Nutrients such as glucose stimulate insulin release from pancreatic ␤-cells through both ATP-sensitive K + channel-independent and -dependent mechanisms, which are most likely interrelated. Although little is known of the molecular basis of ATP-sensitive K + channel-independent insulinotropic nutrient actions, mediation by cytosolic long-chain acyl-CoA has been implicated. Because protein acylation might be a sequel of cytosolic long-chain acyl-CoA accumulation, we examined if this reaction is

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... ngaged in nutrient stimulation of insulin release, using cerulenin, an inhibitor of protein acylation. In isolated rat pancreatic islets, cerulenin inhibited the glucose augmentation of Ca 2+ -stimulated insulin release evoked by a depolarizing concentration of K + in the presence of diazoxide and Ca 2+ -independent insulin release triggered by a combination of forskolin and phorbol ester under stringent Ca 2+ -free conditions. Cerulenin inhibition of glucose effects was concentration dependent, with a 50% inhibitory concentration (IC 50 ) of 5 µg/ml and complete inhibition at 100 µg/ml. Cerulenin also inhibited augmentation of insulin release by ␣-ketoisocaproate, a mitochondrial fuel. Furthermore, cerulenin abolished augmentation of both Ca 2+ -stimulated and Ca 2+ -independent insulin release by 10 µmol/l palmitate, which causes palmitoylation of cellular proteins. In contrast, cerulenin did not attenuate insulin release elicited by nonnutrient secretagogues, such as a depolarizing concentration of K + , activators of protein kinases A and C, and mastoparan. Glucose oxidation, ATP content in islets, and palmitate oxidation were not affected by cerulenin. In conclusion, cerulenin inhibits nutrient augmentation of insulin release with a high selectivity. The finding is consistent with a prominent role of protein acylation in the process of ␤-cell nutrient sensing.