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Blood, 15 February 2007, Vol. 109, No. 4, pp. 1701-1711. Prepublished online as a Blood First Edition Paper on September 28, 2006; DOI 10.1182/blood-2005-03-037648.
NEOPLASIA Hypusination of eukaryotic initiation factor 5A (eIF5A): a novel therapeutic target in BCR-ABLpositive leukemias identified by a proteomics approach1 Department of Oncology and Haematology, University Hospital Eppendorf, Hamburg, Germany; 2 Department of Haematology, Oncology and Immunology, University Medical Center, Tübingen, Germany; 3 Institute for Cell Biology, Department of Molecular Biology, ZBiT/Proteomics, University of Tübingen, Germany; 4 Section of Experimental Haematology, Cancer Division, University of Glasgow, Scotland; 5 Institute for Cell Biology, Department of Molecular Biology, University of Tübingen, Germany; 6 Heinrich-Pette-Institute for Experimental Virology and Immunology, Hamburg, Germany; 7 Proteome Center, University of Tübingen, Germany Inhibition of BCR-ABL tyrosine kinase with imatinib represents a major breakthrough in the treatment of patients with chronic myeloid leukemia (CML). However, resistance to imatinib develops frequently, particularly in late-stage disease. To identify new cellular BCR-ABL downstream targets, we analyzed differences in global protein expression in BCR-ABLpositive K562 cells treated with or without imatinib in vitro. Among the 19 proteins found to be differentially expressed, we detected the down-regulation of eukaryotic initiation factor 5A (eIF5A), a protein essential for cell proliferation. eIF5A represents the only known eukaryotic protein activated by posttranslational hypusination. Hypusination inhibitors (HIs) alone exerted an antiproliferative effect on BCR-ABLpositive and negative leukemia cell lines in vitro. However, the synergistic dose-response relationship found for the combination of imatinib and HI was restricted to Bcr-Ablpositive cells. Furthermore, this synergistic effect was confirmed by cytotoxicity assays, cell-cycle analysis, and CFSE labeling of primary CD34+ CML cells. Specificity of this effect could be demonstrated by cotreatment of K562 cells with imatinib and siRNA against eIF5. In conclusion, through a comparative proteomics approach and further functional analysis, we identified the inhibition of eIF5A hypusination as a promising new approach for combination therapy in BCR-ABLpositive leukemias.
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