Biology subjects

Xiong, J.

Publications and source records attributed to Xiong, J..

At least 55 records · Page 3Linked to original sources

bioRxiv2024

PLA2G15 is a Lysosomal BMP Hydrolase with Ester Position Specificity and Its Targeting Ameliorates Lysosomal Disease

Lysosomes catabolize lipids and other biological molecules, a function essential for cellular and organismal homeostasis. Key to lipid catabolism in the lysosome is bis(monoacylglycero)phosphate (BMP), a major lipid constituent of intralysosomal vesicles and a stimulator of lipid-degrading enzymes. BMP levels are altered in a broad spectrum of human conditions, including neurodegenerative diseases. While a lysosomal BMP synthase was recently discovered, the enzymes that mediate BMP turnover has remained elusive. Here we show that the lysosomal phospholipase PLA2G15 is a physiological BMP hydrolase. We further demonstrate that BMPs resistance to hydrolysis in the lysosome is conferred by the combination of its unique sn2, sn2 esterification position and stereochemistry, as neither feature alone is sufficient to provide this resistance. Purified PLA2G15 catabolizes most BMP species derived from cell and tissue lysosomes under acidic conditions. Furthermore, PLA2G15 catalytic activity against synthesized BMP stereoisomers with primary esters was comparable to its canonical substrates challenging the long-held thought that BMPs unique stereochemistry is sufficient to confer resistance to acid phospholipases. Conversely, BMP with secondary esters and S,S stereoconfiguration is intrinsically stable in vitro and requires acyl migration for hydrolysis in lysosomes. Consistent with our biochemical data, PLA2G15-deficient cells and tissues accumulate multiple BMP species, a phenotype reversible by supplementing wildtype PLA2G15 but not its catalytically dead mutant. In addition, targeting PLA2G15 to increase BMP reverses the cholesterol phenotype in Niemann Pick Disease Type C (NPC1) patient fibroblasts and significantly ameliorates disease pathologies in NPC1-deficient mice leading to extended lifespan. Our findings establish the rules that govern the stability of BMP in the lysosome and identify PLA2G15 as a lysosomal BMP hydrolase and a potential target for therapeutic intervention in neurodegenerative diseases.

cell biology↗

bioRxiv2024

FAPM: Functional Annotation of Proteins using Multi-Modal Models Beyond Structural Modeling

Assigning accurate property labels to proteins, like functional terms and catalytic activity, is challenging, especially for proteins without homologs and "tail labels" with few known examples. Unlike previous methods that mainly focused on protein sequence features, we use a pretrained large natural language model to understand the semantic meaning of protein labels. Specifically, we introduce FAPM, a contrastive multi-modal model that links natural language with protein sequence language. This model combines a pretrained protein sequence model with a pretrained large language model to generate labels, such as Gene Ontology (GO) functional terms and catalytic activity predictions, in natural language. Our results show that FAPM excels in understanding protein properties, outperforming models based solely on protein sequences or structures. It achieves state-of-the-art performance on public benchmarks and in-house experimentally annotated phage proteins, which often have few known homologs. Additionally, FAPMs flexibility allows it to incorporate extra text prompts, like taxonomy information, enhancing both its predictive performance and explainability. This novel approach offers a promising alternative to current methods that rely on multiple sequence alignment for protein annotation. The online demo is at: https://huggingface.co/spaces/wenkai/FAPM_demo.

bioinformatics↗

bioRxiv2024

SLC13A2-transported citrate is a metabolic signal for PKM2 acetylation and degradation to suppress tumor growth

