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A FERONIA-MPK3/6-WRKY3/4 module links auxin signaling to lateral root development in Arabidopsis.

The phytohormone auxin orchestrates root development through intricate signaling networks. In the non-canonical auxin pathway, both the transmembrane kinase (TMK)-mediated signaling and the mitogen-activated protein kinase (MAPK) cascade are shown to be involved in the auxin-regulated lateral root (LR) formation. However, the role and mechanism of the receptor-like kinase FERONIA (FER) in this process remain unclear. Here, quantitative proteomic and phosphoproteomic analyses of Arabidopsis roots identify FER, MPK3/6, and WRKY3/4 as auxin-responsive components. Further analyses reveal that FER functions as a negative regulator of LR development by modulating cell division patterns within LR primordia. FER interacts with and phosphorylates MPK3/6, which then phosphorylate the transcription factors WRKY3 and WRKY4 to form a repressive module that ultimately suppresses LR organogenesis. Collectively, our findings define a FER-MPK3/6-WRKY3/4 signaling module that negatively regulates LR formation, demonstrating a previously unknown integration of FER-mediated signaling into the MAPK cascade in auxin-triggered organogenesis.

Arabidopsis

Searching for New Genes That Cause Usher Syndrome.

PURPOSE: The purpose of this project was to identify novel Usher syndrome (USH) candidate genes from phenotyping data of 9139 knockout (KO) mouse lines. METHODS: We evaluated phenotype data for concurrent retinopathy and hearing abnormalities in single-gene KO mice generated by the International Mouse Phenotyping Consortium (IMPC). A search was performed to determine whether each gene had been previously associated with retinopathy and/or deafness in humans. Bioinformatic tools were used to predict protein interactions, molecular functions, signaling pathways, and the expression of human orthologues of candidate genes in the retina and inner ear. RESULTS: We identified 18 single-gene KO lines exhibiting hearing abnormality and retinopathy after ear and eye examinations, respectively, and/or by histopathology. The molecular functions and signaling pathways of the human orthologues of the 18 candidate genes partially overlapped with those of USH genes. Particularly, FER and DYRK1B proteins were predicted to interact with proteins encoded by known ciliopathy genes. ADIPOR1, ATP8B1, and MPDZ were associated with retinal degeneration in humans. CHSY1 and IDUA may be pathogenic causes of hearing impairment in people. Furthermore, CHSY1, CSTB, and SPRED1 were located adjacent to unsolved genetic loci related to USH. CONCLUSIONS: A screen of 9139 KO mouse lines revealed 18 candidate genes exhibiting both retinal and inner ear abnormalities consistent with the principal clinical features associated with USH. As the observed phenotypes are attributed to gene deletion in mice, these genes warrant further study to determine the causation of retinal degeneration and hearing loss in patients.

Animals

OTOF encodes multiple long and short isoforms: genetic evidence that the long ones underlie recessive deafness DFNB9.

We have recently reported that OTOF underlies an autosomal recessive form of prelingual sensorineural deafness, DFNB9. The isolated 5-kb cDNA predicted a 1,230 amino acid (aa) C-terminus membrane-anchored cytosolic protein with three C2 domains. This protein belongs to a family of mammalian proteins sharing homology with the Caenorhabditis elegans fer-1. The two other known members of this family, dysferlin and myoferlin, both have six predicted C2 domains. By northern blot analysis, a 7-kb otoferlin mRNA could be detected in the human brain. We isolated the corresponding cDNA, which is expected to encode a 1,977-aa-long form of otoferlin with six C2 domains. A 7-kb cDNA derived from the murine orthologous gene, Otof, was also identified in the inner ear and the brain. The determination of the exon-intron structure of the human and murine genes showed that they are composed of 48 coding exons and extend approximately 90 kb and approximately 80 kb, respectively. Alternatively spliced transcripts could be detected that predict several long isoforms (six C2 domains) in humans and mice and short isoforms (three C2 domains) only in humans. Primers were designed to explore the first 19 OTOF exons, henceforth permitting exploration of the complete coding sequence of the gene in DFNB9 patients. In a southwestern Indian family affected by DFNB9, a mutation in the acceptor splice site of intron 8 was detected, which demonstrates that the long otoferlin isoforms are required for inner ear function.

