Kylie M. Wagstaff

The classical nuclear import pathway in eukaryotic cells is mediated by the importin (IMP) α and β1 heterodimer, where IMPα acts as an adaptor protein that recognises and binds to nuclear localisation signals (NLSs) on nuclear protein cargoes. IMPα from Toxoplasma gondii (TgIMPα), the causative agent of toxoplasmosis, is an essential gene and validated druggable target, but its NLS binding properties remain largely uncharacterised. To investigate the NLS binding properties of purified TgIMPα we designed NLS peptides and compared its properties with those of mammalian (mouse) IMPα by AlphaScreen binding assays. The well-characterised viral NLS from simian virus SV40 large tumour-antigen (T-ag NLS) was recognised by TgIMPα with low-nM binding affinity comparable to Mus musculus IMPα (MmIMPα), whereas a T. gondii-specific NLS from the GCN5 gene product (TgGCN5) exhibited high affinity binding to TgIMPα but not MmIMPα. Mutational analysis of basic residues within the NLSs indicated pronounced binding selectivity. To elucidate the structural basis of these interactions, molecular dynamics (MD) simulations of an ab initio TgIMPα model bound to each NLS was performed. Key polar, salt-bridge, and cation-π interactions driving NLS recognition were identified. Critically, the lysine at position 2 (Lys128 in T-ag and Lys95 in TgGCN5) of each NLS engages conserved threonine and aspartate residues at the major binding site, playing an essential role in binding stability. Strikingly, TgIMPα displayed a more extensive and distinct cation-π interaction network than MmIMPα, revealing that, while the overall NLS binding architecture is conserved, specific pocket variations underlie differential high affinity recognition. Collectively, this study provides insights for the first time into the molecular distinctions in NLS binding between parasite and mammalian IMPα, potentially representing the foundation for future selective targeted drug design or peptidomimetic strategies against T. gondii.

Nuclear transport is a vital system that mediates movement of essential biomolecules between the nucleus and cytoplasm. It is tightly regulated by the Importin (IMP) superfamily to maintain separation of cellular compartments. Cellular stress in various forms, particularly oxidative, can suspend nuclear transport and lead to cell death. Prolonged oxidative stress manifests in myriad conditions, including cancer, viral infection and metabolic disease. An IMP protein, Importin-13 (IMP13), retains function under stress, while all other IMP family members tested to date do not. Phylogenetic and structural analysis revealed Transportin-3 (TNPO3) as the closest homologue of IMP13, suggesting it may also retain its function under stress. Subcellular localisation studies indicated that TNPO3 maintained its typical subcellular localisation, even in the presence of stress, unlike most IMP family members. Also, fluorescence recovery after photobleaching (FRAP) demonstrated that TNPO3 shuttling is unaffected under stress. Co-immunoprecipitation studies examining cargo binding revealed the capacity of TNPO3 to bind its cargo in the presence of stress. This demonstrated for the first time that TNPO3 retains functionality under stress conditions, in contrast to other IMPs, but similar to IMP13. Furthermore, both IMP13 and TNPO3 appear to protect against the potentially critical mislocalisation of Ran, a key molecule involved in the maintenance of the nuclear transport system.

