Ecdysone 20-mono-oxygenase in the desert locust, Schistocerca gregaria

RNAi-mediated knockdown of Shade negatively affects ecdysone-20-hydroxylation in the desert locust, Schistocerca gregaria

A major breakthrough in elucidating the ecdysteroid biosynthetic pathway in insects was realized with the molecular identification and further functional characterization of the 'Halloween' genes. These genes were found to encode cytochrome P450 enzymes catalysing the final steps of ecdysteroid biosynthesis in the dipteran, Drosophila melanogaster, and in the Lepidoptera, Manduca sexta and Bombyx mori. A recent report focused on the identification of Halloween orthologs in the desert locust, Schistocerca gregaria, a member of the hemimetabolous insect order of the Orthoptera. In the present study, an additional Halloween gene Shade, is identified in the desert locust. In Diptera and Lepidoptera, this gene encodes a 20-hydroxylase, catalysing the conversion of ecdysone (E) to 20-hydroxyecdysone (20E). However, this enzymatic function has previously been suggested for CYP6H1 in another locust species, the migratory locust, Locusta migratoria. Using q-RT-PCR, the spatial and temporal transcript profiles of S. gregaria orthologs for Shade as well as CYP6H1 were analysed in last larval stage desert locusts. An RNA interference (RNAi)-based approach was employed to study whether these genes could possibly encode a functional 20-hydroxylase in the desert locust.

Effects of plant flavonoids on Manduca sexta (tobacco hornworm) fifth larval instar midgut and fat body mitochondrial transhydrogenase

The reversible, membrane-associated transhydrogenase that catalyzes hydride-ion transfer between NADP(H) and NAD(H) was evaluated and compared to the corresponding NADH oxidase and succinate dehydrogenase activities in midgut and fat body mitochondria from fifth larval instar Manduca sexta. The developmentally significant NADPH-forming transhydrogenation occurs as a nonenergy- or energy-linked activity with energy for the latter derived from either electron transport-dependent NADH or succinate utilization, or ATP hydrolysis by Mg++-dependent ATPase. In general, the plant flavonoids examined (chyrsin, juglone, morine, quercetin, and myricetin) affected all reactions in a dose-dependent fashion. Differences in the responses to the flavonoids were apparent, with the most notable being inhibition of midgut, but stimulation of fat body transhydrogenase by morin, and myricetin as also noted for NADH oxidase and succinate dehydrogenase. Although quercetin inhibited or stimulated transhydrogenase activity depending on the origin of mitochondria, it was without effect on either midgut or fat body NADH oxidase or succinate dehydrogenase. Observed sonication-dependent increases in flavonoid inhibition may well reflect an alteration in membrane configuration, resulting in increased exposure of the enzyme systems to the flavonoids. The effects of flavonoids on the transhydrogenation, NADH oxidase, and succinate dehydrogenase reactions suggest that compounds of this nature may prove valuable in the control of insect populations by affecting these mitochondrial enzyme components.

Identification and expression profile of Halloween genes involved in ecdysteroid biosynthesis in Spodoptera littoralis

20-Hydroxyecdyone (20E), an active form of ecdysteroid, is the key hormone in insect growth and development. The biosynthesis of ecdysteroid is triggered and under the control of the neuropeptide, prothoracicotropic hormone (PTTH). To date, five cytochrome P450 enzymes, namely Spook (Spo), Phantom (Phm), Disembodied (Dib), Shadow (Sad) and Shade (Shd) related to ecdysteroid biosynthesis, are identified and the character of last four enzymes is well studied in Drosophila melanogaster, Bombyx mori and Manduca sexta. These genes are called Halloween genes and mediate the biosynthesis of 20E from cholesterol. In this study, we extended these works to a major pest insect in agriculture, the cotton leafworm Spodoptera littoralis (Lepidoptera: Noctuidae). We identified the sequence of five Halloween genes, and the converted amino acid sequences were compared with those of other insects. The phylogenetic analysis clearly showed separated clusters of each gene and the evolutional conservation in insects with a high similarity in Lepidoptera. Spo, phm, dib and sad were predominantly expressed in prothoracic glands, and shd was expressed in fat body and Malpighian tubules at the last instar larvae. Spo expression was kept high level between day 2 and day 4 after ecdysis. The expression of phm and dib peaked at day 2, and sad and shd expressions peaked at day 2 and day 4 after ecdysis. In addition, the hemolymph ecdysteroid titer showed a small peak at day 2 and a large peak at day 4 after ecdysis. These results suggest the importance of Halloween genes in ecdysone biosynthesis by prothoracic glands and conversion of ecdysone into 20E by fat body in larval-pupal metamorphosis.