Alternative Splicing

Oral Lachnoanaerobaculum Levels and Survival in Patients With Head and Neck Cancer.

IMPORTANCE: The oral microbiome plays a critical role in cancer treatment responses, yet its influence on outcomes in patients with head and neck squamous cell carcinoma (HNSCC) undergoing (chemo)radiotherapy remains poorly understood. Identifying specific microbiome signatures associated with treatment effectiveness could provide novel prognostic biomarkers and therapeutic targets. OBJECTIVE: To investigate the association between salivary Lachnoanaerobaculum spp abundance and treatment outcomes in patients with HNSCC undergoing (chemo)radiotherapy and to explore potential mechanisms. DESIGN, SETTING, AND PARTICIPANTS: This prognostic study analyzed saliva samples from patients with HNSCC who were enrolled in 2 independent prospective biomarker studies (SALIVA and ZissTrans) and underwent definitive (chemo)radiotherapy. Oral microbiome composition was assessed using 16S rRNA gene sequencing. Tumor-infiltrating lymphocytes (TILs) were evaluated via immunohistochemistry in patients with available data. Findings were further assessed using data from The Cancer Microbiome Atlas and The Cancer Genome Atlas. Sample collection occurred from 2008 to 2011 (SALIVA) and from 2017 to 2022 (ZissTrans), and the data for this study were analyzed from July to December 2024. EXPOSURE: Definitive (chemo)radiotherapy. MAIN OUTCOMES AND MEASURES: The primary outcome was locoregional recurrence-free survival (LRFS) and a secondary outcome was overall survival (OS). Additional secondary analyses evaluated the association between Lachnoanaerobaculum spp levels and TIL levels, and the incidence of severe radiation-induced oral mucositis. RESULTS: The analysis included 92 patients with HNSCC (mean [SD] age, 61.1 [7.9] years; 15 female [16.3%] 77 male [83.7%] individuals) and found that higher Lachnoanaerobaculum spp abundance was associated with substantially improved LRFS (median, 69 vs 11 months; hazard ratio [HR], 0.50; 95% CI, 0.29-0.86) and OS (median, 75 vs 27 months; HR, 0.54; 95% CI, 0.30-0.98). This finding was confirmed by multivariable Cox regression (LRFS: HR, 0.50; 95% CI, 0.25-1.00; OS: HR, 0.37; 95% CI, 0.16-0.85). TILs were evaluated in 76 patients (82.2%) and showed that increased Lachnoanaerobaculum spp levels were associated with higher CD4-positive and CD8-positive TIL counts. Lachnoanaerobaculum spp abundance showed no meaningful association with severe radiation-induced oral mucositis. Data from The Cancer Microbiome Atlas (n = 157) indicated that higher intratumoral Lachnoanaerobaculum spp levels were associated with improved OS (HR, 0.62; 95% CI, 0.39-0.98). Transcriptomic analyses in The Cancer Genome Atlas cohort further supported an immune-stimulated tumor microenvironment in Lachnoanaerobaculum-high tumors. CONCLUSIONS AND RELEVANCE: This prognostic study found that higher salivary Lachnoanaerobaculum spp abundance was associated with improved tumor control and survival in patients with HNSCC undergoing (chemo)radiotherapy. These findings support further investigation into microbiome-targeted interventions to improve HNSCC treatment effectiveness.

Humans

Lower urinary tract evaluation in children with cerebral palsy: A crossectional study.

