Publications by authors named "Orel Mizrahi"

7 Publications

  • Page 1 of 1

SARS-CoV-2 uses a multipronged strategy to impede host protein synthesis.

Nature 2021 06 12;594(7862):240-245. Epub 2021 May 12.

Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel.

The coronavirus SARS-CoV-2 is the cause of the ongoing pandemic of COVID-19. Coronaviruses have developed a variety of mechanisms to repress host mRNA translation to allow the translation of viral mRNA, and concomitantly block the cellular innate immune response. Although several different proteins of SARS-CoV-2 have previously been implicated in shutting off host expression, a comprehensive picture of the effects of SARS-CoV-2 infection on cellular gene expression is lacking. Here we combine RNA sequencing, ribosome profiling and metabolic labelling of newly synthesized RNA to comprehensively define the mechanisms that are used by SARS-CoV-2 to shut off cellular protein synthesis. We show that infection leads to a global reduction in translation, but that viral transcripts are not preferentially translated. Instead, we find that infection leads to the accelerated degradation of cytosolic cellular mRNAs, which facilitates viral takeover of the mRNA pool in infected cells. We reveal that the translation of transcripts that are induced in response to infection (including innate immune genes) is impaired. We demonstrate this impairment is probably mediated by inhibition of nuclear mRNA export, which prevents newly transcribed cellular mRNA from accessing ribosomes. Overall, our results uncover a multipronged strategy that is used by SARS-CoV-2 to take over the translation machinery and to suppress host defences.
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http://dx.doi.org/10.1038/s41586-021-03610-3DOI Listing
June 2021

Anti-tumour immunity induces aberrant peptide presentation in melanoma.

Nature 2021 02 16;590(7845):332-337. Epub 2020 Dec 16.

Division of Oncogenomics, Oncode Institute, The Netherlands Cancer Institute, Amsterdam, The Netherlands.

Extensive tumour inflammation, which is reflected by high levels of infiltrating T cells and interferon-γ (IFNγ) signalling, improves the response of patients with melanoma to checkpoint immunotherapy. Many tumours, however, escape by activating cellular pathways that lead to immunosuppression. One such mechanism is the production of tryptophan metabolites along the kynurenine pathway by the enzyme indoleamine 2,3-dioxygenase 1 (IDO1), which is induced by IFNγ. However, clinical trials using inhibition of IDO1 in combination with blockade of the PD1 pathway in patients with melanoma did not improve the efficacy of treatment compared to PD1 pathway blockade alone, pointing to an incomplete understanding of the role of IDO1 and the consequent degradation of tryptophan in mRNA translation and cancer progression. Here we used ribosome profiling in melanoma cells to investigate the effects of prolonged IFNγ treatment on mRNA translation. Notably, we observed accumulations of ribosomes downstream of tryptophan codons, along with their expected stalling at the tryptophan codon. This suggested that ribosomes bypass tryptophan codons in the absence of tryptophan. A detailed examination of these tryptophan-associated accumulations of ribosomes-which we term 'W-bumps'-showed that they were characterized by ribosomal frameshifting events. Consistently, reporter assays combined with proteomic and immunopeptidomic analyses demonstrated the induction of ribosomal frameshifting, and the generation and presentation of aberrant trans-frame peptides at the cell surface after treatment with IFNγ. Priming of naive T cells from healthy donors with aberrant peptides induced peptide-specific T cells. Together, our results suggest that IDO1-mediated depletion of tryptophan, which is induced by IFNγ, has a role in the immune recognition of melanoma cells by contributing to diversification of the peptidome landscape.
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http://dx.doi.org/10.1038/s41586-020-03054-1DOI Listing
February 2021

Context-dependent functional compensation between Ythdf mA reader proteins.

Genes Dev 2020 10 17;34(19-20):1373-1391. Epub 2020 Sep 17.

Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel.

The N6-methyladenosine (mA) modification is the most prevalent post-transcriptional mRNA modification, regulating mRNA decay and splicing. It plays a major role during normal development, differentiation, and disease progression. The modification is regulated by a set of writer, eraser, and reader proteins. The YTH domain family of proteins consists of three homologous mA-binding proteins, Ythdf1, Ythdf2, and Ythdf3, which were suggested to have different cellular functions. However, their sequence similarity and their tendency to bind the same targets suggest that they may have overlapping roles. We systematically knocked out (KO) the Mettl3 writer, each of the Ythdf readers, and the three readers together (triple-KO). We then estimated the effect in vivo in mouse gametogenesis, postnatal viability, and in vitro in mouse embryonic stem cells (mESCs). In gametogenesis, severity is increased as the deletion occurs earlier in the process, and Ythdf2 has a dominant role that cannot be compensated by Ythdf1 or Ythdf3, due to differences in readers' expression pattern across different cell types, both in quantity and in spatial location. Knocking out the three readers together and systematically testing viable offspring genotypes revealed a redundancy in the readers' role during early development that is gene dosage-dependent. Finally, in mESCs there is compensation between the three Ythdf reader proteins, since the resistance to differentiate and the significant effect on mRNA decay occur only in the triple-KO cells and not in the single KOs. Thus, we suggest a new model for the Ythdf readers function, in which there is profound dosage-dependent redundancy when all three readers are equivalently coexpressed in the same cell types.
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http://dx.doi.org/10.1101/gad.340695.120DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7528697PMC
October 2020

The coding capacity of SARS-CoV-2.

