The eukaryotic initiation factor 5A (eIF5A), which contributes to several crucial processes during protein translation, is the only protein that requires activation by a unique post-translational hypusine modification. eIF5A hypusination controls cell proliferation and has been linked to cancer. eIF5A hypusination requires the enzymes deoxyhypusine synthase (DHPS) and deoxyhypusine hydroxylase and uniquely depends on the polyamine (PA) spermidine as the sole substrate. Ornithine decarboxylase (ODC) is the rate-limiting enzyme in PA biosynthesis. Both ODC and PAs control cell proliferation and are frequently dysregulated in cancer. Since only spermidine can activate eIF5A, we chose the hypusine–PA nexus as a rational target to identify new drug combinations with synergistic antiproliferative effects. We show that elevated mRNA levels of the two target enzymes DHPS and ODC correlate with poor prognosis in a large cohort of neuroblastoma (NB) tumors. The DHPS inhibitor GC7 (N1-guanyl-1,7-diaminoheptane) and the ODC inhibitor α-difluoromethylornithine (DFMO) are target-specific and in combination induced synergistic effects in NB at concentrations that were not individually cytotoxic. Strikingly, while each drug alone at higher concentrations is known to induce p21/Rb- or p27/Rb-mediated G1 cell cycle arrest, we found that the drug combination induced caspase 3/7/9, but not caspase 8-mediated apoptosis, in NB cells. Hypusinated eIF5A levels and intracellular spermidine levels correlated directly with drug treatments, signifying specific drug targeting effects. This two-pronged GC7/DFMO combination approach specifically inhibits both spermidine biosynthesis and post-translational, spermidine-dependent hypusine-eIF5A activation, offering an exciting clue for improved NB drug therapy.
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Cover Image
Cover Image
In this issue of the Biochemical Journal, Dukic et al. report that ezrin-anchored PKA phosphorylates serine 369 and 373 on connexin 43 to enhance gap junction assembly, communication, and cell fusion. The cover image, taken from Figure 6 in the article, shows HEK293 cells transfected with mammalian expression vectors encoding siRNA-resistant Cx43 without ability to bind to ezrin and with a phosphomimicking S to D substitution in residue 369.
Synergistic drug combination GC7/DFMO suppresses hypusine/spermidine-dependent eIF5A activation and induces apoptotic cell death in neuroblastoma
Chad R. Schultz, Dirk Geerts, Marie Mooney, Raid El-Khawaja, Jan Koster, André S. Bachmann; Synergistic drug combination GC7/DFMO suppresses hypusine/spermidine-dependent eIF5A activation and induces apoptotic cell death in neuroblastoma. Biochem J 31 January 2018; 475 (2): 531–545. doi: https://doi.org/10.1042/BCJ20170597
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