bims-nucpor 2022-09-25 papers

Issue of 2022–09–25
five papers selected by
Sara Mingu, Johannes Gutenberg University

Nat Chem. 2022 Sep 22.

Molecular interactions of FG nucleoporin repeats at high resolution.

Alain Ibáñez de Opakua, James A Geraets, Benedikt Frieg, Christian Dienemann, Adriana Savastano, Marija Rankovic, Maria-Sol Cima-Omori, Gunnar F Schröder, Markus Zweckstetter.

Proteins that contain repeat phenylalanine-glycine (FG) residues phase separate into oncogenic transcription factor condensates in malignant leukaemias, form the permeability barrier of the nuclear pore complex and mislocalize in neurodegenerative diseases. Insights into the molecular interactions of FG-repeat nucleoporins have, however, remained largely elusive. Using a combination of NMR spectroscopy and cryoelectron microscopy, we have identified uniformly spaced segments of transient β-structure and a stable preformed α-helix recognized by messenger RNA export factors in the FG-repeat domain of human nucleoporin 98 (Nup98). In addition, we have determined at high resolution the molecular organization of reversible FG-FG interactions in amyloid fibrils formed by a highly aggregation-prone segment in Nup98. We have further demonstrated that amyloid-like aggregates of the FG-repeat domain of Nup98 have low stability and are reversible. Our results provide critical insights into the molecular interactions underlying the self-association and phase separation of FG-repeat nucleoporins in physiological and pathological cell activities.

DOI: https://doi.org/10.1038/s41557-022-01035-7

Cell Rep. 2022 Sep 20. pii: S2211-1247(22)01214-1. [Epub ahead of print]40(12): 111379

Nucleoporins are degraded via upregulation of ESCRT-III/Vps4 complex in Drosophila models of C9-ALS/FTD.

Sandeep Kumar Dubey, Kirstin Maulding, Hyun Sung, Thomas E Lloyd.

Disruption of the nuclear pore complex (NPC) and nucleocytoplasmic transport (NCT) have been implicated in the pathogenesis of neurodegenerative diseases. A GGGGCC hexanucleotide repeat expansion (HRE) in an intron of the C9orf72 gene is the most common genetic cause of amyotrophic lateral sclerosis and frontotemporal dementia, but the mechanism by which the HRE disrupts NCT is incompletely understood. We find that expression of GGGGCC repeats in Drosophila neurons induces proteasome-mediated degradation of select nucleoporins of the NPC. This process requires the Vps4 ATPase and the endosomal-sorting complex required for transport complex-III (ESCRT-III), as knockdown of ESCRT-III/Vps4 genes rescues nucleoporin levels, normalizes NCT, and suppresses GGGGCC-mediated neurodegeneration. GGGGCC expression upregulates nuclear ESCRT-III/Vps4 expression, and expansion microscopy demonstrates that the nucleoporins are translocated into the cytoplasm before undergoing proteasome-mediated degradation. These findings demonstrate a mechanism for nucleoporin degradation and NPC dysfunction in neurodegenerative disease.

Keywords: C9ORF72; CP: Neuroscience; Drosophila; ESCRT-III; Rpn10; Vps4; amyotrophic lateral sclerosis; nuclear pore complex; nucleoporin; proteasome

DOI: https://doi.org/10.1016/j.celrep.2022.111379

Front Mol Biosci. 2022 ;9 977653

Establishment and inheritance of epigenetic transcriptional memory.

Bethany Sump, Jason Brickner.

