Publications by authors named "Ivan Topisirovic"

112 Publications

Regulation of gene expression via translational buffering.

Biochim Biophys Acta Mol Cell Res 2021 Sep 30;1869(1):119140. Epub 2021 Sep 30.

Translational Prostate Cancer Research Laboratory, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia; Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, Victoria, Australia; Cancer Program, Biomedicine Discovery Institute and Department of Anatomy and Developmental Biology, Monash University, Clayton, Victoria, Australia. Electronic address:

Translation of an mRNA represents a critical step during the expression of protein-coding genes. As mechanisms governing post-transcriptional regulation of gene expression are progressively unveiled, it is becoming apparent that transcriptional programs are not fully reflected in the proteome. Herein, we highlight a previously underappreciated post-transcriptional mode of regulation of gene expression termed translational buffering. In principle, translational buffering opposes the impact of alterations in mRNA levels on the proteome. We further describe three types of translational buffering: compensation, which maintains protein levels e.g. across species or individuals; equilibration, which retains pathway stoichiometry; and offsetting, which acts as a reversible mechanism that maintains the levels of selected subsets of proteins constant despite genetic alteration and/or stress-induced changes in corresponding mRNA levels. While mechanisms underlying compensation and equilibration have been reviewed elsewhere, the principal focus of this review is on the less-well understood mechanism of translational offsetting. Finally, we discuss potential roles of translational buffering in homeostasis and disease.
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http://dx.doi.org/10.1016/j.bbamcr.2021.119140DOI Listing
September 2021

A hydride transfer complex reprograms NAD metabolism and bypasses senescence.

Mol Cell 2021 09;81(18):3848-3865.e19

CRCHUM, 900 Saint-Denis St, Montréal, QC H2X 0A9, Canada; Département de Biochimie et Médecine Moléculaire, Université de Montréal, Montréal, QC H3C 3J7, Canada. Electronic address:

Metabolic rewiring and redox balance play pivotal roles in cancer. Cellular senescence is a barrier for tumorigenesis circumvented in cancer cells by poorly understood mechanisms. We report a multi-enzymatic complex that reprograms NAD metabolism by transferring reducing equivalents from NADH to NADP. This hydride transfer complex (HTC) is assembled by malate dehydrogenase 1, malic enzyme 1, and cytosolic pyruvate carboxylase. HTC is found in phase-separated bodies in the cytosol of cancer or hypoxic cells and can be assembled in vitro with recombinant proteins. HTC is repressed in senescent cells but induced by p53 inactivation. HTC enzymes are highly expressed in mouse and human prostate cancer models, and their inactivation triggers senescence. Exogenous expression of HTC is sufficient to bypass senescence, rescue cells from complex I inhibitors, and cooperate with oncogenic RAS to transform primary cells. Altogether, we provide evidence for a new multi-enzymatic complex that reprograms metabolism and overcomes cellular senescence.
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http://dx.doi.org/10.1016/j.molcel.2021.08.028DOI Listing
September 2021

The integrated stress response is tumorigenic and constitutes a therapeutic liability in KRAS-driven lung cancer.

Nat Commun 2021 07 30;12(1):4651. Epub 2021 Jul 30.

Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General Hospital, Montreal, QC, Canada.

The integrated stress response (ISR) is an essential stress-support pathway increasingly recognized as a determinant of tumorigenesis. Here we demonstrate that ISR is pivotal in lung adenocarcinoma (LUAD) development, the most common histological type of lung cancer and a leading cause of cancer death worldwide. Increased phosphorylation of the translation initiation factor eIF2 (p-eIF2α), the focal point of ISR, is related to invasiveness, increased growth, and poor outcome in 928 LUAD patients. Dissection of ISR mechanisms in KRAS-driven lung tumorigenesis in mice demonstrated that p-eIF2α causes the translational repression of dual specificity phosphatase 6 (DUSP6), resulting in increased phosphorylation of the extracellular signal-regulated kinase (p-ERK). Treatments with ISR inhibitors, including a memory-enhancing drug with limited toxicity, provides a suitable therapeutic option for KRAS-driven lung cancer insofar as they substantially reduce tumor growth and prolong mouse survival. Our data provide a rationale for the implementation of ISR-based regimens in LUAD treatment.
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http://dx.doi.org/10.1038/s41467-021-24661-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8324901PMC
July 2021

Selective inhibitors of mTORC1 activate 4EBP1 and suppress tumor growth.

Nat Chem Biol 2021 10 24;17(10):1065-1074. Epub 2021 Jun 24.

Program in Molecular Pharmacology, Department of Medicine, Memorial Sloan-Kettering Cancer Center (MSKCC), New York, NY, USA.

