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Breckel CA, Johnson ZM, Hickey CM, Hochstrasser M. Yeast 26S proteasome nuclear import is coupled to nucleus-specific degradation of the karyopherin adaptor protein Sts1. Sci Rep 2024; 14:2048. [PMID: 38267508 PMCID: PMC10808114 DOI: 10.1038/s41598-024-52352-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2023] [Accepted: 01/16/2024] [Indexed: 01/26/2024] Open
Abstract
In eukaryotes, the ubiquitin-proteasome system is an essential pathway for protein degradation and cellular homeostasis. 26S proteasomes concentrate in the nucleus of budding yeast Saccharomyces cerevisiae due to the essential import adaptor protein Sts1 and the karyopherin-α protein Srp1. Here, we show that Sts1 facilitates proteasome nuclear import by recruiting proteasomes to the karyopherin-α/β heterodimer. Following nuclear transport, the karyopherin proteins are likely separated from Sts1 through interaction with RanGTP in the nucleus. RanGTP-induced release of Sts1 from the karyopherin proteins initiates Sts1 proteasomal degradation in vitro. Sts1 undergoes karyopherin-mediated nuclear import in the absence of proteasome interaction, but Sts1 degradation in vivo is only observed when proteasomes successfully localize to the nucleus. Sts1 appears to function as a proteasome import factor during exponential growth only, as it is not found in proteasome storage granules (PSGs) during prolonged glucose starvation, nor does it appear to contribute to the rapid nuclear reimport of proteasomes following glucose refeeding and PSG dissipation. We propose that Sts1 acts as a single-turnover proteasome nuclear import factor by recruiting karyopherins for transport and undergoing subsequent RanGTP-initiated ubiquitin-independent proteasomal degradation in the nucleus.
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Affiliation(s)
- Carolyn Allain Breckel
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, 06520, USA
| | - Zane M Johnson
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, 06520, USA
| | - Christopher M Hickey
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, 06520, USA
- Arvinas, Inc., 5 Science Park, New Haven, CT, USA
| | - Mark Hochstrasser
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, 06520, USA.
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT, 06520, USA.
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Pispa J, Mikkonen E, Arpalahti L, Jin C, Martínez-Fernández C, Cerón J, Holmberg CI. AKIR-1 regulates proteasome subcellular function in Caenorhabditis elegans. iScience 2023; 26:107886. [PMID: 37767001 PMCID: PMC10520889 DOI: 10.1016/j.isci.2023.107886] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2022] [Revised: 07/07/2023] [Accepted: 09/07/2023] [Indexed: 09/29/2023] Open
Abstract
Polyubiquitinated proteins are primarily degraded by the ubiquitin-proteasome system (UPS). Proteasomes are present both in the cytoplasm and nucleus. Here, we investigated mechanisms coordinating proteasome subcellular localization and activity in a multicellular organism. We identified the nuclear protein-encoding gene akir-1 as a proteasome regulator in a genome-wide Caenorhabditis elegans RNAi screen. We demonstrate that depletion of akir-1 causes nuclear accumulation of endogenous polyubiquitinated proteins in intestinal cells, concomitant with slower in vivo proteasomal degradation in this subcellular compartment. Remarkably, akir-1 is essential for nuclear localization of proteasomes both in oocytes and intestinal cells but affects differentially the subcellular distribution of polyubiquitinated proteins. We further reveal that importin ima-3 genetically interacts with akir-1 and influences nuclear localization of a polyubiquitin-binding reporter. Our study shows that the conserved AKIR-1 is an important regulator of the subcellular function of proteasomes in a multicellular organism, suggesting a role for AKIR-1 in proteostasis maintenance.
