Biology subjects

Iwasaki, S.

Publications and source records attributed to Iwasaki, S..

50 records · Page 3Linked to original sources

bioRxiv2021

eIF2B-capturing viral protein NSs suppresses the integrated stress response

Various stressors such as viral infection lead to the suppression of cap-dependent translation and the activation of the integrated stress response (ISR), since the stress-induced phosphorylated eukaryotic translation initiation factor 2 [eIF2(P)] tightly binds to eIF2B to prevent it from exchanging guanine nucleotides on unphosphorylated eIF2. Sandfly fever Sicilian virus (SFSV) evades this cap-dependent translation suppression through the interaction between its nonstructural protein NSs and host eIF2B. Our cryo-electron microscopy (cryo-EM) analysis revealed that SFSV NSs binds to the -subunit of eIF2B in a competitive manner with eIF2(P). Together with SFSV NSs, eIF2B exhibits normal nucleotide exchange activity even in the presence of eIF2(P). A genome-wide ribosome profiling analysis clarified that SFSV NSs in human cultured cells attenuates the ISR. Furthermore, SFSV NSs exhibited neuroprotective effects against the ISR-inducing stress. Since the ISR inhibition is beneficial in various neurological disease models, SFSV NSs is promising as a therapeutic ISR inhibitor.

molecular biology↗

bioRxiv2021

Transient ribosome slowdown at the decoding step triggers mRNA degradation independent of Znf598 in zebrafish

The control of mRNA stability plays a central role in regulating gene expression patterns. Recent studies have revealed that codon composition in the open reading frame (ORF) determines mRNA stability in multiple organisms. Based on genome-wide correlation approaches, this previously unrecognized role of the genetic code is attributable to the kinetics of the codon-decoding process by the ribosome. However, complementary experimental analysis is required to define the codon effects on mRNA stability apart from the related cotranslational mRNA decay pathways such as those triggered by aberrant ribosome stalls. In the current study, we performed a set of reporter-based analyses to define codon-mediated mRNA decay and ribosome stall-dependent mRNA decay in zebrafish embryos. Our analysis showed that the effect of codons on mRNA stability stems from the decoding process, independent of Znf598 and stall-dependent mRNA decay. We propose that codon-mediated mRNA decay is triggered by transiently slowed ribosomes engaging in a productive translation cycle in zebrafish embryos.

molecular biology↗

bioRxiv2021

Nascent polypeptide within the exit tunnel ensures continuous translation elongation by stabilizing the translating ribosome

Continuous translation elongation, irrespective of amino acid sequences, is a prerequisite for living organisms to produce their proteomes. However, the risk of elongation abortion is concealed within nascent polypeptide products. Negatively charged sequences with occasional intermittent prolines, termed intrinsic ribosome destabilization (IRD) sequences, destabilizes the translating ribosomal complex. Thus, some nascent chain sequences lead to premature translation cessation. Here, we show that the risk of IRD is maximal at the N-terminal regions of proteins encoded by dozens of Escherichia coli genes. In contrast, most potential IRD sequences in the middle of open reading frames remain cryptic. We found two elements in nascent chains that counteract IRD: the nascent polypeptide itself that spans the exit tunnel and its bulky amino acid residues that occupy the tunnel entrance region. Thus, nascent polypeptide products have a built-in ability to ensure elongation continuity by serving as a bridge and thus by protecting the large and small ribosomal subunits from dissociation.

biochemistry↗

bioRxiv2020

Splicing modulators elicit global translational repression by condensate-prone proteins translated from introns