The clinical benefits of pan-mTOR active-site inhibitors are limited by toxicity and relief of feedback inhibition of receptor expression. To address these limitations, we designed a series of compounds that selectively inhibit mTORC1 and not mTORC2. These 'bi-steric inhibitors' comprise a rapamycin-like core moiety covalently linked to an mTOR active-site inhibitor. Structural modification of these components modulated their affinities for their binding sites on mTOR and the selectivity of the bi-steric compound. mTORC1-selective compounds potently inhibited 4EBP1 phosphorylation and caused regressions of breast cancer xenografts. Inhibition of 4EBP1 phosphorylation was sufficient to block cancer cell growth and was necessary for maximal antitumor activity. At mTORC1-selective doses, these compounds do not alter glucose tolerance, nor do they relieve AKT-dependent feedback inhibition of HER3. Thus, in preclinical models, selective inhibitors of mTORC1 potently inhibit tumor growth while causing less toxicity and receptor reactivation as compared to pan-mTOR inhibitors.
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http://dx.doi.org/10.1038/s41589-021-00813-7DOI Listing
October 2021

STAT1 potentiates oxidative stress revealing a targetable vulnerability that increases phenformin efficacy in breast cancer.

Nat Commun 2021 06 3;12(1):3299. Epub 2021 Jun 3.

Department of Biochemistry, Microbiology and Immunology, Ottawa Institute of Systems Biology, University of Ottawa, Ottawa, ON, Canada.

Bioenergetic perturbations driving neoplastic growth increase the production of reactive oxygen species (ROS), requiring a compensatory increase in ROS scavengers to limit oxidative stress. Intervention strategies that simultaneously induce energetic and oxidative stress therefore have therapeutic potential. Phenformin is a mitochondrial complex I inhibitor that induces bioenergetic stress. We now demonstrate that inflammatory mediators, including IFNγ and polyIC, potentiate the cytotoxicity of phenformin by inducing a parallel increase in oxidative stress through STAT1-dependent mechanisms. Indeed, STAT1 signaling downregulates NQO1, a key ROS scavenger, in many breast cancer models. Moreover, genetic ablation or pharmacological inhibition of NQO1 using β-lapachone (an NQO1 bioactivatable drug) increases oxidative stress to selectively sensitize breast cancer models, including patient derived xenografts of HER2+ and triple negative disease, to the tumoricidal effects of phenformin. We provide evidence that therapies targeting ROS scavengers increase the anti-neoplastic efficacy of mitochondrial complex I inhibitors in breast cancer.
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http://dx.doi.org/10.1038/s41467-021-23396-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8175605PMC
June 2021

Adaptation to mitochondrial stress requires CHOP-directed tuning of ISR.

Sci Adv 2021 May 26;7(22). Epub 2021 May 26.

Cologne Excellence Cluster on Cellular Stress Responses in Ageing-Associated Diseases (CECAD), Medical Faculty, University of Cologne, D-50931 Cologne, Germany.

In response to disturbed mitochondrial gene expression and protein synthesis, an adaptive transcriptional response sharing a signature of the integrated stress response (ISR) is activated. We report an intricate interplay between three transcription factors regulating the mitochondrial stress response: CHOP, C/EBPβ, and ATF4. We show that CHOP acts as a rheostat that attenuates prolonged ISR, prevents unfavorable metabolic alterations, and postpones the onset of mitochondrial cardiomyopathy. Upon mitochondrial dysfunction, CHOP interaction with C/EBPβ is needed to adjust ATF4 levels, thus preventing overactivation of the ATF4-regulated transcriptional program. Failure of this interaction switches ISR from an acute to a chronic state, leading to early respiratory chain deficiency, energy crisis, and premature death. Therefore, contrary to its previously proposed role as a transcriptional activator of mitochondrial unfolded protein response, our results highlight a role of CHOP in the fine-tuning of mitochondrial ISR in mammals.
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http://dx.doi.org/10.1126/sciadv.abf0971DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8153728PMC
May 2021

Cell size homeostasis is maintained by CDK4-dependent activation of p38 MAPK.

Dev Cell 2021 06 21;56(12):1756-1769.e7. Epub 2021 May 21.

Department of Molecular Genetics, University of Toronto, Toronto, ON M5G 1A8, Canada; Cell Biology, The Hospital for Sick Children, Toronto, ON M5G 0A4, Canada. Electronic address:

While molecules that promote the growth of animal cells have been identified, it remains unclear how such signals are orchestrated to determine a characteristic target size for different cell types. It is increasingly clear that cell size is determined by size checkpoints-mechanisms that restrict the cell cycle progression of cells that are smaller than their target size. Previously, we described a p38 MAPK-dependent cell size checkpoint mechanism whereby p38 is selectively activated and prevents cell cycle progression in cells that are smaller than a given target size. In this study, we show that the specific target size required for inactivation of p38 and transition through the cell cycle is determined by CDK4 activity. Our data suggest a model whereby p38 and CDK4 cooperate analogously to the function of a thermostat: while p38 senses irregularities in size, CDK4 corresponds to the thermostat dial that sets the target size.
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http://dx.doi.org/10.1016/j.devcel.2021.04.030DOI Listing
June 2021

The role of GSK3 in metabolic pathway perturbations in cancer.

Biochim Biophys Acta Mol Cell Res 2021 Jul 12;1868(8):119059. Epub 2021 May 12.