Background and aimsMetabolic reprogramming represents as a pivotal hallmark for cancer, but TCA cycle in tumorigenesis and progression has long been neglected. Solute carrier (SLC) transporters mediate the transport of TCA cycle intermediates across membrane, but their functions in cancer pathogenesis remains unclear. Approaches & ResultsUsing integrated analysis of solute carrier (SLC) transporters for TCA cycle intermediates, we found that SLC13A2 was consistently downregulated in hepatocellular carcinoma (HCC) cells and liver tissues from human patients and heterogeneous mouse models. Adeno-associated virus (AAV)-transduced liver-specific knockout or overexpression of SLC13A2 promoted or ameliorated HCC progression in the primary mouse model, demonstrating that SLC13A2 served as a protective factor during HCC pathogenesis. SLC13A2 inhibited HCC cell proliferation by decreasing mitochondrial function via suppressed oxygen consumption and ATP production. Combined with metabolic flux analysis, we found that SLC13A2 imported citrate, which secreted acetyl-CoA as a precursor for the acetylation of pyruvate kinase muscle isozyme M2 (PKM2), which led to its protein degradation. Decreased activity of pyruvate kinase depleted pyruvate for the TCA cycle, thus inhibiting amino acid synthesis and nucleotide metabolism. Additionally, a decrease in nuclear PKM2 protein transduced to reprogrammed gene transcription for cell proliferation and metabolism which is required for tumor growth. ConclusionsThis study revealed that citrate transported by SLC13A2 acts as a signal to disrupt metabolic homeostasis for tumor growth and suggests potential drug targets for HCC therapy. graphic abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=165 SRC="FIGDIR/small/591017v2_ufig1.gif" ALT="Figure 1"> View larger version (64K): org.highwire.dtl.DTLVardef@80c95eorg.highwire.dtl.DTLVardef@124750corg.highwire.dtl.DTLVardef@809ab4org.highwire.dtl.DTLVardef@12cbe74_HPS_FORMAT_FIGEXP M_FIG C_FIG

cancer biology↗

bioRxiv2024

An Amygdalar Oscillator Coordinates Cellular and Behavioral Rhythms

Circadian rhythms are generated by the master pacemaker suprachiasmatic nucleus (SCN), in concert with local clocks throughout the body. While many brain regions exhibit cycling clock gene expression, the identity of a discrete extra-SCN brain oscillator that produces rhythmic behavior has remained elusive. Here, we show that an extra-SCN oscillator in the lateral amygdala (LA) is defined by expression of the clock-output molecule mWAKE/ANKFN1. mWAKE is enriched in the anterior/dorsal LA (adLA), and strikingly, selective disruption of clock function or excitatory signaling in adLAmWAKE neurons abolishes Period2 (Per2) rhythms throughout the LA. mWAKE levels rise at night and promote rhythmic excitability of adLAmWAKE neurons by upregulating Ca2+-activated K+ channel activity specifically at night. adLAmWAKE neurons coordinate rhythmic sensory perception and anxiety in a clock-dependent and WAKE-dependent manner. Together, these data reveal the cellular identity of an extra-SCN brain oscillator and suggest a multi-level hierarchical system organizing molecular and behavioral rhythms.

neuroscience↗

bioRxiv2024

PackDock: a Diffusion Based Side Chain Packing Model for Flexible Protein-Ligand Docking

Structure-based drug design (SBDD) relies on accurate knowledge of protein structure and ligand-binding conformations. However, most of the static conformations obtained by advanced methods such as structural biology and de novo protein folding algorithms often dont meet the needs for drug design. We introduce PackDock, a flexible docking method that combines "conformation selection" and "induced fit" mechanisms in a two-stage docking pipeline. The core module of this method is PackPocket, which uses a diffusion model to explore the side-chain conformation space in ligand binding pockets, both with or without a ligand. We evaluate our method using several tests that reflect real-world application scenarios. (1) Side-chain packing and Re-docking experiments validate the ability of PackDock to predict accurate side-chain conformations and ligand conformations. (2) Cross-docking experiments with apo and non-homologous ligand-induced holo structures align with real docking scenarios, demonstrating PackDocks practical value. (3) Docking experiments with hypothetical models show that PackPocket can potentially conduct SBDD starting from protein sequence information only. Additionally, we found that PackDock can identify key amino acid conformation changes, which may provide insights for lead compound optimization. We demonstrate PackDock can accurately predict the complex conformations in various application scenarios, by combining the conformation selection theory and the induced fit theory, and by using the ability of PackPocket to accurately predict the side chain conformations in the pocket region. We believe this method can improve the usability of existing structures, providing a new perspective for the SBDD community.

bioinformatics↗

bioRxiv2024

Comparison and Evaluation of Neutralization of Clinically Frequently Used Antimicrobial Agents Using Three Different Culture Media in Simulated Blood Cultures

