Overexpression of Eukaryotic Initiation Factor 4E Induces Critical Transcription Factors Such As c-Myc in Multiple Myeloma Resulting in Enhanced Clonogenic Tumor Growth in Vitro and in Vivo.

The eukaryotic initiation factor 4E (eIF4E) is a critical regulator in protein synthesis. It has been shown that overexpression and/or activation of eIF4E is critical for oncogenic protein synthesis. The precise role of protein translation in multiple myeloma (MM) is less clear. Recently it has been shown that eIF4E protein levels are higher in primary CD138+ MM cells than in normal plasma cells (Li, Jin et al. 2011) and that mutations in genes related to mRNA translation are involved in the pathogenesis of multiple (Chapman, Lawrence et al. 2011). Therefore, understanding the mechanisms that control protein synthesis is an emerging new research area in MM with significant potential for developing innovative therapies. In this study, we analyzed the effects of introduction of ectopic eIF4E in MM cell lines compared with their parent cells in vitro and in vivo.

To examine the effect of overexpressed eIF4E in MM, we transduced MM cell lines with lentiviral particles encoding human eIF4E with GFP as selection marker. Introduction of ectopic eIF4E significantly increased critical factors for myeloma cell growth such as myc, cyclin D1, C/EBP beta and IRF4 as detected by western blotting. Overexpression of eIF4E resulted in a significant (p<0.001) increase of DNA synthesis compared to empty vector control (EV) cells. Cell cycle analysis revealed a decreasing number of cells in G0/G1 phase (62% vs 49%) and cells arresting in the G2/M phase (14% vs 23%), not affecting cell apoptosis. Overexpression of eIF4E further led to the significant increase (p=0.004) of clonogenic tumor growth with expansion of clonogenic colony numbers (22.3 ± 2.5 vs 40.3 ± 2.1) and size. To determine whether overexpressed eIF4E also affects MM tumor growth in vivo, we generated subcutaneous MM xenografts in severe combined immunodeficient x beige (SCID/bg) mice using the EV and eIF4E-OE-U266 cells. In contrast to EV-U266 tumors, animals bearing eIF4E-OE-U266 xenografts showed a significant increase (p<0.001) of tumor growth by 180% after 13 days.

Here we show that eIF4E, a key player in translational machinery, promotes multiple myeloma cell growth both in vitro and in vivo. When eIF4E is overexpressed, it enhances protein expression of a subset of transcripts encoding regulators of the cell cycle and proliferation.

Lentzsch:Celgene: Consultancy, Research Funding.