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Affiliation(s)
- Johanna Pispa
- Department of Biochemistry and Developmental Biology, Medicum, Faculty of Medicine, University of Helsinki, 00290 Helsinki, Finland
| | - Elisa Mikkonen
- Department of Biochemistry and Developmental Biology, Medicum, Faculty of Medicine, University of Helsinki, 00290 Helsinki, Finland
| | - Leena Arpalahti
- Department of Biochemistry and Developmental Biology, Medicum, Faculty of Medicine, University of Helsinki, 00290 Helsinki, Finland
| | - Congyu Jin
- Department of Anatomy, Medicum, Faculty of Medicine, University of Helsinki, 00290 Helsinki, Finland
| | - Carmen Martínez-Fernández
- Modeling Human Diseases in C. elegans Group, Genes, Diseases, and Therapies Program, Institut d'Investigació Biomèdica de Bellvitge - IDIBELL, L'Hospitalet de Llobregat, 08908 Barcelona, Spain
| | - Julián Cerón
- Modeling Human Diseases in C. elegans Group, Genes, Diseases, and Therapies Program, Institut d'Investigació Biomèdica de Bellvitge - IDIBELL, L'Hospitalet de Llobregat, 08908 Barcelona, Spain
| | - Carina I. Holmberg
- Department of Biochemistry and Developmental Biology, Medicum, Faculty of Medicine, University of Helsinki, 00290 Helsinki, Finland
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High-Resolution Crystal Structure of Muscle Phosphoglycerate Mutase Provides Insight into Its Nuclear Import and Role. Int J Mol Sci 2022; 23:ijms232113198. [DOI: 10.3390/ijms232113198] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2022] [Revised: 10/25/2022] [Accepted: 10/27/2022] [Indexed: 11/16/2022] Open
Abstract
Phosphoglycerate mutase (PGAM) is a glycolytic enzyme converting 3-phosphoglycerate to 2-phosphoglycerate, which in mammalian cells is expressed in two isoforms: brain (PGAM1) and muscle (PGAM2). Recently, it was shown that besides its enzymatic function, PGAM2 can be imported to the cell nucleus where it co-localizes with the nucleoli. It was suggested that it functions there to stabilize the nucleolar structure, maintain mRNA expression, and assist in the assembly of new pre-ribosomal subunits. However, the precise mechanism by which the protein translocates to the nucleus is unknown. In this study, we present the first crystal structure of PGAM2, identify the residues involved in the nuclear localization of the protein and propose that PGAM contains a “quaternary nuclear localization sequence (NLS)”, i.e., one that consists of residues from different protein chains. Additionally, we identify potential interaction partners for PGAM2 in the nucleoli and demonstrate that 14-3-3ζ/δ is indeed an interaction partner of PGAM2 in the nucleus. We also present evidence that the insulin/IGF1–PI3K–Akt–mTOR signaling pathway is responsible for the nuclear localization of PGAM2.
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Fernando LM, Quesada-Candela C, Murray M, Ugoaru C, Yanowitz JL, Allen AK. Proteasomal subunit depletions differentially affect germline integrity in C. elegans. Front Cell Dev Biol 2022; 10:901320. [PMID: 36060813 PMCID: PMC9428126 DOI: 10.3389/fcell.2022.901320] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2022] [Accepted: 07/08/2022] [Indexed: 11/25/2022] Open
Abstract
The 26S proteasome is a multi-subunit protein complex that is canonically known for its ability to degrade proteins in cells and maintain protein homeostasis. Non-canonical or non-proteolytic roles of proteasomal subunits exist but remain less well studied. We provide characterization of germline-specific functions of different 19S proteasome regulatory particle (RP) subunits in C. elegans using RNAi specifically from the L4 stage and through generation of endogenously tagged 19S RP lid subunit strains. We show functions for the 19S RP in regulation of proliferation and maintenance of integrity of mitotic zone nuclei, in polymerization of the synaptonemal complex (SC) onto meiotic chromosomes and in the timing of SC subunit redistribution to the short arm of the bivalent, and in turnover of XND-1 proteins at late pachytene. Furthermore, we report that certain 19S RP subunits are required for proper germ line localization of WEE-1.3, a major meiotic kinase. Additionally, endogenous fluorescent labeling revealed that the two isoforms of the essential 19S RP proteasome subunit RPN-6.1 are expressed in a tissue-specific manner in the hermaphrodite. Also, we demonstrate that the 19S RP subunits RPN-6.1 and RPN-7 are crucial for the nuclear localization of the lid subunits RPN-8 and RPN-9 in oocytes, further supporting the ability to utilize the C. elegans germ line as a model to study proteasome assembly real-time. Collectively, our data support the premise that certain 19S RP proteasome subunits are playing tissue-specific roles, especially in the germ line. We propose C. elegans as a versatile multicellular model to study the diverse proteolytic and non-proteolytic roles that proteasome subunits play in vivo.
