Biology subjects

Majzoub, K.

Publications and source records attributed to Majzoub, K..

8 recordsLinked to original sources

bioRxiv2026

The RLR-MAVS-IRF3 axis activates the IFN pathway to restrict Tonate virus (TONV) infection

Tonate virus (TONV) is a neglected mosquito-borne alphavirus of the Venezuelan equine encephalitis complex associated with febrile illness, encephalitis, and fetal central nervous system abnormalities. Yet, host pathways that sense TONV infection and restrict its replication remain poorly defined. Here, we investigated the interaction between TONV and the type I interferon (IFN-I) system in human cells. We show that TONV infection led to the accumulation of cytosolic double-stranded RNA and a robust IFN response. RIG-I and MDA5 depletion as well as that of MAVS and IRF3 strongly reduced TONV-induced IFN response. Disruption of RIG-I, MDA5, MAVS, or IRF3 resulted in an increase of dsRNA-positive cells and a higher viral RNA accumulation. Finally, we found that treatment with exogenous IFN-I strongly inhibits TONV replication reducing both viral RNA loads and infectious particle production. Thus, together, our results identify the RIG-I/MDA5-MAVS-IRF3 axis as a major pathway sensing TONV infection and establishing an IFN-I-dependent antiviral state, providing the first molecular characterization of TONV innate immune sensing in human cells.

immunology↗

bioRxiv2025

Deltaviruses spread through a viral Trojan Horse

Hepatitis D-like viral satellites, known as deltaviruses, have been recently discovered in a wide range of animals. These viruses are thought to expropriate glycoproteins from helper viruses to form infectious particles. Here, we challenge this paradigm and demonstrate that deltaviruses are packaged within helper virus particles, using them as viral Trojan Horses for cell entry. By leveraging orthogonal electronic and photonic super-resolution microscopy, we visualize deltaviruses enclosed within virions from rhabdo-, herpes-, and arenavirus families. We show that this conserved hitchhiking mechanism ensures concomitant deltavirus-helper virus spread, which advantages the dissemination of deltaviruses, broadens their host range and expands their tropism. Our findings reveal a previously unrecognized mode of viral transmission, providing a framework to investigate overlooked deltavirus infections outside of the human liver.

microbiology↗

bioRxiv2025

The methyl-CpG-binding protein 2 inhibits cGAS-associated signaling

The detection of cytosolic dsDNA is tightly regulated to avoid pathological inflammatory responses. A major pathway involved in their detection relies on the cyclic GMP-AMP synthase (cGAS) that triggers activation of the Stimulator of interferon genes (STING) which subsequently drives the expression of inflammatory genes and type I Interferons (IFNs). Here, we show that the methyl-CpG-binding protein 2 (MECP2), a major transcriptional regulator, controls dsDNA-associated inflammatory responses. We show that the presence of cytosolic dsDNA promotes MECP2 export from the nucleus to the cytosol where it interacts with dsDNA, dampening cGAS activation. Our data also indicate that MECP2 export from the nucleus partially phenocopies MECP2 deficiency, leading to the expression of inflammatory and interferon stimulated genes, enforcing an antiviral state. Finally, we also show that MECP2 displacement from the nucleus following dsDNA stimulation is sufficient to disrupt its canonical function, leading to the reactivation of otherwise repressed genes, such endogenous retroelements of the Long interspersed nuclear element-1 (LINE-1) family. Re-expression of the latter led to the accumulation of DNA species feeding cGAS-dependent signaling and can be dampened by reverse transcriptase inhibitors. We thus establish a previously unforeseen direct role of MECP2 in the regulation of the breadth and nature of dsDNA-associated inflammatory responses. Furthermore, our results suggest that targeting dsDNA-associated pathways or pharmacological inhibition of LINE-1 may bear therapeutic hopes for Rett syndrome (RTT) patients that present with MECP2 deficiency.

immunology↗

bioRxiv2024

DNA-PK controls cyclic dinucleotide-associated type I Interferon responses

Inflammatory signal termination is critical for the maintenance of homeostasis. Cyclic dinucleotides (CDN) are second messengers that trigger inflammatory responses through the activation of the Stimulator of Interferon Genes (STING) signaling platform. No broad-acting direct regulator of intracellular CDNs has been identified in mammals to date. We show that the DNA-dependent protein kinase catalytic subunit (DNA-PKcs), a major DNA damage response actor, directly interacts with the intracellular 23-cGAMP CDN through its kinase domain, tempering STING activation. DNA-PKcs also acts on the 33-cGAMP bacterial CDN and pharmacological STING agonists, impacting their bioactivity and ability to mount optimal antiviral responses. STING agonism has been considered as a therapeutic avenue to alleviate immunosuppression in human pathologies. By uncovering DNA-PKcs as a CDN signaling modulator and CDNs as inhibitors of DNA-PKcs kinase activity, we provide critical insights into CDN regulation, with implications for the development of STING-targeting therapeutics.

immunology↗

bioRxiv2023

Unraveling human, rodent and snake Kolmioviridae replication to anticipate cross-species transmission

