THE PHOSPHOLIPASE-C SIGNALING PATHWAY IN LOCUST FAT-BODY IS ACTIVATEDVIA G(Q) AND NOT AFFECTED BY CAMP

Crosstalk between signal transduction pathways provides a complex intr acellular avenue for fine tuning of hormone-induced signals. Over the last few years, we have studied the signaling mechanisms of three locu st adipokinetic hormones (AKHs), which control mobilization of energy reserves from insect fat body as fuels for flight and transduce their signals via adenylyl cyclase- and phospholipase C- (PLC) dependent pat hways. In this study, we examine possible crosstalk between these sign aling routes. We show that cAMP does not affect basal and AKH-stimulat ed inositol phosphate (InsP(n)) production. Incubation of fat body wit h aluminium fluoride, an activator of G proteins, increased InsP(n) le vels by 77%, whereas cholera toxin and pertussis toxin were ineffectiv e. This implies that fat body PLC is not activated by G beta gamma, bu t possibly by G(q)alpha. The involvement of this G protein in AKH sign aling was demonstrated by our observation that the GPAntagonist-2A, wh ich antagonizes G(q), attenuated glycogen phosphorylase activation by AKH-I. As plasma membrane Ca2+ channels may constitute another target for cAMP-mediated modulation, we studied the type of channels involved in AKH signaling using a variety of L-, N- and T-type Ca2+ channel in hibitors. None of these blocked AKH-induced glycogen phosphorylase act ivation, suggesting that voltage-dependent Ca2+ channels do not mediat e AKH-induced Ca2+ influx. (C) 1998 Elsevier Science Ltd. All rights r eserved.