Chemical splicing modulators that bind to the spliceosome have provided an attractive venue for cancer treatment. Splicing modulators induce accumulation and subsequent translation of a subset of intron-retained mRNAs. Yet, the biological effect of proteins containing translated intron sequences remains unclear. Here we identified a number of truncated proteins generated upon treatment with the splicing modulator spliceostatin A (SSA) using genome-wide ribosome profiling and bio-orthogonal non-canonical amino-acid tagging (BONCAT) mass spectrometry. A subset of these truncated proteins has intrinsically disordered regions, forms insoluble cellular condensates, and triggers the proteotoxic stress response through JNK phosphorylation, thereby inhibiting the mTORC1 pathway. In turn, this reduces global translation. These findings indicate that creating an overburden of condensate-prone proteins derived from introns represses translation and prevents further production of harmful truncated proteins. This mechanism appears to contribute to the antiproliferative and proapoptotic activity of splicing modulators.

molecular biology↗

bioRxiv2020

Selective translation of epigenetic modifiers drives the developmental clock of neural stem cells

The cerebral cortex is formed by diverse neurons generated sequentially from neural stem cells (NSCs). A clock mechanism has been suggested to underlie the temporal progression of NSCs, which is mainly defined by the transcriptome and the epigenetic state. However, what drives such a developmental clock remains elusive. We show that translational control of histone H3 trimethylation at Lys27 (H3K27me3) modifiers is part of this clock. We found that depletion of Fbl, an rRNA methyltransferase, reduces translation of both the Ezh2 methyltransferase and Kdm6b demethylase of H3K27me3 and delays progression of the NSC state. These defects are phenocopied by simultaneous inhibition of H3K27me3 methyltransferase and demethylase, indicating the role of Fbl in the genome-wide H3K27me3 pattern. Fbl selectively enhances the translation of H3K27me3 modifiers via a cap-independent mechanism. We thus propose that Fbl drives the intrinsic clock through the translational enhancement of H3K27me3 modifiers that predominantly define the NSC state.

developmental biology↗

bioRxiv2020

Ribosomal protein S7 ubiquitination during ER stress in yeast is associated with selective mRNA translation and stress outcome

eIF2 phosphorylation-mediated translational regulation is crucial for global translation repression by various stresses, including the unfolded protein response (UPR). However, translational control during UPR has not been demonstrated in yeast. This study investigated ribosome ubiquitination-mediated translational controls during UPR. Tunicamycin-induced ER stress enhanced the levels of ubiquitination of the ribosomal proteins uS10, uS3 and eS7. Not4-mediated monoubiquitination of eS7A was required for resistance to tunicamycin, whereas E3 ligase Hel2-mediated ubiquitination of uS10 was not. Ribosome profiling showed that the monoubiquitination of eS7A was crucial for translational regulation, including the upregulation of the spliced form of HAC1 (HAC1i) mRNA and the downregulation of Histidine triad NucleoTide-binding 1 (HNT1) mRNA. Downregulation of the deubiquitinating enzyme complex Upb3-Bre5 increased the levels of ubiquitinated eS7A during UPR in an Ire1-independent manner. These findings suggest that the monoubiquitination of ribosomal protein eS7A plays a crucial role in translational controls during the ER stress response in yeast.

molecular biology↗

bioRxiv2020

Ribosome stalling caused by the Argonaute-miRNA-SGS3 complex regulates production of secondary siRNA biogenesis in plants

The path of ribosomes on mRNAs can be impeded by various obstacles. One such example is halting of ribosome movement by microRNAs, though the exact mechanism and physiological role remain unclear. Here, we find that ribosome stalling caused by the Argonaute-microRNA-SGS3 complex regulates the production of secondary small interfering RNAs (siRNAs) in plants. We show that the double-stranded RNA-binding protein SGS3 directly interacts with the 3' end of the microRNA in an Argonaute protein, resulting in ribosome stalling. Importantly, microRNA-mediated ribosome stalling positively correlates with efficient production of secondary siRNAs from target mRNAs. Our results illustrate a role for paused ribosomes in regulation of small RNA function that may have broad biological implications across the plant kingdom.

molecular biology↗

bioRxiv2020

Efficacy of a novel SARS-CoV-2 detection kit without RNA extraction and purification