INTRODUCTION: Cerebral palsy (CP) is a chronic, non-progressive motor disorder affecting voluntary movement and posture. Lower urinary tract (LUT) dysfunction is highly prevalent in children with CP. This study aims to evaluate LUT function in children with CP. MATERIAL AND METHODS: This cross-sectional study was conducted at a tertiary care hospital. Patients aged 5-18 years with established CP diagnosis were included. Evaluation included clinical history, physical examination, urinary ultrasonography with post-void residual (PVR) measurement, and urodynamic studies when indicated. Patients were categorized into three groups; group-1 (LUT dysfunction), group-2 (symptomatic), and group-3 (asymptomatic) for analysis. RESULTS: The study included 97 children with CP (41 girls, 56 boys; median age 8 years). Of the patients, 61.8% were ambulatory (GMFCS I-III) and 38.2% were non-ambulatory (GMFCS IV-V). At least one LUT symptom was detected in 75.3% of patients. Incontinence was the most common symptom at 69.1%. Incontinence prevalence was significantly higher in non-ambulatory patients (81.1% vs 61.7%, p = 0.044). Invasive urodynamics was performed in 19 patients, and LUT dysfunction was diagnosed in 89.5% of them (19.3% of the entire population). Prematurity rate was significantly higher in patients with LUT dysfunction (94.1% vs 64.8%, p = 0.017). Binary logistic regression analysis identified elevated PVR as the strongest independent risk factor for LUT dysfunction (OR = 108, p < 0.001). Abnormal urinary frequency (OR = 14.9, p = 0.022) and quadriplegia (OR = 10.3, p = 0.016) were other independent risk factors. ROC analysis determined the optimal cut-off value for PVR as 19 mL (sensitivity 58.82%, specificity 94.92%). In the intergroup analysis, multinomial logistic regression identified elevated PVR as the strongest predictor (Group-1 vs Group-2: OR = 101; Group-1 vs Group-3: OR = 24, both p < 0.003). Lower gestational age was also an independent risk factor in both comparisons (OR = 1.25-1.26, p < 0.020). DISCUSSION: This study demonstrates LUT dysfunction affects 19.3% of children with CP, strongly correlating with motor impairment severity. Elevated PVR emerged as the strongest independent predictor (OR = 108), offering a practical non-invasive screening tool. Our proposed urodynamic criteria achieved 94.7% diagnostic yield, enabling selective evaluation. Limitations include single-center design and cross-sectional methodology without longitudinal follow-up. These findings support integrating systematic urological assessment into standard CP care for early intervention. CONCLUSION: LUT dysfunction prevalence is high in children with CP, and symptom frequency increases with higher GMFCS levels. Elevated PVR is the strongest predictor, with a clinically applicable cut-off value of 19 mL. Particularly in quadriplegic, non-ambulatory, and premature patients, close follow-up and urodynamic evaluation when necessary should be performed with a multidisciplinary approach.

Humans

The histone modifier KAT2A presents a selective target in a subset of well-differentiated microsatellite-stable colorectal cancers.

Lysine acetyltransferase 2&#x2009;A (KAT2A) plays a pivotal role in epigenetic gene regulation across various types of cancer. In colorectal cancer (CRC), increased KAT2A expression is associated with a more aggressive phenotype. Our study aims to elucidate the molecular underpinnings of KAT2A dependency in CRC and assess the consequences of KAT2A depletion. We conducted a comprehensive analysis by integrating CRISPR-Cas9 screening data with genomics, transcriptomics, and global acetylation patterns in CRC cell lines to pinpoint molecular markers indicative of KAT2A dependency. Additionally, we characterized the phenotypic effect of a CRISPR-interference-mediated KAT2A knockdown in CRC cell lines and patient-derived 3D spheroid cultures. Moreover, we assessed the effect of KAT2A depletion within a patient-derived xenograft mouse model in vivo. Our findings reveal that KAT2A dependency is closely associated with microsatellite stability, lower mutational burden, and increased molecular differentiation signatures in CRC, independent of the KAT2A expression levels. KAT2A-dependent CRC cells display higher gene expression levels and enriched H3K27ac marks at gene loci linked to enterocytic differentiation. Furthermore, loss of KAT2A leads to decreased cell growth and viability in vitro and in vivo, downregulation of proliferation- and stem cell-associated genes, and induction of differentiation markers. Altogether, our data show that a specific subset of CRCs with a more differentiated phenotype relies on KAT2A. For these CRC cases, KAT2A might represent a promising novel therapeutic target.

