Biology subjects

Xiao, T.

Publications and source records attributed to Xiao, T..

89 records · Page 5Linked to original sources

bioRxiv2020

The GET Pathway Safeguards Against Non-Imported Mitochondrial Protein Stress

Deficiencies in mitochondrial import cause the toxic accumulation of non-imported mitochondrial precursor proteins. Numerous fates for non-imported mitochondrial precursors have been identified, including proteasomal destruction, deposition into protein aggregates, and mis-targeting to other organelles. Amongst organelles, the endoplasmic reticulum (ER) has emerged as a key destination for non-imported mitochondrial proteins, but how ER-targeting of these proteins is achieved remains unclear. Here, we show that the guided entry of tail-anchored proteins (GET) complex is required for ER-targeting of endogenous mitochondrial multi-transmembrane proteins. Without a functional GET pathway, non-imported mitochondrial proteins destined for the ER are alternatively sequestered into Hsp42-dependent protein foci. The ER targeting of non-imported mitochondrial proteins by the GET complex prevents cellular toxicity and facilitates re-import of mitochondrial proteins from the ER via the recently identified ER-SURF pathway. Overall, this study outlines an important and unconventional role for the GET complex in mitigating stress associated with non-imported mitochondrial proteins.

cell biology↗

bioRxiv2020

Characterization of a gene-trap knockout mouse model of Scn2a encoding voltage-gated sodium channel Nav1.2

Recent large-scale genomic studies have revealed SCN2A as one of the most frequently mutated gene in patients with neurodevelopmental disorders including autism spectrum disorder and intellectual disability. SCN2A encodes for voltage-gated sodium channel isoform 1.2 (Nav1.2), which is mainly expressed in the central nervous system and responsible for the propagation of neuronal action potentials. Homozygous knockout (null) of Scn2a is perinatal lethal, whereas heterozygous knockout of Scn2a results in mild behavior abnormalities. To achieve a more substantial, but not complete, reduction of Scn2a expression, we characterized a Scn2a deficient mouse model using a targeted gene trap knockout (gtKO) strategy to recapitulate loss-of-function SCN2A disorders. This model produces viable homozygous mice (Scn2agtKO/gtKO) that can survive to adulthood, with markedly low but detectable Nav1.2 expression. Although Scn2agtKO/gtKO adult mice possess normal olfactory, taste, hearing, and mechanical sensitivity, they have decreased thermal and cold tolerance. Innate behaviors are profoundly impaired including impaired nesting, marble burying, and mating. These mice also have increased food and water intake with subsequent increases in fecal excretion of more but smaller fecal boli. This novel Scn2a gene trap knockout mouse thus provides a unique model to study pathophysiology associated with Scn2a deficiency.

neuroscience↗

bioRxiv2020

Identification of novel tetracycline resistance gene tet(X14) and its co-occurrence with tet(X2) in a tigecycline-resistant and colistin-resistant Empedobacter stercoris

Tigecycline is one of the last-resort antibiotics to treat severe infections. Recently, tigecycline resistance has sporadically emerged with an increasing trend, and Tet(X) family represents a new resistance mechanism of tigecycline. In this study, a novel chromosome-encoded tigecycline resistance gene, tet(X14), was identified in a tigecycline-resistant and colistin-resistant Empedobacter stercoris strain ES183 recovered from a pig fecal sample in China. Tet(X14) shows 67.14-96.39% sequence identity to the other variants [Tet(X) to Tet(X13)]. Overexpression of Tet(X14) in Escherichia coli confers 16-fold increase in tigecycline MIC (from 0.125 to 2 mg/L), which is lower than that of Tet(X3), Tet(X4) and Tet(X6). Structural modelling predicted that Tet(X14) shared a high homology with the other 12 variants with RMSD value from 0.003 to 0.055, and Tet(X14) can interact with tetracyclines by a similar pattern as the other Tet(X)s. tet(X14) and two copies of tet(X2) were identified on a genome island with abnormal GC content carried by the chromosome of ES183, and no mobile genetic elements were found surrounding, suggesting that tet(X14) might be heterologously obtained by ES183 via recombination. Blasting in Genbank revealed that Tet(X14) was exclusively detected on the chromosome of Riemerella anatipestifer, mainly encoded on antimicrobial resistance islands. E. stercoris and R. anatipestifer belong to the family Flavobacteriaceae, suggesting that the members of Flavobacteriaceae maybe the major reservoir of tet(X14). Our study reports a novel chromosome-encoded tigecycline resistance gene tet(X14). The expanded members of Tet(X) family warrants the potential large-scale dissemination and the necessity of continuous surveillance for tet(X)-mediated tigecycline resistance.