Lady Davis Institute for Medical Research, 3755 Chemin de la Côte-Sainte-Catherine, Montréal, QC H3T 1E2, Canada; Gerald Bronfman Department of Oncology, McGill University, 5100 Maisonneuve Blvd West, Montréal, QC H4A 3T2, Canada; Department of Medicine, Division of Experimental Medicine, McGill University, 1001 Décarie Blvd, Montréal, QC H4A 3J1, Canada; Department of Biochemistry, McGill University, 3655 Promenade Sir William Osler, Montréal, QC H3G 1Y6, Canada.

Malignant transformation and tumor progression are accompanied by significant perturbations in metabolic programs. As such, cancer cells support high ATP turnover to construct the building blocks needed to fuel neoplastic growth. The coordination of metabolic networks in malignant cells is dependent on the collaboration with cellular signaling pathways. Glycogen synthase kinase 3 (GSK3) lies at the convergence of several signaling axes, including the PI3K/AKT/mTOR, AMPK, and Wnt pathways, which influence cancer initiation, progression and therapeutic responses. Accordingly, GSK3 modulates metabolic processes, including protein and lipid synthesis, glucose and mitochondrial metabolism, as well as autophagy. In this review, we highlight current knowledge of the role of GSK3 in metabolic perturbations in cancer.
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http://dx.doi.org/10.1016/j.bbamcr.2021.119059DOI Listing
July 2021

Perturbations of cancer cell metabolism by the antidiabetic drug canagliflozin.

Neoplasia 2021 04 27;23(4):391-399. Epub 2021 Mar 27.

Department of Biochemistry, McGill University, Montréal, QC, Canada; Departments of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, ON, Canada; Ottawa Institute of Systems Biology, University of Ottawa, Ottawa, ON, Canada. Electronic address:

Notwithstanding that high rates of glucose uptake and glycolysis are common in neoplasia, pharmacological efforts to inhibit glucose utilization for cancer treatment have not been successful. Recent evidence suggests that in addition to classical glucose transporters, sodium-glucose transporters (SGLTs) are expressed by cancers. We therefore investigated the possibility that SGLT inhibitors, which are used in treatment of type 2 diabetes, may exert antineoplastic activity by limiting glucose uptake. We show that the SGLT2 inhibitor canagliflozin inhibits proliferation of breast cancer cells. Surprisingly, the antiproliferative effects of canagliflozin are not affected by glucose availability nor by the level of expression of SGLT2. Canagliflozin reduces oxygen consumption and glutamine metabolism through the citric acid cycle. The antiproliferative effects of canagliflozin are linked to inhibition of glutamine metabolism that fuels respiration, which represents a previously unanticipated mechanism of its potential antineoplastic action.
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http://dx.doi.org/10.1016/j.neo.2021.02.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8027095PMC
April 2021

Inhibiting the MNK1/2-eIF4E axis impairs melanoma phenotype switching and potentiates antitumor immune responses.

J Clin Invest 2021 04;131(8)

Lady Davis Institute, Jewish General Hospital, Montréal, Quebec, Canada.

Melanomas commonly undergo a phenotype switch, from a proliferative to an invasive state. Such tumor cell plasticity contributes to immunotherapy resistance; however, the mechanisms are not completely understood and thus are therapeutically unexploited. Using melanoma mouse models, we demonstrated that blocking the MNK1/2-eIF4E axis inhibited melanoma phenotype switching and sensitized melanoma to anti-PD-1 immunotherapy. We showed that phospho-eIF4E-deficient murine melanomas expressed high levels of melanocytic antigens, with similar results verified in patient melanomas. Mechanistically, we identified phospho-eIF4E-mediated translational control of NGFR, a critical effector of phenotype switching. Genetic ablation of phospho-eIF4E reprogrammed the immunosuppressive microenvironment, exemplified by lowered production of inflammatory factors, decreased PD-L1 expression on dendritic cells and myeloid-derived suppressor cells, and increased CD8+ T cell infiltrates. Finally, dual blockade of the MNK1/2-eIF4E axis and the PD-1/PD-L1 immune checkpoint demonstrated efficacy in multiple melanoma models regardless of their genomic classification. An increase in the presence of intratumoral stem-like TCF1+PD-1+CD8+ T cells, a characteristic essential for durable antitumor immunity, was detected in mice given a MNK1/2 inhibitor and anti-PD-1 therapy. Using MNK1/2 inhibitors to repress phospho-eIF4E thus offers a strategy to inhibit melanoma plasticity and improve response to anti-PD-1 immunotherapy.
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http://dx.doi.org/10.1172/JCI140752DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8262472PMC
April 2021

Cancer Plasticity: The Role of mRNA Translation.

Trends Cancer 2021 02 13;7(2):134-145. Epub 2020 Oct 13.

