LAUSR

In the present study, the participation of protein kinase C (PKC) signaling in prothoracicotropic hormone (PTTH)-stimulated ecdysteroidogenesis in Bombyx prothoracic glands (PGs) is demonstrated and characterized. PTTH stimulated phosphorylation of a 37-kDa protein in Bombyx PGs both in vitro and in vivo, as recognized by a PKC substrate antibody. Treatment with either A23187 or thapsigargin also stimulated this 37 kDa protein phosphorylation. PTTH-stimulated phosphorylation of the 37-kDa protein was markedly attenuated in the absence of Ca2+ . The phospholipase C (PLC) inhibitor, U73122, greatly inhibited PTTH-stimulated phosphorylation of this protein, indicating the involvement of Ca2+ and PLC. A mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitor (U0126), a phosphoinositide 3-kinase (PI3K) inhibitor (LY294002), and a chemical activator of adenosine 5'-monophosphate-activated protein kinase (AMPK) (5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside, AICAR) did not affect PTTH-stimulated phosphorylation of the 37-kDa protein, implying that ERK and PI3K/AMPK are not the upstream signaling pathways for PKC-dependent protein phosphorylation. The mitochondrial oxidative phosphorylation inhibitors (the uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) and diphenylene iodonium (DPI)) inhibited PTTH-stimulated phosphorylation of the 37-kDa protein, indicating its redox regulation. Treatment with PKC inhibitors (either calphostin C, chelerythrine C, or rottlerin) reduced PTTH-stimulated phosphorylation of the 37-kDa protein. PTTH-stimulated ecdysteroidogenesis was also inhibited by treatment with rottlerin, thus further confirming participation of PKC-dependent phosphorylation in PTTH signaling. From these results, we demonstrated that redox-regulated PTTH-stimulated PKC signaling is involved in ecdysteroid secretion in Bombyx PGs. This article is protected by copyright. All rights reserved.