Expression of Eukaryotic Initiation Factor 5A and Hypusine Forming Enzymes in Glioblastoma Patient Samples: Implications for New Targeted Therapies

Abstract

Glioblastomas are highly aggressive brain tumors of adults with poor clinical outcome. Despite a broad range of new and more specific treatment strategies, therapy of glioblastomas remains challenging and tumors relapse in all cases. Recent work demonstrated that the posttranslational hypusine modification of the eukaryotic initiation factor 5A (eIF-5A) is a crucial regulator of cell proliferation, differentiation and an important factor in tumor formation, progression and maintenance. Here we report that eIF-5A as well as the hypusine-forming enzymes deoxyhypusine synthase (DHS) and deoxyhypusine hydroxylase (DOHH) are highly overexpressed in glioblastoma patient samples. Importantly, targeting eIF-5A and its hypusine modification with GC7, a specific DHS-inhibitor, showed a strong antiproliferative effect in glioblastoma cell lines in vitro, while normal human astrocytes were not affected. Furthermore, we identified p53 dependent premature senescence, a permanent cell cycle arrest, as the primary outcome in U87-MG cells after treatment with GC7. Strikingly, combined treatment with clinically relevant alkylating agents and GC7 had an additive antiproliferative effect in glioblastoma cell lines. In addition, stable knockdown of eIF-5A and DHS by short hairpin RNA (shRNA) could mimic the antiproliferative effects of GC7. These findings suggest that pharmacological inhibition of eIF-5A may represent a novel concept to treat glioblastomas and may help to substantially improve the clinical course of this tumor entity.

Biological Relevance and Therapeutic Potential of the Hypusine Modification System

“…Indeed, certain oncogenes like c-abl contain polyproline stretches and should therefore be translationally regulated by eIF-5A1. Furthermore, our studies on glioblastoma cell lines have shown a higher sensitivity of tumor cells against the inhibition of hypusine synthesis compared with normal human astrocytes (16), suggesting that certain malignant cells depend on an activated hypusinedependent translation that is above the activation level in normal cells. An intriguing observation made by using another tumor model is that haploinsufficiency of ribosomal proteins attenuates Myc-dependent malignant transformation without affecting normal cells (72).…”

“…It is common knowledge that tumor cells accelerate their translational activity to adapt to the increasing cellular demands (2). Accordingly, previous work unveiled that the hypusine modification system is frequently overexpressed in cancer tissue (16,17,70), supporting the hypothesis that eIF-5A facilitates translation of genes with tumor promoting activity as described for other translation factors (71). Indeed, certain oncogenes like c-abl contain polyproline stretches and should therefore be translationally regulated by eIF-5A1.…”

“…Up-regulation of the eIF-5A1 isoform and the hypusine-forming enzymes can be found in many types of tumors, and inhibition of hypusination by siRNA or small molecules showed anti-proliferative effects in numerous tumor entities (16,17). However, the hypusine system may have pleiotropic functions, as seen for the tumor suppressor activity of eIF-5A1 and DHS in lymphoma development (18).…”

A Hypusine–eIF5A–PEAK1 Switch Regulates the Pathogenesis of Pancreatic Cancer

“…Indeed, many cell cycle, apoptosis, and signal transduction proteins contain polyproline regions [15-17]. Increased demands for such proteins may explain why eIF5A expression is increased in several cancers including glioblastoma, leukemia, liver, colon, lung, cervical, and ovarian cancer [18-25]. …”

Eukaryotic translation initiation factor 3, subunit C is overexpressed and promotes cell proliferation in human glioma U-87 MG cells

“…Overexpression of eIFs is common in numerous types of cancer and the aberrant expression of several eIFs, including eIF3b (22), eIF4e (23) and eIF5a (24), has also been observed in tissues obtained from patients with glioma, emphasizing the critical role of eIFs in glioma. The upregulation of eIF3c, a component of the eIF3 complex, has been reported in several tumour types, including colon cancer (14), testicular seminoma (12) and meningioma (25).…”