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 knockout mouse models for the hypusine modifying enzymes deoxyhypusine synthase (DHS) and deoxyhypusine hydroxylase (DOHH) as well as for the cancer-related isoform eIF-5A2. We uncovered that homozygous depletion of DHS or DOHH causes lethality in adult mice with different penetrance compared to 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 first genetic evidence that the hypusine modification in eIF-5A is crucial for homeostasis in mammals. Moreover, these findings highlight functional diversity of the hypusine system compared to lower eukaryotes and indicate eIF-5A2 as a valuable and safe target for therapeutic intervention in cancer.
