Biological Relevance and Therapeutic Potential of the Hypusine Modification System

Hypusine modification of the eukaryotic initiation factor 5A (eIF-5A) is emerging as a crucial regulator in cancer, infections, and inflammation. Although its contribution in translational regulation of proline repeat-rich proteins has been sufficiently demonstrated, its biological role in higher eukaryotes remains poorly understood. To establish the hypusine modification system as a novel platform for therapeutic strategies, we aimed to investigate its functional relevance in mammals by generating and using a range of new knock-out mouse models for the hypusine-modifying enzymes deoxyhypusine synthase and deoxyhypusine hydroxylase as well as for the cancer-related isoform eIF-5A2. We discovered that homozygous depletion of deoxyhypusine synthase and/or deoxyhypusine hydroxylase causes lethality in adult mice with different penetrance compared with haploinsufficiency. Network-based bioinformatic analysis of proline repeat-rich proteins, which are putative eIF-5A targets, revealed that these proteins are organized in highly connected protein-protein interaction networks. Hypusine-dependent translational control of essential proteins (hubs) and protein complexes inside these networks might explain the lethal phenotype observed after deletion of hypusine-modifying enzymes. Remarkably, our results also demonstrate that the cancer-associated isoform eIF-5A2 is dispensable for normal development and viability. Together, our results provide the first genetic evidence that the hypusine modification in eIF-5A is crucial for homeostasis in mammals. More-over, these findings highlight functional diversity of the hypusine system compared with lower eukaryotes and indicate eIF-5A2 as a valuable and safe target for therapeutic intervention in cancer.