As tuberculosis (TB) toll is revised upward according to the WHO's last estimates, the lack of vaccine strategy and the lengthy antibiotic treatments that unfortunately promote the emergence of drug resistance are a major set back in the fight against this pathogen. In this issue of EMBO Molecular Medicine, Schiebler et al (Mtb) propose a novel and compelling new approach to target Mycobacterium tuberculosis (Mtb) by pharmacologically stimulating intracellular mycobacteria clearance through autophagy.
Mycobacterium tuberculosis (MTB) remains a major challenge to global health made worse by the spread of multidrug resistance. We therefore examined whether stimulating intracellular killing of mycobacteria through pharmacological enhancement of macroautophagy might provide a novel therapeutic strategy. Despite the resistance of MTB to killing by basal autophagy, cell-based screening of FDA-approved drugs revealed two anticonvulsants, carbamazepine and valproic acid, that were able to stimulate autophagic killing of intracellular M. tuberculosis within primary human macrophages at concentrations achievable in humans. Using a zebrafish model, we show that carbamazepine can stimulate autophagy in vivo and enhance clearance of M. marinum, while in mice infected with a highly virulent multidrug-resistant MTB strain, carbamazepine treatment reduced bacterial burden, improved lung pathology and stimulated adaptive immunity. We show that carbamazepine induces antimicrobial autophagy through a novel, evolutionarily conserved, mTOR-independent pathway controlled by cellular depletion of myo-inositol. While strain-specific differences in susceptibility to in vivo carbamazepine treatment may exist, autophagy enhancement by repurposed drugs provides an easily implementable potential therapy for the treatment of multidrug-resistant mycobacterial infection.
autophagy; multidrug-resistant; myo-inositol; tuberculosis
Immunoparalysis is an important pathological mechanism in sepsis. However, an effective small molecule therapy is lacking. Here, we show that ouabain, a Na+,K+-ATPase ligand, can reverse immunoparalysis in vitro, in vivo, and in clinical samples. Notably, the effect of ouabain was critically dependent on TNF-α expression. However, ouabain had opposing effects on the stability of TNF-α mRNA: Ouabain triggered miR-181 transcription, which promoted TNF-α mRNA degradation and induced immunoparalysis, and ouabain triggered the nuclear export of human antigen R (HuR), which stabilized TNF-α mRNA and suppressed immuno-paralysis. Interestingly, because the miR-181 binding site is located within the HuR binding site in the 3′-untranslated region of TNF-α, in ouabain-treated cells, HuR competed with miR-181 for binding to TNF-α mRNA and recruited TNF-α mRNA to stress granules, thereby stabilizing TNF-α mRNA and reversing immunoparalysis. Ouabain also induced GM-CSF and interferon-γ expression in a HuR-dependent manner. Hence, the fine-tuning of TNF-α mRNA stability by HuR and miR181 plays a crucial role in immunoparalysis, and Na+,K+-ATPase ligands are promising agents for immunoparalysis therapy.
human antigen R; immunoparalysis; microRNA181; ouabain; tumor necrosis factor α
Metabolite accumulation in lysosomal storage disorders (LSDs) results in impaired cell function and multi-systemic disease. Although substrate reduction and lysosomal overload-decreasing therapies can ameliorate disease progression, the significance of lysosomal overload-independent mechanisms in the development of cellular dysfunction is unknown for most LSDs. Here, we identify a mechanism of impaired chaperone-mediated autophagy (CMA) in cystinosis, a LSD caused by defects in the cystine transporter cystinosin (CTNS) and characterized by cystine lysosomal accumulation. We show that, different from other LSDs, autophagosome number is increased, but macroautophagic flux is not impaired in cystinosis while mTOR activity is not affected. Conversely, the expression and localization of the CMA receptor LAMP2A are abnormal in CTNS-deficient cells and degradation of the CMA substrate GAPDH is defective in Ctns−/− mice. Importantly, cysteamine treatment, despite decreasing lysosomal overload, did not correct defective CMA in Ctns−/− mice or LAMP2A mislocalization in cystinotic cells, which was rescued by CTNS expression instead, suggesting that cystinosin is important for CMA activity. In conclusion, CMA impairment contributes to cell malfunction in cystinosis, highlighting the need for treatments complementary to current therapies that are based on decreasing lysosomal overload.
