Using an in vitro system to measure glandular response, we are currently delineating intracellular signaling pathways for prothoracicotropic hormone (PTTH) and other potential insect growth regulating hormones in the tobacco hornworm, Manduca sexta. We have recently found that PTTH stimulates tyrosine phosphorylation of prothoracic gland proteins, a biochemical change that typifies the action of growth factors. PTTH-stimulated tyrosine phosphorylation is blocked by an inhibitor of Src-family tyrosine kinases, 4-amino-5-(4-methylphenyl)-7- (t-butyl)pyrazolo[3,4-d]- pyrimidine (PP1). The inhibitor also blocks PTTH-stimulated ecdysone secretion and PTTH-stimulated calcium mobilization, the latter effect measured by confocal microscopy using a calcium-sensitive dye. The results suggest that prothoracic gland calcium channels are regulated in some manner by tyrosine phosphorylation. PTTH also stimulates serine/threonine phosphorylation of the growth factor signaling proteins Akt and GSK in the prothoracic glands. Phosphorylation of GSK in growing wing discs does not appear to be stimulated by PTTH. However, in wing discs, phospho-GSK content changes during development, and is strongly affected by nutritional state. Our findings suggest a means by which PTTH may directly increase prothoracic gland size and secretory capacity, and provide novel loci for the targeting of insect control agents. Research supported by NIDDK (R01 53992) and Northeastern University.
Species 1: Lepidoptera Sphingidae Manduca sexta (Carolina sphinx moth, tobacco hornworm)
Keywords: PTTH, ecdysone
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