, and Arg-387/Arg-319 interacts pest management EcR is the target of the with the C3-OH group of both ponA and environmentally safe bisacylhydrazine eCH. Trp- 526/Trp-457 has been proposed to insecticides used against pests which cause be part of a tryptophan/histidine activation severe damage to agriculture. N-tert-butyl- switch in LXR (Williams and others 2003). N,N’- dibenzoylhydrazines (DBHs) were Carmichael and colleagues (2005), however, discovered as molting hormonal , and suggested that this tryptophan does not causes incomplete molting in insects leading participate in an activation switch in EcR to death. A number of DBH analogues with because this would not explain why ponA, various substitutes at benzene rings were which lacks the 25-hydroxyl group, is an synthesized and the structure-activity agonist for EcR. Several amino acids of EcR relationship (SAR) studies performed. that interact with the hydroxyl groups of Recently, four DBH compounds including ponA are not conserved in LXR, which likely , methoxyfenozide, is due to the absence of these hydroxyl groups chromafenozide and halofenozide have been in the ligands that bind LXR. For example, commercialized. Chromafenozide is found to Tyr-408 in EcR, which forms a strong be significantly potent against various hydrogen bond to the 20-OH group of ponA, lepidopterous insects, but at the same time is a phenylalanine in LXR. Other key almost non-toxic to non-lepidopterous differences between the hormone binding species, including pollinators, predators and pockets of EcR and LXR include Arg-383/ parasitoids. Even though 20E is commonly Glu-281 and Glu-309/Asn-239. Different used as molting hormone in most of insects types of inhibitors or insecticides bind on and has similar potency among insects, SARs these binding sites where ecdysone bound, of non-steroidal ecdysone agonists varied some inhibitors act as antagonist and other act among insect species. The reason for the as agonists. Agonists act as growth regulators difference of SARs between ecdysteroids and and thus help pre metamorphosis because of non-steroidal compounds is disclosed by the that insects died. As compared to it antagonist three dimensional structure analysis of ligand- retard the growth of insects and because of bound EcR, showing that ponasterone A that metamorphosis not occur and adult insect (PonA), one of the most potent ecdysteroids, are not formed. So various insecticides binds does not necessarily overlap with a at these binding sites and help to control pest chromafenozide analog (BYI06830) in the by retard the insects development, growth, binding pocket, and therefore, the interaction molting, metamorphosis. between EcR and DBHs can be species- dependent. References

Comparison of 3D structures of hormone- Gilbert, L. I., Rybczynski, R. and Warren, J. binding pockets in EcR and LXR T. Control and biochemical nature of the ecdysteroidogenic pathway. Annu. As we found for TR and RAR, comparison of Rev. Entomol. 47, 883–916 (2002). the 3D structure of the hormone-binding Henrich, V.C., Siiter, T.J., Lubahn, D.B., domains of EcR and LXR revealed that some Maclntyre, A., Gilbert, L.I. A

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steroid/thyroid hormone receptor D.S. The Drosophila EcRgene encodes superfamily member in Drosophila an ecdysone receptor, a new member of melanogaster that shares extensive the steroid receptor superfamily. Cell sequence similarity with a mammalian 1991, 67, 59–77 homologue. Nucl. Acids Res. 1990, 18, Riddiford, L. M., Cherbas, P. and Truman, J. 4143–4148. W. Ecdysone receptors and their Koelle, M. R. et al., The Drosophila EcR biological actions. Vitam. Horm. 60, 1– gene encodes an ecdysone receptor, a 73 (2001) new member of the steroid receptor Thummel CS. 1996. on steroids— superfamily. Cell, 67, 59–77 (1991) Drosophila metamorphosis and the Koelle, M.R., Talbot, W.S., Segraves, W.A., mechanisms of steroid hormone action. Bender, M.T., Cherbas, P., Hogness, Trends Genet 12:306–10.

How to cite this article:

Gagan Rani, Neha Gupta, Neeru Singh Redhu and Sudhir Kumar. 2018. Ecdysone Receptor Present in Insects is a Novel Target for Insecticide. Int.J.Curr.Microbiol.App.Sci. 7(05): 1548- 1553. doi: https://doi.org/10.20546/ijcmas.2018.705.183

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