autophagy; CTNS; cystinosis; lysosomal storage disorder; lysosomal trafficking
The β-site amyloid precursor protein cleaving enzyme-1 (BACE1), an essential protease for the generation of amyloid-β (Aβ) peptide, is a major drug target for Alzheimer's disease (AD). However, there is a concern that inhibiting BACE1 could also affect several physiological functions. Here, we show that BACE1 is modified with bisecting N-acetylglucosamine (GlcNAc), a sugar modification highly expressed in brain, and demonstrate that AD patients have higher levels of bisecting GlcNAc on BACE1. Analysis of knockout mice lacking the biosynthetic enzyme for bisecting GlcNAc, GnT-III (Mgat3), revealed that cleavage of Aβ-precursor protein (APP) by BACE1 is reduced in these mice, resulting in a decrease in Aβ plaques and improved cognitive function. The lack of this modification directs BACE1 to late endosomes/lysosomes where it is less colocalized with APP, leading to accelerated lysosomal degradation. Notably, other BACE1 substrates, CHL1 and contactin-2, are normally cleaved in GnT-III-deficient mice, suggesting that the effect of bisecting GlcNAc on BACE1 is selective to APP. Considering that GnT-III-deficient mice remain healthy, GnT-III may be a novel and promising drug target for AD therapeutics.
Alzheimer's disease (AD); amyloid-β (Aβ); BACE1; bisecting GlcNAc; GnT-III (Mgat3)
Alzheimer's disease (AD) is associated with peripheral metabolic disorders. Clinical/epidemiological data indicate increased risk of diabetes in AD patients. Here, we show that intracerebroventricular infusion of AD-associated Aβ oligomers (AβOs) in mice triggered peripheral glucose intolerance, a phenomenon further verified in two transgenic mouse models of AD. Systemically injected AβOs failed to induce glucose intolerance, suggesting AβOs target brain regions involved in peripheral metabolic control. Accordingly, we show that AβOs affected hypothalamic neurons in culture, inducing eukaryotic translation initiation factor 2α phosphorylation (eIF2α-P). AβOs further induced eIF2α-P and activated pro-inflammatory IKKβ/NF-κB signaling in the hypothalamus of mice and macaques. AβOs failed to trigger peripheral glucose intolerance in tumor necrosis factor-α (TNF-α) receptor 1 knockout mice. Pharmacological inhibition of brain inflammation and endoplasmic reticulum stress prevented glucose intolerance in mice, indicating that AβOs act via a central route to affect peripheral glucose homeostasis. While the hypothalamus has been largely ignored in the AD field, our findings indicate that AβOs affect this brain region and reveal novel shared molecular mechanisms between hypothalamic dysfunction in metabolic disorders and AD.
Alzheimer's disease; ER stress; hypothalamus; inflammation; insulin resistance
Physiologically, the retinal pigment epithelium (RPE) expresses immunosuppressive signals such as FAS ligand (FASL), which prevents the accumulation of leukocytes in the subretinal space. Age-related macular degeneration (AMD) is associated with a breakdown of the subretinal immunosuppressive environment and chronic accumulation of mononuclear phagocytes (MPs). We show that subretinal MPs in AMD patients accumulate on the RPE and express high levels of APOE. MPs of Cx3cr1−/− mice that develop MP accumulation on the RPE, photoreceptor degeneration, and increased choroidal neovascularization similarly express high levels of APOE. ApoE deletion in Cx3cr1−/− mice prevents pathogenic age- and stress-induced subretinal MP accumulation. We demonstrate that increased APOE levels induce IL-6 in MPs via the activation of the TLR2-CD14-dependent innate immunity receptor cluster. IL-6 in turn represses RPE FasL expression and prolongs subretinal MP survival. This mechanism may account, in part, for the MP accumulation observed in Cx3cr1−/− mice. Our results underline the inflammatory role of APOE in sterile inflammation in the immunosuppressive subretinal space. They provide rationale for the implication of IL-6 in AMD and open avenues toward therapies inhibiting pathogenic chronic inflammation in late AMD.
age-related macular degeneration; apolipoprotein E; interleukin 6; mononuclear phagocyte; neuroinflammation
Cancer metastasis is the main cause of cancer-related death, and dissemination of tumor cells through the blood circulation is an important intermediate step that also exemplifies the switch from localized to systemic disease. Early detection and characterization of circulating tumor cells (CTCs) is therefore important as a general strategy to monitor and prevent the development of overt metastatic disease. Furthermore, sequential analysis of CTCs can provide clinically relevant information on the effectiveness and progression of systemic therapies (e.g., chemo-, hormonal, or targeted therapies with antibodies or small inhibitors). Although many advances have been made regarding the detection and molecular characterization of CTCs, several challenges still exist that limit the current use of this important diagnostic approach. In this review, we discuss the biology of tumor cell dissemination, technical advances, as well as the challenges and potential clinical implications of CTC detection and characterization.
