Protein phosphorylation in the prothoracic glands as a cellular model for juvenile hormone-prothoracicotropic hormone interactions

Abstract Prothoracicotropic hormone (PTTH) is a brain peptide that initiates the molting process by acting directly at the cell membrane of the prothoracic glands to increase the intracellular levels of free Ca 2+ and cyclic AMP (cAMP). This, in turn, leads to enhanced cAMP-dependent protein kinase activity resulting in the phosphorylation of a specific protein (M r 34,000), and ultimately to a stimulation of ecdysone synthesis. When prothoracic glands are incubated in the presence of juvenile hormone (JH I) or (7 S ) hydroprene and then challenged with PTTH, the phosphorylation of the 34 kDa protein is decreased in a dose-dependent manner. The morphogenetically inactive methyl farnesoate is ineffective in preventing this downstream effect of PTTH. The JH effect does not appear to be stage specific, as early last larval, late last larval and pupal Manduca sexta prothoracic glands are similarly affected. The mechanism by which JH may prevent this PTTH-stimulated phosphorylation is discussed in terms of inhibition of phosphorylation via stimulation of an ATPase and stimulation of dephosphorylation by activation of a phosphoprotein phosphatase.