Department of Oncology, University of Alberta, Edmonton, AB, Canada; Department of Biomedical and Molecular Sciences, Queen's University, Kingston, ON, Canada. Electronic address:

Tumor progression is associated with dedifferentiated histopathologies concomitant with cancer cell survival within a changing, and often hostile, tumor microenvironment. These processes are enabled by cellular plasticity, whereby intracellular cues and extracellular signals are integrated to enable rapid shifts in cancer cell phenotypes. Cancer cell plasticity, at least in part, fuels tumor heterogeneity and facilitates metastasis and drug resistance. Protein synthesis is frequently dysregulated in cancer, and emerging data suggest that translational reprograming collaborates with epigenetic and metabolic programs to effectuate phenotypic plasticity of neoplasia. Herein, we discuss the potential role of mRNA translation in cancer cell plasticity, highlight emerging histopathological correlates, and deliberate on how this is related to efforts to improve understanding of the complex tumor ecology.
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http://dx.doi.org/10.1016/j.trecan.2020.09.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8023421PMC
February 2021

The mTORC1/S6K/PDCD4/eIF4A Axis Determines Outcome of Mitotic Arrest.

Cell Rep 2020 10;33(1):108230

Goodman Cancer Research Center, McGill University, Montréal, QC, Canada; Department of Biochemistry, McGill University, Montréal, QC, Canada. Electronic address:

mTOR is a serine/threonine kinase and a master regulator of cell growth and proliferation. Raptor, a scaffolding protein that recruits substrates to mTOR complex 1 (mTORC1), is known to be phosphorylated during mitosis, but the significance of this phosphorylation remains largely unknown. Here we show that raptor expression and mTORC1 activity are dramatically reduced in cells arrested in mitosis. Expression of a non-phosphorylatable raptor mutant reactivates mTORC1 and significantly reduces cytotoxicity of the mitotic poison Taxol. This effect is mediated via degradation of PDCD4, a tumor suppressor protein that inhibits eIF4A activity and is negatively regulated by the mTORC1/S6K pathway. Moreover, pharmacological inhibition of eIF4A is able to enhance the effects of Taxol and restore sensitivity in Taxol-resistant cancer cells. These findings indicate that the mTORC1/S6K/PDCD4/eIF4A axis has a pivotal role in the death versus slippage decision during mitotic arrest and may be exploited clinically to treat tumors resistant to anti-mitotic agents.
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http://dx.doi.org/10.1016/j.celrep.2020.108230DOI Listing
October 2020

Genome-Wide Screens Reveal that Resveratrol Induces Replicative Stress in Human Cells.

Mol Cell 2020 09 4;79(5):846-856.e8. Epub 2020 Aug 4.

Institute for Research in Immunology and Cancer, Université de Montréal, PO Box 6128, Downtown Station, Montréal, QC H3C 3J7, Canada. Electronic address:

Resveratrol is a natural product associated with wide-ranging effects in animal and cellular models, including lifespan extension. To identify the genetic target of resveratrol in human cells, we conducted genome-wide CRISPR-Cas9 screens to pinpoint genes that confer sensitivity or resistance to resveratrol. An extensive network of DNA damage response and replicative stress genes exhibited genetic interactions with resveratrol and its analog pterostilbene. These genetic profiles showed similarity to the response to hydroxyurea, an inhibitor of ribonucleotide reductase that causes replicative stress. Resveratrol, pterostilbene, and hydroxyurea caused similar depletion of nucleotide pools, inhibition of replication fork progression, and induction of replicative stress. The ability of resveratrol to inhibit cell proliferation and S phase transit was independent of the histone deacetylase sirtuin 1, which has been implicated in lifespan extension by resveratrol. These results establish that a primary impact of resveratrol on human cell proliferation is the induction of low-level replicative stress.
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http://dx.doi.org/10.1016/j.molcel.2020.07.010DOI Listing
September 2020

Copper bioavailability is a KRAS-specific vulnerability in colorectal cancer.

Nat Commun 2020 07 24;11(1):3701. Epub 2020 Jul 24.

Institute for Research in Immunology and Cancer (IRIC), Université de Montréal, Montreal, 2950, Chemin de la Polytechnique, Montréal, QC, H3T 1J4, Canada.

Despite its importance in human cancers, including colorectal cancers (CRC), oncogenic KRAS has been extremely challenging to target therapeutically. To identify potential vulnerabilities in KRAS-mutated CRC, we characterize the impact of oncogenic KRAS on the cell surface of intestinal epithelial cells. Here we show that oncogenic KRAS alters the expression of a myriad of cell-surface proteins implicated in diverse biological functions, and identify many potential surface-accessible therapeutic targets. Cell surface-based loss-of-function screens reveal that ATP7A, a copper-exporter upregulated by mutant KRAS, is essential for neoplastic growth. ATP7A is upregulated at the surface of KRAS-mutated CRC, and protects cells from excess copper-ion toxicity. We find that KRAS-mutated cells acquire copper via a non-canonical mechanism involving macropinocytosis, which appears to be required to support their growth. Together, these results indicate that copper bioavailability is a KRAS-selective vulnerability that could be exploited for the treatment of KRAS-mutated neoplasms.
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http://dx.doi.org/10.1038/s41467-020-17549-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7381612PMC
July 2020

PRDM15 is a key regulator of metabolism critical to sustain B-cell lymphomagenesis.