Background: The efficacy of a single oral dose of Ivermectin as prophylaxis for SARS-CoV-2 is uncertain. This trial sought to evaluate the effectiveness of a single oral low dose of Ivermectin to prevent SARS-CoV-2 infection or reduce symptoms if infection did occur. Methods: Asymptomatic community-dwelling adults were enrolled in this study within 72 h of close contact with a case of SARS-CoV-2. Participants were randomised, stratified by vaccination status and exposure site, to a single oral 200 µg/kg dose of Ivermectin or placebo. The primary outcome was conversion to a positive polymerase chain reaction (PCR) or rapid antigen test (RAT) for SARS-CoV-2 within 14 days of close contact. Secondary outcomes were restricted to those who met the primary outcome. They included the following: days alive free of symptoms in the 14 (DAFS1-14) and 28 (DAFS1-28) days following intervention and days from close contact until a positive PCR or RAT for SARS-CoV-2. Results: A total of 536 participants registered for this trial. Of these, 86 met inclusion criteria and were randomised. 68 adhered to the trial protocol and were included in the analysis. A total of 11/36 (Ivermectin arm) and 11/32 (placebo arm) met the primary outcome. After controlling for age and prior SARS-CoV-2 infection, the estimate (95% confidence interval (95% CI)) of the effect of Ivermectin (compared to placebo) on the absolute value of the proportion of participants converting to a positive PCR or RAT was −0.051 (−0.26 to 0.16), p = 0.63. After controlling for prior SARS-CoV-2 infection, age, body mass index, hypertension and lung disease, the average treatment effect (Ivermectin versus placebo) on DAFS1-14 was 2.5 days (95%CI 1.1 to 4.5), p = 0.036, and for DAFS1-28, was 2.3 days (95% CI 0.7 to 3.3), p = 0.35. The mean (standard deviation) number of days from close contact until a positive PCR or RAT was 5.0 (4.1) days for the Ivermectin group versus 2.6 (0.8) days for the placebo group. After controlling for age and prior SARS-CoV-2 infection, the average treatment effect (95%CI), Ivermectin versus placebo, on days from close contact until a positive PCR or RAT was 2.3 days (95% CI 1.1 to 3.4), p = 0.033. Conclusions: We did not demonstrate that a single oral low dose of Ivermectin administered to asymptomatic adults within 72 h of close contact with a case of SARS-CoV-2 prevents conversion to a positive PCR or RAT. However, the trial had a small sample size and does not exclude a clinically meaningful effect of Ivermectin on conversion to a positive PCR or RAT. Amongst those who did convert to a positive PCR or RAT, the use of Ivermectin significantly lengthened the time from close contact to conversion and increased the number of days alive free of symptoms following intervention.

Human parvovirus B19 (B19V) is a major human pathogen in which the ssDNA genome is replicated within the nucleus of infected human erythroid progenitor cells (EPCs) through a process involving both cellular and viral proteins, including the non-structural protein (NS)1. We previously characterized the interaction between NS1 classical nuclear localization signal (cNLS: GACHAKKPRIT-182) and host cell importin (IMP)α and proposed it as a potential target for antiviral drug development. Here, we further extend on such findings. First, we demonstrate that NS1 nuclear localization is required for viral production since introducing the K177T substitution in a cloned, infectious viral genome resulted in a non-viable virus. Secondly, we demonstrate that the antiparasitic drug ivermectin (IVM), known to inhibit the IMPα/β dependent nuclear import pathway, could impair the NS1-NLS:IMPα interaction and suppress viral replication in UT7/EpoS1 cells in a dose-dependent manner. We also show that a panel of structurally related avermectins (AVMs) can dissociate the NS1-NLS:IMPα complex with half-maximal inhibitory concentrations in the nanomolar range. Among them, Eprinomectin emerged as the most selective inhibitor of B19V replication, with a selectivity index of c. 5.0. However, when tested in EPCs generated from peripheral blood mononuclear cells, which constitute a cellular population close to the natural target cells in bone marrow, the inhibitory effect of IVM and Eprinomectin was demonstrated to a lesser extent, and both compounds exhibited high toxicity, thus highlighting the need for more specific inhibitors of the NS1-NLS:IMPα interaction.

Common treatment approaches for triple-negative breast cancer (TNBC) are associated with severe side effects due to the unfavorable biodistribution profile of potent chemotherapeutics. Here, we explored the potential of TNBC-targeting aptamer-decorated porous silicon nanoparticles (pSiNPs) as targeted nanocarriers for TNBC. A "salt-aging" strategy was employed to fabricate a TNBC-targeting aptamer functionalized pSiNP that was highly colloidally stable. Doxorubicin (Dox) was efficiently loaded into nanoparticles (179 ± 5 μg/mg of pSiNP) and experienced pH-dependent release kinetics. Further experiments highlighted that clathrin-mediated endocytosis was the primary route that aptamer-pSiNP conjugates take to enter the endolysosomal compartment of the MCF10Ca1h TNBC cells. A time-interval colocalization study shows the accumulation of an aptamer-decorated pSiNP conjugate in the lysosomes of TNBC cells, unlike for antibody-decorated pSiNPs, leading to particle-induced lysosomal swelling and membrane destabilization. Dox-loaded aptamer-pSiNPs efficiently reduced the viability of the TNBC cells (11.8 ± 1.5%) compared to nontargeted nanoparticles (58.2 ± 8.8%) while the developed system showed a low level of toxicity in healthy cells, both in vitro and in vivo. These findings have laid the foundation for further investigating the potential of aptamer-pSiNP conjugates as a targeted treatment strategy in preclinical TNBC models.