Midgut mitochondrial transhydrogenase in wandering stage larvae of the tobacco hornworm, Manduca sexta

Midgut mitochondria from fifth larval instar Manduca sexta exhibited a transhydrogenase that catalyzes the following reversible reaction: NADPH + NAD(+) <--> NADP(+) + NADH. The NADPH-forming transhydrogenation occurred as a nonenergy- and energy-linked activity. Energy for the latter was derived from the electron transport-dependent utilization of NADH or succinate, or from Mg++-dependent ATP hydrolysis by ATPase. The NADH-forming and all of the NADPH-forming reactions appeared optimal at pH 7.5, were stable to prolonged dialysis, and displayed thermal lability. N,N'-dicyclohexylcarbodiimide (DCCD) inhibited the NADPH --> NAD(+) and energy-linked NADH --> NADP(+) transhydrogenations, but not the nonenergy-linked NADH --> NADP(+) reaction. Oligomycin only inhibited the ATP-dependent energy-linked activity. The NADH-forming, nonenergy-linked NADPH-forming, and the energy-linked NADPH-forming activities were membrane-associated in M. sexta mitochondria. This is the first demonstration of the reversibility of the M. sexta mitochondrial transhydrogenase and, more importantly, the occurrence of nonenergy-linked and energy-linked NADH --> NADP(+) transhydrogenations. The potential relationship of the transhydrogenase to the mitochondrial, NADPH-utilizing ecdysone-20 monooxygenase of M. sexta is considered.

Role of ecdysone 20-monooxygenase in regulation of 20-hydroxyecdysone levels by juvenile hormone and biogenic amines in Drosophila

The effects of increased levels of dopamine (feeding flies with dopamine precursor, L: -dihydroxyphenylalanine) and octopamine (feeding flies with octopamine) on ecdysone 20-monooxygenase activity in young (2 days old) wild type females (the strain wt) of Drosophila virilis have been studied. L: -dihydroxyphenylalanine and octopamine feeding increases ecdysone 20-monooxygenase activity by a factor of 1.6 and 1.7, respectively. Ecdysone 20-monooxygenase activity in the young (1 day old) octopamineless females of the strain Tbetah ( nM18 ), in females of the strain P845 (precursor of Tbetah ( nM18 ) strain) and in wild type females (Canton S) of Drosophila melanogaster have been measured. The absence of octopamine leads to a considerable decrease in the enzyme activity. We have also studied the effects of juvenile hormone application on ecdysone 20-monooxygenase activity in 2-day-old wt females of D. virilis and demonstrated that an increase in juvenile hormone titre leads to an increase in the enzyme activity. We discuss the supposition that ecdysone 20-monooxygenase occupies a key position in the regulation of 20-hydroxyecdysone titre under the conditions that lead to changes in juvenile hormone titre and biogenic amine levels.

Developmental expression of Manduca shade, the P450 mediating the final step in molting hormone synthesis

The ecdysone 20-monooxygenase (E20MO; 20-hydroxylase) is the enzyme that mediates the conversion of ecdysone (E) to the active insect molting hormone, 20-hydroxyecdysone (20E), which coordinates developmental progression. We report the identification and developmental expression of the Halloween gene shade (shd; CYP314A1) that encodes the E20MO in the tobacco hornworm, Manduca sexta. Manduca Shd (MsShd) mediates the conversion of E to 20E when expressed in Drosophila S2 cells. In accord with the central dogma, the data show that Msshd is expressed mainly in the midgut, Malpighian tubules, fat body and epidermis with very low expression in the prothoracic gland and nervous system. Developmental variations in E20MO enzymatic activity are almost perfectly correlated with comparable changes in the gene expression of Msshd in the fat body and midgut during the fifth instar and the beginning of pupal-adult development. The results indicate three successive and overlapping peaks of expression in the fat body, midgut and Malpighian tubules, respectively, during the fifth larval instar. The data suggest that precise tissue-specific transcriptional regulation controls the levels, and thereby the activity, of the Manduca E20MO.