The recent discovery of Hepatitis D (HDV)-like viruses across a wide range of taxa led to the establishment of the Kolmioviridae family. Recent studies suggest that kolmiovirids can be satellites of viruses other than Hepatitis B virus (HBV), challenging the strict HBV/HDV-association dogma. Studying whether kolmiovirids are able to replicate in any animal cell they enter is essential to assess their zoonotic potential. Here, we compared replication of three kolmiovirids: HDV, rodent (RDeV) and snake deltavirus (SDeV) in vitro and in vivo. We show that SDeV has the narrowest and RDeV the broadest host cell range. High resolution imaging of infected cells revealed nuclear viral hubs with a peculiar RNA-protein organization. Finally, in vivo hydrodynamic delivery of infectious clones showed that both HDV and RDeV, but not SDeV, efficiently replicate in mouse liver, forming massive nuclear viral hubs. Our comparative analysis lays the foundation for the discovery of specific host factors controlling Kolmioviridae host-shifting.

microbiology↗

bioRxiv2019

Mammalian Y RNAs are modified at discrete guanosine residues with N-glycans

Glycans modify lipids and proteins to mediate inter- and intramolecular interactions across all domains of life. RNA, another multifaceted biopolymer, is not thought to be a major target of glycosylation. Here, we challenge this view with evidence that mammalian cells use RNA as a third scaffold for glycosylation in the secretory pathway. Using a battery of chemical and biochemical approaches, we find that a select group of small noncoding RNAs including Y RNAs are modified with complex, sialylated N-glycans (glycoRNAs). These glycoRNA are present in multiple cell types and mammalian species, both in cultured cells and in vivo. Finally, we find that RNA glycosylation depends on the canonical N-glycan biosynthetic machinery within the ER/Golgi luminal spaces. Collectively, these findings suggest the existence of a ubiquitous interface of RNA biology and glycobiology suggesting an expanded role for glycosylation beyond canonical lipid and protein scaffolds.

molecular biology↗

bioRxiv2018

Immuno-proteomic interrogation of dengue infection reveals novel HLA haplotype-specific MHC-I antigens

Broadly effective vaccines against dengue virus (DENV) infection have remained elusive, despite rising infection rates in the developing world. Infection-specific peptide ligands presented on Major Histocompatibility Complexes (MHC) open new avenues for developing T-cell-based interventions. Past efforts towards mapping viral MHC epitopes were based on computational predictions that only partially reflected actual antigen presentation. To empirically identify DENV-specific MHC ligands, we developed an immuno-proteomics approach for interrogating DENV- and self-derived MHC ligands from infected B-lymphocytes. Here, we report four fundamental findings: First, over 700 infection-specific MHC-ligands reflected host cellular responses to DENV that were not apparent from the proteome. Second, we report 121 viral MHC-I ligands (108 novel) which clustered into discrete hotspots across the DENV polyprotein, some of which spanned DENV polyprotein components, described here as MHC ligands for the first time. Third, we found DENV ligands which were distinctly presented by MHC alleles previously associated with either high or low anti-DENV response. Fourth, we demonstrate that while our in vitro assay only overlapped with a small fraction of previously described DENV T-cell epitopes, several novel MHC ligands identified here were recognized by T-cells from DENV-infected patients despite having low binding affinities. Together, these discoveries suggest that virus and host-derived MHC ligands have under-exploited potential for describing the cell biology of DENV infection, and as candidates for designing effective DENV vaccines.

immunology↗

bioRxiv2018

Impact of a Patient-Derived Hepatitis C Viral RNA Genome with a Mutated MicroRNA Binding Site

Hepatitis C virus (HCV) depends on liver-specific microRNA miR-122 for efficient viral RNA amplification in liver cells. This microRNA interacts with two different conserved sites at the very 5 end of the viral RNA, enhancing miR-122 stability and promoting replication of the viral RNA. Treatment of HCV patients with oligonucleotides that sequester mir-122 resulted in profound loss of viral RNA in phase II clinical trials. However, some patients accumulated in their sera a viral RNA genome that contained a single cytidine to uridine mutation at the third nucleotide from the 5 genomic end. It is shown here that this C3U variant indeed displayed higher rates of replication than that of wild-type HCV when miR-122 abundance is low in liver cells. However, when miR-122 abundance is high, binding of miR-122 to site 1, most proximal to the 5 end in the C3U variant RNA, is impaired without disrupting the binding of miR-122 to site 2. As a result, C3U RNA displays a much lower rate of replication than wild-type mRNA when miR-122 abundance is high in the liver. These findings suggest that sequestration of miR-122 leads to a resistance-associated mutation that has only been observed in treated patients so far, and raises the question about the function of the C3U variant in the peripheral blood.\n\nAuthor SummaryWith the advent of potent direct-acting antivirals (DAA), hepatitis C virus (HCV) can now be eliminated from the majority of patients, using multidrug therapy with DAAs. However, such DAAs are not available for the treatment of most RNA virus infections. The main problem is the high error rate by which RNA-dependent RNA polymerases copy viral RNA genomes, allowing the selection of mutations that are resistant to DAAs. Thus, targeting host-encoded functions that are essential for growth of the virus but not for the host cell offer promising, novel approaches. HCV needs host-encoded microRNA miR-122 for its viral RNA replication in the liver, and depletion of miR-122 in HCV patients results in loss of viral RNA. This study shows that a single-nucleotide mutation in HCV allows viral RNA amplification when miR-122 abundances are low, concomitant with changes in its tropism.

microbiology↗