Humans

Genome-wide bidirectional CRISPR screens identify mucins as host factors modulating SARS-CoV-2 infection.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes a range of symptoms in infected individuals, from mild respiratory illness to acute respiratory distress syndrome. A systematic understanding of host factors influencing viral infection is critical to elucidate SARS-CoV-2-host interactions and the progression of Coronavirus disease 2019 (COVID-19). Here, we conducted genome-wide CRISPR knockout and activation screens in human lung epithelial cells with endogenous expression of the SARS-CoV-2 entry factors ACE2 and TMPRSS2. We uncovered proviral and antiviral factors across highly interconnected host pathways, including clathrin transport, inflammatory signaling, cell-cycle regulation, and transcriptional and epigenetic regulation. We further identified mucins, a family of high molecular weight glycoproteins, as a prominent viral restriction network that inhibits SARS-CoV-2 infection in vitro and in murine models. These mucins also inhibit infection of diverse respiratory viruses. This functional landscape of SARS-CoV-2 host factors provides a physiologically relevant starting point for new host-directed therapeutics and highlights airway mucins as a host defense mechanism.

Animals

Efficacy of a self-guided online resilience intervention for improving mental health among university students: A randomized controlled trial.

Epidemiological data indicates that university students are an at-risk population for the development of mental disorders. Online interventions have been proposed as promising tools for reducing barriers to treatment and establishing easily accessible health-care services promoting mental health and resilience. This study investigated the efficacy of a Learning Management System (LMS)-based self-guided online resilience intervention. 216 university students took part in a randomized controlled trial with an intervention and a waitlist control group and three measurement points (pre, post and follow-up). We conducted per-protocol (PP) and intention-to-treat (ITT) analyses with mental distress as primary outcome, and self-reported resilience and resilience factors as secondary outcomes. Further, attitudes towards online interventions, adherence, satisfaction and possible negative effects were explored. Satisfaction with the intervention was high and PP analyses (n&#x2009;=&#x2009;150) revealed significant improvements in mental distress and self-compassion at post-test and acceptance at follow-up. No favourable effects were found for self-reported resilience and resilience factors. Adherence was low and ITT analyses revealed no significant effects. Overall, the study provides preliminary evidence for the LMS-based self-guided online intervention as a potentially valuable tool for university mental health services under optimal adherence conditions. Further research into determinants of adherence is needed to improve intervention reach.

Humans

Inference of differential kinase interaction networks with KINference.

MOTIVATION: Differential kinase interaction networks (DKINs) are networks containing kinase-substrate links that are differentially active between two conditions. Existing methods are either able to predict condition-agnostic kinase-substrate links or condition-specific differential kinase activity, but do not provide differential kinase-substrate links. Moreover, existing methods for predicting kinase-substrate links usually rely on curated biochemical knowledge. Thus, there is a lack of data-driven DKIN inference methods that are also applicable when prior knowledge is scarce. RESULTS: To address this need, we present KINference. KINference combines computation of a baseline KIN representing the space of all possible kinase-substrate links with filters applied to nodes and edges to identify differentially active subnetworks that are relevant in the context of a specific phosphoproteomics dataset. For the node filters, we rely on functional relevance and differential phosphorylation scores; for the edge filters, we make use of prize-collecting Steiner trees and correlations between phosphorylation sites of kinases and their target proteins. Tests on two phosphoproteomics datasets (kinase inhibition in breast cancer cells, SARS-CoV-2 infection in Calu-3 cells) show that the proposed filters produce significant results in terms of overlap with known interactions between kinases and phosphorylation sites. Furthermore, a case study on the SARS-CoV-2 infection data, suggests a potential host pathway linked to virus replication, showcasing the process of hypothesis generation utilizing DKINs computed by KINference. AVAILABILITY AND IMPLEMENTATION: KINference is available as an R package at https://github.com/bionetslab/KINference and https://doi.org/10.5281/zenodo.15411150. Scripts to reproduce the results are available at https://github.com/bionetslab/KINference-Evaluation-Scripts and https://doi.org/10.5281/zenodo.15424599.