Nat Commun 2020 07 14;11(1):3520. Epub 2020 Jul 14.

Division of Cellular and Molecular Research, National Cancer Centre Singapore, Singapore, Singapore.

PRDM (PRDI-BF1 and RIZ homology domain containing) family members are sequence-specific transcriptional regulators involved in cell identity and fate determination, often dysregulated in cancer. The PRDM15 gene is of particular interest, given its low expression in adult tissues and its overexpression in B-cell lymphomas. Despite its well characterized role in stem cell biology and during early development, the role of PRDM15 in cancer remains obscure. Herein, we demonstrate that while PRDM15 is largely dispensable for mouse adult somatic cell homeostasis in vivo, it plays a critical role in B-cell lymphomagenesis. Mechanistically, PRDM15 regulates a transcriptional program that sustains the activity of the PI3K/AKT/mTOR pathway and glycolysis in B-cell lymphomas. Abrogation of PRDM15 induces a metabolic crisis and selective death of lymphoma cells. Collectively, our data demonstrate that PRDM15 fuels the metabolic requirement of B-cell lymphomas and validate it as an attractive and previously unrecognized target in oncology.
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http://dx.doi.org/10.1038/s41467-020-17064-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7360777PMC
July 2020

SPANX Control of Lamin A/C Modulates Nuclear Architecture and Promotes Melanoma Growth.

Mol Cancer Res 2020 10 22;18(10):1560-1573. Epub 2020 Jun 22.

Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California.

Mechanisms regulating nuclear organization control fundamental cellular processes, including the cell and chromatin organization. Their disorganization, including aberrant nuclear architecture, has been often implicated in cellular transformation. Here, we identify Lamin A, among proteins essential for nuclear architecture, as SPANX (sperm protein associated with the nucleus on the X chromosome), a cancer testis antigen previously linked to invasive tumor phenotypes, interacting protein in melanoma. SPANX interaction with Lamin A was mapped to the immunoglobulin fold-like domain, a region critical for Lamin A function, which is often mutated in laminopathies. SPANX downregulation in melanoma cell lines perturbed nuclear organization, decreased cell viability, and promoted senescence-associated phenotypes. Moreover, SPANX knockdown (KD) in melanoma cells promoted proliferation arrest, a phenotype mediated in part by IRF3/IL1A signaling. SPANX KD in melanoma cells also prompted the secretion of IL1A, which attenuated the proliferation of naïve melanoma cells. Identification of SPANX as a nuclear architecture complex component provides an unexpected insight into the regulation of Lamin A and its importance in melanoma. IMPLICATIONS: SPANX, a testis protein, interacts with LMNA and controls nuclear architecture and melanoma growth.
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http://dx.doi.org/10.1158/1541-7786.MCR-20-0291DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7541784PMC
October 2020

Translational control of breast cancer plasticity.

Nat Commun 2020 05 19;11(1):2498. Epub 2020 May 19.

Department of Oncology, University of Alberta, Edmonton, AB, Canada.

Plasticity of neoplasia, whereby cancer cells attain stem-cell-like properties, is required for disease progression and represents a major therapeutic challenge. We report that in breast cancer cells NANOG, SNAIL and NODAL transcripts manifest multiple isoforms characterized by different 5' Untranslated Regions (5'UTRs), whereby translation of a subset of these isoforms is stimulated under hypoxia. The accumulation of the corresponding proteins induces plasticity and "fate-switching" toward stem cell-like phenotypes. Mechanistically, we observe that mTOR inhibitors and chemotherapeutics induce translational activation of a subset of NANOG, SNAIL and NODAL mRNA isoforms akin to hypoxia, engendering stem-cell-like phenotypes. These effects are overcome with drugs that antagonize translational reprogramming caused by eIF2α phosphorylation (e.g. ISRIB), suggesting that the Integrated Stress Response drives breast cancer plasticity. Collectively, our findings reveal a mechanism of induction of plasticity of breast cancer cells and provide a molecular basis for therapeutic strategies aimed at overcoming drug resistance and abrogating metastasis.
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http://dx.doi.org/10.1038/s41467-020-16352-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7237473PMC
May 2020

Enhanced translation expands the endo-lysosome size and promotes antigen presentation during phagocyte activation.

PLoS Biol 2019 12 4;17(12):e3000535. Epub 2019 Dec 4.

Graduate Program in Molecular Science, Ryerson University, Toronto, Ontario, Canada.