For certain inducible genes, the rate and molecular mechanism of transcriptional activation depends on the prior experiences of the cell. This phenomenon, called epigenetic transcriptional memory, accelerates reactivation and requires both changes in chromatin structure and recruitment of poised RNA Polymerase II (RNAPII) to the promoter. Forms of epigenetic transcriptional memory have been identified in S. cerevisiae, D. melanogaster, C. elegans, and mammals. A well-characterized model of memory is found in budding yeast where memory of inositol starvation involves a positive feedback loop between gene-and condition-specific transcription factors, which mediate an interaction with the nuclear pore complex and a characteristic histone modification: histone H3 lysine 4 dimethylation (H3K4me2). This histone modification permits recruitment of a memory-specific pre-initiation complex, poising RNAPII at the promoter. During memory, H3K4me2 is essential for recruitment of RNAPII and faster reactivation, but RNAPII is not required for H3K4me2. Unlike the RNAPII-dependent H3K4me2 associated with active transcription, RNAPII-independent H3K4me2 requires Nup100, SET3C, the Leo1 subunit of the Paf1 complex and can be inherited through multiple cell cycles upon disrupting the interaction with the Nuclear Pore Complex. The H3K4 methyltransferase (COMPASS) physically interacts with the potential reader (SET3C), suggesting a molecular mechanism for the spreading and re-incorporation of H3K4me2 following DNA replication. Thus, epigenetic transcriptional memory is a conserved adaptation that utilizes a heritable chromatin state, allowing cells and organisms to alter their gene expression programs in response to recent experiences over intermediate time scales.

Keywords: S. cerevisiae; chromatin; chromosomes; epigentics; heritable histones; nuclear pore; transcriptional memory

DOI: https://doi.org/10.3389/fmolb.2022.977653

Nanoscale Adv. 2022 Jun 14. 4(12): 2637-2641

Exportin-inspired artificial cell nuclear-exporting nanosystems.

Mitsuo Inui, Yuta Hamada, Nana Sejima, Natsumi Ueda, Tokitaka Katayama, Kimika Ono, Koji Nagahama.

Inspired by the structural and chemical features of naturally occurring importin/exportin that allows them to pass through the nuclear pore complexes, we successfully developed an artificial nuclear-exporting nanosystem capable of eliminating compounds accumulated abnormally in the nucleus.

DOI: https://doi.org/10.1039/d2na00050d

Front Endocrinol (Lausanne). 2022 ;13 954629

Importins involved in the nuclear transportation of steroid hormone receptors: In silico and in vitro data.

Konstantina Kalyvianaki, Athanasios A Panagiotopoulos, Maria Patentalaki, Elias Castanas, Marilena Kampa.

The nuclear receptor superfamily (NRS) consists of 48 receptors for lipophilic substances and is divided into 7 different subfamilies, with subfamily 3 comprising steroid hormone receptors. Several nuclear receptors usually bind their cognate ligands in the cytosol and the complex (mono- or dimerized) is transported to the nucleus, where it acts as a transcription initiating factor for a number of genes. The general structure of nuclear receptors consists of an N-terminal activating domain (A/B), important for the binding of activating or inhibitory co-factors, the DNA-binding domain (C), responsible for the association of the receptor-ligand-co-factor complex to the nucleus, the ligand-AF2 domain (E/F), where ligand binding occurs as well as that of ligand-dependent activating/inhibiting factors, and a flexible/non-structured domain (D), linking the DBD and LBD, called hinge region, on which a significant number of post-translational modifications occur. This hinge domain, for the sub-class of steroid receptors, is a non-structured domain and was reported as mainly responsible for the nuclear transport of steroid receptors, since it contains a specific amino acid sequence (Nuclear Localization Signal-NLS), recognized by importin α. In addition to the importin α/β complex, a number of other importins have been discovered and reported to be responsible for the nuclear transport of a number of significant proteins; however, the corresponding recognition sequences for these importins have not been identified. Recently, we have reported the identification of the NLS sequences for importins 4, 5 and 7. In this work, we provide in silico data, followed by experimental in vitro validation, showing that these alternative importins are responsible for the nuclear transportation of steroid hormone receptors such as ERα, AR and PR, and therefore they may consist of alternative targets for the pharmacological manipulation of steroid hormone actions. Moreover, we provide additional in silico data for the hinge region of steroid hormone receptors which is highly enriched with NLS sequences for importins 4, 5 and 7, in addition to the recognition NLS for importin α/β.

Keywords: NLS; hinge region; importins; nuclear translocation; steroid receptors

DOI: https://doi.org/10.3389/fendo.2022.954629