Humans

A Multitrait Locus Regulates Sarbecovirus Pathogenesis.

Infectious diseases have shaped the human population genetic structure, and genetic variation influences the susceptibility to many viral diseases. However, a variety of challenges have made the implementation of traditional human Genome-wide Association Studies (GWAS) approaches to study these infectious outcomes challenging. In contrast, mouse models of infectious diseases provide an experimental control and precision, which facilitates analyses and mechanistic studies of the role of genetic variation on infection. Here we use a genetic mapping cross between two distinct Collaborative Cross mouse strains with respect to severe acute respiratory syndrome coronavirus (SARS-CoV) disease outcomes. We find several loci control differential disease outcome for a variety of traits in the context of SARS-CoV infection. Importantly, we identify a locus on mouse chromosome 9 that shows conserved synteny with a human GWAS locus for SARS-CoV-2 severe disease. We follow-up and confirm a role for this locus, and identify two candidate genes, CCR9 and CXCR6, that both play a key role in regulating the severity of SARS-CoV, SARS-CoV-2, and a distantly related bat sarbecovirus disease outcomes. As such we provide a template for using experimental mouse crosses to identify and characterize multitrait loci that regulate pathogenic infectious outcomes across species. IMPORTANCE Host genetic variation is an important determinant that predicts disease outcomes following infection. In the setting of highly pathogenic coronavirus infections genetic determinants underlying host susceptibility and mortality remain unclear. To elucidate the role of host genetic variation on sarbecovirus pathogenesis and disease outcomes, we utilized the Collaborative Cross (CC) mouse genetic reference population as a model to identify susceptibility alleles to SARS-CoV and SARS-CoV-2 infections. Our findings reveal that a multitrait loci found in chromosome 9 is an important regulator of sarbecovirus pathogenesis in mice. Within this locus, we identified and validated CCR9 and CXCR6 as important regulators of host disease outcomes. Specifically, both CCR9 and CXCR6 are protective against severe SARS-CoV, SARS-CoV-2, and SARS-related HKU3 virus disease in mice. This chromosome 9 multitrait locus may be important to help identify genes that regulate coronavirus disease outcomes in humans.

Animals

Dysregulation of lung epithelial cell homeostasis and immunity contributes to Middle East respiratory syndrome coronavirus disease severity.

