Translational Control of Gene Expression

Eukaryotic gene expression is regulated at the transcriptional and post-transcriptional levels. Regulation at the level of translation initiation is becoming increasingly evident. Most mRNAs encoding oncoproteins and factors related to cell proliferation possess a long, GC-rich, structured mRNA leader sequence with one or more AUG triplets upstream of the translation initiation codon. Some of such extraordinary features constitute an i nternal r ibosomal e ntry s ite (IRES) element that may confer translational advantage to the mRNA under certain cellular conditions, when global translation is down-regulated.

Interested in elucidating the mechanism of IRES function and regulation, we are studying various cellular IRES elements, in living cultured cells as well as in a cell-free translation system. Interested in cloning RNA-binding proteins that function as trans -acting factors we have used a yeast three-hybrid screen. Several interesting genes were selected, some of which pointed at the involvement of subunit 5 of the anaphase promoting complex (APC/C) in the regulation of IRES-mediated translation. We have found that poly(A)-binding protein stimulates IRES function in a poly(A)-dependent manner and that Apc5 counteracts such stimulation. Our data suggests a regulatory mechanism that depends on the availability of PABP to stimulate the IRES and the availability of Apc5 to prevent it. We are currently interested in the mechanism of IRES regulation by PABP throughout the cell cycle and in response physiological conditions that lead to cellular differentiation.

We are also interested in a fatal genetic disease caused by mutations in eukaryotic translation initiation factor 2B (eIF2B) genes. This neurodegenerative disease is termed Childhood ataxia with central nervous system hypomyelination (CACH), and also called vanishing white matter (VWM) leukoencephalopathy. The five subunits eIF2B factor is critical for translation initiation under normal conditions and regulates protein synthesis in response to cellular stresses. We found that although primary fibroblasts from CACH/VWM patients respond normally to stress in the endoplasmic reticulum by reduced global translation rates, they exhibit significantly greater increase in ATF4 induction compared to normal controls. We are currently seeking for additional genes that are translationally regulated similarly to ATF4, which may be involved in the deterioration of the disease upon physiological stress. In addition, this approach is being combined with stem cell research in efforts to differentiate mouse and human stem cells to produce neural cell types implicated in the disease.

1. Bernstein, J., I. Sheffler, O. Elroy-Stein. (1995) The translational repression mediated by the PDGF/c-sis mRNA leader is relieved during megakaryocytic differentiation. J. Biol. Chem. 270, 10559-10565.

2. Bernstein, J., O. Sella, S-Y. Le, O. Elroy-Stein. (1997) PDFG2/c-sis mRNA leader contains a differentiation-induced internal ribosomal entry site (D-IRES). J. Biol. Chem. 272, 9356-9362.

3. Akiri, G., D. Nahari, Y. Finkelstein, S.-Y. Le, O. Elroy-Stein, B.-Z. Levi. (1998) Regulation of vascular endothelial growth factor (VEGF) expression is mediated by internal initiation of translation and alternative initiation of transcription. Oncogene 17, 227-237.

4. Sella, O., S-Y. Le, G. Gerlitz, O. Elroy-Stein. (1999) Differentiation-induced internal translation of PDGF2/c-cis mRNA: analysis of the cis-elements and their differentiation-linked binding to hnRNP-C. Molec. Cell Biol. 19, 5429-5440.

5. Pozner, A., V. Negreanu, D. Goldenberg, S.-Y. Le, O. Elroy- Stein, D. Levanon, Y. Groner. (2000) Transcription Coupled-Translation Control of AML1/RUNX1 is Mediated by Cap- and IRES-dependent Mechanisms. Molec. Cell Biol. 20, 2297-2307.

6. Gerlitz, G., R. Jagus, O. Elroy-Stein. ( 2002) Phosphorylation of initiation factor 2a is required for activation of internal translation initiation during cell differentiation. Eur. J. Biochem. 269, 2810-2819.

