title: Stimulation of orphan nuclear receptor HR38 gene expression by PTTH in prothoracic glands of the silkworm, Bombyx mori.
abstract: A complex signaling network appears to be involved in prothoracicotropic hormone (PTTH)-stimulated ecdysteroidogenesis in insect prothoracic glands (PGs). Less is known about the genomic action of PTTH signaling. In the present study, we investigated the effect of PTTH on the expression of Bombyx mori HR38, an immediate early gene (IEG) identified in insect systems. Our results showed that treatment of B. mori PGs with PTTH in vitro resulted in a rapid increase in HR38 expression. Injection of PTTH into day-5 last instar larvae also greatly increased HR38 expression, verifying the in vitro effect. Cycloheximide did not affect induction of HR38 expression, suggesting that protein synthesis is not required for PTTH's effect. A mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitor (U0126), and a phosphoinositide 3-kinase (PI3K) inhibitor (LY294002), partially inhibited PTTH-stimulated HR38 expression, implying the involvement of both the ERK and PI3K signaling pathways. When PGs were treated with agents that directly elevate the intracellular Ca(2+) concentration (either A23187 or thapsigargin), an increase in HR38 expression was also detected, indicating that Ca(2+) is involved in PTTH-stimulated HR38 gene expression. A Western blot analysis showed that PTTH treatment increased the HR38 protein level, and protein levels showed a dramatic increase during the later stages of the last larval instar. Expression of HR38 transcription in response to PTTH appeared to undergo development-specific changes. Treatment with ecdysone in vitro did not affect HR38 expression. However, 20-hydroxyecdysone treatment decreased HR38 expression. Taken together, these results demonstrate that HR38 is a PTTH-stimulated IEG that is, at least in part, induced through Ca(2+)/ERK and PI3K signaling. The present study proposes a potential cross talk mechanism between PTTH and ecdysone signaling to regulate insect development and lays a foundation for a better understanding of the mechanisms of PTTH's actions.
authors.affiliation: Department of Biology, National Museum of Natural Science, 1 Kuan-Chien Road, Taichung 404, Taiwan, ROC. Electronic address: gu330@mail.nmns.edu.tw.
authors.forename: Shi-Hong
authors.initials: SH
authors.lastname: Gu
authors.affiliation: Department of Biology, National Museum of Natural Science, 1 Kuan-Chien Road, Taichung 404, Taiwan, ROC.
authors.forename: Yun-Chih
authors.initials: YC
authors.lastname: Hsieh
authors.affiliation: Department of Biology, National Museum of Natural Science, 1 Kuan-Chien Road, Taichung 404, Taiwan, ROC.
authors.forename: Pei-Ling
authors.initials: PL
authors.lastname: Lin
mesh_terms: D000818:Animals; D012831:Bombyx / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D026461:Ecdysteroids / Q000378:metabolism; D005088:Exocrine Glands / Q000378:metabolism; D007301:Insect Hormones / Q000378:metabolism*; D019476:Insect Proteins / Q000235:genetics* / Q000378:metabolism; D007814:Larva / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D057093:Orphan Nuclear Receptors / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA
chemical_list: D026461:Ecdysteroids; D007301:Insect Hormones; D019476:Insect Proteins; D057093:Orphan Nuclear Receptors; D012333:RNA, Messenger; C009089:prothoracicotropic hormone
keywords: Ecdysone; HR38; Immediate early gene; Nuclear receptor; PTTH; Signaling