PROTHORACICOTROPICHORMONE INDUCES TYROSINEPHOSPHORYLATION INPROTHORACIC GLANDS OF THESILKWORM, Bombyx mori

摘要

In the present study, we investigated the tyrosine phosphorylation ofBombyx mori prothoracic glands using phosphotyrosine-specific anti bodies and Western blot analysis. Results showed that prothoracicotropichormone (PTTH) stimulates a rapid increase in tyrosine phosphorylationof at least 2 proteins in prothoracic glands, one of which was identified asextracellular signal-regulated kinase (ERK). The phosphorylation ofanother 120-kDa protein showed dose- and time-dependent stimulationby PTTH in vitro. In vitro activation of tyrosine phosphorylation wasalso verified by in vivo experiments: injection of PTTH into day-6last-instar larvae greatly increased tyrosine phosphorylation. Treatmentof prothoracic glands with the protein tyrosine phosphatase inhibitor,sodium orthovanadate, also resulted in tyrosine phosphorylation ofseveral proteins and increased ecdysteroidogenesis. The PTTH-stimulated phosphorylation of the 120-kDa protein was markedlyattenuated by genistein, a broad-spectrum tyrosine kinase inhibitor, butnot by HNMPA-(AM)_3, a specific inhibitor of insulin receptor tyrosinekinase. PP2, a more-selective inhibitor of the Src-family tyrosine kinases,partially inhibited PTTH-stimulated tyrosine phosphorylation, but notecdysteroidogenesis. This result implies the possibility that in addition toERK, the phosphorylation of the 120-kDa protein, which is notSrc-family tyrosine kinase, is likely also involved in PTTH-stimulatedecdysteroidogenesis in B. mori.