Second messengers and the action of prothoracicotropic hormone in Manduca sexta

Abstract

SYNOPSIS. The large (26 kDa) prothoracicotropic hormone of Manduca sexta stimulates ecdysteroid secretion by the prothoracic glands through the action of cyclic AMP (cAMP). Adenylate cyclase in the prothoracic glands is sensitive to calcium/calmodulin, and enhancement of intracellular calcium levels may be the means by which PTTH stimulates cAMP synthesis. The cyclic nucleotide in turn activates cAMP-dependent protein kinase and protein phosphorylation, most notably of a 34 kDa membraneassociated protein. It does not appear that protein kinase C plays a role in the acute action of PTTH, nor has the hormone been found to stimulate formation of inositol trisphosphate undercurrent assay conditions. PTTH rapidly increases protein synthesis by the prothoracic glands, and translation inhibitors block PTTH-stimulated ecdysteroid secretion. Connections between protein phosphorylation, protein synthesis, and ecdysone secretion remain to be clarified. © 1993 by the American Society of Zoologists.