Effects of anti-ecdysteroid quaternary derivatives of azole analogues of metyrapone on the post-embryonic development of the red cotton bug (Dysdercus cingulatus F)

In order to improve the larvicidal activity of the azole analogues of metyrapone, previously found to have a strong inhibitory activity on ecdysone 20-monooxygenase (E-20-M) from the fleshfly Neobellieria bullata Parker, soft-alkylated compounds (3-(1,1-dimethyl-2-oxo-2-phenylethyl)-1-dodecanoyloxymethyl-1H-imidazolium chloride, sPIM) and (1-(1,1-dimethyl-2-oxo-2-phenylethyl)-4-dodecanoyloxymethyl-1H-1,2,4-triazolium chloride, sPTM), derivatives of phenyl-imidazolyl-metyrapone (PIM) and phenyl-1,2,4-triazolyl-metyrapone (PTM), respectively, were synthesized. Both sPIM and sPTM, designed as propesticides, inhibited E-20-M in vitro at 10(-4) M concentration, which was unexpected since they had been expected to be inactive in vitro and to gain activity only within the organism. sPTM significantly delayed the pupariation of N. bullata larvae and this effect could be reversed by the simultaneous application of 20-hydroxyecdysone (20E), supporting the hypothesis that sPTM can act by interfering with the moulting hormone system. Due to this in vitro activity, sPTM and sPIM cannot be considered to be simple drug precursors, and their structure should contain structural elements (pharmacophores) responsible for the observed biological effects. In order to examine this hypothesis, derivatives of sPTM and sPIM were synthesised in which the hydrolytically labile N(+)-CH2O(CO)- moiety was changed to the more stable N(+)-CH2CH2(CO)-group. In three new stable derivatives, a dodecylamino or a phenyl group, respectively, is attached to the carbonyl group to obtain PTM and PIM derivatives quaternised with a 2-dodecylcarbamoylethyl or a 3-oxo-3-phenylpropyl group. In one derivative, the 2-oxo-2-phenylethyl quaternising group has one fewer carbon atom. In addition to their moderate activity (LC50 = 10(-6)-10(-5) M) against the red cotton bug Dysdercus cingulatus F, they delayed development and caused developmental abnormalities, including mortality in the pharate phase, mortality during moulting and wing deformations. These symptoms and the delay in development are characteristic of known compounds inhibiting the synthesis of 20E or interfering in the moulting processes. The facts that the frequent appearance of insects with developmental abnormalities and the delay in development could be reversed by co-application of 20E indicate that the moulting system might be the site of action. We presume that the quaternary azole derivatives of PIM and PTM can themselves also interact with the moulting system.

Characterization of ecdysteroid 26-hydroxylase: an enzyme involved in molting hormone inactivation

Insect molting hormone (ecdysteroid) inactivation occurs by several routes, including 26-hydroxylation and further oxidation to the 26-oic acids. Thus, the ecdysteroid 26-hydroxylase is a critical enzyme involved in precise regulation of ecdysteroid titers during insect development. Administration of the ecdysteroid agonist, RH-5849 (1,2-dibenzoyl, 1-tert-butyl hydrazone), or 20-hydroxyecdysone to the tobacco hornworm, Manduca sexta, results in induction of ecdysteroid 26-hydroxylase activity in midgut mitochondria and microsomes. The biochemical and kinetic properties of the ecdysteroid 26-hydroxylase were investigated. The mitochondrial enzyme was found to have optimal activity at a pH of 7. 5 in a Hepes or sodium phosphate buffer at 30-37 degrees C. The apparent K(m) of the microsomal 26-hydroxylase for 20-hydroxyecdysone substrate was lower than that of the mitochondrial enzyme for either 20-hydroxyecdysone or ecdysone substrate. The V(max) of the 26-hydroxylase in both subcellular fractions was slightly higher using 20-hydroxyecdysone as substrate compared to ecdysone. Demonstration that activity of the mitochondrial 26-hydroxylase was inhibited by incubation in a CO (or N(2)) atmosphere, taken together with the requirement for reducing cofactor and the efficacy of the P450 inhibitors, ketoconazole and fenarimol, provided strong evidence that the hydroxylase is cytochrome P450-dependent. Indirect evidence suggested that the mitochondrial and microsomal ecdysteroid 26-hydroxylase(s) could exist in a less active dephosphorylated state or more active phosphorylated state. Using Escherichia coli alkaline phosphatase to remove covalently bound phosphate groups, the activity of the 26-hydroxylase was decreased and, conversely, activity was enhanced using a cAMP-dependent protein kinase with appropriate cofactors. In addition, the protein kinase was shown to reactivate the 26-hydroxylase activity in alkaline phosphatase-treated fractions.