Disseminating tumor cells (DTC); EMT; metastasis; tumor cell dormancy; tumor cell plasticity
Discovery and translational research has led to the identification of a series of “cancer drivers”—genes that, when mutated or otherwise misregulated, can drive malignancy. An increasing number of drugs that directly target such drivers have demonstrated activity in clinical trials and are shaping a new landscape for molecularly targeted cancer therapies. Such therapies rely on molecular and genetic diagnostic tests to detect the presence of a biomarker that predicts response. Here, we highlight some of the key discoveries bringing precision oncology to cancer patients. Large-scale “omics” approaches as well as modern, hypothesis-driven science in both academic and industry settings have significantly contributed to the field. Based on these insights, we discuss current challenges and how to foster future biomedical innovation in cancer drug discovery and development.
The severe Ebola virus disease epidemic occurring in West Africa stems from a single zoonotic transmission event to a 2-year-old boy in Meliandou, Guinea. We investigated the zoonotic origins of the epidemic using wildlife surveys, interviews, and molecular analyses of bat and environmental samples. We found no evidence for a concurrent outbreak in larger wildlife. Exposure to fruit bats is common in the region, but the index case may have been infected by playing in a hollow tree housing a colony of insectivorous free-tailed bats (Mops condylurus). Bats in this family have previously been discussed as potential sources for Ebola virus outbreaks, and experimental data have shown that this species can survive experimental infection. These analyses expand the range of possible Ebola virus sources to include insectivorous bats and reiterate the importance of broader sampling efforts for understanding Ebola virus ecology.
bat; Ebola; West Africa; wildlife; zoonosis
RNA-sensing toll-like receptors (TLRs) mediate innate immunity and regulate anti-viral response. We show here that TLR3 regulates host immunity and the loss of TLR3 aggravates pathology in Chikungunya virus (CHIKV) infection. Susceptibility to CHIKV infection is markedly increased in human and mouse fibroblasts with defective TLR3 signaling. Up to 100-fold increase in CHIKV load was observed in Tlr3−/− mice, alongside increased virus dissemination and pro-inflammatory myeloid cells infiltration. Infection in bone marrow chimeric mice showed that TLR3-expressing hematopoietic cells are required for effective CHIKV clearance. CHIKV-specific antibodies from Tlr3−/− mice exhibited significantly lower in vitro neutralization capacity, due to altered virus-neutralizing epitope specificity. Finally, SNP genotyping analysis of CHIKF patients on TLR3 identified SNP rs6552950 to be associated with disease severity and CHIKV-specific neutralizing antibody response. These results demonstrate a key role for TLR3-mediated antibody response to CHIKV infection, virus replication and pathology, providing a basis for future development of immunotherapeutics in vaccine development.
Chikungunya virus; innate immunity; joint inflammation; neutralizing antibodies; TLR3
Cutaneous atrophy is the major adverse effect of topical glucocorticoids; however, its molecular mechanisms are poorly understood. Here, we identify stress-inducible mTOR inhibitor REDD1 (regulated in development and DNA damage response 1) as a major molecular target of glucocorticoids, which mediates cutaneous atrophy. In REDD1 knockout (KO) mice, all skin compartments (epidermis, dermis, subcutaneous fat), epidermal stem, and progenitor cells were protected from atrophic effects of glucocorticoids. Moreover, REDD1 knockdown resulted in similar consequences in organotypic raft cultures of primary human keratinocytes. Expression profiling revealed that gene activation by glucocorticoids was strongly altered in REDD1 KO epidermis. In contrast, the down-regulation of genes involved in anti-inflammatory glucocorticoid response was strikingly similar in wild-type and REDD1 KO mice. Integrative bioinformatics analysis of our and published gene array data revealed similar changes of gene expression in epidermis and in muscle undergoing glucocorticoid-dependent and glucocorticoid-independent atrophy. Importantly, the lack of REDD1 did not diminish the anti-inflammatory effects of glucocorticoids in preclinical model. Our findings suggest that combining steroids with REDD1 inhibitors may yield a novel, safer glucocorticoid-based therapies.