Rapid detection of SARS-CoV-2 is critical for the diagnosis of coronavirus disease 2019 (COVID-19) and preventing the spread of the virus. A novel "2019 Novel Coronavirus Detection Kit (nCoV-DK)" halves detection time by eliminating the steps of RNA extraction and purification. We evaluated concordance between the nCoV-DK and direct PCR. The virus was detected in 53/71 fresh samples by the direct method and 55/71 corresponding frozen samples by the nCoV-DK. The overall concordance rate of the virus detection between the two methods was 94.4% (95% CI, 86.2-98.4). Concordance rates were 95.2% (95% CI, 83.8-99.4), 95.5% (95% CI, 77.2-99.9), 85.7% (95% CI, 42.1-99.6) in nasopharyngeal swab, saliva, and sputum samples, respectively. These results indicate that the nCoV-DK effectively detects SARS-CoV-2 in all types of the samples including saliva, while reducing time required for detection, labor, and risk of human error.

microbiology↗

bioRxiv2019

A widespread family of heat-resistant obscure (Hero) proteins protect against protein instability and aggregation

Proteins are typically denatured and aggregated by heat. Exceptions to this principle include highly disordered and heat-resistant proteins found in extremophiles, which help these organisms tolerate extreme conditions such as drying, freezing, and high salinity. In contrast, the functions of heat-soluble proteins in non-extremophilic organisms including humans remain largely unexplored. Here we report that heat-resistant obscure (Hero) proteins, which remain soluble after boiling at 95{degrees}C, are widespread in Drosophila and humans. Hero proteins are hydrophilic and highly charged, and function to stabilize various "client" proteins, protecting them from denaturation even under stress conditions such as heat shock, desiccation, and exposure to organic solvents. Hero proteins can also block several different types of pathological protein aggregations in cells and in Drosophila strains that model neurodegenerative diseases. Moreover, Hero proteins can extend lifespan of Drosophila. Our study reveals that organisms naturally use Hero proteins as molecular shields to stabilize protein functions, highlighting their biotechnological and therapeutic potential.

molecular biology↗

bioRxiv2019

Genome-wide survey of ribosome collision

In protein synthesis, ribosome movement is not always smooth and is rather often impeded for numerous reasons. Although the deceleration of the ribosome defines the fates of the mRNAs and synthesizing proteins, fundamental issues remain to be addressed, including where ribosomes pause in mRNAs, what kind of RNA/amino acid sequence causes this pause, and the physiological significance of this slowdown of protein synthesis. Here, we surveyed the positions of ribosome collisions caused by ribosome pausing in humans and zebrafish on a genome-wide level using modified ribosome profiling. The collided ribosomes, i.e., disomes, emerged at various sites: the proline-proline-lysine motif, stop codons, and the 3' untranslated region (UTR). The number of ribosomes involved in a collision is not limited to two, but rather four to five ribosomes can form a queue of ribosomes. In particular, XBP1, a key modulator of the unfolded protein response, shows striking queues of collided ribosomes and thus acts as a substrate for ribosome-associated quality control (RQC) to avoid the accumulation of undesired proteins in the absence of stress. Our results provide an insight into the causes and consequences of ribosome slowdown by dissecting the specific architecture of ribosomes.

molecular biology↗

bioRxiv2019

Codon Optimality Confers GC-Rich-Induced Stability to mRNAs in Humans

Codon bias has been implicated as one of the major factors contributing to mRNA stability in yeast. However, the effects of codon-bias on mRNA stability remain unclear in humans. Here we show that human cells possess a mechanism to modulate RNA stability through a unique codon bias different from that of yeast. Bioinformatics analysis showed that codons could be clustered into two distinct groups - codons with G or C at the third base position (GC3) and codons with either A or T at the third base position (AT3); the former stabilizing while the latter destabilizing mRNA. Quantification of codon bias showed that increased GC3 content entails proportionately higher GC content. Through bioinformatics, ribosome profiling and in vitro analysis, we show that decoupling of the effects of codon bias reveals two modes of mRNA regulation, GC3- and GC-content dependent. Employing an immunoprecipitation-based strategy, we identified ILF2 as an RNA binding protein that differentially regulates global mRNA abundances based on codon bias. Our results demonstrate that codon bias is a two-pronged system that governs mRNA abundance.

