ISSN:
0192-253X
Keywords:
Insect molting
;
ecdysteroid
;
S6 kinase
;
rapamycin
;
immunosuppressant
;
Life and Medical Sciences
;
Genetics
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
Notes:
The insect prothoracic glands are the source of steroidal molting hormone precursors and the glands are stimulated by a brain neuropeptide, prothoracicotropic hormone (PTTH). Previous work from this laboratory revealed that PTTH acts via a cascade including Ca2+/calmodulin activation of adenylate cyclase, protein kinase A, and the subsequent phosphorylation of a 34 kDa protein (p34) hypothesized, but not proven, to be the 56 protein of the 40S ribosomal subunit. The jmmunosuppressive macrolide, rapamycin, is a potent inhibitor of cell proliferation, a signal transduction blocker, and also prevents ribosomal S6 phosphorylation in mammalian systems. We demonstrate here that rapamycin inhibited PTTH-stimulated ecdysteroidogenesis in vitro by the prothoracic glands of the tobacco hornworm, Manduca sexta, with half-maximal inhibition at a concentration of about 5 nM. At concentrations above 5 nM, there was a 75% inhibition of ecdysteroid biosynthesis. Similar results, were observed with the calcium ionophore (A23187), a known stimulator of ecdysteroidogenesis. Most importantly, the inhibition of ecdysteroid biosynthesis was accompanied by the specific inhibition of the phosphorylation of p34, indicating that p34 indeed is ribosomal protein S6. In vivo assays revealed that injection of rapamycin into day 6 fifth instar larvae resulted in a decreased hemolymph ecdysteroid titer and a dose-dependent delay in molting and metamor-phosis. When S6 kinase (S6K) activity was examined using rapamycin-treated prothoracic glands as the enzyme source and a synthetic peptide (S6-21) or a 40S ribosomal subunit fraction from Manduca tissues as substrate, the date revealed that rapamycin inhibited S6K activity. The composite data suggest that rapamycin inhibits a signal transduction element leading to p34 phosphorylation that is necessary for PTTH-stimulated ecdysteroidogenesis in this insect endocrine gland, and lend further support to the concept that p34 is S6. © 1994 Wiley-Liss, Inc.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/dvg.1020150404