glucocorticoid; glucocorticoid receptor; mTOR; REDD1; skin atrophy
The evolutionarily conserved IGF-1 signalling pathway is associated with longevity, metabolism, tissue homeostasis, and cancer progression. Its regulation relies on the delicate balance between activating kinases and suppressing phosphatases and is still not very well understood. We report here that IGF-1 signalling in vitro and in a murine ageing model in vivo is suppressed in response to accumulation of superoxide anions () in mitochondria, either by chemical inhibition of complex I or by genetic silencing of -dismutating mitochondrial Sod2. The -dependent suppression of IGF-1 signalling resulted in decreased proliferation of murine dermal fibroblasts, affected translation initiation factors and suppressed the expression of α1(I), α1(III), and α2(I) collagen, the hallmarks of skin ageing. Enhanced led to activation of the phosphatases PTP1B and PTEN, which via dephosphorylation of the IGF-1 receptor and phosphatidylinositol 3,4,5-triphosphate dampened IGF-1 signalling. Genetic and pharmacologic inhibition of PTP1B and PTEN abrogated -induced IGF-1 resistance and rescued the ageing skin phenotype. We thus identify previously unreported signature events with , PTP1B, and PTEN as promising targets for drug development to prevent IGF-1 resistance-related pathologies.
ageing; IGF-1; phosphatase; reactive oxygen species; superoxide anions
Mutant ataxin-1 (Atxn1), which causes spinocerebellar ataxia type 1 (SCA1), binds to and impairs the function of high-mobility group box 1 (HMGB1), a crucial nuclear protein that regulates DNA architectural changes essential for DNA damage repair and transcription. In this study, we established that transgenic or virus vector-mediated complementation with HMGB1 ameliorates motor dysfunction and prolongs lifespan in mutant Atxn1 knock-in (Atxn1-KI) mice. We identified mitochondrial DNA damage repair by HMGB1 as a novel molecular basis for this effect, in addition to the mechanisms already associated with HMGB1 function, such as nuclear DNA damage repair and nuclear transcription. The dysfunction and the improvement of mitochondrial DNA damage repair functions are tightly associated with the exacerbation and rescue, respectively, of symptoms, supporting the involvement of mitochondrial DNA quality control by HMGB1 in SCA1 pathology. Moreover, we show that the rescue of Purkinje cell dendrites and dendritic spines by HMGB1 could be downstream effects. Although extracellular HMGB1 triggers inflammation mediated by Toll-like receptor and receptor for advanced glycation end products, upregulation of intracellular HMGB1 does not induce such side effects. Thus, viral delivery of HMGB1 is a candidate approach by which to modify the disease progression of SCA1 even after the onset.
AAV; DNA damage repair; HMGB1; mitochondria; SCA1
Peritoneal dialysis (PD) is a form of renal replacement therapy whose repeated use can alter dialytic function through induction of epithelial–mesenchymal transition (EMT) and fibrosis, eventually leading to PD discontinuation. The peritoneum from Cav1−/− mice showed increased EMT, thickness, and fibrosis. Exposure of Cav1−/− mice to PD fluids further increased peritoneal membrane thickness, altered permeability, and increased the number of FSP-1/cytokeratin-positive cells invading the sub-mesothelial stroma. High-throughput quantitative proteomics revealed increased abundance of collagens, FN, and laminin, as well as proteins related to TGF-β activity in matrices derived from Cav1−/− cells. Lack of Cav1 was associated with hyperactivation of a MEK-ERK1/2-Snail-1 pathway that regulated the Smad2-3/Smad1-5-8 balance. Pharmacological blockade of MEK rescued E-cadherin and ZO-1 inter-cellular junction localization, reduced fibrosis, and restored peritoneal function in Cav1−/− mice. Moreover, treatment of human PD-patient-derived MCs with drugs increasing Cav1 levels, as well as ectopic Cav1 expression, induced re-acquisition of epithelial features. This study demonstrates a pivotal role of Cav1 in the balance of epithelial versus mesenchymal state and suggests targets for the prevention of fibrosis during PD.
caveolin-1; epithelial–mesenchymal transition; fibrosis; MEK-ERK1/2 pathway; peritoneal dialysis
MYC family oncoproteins (MYC, N-MYC and L-MYC) function as basic helix-loop-helix-leucine zipper
(bHLH-Zip) transcription factors that are activated (i.e., overexpressed) in well over half of all
human malignancies (Boxer & Dang, 2001; Beroukhim
et al, 2010). In this issue of
EMBO Molecular Medicine, Eilers and colleagues (Peter
et al, 2014) describe a novel
approach to disable MYC, whereby inhibition of the ubiquitin ligase HUWE1 stabilizes MIZ1 and leads
to the selective repression of MYC-activated target genes.