Coronaviruses (CoV) emerge suddenly from animal reservoirs to cause novel diseases in new hosts. Discovered in 2012, the Middle East respiratory syndrome coronavirus (MERS-CoV) is endemic in camels in the Middle East and is continually causing local outbreaks and epidemics. While all three newly emerging human CoVs from the past 20 years (SARS-CoV, SARS-CoV-2, and MERS-CoV) cause respiratory disease, each CoV has unique host interactions that drive differential pathogeneses. To better understand the virus and host interactions driving lethal MERS-CoV infection, we performed a longitudinal multi-omics analysis of sublethal and lethal MERS-CoV infection in mice. Significant differences were observed in body weight loss, virus titers, and acute lung injury among lethal and sub-lethal virus doses. Virus-induced apoptosis of type I and II alveolar epithelial cells suggests that loss or dysregulation of these key cell populations was a major driver of severe disease. Omics analysis suggested differential pathogenesis was multi-factorial with clear differences among innate and adaptive immune pathways as well as those that regulate lung epithelial homeostasis. Infection of mice lacking functional T and B cells showed that adaptive immunity was important in controlling viral replication but also increased pathogenesis. In summary, we provide a high-resolution host response atlas for MERS-CoV infection and disease severity. Multi-omics studies of viral pathogenesis offer a unique opportunity to not only better understand the molecular mechanisms of disease but also to identify genes and pathways that can be exploited for therapeutic intervention all of which is important for our future pandemic preparedness.IMPORTANCEEmerging coronaviruses like SARS-CoV, SARS-CoV-2, and MERS-CoV cause a range of disease outcomes in humans from an asymptomatic, moderate, and severe respiratory disease that can progress to death but the factors causing these disparate outcomes remain unclear. Understanding host responses to mild and life-threatening infections provides insight into virus-host networks within and across organ systems that contribute to disease outcomes. We used multi-omics approaches to comprehensively define the host response to moderate and severe MERS-CoV infection. Severe respiratory disease was associated with dysregulation of the immune response. Key lung epithelial cell populations that are essential for lung function get infected and die. Mice lacking key immune cell populations experienced greater virus replication but decreased disease severity implicating the immune system in both protective and pathogenic roles in response to MERS-CoV. These data could be utilized to design new therapeutic strategies targeting specific pathways that contribute to severe disease.

Animals

Prognostic value of circulating tumor DNA and copy-number alterations in patients receiving tandem [225Ac]Ac-/[177Lu]Lu-PSMA-617 therapy for metastatic castration-resistant prostate cancer: a prospective observational study.

BACKGROUND: Prostate-specific membrane antigen-targeted radioligand therapy (PSMA-RLT) demonstrates clinical efficacy in metastatic castration-resistant prostate cancer (mCRPC), yet robust biomarkers for dynamic treatment monitoring and resistance remain lacking. We investigated circulating tumor DNA (ctDNA)-derived tumor fraction (TFx) and genome-wide copy-number alterations (CNAs) as non-invasive biomarkers of treatment response and resistance biology. METHODS: Seventy-eight patients with advanced mCRPC receiving tandem [225Ac]Ac-/[177Lu]Lu-PSMA-617 were prospectively enrolled. Plasma samples collected longitudinally (n&#x2009;=&#x2009;172) underwent ultra-low-pass whole-genome sequencing. TFx was estimated using ichorCNA, and recurrent CNAs were identified using GISTIC2.0. Associations with progression and overall survival (OS) were assessed using Cox proportional hazards models, including time-dependent analyses. RESULTS: Baseline TFx differed across metastatic disease stages (p&#x2009;=&#x2009;0.027) and dynamic TFx changes paralleled PSA kinetics during early treatment. Modelled as a time-dependent variable, TFx was associated with a significantly increased risk of progression (HR 4.9, 95% CI 1.2-20.1, p&#x2009;=&#x2009;0.026). Unsupervised clustering identified distinct high- and low-CNA burden groups strongly correlated with TFx (p&#x2009;=&#x2009;8.09&#x2009;&#xd7;&#x2009;10&#x207b;8). High CNA burden was associated with shorter median OS (8.3 vs 13.8&#xa0;months). Multivariable analysis identified baseline logPSA and logALP as independent predictors of OS. Recurrent CNAs affected key tumor suppressors (PTEN, RB1, BRCA2, ATM) and were enriched in pathways related to TP53 signalling, homologous recombination repair, and oncogenic signaling. Longitudinal analyses demonstrated persistence and expansion of specific amplifications at progression. CONCLUSIONS: ctDNA-derived TFx represents a dynamic biomarker of treatment response and progression risk, while CNA profiling provides insight into resistance mechanisms in mCRPC treated with PSMA-RLT. These findings support the integration of ctDNA-based biomarkers into clinical stratification and real-time monitoring strategies.