The mechanisms that govern organelle adaptation and remodelling remain poorly defined. The endo-lysosomal system degrades cargo from various routes, including endocytosis, phagocytosis, and autophagy. For phagocytes, endosomes and lysosomes (endo-lysosomes) are kingpin organelles because they are essential to kill pathogens and process and present antigens. During phagocyte activation, endo-lysosomes undergo a morphological transformation, going from a collection of dozens of globular structures to a tubular network in a process that requires the phosphatidylinositol-3-kinase-AKT-mechanistic target of rapamycin (mTOR) signalling pathway. Here, we show that the endo-lysosomal system undergoes an expansion in volume and holding capacity during phagocyte activation within 2 h of lipopolysaccharides (LPS) stimulation. Endo-lysosomal expansion was paralleled by an increase in lysosomal protein levels, but this was unexpectedly largely independent of the transcription factor EB (TFEB) and transcription factor E3 (TFE3), which are known to scale up lysosome biogenesis. Instead, we demonstrate a hitherto unappreciated mechanism of acute organelle expansion via mTOR Complex 1 (mTORC1)-dependent increase in translation, which appears to be mediated by both S6Ks and 4E-BPs. Moreover, we show that stimulation of RAW 264.7 macrophage cell line with LPS alters translation of a subset but not all of mRNAs encoding endo-lysosomal proteins, thereby suggesting that endo-lysosome expansion is accompanied by functional remodelling. Importantly, mTORC1-dependent increase in translation activity was necessary for efficient and rapid antigen presentation by dendritic cells. Collectively, we identified a previously unknown and functionally relevant mechanism for endo-lysosome expansion that relies on mTORC1-dependent translation to stimulate endo-lysosome biogenesis in response to an infection signal.
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http://dx.doi.org/10.1371/journal.pbio.3000535DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6913987PMC
December 2019

Translational reprogramming marks adaptation to asparagine restriction in cancer.

Nat Cell Biol 2019 12 18;21(12):1590-1603. Epub 2019 Nov 18.

Tumor Initiation and Maintenance Program, Cancer Center, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, CA, USA.

While amino acid restriction remains an attractive strategy for cancer therapy, metabolic adaptations limit its effectiveness. Here we demonstrate a role of translational reprogramming in the survival of asparagine-restricted cancer cells. Asparagine limitation in melanoma and pancreatic cancer cells activates receptor tyrosine kinase-MAPK signalling as part of a feedforward mechanism involving mammalian target of rapamycin complex 1 (mTORC1)-dependent increase in MAPK-interacting kinase 1 (MNK1) and eukaryotic translation initiation factor 4E (eIF4E), resulting in enhanced translation of activating transcription factor 4 (ATF4) mRNA. MAPK inhibition attenuates translational induction of ATF4 and the expression of its target asparagine synthetase (ASNS), sensitizing melanoma and pancreatic tumours to asparagine restriction, reflected in inhibition of their growth. Correspondingly, low ASNS expression is among the top predictors of response to inhibitors of MAPK signalling in patients with melanoma and is associated with favourable prognosis when combined with low MAPK signalling activity. These studies reveal an axis of adaptation to asparagine deprivation and present a rationale for clinical evaluation of MAPK inhibitors in combination with asparagine restriction approaches.
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http://dx.doi.org/10.1038/s41556-019-0415-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7307327PMC
December 2019

RITA requires eIF2α-dependent modulation of mRNA translation for its anti-cancer activity.

Cell Death Dis 2019 11 7;10(11):845. Epub 2019 Nov 7.

Department of Onkology-Pathology, Science for Life Laboratories, Karolinska Institutet, Stockholm, Sweden.

Tumor protein 53 (p53, encoded by the TP53 gene) is a key tumor suppressor regulating cell fates in response to internal and external stresses. As TP53 is mutated or silenced in a majority of tumors, reactivation of p53 by small molecules represents a promising strategy in cancer therapeutics. One such agent is RITA (reactivation of p53 and induction of tumor cell apoptosis), which restores p53 expression in cells with hyperactive HDM2 and induces apoptosis. Yet, mechanisms underlying the anticancer activity of RITA are incompletely understood. Here we show that RITA suppresses mRNA translation independently of p53 by inducing eIF2α phosphorylation. Surprisingly, reactivation of p53 following RITA treatment is critically dependent on eIF2α phosphorylation. Moreover, inhibition of eIF2α phosphorylation attenuates pro-apoptotic and anti-neoplastic effects of RITA, while inducing phosphorylation of eIF2α enhances the anticancer activity of RITA. Collectively, these findings demonstrate that the translational machinery plays a major role in determining the antineoplastic activity of RITA, and suggest that combining p53 activators and translation modulators may be beneficial.
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http://dx.doi.org/10.1038/s41419-019-2074-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6838152PMC
November 2019

Translational offsetting as a mode of estrogen receptor α-dependent regulation of gene expression.

EMBO J 2019 12 26;38(23):e101323. Epub 2019 Sep 26.

Prostate Cancer Translational Research Laboratory, Peter MacCallum Cancer Centre, Melbourne, Vic., Australia.

