The expression of preprosomatostatin II mRNAs in the Brockmann bodies of rainbow trout, Oncorhynchus mykiss, is regulated by glucose

We previously characterized two cDNAs that encode for distinct preprosomatostatin molecules containing [Tyr⁷, Gly¹⁰]-somatostatin-14 at their C-termini (PPSS II' and PPSS II') and found that these cDNAs were differentially expressed in the endocrine pancreas (Brockmann body) of rainbow trout, Oncorhynchus mykiss. In this study, we examined the control of PPSSII' mRNA and PPSS II' mRNA expression by glucose. Fish injected with glucose displayed elevated plasma levels of glucose in association with nearly three-fold higher levels of PPSS II mRNAs compared to saline-injected control animals. Glucose directly stimulated the expression of both PPSS II mRNAs in vitro in a dose-dependent manner; however, glucose was a more potent stimulator of PPSS II' expression than of PPSS II' expression. The hexoses, mannose, galactose, and fructose, as well as glucose, all induced the expression of PPSS II mRNAs, whereas, sucrose and the glucose analogs, 3-o- methylglucose and 2-deoxyglucose, were without effect. In addition, the expression of PPSS II mRNAs was stimulated by dihydroxyacetone, pyruvate, lactate, acetate, and citrate. Furthermore, the expression of PPSS II mRNAs was inhibited by iodoacetate, an inhibitor of glycolysis, but was stimulated by dichloroacetate, a stimulator of Krebs cycle flux via pyruvate dehydrogenase activation. Finally, glucose-stimulated PPSS II expression was inhibited by actinomycin. These results indicate that the expression of PPSS II mRNAs in the Brockmann body of trout is regulated by nutrients such as glucose and suggest that glucose-stimulated expression of PPSS II mRNAs requires the uptake and subsequent metabolism of the sugar and is transcription sensitive. (C) 2000 Academic Press.