Activation of an extracellular signal-regulated kinase (ERK) by the insectprothoracicotropic hormone

Ecdysteroid hormones are crucial in controlling the growth, molting and met amorphosis of insects. The predominant source of ecdysteroids in pre-adult insects is the prothoracic gland, which is under the acute control of the n europeptide hormone prothoracicotropic hormone (PTTH). Previous studies usi ng the tobacco hornworm, Manduca sexta, have shown that PTTH stimulates ecd ysteroid synthesis via a series of events, including the activation of prot ein kinase A and the 70 kDa S6 kinase (p70(S6k)). In this study, PTTH was s hown to stimulate also mitogen-activated protein kinase (MAPK) phosphorylat ion and activity in the Manduca prothoracic gland. The MAPK involved appear s to be an extracellular signal-regulated kinase (ERK) homologue. The ERK p hosphorylation inhibitors PD 98059 and UO 126 blocked basal and PTTH-stimul ated ERK phosphorylation and ecdysteroid synthesis. PTTH-stimulated ERK act ivity may be important for both rapid regulation of ecdysteroid synthesis a nd for longer-term changes in the size and function of prothoracic gland ce lls. (C) 2001 Published by Elsevier Science Ireland Ltd.