Biology subjects

Roberge, M.

Publications and source records attributed to Roberge, M..

7 recordsLinked to original sources

bioRxiv2021

Aminoglycoside-induced premature termination codon readthrough of COL4A5 nonsense mutations that cause Alport syndrome

Alport syndrome (AS) is characterized by glomerular basement membrane (GBM) abnormalities leading to progressive glomerulosclerosis. Mutations in the COL4A3, COL4A4 or COL4A5 genes encoding type IV collagen 345 cause AS. Truncated 3, 4, and 5 chains lacking an intact COOH-terminal noncollagenous domain due to a premature termination codon (PTC) cannot assemble into heterotrimers or incorporate into the GBM. Therefore, achieving full-length protein expression is a potential therapy for AS caused by truncating nonsense mutations. Small molecule-based PTC readthrough (PTC-RT) therapy has been well studied in other genetic diseases, but whether PTC-RT is applicable to AS is unexplored. To investigate the feasibility of PTC-RT therapy in AS, we made a cDNA to express COL4A5 fused to a C-terminal NanoLuc luciferase (NLuc) to monitor full-length translation. Full-length COL4A5-NLuc produces luminescence, but mutants truncated due to a PTC do not. To screen for COL4A5 nonsense mutants susceptible to PTC-RT, we introduced 49 individual nonsense mutations found in AS patients into the COL4A5-NLuc cDNA. Luciferase assays revealed that 11 mutations (C29X, S36X, E130X, C1521X, R1563X, C1567X, W1594X, S1632X, R1683X, C1684X and K1689X) were susceptible to PTC-RT induced by G418, which is known to have high readthrough activity. Moreover, we found that some next-generation "designer" PTC-RT drugs induced RT, and RT enhancer compounds increased the efficacy of PTC-RT in a G418-susceptible PTC mutant. These results suggest that PTC-RT therapy is a feasible approach for some patients with AS. Our luciferase-based COL4A5 translation reporter system will contribute to further development of PTC-RT therapies in a personalized medicine approach to treating AS.

genetics↗

bioRxiv2021

Suppression of aminoglycoside-induced premature termination codon readthrough by the TRP channel inhibitor AC1903

Nonsense mutations, which occur in ~11% of patients with genetic disorders, introduce premature termination codons (PTCs) that lead to truncated proteins and promote nonsense-mediated mRNA decay. Aminoglycosides such as gentamicin and G418 permit PTC readthrough and so may address this problem. However, their effects are variable between patients, making clinical use of aminoglycosides challenging. In this study, we addressed the hypothesis that TRP non-selective cation channels contribute to the variable effect of aminoglycosides by controlling their cellular uptake. To attempt to identify the channel type involved, we tested AC1903, a 2-aminobenzimidazole derivative recently reported to selectively inhibit TRPC5 cation channels. AC1903 consistently suppressed G418 uptake and G418-induced PTC readthrough in the DMS-114 cell line and patient-derived JEB01 keratinocytes. In an effort to validate the suggested role of TRPC5, we tested an independent and more potent inhibitor called Pico145, which affects channels containing TRPC1, TRPC4 and TRPC5 but not other TRPCs or other channels. Unexpectedly, Pico145 was completely without effect, suggesting that AC1903 may work through other or additional targets. Consistent with this suggestion, AC1903 inhibited multiple TRPC channels including homomeric TRPC3, TRPC4, TRPC5, TRPC6 as well as concatemeric TRPC4-C1 and TRPC5-C1 channels, all with low micromolar IC50 values. It also inhibited TRPV4 channels but had weak or no effects on TRPV1 and no effect on another non-selective cation channel, PIEZO1. Overall, our study reveals a suppressor of aminoglycoside-mediated PTC readthrough (i.e., AC1903) but suggests that this compound has previously unrecognised effects. These effects require further investigation to determine the molecular mechanism by which AC1903 suppresses aminoglycoside uptake and PTC readthrough.

pharmacology and toxicology↗

bioRxiv2020

Thiopurines activate an antiviral unfolded protein response that blocks viral glycoprotein accumulation in cell culture infection model