Nature 2021 01 9;589(7840):125-130. Epub 2020 Sep 9.

Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause of the ongoing coronavirus disease 2019 (COVID-19) pandemic. To understand the pathogenicity and antigenic potential of SARS-CoV-2 and to develop therapeutic tools, it is essential to profile the full repertoire of its expressed proteins. The current map of SARS-CoV-2 coding capacity is based on computational predictions and relies on homology with other coronaviruses. As the protein complement varies among coronaviruses, especially in regard to the variety of accessory proteins, it is crucial to characterize the specific range of SARS-CoV-2 proteins in an unbiased and open-ended manner. Here, using a suite of ribosome-profiling techniques, we present a high-resolution map of coding regions in the SARS-CoV-2 genome, which enables us to accurately quantify the expression of canonical viral open reading frames (ORFs) and to identify 23 unannotated viral ORFs. These ORFs include upstream ORFs that are likely to have a regulatory role, several in-frame internal ORFs within existing ORFs, resulting in N-terminally truncated products, as well as internal out-of-frame ORFs, which generate novel polypeptides. We further show that viral mRNAs are not translated more efficiently than host mRNAs; instead, virus translation dominates host translation because of the high levels of viral transcripts. Our work provides a resource that will form the basis of future functional studies.
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http://dx.doi.org/10.1038/s41586-020-2739-1DOI Listing
January 2021

Virus-Induced Changes in mRNA Secondary Structure Uncover cis-Regulatory Elements that Directly Control Gene Expression.

Mol Cell 2018 12 11;72(5):862-874.e5. Epub 2018 Oct 11.

Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel. Electronic address:

mRNAs carry two layers of information, the genetic code and the information that dictates their post-transcriptional fate. The latter function relies on a complex interplay between cis-elements and trans-regulators, and unbiased identification of these elements is still challenging. To identify cis-elements that control gene expression, we use dimethyl sulfate (DMS) mutational profiling with sequencing and map changes in mRNA secondary structure following viral infection. Our dynamic structural data reveal a major role for ribosomes in unwinding secondary structures, which is further supported by the relationship we uncover between structure and translation efficiency. Moreover, our analysis revealed dozens of regions in viral and cellular mRNAs that exhibit changes in secondary structure. In-depth analysis of these regions reveals cis-elements in 3' UTRs that regulate mRNA stability and elements within coding sequences that control translation. Overall, our study demonstrates how mapping dynamic changes in mRNA structure allows unbiased identification of functional regulatory elements.
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http://dx.doi.org/10.1016/j.molcel.2018.09.003DOI Listing
December 2018

RNA editing by ADAR1 leads to context-dependent transcriptome-wide changes in RNA secondary structure.

Nat Commun 2017 11 13;8(1):1440. Epub 2017 Nov 13.

Cancer Research Center, Sheba Medical Center, Tel Hashomer, 52621, Ramat-Gan, Israel.

Adenosine deaminase acting on RNA 1 (ADAR1) is the master RNA editor, catalyzing the deamination of adenosine to inosine. RNA editing is vital for preventing abnormal activation of cytosolic nucleic acid sensing pathways by self-double-stranded RNAs. Here we determine, by parallel analysis of RNA secondary structure sequencing (PARS-seq), the global RNA secondary structure changes in ADAR1 deficient cells. Surprisingly, ADAR1 silencing resulted in a lower global double-stranded to single-stranded RNA ratio, suggesting that A-to-I editing can stabilize a large subset of imperfect RNA duplexes. The duplexes destabilized by editing are composed of vastly complementary inverted Alus found in untranslated regions of genes performing vital biological processes, including housekeeping functions and type-I interferon responses. They are predominantly cytoplasmic and generally demonstrate higher ribosomal occupancy. Our findings imply that the editing effect on RNA secondary structure is context dependent and underline the intricate regulatory role of ADAR1 on global RNA secondary structure.
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http://dx.doi.org/10.1038/s41467-017-01458-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5682290PMC
November 2017

Global mRNA polarization regulates translation efficiency in the intestinal epithelium.

Science 2017 09 10;357(6357):1299-1303. Epub 2017 Aug 10.

Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot, Israel.

Asymmetric messenger RNA (mRNA) localization facilitates efficient translation in cells such as neurons and fibroblasts. However, the extent and importance of mRNA polarization in epithelial tissues are unclear. Here, we used single-molecule transcript imaging and subcellular transcriptomics to uncover global apical-basal intracellular polarization of mRNA in the mouse intestinal epithelium. The localization of mRNAs did not generally overlap protein localization. Instead, ribosomes were more abundant on the apical sides, and apical transcripts were consequently more efficiently translated. Refeeding of fasted mice elicited a basal-to-apical shift in polarization of mRNAs encoding ribosomal proteins, which was associated with a specific boost in their translation. This led to increased protein production, required for efficient nutrient absorption. These findings reveal a posttranscriptional regulatory mechanism involving dynamic polarization of mRNA and polarized translation.
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http://dx.doi.org/10.1126/science.aan2399DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5955215PMC
September 2017