Ecdysone deprivation affects polyamine metabolism in the house cricket Acheta domesticus

The basic importance of polyamines, which are involved in the regulation of DNA, RNA and protein synthesis, are underlined in numerous works. Using HPLC analysis, we determined polyamine levels in several tissues of 10-day old adult crickets subjected to different hormonal conditions. Ovariectomy performed during the last larval instar suppressed haemolymph ecdysteroids and significantly increased the spermidine titres in nervous tissue whereas it decreased the overall polyamine levels in the fat body. Ecdysone injections into ovariectomized females reduced the spermidine content in nervous tissue and markedly increased the overall fat body polyamine levels, an effect which was mimicked by saline injections in this last tissue. As compared to control values, the activity of ornithine decarboxylase (ODC), the first key enzyme in polyamine biosynthesis was significantly reduced by ovariectomy either in nervous tissue or in fat body. In ovariectomized females, ecdysone injections significantly stimulated only the fat body ODC activity. The effects of polyamines on protein phosphorylation was examined. The phosphorylation of two proteins (207 and 128 kDa respectively) present in the fat body and the nervous tissue of control and ovariectomized females decreased in the presence of polyamines. The phosphorylation of a 53.5 kDa phosphoprotein only present in the nervous tissue differed according to the hormonal status of the female and was strongly enhanced by polyamines. Polyamines also stimulated the phosphorylation of a 37.5 kDa phosphoprotein present in both nervous tissue and fat body. In this last tissue, the phosphorylation of a 20 kDa phosphoprotein present in ovariectomized females was inhibited by the addition of polyamines. This work demonstrates an action of ecdysone on polyamine levels in nervous tissue and underlines the ability of polyamines to modulate the phosphorylation of specific phosphoproteins which are under hormonal control. These data emphasize the importance of polyamines in the regulation of cell functions.