The performance of BACT/ALERT FA/FN Plu (France) blood culture containing a novel resin, DL (China) blood culture containing common resin, and adsorbent-free Thermo (USA) blood culture relying on dilution for antimicrobial neutralization at %peak serum concentration was evaluated by measuring the recovery of organisms and time to detection (TTD) in nine simulated microorganism-antimicrobial combination blood cultures.There was a significant difference in recovery rates between the aerobic media: 35/40 (87.5%) for BACT/ALERT media, 15/35 (42.9%) for DL media, and 5/40 (12.5%) for Thermo media; whereas, there was no statistical difference in TTD between FA Plus media and DL aerobic media. The recovery rates of the anaerobic media were 32/35 (91.4%) for BACT/ALERT media, 1/35 (2.9%) for DL media, and 5/35 (14.3%) for Thermo media, with significant differences only between BACT/ALERT FN Plus media and the others. Among the seven main antimicrobial categories, only BACT/ALERT FA/FN Plus culture media showed high recovery of microorganisms, except for carbapenems. The DL culture media exhibited a relatively high recovery rate of piperacillin/tazobactam, levofloxacin, and gentamicin only in aerobic media, and Thermo media only displayed the recovery of gentamicin.BACT/ALERT FA/FN Plus culture media with novel resin showed absolute advantages over DL and Thermo culture media and, thus, can be selectively applied clinically with prior use of antimicrobials before pathogen detection. DL culture media containing common resin outperformed adsorbent-free dilution-based Thermo culture media, which can be a backup option. We should focus on improving the neutralization of carbapenems with low efficiency in all three media.

microbiology↗

bioRxiv2023

Comprehensive characterization of the integrin family across 32 cancer types

Integrin genes widely involve in tumorigenesis. Yet, a comprehensive characterization of integrin family and their interactome on the pan-cancer level is lacking. Here, we systematically dissect integrin family in nearly 10000 tumors across 32 cancer types. Globally, integrins represent a frequently altered and misexpressed pathway, with alteration and dysregulation overall being protumorigenic. Expression dysregulation, better than mutational landscape, of integrin family successfully identifies a subgroup of aggressive tumors demonstrating a high level of proliferation and stemness. We identify that several molecular mechanisms jointly regulate integrin expression in a context-dependent manner. For potential clinical usage, we construct a weighted score, integrinScore, to measure integrin signaling patterns in individual tumors. Remarkably, integrinScore consistently correlates with predefined molecular subtypes in multiple cancers, with integrinScore high tumors being more aggressive. Importantly, integrinScore is cancer-dependently and closely associated with proliferation, stemness, tumor microenvironment, metastasis, and immune signatures. IntegrinScore also predicts patients response to immunotherapy. By mining drug databases, we unravel an array of compounds that may serve as integrin signaling modulators. Finally, we build a user-friendly database to facilitate researchers to explore integrin-related knowledge. Collectively, we provide a comprehensive characterization of integrins across cancers, which offers gene- and cancer-specific rationales for developing integrin-targeted therapy.

bioinformatics↗

bioRxiv2023

A framework for defining mesenchymal cell types associated with murine periosteal and endosteal bone

