bims-nucpor 2022-06-05 papers

Issue of 2022–06–05
four papers selected by
Sara Mingu, Johannes Gutenberg University

J Biol Chem. 2022 May 27. pii: S0021-9258(22)00524-5. [Epub ahead of print] 102083

Intracellular localization of the proteasome in response to stress conditions.

Cordula Enenkel, Ryu Won Kang, Florian Wilfling, Oliver P Ernst.

The ubiquitin-proteasome-system (UPS) fulfills an essential role in regulating protein homeostasis by spatially and temporally controlling proteolysis in an ATP- and ubiquitin-dependent manner. However, the localization of proteasomes is highly variable under diverse cellular conditions. In yeast, newly synthesized proteasomes are primarily localized to the nucleus during cell proliferation. Yeast proteasomes are transported into the nucleus through the nuclear pore either as immature subcomplexes or as mature enzymes via adaptor proteins Sts1 and Blm10, while in mammalian cells, post-mitotic uptake of proteasomes into the nucleus is mediated by AKIRIN2, an adaptor protein essentially required for nuclear protein degradation. Stressful growth conditions and the reversible halt of proliferation, i.e. quiescence, are associated with a decline in ATP and the re-organization of proteasome localization. Cellular stress leads to proteasome accumulation in membraneless granules either in the nucleus or in the cytoplasm. In quiescence, yeast proteasomes are sequestered in a ubiquitin-dependent manner into motile and reversible proteasome storage granules (PSGs) in the cytoplasm. In cancer cells upon amino acid deprivation, heat shock, osmotic stress, oxidative stress, or the inhibition of either proteasome activity or nuclear export, reversible proteasome foci containing poly-ubiquitinated substrates are formed by liquid-liquid phase separation in the nucleus. In this review, we summarize recent literature revealing new links between nuclear transport, ubiquitin signaling and the intracellular organization of proteasomes during cellular stress conditions.

Keywords: liquid-liquid phase separation; nuclear transport; proteasome foci; proteasome storage granule; protein quality control; stress response; ubiquitin-proteasome-system

DOI: https://doi.org/10.1016/j.jbc.2022.102083

Plant Sci. 2022 Jul;pii: S0168-9452(22)00120-0. [Epub ahead of print]320 111296

A Nucleoporin NUP58 modulates responses to drought and salt stress in maize (Zea mays L.).

Zhixue Liu, Salah Fatouh Abou-Elwafa, Jiarong Xie, Yajing Liu, Siyuan Li, Maha Aljabri, Dongling Zhang, Fengran Gao, Lili Zhang, Zhiyong Wang, Chongyu Sun, Bingqi Zhu, Miaomiao Bao, Xiaomeng Hu, Yanhui Chen, Lixia Ku, Zhenzhen Ren, Li Wei.

Nuclear pore complex (NUP) is the main transport channel between cytoplasm and nucleoplasm, which plays an important role in stress response. The function of NUPs was widely reported in yeast and vertebrate but rarely in plants. Here, we identified a nuclear pore complex (ZmNUP58), that is tightly associated with drought and salt tolerance phenotype accompanied with phenotypic and physiological changes under drought and salt stress. The overexpression of ZmNUP58 in maize (Zea mays L.) significantly promotes both chlorophyll content and activities of antioxidant enzymes under drought- and salt-stressed conditions. RNA-Seq analysis showed that ZmNUP58 could regulate the expression of genes related to phytohormone synthesis and signaling, osmotic adjustment substances, antioxidant enzyme system, cell wall biosynthesis, glucose metabolism and aquaporin. The results provide novel insights into the regulatory role of ZmNUP58 in improving drought and salt tolerance through regulating phytohormone and other stress response genes in maize.

Keywords: Drought tolerance; Maize; RNA-Seq; Salt stress; ZmNUP58

DOI: https://doi.org/10.1016/j.plantsci.2022.111296

J Virol. 2022 May 31. e0220521

Invasion and Propagation of White Spot Syndrome Virus: Hijacking of the Cytoskeleton, Intracellular Transport Machinery, and Nuclear Import Transporters.

Dong-Li Li, Ming-Han Yang, Ling-Ke Liu, Chuang Meng, Mei-Qiong Li, Hai-Peng Liu.