genetics↗

bioRxiv2020

Distinct conformational states of SARS-CoV-2 spike protein

The ongoing SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) pandemic has created urgent needs for intervention strategies to control the crisis. The spike (S) protein of the virus forms a trimer and catalyzes fusion between viral and target cell membranes - the first key step of viral infection. Here we report two cryo-EM structures, both derived from a single preparation of the full-length S protein, representing the prefusion (3.1[A] resolution) and postfusion (3.3[A] resolution) conformations, respectively. The spontaneous structural transition to the postfusion state under mild conditions is independent of target cells. The prefusion trimer forms a tightly packed structure with three receptor-binding domains clamped down by a segment adjacent to the fusion peptide, significantly different from recently published structures of a stabilized S ectodomain trimer. The postfusion conformation is a rigid tower-like trimer, but decorated by N-linked glycans along its long axis with almost even spacing, suggesting possible involvement in a mechanism protecting the virus from host immune responses and harsh external conditions. These findings advance our understanding of how SARS-CoV-2 enters a host cell and may guide development of vaccines and therapeutics.

biochemistry↗

bioRxiv2020

Silent dissemination of plasmid-borne tigecycline resistance gene tet(X6) in livestock-associated Acinetobacter towneri

A tigecycline-resistance gene, tet(X6), was detected on a 159-kb novel plasmid carried by a tigecycline-susceptible livestock-associated Acinetobacter towneri isolate. The genetic context of tet(X6) ({Delta}ISVsa3-tet(X6)-abh-guaA-ISVsa3) is highly similar with that of the other plasmid-borne tet(X) variants. The 23-Ala residue of the first FAD binding site conferred higher activity to Tet(X6) than the 23-Gly reside conserved in the other plasmid-borne tet(X)s. To our knowledge, this is the first report of tet(X6) carried by the plasmid.

genetics↗

bioRxiv2020

MSCs Successfully Deliver Oncolytic Virotherapy to Diffuse Intrinsic Pontine Glioma

Diffuse intrinsic pontine glioma (DIPG) is among the deadliest of pediatric brain tumors. Radiation therapy is the standard of care treatment for DIPG, but offers only transient relief of symptoms for DIPG patients without providing significant survival benefit. Oncolytic virotherapy (OV) is an anticancer treatment that has been investigated for treating various types of brain tumors. Here, we have explored the use of mesenchymal stem cells (MSC) for OV delivery and evaluated treatment efficacy using preclinical models of DIPG. Our results show that DIPG cells and tumors exhibit robust expression of cell surface proteins that are important for OV entry, and that MSCs loaded with OV disseminate within and release OV throughout the tumor in mice bearing DIPG brainstem xenografts. When combining administration of OV-loaded MSCs with radiotherapy, mice bearing brainstem DIPG xenografts experience a significant survival benefit, relative to that conferred by either therapy alone (p<0.0001). Our results support further preclinical investigation of cell-based OV therapy with radiation for potential translation in treating DIPG patients.

cancer biology↗

bioRxiv2019

Genome-wide CRISPR screens identify essential cell growth mediators in BRAF-inhibitor resistant melanoma