Single-cell RNA sequencing has led to numerous novel designations for mesenchymal cell types associated with bone. Consequently, there are now multiple designations for what appear to be the same cell type. In addition, existing datasets contain relatively small numbers of mature osteoblasts and osteocytes and there has been no comparison of periosteal bone cells to those at the endosteum and trabecular bone. The main goals of this study were to increase the amount of single cell RNA sequence data for osteoblasts and osteocytes, to compare cells from the periosteum to those inside bone, and to clarify the major categories of cell types associated with murine bone. To do this, we created an atlas of murine bone-associated cells by harmonizing published datasets with in-house data from cells targeted by Osx1-Cre and Dmp1-Cre driver strains. Cells from periosteal bone were analyzed separately from those isolated from the endosteum and trabecular bone. Over 100,000 mesenchymal cells were mapped to reveal 11 major clusters designated fibro-1, fibro-2, chondrocytes, articular chondrocytes, tenocytes, adipo-CAR, osteo-CAR, pre-osteoblasts, osteoblasts, osteocytes, and osteo-X, the latter defined in part by Postn expression. Osteo-X, osteo-CAR, and pre-osteoblasts were closely associated with osteoblasts at the trabecular bone surface. Wnt16 was expressed in multiple cell types from the periosteum but not in any cells from endocortical or cancellous bone. Fibro-2 cells, which express markers of skeletal stem cells, localized to the periosteum but not trabecular bone in adult mice. Suppressing bone remodeling eliminated osteoblasts and altered gene expression in pre-osteoblasts but did not change the abundance or location of osteo-X or osteo-CAR cells. These results provide a framework for identifying bone cell types in murine single cell RNA sequencing datasets and suggest that osteoblast progenitors reside near the surface of remodeling bone. Author SummaryThe skeleton of vertebrate animals is produced by bone forming cells known as osteoblasts. New osteoblasts are continually produced throughout life to maintain the skeleton. However, the identity of the cells from which new osteoblasts are derived is not clear. Single cell RNA sequencing provides a gene expression profile of individual cells and allows them to be grouped into clusters of cells with similar profiles. In many cases, distinct clusters represent distinct cell types. Recent single cell RNA sequencing studies of mouse bones by several different laboratories have identified many novel cell types, some of which may be osteoblast progenitors. In many cases, different laboratories have created different names for what appear to be the same cell type. To help clarify this situation, we performed single cell RNA sequencing studies and combined our results with those from several published studies to create a harmonized map of the cell types associated with mouse bones. We also identified gene signatures for each cell type that can be used to improve the consistency of cell type designation in future single cell RNA sequencing studies of mouse bone.

genomics↗

bioRxiv2023

A seven-sex species recognizes self and non-self mating-type via a novel protein complex

Although most species have two sexes, multisexual (or multi-mating type) species are also widespread. However, it is unclear how mating-type recognition is achieved at the molecular level in multisexual species. The unicellular ciliate Tetrahymena thermophila has seven mating types, which are determined by the MTA and MTB proteins. In this study, we found that both proteins are essential for cells to send or receive complete mating-type information, and transmission of the mating-type signal requires both proteins to be expressed in the same cell. We found that MTA and MTB form a mating-type recognition complex that localizes to the plasma membrane, but not to the cilia. Stimulation experiments showed that the mating-type-specific regions of MTA and MTB mediate both self- and non-self-recognition, indicating that T. thermophila uses a dual approach to achieve mating-type recognition. Our results suggest that MTA and MTB form an elaborate multifunctional protein complex that can identify cells of both self and non-self mating types in order to inhibit or activate mating, respectively. Impact statementA giant multifunctional protein complex mediates mating-type recognition through a non-ligand-receptor mechanism in a multisexual species.

genetics↗

bioRxiv2023

GammaGateR: semi-automated marker gating for single-cell multiplexed imaging

MotivationMultiplexed immunofluorescence (mIF) is an emerging assay for multichannel protein imaging that can decipher cell-level spatial features in tissues. However, existing automated cell phenotyping methods, such as clustering, face challenges in achieving consistency across experiments and often require subjective evaluation. As a result, mIF analyses often revert to marker gating based on manual thresholding of raw imaging data. ResultsTo address the need for an evaluable semi-automated algorithm, we developed GammaGateR, an R package for interactive marker gating designed specifically for segmented cell-level data from mIF images. Based on a novel closed-form gamma mixture model, GammaGateR provides estimates of marker-positive cell proportions and soft clustering of marker-positive cells. The model incorporates user-specified constraints that provide a consistent but slide-specific model fit. We compared GammaGateR against the newest unsupervised approach for annotating mIF data, employing two colon datasets and one ovarian cancer dataset for the evaluation. We showed that GammaGateR produces highly similar results to a silver standard established through manual annotation. Furthermore, we demonstrated its effectiveness in identifying biological signals, achieved by mapping known spatial interactions between CD68 and MUC5AC cells in the colon and by accurately predicting survival in ovarian cancer patients using the phenotype probabilities as input for machine learning methods. GammaGateR is a highly efficient tool that can improve the replicability of marker gating results, while reducing the time of manual segmentation. Availability and ImplementationThe R package is available at https://github.com/JiangmeiRubyXiong/GammaGateR. ContactPlease address correspondence to jiangmei.xiong@vanderbilt.edu and simon.vandekar@vumc.org. Key PointsO_LIGammaGateR is the first semi-automated marker gating tool for mIF image, and it will help to diminish the inconsistency with manual marker gating. C_LIO_LIWith novel cfGMM, GammaGateR can fit flexibly across slides with different distributions and incorporate biology priors. C_LIO_LIGammaGateR is proven to reveal credible prognostic information, and it can quantify known findings in tumor cell populations. C_LI