The pathogenesis of white spot syndrome virus (WSSV) is largely unclear. In this study, we found that actin nucleation and clathrin-mediated endocytosis were recruited for internalization of WSSV into crayfish hematopoietic tissue (Hpt) cells. This internalization was followed by intracellular transport of the invading virions via endocytic vesicles and endosomes. After envelope fusion within endosomes, the penetrated nucleocapsids were transported along microtubules toward the periphery of the nuclear pores. Furthermore, the nuclear transporter CqImportin α1/β1, via binding of ARM repeat domain within CqImportin α1 to the nuclear localization sequences (NLSs) of viral cargoes and binding of CqImportin β1 to the nucleoporins CqNup35/62 with the action of CqRan for docking to nuclear pores, was hijacked for both targeting of the incoming nucleocapsids toward the nuclear pores and import of the expressed viral structural proteins containing NLS into the cell nucleus. Intriguingly, dysfunction of CqImportin α1/β1 resulted in significant accumulation of incoming nucleocapsids on the periphery of the Hpt cell nucleus, leading to substantially decreased introduction of the viral genome into the nucleus and remarkably reduced nuclear import of expressed viral structural proteins with NLS; both of these effects were accompanied by significantly inhibited viral propagation. Accordingly, the survival rate of crayfish post-WSSV challenge was significantly increased after dysfunction of CqImportin α1/β1, also showing significantly reduced viral propagation, and was induced either by gene silencing or by pharmacological blockade via dietary administration of ivermectin per os. Collectively, our findings improve our understanding of WSSV pathogenesis and support future antiviral designing against WSSV. IMPORTANCE As one of the largest animal DNA viruses, white spot syndrome virus (WSSV) has been causing severe economical loss in aquaculture due to the limited knowledge on WSSV pathogenesis for an antiviral strategy. We demonstrate that the actin cytoskeleton, endocytic vesicles, endosomes, and microtubules are hijacked for WSSV invasion; importantly, the nuclear transporter CqImportin α1/β1 together with CqRan were recruited, via binding of CqImportin β1 to the nucleoporins CqNup35/62, for both the nuclear pore targeting of the incoming nucleocapsids and the nuclear import of expressed viral structural proteins containing the nuclear localization sequences (NLSs). This is the first report that NLSs from both viral structure proteins and host factor are elaborately recruited together to facilitate WSSV infection. Our findings provide a novel explanation for WSSV pathogenesis involving systemic hijacking of host factors, which can be used for antiviral targeting against WSSV disease, such as the blockade of CqImportin α1/β1 with ivermectin.

Keywords: antiviral targeting; importin; intracellular trafficking; ivermectin; nuclear localization sequence; nuclear translocation; white spot syndrome virus

DOI: https://doi.org/10.1128/jvi.02205-21

FEBS J. 2022 Jun 02.

Staufen-2 functions as a cofactor for enhanced Rev-mediated nucleocytoplasmic trafficking of HIV-1 genomic RNA via the CRM1 pathway.

Kannan Balakrishnan, Punnagai Munusami, Krishnaveni Mohareer, U Deva Priyakumar, Atoshi Banerjee, Tom Luedde, Shekhar C Mande, Carsten Münk, Sharmistha Banerjee.

Nucleocytoplasmic shuttling of viral elements, supported by several host factors, is essential for the replication of the Human Immunodeficiency Virus (HIV). HIV-1 uses a nuclear RNA export pathway mediated by viral protein Rev to transport its Rev Response Element (RRE)-containing partially spliced and unspliced transcripts aided by the host nuclear RNA export protein CRM1. The factor(s) interacting with the CRM1-Rev complex are potential anti-retroviral target(s) and could serve as a retroviral model system to study nuclear export machinery adapted by these viruses. We earlier reported that cellular Staufen-2 interacts with Rev, facilitating viral RNA export. Here, we identified the formation of a complex between Staufen-2, CRM1, and Rev. Molecular docking and simulations mapped the interacting residues in the RNA-Binding-Domain-4 of Staufen-2 as R336 and R337, which were experimentally verified to be critical for interactions among Staufen-2, CRM1, and Rev by mutational analysis. Staufen-2 mutants defective in interaction with CRM1 or Rev failed to supplement the Rev-RNA export activity and viral production, demonstrating the importance of these interactions. Rev-dependent reporter assays and proviral DNA-construct transfection-based studies in Staufen-2 knockout cells in the presence of leptomycin-B (LMB) revealed a significant reduction in CRM1-mediated Rev-dependent RNA export with decreased virus production as compared to Staufen-2 knockout background or LMB treatment alone, suggesting the relevance of these interactions in augmenting RNA export activity of Rev. Our observations provide further insights into the mechanistic intricacies of unspliced viral RNA export to the cytoplasm and support the notion that abrogating such interactions can reduce HIV-1 proliferation.

Keywords: CRM1 RNA export; HIV-1 Rev; RRE RNA export; SCR complex; Staufen-2

DOI: https://doi.org/10.1111/febs.16546