BRAF is a serine-threonine kinase that harbors activating mutations in [~]7% of human malignancies and [~]60% of melanomas. Despite initial clinical responses to BRAF inhibitors (BRAFi), patients frequently develop drug resistance. To identify candidate therapeutic targets for BRAFi-resistant melanoma, we conducted CRISPR screens in melanoma cells harboring an activating BRAF mutation that had also acquired resistance to BRAFi. The screens identified pathways and genes critical for BRAFi resistance in melanoma cells. To investigate the mechanisms and pathways enabling resistance to BRAFi in melanomas, we integrated expression data, ATAC-seq, and CRISPR screen results. We identified the JUN family of transcription factors and the ETS family transcription factor ETV5 as key regulators of CDK6 that enabled resistance to BRAFi in melanoma cells. Our findings reveal genes whose loss of function conferred resistance to a selective BRAF inhibitor, providing new insight into signaling pathways that contribute to acquired resistance in melanoma.

cancer biology↗

bioRxiv2019

CRISPR screening of porcine sgRNA library identified host factors essential for Japanese encephalitis virus replication

Japanese encephalitis virus (JEV) is a mosquito-borne zoonotic flavivirus that causes encephalitis and reproductive disorders in mammalian species. However, key host genes involved in the JEV life cycle and cell death are poorly understood. Here, we designed 85,674 single guide RNAs (sgRNAs) targeting 17,743 protein-coding genes, 11,053 long ncRNAs (lncRNAs), and 551 microRNAs (miRNAs) in the porcine genome, and subsequently developed a porcine sgRNA library and genome-scale CRISPR/Cas9 knockout (PigGeCKO) system. These sgRNAs were delivered into porcine kidney-15 (PK-15) cells that constitutively express Cas9, positive selection screening of the resulting PigGeCKO cell collection for resistance to JEV-induced cell death led to the identification of several previously unreported genes required for JEV infection. We conducted follow-up studies to verify the dependency of JEV on these genes, and identified functional contributions for six of the many candidate JEV-related host genes, including an endoplasmic reticulum membrane protein complex subunit 3 (EMC3) and calreticulin (CALR). Additionally, we identified that four genes associated with heparan sulfate proteoglycans (HSPGs) metabolism, specifically those responsible for HSPG sulfurylation, facilitated JEV entry into PK-15 cells. Thus, beyond our development of the largest CRISPR-based functional genomic screening platform for pig research to date, this work deepens our basic understanding of flavivirus infection and identifies multiple potentially vulnerable targets for the development of medical and breeding technologies to prevent and treat diseases caused by Japanese encephalitis virus.

genetics↗

bioRxiv2019

Ligand Entry into Fatty Acid Binding Protein via Local Unfolding instead of Gap Widening

Fatty acid binding proteins (FABPs) play an important role in transportation of fatty acids. Despite intensive studies, how fatty acids enter the protein cavity for binding is still controversial. Here, a gap-closed variant of human intestinal FABP was generated by mutagenesis, in which the gap is locked by a disulfide bridge. According to its structure determined here by NMR, this variant has no obvious openings as the ligand entrance and the gap cannot be widened by internal dynamics. Nevertheless, it still uptakes fatty acids and other ligands. NMR relaxation dispersion, chemical exchange saturation transfer and hydrogen-deuterium exchange experiments show that the variant exists in a major native state, two minor native-like state, and two locally unfolded states in aqueous solution. Local unfolding of either {beta}B-{beta}D or helix 2 can generate an opening large enough for ligands to enter the protein cavity, but only the fast local unfolding of helix 2 is relevant to the ligand entry process.\n\nStatement of SignificanceFatty acid binding proteins transport fatty acids to specific organelles in the cell. To enable the transport, fatty acids must enter and leave the protein cavity. In spite of many studies, how fatty acids enter the protein cavity remains controversial. Using mutagenesis and biophysical techniques, we have resolved the disagreement and further showed that local unfolding of the second helix can generate a transient opening to allow ligands to enter the protein cavity. Since lipid binding proteins are highly conserved in 3D structures and ligand binding, all of them may use the same local unfolding mechanism for ligand uptake and release.