Signal-dependent transport into and out of the nucleus mediated by members of the importin (IMP) superfamily is crucial for eukaryotic function, with inhibitors targeting IMPα being of key interest as anti-infectious agents, including against the apicomplexan Plasmodium species and Toxoplasma gondii, causative agents of malaria and toxoplasmosis, respectively. We recently showed that the FDA-approved macrocyclic lactone ivermectin, as well as several other different small molecule inhibitors, can specifically bind to and inhibit P. falciparum and T. gondii IMPα functions, as well as limit parasite growth. Here we focus on the FDA-approved antiparasitic moxidectin, a structural analogue of ivermectin, for its IMPα-targeting and anti-apicomplexan properties for the first time. We use circular dichroism and intrinsic tryptophan fluorescence measurements to show that moxidectin can bind directly to apicomplexan IMPαs, thereby inhibiting their key binding functions at low μM concentrations, as well as possessing anti-parasitic activity against P. falciparum in culture. The results imply a class effect in terms of IMPα’s ability to be targeted by macrocyclic lactone compounds. Importantly, in the face of rising global emergence of resistance to approved anti-parasitic agents, the findings highlight the potential of moxidectin and possibly other macrocyclic lactone compounds as antimalarial agents.

Many viruses target the host nuclear transport machinery to traffic their own proteins or restrict trafficking of host cargo, including mediators of antiviral immune signalling. Nucleocapsid (N) proteins from several coronaviruses traffic to the nucleus/nucleolus, with roles in cell cycle regulation. While N-protein from severe acute respiratory syndrome virus 2 (SARS-COV-2), the causative agent of the global COVID-19 pandemic, is widely reported to localise to the cytoplasm, we identify multiple, functionally distinct interactions of N-protein with the host’s nuclear transport machinery. Using quantitative cell imaging, including fluorescence recovery after photobleaching, and protein-protein interaction analysis, we describe a sub-population of SARS-COV-2 N-protein that localises more diffusely between the nucleus and cytoplasm, undergoes active nuclear import, and re-localises nuclear import receptors (karyopherins) KPNB1 and KPNA2 to the nucleus and cytoplasm, respectively. Truncation analyses identify at least two distinct KPNA2/KPNB1 binding sites located in the N-terminal and C-terminal regions of N-protein. Interestingly, while mutation of K/R-rich sites within these domains reduces KPNA2/KPNB1 binding and disables re-localisation of KPNA2, re-localisation of KPNB1 and nuclear import of N-protein remain intact, indicating that these are molecularly and functionally distinct mechanisms. siRNA knockdown confirms a role for KPNB1 in N-protein nuclear trafficking, while KPNA2 binding and mislocalisation may be antagonistic. Thus, SARS-COV-2 N-protein binds to karyopherins via multiple distinct sites to facilitate import and other functions.