See also: S Peter et al (December 2014)
Extensive efforts have now characterized the somatic molecular alterations in human breast cancer (Cancer Genome Atlas Network, 2012; Stephens et al, 2012) and have led to a re-definition of the disease as a constellation of 10 distinct driver-based subtypes (IntClust subtypes) (Curtis et al, 2012). The pursuit of druggable targets for each of these subtypes is now pressing. This is elegantly illustrated by the work of Liu et al (2014).
Anti-angiogenic drugs are approved for the treatment of several cancer types, generally in the
inoperable locally advanced or metastatic setting and in combination with other anti-cancer agents.
Recent clinical studies also suggest that anti-angiogenic drugs can be useful in the pre-operative
(neoadjuvant) setting, by facilitating the shrinkage of the primary tumour and its surgical
resection. However, the effects of neoadjuvant anti-angiogenic therapy on the ability of tumours to
form distant metastases are unclear. In this issue of EMBO Molecular
Medicine, Ebos et al (2014)
present carefully performed pre-clinical studies in mice that analyse the effects of pre-operative
anti-angiogenic therapy on tumour metastasis and survival.
In this issue of EMBO Molecular Medicine, Bhuvanagiri
et al report on a chemical means to convert molecular junk into gold. They
identify a chemical inhibitor of a quality control pathway that is best known for its ability to
clear cells of rubbish, but that in certain cases can be detrimental because it eliminates
“useful” garbage. The chemical inhibitor identified by Bhuvanagiri
et al perturbs Nonsense-Mediated RNA Decay (NMD), a RNA surveillance pathway
that targets mRNAs harboring premature termination codons (PTCs) for degradation (Kervestin &
Increasing evidence suggests that the heart controls the metabolism of peripheral organs. Olson
and colleagues previously demonstrated that miR-208a controls systemic energy homeostasis through
the regulation of MED13 in cardiomyocytes (Grueter et al, 2012). In their follow-up study in this issue of EMBO
Molecular Medicine, white adipose tissue (WAT) and liver are identified as the
physiological targets of cardiac MED13 signaling, most likely through cardiac-derived circulating
factors, which boost energy consumption by upregulating metabolic gene expression and
increasing mitochondrial numbers (Baskin et al, 2014). In turn, increased energy expenditure in WAT and the liver confers leanness.
These findings strengthen the evidence of metabolic crosstalk between the heart and peripheral
tissues through cardiokines and also set the stage for the development of novel treatments for
Deregulated expression of MYC is a driver of colorectal carcinogenesis, necessitating novel
strategies to inhibit MYC function. The ubiquitin ligase HUWE1 (HECTH9, ARF-BP1, MULE) associates
with both MYC and the MYC-associated protein MIZ1. We show here that HUWE1 is required for growth of
colorectal cancer cells in culture and in orthotopic xenograft models. Using high-throughput
screening, we identify small molecule inhibitors of HUWE1, which inhibit MYC-dependent
transactivation in colorectal cancer cells, but not in stem and normal colon epithelial cells.
Inhibition of HUWE1 stabilizes MIZ1. MIZ1 globally accumulates on MYC target genes and contributes
to repression of MYC-activated target genes upon HUWE1 inhibition. Our data show that
transcriptional activation by MYC in colon cancer cells requires the continuous degradation of MIZ1
and identify a novel principle that allows for inhibition of MYC function in tumor cells.
See also: FX Schaub & JL Cleveland (December 2014)
colorectal cancer; HUWE1; MIZ1; MYC; ubiquitination
The tumor suppressors Pten and p53 are frequently lost in breast cancer, yet the consequences of
their combined inactivation are poorly understood. Here, we show that mammary-specific deletion of
Pten via WAP-Cre, which targets alveolar progenitors, induced tumors with shortened latency compared
to those induced by MMTV-Cre, which targets basal/luminal progenitors. Combined Pten-p53 mutations
accelerated formation of claudin-low, triple-negative-like breast cancer (TNBC) that exhibited
hyper-activated AKT signaling and more mesenchymal features relative to Pten or p53 single-mutant
tumors. Twenty-four genes that were significantly and differentially expressed between
WAP-Cre:Pten/p53 and MMTV-Cre:Pten/p53 tumors predicted poor survival for claudin-low patients.