7. Koloteva-Levine, N., M. Amichay, O. Elroy-Stein. (2002) Interaction of hnRNP-C1/C2 proteins with RNA: analysis using the yeast three-hybrid system. FEBS Letters 523, 73-78.

8. Koloteva-Levine, N., D. Pinchasi, I. Pereman, A. Zur, M. Brandeis, O. Elroy-Stein. (2004) The Apc5 subunit of APC/Cyclosome interacts with PABP and represses IRES-mediated translation. Molec. Cell. Biol. 24, 3577-3587.

9. Dahary D., O. Elroy-Stein, R. Soreq. (2005) Naturally occurring antisense: transcriptional leakage or real overlap? Genome Res. Mar15(3), 364-368.

10. Kantor L, H.P. Harding, D. Ron, R. Schiffmann, C.R. Kaneski, S.R. Kimball, O. Elroy-Stein . (2005) Heightened stress response in primary fibroblasts expressing mutant eIF2B genes from CACH/VWM leukodystrophy patients. Hum Genet. 118, 99-106.

11. Silvera D, N. Koloteva-Levine, S. Burma, O. Elroy-Stein. (2006) Effect of Ku proteins on IRES-mediated translation. Biol Cell. 98, 353-361.

12. Schiffmann R, and O. Elroy-Stein. (2006) Childhood ataxia with CNS hypomyelination/vanishing white matter disease--a common leukodystrophy caused by abnormal control of protein synthesis. Mol Genet Metab. 88, 7-15. Review .

13. Sivan G, N. Kedersha , O. Elroy-Stein. (2007) Ribosomal slowdown mediates translational arrest during cellular division. Mol Cell Biol. 27, 6639-6646.

14. Sivan G, O. Elroy-Stein. (2008) Regulation of mRNA Translation during cellular division. Cell Cycle. 7, 741-744. Review.

 
15. Marash L, Liberman N, Henis-Korenblit S, Sivan G, Reem E, Elroy-Stein O, A. Kimchi (2008) DAP5 promotes cap-independent translation of Bcl-2 and CDK1 to facilitate cell survival during mitosis. Mol Cell. 30, 447-459.

16. Kantor L, Pinchasi D, Mintz M, Hathout Y, Vanderver A, O. Elroy-Stein. (2008) A point mutation in translation initiation factor 2B leads to a continuous hyper stress state in oligodendroglial-derived cells. PLoS One. 3(11):e3783.

17. Marom L, Hen-Avivi S, Pinchasi D, Chekanova JA, Belostotsky DA, O. Elroy-Stein. (2009) Diverse poly(A) binding proteins mediate internal translational initiation by a plant viral IRES. RNA Biol. 6, 446-454.

18. Raveh-Amit H, Maissel A, Poller J, Marom L, Elroy-Stein O, Shapira M, E. Livneh. (2009) Translational control of protein kinase Ceta by two upstream open reading frames. Mol Cell Biol. 29, 6140-6148.

19. Geva M, Cabilly Y, Assaf Y, Mindroul N, Marom L, Raini G, Pinchasi D, O. Elroy-Stein. (2010) A mouse model for eukaryotic translation initiation factor 2B-leucodystrophy reveals abnormal development of brain white matter. Brain. 133, 2448-2461.

20. Mor E, Cabilly Y, Goldshmit Y, Zalts H, Modai S, Edry L, Elroy-Stein O, Shomron N. (2011) Species-specific microRNA roles elucidated following astrocyte activation. Nucleic Acids Res. 39, 3710-3723.

21. Sivan G, Aviner R, Elroy-Stein O. (2011) Mitotic Modulation of Translation Elongation Factor 1 Leads to Hindered tRNA Delivery to Ribosomes. J Biol Chem. 286, 27927-27935.

22. Barhoom S, Kaur J, Cooperman BS, Smorodinsky NI, Smilansky Z, Ehrlich M, Elroy-Stein O. (2011) Quantitative single cell monitoring of protein synthesis at subcellular resolution using fluorescently labeled tRNA. Nucleic Acids Res. Jul 27. [Epub ahead of print]