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Cariulo C, Martufi P, Verani M, Toledo-Sherman L, Lee R, Dominguez C, Petricca L, Caricasole A. IKBKB reduces huntingtin aggregation by phosphorylating serine 13 via a non-canonical IKK pathway. Life Sci Alliance 2023; 6:e202302006. [PMID: 37553253 PMCID: PMC10410066 DOI: 10.26508/lsa.202302006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2023] [Revised: 07/27/2023] [Accepted: 07/31/2023] [Indexed: 08/10/2023] Open
Abstract
N-terminal phosphorylation at residues T3 and S13 is believed to have important beneficial implications for the biological and pathological properties of mutant huntingtin, where inhibitor of nuclear factor kappa B kinase subunit beta (IKBKB) was identified as a candidate regulator of huntingtin N-terminal phosphorylation. The paucity of mechanistic information on IKK pathways, together with the lack of sensitive methods to quantify endogenous huntingtin phosphorylation, prevented detailed study of the role of IKBKB in Huntington's disease. Using novel ultrasensitive assays, we demonstrate that IKBKB can regulate endogenous S13 huntingtin phosphorylation in a manner, dependent on its kinase activity and known regulators. We found that the ability of IKBKB to phosphorylate endogenous huntingtin S13 is mediated through a non-canonical interferon regulatory factor3-mediated IKK pathway, distinct from the established involvement of IKBKB in mutant huntingtin's pathological mechanisms mediated via the canonical pathway. Furthermore, increased huntingtin S13 phosphorylation by IKBKB resulted in decreased aggregation of mutant huntingtin in cells, again dependent on its kinase activity. These findings point to a non-canonical IKK pathway linking S13 huntingtin phosphorylation to the pathological properties of mutant huntingtin aggregation, thought to be significant to Huntington's disease.
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Affiliation(s)
- Cristina Cariulo
- Neuroscience Unit, Translational and Discovery Research Department, IRBM S.p.A., Rome, Italy
| | - Paola Martufi
- Neuroscience Unit, Translational and Discovery Research Department, IRBM S.p.A., Rome, Italy
| | - Margherita Verani
- Neuroscience Unit, Translational and Discovery Research Department, IRBM S.p.A., Rome, Italy
| | - Leticia Toledo-Sherman
- Rainwatercf.org Tau Consortium, Rainwater Charitable Foundation, Fort Worth, TX, USA
- UCLA, Department of Neurology, University of California Los Angeles, Los Angeles, CA, USA
| | - Ramee Lee
- CHDI Management/CHDI Foundation, Princeton, NJ, USA
| | | | - Lara Petricca
- Neuroscience Unit, Translational and Discovery Research Department, IRBM S.p.A., Rome, Italy
| | - Andrea Caricasole
- Neuroscience Unit, Translational and Discovery Research Department, IRBM S.p.A., Rome, Italy
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Bagnéris C, Senthil Kumar SL, Baratchian M, Britt HM, Assafa TE, Thalassinos K, Collins MK, Barrett TE. Mechanistic insights into the activation of the IKK kinase complex by the Kaposi's Sarcoma Herpes virus oncoprotein vFLIP. J Biol Chem 2022; 298:102012. [PMID: 35525271 PMCID: PMC9163697 DOI: 10.1016/j.jbc.2022.102012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2021] [Revised: 04/27/2022] [Accepted: 04/28/2022] [Indexed: 11/23/2022] Open
Abstract
Constitutive activation of the canonical NF-κB signaling pathway is a major factor in Kaposi’s sarcoma-associated herpes virus pathogenesis where it is essential for the survival of primary effusion lymphoma. Central to this process is persistent upregulation of the inhibitor of κB kinase (IKK) complex by the virally encoded oncoprotein vFLIP. Although the physical interaction between vFLIP and the IKK kinase regulatory component essential for persistent activation, IKKγ, has been well characterized, it remains unclear how the kinase subunits are rendered active mechanistically. Using a combination of cell-based assays, biophysical techniques, and structural biology, we demonstrate here that vFLIP alone is sufficient to activate the IKK kinase complex. Furthermore, we identify weakly stabilized, high molecular weight vFLIP–IKKγ assemblies that are key to the activation process. Taken together, our results are the first to reveal that vFLIP-induced NF-κB activation pivots on the formation of structurally specific vFLIP–IKKγ multimers which have an important role in rendering the kinase subunits active through a process of autophosphorylation. This mechanism of NF-κB activation is in contrast to those utilized by endogenous cytokines and cellular FLIP homologues.
