bims-nucpor Biomed News
on Nuclear pore complex and nucleoporins in stress, aging and disease
Issue of 2021‒08‒29
nine papers selected by
Sara Mingu
Johannes Gutenberg University

  1. J Cell Sci. 2021 Jan 15. pii: jcs247874. [Epub ahead of print]134(2):
      Bidirectional transport of macromolecules across the nuclear envelope is a hallmark of eukaryotic cells, in which the genetic material is compartmentalized inside the nucleus. The nuclear pore complex (NPC) is the major gateway to the nucleus and it regulates nucleocytoplasmic transport, which is key to processes including transcriptional regulation and cell cycle control. Accordingly, components of the nuclear transport machinery are often found to be dysregulated or hijacked in diseases. In this Cell Science at a Glance article and accompanying poster, we provide an overview of our current understanding of cargo transport through the NPC, from the basic transport signals and machinery to more emerging aspects, all from a 'cargo perspective'. Among these, we discuss the transport of large cargoes (>15 nm), as well as the roles of different cargo properties to nuclear transport, from size and number of bound nuclear transport receptors (NTRs), to surface and mechanical properties.
    Keywords:  Gene therapy; Large cargoes; Multivalent binding; Nuclear pore complex; Nuclear transport; Nuclear transport receptors; Virus
  2. Cells. 2021 Aug 18. pii: 2123. [Epub ahead of print]10(8):
      Nuclear pore complexes (NPCs) at the surface of nuclear membranes play a critical role in regulating the transport of both small molecules and macromolecules between the cell nucleus and cytoplasm via their multilayered spiderweb-like central channel. During mitosis, nuclear envelope breakdown leads to the rapid disintegration of NPCs, allowing some NPC proteins to play crucial roles in the kinetochore structure, spindle bipolarity, and centrosome homeostasis. The aberrant functioning of nucleoporins (Nups) and NPCs has been associated with autoimmune diseases, viral infections, neurological diseases, cardiomyopathies, and cancers, especially leukemia. This Special Issue highlights several new contributions to the understanding of NPC proteostasis.
    Keywords:  HS-AFM; biomacromolecule; liquid–liquid phase separation; nanoimaging; nanomedicine; nuclear pore complex; nucleoporin
  3. Cells. 2021 Jul 30. pii: 1937. [Epub ahead of print]10(8):
      The nuclear basket (NB) scaffold, a fibrillar structure anchored to the nuclear pore complex (NPC), is regarded as constructed of polypeptides of the coiled-coil dominated protein TPR to which other proteins can bind without contributing to the NB's structural integrity. Here we report vertebrate protein ZC3HC1 as a novel inherent constituent of the NB, common at the nuclear envelopes (NE) of proliferating and non-dividing, terminally differentiated cells of different morphogenetic origin. Formerly described as a protein of other functions, we instead present the NB component ZC3HC1 as a protein required for enabling distinct amounts of TPR to occur NB-appended, with such ZC3HC1-dependency applying to about half the total amount of TPR at the NEs of different somatic cell types. Furthermore, pointing to an NB structure more complex than previously anticipated, we discuss how ZC3HC1 and the ZC3HC1-dependent TPR polypeptides could enlarge the NB's functional repertoire.
    Keywords:  NIPA; ZC3HC1; nuclear basket; nuclear interacting partner of ALK; nuclear pore complex; nucleoprotein TPR; translocated promoter region
  4. Viruses. 2021 Aug 19. pii: 1650. [Epub ahead of print]13(8):
      Viral interferon (IFN) antagonist proteins mediate evasion of IFN-mediated innate immunity and are often multifunctional, with distinct roles in viral replication. The Ebola virus IFN antagonist VP24 mediates nucleocapsid assembly, and inhibits IFN-activated signaling by preventing nuclear import of STAT1 via competitive binding to nuclear import receptors (karyopherins). Proteins of many viruses, including viruses with cytoplasmic replication cycles, interact with nuclear trafficking machinery to undergo nucleocytoplasmic transport, with key roles in pathogenesis; however, despite established karyopherin interaction, potential nuclear trafficking of VP24 has not been investigated. We find that inhibition of nuclear export pathways or overexpression of VP24-binding karyopherin results in nuclear localization of VP24. Molecular mapping indicates that cytoplasmic localization of VP24 depends on a CRM1-dependent nuclear export sequence at the VP24 C-terminus. Nuclear export is not required for STAT1 antagonism, consistent with competitive karyopherin binding being the principal antagonistic mechanism, while export mediates return of nuclear VP24 to the cytoplasm where replication/nucleocapsid assembly occurs.