biophysics↗

bioRxiv2019

CD8+ T-cell-mediated immunoediting influences genomic evolution and immune evasion in murine gliomas

Cancer immunoediting shapes tumor progression by the selection of tumor cell variants that can evade immune recognition. Given the immune evasion and intra-tumor heterogeneity intrinsic to gliomas, we hypothesized that CD8+ T-cells mediate immunoediting in these tumors. We evaluated glioma progression in the absence of CD8+ T-cells by depleting this immune cell population in transgenic murine gliomas. Upon transplantation, gliomas that developed in the absence of CD8+ T-cells engrafted poorly in recipients with intact immunity but engrafted well in those with CD8+ T-cell depletion. Gliomas developed in absence of CD8+ T-cells exhibited increased chromosomal instability, MAPK signaling, gene fusions, and macrophage/microglial infiltration. MAPK activation correlated with macrophage/microglial recruitment in this model and in the human disease. Our results indicate that CD8+ T-cells mediate immunoediting during gliomagenesis, influencing the genomic stability of glioma and its microenvironment, leading to immune evasion.\n\nSignificanceImmune evasion renders cancer resistant to anti-tumoral immunity. Therapeutic intervention often fails for gliomas because of the plasticity of tumor cell variants that resist immune surveillance. Our results demonstrate a mechanism of immune evasion in gliomas that derives from CD8+ T-cells during the development and progression of this disease.

cancer biology↗

bioRxiv2019

A comprehensive genome-scale model for Rhodosporidium toruloides IFO0880 accounting for functional genomics and phenotypic data

BackgroundRhodosporidium toruloides is a basidiomycetes yeast that can accumulate large amount of lipids and natively produce carotenoids. To better assess this non-model yeasts metabolic capabilities, we reconstruct a genome-scale model of R. toruloides IFO0880s metabolic network (iRhto1108) using recent functional genomics and phenotypic data in literature or generated herein.\n\nResultsThe model iRhto1108 accounts for 2,203 reactions, 1,985 metabolites and 1,108 genes. In this work, we integrate and supplement the current knowledge with in-house generated biomass composition and experimental measurements pertaining to the organisms metabolic capabilities. Phenotype-genotype relationship predictions were improved through manual curation of gene-protein-reaction rules for 543 reactions and validations with gene essentiality data leading to correct recapitulations of 84.5% of gene essentiality data (sensitivity of 94.3% and specificity of 53.8%). Organism-specific macromolecular composition and ATP maintenance requirements were experimentally measured for two separate growth conditions: (i) carbon and (ii) nitrogen limitations. Overall, iRhto1108 reproduced R. toruloidess utilization capabilities for 18 alternate substrates, matched measured wild-type growth yield, and recapitulated the viability of 772 out of 819 deletion mutants. As a demonstration to the models fidelity in guiding engineering interventions, the OptForce procedure was applied on iRhto1108 for the overproduction of triacylglycerol. Suggested interventions recapitulated many of the previously successfully implemented genetic modifications and put forth a few new ones.\n\nConclusioniRhto1108 offers a highly curated model for a non-model yeast supported by multiple layers of experimental data that can be used to inform genetic interventions.

systems biology↗

bioRxiv2018

Activation of dopamine receptor 2 (DRD2) prompts transcriptomic and metabolic plasticity in glioblastoma