Effects of the adenylate cyclase activator forskolin and its inactive derivative 1,9-dideoxyforskolin on insect cytochrome P-450 dependent steroid hydroxylase activity

The adenylate cyclase activator forskolin and its pharmacologically inactive derivative 1,9-dideoxyforskolin were found to inhibit in a dose-dependent fashion the ecdysone 20-monooxygenase activity associated with wandering stage larvae of Drosophila melanogaster and fat body and midgut from last instar larvae of the tobacco hornworm, Manduca sexta. The concentrations of these labdane diterpenes required to elicit a 50% inhibition of the cytochrome P-450 dependent steroid hydroxylase activity in the insect tissues ranged from approximately 5 x 10(-6) to 5 x 10(-4) M.

Regulation of cytochrome P-450 dependent steroid hydroxylase activity in Manduca sexta: effects of the ecdysone agonist RH 5849 on ecdysone 20-monooxygenase activity

The non-steroidal ecdysone agonist RH 5849 (1,2-dibenzoyl-1-tert-butylhydrazine) was found to inhibit in a dose-response and apparently competitive fashion the cytochrome P-450 dependent ecdysone 20-monooxygenase activity in the midgut of wandering stage last instar larvae of the tobacco hornworn, Manduca sexta. More effectively on a per molar basis than the naturally occurring molting hormones ecdysone and 20-hydroxyecdysone, RH 5849 was also found to elicit the dramatic 50-fold increase in midgut steroid hydroxylase activity (which normally occurs with the onset of the wandering stage) when injected into competent head or thoracic ligated pre-wandering last instar larvae. These data support and extend the potential usefulness of RH 5849 as a pharmacological probe for further investigating the actions of ecdysteroids and their role(s) in the regulation of ecdysteroid monooxygenases.

Regulation of cytochrome P-450 dependent steroid hydroxylase activity in Manduca sexta: evidence for the involvement of a neuroendocrine-endocrine axis during larval-pupal development

Ecdysone 20-monooxygenase activity and the factors which may regulate this steroid hydroxylase were examined in the midgut of the tobacco hornworm, Manduca sexta, during the last larval stadium. Radioassay experiments revealed that midgut ecdysone 20-monooxygenase undergoes a single 50-fold increase in activity temporally coincident with the onset of the wandering stage. The increase in midgut monooxygenase activity was prevented by actinomycin D and cycloheximide, and could be elicited in head (but not thoracic) ligated animals by a brain-retrocerebral complex factor(s) released at the same time as prothoracicotropic hormone. In contrast, ecdysone or 20-hydroxyecdysone could elicit the increase in enzyme activity in both head and thoracic ligated animals. These data suggest the operation of a neuroendocrine-endocrine axis in the regulation of midgut ecdysone 20-monooxygenase activity.

Characterization of three hydroxylases involved in the final steps of biosynthesis of the steroid hormone ecdysone in Locusta migratoria (Insecta, Orthoptera)

It is most generally accepted that the last three enzymatic reactions in the biosynthetic pathway of ecdysone are, in this order, the hydroxylations at positions C-25, C-22 and C-2. Using high specific activity tritiated ecdysone precursors (2,22,25-trideoxyecdysone, 2,22-dideoxyecdysone and 2-deoxyecdysone) we have characterized the hydroxylases involved in these reactions, in the major biosynthetic tissue of ecdysone, i.e. the prothoracic glands. We show that C-2 hydroxylase is a mitochondrial oxygenase which differs from conventional cytochrome P-450-dependent monooxygenases by its relative insensitivity to CO. In contrast, C-22 and C-25 hydroxylases appear as classical cytochrome P-450 monooxygenases; C-22 hydroxylase is a mitochondrial enzyme whereas our data point to a microsomal localization of the C-25 hydroxylase.