Estrogen receptor alpha (ERα) activity is associated with increased cancer cell proliferation. Studies aiming to understand the impact of ERα on cancer-associated phenotypes have largely been limited to its transcriptional activity. Herein, we demonstrate that ERα coordinates its transcriptional output with selective modulation of mRNA translation. Importantly, translational perturbations caused by depletion of ERα largely manifest as "translational offsetting" of the transcriptome, whereby amounts of translated mRNAs and corresponding protein levels are maintained constant despite changes in mRNA abundance. Transcripts whose levels, but not polysome association, are reduced following ERα depletion lack features which limit translation efficiency including structured 5'UTRs and miRNA target sites. In contrast, mRNAs induced upon ERα depletion whose polysome association remains unaltered are enriched in codons requiring U34-modified tRNAs for efficient decoding. Consistently, ERα regulates levels of U34-modifying enzymes and thereby controls levels of U34-modified tRNAs. These findings unravel a hitherto unprecedented mechanism of ERα-dependent orchestration of transcriptional and translational programs that may be a pervasive mechanism of proteome maintenance in hormone-dependent cancers.
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http://dx.doi.org/10.15252/embj.2018101323DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6885737PMC
December 2019

mTOR as a central regulator of lifespan and aging.

F1000Res 2019 2;8. Epub 2019 Jul 2.

Département de Biochimie et Médecine Moléculaire, Université de Montréal, CP 6128, Succursale Centre-Ville, Montréal, QC, H3C 3J7, Canada.

The mammalian/mechanistic target of rapamycin (mTOR) is a key component of cellular metabolism that integrates nutrient sensing with cellular processes that fuel cell growth and proliferation. Although the involvement of the mTOR pathway in regulating life span and aging has been studied extensively in the last decade, the underpinning mechanisms remain elusive. In this review, we highlight the emerging insights that link mTOR to various processes related to aging, such as nutrient sensing, maintenance of proteostasis, autophagy, mitochondrial dysfunction, cellular senescence, and decline in stem cell function.
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http://dx.doi.org/10.12688/f1000research.17196.1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6611156PMC
June 2020

An ErbB2/c-Src axis links bioenergetics with PRC2 translation to drive epigenetic reprogramming and mammary tumorigenesis.

Nat Commun 2019 07 1;10(1):2901. Epub 2019 Jul 1.

Department of Physiology, Michigan State University, East Lansing, MI, 48824, USA.

Dysregulation of histone modifications promotes carcinogenesis by altering transcription. Breast cancers frequently overexpress the histone methyltransferase EZH2, the catalytic subunit of Polycomb Repressor Complex 2 (PRC2). However, the role of EZH2 in this setting is unclear due to the context-dependent functions of PRC2 and the heterogeneity of breast cancer. Moreover, the mechanisms underlying PRC2 overexpression in cancer are obscure. Here, using multiple models of breast cancer driven by the oncogene ErbB2, we show that the tyrosine kinase c-Src links energy sufficiency with PRC2 overexpression via control of mRNA translation. By stimulating mitochondrial ATP production, c-Src suppresses energy stress, permitting sustained activation of the mammalian/mechanistic target of rapamycin complex 1 (mTORC1), which increases the translation of mRNAs encoding the PRC2 subunits Ezh2 and Suz12. We show that Ezh2 overexpression and activity are pivotal in ErbB2-mediated mammary tumourigenesis. These results reveal the hitherto unknown c-Src/mTORC1/PRC2 axis, which is essential for ErbB2-driven carcinogenesis.
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http://dx.doi.org/10.1038/s41467-019-10681-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6603039PMC
July 2019

c-Myc steers translation in lymphoma.

J Exp Med 2019 07 17;216(7):1471-1473. Epub 2019 Jun 17.

Lady Davis Institute, Sir Mortimor B. Davis Jewish General Hospital, Montreal, Quebec, Canada

Members of the MYC family of oncogenes are master regulators of mRNA translation. In this issue of , Singh et al. (https://doi.org/10.1084/jem.20181726) demonstrate that c-Myc governs protein synthesis in lymphoma cells by interfering with SRSF1- and RBM42-mediated suppression of mRNA translation and by altering selection of translation initiation sites.
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http://dx.doi.org/10.1084/jem.20190721DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6605756PMC
July 2019

Generally applicable transcriptome-wide analysis of translation using anota2seq.

Nucleic Acids Res 2019 07;47(12):e70

Department of Oncology-Pathology, Science for Life Laboratory, Karolinska Institutet, Stockholm, Sweden.

mRNA translation plays an evolutionarily conserved role in homeostasis and when dysregulated contributes to various disorders including metabolic and neurological diseases and cancer. Notwithstanding that optimal and universally applicable methods are critical for understanding the complex role of translational control under physiological and pathological conditions, approaches to analyze translatomes are largely underdeveloped. To address this, we developed the anota2seq algorithm which outperforms current methods for statistical identification of changes in translation. Notably, in contrast to available analytical methods, anota2seq also allows specific identification of an underappreciated mode of gene expression regulation whereby translation acts as a buffering mechanism which maintains protein levels despite fluctuations in corresponding mRNA abundance ('translational buffering'). Thus, the universal anota2seq algorithm allows efficient and hitherto unprecedented interrogation of translatomes which is anticipated to advance knowledge regarding the role of translation in homeostasis and disease.
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http://dx.doi.org/10.1093/nar/gkz223DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6614820PMC
July 2019

Hepatic posttranscriptional network comprised of CCR4-NOT deadenylase and FGF21 maintains systemic metabolic homeostasis.