molecular biology↗

bioRxiv2018

Proximity RNA labeling by APEX-Seq Reveals the Organization of Translation Initiation Complexes and Repressive RNA Granules

Diverse ribonucleoprotein complexes control messenger RNA processing, translation, and decay. Transcripts in these complexes localize to specific regions of the cell and can condense into non-membrane-bound structures such as stress granules. It has proven challenging to map the RNA composition of these large and dynamic structures, however. We therefore developed an RNA proximity labeling technique, APEX-Seq, which uses the ascorbate peroxidase APEX2 to probe the spatial organization of the transcriptome. We show that APEX-Seq can resolve the localization of RNAs within the cell and determine their enrichment or depletion near key RNA-binding proteins. Matching the spatial transcriptome, as revealed by APEX-Seq, with the spatial proteome determined by APEX-mass spectrometry (APEX-MS) provides new insights into the organization of translation initiation complexes on active mRNAs, as well as exposing unanticipated complexity in stress granule composition, and provides a powerful and general approach to explore the spatial environment of macromolecules.

genomics↗

bioRxiv2018

UPA-Seq: Prediction of Functional LncRNAs Using Differential Sensitivity to UV Crosslinking

While a large number of long noncoding RNAs (lncRNAs) are transcribed from the genome of higher eukaryotes, systematic prediction of their functionality has been challenging due to the lack of conserved sequence motifs or structures. Assuming that lncRNAs function as large ribonucleoprotein complexes and thus are easily crosslinked to proteins upon UV irradiation, we performed RNA-Seq analyses of RNAs recovered from the aqueous phase after UV irradiation and phenol-chloroform extraction (UPA-Seq). As expected, the numbers of UPA-Seq reads mapped to known functional lncRNAs were remarkably reduced upon UV irradiation. Comparison with ENCODE eCLIP data revealed that lncRNAs that exhibited greater decreases upon UV irradiation preferentially associated with proteins containing prion-like domains (PrLDs). Fluorescent in situ hybridization (FISH) analyses revealed the nuclear localization of novel functional lncRNA candidates, including one that accumulated at the site of transcription. We propose that UPA-Seq provides a useful tool for the selection of lncRNA candidates to be analyzed in depth in subsequent functional studies.

molecular biology↗

bioRxiv2017

Cell Type Specific Survey of Epigenetic Modifications by Tandem Chromatin Immunoprecipitation Sequencing

BackgroundThe nervous system of higher eukaryotes is composed of numerous types of neurons and glia that together orchestrate complex neuronal responses. However, this complex pool of cells typically poses analytical challenges in investigating gene expression profiles and their epigenetic basis for specific cell types. Here, we developed a novel method that enables cell type-specific analyses of epigenetic modifications using tandem chromatin immunoprecipitation sequencing (tChIP-Seq).\n\nResultsFLAG-tagged histone H2B, a constitutive chromatin component, was first expressed in Camk2a-positive pyramidal cortical neurons and used to purify chromatin in a cell type-specific manner. Subsequent chromatin immunoprecipitation using antibodies against H3K4me3--an active promoter mark--allowed us to survey neuron-specific coding and non-coding transcripts. Indeed, tChIP-Seq identified hundreds of genes associated with neuronal functions and genes with unknown functions expressed in cortical neurons.\n\nConclusionstChIP-Seq thus provides a versatile approach to investigating the epigenetic modifications of particular cell types in vivo.

molecular biology↗