Biology subjects

Hubbard, S. J.

Publications and source records attributed to Hubbard, S. J..

5 recordsLinked to original sources

bioRxiv2021

Cytosolic aspartate aminotransferase moonlights as a ribosome binding modulator of Gcn2 activity during oxidative stress

Regulation of translation is a fundamental facet of the cellular response to rapidly changing external conditions. Specific RNA-binding proteins (RBPs) co-ordinate the translational regulation of distinct mRNA cohorts during stress. To identify RBPs with previously under-appreciated roles in translational control, we used polysome profiling and mass spectrometry to identify and quantify proteins associated with translating ribosomes in unstressed yeast cells and during oxidative stress and amino acid starvation, which both induce the integrated stress response (ISR). Over 800 proteins were identified across polysome gradient fractions, including ribosomal proteins, translation factors and many others without previously described translation-related roles, including numerous metabolic enzymes. We identified variations in patterns of polysome enrichment in both unstressed and stressed cells and identified proteins enriched in heavy polysomes during stress. Genetic screening of polysome-enriched RBPs identified the cytosolic aspartate aminotransferase, Aat2, as a ribosome-associated protein whose deletion conferred growth sensitivity to oxidative stress. Loss of Aat2 caused aberrantly high activation of the ISR via enhanced eIF2 phosphorylation and GCN4 activation. Importantly, non-catalytic AAT2 mutants retained polysome association and did not show heightened stress sensitivity. Aat2 therefore has a separate ribosome-associated translational regulatory or moonlighting function that modulates the ISR independent of its aspartate aminotransferase activity.

biochemistry↗

bioRxiv2021

Senescence inhibits the chaperone response to thermal stress

Cells respond to stress by synthesising chaperone proteins that correct protein misfolding to maintain function. However, protein homeostasis is lost in ageing, leading to aggregates characteristic of protein-folding diseases. Whilst much is known about how these diseases progress, discovering what causes protein-folding to deteriorate could be key to their prevention. Here, we examined primary human mesenchymal stem cells (hMSCs), cultured to a point of replicative senescence and subjected to heat shock, as an in vitro model of the ageing stress response. We found through proteomic analysis that the maintenance of homeostasis deteriorated in senescent cells. Time-resolved analysis of factors regulating heat shock protein 70 kDa (HSPA1A) revealed a lack of capacities for protein turnover and translation to be key factors in limiting the stress response during senescence. A kinetic model predicted a consequence of these reduced capacities to be the accumulation of misfolded protein, a hypothesis supported by evidence of systematic changes to protein fold state. These results thus further our understanding of the underlying mechanistic links between ageing and loss of protein homeostasis.

cell biology↗

bioRxiv2021

Implementing the re-use of public DIA proteomics datasets: from the PRIDE database to Expression Atlas

The number of mass spectrometry (MS)-based proteomics datasets in the public domain keeps increasing, particularly those generated by Data Independent Acquisition (DIA) approaches such as SWATH-MS. Unlike Data Dependent Acquisition datasets, the re-use of DIA datasets has been rather limited to date, despite its high potential, due to the technical challenges involved. We introduce a (re-)analysis pipeline for public SWATH-MS datasets which includes a combination of metadata annotation protocols, automated workflows for MS data analysis, statistical analysis, and the integration of the results into the Expression Atlas resource. Automation is orchestrated with Nextflow, using containerised open analysis software tools, rendering the pipeline readily available and reproducible. To demonstrate its utility, we reanalysed 10 public DIA datasets from the PRIDE database, comprising 1,278 SWATH-MS runs. The robustness of the analysis was evaluated, and the results compared to those obtained in the original publications. The final expression values were integrated into Expression Atlas, making SWATH-MS experiments more widely available and combining them with expression data originating from other proteomics and transcriptomics datasets.

bioinformatics↗

bioRxiv2020

Functional analysis of caspase cleavable proteoforms from the Drosophila GSK-3 gene shaggy.

The Drosophila shaggy (sgg) gene encodes the major fly orthologue of Glycogen Synthase Kinase -3 (GSK-3), a key highly conserved kinase at the heart of many signalling pathways. The sgg locus is complex, encoding multiple protein isoforms that are expressed in distinct temporal and tissue-specific patterns across development. Its isoforms predominantly differ at the carboxy and amino termini due to the use of different transcriptional start sites and alternative splicing events that include internal and terminal exons. One interesting class of proteins isoforms is represented by the Sgg-PD class (Sgg46), three proteoforms that contain a large 582 amino acid N-terminal domain which contains recognition sites for caspase-mediated cleavage. Regulated cleavage at these sites by non-apoptotic caspases has previously been implicated in the regulation of Sgg activity in adult bristle development. Here, we take a genome engineering approach to introduce specific tags into this unique Sgg-PD exon and utilise these for localisation and protein interaction studies. We also generated new loss of function alleles and specific mutations in the caspase cleavage motifs. We find that loss of functions Sgg-PD class alleles are viable and fertile, but exhibit adult locomotor and bristle defects. Expression analysis of lines carrying tags on both sides of the caspase cleavage sites indicates that the cleavage is developmentally regulated during embryogenesis. Surprisingly, we found that in some cells, particularly embryonic hemocytes, the N-terminal domain released by caspase cleavage is retained while the polypeptide containing the conserved kinase domain is apparently lost. Transcriptomic analysis of embryos homozygous for the new caspase-insensitive allele indicates a role for Sgg-PD in the regulation of cytoskeletal and cell junction functions, which is supported by proteomics analysis using specific in locus tags to identify common and unique protein interaction partners with N- and C-terminal domains. Taken together, our work identifies new activities for the Sgg protein and uncovers unexpected roles for caspase cleavage in Sgg biology.

developmental biology↗

bioRxiv2020

Integrated multi-omics reveals common properties underlying stress granule and P-body formation

Non-membrane-bound compartments such as P-bodies (PBs) and stress granules (SGs) play important roles in the regulation of gene expression following environmental stresses. We have systematically determined the protein and mRNA composition of PBs and SGs formed in response to a common stress condition imposed by glucose depletion. We find that high molecular weight (HMW) complexes exist prior to glucose depletion that may act as seeds for the further condensation of proteins forming mature PBs and SGs. Both before and after glucose depletion, these HMW complexes are enriched for proteins containing low complexity and RNA binding domains. The mRNA content of these HMW complexes is enriched for long, structured mRNAs that become more poorly translated following glucose depletion. Many proteins and mRNAs are shared between PBs and SGs including several multivalent RNA binding proteins that may promote condensate interactions during liquid-liquid phase separation. Even where the precise identity of mRNAs and proteins localizing to PBs and SGs is distinct, the mRNAs and proteins share common biophysical and chemical features that likely trigger their phase separation.

biochemistry↗