Humans

Multi-ancestry genome-wide meta-analysis of 56,241 individuals identifies known and novel cross-population and ancestry-specific associations as novel risk loci for Alzheimer's disease.

BACKGROUND: Limited ancestral diversity has impaired our ability to detect risk variants more prevalent in ancestry groups of predominantly non-European ancestral background in genome-wide association studies (GWAS). We construct and analyze a multi-ancestry GWAS dataset in the Alzheimer's Disease Genetics Consortium (ADGC) to test for novel shared and population-specific late-onset Alzheimer's disease (LOAD) susceptibility loci and evaluate underlying genetic architecture in 37,382 non-Hispanic White (NHW), 6728 African American, 8899 Hispanic (HIS), and 3232 East Asian individuals, performing within ancestry fixed-effects meta-analysis followed by a cross-ancestry random-effects meta-analysis. RESULTS: We identify 13 loci with cross-population associations including known loci at/near CR1, BIN1, TREM2, CD2AP, PTK2B, CLU, SHARPIN, MS4A6A, PICALM, ABCA7, APOE, and two novel loci not previously reported at 11p12 (LRRC4C) and 12q24.13 (LHX5-AS1). We additionally identify three population-specific loci with genome-wide significance at/near PTPRK and GRB14 in HIS and KIAA0825 in NHW. Pathway analysis implicates multiple amyloid regulation pathways and the classical complement pathway. Genes at/near our novel loci have known roles in neuronal development (LRRC4C, LHX5-AS1, and PTPRK) and insulin receptor activity regulation (GRB14). CONCLUSIONS: Using cross-population GWAS meta-analyses, we identify novel LOAD susceptibility loci in/near LRRC4C and LHX5-AS1, both with known roles in neuronal development, as well as several novel population-unique loci. Reflecting the power of diverse ancestry in GWAS, we detect the SHARPIN locus with only 13.7% of the sample size of the NHW GWAS study (n&#x2009;= 409,589) in which this locus was first observed. Continued expansion into larger multi-ancestry studies will provide even more power for further elucidating the genomics of late-onset Alzheimer's disease.

Humans

A novel dimerization site in non-structural protein 5A of hepatitis C virus regulates viral replication fitness.

We previously found that high genome replication fitness of the hepatitis C virus (HCV) was associated with severe disease in immunocompromised patients. Elevated replication fitness was mediated by accumulation of mutations in the replication enhancing domain (ReED) within domain (D) 2 of non-structural protein (NS) 5A. NS5A is a partially unstructured phosphoprotein lacking enzymatic activity but fulfilling a key role in HCV replication due to interacting with various cellular and viral proteins. It can exist in a variety of dimeric and oligomeric conformations mediated by NS5A D1 with clinically approved NS5A inhibitors proposed to exert their antiviral function by fixing these dimers in distinct conformations. In this study, we aimed at elucidating the ReED's mode of action. AlphaFold modelling indicated a so far unrecognized NS5A dimerization site in the ReED. Indeed, split nano luciferase assays revealed a significantly stronger NS5A dimerization of high replicator ReED variants, suggesting that high replication fitness is mediated by enforcement of NS5A self-interaction. This hypothesis was supported by the effect of low dose (1 pM) NS5A inhibitor treatment, increasing replication fitness and phenocopying the effects of ReED mutations. Furthermore, we found that HCV isolate JFH1, replicating with very high efficiency, is completely resistant to the regulatory function of the ReED. Chimeric replicons composed of ReED resistant JFH1 and the ReED sensitive isolate J6 identified NS3 helicase and NS5B polymerase as critical genetic elements mediating ReED sensitivity/resistance. Our data overall suggest that the ReED in NS5A is a negative regulator of HCV replication fitness with dimerization releasing the inhibitory interaction with helicase and/or polymerase, thereby likely facilitating initiation of RNA synthesis.

Viral Nonstructural Proteins