bioinformatics↗

bioRxiv2023

Stabilization of RRBP1 mRNA via an m6A-dependent manner in prostate cancer constitutes a therapeutic vulnerability amenable to small-peptide inhibition of METTL3

Mounting evidence has implicated the RNA m6A methylation catalyzed by METTL3 in a wide range of physiological and pathological processes, including tumorigenesis. The detailed m6A landscape and molecular mechanism of METTL3 in prostate cancer (PCa) remains ill-defined. We find that METTL3 is overexpressed in PCa and correlates with worse patient survival. Functional studies establish METTL3 as an oncoprotein dependent on its m6A enzymatic activity in both AR+ and AR- PCa cells. To dissect the regulatory network of m6A pathway in PCa, we map the m6A landscape in clinical tumor samples using m6A-seq and identify genome-wide METTL3-binding transcripts via RIP-seq. Mechanistically, we discover RRBP1 as a direct METTL3 target in which METTL3 stabilizes RRBP1 mRNA in an m6A-dependent manner. RRBP1 positively correlates with METTL3 expression in PCa cohorts and exerts an oncogenic role in aggressive PCa cells. Leveraging the 3D structural protein-protein interaction between METTL3 and METTL14, we successfully develop two potential METTL3 peptide inhibitors (RM3 and RSM3) that effectively suppress cancer cell proliferation in vitro and tumor growth in vivo. Collectively, our study reveals a novel METTL3/m6A/RRBP1 axis in enhancing aggressive traits of PCa, which can be therapeutically targeted by small-peptide METTL3 antagonists.

cancer biology↗

bioRxiv2023

AMPK targets PDZD8 to trigger carbon source shift to glutamine

The shift of carbon utilisation from glucose to other nutrients is a fundamental metabolic adaptation to cope with the decreased glucose oxidation during fasting or starvation1. AMP-activated protein kinase (AMPK) plays crucial roles in manifesting physiological benefits accompanying glucose starvation or calorie restriction2. However, the underlying mechanisms are unclear. Here, we show that low glucose-induced activation of AMPK plays a decisive role in the shift of carbon utilisation from glucose to glutamine. We demonstrate that endoplasmic reticulum (ER)-localised PDZD8, which we identify to be a new substrate of AMPK, is required for the glucose starvation-promoted glutaminolysis. AMPK phosphorylates PDZD8 at threonine 527 (T527), and promotes it to interact with and activate the mitochondrial glutaminase 1 (GLS1), a rate-limiting enzyme of glutaminolysis3-5, and as a result the ER-mitochondria contact is strengthened. In vivo, PDZD8 enhances glutaminolysis, and triggers mitohormesis that is required for extension of lifespan and healthspan in Caenorhabditis elegans subjected to glucose starvation or caloric restriction. Muscle-specific re-introduction of wildtype PDZD8, but not the AMPK-unphosphorylable PDZD8-T527A mutant, to PDZD8-/- mice is able to rescue the increase of glutaminolysis, and the rejuvenating effects of caloric restriction in aged mice, including grip strength and running capacity. Together, these findings reveal an AMPK-PDZD8-GLS1 axis that promotes glutaminolysis and executes the anti-ageing effects of calorie restriction by promoting inter-organelle crosstalk between ER and mitochondria.

cell biology↗

bioRxiv2023

Transfer Learning Enhanced Graph Neural Network for Aldehyde Oxidase Metabolism Prediction and Its Experimental Application