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Affiliation(s)
- Claire Bagnéris
- Department of Biological Sciences, Institute of Structural Molecular Biology, Birkbeck College, London, UK
| | - Swathi L Senthil Kumar
- Department of Biological Sciences, Institute of Structural Molecular Biology, Birkbeck College, London, UK
| | - Mehdi Baratchian
- Genitourinary Malignancies Research Center, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio, USA
| | - Hannah M Britt
- Division of Biosciences, Institute of Structural and Molecular Biology, University College London, London, UK
| | - Tufa E Assafa
- Chemistry and Biochemistry Department, University of California Santa Cruz, Santa Cruz, California, USA
| | - Konstantinos Thalassinos
- Department of Biological Sciences, Institute of Structural Molecular Biology, Birkbeck College, London, UK; Division of Biosciences, Institute of Structural and Molecular Biology, University College London, London, UK
| | - Mary K Collins
- Okinawa Institute of Science and Technology, Graduate University, Onna-son, Okinawa, Japan
| | - Tracey E Barrett
- Department of Biological Sciences, Institute of Structural Molecular Biology, Birkbeck College, London, UK.
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Ko MS, Cohen SN, Polley S, Mahata SK, Biswas T, Huxford T, Ghosh G. Regulatory subunit NEMO promotes polyubiquitin-dependent induction of NF-κB through a targetable second interaction with upstream activator IKK2. J Biol Chem 2022; 298:101864. [PMID: 35339487 PMCID: PMC9035715 DOI: 10.1016/j.jbc.2022.101864] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2021] [Revised: 02/21/2022] [Accepted: 02/24/2022] [Indexed: 01/16/2023] Open
Abstract
Canonical NF-κB signaling through the inhibitor of κB kinase (IKK) complex requires induction of IKK2/IKKβ subunit catalytic activity via specific phosphorylation within its activation loop. This process is known to be dependent upon the accessory ubiquitin (Ub)-binding subunit NF-κB essential modulator (NEMO)/IKKγ as well as poly-Ub chains. However, the mechanism through which poly-Ub binding serves to promote IKK catalytic activity is unclear. Here, we show that binding of NEMO/IKKγ to linear poly-Ub promotes a second interaction between NEMO/IKKγ and IKK2/IKKβ, distinct from the well-characterized interaction of the NEMO/IKKγ N terminus to the "NEMO-binding domain" at the C terminus of IKK2/IKKβ. We mapped the location of this second interaction to a stretch of roughly six amino acids immediately N-terminal to the zinc finger domain in human NEMO/IKKγ. We also showed that amino acid residues within this region of NEMO/IKKγ are necessary for binding to IKK2/IKKβ through this secondary interaction in vitro and for full activation of IKK2/IKKβ in cultured cells. Furthermore, we identified a docking site for this segment of NEMO/IKKγ on IKK2/IKKβ within its scaffold-dimerization domain proximal to the kinase domain-Ub-like domain. Finally, we showed that a peptide derived from this region of NEMO/IKKγ is capable of interfering specifically with canonical NF-κB signaling in transfected cells. These in vitro biochemical and cell culture-based experiments suggest that, as a consequence of its association with linear poly-Ub, NEMO/IKKγ plays a direct role in priming IKK2/IKKβ for phosphorylation and that this process can be inhibited to specifically disrupt canonical NF-κB signaling.
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Affiliation(s)
- Myung Soo Ko
- