TOR signaling is involved in PTTH-stimulated ecdysteroidogenesis by prothoracic glands in the silkworm, Bombyx mori.
The prothoracicotropic hormone (PTTH) is a stimulator of ecdysteroidogenesis in prothoracic gland of larval insects. Our recent studies showed that phosphoinositide 3-kinase (PI3K)/Akt signaling was involved in PTTH-stimulated ecdysteroidogenesis by Bombyx mori prothoracic glands. In the present study, downstream signaling of PI3K/Akt was further investigated. Results showed that PTTH rapidly enhanced the phosphorylation of translational repressor 4E-binding protein (4E-BP) and p70 ribosomal protein S6 kinase (S6K), two known downstream signaling targets of the target of rapamycin complex 1 (TORC1). PTTH stimulated 4E-BP phosphorylation in time- and dose-dependent manners. Injection of PTTH into day-6 last instar larvae greatly increased 4E-BP phosphorylation, verifying the in vitro effect. PTTH-stimulated 4E-BP phosphorylation was blocked by both LY294002 and wortmannin, indicating the involvement of PI3K. Mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitors (PD 98059 and U0126), did not inhibit PTTH-stimulated 4E-BP phosphorylation, implying that ERK signaling is not related to PTTH-stimulated 4E-BP phosphorylation. The phosphorylation of S6K was also stimulated by PTTH both in vitro and in vivo. PI3K signaling appears to be involved in PTTH-stimulated phosphorylation of S6K. Rapamycin, a specific inhibitor of mammalian TOR signaling attenuated PTTH-stimulated phosphorylation of 4E-BP and S6K of the glands, and greatly inhibited PTTH-stimulated ecdysteroidogenesis. Examination of gene expression levels of 4E-BP and S6K showed that PTTH inhibited mRNA levels of both 4E-BP and S6K, indicating that PTTH may exert its action at both the transcriptional and phosphorylation levels. These results suggest that PTTH/PI3K/TOR/4E-BP (S6K) signaling is involved in PTTH-stimulated ecdysteroidogenesis by prothoracic glands in B. mori.
Department of Zoology, National Museum of Natural Science, 1 Kuan-Chien Road, Taichung, Taiwan 404, ROC. gu330@mail.nmns.edu.tw
Shi-Hong
SH
Gu
Wei-Lan
WL
Yeh
Shun-Chieh
SC
Young
Pei-Ling
PL
Lin
Sheng
S
Li
D000818:Animals; D012831:Bombyx / Q000378:metabolism*; D002070:Butadienes; D026461:Ecdysteroids / Q000096:biosynthesis*; D005419:Flavonoids; D015870:Gene Expression; D007301:Insect Hormones / Q000378:metabolism*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors; D009570:Nitriles; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D015398:Signal Transduction; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*
D002070:Butadienes; D026461:Ecdysteroids; D005419:Flavonoids; D007301:Insect Hormones; D009570:Nitriles; D000081082:Phosphoinositide-3 Kinase Inhibitors; C113580:U 0126; C009089:prothoracicotropic hormone; D019893:Ribosomal Protein S6 Kinases; D058570:TOR Serine-Threonine Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D020123:Sirolimus