bims-nucpor 2021-06-27 papers

Issue of 2021–06–27
five papers selected by
Sara Mingu, Johannes Gutenberg University

Anal Bioanal Chem. 2021 Jun 25.

Synthetic hydrogel mimics of the nuclear pore complex for the study of nucleocytoplasmic transport defects in C9orf72 ALS/FTD.

Alicia K Friedman, Steven Boeynaems, Lane A Baker.

Dipeptide repeats (DPRs) associated with C9orf72 repeat expansions perturb nucleocytoplasmic transport and are implicated in the pathogenesis of amyotrophic lateral sclerosis. We present a synthetic hydrogel platform that can be used to analyze aspects of the molecular interaction of dipeptide repeats and the phenylalanine-glycine (FG) phase of the nuclear pore complex (NPC). Hydrogel scaffolds composed of acrylamide and copolymerized with FG monomers are first formed to recapitulate key FG interactions found in the NPC. With labeled probes, we find evidence that toxic arginine-rich DPRs (poly-GR and poly-PR), but not the non-toxic poly-GP, target NPC hydrogel mimics and block selective entry of a key nuclear transport receptor, importin beta (Impβ). The ease with which these synthetic hydrogel mimics can be adjusted/altered makes them an invaluable tool to dissect complex molecular interactions that underlie cellular transport processes and their perturbation in disease.

Keywords: ALS; Biomimetic; Biomolecular condensate; C9orf72; Hydrogel; Nuclear pore complex

DOI: https://doi.org/10.1007/s00216-021-03478-2

Mol Plant. 2021 Jun 18. pii: S1674-2052(21)00223-9. [Epub ahead of print]

A karyopherin constrains nuclear activity of the NLR protein SNC1 and is essential to prevent autoimmunity in Arabidopsis.

Min Jia, Xueqi Shen, Yu Tang, Xuetao Shi, Yangnan Gu.

The nucleotide-binding and leucine-rich repeat (NLR) proteins comprise a major class of intracellular immune receptors that are capable of detecting pathogen-derived molecules and activating immunity and cell death in plants. The activity of some NLRs, particularly TIR type, is highly correlated with their nucleocytoplasmic distribution. However, whether and how the nucleocytoplasmic homeostasis of NLRs is coordinated through a bi-directional nuclear shuttling mechanism remains unclear. Here, we identified a nuclear transport receptor KA120 that is capable of affecting the nucleocytoplasmic distribution of an NLR protein and is essential to prevent its autoactivation. We showed that the ka120 mutant displays an autoimmune phenotype and NLR-induced transcriptome features. Through a targeted genetic screen using an artificial NLR microRNA library, we identified the TIR-NLR gene SNC1 as a genetic interactor of KA120. Loss-of-function snc1 mutations as well as compromising SNC1 protein activities all substantially suppressed ka120-induced autoimmune activation, and the enhanced SNC1 activity in the absence of KA120 appeared to occur at the protein level. Overexpression of KA120 efficiently repressed SNC1 activity and led to a nearly complete suppression of the autoimmune phenotype caused by the gain-of-function snc1-1 mutation or SNC1 overexpression in plants. Further florescence imaging analysis indicated that SNC1 undergoes altered nucleocytoplasmic distribution with significantly reduced nuclear signal when KA120 is constitutively expressed, supporting a role of KA120 in coordinating SNC1 nuclear abundance and activity. Consistently, compromising the SNC1 nuclear level by disrupting the nuclear pore complex could also partially rescue ka120-induced autoimmunity. Together, our study demonstrates that KA120 is essential to avoid autoimmune activation in the absence of pathogens and is required to constrain the nuclear activity of SNC1, possibly through coordinating SNC1 nucleocytoplasmic homeostasis as a potential mechanism.

DOI: https://doi.org/10.1016/j.molp.2021.06.011

Mol Microbiol. 2021 Jun 19.

Selective nuclear export of mRNAs is promoted by DRBD18 in Trypanosoma brucei.

Amartya Mishra, Jan Naseer Kaur, Daniel I McSkimming, Eva Hegedűsová, Ashutosh P Dubey, Martin Ciganda, Zdeněk Paris, Laurie K Read.