Protozoan parasites of the phylum Apicomplexa, including Plasmodium falciparum and Toxoplasma gondii , cause widespread disease in humans. New drugs and protein targets are required for the treatment of these diseases, particularly therapies targeting multiple stages of the parasite life cycles. Nuclear import, carried out by the transporter’s importin (IMP) α and β subunits, is a valid target for the discovery of lead compounds against these protozoan parasites: small molecules were identified that inhibit interactions between IMPα and nuclear localisation signals in vitro and also inhibit the growth of the rapidly-dividing stages of P. falciparum and T. gondii (asexual stages and tachyzoites) in culture. In this report, we add another small molecule (Bay 11-7082) to the panel of inhibitors of IMPα and test the ability of these inhibitors to first, inhibit nuclear transport in the rapidly dividing stages and, next, the maturation of differentiated stages of both parasites. We show that GW5074 and CAPE inhibit nuclear transport in the P. falciparum blood stages, while Bay 11-7085 inhibits nuclear transport in T. gondii tachyzoites. Interestingly, CAPE strongly inhibits gametocyte maturation, the sexual stages of P. falciparum , and Bay 11-7085 weakly inhibits bradyzoite differentiation, the latent stages of T. gondii . As differentiation of both these stages is dependent on activation of gene expression, triggered by the nuclear translocation of transcription factors, our work provides a “proof of concept” that targeting nuclear import is a viable strategy for the development of therapeutics against multiple stages of apicomplexan parasites, some of them recalcitrant to existing drugs.

Background: The glycolytic enzyme alpha-enolase is a known biomarker of many cancers and involved in tumorigenic functions unrelated to its key role in glycolysis. Here, we show that expression of alpha-enolase correlates with subcellular localisation and tumorigenic status in the MCF10 triple negative breast cancer isogenic tumour progression model, where non-tumour cells show diffuse nucleocytoplasmic localisation of alpha-enolase, whereas tumorigenic cells show a predominantly cytoplasmic localisation. Alpha-enolase nucleocytoplasmic localisation may be regulated by tumour cell-specific phosphorylation at S419, previously reported in pancreatic cancer. Results: Here we show ENO1 phosphorylation can also be observed in triple negative breast cancer patient samples and MCF10 tumour progression cell models. Furthermore, prevention of alpha-enolase-S419 phosphorylation by point mutation or a casein kinase-1 specific inhibitor D4476, induced tumour-specific nuclear accumulation of alpha-enolase, implicating S419 phosphorylation and casein kinase-1 in regulating subcellular localisation in tumour cell-specific fashion. Strikingly, alpha-enolase nuclear accumulation was induced in tumour cells by treatment with the specific exportin-1-mediated nuclear export inhibitor Leptomycin B. This suggests that S419 phosphorylation in tumour cells regulates alpha-enolase subcellular localisation by inducing its exportin-1-mediated nuclear export. Finally, as a first step to analyse the functional consequences of increased cytoplasmic alpha-enolase in tumour cells, we determined the alpha-enolase interactome in the absence/presence of D4476 treatment, with results suggesting clear differences with respect to interaction with cytoskeleton regulating proteins. Conclusions: The results suggest for the first time that tumour-specific S419 phosphorylation may contribute integrally to alpha-enolase cytoplasmic localisation, to facilitate alpha-enolase’s role in modulating cytoskeletal organisation in triple negative breast cancer. This new information may be used for development of triple negative breast cancer specific therapeutics that target alpha-enolase.

Conferring multifunctional properties to proteins viaenzymaticapproaches has greatly facilitated recent progress in protein nanotechnology.In this regard, sortase (Srt) A transpeptidation has facilitated manyof these developments due to its exceptional specificity, mild reactionconditions, and complementation with other bioorthogonal techniques,such as click chemistry. In most of these developments, Srt A is usedto seamlessly tether oligoglycine-containing molecules to a proteinof interest that is equipped with the enzyme's recognitionsequence, LPXTG. However, the dependence on oligoglycine attackingnucleophiles and the associated cost of certain derivatives (e.g.,cyclooctyne) limit the utility of this approach to lab-scale applicationsonly. Thus, the quest to identify appropriate alternatives and understandtheir effectiveness remains an important area of research. This studyidentifies that steric and nucleophilicity-associated effects influenceSrt A transpeptidation when two oligoglycine surrogates were examined.The approach was further used in complementation with click chemistryto synthesize bivalent and bifunctional nanobody conjugates for applicationin epithelial growth factor receptor targeting. The overall techniqueand tools developed here may facilitate the advancement of futurenanotechnologies.