bims-nucpor 2022-03-13 papers

Issue of 2022–03–13
four papers selected by
Sara Mingu, Johannes Gutenberg University

Int J Mol Sci. 2022 Feb 25. pii: 2578. [Epub ahead of print]23(5):

Function of the Nuclear Transport Machinery in Maintaining the Distinctive Compositions of the Nucleus and Cytoplasm.

Although the separation of transcription and translation, mediated by the nuclear envelope, is the defining characteristic of Eukaryotes, the barrier between the nuclear and cytoplasmic compartments needs to be semipermeable to enable material to be moved between them. Moreover, each compartment needs to have a distinctive complement of macromolecules to mediate specific functions and so movement between them needs to be controlled. This is achieved through the selective active transport of macromolecules through the nuclear pores that stud the nuclear envelope, and which serve as a conduit between these compartments. Nuclear pores are huge cylindrical macromolecular assemblies and are constructed from the order of 30 different proteins called nucleoporins. Nuclear pores have a central transport channel that is filled with a dense network of natively unfolded portions of many different nuclear pore proteins (nucleoporins or nups). This network generates a barrier that impedes, but does not entirely prevent, the diffusion of many macromolecules through the pores. The rapid movement of a range of proteins and RNAs through the pores is mediated by a range of transport factors that bind their cargo in one compartment and release it in the other. However, although as their size increases the diffusion of macromolecules through nuclear pores is progressively impaired, additional mechanisms, including the binding of some macromolecules to immobile components of each compartment and also the active removal of macromolecules from the inappropriate compartment, are needed to fully maintain the distinctive compositions of each compartment.

Keywords: nuclear pore; nuclear transport; nucleoporin; thermal ratchet

DOI: https://doi.org/10.3390/ijms23052578

mBio. 2022 Mar 08. e0292321

Nup98 Is Subverted from Annulate Lamellae by Hepatitis C Virus Core Protein to Foster Viral Assembly.

Bertrand Boson, Chloé Mialon, Konstanze Schichl, Solène Denolly, François-Loïc Cosset.

Nup98, an essential component of the nuclear pore that also participates in annulate lamella pore structures localized in the cytosol, is involved in hepatitis C virus (HCV) assembly. Here, we combined confocal microscopy and biochemical assays to study the interplay between Nup98, core (i.e., the HCV capsid protein), and viral genomes. Our results show that in HCV-infected cells, core protein is necessary and sufficient to induce relocalization of Nup98 from annulate lamellae to lipid droplet-apposed areas in which core/NS5A and HCV genomic RNA [(+)RNA] are clustered to promote viral assembly. Furthermore, we found that Nup98 interacts with HCV RNA and that upon Nup98 downregulation, the viral (+)RNA genome was specifically excluded from areas that contain active translating ribosomes and the core and NS5A proteins. Altogether, these results indicate that Nup98 is recruited by HCV core from annulate lamellae to viral assembly sites to locally increase the concentration of (+)RNA genome, which may favor its encapsidation into nascent virions. IMPORTANCE Nup98 is an essential component of the nuclear pore that also participates in annulate lamella pore structures localized in the cytosol. Nup98 is involved in HCV assembly, though its role remains elusive. Here, we show that Nup98 is retrieved from annulate lamellae during HCV infection. We demonstrate that Nup98 interacts with viral genome within infected cells and that these interactions are essential to maintain viral (+)RNAs in subcellular regions promoting viral replication, assembly, and translation. Importantly, we also show that HCV core nucleocapsid protein is the viral component responsible for the retrieval of Nup98 protein from annulate lamellae, hence allowing an enrichment of Nup98 complexed with viral (+)RNAs in core protein-containing areas. Altogether, our results indicate that Nup98 is recruited from annulate lamellae to viral assembly sites by HCV core protein to promote viral assembly, which highlights a novel virus-induced subversion mechanism of nuclear pore complex components.

Keywords: Nup98; annulate lamellae; assembly; hepatitis C virus; viral RNA

DOI: https://doi.org/10.1128/mbio.02923-21

Semin Cell Dev Biol. 2022 Mar 03. pii: S1084-9521(22)00067-2. [Epub ahead of print]

Nuclear envelope assembly and dynamics during development.

Bernhard Hampoelz, Janina Baumbach.

The nuclear envelope (NE) protects but also organizes the eukaryotic genome. In this review we will discuss recent literature on how the NE disassembles and reassembles, how it varies in surface area and protein composition and how this translates into chromatin organization and gene expression in the context of animal development.

Keywords: Embryogenesis; Nuclear envelope; Nuclear lamina; Nuclear pore complex

DOI: https://doi.org/10.1016/j.semcdb.2022.02.028

Cell Rep. 2022 Mar 08. pii: S2211-1247(22)00205-4. [Epub ahead of print]38(10): 110472

CRM1-spike-mediated nuclear export of hepatitis B virus encapsidated viral RNA.

Ching-Chun Yang, Chih-Hsu Chang, Heng-Li Chen, Ming-Chieh Chou, Ching-Jen Yang, Ren-Shiang Jhou, Er-Yi Huang, Hung-Cheng Li, Ching-Shu Suen, Ming-Jing Hwang, Chiaho Shih.

Hepatitis B virus (HBV) is a global pathogen. We report here that the cellular CRM1 machinery can mediate nuclear export of entire HBV core (HBc) particles containing encapsidated viral RNAs. Two CRM1-mediated nuclear export signals (NESCRM1) cluster at the conformationally flexible spike tips of HBc particles. Mutant NESCRM1 capsids exhibit strongly reduced associations with CRM1 and nucleoporin358 in vivo. CRM1 and NXF1 machineries mediate nuclear export of HBc particles independently. Inhibition of nuclear export has pleiotropic consequences, including nuclear accumulation of HBc particles, a significant reduction of encapsidated viral RNAs in the cytoplasm but not in the nucleus, and barely detectable viral DNA. We hypothesize an HBV life cycle where encapsidation of the RNA pregenome can initiate early in the nucleus, whereas DNA genome maturation occurs mainly in the cytoplasm. We identified a druggable target for HBV by blocking its intracellular trafficking.

Keywords: CRM1; HBV core protein (HBc); HBc capsids; NXF1; encapsidation; hepatitis B virus (HBV); nuclear export; pregenomic RNA (pgRNA); spike; therapeutics

DOI: https://doi.org/10.1016/j.celrep.2022.110472