The Unique Hypusine Modification of eIF5A Promotes Islet Inflammation and Dysfunction in the Development of Diabetes

The production and release of proinflammatory cytokines by invading immune cells and the consequent production of iNOS are seminal to the pathogenesis of pancreatic beta cell dysfunction characteristic of both type 1 and type 2 diabetes. The ubiquitous translation factor eIF5A containing a unique hypusine post-translational modification is thought to mediate cellular stress. Islets depleted of eIF5A in vivo using RNA interference showed improved glucose-stimulated calcium mobilization and insulin secretion in the presence of proinflammatory cytokines (IFN-gamma, IL-1beta, TNF-alpha). These effects appear to be mediated by the substantial reduction in the translation of mRNA encoding iNOS (Nos2). INS-1 beta cells co-incubated with cytokines and inhibitors of hypusine synthesis exhibited preserved glucose coupling and a dose-dependent block in iNOS production, suggesting the requirement of the hypusine residue of eIF5A in the translation of Nos2 transcripts. Subcellular fractionation revealed that hypusinated eIF5A is required for efficient nucleocytoplasmic shuttling of Nos2 mRNA and that this process is mediated by interactions between hypusinated eIF5A, Nos2 mRNA, and the export protein exportin1/CRM1. Consistent with these data, inhibition of hypusination led to a block in the nucleocytoplasmic shuttling of eIF5A and to impaired degradation of Nos2 transcripts. Similarly, daily intraperitoneal injection of stabilized siRNA the hypusination inhibitor GC7, protected C57BL/6J mice from the STZ-induced beta cell death and dysfunction. Both western blot and immunohistochemical analysis of GC7 and si-eIF5A treated animals reveal an attenuation of islet iNOS protein relative to saline and si-Control treated animals. Taken together, these data suggest that hypusinated eIF5A is an essential protein in the cytokine response cascade linking Nos2 transcription to iNOS translation and the production of nitric oxide. The hypusine modification of eIF5A therefore represents a novel target for preserving islet function in inflammatory states.