Kinome screens identified eukaryotic elongation factor-2 kinase (eEF2K) inhibitors as more potent
than PI3K/AKT/mTOR inhibitors on both mouse and human Pten/p53-deficient TNBC cells. Sensitivity to
eEF2K inhibition correlated with AKT pathway activity. eEF2K monotherapy suppressed growth of
Pten/p53-deficient TNBC xenografts in vivo and cooperated with doxorubicin to
efficiently kill tumor cells in vitro. Our results identify a prognostic signature
for claudin-low patients and provide a rationale for using eEF2K inhibitors for treatment of TNBC
with elevated AKT signaling.
eEF2K; p53; prognosis; Pten; triple-negative breast cancer
Thousands of cancer patients are currently in clinical trials evaluating antiangiogenic therapy
in the neoadjuvant setting, which is the treatment of localized primary tumors prior to surgical
intervention. The rationale is that shrinking a tumor will improve surgical outcomes and minimize
growth of occult micrometastatic disease—thus delaying post-surgical recurrence and improving
survival. But approved VEGF pathway inhibitors have not been tested in clinically relevant
neoadjuvant models that compare pre- and post-surgical treatment effects. Using mouse models of
breast, kidney, and melanoma metastasis, we demonstrate that primary tumor responses to neoadjuvant
VEGFR TKI treatment do not consistently correlate with improved post-surgical survival, with
survival worsened in certain settings. Similar negative effects did not extend to protein-based VEGF
pathway inhibitors and could be reversed with altered dose, surgical timing, and treatment duration,
or when VEGFR TKIs are combined with metronomic ‘anti-metastatic’ chemotherapy
regimens. These studies represent the first attempt to recapitulate the complex clinical parameters
of neoadjuvant therapy in mice and identify a novel tool to compare systemic antiangiogenic
treatment effects on localized and disseminated disease.
antibodies; neoadjuvant; surgery; tyrosine kinase inhibitors; VEGF
Mutations of the von Hippel–Lindau (VHL) gene are associated with pheochromocytomas and paragangliomas, but the role of VHL in sympathoadrenal homeostasis is unknown. We generated mice lacking Vhl in catecholaminergic cells. They exhibited atrophy of the carotid body (CB), adrenal medulla, and sympathetic ganglia. Vhl-null animals had an increased number of adult CB stem cells, although the survival of newly generated neuron-like glomus cells was severely compromised. The effects of Vhl deficiency were neither prevented by pharmacological inhibition of prolyl hydroxylases or selective genetic down-regulation of prolyl hydroxylase-3, nor phenocopied by hypoxia inducible factor overexpression. Vhl-deficient animals appeared normal in normoxia but survived for only a few days in hypoxia, presenting with pronounced erythrocytosis, pulmonary edema, and right cardiac hypertrophy. Therefore, in the normal sympathoadrenal setting, Vhl deletion does not give rise to tumors but impairs development and plasticity of the peripheral O2-sensing system required for survival in hypoxic conditions.
adult carotid body neurogenesis; intolerance to hypoxia; sympathoadrenal tumorigenesis; Vhl-deficient mouse model; von Hippel–Lindau protein
Nonsense-mediated RNA decay (NMD) is an RNA-based quality control mechanism that eliminates
transcripts bearing premature translation termination codons (PTC). Approximately, one-third of all
inherited disorders and some forms of cancer are caused by nonsense or frame shift mutations that
introduce PTCs, and NMD can modulate the clinical phenotype of these diseases. 5-azacytidine is an
analogue of the naturally occurring pyrimidine nucleoside cytidine, which is approved for the
treatment of myelodysplastic syndrome and myeloid leukemia. Here, we reveal that 5-azacytidine
inhibits NMD in a dose-dependent fashion specifically upregulating the expression of both
PTC-containing mutant and cellular NMD targets. Moreover, this activity of 5-azacytidine depends on
the induction of MYC expression, thus providing a link between the effect of this drug and one of
the key cellular pathways that are known to affect NMD activity. Furthermore, the effective
concentration of 5-azacytidine in cells corresponds to drug levels used in patients, qualifying
5-azacytidine as a candidate drug that could potentially be repurposed for the treatment of
Mendelian and acquired genetic diseases that are caused by PTC mutations.
5-azacytidine; MYC; nonsense-mediated decay; premature termination codons