Induction of Enzymes Involved in Molting Hormone (Ecdysteroid) Inactivation by Ecdysteroids and an Agonist, 1,2-Dibenzoyl-1-tert-butylhydrazine (RH-5849)*
- From the Department of Biochemistry, University of Liverpool, Life Sciences Building, Crown Street, Liverpool L69 7ZB, United Kingdom
- ‡ To whom correspondence should be addressed: Tel.: 44-151-794-4352; Fax: 44-151-794-4349; E-mail: reeshh{at}liv.ac.uk
Abstract
Molting in insects is regulated by molting hormones (ecdysteroids). The major active hormone, 20-hydroxyecdysone, is formed by ecdysone 20-monooxygenase-catalyzed hydroxylation of ecdysone. During times of decreasing hormone titers, inactivation occurs by several routes including (i) 26-hydroxylation and further oxidation to the 26-oic acid, (ii) formation of various conjugates (e.g. phosphates), and (iii) in Lepidoptera in particular, ecdysone oxidase-catalyzed formation of 3-dehydroecdysteroid, which is reduced to 3-epiecdysteroid, followed by phosphotransferase-catalyzed formation of phosphate conjugates. Administration of the nonsteroidal ecdysteroid agonist RH-5849 (1,2-dibenzoyl-1-tert-butylhydrazine), but not 20-hydroxyecdysone, to tobacco hornworm (Manduca sexta) resulted in induction of midgut cytosolic ecdysone oxidase and ecdysteroid phosphotransferase activities. In addition, both 20-hydroxyecdysone and RH-5849 caused induction of ecdysteroid 26-hydroxylase activity in midgut mitochondria and microsomes, whereas 20-hydroxylase was induced to a lesser extent by 20-hydroxyecdysone in mitochondria and by either RH-5849 or 20-hydroxyecdysone in microsomes. Commensurate with induction of the enzymes by ecdysteroid and RH-5849 is a requirement for RNA and protein synthesis, without precluding indirect mechanisms. These results indicate that molting hormone stimulates at least one universal route of its own inactivation by inducing ecdysteroid 26-hydroxylase activity and are discussed in relation to an analogous phenomenon observed for vitamin D inactivation in vertebrates.
Footnotes
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↵* This work was supported by Rohm and Haas Co. and The University of Liverpool. The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵1 The abbreviations used are:
- RH-5849
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1,2-dibenzoyl-1-tert-butylhydrazine
- HPLC
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high-performance liquid chromatography
- MES
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4-morpholineethanesulfonic acid
- Rt
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retention time.
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↵2D. R. Williams, J.-H. Chen, M. J. Fisher, and H. H. Rees, unpublished results.
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↵3I. Davies and H. H. Rees, unpublished results.
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- Received July 23, 1996.
- Revision received December 2, 1996.
- © 1997 by The American Society for Biochemistry and Molecular Biology, Inc.