    Keywords:  Ebola virus; VP24; interferon antagonist; nuclear export sequence; nuclear transport
  5. Viruses. 2021 Jul 22. pii: 1425. [Epub ahead of print]13(8):
      HIV-1 can infect non-dividing cells. The nuclear envelope therefore represents a barrier that HIV-1 must traverse in order to gain access to the host cell chromatin for integration. Hence, nuclear entry is a critical step in the early stages of HIV-1 replication. Following membrane fusion, the viral capsid (CA) lattice, which forms the outer face of the retroviral core, makes numerous interactions with cellular proteins that orchestrate the progress of HIV-1 through the replication cycle. The ability of CA to interact with nuclear pore proteins and other host factors around the nuclear pore determines whether nuclear entry occurs. Uncoating, the process by which the CA lattice opens and/or disassembles, is another critical step that must occur prior to integration. Both early and delayed uncoating have detrimental effects on viral infectivity. How uncoating relates to nuclear entry is currently hotly debated. Recent technological advances have led to intense discussions about the timing, location, and requirements for uncoating and have prompted the field to consider alternative uncoating scenarios that presently focus on uncoating at the nuclear pore and within the nuclear compartment. This review describes recent advances in the study of HIV-1 nuclear entry, outlines the interactions of the retroviral CA protein, and discusses the challenges of investigating HIV-1 uncoating.
    Keywords:  HIV-1; NPC; capsid; core; nuclear entry; uncoating
  6. Viruses. 2021 Aug 05. pii: 1544. [Epub ahead of print]13(8):
      Herpes simplex virus type 1 nucleocapsids are released from the host nucleus by a budding process through the nuclear envelope called nuclear egress. Two viral proteins, the integral membrane proteins pUL34 and pUL31, form the nuclear egress complex at the inner nuclear membrane, which is critical for this process. The nuclear import of both proteins ensues separately from each other: pUL31 is actively imported through the central pore channel, while pUL34 is transported along the peripheral pore membrane. With this study, we identified a functional bipartite NLS between residues 178 and 194 of pUL34. pUL34 lacking its NLS is mislocalized to the TGN but retargeted to the ER upon insertion of the authentic NLS or a mimic NLS, independent of the insertion site. If co-expressed with pUL31, either of the pUL34-NLS variants is efficiently, although not completely, targeted to the nuclear rim where co-localization with pUL31 and membrane budding seem to occur, comparable to the wild-type. The viral mutant HSV1(17+)Lox-UL34-NLS mt is modestly attenuated but viable and associated with localization of pUL34-NLS mt to both the nuclear periphery and cytoplasm. We propose that targeting of pUL34 to the INM is facilitated by, but not dependent on, the presence of an NLS, thereby supporting NEC formation and viral replication.
    Keywords:  HSV1; NEC; TA membrane proteins; importins; inner nuclear membrane (INM); nuclear egress; nuclear import; pUL31; pUL34; targeting integral membrane proteins
  7. J Clin Transl Hepatol. 2021 Aug 28. 9(4): 458-465
      Background and Aims: Ras-related nuclear (RAN) protein is a small GTP-binding protein that is indispensable for the translocation of RNA and proteins through the nuclear pore complex. Recent studies have indicated that RAN plays an important role in virus infection. However, the role of RAN in hepatitis C virus (HCV) infection is unclear. The objective of this study was to investigate the role and underlying mechanisms of RAN in HCV infection.Methods: Huh7.5.1 cells were infected with the JC1-Luc virus for 24 h and then were incubated with complete medium for an additional 48 h. HCV infection and RAN expression were determined using luciferase assay, quantitative reverse transcription-PCR and western blotting. Small interfering RNA was used to silence RAN. Western blotting and immunofluorescence were used to evaluate the cytoplasmic translocation of polypyrimidine tract-binding (PTB), and coimmunoprecipitation was used to examine the interaction between RAN and PTB.