Glioblastoma (GBM) is one of the most aggressive and lethal tumor types. Evidence continues to accrue indicating that the complex relationship between GBM and the brain microenvironment contributes to this malignant phenotype. However, the interaction between GBM and neurotransmitters, signaling molecules involved in neuronal communication, remains incompletely understood. Here we examined, in both sexes of humans and mice, how the monoamine dopamine influences GBM cells. We demonstrate that GBM cells express DRD2, with elevated expression in the glioma-initiating cell (GIC) population. Stimulation of DRD2 caused neuron-like depolarization exclusively in GICs. In addition, long-term activation of DRD2 heightened the sphere-forming capacity of GBM cells as well as tumor engraftment efficiency. Mechanistic investigation revealed that DRD2 signaling activates the hypoxia response and functionally alters metabolism. Finally, we found that GBM cells synthesize and secrete dopamine themselves, suggesting a potential autocrine mechanism. These results identify dopamine signaling as a potential therapeutic target in GBM and further highlight neurotransmitters as a key feature of the pro-tumor microenvironment.\n\nSignificance StatementThis work offers critical insight into the role of the neurotransmitter dopamine in the progression of GBM. We show that dopamine induces specific changes in the state of tumor cells, augmenting their growth and shifting them to a more stem-cell like state. Further, we show that dopamine can alter the metabolic behavior of GBM cells, increasing glycolysis. Finally, we show that GBM cells, including tumor samples from patients, can synthesize and secrete dopamine, suggesting an autocrine signaling process underlying these results. These results describe a novel connection between neurotransmitters and brain cancer, further highlighting the critical influence of the brain milieu on GBM.

cancer biology↗

bioRxiv2018

CRISPR/Cas9 screens Reveal Dasatinib Targets of Inhibiting T cell Activation and Proliferation

Immune response by T cells is essential for a healthy body against cancer, infection, and pathophysiological alteration. The activation and expansion of T cells can be inhibited by dasatinib, a tyrosine inhibitor, thus improving the outcome of diseases, such as autoimmune disease, graft-versus-host disease, and transplant rejection. The underlying mechanism of inhibition by dasatinib is elusive. Here, we designed and synthesized a CRISPR/Cas9 screening library that includes 6,149 genes. Using the library, we performed dasatinib CRISPR/cas9 screening in Jurkat cell, a T lymphocyte cell. We firstly identified survival essential genes for Jurkat cells. Comparing with other CRISPR/Cas9 screenings, we obtained Jurkat cell specific essential genes. By comparing dasatinib treatment to control, we identified a set of dasatinib targets, which includes known targets: CSK, LCK, ZAP70, and previously unknown targets: ZFP36L2, LRPPRC, CFLAR, PD-1, CD45 et al. Visualizing these target genes on T cell receptor signaling pathway, we found several genes could be inhibited by dasatinib. Furthermore, we introduced a framework, 9-square, to classify genes and found a group of genes that are associated with dasatinib resistance, possibly linking the side effects of dasatinib. These data reveal a set of dasatinib targets and demonstrate the molecular potential functions of dasatinib. Identification of dasatinib targets will broaden our understanding to its molecular mechanism, and thus benefits to clinical outcome.

cancer biology↗

bioRxiv2018

TP53I11 Suppresses Extracellular Matrix-independent Survival and Mesenchymal Transition in Mammary Epithelial Cells

Extracellular matrix (ECM)-independent survival is an essential prerequisite for tumor metastasis and a hallmark of epithelial cancer stem cells and epithelial-mesenchymal transition (EMT). We found that, in MCF10A and MDA-MB-231 cells, loss of TP53I11 (Tumor Protein P53 Inducible Protein 11) enhanced the ECM-independent survival and suppressed glucose starvation induced cell death by increasing the activation of AMPK that confer cells metabolic flexibility to survive under stress conditions. We show here that, TP53I11 enhanced glycolysis and promoted proliferation of MCF10A and MDA-MB-231 cells in normal culture, but exerted negative effect on EMT, cell migration and invasion, and its overexpression suppressed tumor progression and metastasis of MDA-MB-231 cells in vivo. Considering cancer cells also are confronted with the hostile environment such as nutrient scarcity during tumorigenesis and metastasis, our findings suggested that the disruption of metabolic flexibility by TP53I11 through inhibiting AMPK activation resulted in the suppression of tumorigenesis and metastasis of breast cancer.

