title: Involvement of phosphorylation of adenosine 5'-monophosphate-activated protein kinase in PTTH-stimulated ecdysteroidogenesis in prothoracic glands of the silkworm, Bombyx mori.
abstract: In this study, we investigated inhibition of the phosphorylation of adenosine 5'-monophosphate-activated protein kinase (AMPK) by prothoracicotropic hormone (PTTH) in prothoracic glands of the silkworm, Bombyx mori. We found that treatment with PTTH in vitro inhibited AMPK phosphorylation in time- and dose-dependent manners, as seen on Western blots of glandular lysates probed with antibody directed against AMPKα phosphorylated at Thr172. Moreover, in vitro inhibition of AMPK phosphorylation by PTTH was also verified by in vivo experiments: injection of PTTH into day 7 last instar larvae greatly inhibited glandular AMPK phosphorylation. PTTH-inhibited AMPK phosphorylation appeared to be partially reversed by treatment with LY294002, indicating involvement of phosphatidylinositol 3-kinase (PI3K) signaling. A chemical activator of AMPK (5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside, AICAR) increased both basal and PTTH-inhibited AMPK phosphorylation. Treatment with AICAR also inhibited PTTH-stimulated ecdysteroidogenesis of prothoracic glands. The mechanism underlying inhibition of PTTH-stimulated ecdysteroidogenesis by AICAR was further investigated by determining the phosphorylation of eIF4E-binding protein (4E-BP) and p70 ribosomal protein S6 kinase (S6K), two known downstream signaling targets of the target of rapamycin complex 1 (TORC1). Upon treatment with AICAR, decreases in PTTH-stimulated phosphorylation of 4E-BP and S6K were detected. In addition, treatment with AICAR did not affect PTTH-stimulated extracellular signal-regulated kinase (ERK) phosphorylation, indicating that AMPK phosphorylation is not upstream signaling for ERK phosphorylation. Examination of gene expression levels of AMPKα, β, and γ by quantitative real-time PCR (qRT-PCR) showed that PTTH did not affect AMPK transcription. From these results, it is assumed that inhibition of AMPK phosphorylation, which lies upstream of PTTH-stimulated TOR signaling, may play a role in PTTH stimulation of ecdysteroidogenesis.
authors.affiliation: Department of Zoology, National Museum of Natural Science, Taichung, Taiwan, Republic of China. gu330@mail.nmns.edu.tw
authors.forename: Shi-Hong
authors.initials: SH
authors.lastname: Gu
authors.forename: Yun-Chin
authors.initials: YC
authors.lastname: Hsieh
authors.forename: Shun-Chieh
authors.initials: SC
authors.lastname: Young
authors.forename: Pei-Ling
authors.initials: PL
authors.lastname: Lin
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D012831:Bombyx / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D002867:Chromones / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D026461:Ecdysteroids / Q000096:biosynthesis*; D004702:Endocrine Glands / Q000187:drug effects* / Q000378:metabolism; D039642:Eukaryotic Initiation Factors / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D007301:Insect Hormones / Q000494:pharmacology*; D019476:Insect Proteins / Q000378:metabolism*; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D007814:Larva / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012265:Ribonucleotides / Q000494:pharmacology; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013997:Time Factors
chemical_list: D055372:AMP-Activated Protein Kinases; D000620:Aminoimidazole Carboxamide; D002867:Chromones; D026461:Ecdysteroids; D039642:Eukaryotic Initiation Factors; D007301:Insect Hormones; D019476:Insect Proteins; D007527:Isoenzymes; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D012265:Ribonucleotides; D038762:Ribosomal Protein S6 Kinases, 70-kDa; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C009089:prothoracicotropic hormone; C031143:AICA ribonucleotide