bims-nucpor 2024-03-10 papers

Issue of 2024–03–10
four papers selected by
Sara Mingu, Johannes Gutenberg University

Heliyon. 2024 Feb 29. 10(4): e26393

Disrupted nuclear import of cell cycle proteins in Huntington's/PolyQ disease causes neurodevelopment defects in cellular and Drosophila model.

Sandeep Kumar Dubey, Thomas E Lloyd, Madhu G Tapadia.

Huntington's disease is caused by an expansion of CAG repeats in exon 1 of the huntingtin gene encoding an extended PolyQ tract within the Huntingtin protein (mHtt). This expansion results in selective degeneration of striatal medium spiny projection neurons in the basal ganglia. The mutation causes abnormalities during neurodevelopment in human and mouse models. Here, we report that mHtt/PolyQ aggregates inhibit the cell cycle in the Drosophila brain during development. PolyQ aggregates disrupt the nuclear pore complexes of the cells preventing the translocation of cell cycle proteins such as Cyclin E, E2F and PCNA from cytoplasm to the nucleus, thus affecting cell cycle progression. PolyQ aggregates also disrupt the nuclear pore complex and nuclear import in mHtt expressing mammalian CAD neurons. PolyQ toxicity and cell cycle defects can be restored by enhancing RanGAP-mediated nuclear import, suggesting a potential therapeutic approach for this disease.

Keywords: Brain; CAD neuron; Drosophila; Huntington's disease; Neurodevelopment; Nuclear pore complex; Nucleocytoplasmic transport; PolyQ

DOI: https://doi.org/10.1016/j.heliyon.2024.e26393

J Gen Virol. 2024 Mar;105(3):

Structural basis for nuclear import of bat adeno-associated virus capsid protein.

Mikayla Hoad, Justin A Roby, Jade K Forwood.

Adeno-associated viruses (AAV) are one of the world's most promising gene therapy vectors and as a result, are one of the most intensively studied viral vectors. Despite a wealth of research into these vectors, the precise characterisation of AAVs to translocate into the host cell nucleus remains unclear. Recently we identified the nuclear localization signals of an AAV porcine strain and determined its mechanism of binding to host importin proteins. To expand our understanding of diverse AAV import mechanisms we sought to determine the mechanism in which the Cap protein from a bat-infecting AAV can interact with transport receptor importins for translocation into the nucleus. Using a high-resolution crystal structure and quantitative assays, we were able to not only determine the exact region and residues of the N-terminal domain of the Cap protein which constitute the functional NLS for binding with the importin alpha two protein, but also reveal the differences in binding affinity across the importin-alpha isoforms. Collectively our results allow for a detailed molecular view of the way AAV Cap proteins interact with host proteins for localization into the cell nucleus.

Keywords: adeno-associated virus; importin; karyopherin; nuclear import

DOI: https://doi.org/10.1099/jgv.0.001960

Front Immunol. 2024 ;15 1330738

The nuclear pore protein NUP98 impedes LTR-driven basal gene expression of HIV-1, viral propagation, and infectivity.

Kumaraswami Chintala, Sriram Yandrapally, Warisha Faiz, Chhaya Rani Kispotta, Satarupa Sarkar, Krishnaveni Mishra, Sharmistha Banerjee.

Nucleoporins (NUPs) are cellular effectors of human immunodeficiency virus-1 (HIV-1) replication that support nucleocytoplasmic trafficking of viral components. However, these also non-canonically function as positive effectors, promoting proviral DNA integration into the host genome and viral gene transcription, or as negative effectors by associating with HIV-1 restriction factors, such as MX2, inhibiting the replication of HIV-1. Here, we investigated the regulatory role of NUP98 on HIV-1 as we observed a lowering of its endogenous levels upon HIV-1 infection in CD4+ T cells. Using complementary experiments in NUP98 overexpression and knockdown backgrounds, we deciphered that NUP98 negatively affected HIV-1 long terminal repeat (LTR) promoter activity and lowered released virus levels. The negative effect on promoter activity was independent of HIV-1 Tat, suggesting that NUP98 prevents the basal viral gene expression. ChIP-qPCR showed NUP98 to be associated with HIV-1 LTR, with the negative regulatory element (NRE) of HIV-1 LTR playing a dominant role in NUP98-mediated lowering of viral gene transcription. Truncated mutants of NUP98 showed that the attenuation of HIV-1 LTR-driven transcription is primarily contributed by its N-terminal region. Interestingly, the virus generated from the producer cells transiently expressing NUP98 showed lower infectivity, while the virus generated from NUP98 knockdown CD4+ T cells showed higher infectivity as assayed in TZM-bl cells, corroborating the anti-HIV-1 properties of NUP98. Collectively, we show a new non-canonical function of a nucleoporin adding to the list of moonlighting host factors regulating viral infections. Downregulation of NUP98 in a host cell upon HIV-1 infection supports the concept of evolutionary conflicts between viruses and host antiviral factors.

Keywords: HIV-1 LTR; NUP98; nuclear pore complexes; transcription; viral gene expression

DOI: https://doi.org/10.3389/fimmu.2024.1330738

Front Cell Dev Biol. 2024 ;12 1206067

A bipartite NLS motif mediates the nuclear import of Drosophila moesin.

Zoltán Kovács, Csaba Bajusz, Anikó Szabó, Péter Borkúti, Balázs Vedelek, Réka Benke, Zoltán Lipinszki, Ildikó Kristó, Péter Vilmos.

The ERM protein family, which consists of three closely related proteins in vertebrates, ezrin, radixin, and moesin (ERM), is an ancient and important group of cytoplasmic actin-binding and organizing proteins. With their FERM domain, ERMs bind various transmembrane proteins and anchor them to the actin cortex through their C-terminal F-actin binding domain, thus they are major regulators of actin dynamics in the cell. ERMs participate in many fundamental cellular processes, such as phagocytosis, microvilli formation, T-cell activation and tumor metastasis. We have previously shown that, besides its cytoplasmic activities, the single ERM protein of Drosophila melanogaster, moesin, is also present in the cell nucleus, where it participates in gene expression and mRNA export. Here we study the mechanism by which moesin enters the nucleus. We show that the nuclear import of moesin is an NLS-mediated, active process. The nuclear localization sequence of the moesin protein is an evolutionarily highly conserved, conventional bipartite motif located on the surface of the FERM domain. Our experiments also reveal that the nuclear import of moesin does not require PIP2 binding or protein activation, and occurs in monomeric form. We propose, that the balance between the phosphorylated and non-phosphorylated protein pools determines the degree of nuclear import of moesin.

Keywords: Drosophila; ERM; NLS; PIP2; importin; moesin; nucleus; phosphorylation

DOI: https://doi.org/10.3389/fcell.2024.1206067