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Dedos SG, Wicher D, Kaltofen S, Birkenbeil H. Different Ca2+ signalling cascades manifested by mastoparan in the prothoracic glands of the tobacco hornworm, Manduca sexta, and the silkworm, Bombyx mori. ARCHIVES OF INSECT BIOCHEMISTRY AND PHYSIOLOGY 2007; 65:52-64. [PMID: 17523173 DOI: 10.1002/arch.20180] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Application of the tetradecapeptide mastoparan to the prothoracic glands (PGs) of the tobacco hornworm, Manduca sexta, and the silkworm, Bombyx mori, resulted in increases in intracellular Ca(2+) ([Ca(2+)](i)). In M. sexta, Gi proteins are involved in the mastoparan-stimulated increase in [Ca(2+)](i). However, there is no involvement of Gi proteins in the mastoparan-stimulated increase in [Ca(2+)](i) in prothoracic gland cells from B. mori. Unlike in M. sexta prothoracic glands, in B. mori prothoracic glands mastoparan increases [Ca(2+)](i) even in the absence of extracellular Ca(2+). Pharmacological manipulation of the Ca(2+) signalling cascades in the prothoracic glands of both insect species suggests that in M. sexta prothoracic glands, mastoparan's first site of action is influx of Ca(2+) through plasma membrane Ca(2+) channels while in B. mori prothoracic glands, mastoparan's first site of action is mobilization of Ca(2+) from intracellular stores. In M. sexta, the combined results indicate the presence of mastoparan-sensitive plasma membrane Ca(2+) channels, distinct from those activated by prothoracicotropic hormone or the IP(3) signalling cascade, that coordinate spatial increases in [Ca(2+)](i) in prothoracic gland cells. We propose that in B. mori, mastoparan stimulates Ca(2+) mobilization from ryanodine-sensitive intracellular Ca(2+) stores in prothoracic gland cells.
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Affiliation(s)
- Skarlatos G Dedos
- Saxon Academy of Sciences at Leipzig, Department of Neurohormones, Jena, Germany.
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Fellner SK, Rybczynski R, Gilbert LI. Ca2+ signaling in prothoracicotropic hormone-stimulated prothoracic gland cells of Manduca sexta: evidence for mobilization and entry mechanisms. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2005; 35:263-275. [PMID: 15763463 DOI: 10.1016/j.ibmb.2004.11.006] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2004] [Revised: 11/15/2004] [Accepted: 11/16/2004] [Indexed: 05/24/2023]
Abstract
Prothoracicotropic hormone (PTTH) stimulates ecdysteroidogenesis in lepidopteran prothoracic glands (PGs), thus indirectly controlling molting and metamorphosis. PTTH triggers a signal transduction cascade in PGs that involves an early influx of Ca2+. Although the importance of Ca2+ has been long known, the mechanism(s) of PTTH-stimulated changes in cytoplasmic Ca2+ [Ca2+]i are not yet well understood. PGs from the fifth instar of Manduca sexta were exposed to PTTH in vitro. The resultant changes in [Ca2+]i were measured using ratiometric analysis of a fura-2 fluorescence signal in the presence and absence of inhibitors of specific cellular signaling mechanisms. The phospholipase C (PLC) inhibitor U-73122 nearly abolished the PTTH-stimulated increase in [Ca2+]i, as well as PTTH-stimulated ecdysteroidogenesis and extracellular-signal regulated kinase phosphorylation, thus establishing a role for PLC and implicating inositol trisphosphate (IP3) in PTTH signal transduction. Two antagonists of the IP3 receptor, 2-APB and TMB-8, likewise blocked the [Ca2+]i response by a mean of 92%. We describe for the first time the presence of Ca2+ oscillations in PTTH-stimulated cells in Ca2+-free medium. External Ca2+ entered PG cells via at least two routes: store-operated (capacitative) Ca2+ entry channels and L-type voltage-gated Ca2+ channels. We propose that PTTH initiates a transductory cascade typical of many G-protein coupled receptors, involving both Ca2+ mobilization and entry pathways.