Aldehyde oxidase (AOX) is a molybdoenzyme that is primarily expressed in the liver and is involved in the metabolism of drugs and other xenobiotics. AOX-mediated metabolism can result in unexpected outcomes, such as the production of toxic metabolites and high metabolic clearance, which can lead to the clinical failure of novel therapeutic agents. Computational models can assist medicinal chemists in rapidly evaluating the AOX metabolic risk of compounds during the early phases of drug discovery and provide valuable clues for manipulating AOX-mediated metabolism liability. In this study, we developed a novel graph neural network called AOMP for predicting AOX-mediated metabolism. AOMP integrated the tasks of metabolic substrate/non-substrate classification and metabolic site prediction, while utilizing transfer learning from 13C nuclear magnetic resonance data to enhance its performance on both tasks. AOMP significantly outperformed the benchmark methods in both cross-validation and external testing. Using AOMP, we systematically assessed the AOX-mediated metabolism of common fragments in kinase inhibitors and successfully identified four new scaffolds with AOX metabolism liability, which were validated through in vitro experiments. Furthermore, for the convenience of the community, we established the first online service for AOX metabolism prediction based on AOMP, which is freely available at https://aomp.alphama.com.cn.

bioinformatics↗

bioRxiv2023

Study design features that improve effect sizes in cross-sectional and longitudinal brain-wide association studies

Brain-wide association studies (BWAS) are a fundamental tool in discovering brain-behavior associations. Several recent studies showed that thousands of study participants are required for good replicability of BWAS because the standardized effect sizes (ESs) are much smaller than the reported standardized ESs in smaller studies. Here, we perform analyses and meta-analyses of a robust effect size index using 63 longitudinal and cross-sectional magnetic resonance imaging studies from the Lifespan Brain Chart Consortium (77,695 total scans) to demonstrate that optimizing study design is critical for increasing standardized ESs and replicability in BWAS. A meta-analysis of brain volume associations with age indicates that BWAS with larger variability in covariate have larger reported standardized ES. In addition, the longitudinal studies we examined reported systematically larger standardized ES than cross-sectional studies. Analyzing age effects on global and regional brain measures from the United Kingdom Biobank and the Alzheimers Disease Neuroimaging Initiative, we show that modifying longitudinal study design through sampling schemes improves the standardized ESs and replicability. Sampling schemes that improve standardized ESs and replicability include increasing between-subject age variability in the sample and adding a single additional longitudinal measurement per subject. To ensure that our results are generalizable, we further evaluate these longitudinal sampling schemes on cognitive, psychopathology, and demographic associations with structural and functional brain outcome measures in the Adolescent Brain and Cognitive Development dataset. We demonstrate that commonly used longitudinal models can, counterintuitively, reduce standardized ESs and replicability. The benefit of conducting longitudinal studies depends on the strengths of the between-versus within-subject associations of the brain and non-brain measures. Explicitly modeling between-versus within-subject effects avoids averaging the effects and allows optimizing the standardized ESs for each separately. Together, these results provide guidance for study designs that improve the replicability of BWAS.

neuroscience↗

bioRxiv2023

Utilizing Pre-trained Network Medicine Models for Generating Biomarkers, Targets, Re-purposing Drugs, and Personalized Therapeutic Regimes: COVID-19 Applications

In this paper, we present a novel pre-trained network medicine model called Selective Remodeling of Protein Networks by Chemicals (SEMO). We divide the global human protein-protein interaction (PPI) network into smaller sub-networks, and quantify the potential effects of chemicals by statistically comparing their target and non-target gene sets. By combining 9607 PPI gene sets with 2658 chemicals, we created a pre-trained pool of SEMOs, which we then used to identify SEMOs related to Covid-19 severity using DNA methylation profiling data from two clinical cohorts. The nutraceutical-derived SEMO features provided an effective model for predicting Covid-19 severity, with an AUC score of 81% in the training data and 80% in the independent validation data. Our findings suggest that Vitamin D3, Lipoic Acid, Citrulline, and Niacin, along with their associated protein networks, particularly STAT1, MMP2, CD8A, and CXCL8 as hub nodes,could be used to effectively predict Covid-19 severity. Furthermore, the severity-associated SEMOs were found to be significantly correlated with CD4+ and monocyte cell proportions. These insights can be used to generate personalized nutraceutical regimes by ranking the relative severity risk associated with each SEMO. Thus, our pre-trained SEMO model can serve as a fundamental knowledge map when coupled with DNA methylation measurements, allowing us to simultaneously generate biomarkers, targets, re-purposing drugs, and nutraceutical interventions.