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Affiliation(s)
| | - Cristina Quesada-Candela
- Magee-Womens Research Institute and Department of Obstetrics, Gynecology, and Reproductive Sciences, University of Pittsburgh School of Medicine, Pittsburgh, PA, United States
| | - Makaelah Murray
- Department of Biology, Howard University, Washington, DC, United States
| | - Caroline Ugoaru
- Department of Biology, Howard University, Washington, DC, United States
| | - Judith L. Yanowitz
- Magee-Womens Research Institute and Department of Obstetrics, Gynecology, and Reproductive Sciences, University of Pittsburgh School of Medicine, Pittsburgh, PA, United States
- Departments of Developmental Biology, Microbiology, and Molecular Genetics, The Hillman Cancer Center, University of Pittsburgh School of Medicine, Pittsburgh, PA, United States
- *Correspondence: Judith L. Yanowitz, ; Anna K. Allen,
| | - Anna K. Allen
- Department of Biology, Howard University, Washington, DC, United States
- *Correspondence: Judith L. Yanowitz, ; Anna K. Allen,
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Guo X. Localized Proteasomal Degradation: From the Nucleus to Cell Periphery. Biomolecules 2022; 12:biom12020229. [PMID: 35204730 PMCID: PMC8961600 DOI: 10.3390/biom12020229] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2022] [Revised: 01/25/2022] [Accepted: 01/27/2022] [Indexed: 12/31/2022] Open
Abstract
The proteasome is responsible for selective degradation of most cellular proteins. Abundantly present in the cell, proteasomes not only diffuse in the cytoplasm and the nucleus but also associate with the chromatin, cytoskeleton, various membranes and membraneless organelles/condensates. How and why the proteasome gets to these specific subcellular compartments remains poorly understood, although increasing evidence supports the hypothesis that intracellular localization may have profound impacts on the activity, substrate accessibility and stability/integrity of the proteasome. In this short review, I summarize recent advances on the functions, regulations and targeting mechanisms of proteasomes, especially those localized to the nuclear condensates and membrane structures of the cell, and I discuss the biological significance thereof in mediating compartmentalized protein degradation.
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Affiliation(s)
- Xing Guo
- Life Sciences Institute, Zhejiang University, Hangzhou 310058, China;
- Zhejiang Provincial Key Laboratory for Cancer Molecular Cell Biology, Hangzhou 310058, China
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Chen X, Walters KJ. Nuclear destruction: A suicide mission by AKIRIN2 brings intact proteasomes into the nucleus. Mol Cell 2022; 82:13-14. [PMID: 34995507 PMCID: PMC11218005 DOI: 10.1016/j.molcel.2021.11.020] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
de Almeida et al. (2021) developed a temporally controlled CRISPR-Cas9 screen to identify mechanisms controlling MYC levels and discovered that intact proteasomes are imported into the nucleus by AKIRIN2 binding to proteasomes at one end and a nuclear import receptor at the other.
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Affiliation(s)
- Xiang Chen
- Protein Processing Section, Center for Structural Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Frederick, MD 21702, USA
| | - Kylie J Walters
- Protein Processing Section, Center for Structural Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Frederick, MD 21702, USA.
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AKIRIN2 controls the nuclear import of proteasomes in vertebrates. Nature 2021; 599:491-496. [PMID: 34711951 DOI: 10.1038/s41586-021-04035-8] [Citation(s) in RCA: 45] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Accepted: 09/16/2021] [Indexed: 02/08/2023]
Abstract
Protein expression and turnover are controlled through a complex interplay of transcriptional, post-transcriptional and post-translational mechanisms to enable spatial and temporal regulation of cellular processes. To systematically elucidate such gene regulatory networks, we developed a CRISPR screening assay based on time-controlled Cas9 mutagenesis, intracellular immunostaining and fluorescence-activated cell sorting that enables the identification of regulatory factors independent of their effects on cellular fitness. We pioneered this approach by systematically probing the regulation of the transcription factor MYC, a master regulator of cell growth1-3. Our screens uncover a highly conserved protein, AKIRIN2, that is essentially required for nuclear protein degradation. We found that AKIRIN2 forms homodimers that directly bind to fully assembled 20S proteasomes to mediate their nuclear import. During mitosis, proteasomes are excluded from condensing chromatin and re-imported into newly formed daughter nuclei in a highly dynamic, AKIRIN2-dependent process. Cells undergoing mitosis in the absence of AKIRIN2 become devoid of nuclear proteasomes, rapidly causing accumulation of MYC and other nuclear proteins. Collectively, our study reveals a dedicated pathway controlling the nuclear import of proteasomes in vertebrates and establishes a scalable approach to decipher regulators in essential cellular processes.
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