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Affiliation(s)
- Susan K Fellner
- Department of Cell and Molecular Physiology (CB# 7545), University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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Dedos SG, Wicher D, Fugo H, Birkenbeil H. Regulation of capacitative Ca2+ entry by prothoracicotropic hormone in the prothoracic glands of the silkworm, Bombyx mori. ACTA ACUST UNITED AC 2005; 303:101-12. [PMID: 15662666 DOI: 10.1002/jez.a.133] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Measurements of Ca2+ influx in Fura-2/AM loaded steroidogenic cells (prothoracic glands; PGs) of the silkworm, Bombyx mori showed that application of the neuropeptide prothoracicotropic hormone (PTTH) can increase the intracellular [Ca2+]i. This PTTH-mediated Ca2+ influx in PG cells had kinetic patterns and pharmacological characteristics similar to those induced by thapsigargin. Namely, it produced increases in intracellular Ca2+ levels only in the presence of extracellular Ca2+, it was blocked by Gd3+ and 2-Aminoethoxydiphenylborate (2-APB), and it was unaffected by several toxins or compounds that block voltage-activated Ca2+ channels. Moreover, the PTTH-stimulated increase of Ca2+ levels was eliminated in the presence of heparin (an IP3 receptor blocker), and by TMB-8 which also blocked any PTTH-dependent increase of ecdysteroid secretion. The PTTH-mediated increase of Ca2+ levels was not affected by the non-hydrolysable GDP analogue, GDPbetaS, an indication that a G protein is not downstream of the PTTH receptor. These results argue strongly in favor of gating by the PTTH receptor of capacitative Ca2+ entry (CCE) channels (or store-operated Ca2+ channels (SOCs)) by a mechanism that does not involve any G proteins but requires the presence of functional IP3 receptors. Because the ability of PTTH to stimulate the [Ca2+]i levels of PG cells was completely mimicked by thapsigargin and exhibited a pharmacological profile similar to CCE mechanisms, we believe that PTTH directly regulates a CCE pathway in PG cells thereby activating a plethora of downstream regulators responsible for ecdysteroid secretion by the PGs of Bombyx mori.
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Affiliation(s)
- Skarlatos G Dedos
- Saxon Academy of Sciences at Leipzig, Dept. Neurohormones, PF 100322, 07703 Jena, Germany.
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Priester J, Smith WA. Inhibition of tyrosine phosphorylation blocks hormone-stimulated calcium influx in an insect steroidogenic gland. Mol Cell Endocrinol 2005; 229:185-92. [PMID: 15607542 DOI: 10.1016/j.mce.2004.07.002] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/13/2004] [Revised: 06/30/2004] [Accepted: 07/06/2004] [Indexed: 01/29/2023]
Abstract
In the tobacco hornworm Manduca sexta (M. sexta) as in other insects, ecdysone synthesis occurs in the prothoracic glands and is stimulated by the brain neuropeptide prothoracicotropic hormone (PTTH). PTTH activates the prothoracic glands through the second messenger cAMP, the synthesis of which is stimulated by calcium. We previously found that the Src kinase inhibitor 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-D]-pyrimidine (PP1) inhibits PTTH-stimulated cAMP synthesis and ecdysone secretion. In the present study, we show that by contrast, PP1 does not block cAMP synthesis stimulated by the calcium ionophore A23187, and that PP1 augments A23187-stimulated ecdysone secretion. Hence, once glandular levels of calcium are elevated, Src family kinase activity is no longer needed for, and may actually inhibit, steroidogenesis. PP1 blocks calcium influx in PTTH-stimulated prothoracic glands, indicating that tyrosine phosphorylation by a member of the Src kinase family is required for calcium influx. These results suggest that prothoracic gland calcium channels are regulated either directly or indirectly by tyrosine phosphorylation.
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Affiliation(s)
- Jennifer Priester
- Department of Biology, 433 Richards Hall, Northeastern University, 360 Huntington Ave, Boston, MA 02115, USA
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Smith W, Priester J, Morais J. PTTH-stimulated ecdysone secretion is dependent upon tyrosine phosphorylation in the prothoracic glands of Manduca sexta. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2003; 33:1317-1325. [PMID: 14599503 DOI: 10.1016/j.ibmb.2003.06.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
PTTH stimulates ecdysteroid secretion by the insect prothoracic glands. The peptide activates cAMP synthesis in a calcium-dependent manner, ultimately enhancing ecdysteroid synthesis. We have found that PTTH stimulates a rapid increase in tyrosine phosphorylation of at least four proteins in the prothoracic glands of larval Manduca sexta, as seen on Western blots of glandular lysates probed with antibody directed against phosphotyrosine. PTTH-stimulated tyrosine phosphorylation is blocked by an inhibitor of Src family tyrosine kinases, 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]-pyrimidine (PP1). The inhibitor also blocks PTTH-stimulated ecdysone secretion, as well as PTTH-stimulated cAMP synthesis. Direct activation of the catalytic subunit of adenylyl cyclase by forskolin is not affected by PP1. In addition, ecdysteroid secretion stimulated by the cAMP analog dbcAMP is not blocked by PP1. These findings point to an important role for a Src-family tyrosine kinase at a very early step in the PTTH signaling pathway, prior to the activation of adenylyl cyclase.