bioinformatics↗

bioRxiv2023

A cleaved METTL3 potentiates the METTL3-WTAP interaction and breast cancer progression

N6-methyladenosine (m6A) methylation of RNA by the methyltransferase complex (MTC), with core components including METTL3-METTL14 heterodimers and Wilms tumor 1-associated protein (WTAP), contributes to breast tumorigenesis, but the underlying regulatory mechanisms remain elusive. Here, we identify a novel cleaved form METTL3a (residues 239-580 of METTL3). We find that METTL3a is required for the METTL3-WTAP interaction, RNA m6A deposition, as well as cancer cell proliferation. Mechanistically, we find that METTL3a is essential for the METTL3-METTL3 interaction, which is a prerequisite step for recruitment of WTAP in MTC. Analysis of m6A sequencing data shows that depletion of METTL3a globally disrupts m6A deposition, and METTL3a mediates mTOR activation via m6A-mediated suppression of TMEM127 expression. Moreover, we find that METTL3 cleavage is mediated by proteasome in an mTOR-dependent manner, revealing positive regulatory feedback between METTL3a and mTOR signaling. Our findings reveal METTL3a as an important component of MTC, and suggest the METTL3a-mTOR axis as a potential therapeutic target for breast cancer.

cell biology↗

bioRxiv2023

Insm1 regulates the development of mTECs and immune tolerance

The Insm1 gene encodes a zinc finger protein with known functions in neuroendocrine cells and neurons. Here we characterized the expression and function of Insm1 in medullary thymic epithelial cells (mTECs). Insm1 is co-expressed with Aire in majority of Insm1 or Aire positive cells, while a few Insm1 positive cells did not express Aire. Mutation of Insm1 impair the expression of Aire and the generation of normal numbers of Aire-expressing mTECs during development. We detected downregulation of genes that expressed specifically in Aire-expressing mTEC and mimetic cells in Insm1 mutant mTECs. Conversely, when Insm1 was overexpressed in thymic epithelial cells in vivo, the size of the mTECs compartment was enlarged and the expression of Aire and genes expressed specifically in the neuroendocrine mimetic cells were increased. Mechanistically, Insm1 bound DNA in mTECs and the majority of the Insm1 binding sites were co-occupied by Aire. These Insm1 binding sites were enriched on super-enhancer regions and thus may contributed to remoted regulation. Both, mice with a thymus-specific mutation in Insm1 or nude mice transplanted with Insm1 mutant thymus, displayed autoimmune responses in multiple peripheral tissues. Together, our data demonstrate a role of Insm1 in development of mTECs and immune tolerance.

immunology↗

bioRxiv2022

Systematic comparison and rational design of theophylline riboswitches for efficient gene repression

Riboswitches are promising regulatory tools in synthetic biology. To date, 25 theophylline riboswitches have been developed for gene expression regulation in bacteria. However, no one has systematically evaluated their regulatory effects. To facilitate rational selection of theophylline riboswitches, we examined 25 theophylline riboswitches in Escherichia coli and surprised to find that none of the five repressive riboswitches were more than 2-fold effective. To solve this problem, we rationally designed a transcriptional repressive riboswitch and demonstrated its effect not only in various bacterial strains but also in different growth media or different temperatures. By introducing two copies of theophylline riboswitches and a RepA protein degradation tag coding sequence at the 5-end of a reporter gene, we successfully constructed a dual gene expression regulatory system with up to 150-fold potency, namely the R2-RepA system. R2-RepA system is only 218 bp in length, expression of any protein could be repressed efficiently by simply inserting this system upstream of the target protein-coding sequence. This study represented a crucial step toward harnessing theophylline riboswitches and expanding the synthetic biology toolbox.

synthetic biology↗