molecular biology↗

bioRxiv2018

Reducing False Positives in CRISPR/Cas9 Screens from Copy Number Variations

CRISPR/Cas9 knockout screens have been widely used to interrogate gene functions across a wide range of cell systems. However, the screening outcome is biased in amplified genomic regions, due to the ability of the Cas9 nuclease to induce multiple double-stranded breaks and strong DNA damage responses at these regions. We developed algorithms to correct biases associated with copy number variations (CNV), even when the CNV profiles are unknown. We demonstrated that our methods effectively reduced false positives in amplified regions while preserving signals of true positives. In addition, we developed a sliding window approach to estimate regions of high copy numbers for cases in which CNV information is not available. These copy number estimations can subsequently be used to effectively correct CNV-related biases in CRISPR screening experiments. Our approach is integrated into the existing MAGeCK/MAGeCK-VISPR analysis pipelines and provides a convenient framework to improve the precision of CRISPR screening results.

bioinformatics↗

bioRxiv2017

Sodium valproate rescues expression of TRANK1 in iPSC-derived neural cells that carry a genetic variant associated with serious mental illness

Biological characterization of genetic variants identified in genome-wide association studies (GWAS) remains a substantial challenge. Here we used human induced pluripotent stem cells (hiPSC) and their neural derivatives to characterize common variants on chromosome 3p22 that have been associated by GWAS with major mental illnesses. HiPSC-derived neural progenitor cells carrying the risk allele of the single nucleotide polymorphism (SNP), rs9834970, displayed lower baseline TRANK1 expression that was rescued by chronic treatment with therapeutic dosages of valproic acid (VPA). Although rs9834970 has no known function, we demonstrated that a nearby SNP, rs90832, strongly affects binding by the transcription factor, CTCF, and that the high-affinity allele usually occurs on haplotypes carrying the rs9834970 risk allele. Decreased expression of TRANK1 perturbed expression of many genes involved in neural development and differentiation. These findings have important implications for the pathophysiology of major mental illnesses and the development of novel therapeutics.\n\nHighlightsO_LIhiPSC-derived neural cells carrying a mental illness risk allele showed lower expression of TRANK1\nC_LIO_LIValproic acid rescued TRANK1expression in cells carrying the risk allele\nC_LIO_LIRisk haplotypes usually carry an allele that increased CTCF binding\nC_LIO_LIReduced expression of TRANK1 perturbed genes involved in neural development and differentiation\nC_LI\n\nIn BriefUsing neural derivatives of human induced pluripotent stem cells, Jiang et al. demonstrate that genetic variants associated with mental illness alter transcription factor binding and decrease expression of a nearby gene, an effect which is rescued by valproic acid.

genetics↗

bioRxiv2017

Integrative analysis and refined design of CRISPR knockout screens

Genome-wide CRISPR-Cas9 screen has been widely used to interrogate gene functions. However, the analysis remains challenging and rules to design better libraries beg further refinement. Here we present MAGeCK-NEST, which integrates protein-protein interaction (PPI), improves the inference accuracy when fewer guide-RNAs (sgRNAs) are available, and assesses screen qualities using information on PPI. MAGeCK-NEST also adopts a maximum-likelihood approach to remove sgRNA outliers, which are characterized with higher G-nucleotide counts, especially in regions distal from the PAM motif. Using MAGeCK-NEST, we found that choosing non-targeting sgRNAs as negative controls lead to strong bias, which can be mitigated by sgRNAs targeting the \"safe harbor\" regions. Custom-designed screens confirmed our findings, and further revealed that 19nt sgRNAs consistently gave the best signal-to-noise separation. Collectively, our method enabled robust calling of CRISPR screen hits and motivated the design of an improved genome-wide CRISPR screen library.

bioinformatics↗