Kinetoplastids, including Trypanosoma brucei, control gene expression primarily at the posttranscriptional level. Nuclear mRNA export is an important, but understudied, step in this process. The general heterodimeric export factors, Mex67/Mtr2, function in the export of mRNAs and tRNAs in T. brucei, but RNA binding proteins (RBPs) that regulate export processes by controlling the dynamics of Mex67/Mtr2 ribonucleoprotein formation or transport have not been identified. Here, we report that DRBD18, an essential and abundant T. brucei RBP, associates with Mex67/Mtr2 in vivo, likely through its direct interaction with Mtr2. DRBD18 downregulation results in partial accumulation of poly(A)+ mRNA in the nucleus, but has no effect on localization of intron-containing or mature tRNAs. Comprehensive analysis of transcriptomes from whole cell and cytosol in DRBD18 knockdown parasites demonstrates that depletion of DRBD18 leads to impairment of nuclear export of a subset of mRNAs. CLIP experiments reveal association of DRBD18 with several of these mRNAs. Moreover, DRBD18 knockdown leads to a partial accumulation of the Mex67/Mtr2 export receptors in the nucleus. Taken together, the current study supports a model in which DRBD18 regulates the selective nuclear export of mRNAs by promoting the mobilization of export competent mRNPs to the cytosol through the nuclear pore complex.

Keywords: FISH; Nucleoporin; RNA binding protein; RNAseq; Trypanosome; mRNA export

DOI: https://doi.org/10.1111/mmi.14773

Hum Mol Genet. 2021 Jun 25. pii: ddab160. [Epub ahead of print]

Expanding the phenotype of NUP85 mutations beyond nephrotic syndrome to primary autosomal recessive microcephaly and Seckel syndrome spectrum disorders.

Primary autosomal recessive microcephaly and Seckel syndrome spectrum disorders (MCPH-SCKS) include a heterogeneous group of autosomal recessive inherited diseases characterized by primary (congenital) microcephaly, the absence of visceral abnormalities, and a variable degree of cognitive impairment, short stature and facial dysmorphism. Recently, biallelic variants in the nuclear pore complex (NPC) component nucleoporin 85 gene (NUP85) were reported to cause steroid-resistant nephrotic syndrome (SRNS). Here, we report biallelic variants in NUP85 in two pedigrees with an MCPH-SCKS phenotype spectrum without SRNS, thereby expanding the phenotypic spectrum of NUP85-linked diseases. Structural analysis predicts the identified NUP85 variants cause conformational changes that could have an effect on NPC architecture or on its interaction with other NUPs. We show that mutant NUP85 is, however, associated with a reduced number of NPCs but unaltered nucleocytoplasmic compartmentalization, abnormal mitotic spindle morphology, and decreased cell viability and proliferation in one patient's cells. Our results also indicate the link of common cellular mechanisms involved in MCPH-SCKS spectrum disorders and NUP85-associated diseases. In addition to the previous studies, our results broaden the phenotypic spectrum of NUP85-linked human disease and propose a role for NUP85 in nervous system development.

DOI: https://doi.org/10.1093/hmg/ddab160

Antiviral Res. 2021 Jun 19. pii: S0166-3542(21)00105-4. [Epub ahead of print] 105115

Selinexor, a novel selective inhibitor of nuclear export, reduces SARS-CoV-2 infection and protects the respiratory system in vivo.

Trinayan Kashyap, Jackelyn Murray, Christopher J Walker, Hua Chang, Sharon Tamir, Bing Hou, Sharon Shacham, Michael G Kauffman, Ralph A Tripp, Yosef Landesman.

The novel coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for the recent global pandemic. The nuclear export protein (XPO1) has a direct role in the export of SARS-CoV proteins including ORF3b, ORF9b, and nucleocapsid. Inhibition of XPO1 induces anti-inflammatory, anti-viral, and antioxidant pathways. Selinexor is an FDA-approved XPO1 inhibitor. Through bioinformatics analysis, we predicted nuclear export sequences in the ACE-2 protein and confirmed by in vitro testing that inhibition of XPO1 with selinexor induces nuclear localization of ACE-2. Administration of selinexor inhibited viral infection prophylactically as well as therapeutically in vitro. In a ferret model of COVID-19, selinexor treatment reduced viral load in the lungs and protected against tissue damage in the nasal turbinates and lungs in vivo. Our studies demonstrated that selinexor downregulated the pro-inflammatory cytokines IL-1β, IL-6, IL-10, IFN-γ, TNF-α, and GMCSF, commonly associated with the cytokine storm observed in COVID-19 patients. Our findings indicate that nuclear export is critical for SARS-CoV-2 infection and for COVID-19 pathology and suggest that inhibition of XPO1 by selinexor could be a viable anti-viral treatment option.

Keywords: COVID19; CRM1; Exportin-1; SARS-CoV-2; SINE compound; Selinexor; XPO1

DOI: https://doi.org/10.1016/j.antiviral.2021.105115