Enveloped viruses, including influenza A viruses (IAVs) and coronaviruses (CoVs), utilize the host cell secretory pathway to synthesize viral glycoproteins and direct them to sites of assembly. Using an image-based high-content screen, we identified two thiopurines, 6-thioguanine (6-TG) and 6-thioguanosine (6-TGo), that selectively disrupted the processing and accumulation of IAV glycoproteins hemagglutinin (HA) and neuraminidase (NA). Selective disruption of IAV glycoprotein processing and accumulation by 6-TG and 6-TGo correlated with unfolded protein response (UPR) activation and HA accumulation could be partially restored by the chemical chaperone 4-phenylbutyrate (4PBA). Chemical inhibition of the integrated stress response (ISR) restored accumulation of NA monomers in the presence of 6-TG or 6-TGo, but did not restore NA glycosylation or oligomerization. Thiopurines inhibited replication of the human coronavirus OC43 (HCoV-OC43), which also correlated with UPR/ISR activation and diminished accumulation of ORF1ab and nucleocapsid (N) mRNAs and N protein, which suggests broader disruption of coronavirus gene expression in ER-derived cytoplasmic compartments. The chemically similar thiopurine 6-mercaptopurine (6-MP) had little effect on the UPR and did not affect IAV or HCoV-OC43 replication. Consistent with reports on other CoV Spike (S) proteins, ectopic expression of SARS-CoV-2 S protein caused UPR activation. 6-TG treatment inhibited accumulation of full length S0 or furin-cleaved S2 fusion proteins, but spared the S1 ectodomain. DBeQ, which inhibits the p97 AAA-ATPase required for retrotranslocation of ubiquitinated misfolded proteins during ER-associated degradation (ERAD) restored accumulation of S0 and S2 proteins in the presence of 6-TG, suggesting that 6-TG induced UPR accelerates ERAD-mediated turnover of membrane-anchored S0 and S2 glycoproteins. Taken together, these data indicate that 6-TG and 6-TGo are effective host-targeted antivirals that trigger the UPR and disrupt accumulation of viral glycoproteins. Importantly, our data demonstrate for the first time the efficacy of these thiopurines in limiting IAV and HCoV-OC43 replication in cell culture models. IMPORTANCESecreted and transmembrane proteins are synthesized in the endoplasmic reticulum (ER), where they are folded and modified prior to transport. During infection, many viruses burden the ER with the task of creating and processing viral glycoproteins that will ultimately be incorporated into viral envelopes. Some viruses refashion the ER into replication compartments where viral gene expression and genome replication take place. This viral burden on the ER can trigger the cellular unfolded protein response (UPR), which attempts to increase the protein folding and processing capacity of the ER to match the protein load. Much remains to be learned about how viruses co-opt the UPR to ensure efficient synthesis of viral glycoproteins. Here, we show that two FDA-approved thiopurine drugs, 6-TG and 6-TGo, induce the UPR in a manner that impedes viral glycoprotein accumulation for enveloped influenza viruses and coronaviruses. These drugs may impede the replication of viruses that require precise tuning of the UPR to support viral glycoprotein synthesis for the successful completion of a replication cycle.

microbiology↗

bioRxiv2020

Biophysical characterization of the ETV6 PNT domain polymerization interfaces

ETV6 is an ETS family transcriptional repressor that self-associates by its PNT domain to facilitate cooperative DNA binding. Chromosomal translocations frequently generate constitutively active oncoproteins with the ETV6 PNT domain fused to the kinase domain of one of many protein tyrosine kinases. Although an attractive target for therapeutic intervention, the propensity of the ETV6 PNT domain to polymerize via the tight head-to-tail association of two relatively flat interfaces makes it challenging to identify suitable small molecule inhibitors of this protein-protein interaction. Herein we provide a comprehensive biophysical characterization of the ETV6 PNT domain interaction interfaces to aid future drug discovery efforts and help define the mechanisms by which its self-association mediates transcriptional repression. Using NMR spectroscopy, X-ray crystallography, and molecular dynamics simulations, we demonstrate that ETV6 PNT domain variants with monomerizing mutations adopt very stable helical bundle folds that do not change in conformation upon self-association. Amide hydrogen exchange and surface plasmon resonance-monitored alanine scanning mutagenesis studies identified hot spot regions within the self-association interfaces. These regions include both central hydrophobic residues and flanking salt-bridging residues. Collectively, these studies indicate that small molecules targeted to these hydrophobic or charged regions within the relatively rigid interfaces could potentially serve as orthosteric inhibitors of ETV6 PNT domain polymerization.