    Results: HCV infection significantly induced RAN expression and cytoplasmic redistribution of PTB. Knockdown of RAN dramatically inhibited HCV infection and the cytoplasmic accumulation of PTB. Colocalization of RAN and PTB was determined by immunofluorescence, and a direct interaction of RAN with PTB was demonstrated by coimmunoprecipitation.
    Conclusions: PTB in the host cytoplasm is directly associated with HCV replication. These findings demonstrate that the involvement of RAN in HCV infection is mediated by influencing the cytoplasmic translocation of PTB.
    Keywords:  HCV infection; Novel anti-HCV therapeutics; Nucleo-cytoplasmic translocation; Polypyrimidine tract-binding protein; Ras-related nuclear protein
  8. Semin Cell Dev Biol. 2021 Aug 20. pii: S1084-9521(21)00206-8. [Epub ahead of print]
      Regulated nucleocytoplasmic transport is central to the changes in gene expression that underpin cellular development and homeostasis, including in the testis, and proteins in the importin family are the predominant facilitators of cargo transport through the nuclear envelope. Reports documenting cell-specific profiles of importin transcripts and proteins during spermatogenesis led us to hypothesize that importins facilitate developmental switches in the testis. More recently, importins have been shown to serve additional functions, both inside and outside the nucleus; these include acting as subcellular scaffolding, mediating cellular stress responses, and controlling transcription. This paper seeks to provide an overview and update on the functions of importin proteins, with a focus on testis development and spermatogenesis. We present an extended survey of importins by combining published single cell RNAseq data with immunohistochemistry on developing and adult mouse testes. This approach reinforces and broadens knowledge of importins in biological processes, including in spermatogenesis and during testis development, revealing additional avenues for impactful investigations.
    Keywords:  Development; Karyopherins; Nucleocytoplasmic transport; ScRNAseq; Spermatogenesis; Testis
  9. Oxid Med Cell Longev. 2021 ;2021 6682336
      Brain aging is characterized by dysfunctional autophagy and cellular senescence, among other features. While autophagy can either promote or suppress cellular senescence in proliferating cells, in postmitotic cells, such as neurons, autophagy impairment promotes cellular senescence. CRM1 (exportin-1/XPO1) exports hundreds of nuclear proteins into the cytoplasm, including the transcription factors TFEB (the main inducer of autophagy and lysosomal biogenesis genes) and STAT3, another autophagy modulator. It appears that CRM1 is a modulator of aging-associated senescence and autophagy, because pharmacological inhibition of CRM1 improved autophagic degradation in flies, by increasing nuclear TFEB levels, and because enhanced CRM1 activity is mechanistically linked to senescence in fibroblasts from Hutchinson-Gilford progeria syndrome patients and old healthy individuals; furthermore, the exogenous overexpression of CRM1 induced senescence in normal fibroblasts. In this work, we tested the hypothesis that impaired autophagic flux during brain aging occurs due to CRM1 accumulation in the brain. We found that CRM1 levels and activity increased in the hippocampus and cortex during physiological aging, which resulted in a decrease of nuclear TFEB and STAT3. Consistent with an autophagic flux impairment, we observed accumulation of the autophagic receptor p62/SQSTM1 in neurons of old mice, which correlated with increased neuronal senescence. Using an in vitro model of neuronal senescence, we demonstrate that CRM1 inhibition improved autophagy flux and reduced SA-β-gal activity by restoring TFEB nuclear localization. Collectively, our data suggest that enhanced CRM1-mediated export of proteins during brain aging perturbs neuronal homeostasis, contributing to autophagy impairment, and neuronal senescence.