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Affiliation(s)
- Wendy Smith
- Department of Biology, Northeastern University, 433 Richards Hall, 360 Huntington Avenue, Boston, MA 02115, USA.
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Dedos SG, Birkenbeil H. Inhibition of cAMP signalling cascade-mediated Ca2+ influx by a prothoracicostatic peptide (Mas-MIP I) via dihydropyridine-sensitive Ca2+ channels in the prothoracic glands of the silkworm, Bombyx mori. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2003; 33:219-228. [PMID: 12535680 DOI: 10.1016/s0965-1748(02)00206-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Measurements of Ca(2+) influx in Fura-2/AM loaded prothoracic glands (PGs) of the silkworm, Bombyx mori, after application of forskolin or the cAMP analogue, 8-bromo-cAMP, showed a steady increase in [Ca(2+)](i), which was of extracellular origin and was inhibited, in both cases, by the dihydropyridine (DHP) derivative, nitrendipine. Nitrendipine also inhibited the abrupt S(-).Bay K 8644-mediated increase in [Ca(2+)](i) and its effects were mimicked by a myoinhibitory/prothoracicostatic peptide (Mas-MIP I/PTSP), which was isolated from Manduca sexta and was found to possess ecdysteroidostatic activity in Bombyx mori PGs. This peptide blocked both the forskolin and S(-).Bay K 8644-mediated increase in [Ca(2+)](i) of PG cells. It was ineffective, however, in blocking the recombinant prothoracicotropic hormone (rPTTH)-stimulated high increase in [Ca(2+)](i) of PG cells suggesting that distinct and independently regulated Ca(2+) influx mechanisms operate in the PG cells of Bombyx mori. The dependence of DHP-sensitive Ca(2+) channels on the cAMP-signalling cascade was further corroborated by the inabilitity of nitrendipine to block the thapsigargin-stimulated high increase in [Ca(2+)](i) after depletion of Ca(2+) from the intracellular stores. This, together with the inability of thapsigargin to stimulate the cAMP levels of PG cells suggest that there is a tightly regulated cross-talk mechanism between the two signalling cascades of Ca(2+) and cAMP. The combined results suggest a cAMP-mediated regulation of the opening-state of DHP-sensitive Ca(2+) channels and stimulation of [Ca(2+)](i) increases and ecdysteroid secretion by a positive feedback mechanism. Mas-MIP I/PTSP interferes with this mechanism by blocking DHP-sensitive Ca(2+) channels. This regulatory mechanism appears to be autonomously stimulating ecdysteroidogenesis by the PGs, it is regulated by Mas-MIP I/PTSPS, and it is not involved in other Ca(2+) influx mechanisms that operate within the PG cells of Bombyx mori.
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Affiliation(s)
- S G Dedos
- Saxon Academy of Sciences at Leipzig, AG Prof. Dr. H. Penzlin, Erbertstr. 1, PF 100322, 07703 Jena, Germany.
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Birkenbeil H, Dedos SG. Ca(2+) as second messenger in PTTH-stimulated prothoracic glands of the silkworm, Bombyx mori. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2002; 32:1625-1634. [PMID: 12429114 DOI: 10.1016/s0965-1748(02)00101-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Measurements of Ca(2+) influx and [Ca(2+)](i) changes in Fura-2/AM-loaded prothoracic glands (PGs) of the silkworm, Bombyx mori, were used to identify Ca(2+) as the actual second messenger of the prothoracicotropic hormone (PTTH) of this insect. Dose-dependent increases of [Ca(2+)](i) in PG cells were recorded in the presence of recombinant PTTH (rPTTH) within 5 minutes. The rPTTH-mediated increases of [Ca(2+)](i) levels were dependent on extracellular Ca(2+). They were not blocked by the dihydropyridine derivative, nitrendipine, an antagonist of high-voltage-activated (HVA) Ca(2+) channels, and by bepridil, an antagonist of low-voltage-activated (LVA) Ca(2+) channels. The trivalent cation La(3+), a non-specific blocker of plasma membrane Ca(2+) channels, eliminated the rPTTH-stimulated increase of [Ca(2+)](i) levels in PG cells and so did amiloride, an inhibitor of T-type Ca(2+) channels. Incubation of PG cells with thapsigargin resulted in an increase of [Ca(2+)](i) levels, which was also dependent on extracellular Ca(2+) and was quenched by amiloride, suggesting the existence of store-operated plasma membrane Ca(2+) channels, which can also be inhibited by amiloride. Thapsigargin and rPTTH did not operate independently in stimulating increases of [Ca(2+)](i) levels and one agent's mediated increase of [Ca(2+)](i) was eliminated in the presence of the other. TMB-8, an inhibitor of intracellular Ca(2+) release from inositol 1,4,5 trisphosphate (IP(3))-sensitive Ca(2+) stores, blocked the rPTTH-stimulated increases of [Ca(2+)](i) levels, suggesting an involvement of IP(3) in the initiation of the rPTTH signaling cascade, whereas ryanodine did not influence the rPTTH-stimulated increases of [Ca(2+)](i) levels. The combined results indicate the presence of a cross-talk mechanism between the [Ca(2+)](i) levels, filling state of IP(3)-sensitive intracellular Ca(2+) stores and the PTTH-receptor's-mediated Ca(2+) influx.