biochemistry↗

bioRxiv2020

A Multi-pronged Screening Approach Targeting Inhibition of ETV6 PNT Domain Polymerization

ETV6 is an ETS family transcriptional repressor for which head-to-tail polymerization of its PNT domain facilitates cooperative binding to DNA by its ETS domain. Chromosomal translocations frequently fuse the ETV6 PNT domain to one of several protein tyrosine kinases. The resulting chimeric oncoproteins undergo ligand-independent self-association, autophosphorylation, and aberrant stimulation of downstream signaling pathways leading to a variety of cancers. Currently, no small molecules inhibitors of ETV6 PNT domain polymerization are known and no assays targeting PNT domain polymerization have been described. In this study, we developed complementary experimental and computational approaches for identifying such inhibitory compounds. One mammalian cellular approach utilized a mutant PNT domain heterodimer system covalently attached to split Gaussia luciferase fragments. In this protein fragment complementation assay, inhibition of PNT domain heterodimerization reduces luminescence. A yeast assay took advantage of activation of the reporter HIS3 gene upon heterodimerization of mutant PNT domains fused to DNA-binding and transactivation domains. In this two-hybrid screen, inhibition of PNT domain heterodimerization prevents cell growth in medium lacking histidine. The Bristol University Docking Engine (BUDE) was used to identify virtual ligands from the ZINC8 library predicted to bind the PNT domain polymerization interfaces. Over 75 hits from these three assays were tested by NMR spectroscopy for binding to the purified ETV6 PNT domain. Although none were found to bind, lessons learned from this study may facilitate future approaches for developing therapeutics that act against ETV6 oncoproteins by disrupting PNT domain polymerization.

biochemistry↗

bioRxiv2018

Gentamicin B1 is not a minor gentamicin component with major nonsense mutation suppression activity

Nonsense mutations are single base substitutions that introduce a premature termination codon (PTC) preventing the formation of full-length protein. They are the causative mutations in about 10% of patients in a large number of rare genetic diseases. High concentrations of the antibiotic gentamicin can induce the incorporation of an amino acid at a PTC and formation of full-length protein, a process called PTC readthrough. Gentamicin is composed of several related aminoglycosides. We recently reported (doi/10.1073/pnas.1620982114) that the major gentamicin components that are responsible for its antibacterial activity showed weak to no PTC readthrough activity but that the minor component gentamicin B1 was a potent readthrough inducer. We have now determined that gentamicin B1 acquired from the sole supplier at the time the study was carried out was not gentamicin B1 but instead the closely related aminoglycoside G418. Gentamicin B1 recently became available from a second commercial source. Here, we provide nuclear magnetic resonance (NMR) assignment data for the two commercial compounds and verify only the second is indeed gentamicin B1. We show that gentamicin B1 lacks PTC readthrough activity in HDQ-P1 and DMS-114 cells homozygous for the TP53 R213X nonsense mutation, as well as in a cell-free translation assay.

biochemistry↗

bioRxiv2018

A new in vitro assay measuring direct interaction of nonsense suppressors with the eukaryotic protein synthesis machinery

Nonsense suppressors (NonSups) induce \"readthrough\", i.e., the selection of near cognate tRNAs at premature termination codons and insertion of the corresponding amino acid into nascent polypeptide. Prior readthrough measurements utilized contexts in which NonSups can promote readthrough directly, by binding to one or more of the components of the protein synthesis machinery, or indirectly, by several other mechanisms. Here we utilize a new, highly-purified in vitro assay to measure exclusively direct nonsense suppressor-induced readthrough. Of 16 NonSups tested, 12 display direct readthrough, with results suggesting that such NonSups act by at least two different mechanisms. In preliminary work we demonstrate the potential of single molecule fluorescence energy transfer measurements to elucidate mechanisms of NonSup-induced direct readthrough, which will aid efforts to identify NonSups having improved clinical efficacy.\n\nTable of Contents artwork\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=108 SRC=\"FIGDIR/small/330506_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (18K):\norg.highwire.dtl.DTLVardef@a548dborg.highwire.dtl.DTLVardef@15237bcorg.highwire.dtl.DTLVardef@c93d3forg.highwire.dtl.DTLVardef@1d40e2c_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