Journal
INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY
Volume 35, Issue 4, Pages 263-275Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.ibmb.2004.11.006
Keywords
phospholipase C; ERK; phosphorylation of [Ca2+]i oscillations; inositol trisphosphate; store-operated Ca2+ entry; prothoracicotropic hormone (PTTH).; voltage-gated Ca2+ channels
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Funding
- NIGMS NIH HHS [GM63198-01] Funding Source: Medline
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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 Manduea 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. (c) 2005 Elsevier Ltd. All rights reserved.
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