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Affiliation(s)
- Heiner Birkenbeil
- Sächsische Akademie der Wissenschaften zu Leipzig AG Neurohormonale Wirkungsmechanismen, Erbert-Str. 1, PF 100322, 07703, Jena, Germany.
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Gilbert LI, Rybczynski R, Warren JT. Control and biochemical nature of the ecdysteroidogenic pathway. ANNUAL REVIEW OF ENTOMOLOGY 2002; 47:883-916. [PMID: 11729094 DOI: 10.1146/annurev.ento.47.091201.145302] [Citation(s) in RCA: 336] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Molting is elicited by a critical titer of ecdysteroids that includes the principal molting hormone, 20-hydroxyecdysone (20E), and ecdysone (E), which is the precursor of 20E but also has morphogenetic roles of its own. The prothoracic glands are the predominate source of ecdysteroids, and the rate of synthesis of these polyhydroxylated sterols is critical for molting and metamorphosis. This review concerns three aspects of ecdysteroidogenesis: (a) how the brain neuropeptide prothoracicotropic hormone (PTTH) initiates a transductory cascade in cells of the prothoracic gland, which results in an increased rate of ecdysteroid biosynthesis (upregulation); (b) how the concentrations of 20E in the hemolymph feed back on the prothoracic gland to decrease rates of ecdysteroidogenesis (downregulation); and (c) how the prothoracic gland cells convert cholesterol to the precursor of E and then 20E, a series of reactions only now being understood because of the use of a combination of classical biochemistry and molecular genetics.
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Affiliation(s)
- Lawrence I Gilbert
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3280, USA.
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Spaziani E, Jegla TC, Wang WL, Booth JA, Connolly SM, Conrad CC, Dewall MJ, Sarno CM, Stone DK, Montgomery R. Further Studies on Signaling Pathways for Ecdysteroidogenesis in Crustacean Y-Organs1. ACTA ACUST UNITED AC 2001. [DOI: 10.1668/0003-1569(2001)041[0418:fsospf]2.0.co;2] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Spaziani E, Jegla TC, Wang WL, Booth JA, Connolly SM, Conrad CC, Dewall MJ, Sarno CM, Stone DK, Montgomery R. Further Studies on Signaling Pathways for Ecdysteroidogenesis in Crustacean Y-Organs. ACTA ACUST UNITED AC 2001. [DOI: 10.1093/icb/41.3.418] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Chen CH, Gu SH, Chow YS. Adenylate cyclase in prothoracic glands during the last larval instar of the silkworm, Bombyx mori. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2001; 31:659-664. [PMID: 11267904 DOI: 10.1016/s0965-1748(00)00171-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
We have previously reported that the absence of prothoracicotropic hormone (PTTH) signal transduction during the early last larval instar of Bombyx mori plays a role in leading to very low ecdysteroid levels in the hemolymph, inactivation of the corpora allata, as well as larval-pupal transformation. In the present study, adenylate cyclase was characterized in crude preparations of prothoracic gland cell membranes in an effort to localize the cause of refractoriness to PTTH. It was found that cyclase activity of the prothoracic glands from the day 6 last instar showed activation responses to fluoride, a guanine nucleotide analogue, as well as calmodulin (CaM) in dose-dependent fashions. The additive effects of day 5 prothoracic gland adenylate cyclase stimulation by fluoride and CaM imply that there may exist Gs protein-dependent and CaM-dependent forms of adenylate cyclase. For day 1 last instar prothoracic glands, which showed no response to stimulation by PTTH in either cAMP generation or ecdysteroidogenesis, adenylate cyclase activity exhibited far less responsiveness to Ca(2+)/CaM than did that from day 5 glands. These findings suggest that day 1 prothoracic glands may possess some lesions in the receptor-Ca(2+) influx-adenylate cyclase signal transduction pathway and these impairments in PTTH signal transduction may be, at least in part, responsible for decreased ecdysteroidogenesis.
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Affiliation(s)
- C H Chen
- Chung Hwa College of Medical Technology, 89 Wen-Hwa 1st Road, Jen-Te Hsiang, Tainan County 717, Taiwan, ROC
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