Proc Natl Acad Sci U S A 2019 04 29;116(16):7973-7981. Epub 2019 Mar 29.

Department of Biochemistry, McGill University, Montreal, QC H3A 1A3, Canada;

Whole-body metabolic homeostasis is tightly controlled by hormone-like factors with systemic or paracrine effects that are derived from nonendocrine organs, including adipose tissue (adipokines) and liver (hepatokines). Fibroblast growth factor 21 (FGF21) is a hormone-like protein, which is emerging as a major regulator of whole-body metabolism and has therapeutic potential for treating metabolic syndrome. However, the mechanisms that control FGF21 levels are not fully understood. Herein, we demonstrate that FGF21 production in the liver is regulated via a posttranscriptional network consisting of the CCR4-NOT deadenylase complex and RNA-binding protein tristetraprolin (TTP). In response to nutrient uptake, CCR4-NOT cooperates with TTP to degrade AU-rich mRNAs that encode pivotal metabolic regulators, including FGF21. Disruption of CCR4-NOT activity in the liver, by deletion of the catalytic subunit CNOT6L, increases serum FGF21 levels, which ameliorates diet-induced metabolic disorders and enhances energy expenditure without disrupting bone homeostasis. Taken together, our study describes a hepatic CCR4-NOT/FGF21 axis as a hitherto unrecognized systemic regulator of metabolism and suggests that hepatic CCR4-NOT may serve as a target for devising therapeutic strategies in metabolic syndrome and related morbidities.
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http://dx.doi.org/10.1073/pnas.1816023116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6475422PMC
April 2019

METTL13 Methylation of eEF1A Increases Translational Output to Promote Tumorigenesis.

Cell 2019 01 3;176(3):491-504.e21. Epub 2019 Jan 3.

Department of Biology, Stanford University, Stanford, CA 94305, USA. Electronic address:

Increased protein synthesis plays an etiologic role in diverse cancers. Here, we demonstrate that METTL13 (methyltransferase-like 13) dimethylation of eEF1A (eukaryotic elongation factor 1A) lysine 55 (eEF1AK55me2) is utilized by Ras-driven cancers to increase translational output and promote tumorigenesis in vivo. METTL13-catalyzed eEF1A methylation increases eEF1A's intrinsic GTPase activity in vitro and protein production in cells. METTL13 and eEF1AK55me2 levels are upregulated in cancer and negatively correlate with pancreatic and lung cancer patient survival. METTL13 deletion and eEF1AK55me2 loss dramatically reduce Ras-driven neoplastic growth in mouse models and in patient-derived xenografts (PDXs) from primary pancreatic and lung tumors. Finally, METTL13 depletion renders PDX tumors hypersensitive to drugs that target growth-signaling pathways. Together, our work uncovers a mechanism by which lethal cancers become dependent on the METTL13-eEF1AK55me2 axis to meet their elevated protein synthesis requirement and suggests that METTL13 inhibition may constitute a targetable vulnerability of tumors driven by aberrant Ras signaling.
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http://dx.doi.org/10.1016/j.cell.2018.11.038DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6499081PMC
January 2019

Translational and HIF-1α-Dependent Metabolic Reprogramming Underpin Metabolic Plasticity and Responses to Kinase Inhibitors and Biguanides.

Cell Metab 2018 12 20;28(6):817-832.e8. Epub 2018 Sep 20.

Lady Davis Institute, SMBD JGH, McGill University, Montreal, QC H3A 1A3, Canada; Gerald Bronfman Department of Oncology, McGill University, Montreal, QC H3A 1A3, Canada; Department of Biochemistry, McGill University, Montreal, QC H3A 1A3, Canada; Department of Experimental Medicine, McGill University, Montreal, QC H3A 1A3, Canada. Electronic address:

There is increasing interest in therapeutically exploiting metabolic differences between normal and cancer cells. We show that kinase inhibitors (KIs) and biguanides synergistically and selectively target a variety of cancer cells. Synthesis of non-essential amino acids (NEAAs) aspartate, asparagine, and serine, as well as glutamine metabolism, are major determinants of the efficacy of KI/biguanide combinations. The mTORC1/4E-BP axis regulates aspartate, asparagine, and serine synthesis by modulating mRNA translation, while ablation of 4E-BP1/2 substantially decreases sensitivity of breast cancer and melanoma cells to KI/biguanide combinations. Efficacy of the KI/biguanide combinations is also determined by HIF-1α-dependent perturbations in glutamine metabolism, which were observed in VHL-deficient renal cancer cells. This suggests that cancer cells display metabolic plasticity by engaging non-redundant adaptive mechanisms, which allows them to survive therapeutic insults that target cancer metabolism.
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http://dx.doi.org/10.1016/j.cmet.2018.09.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7252493PMC
December 2018
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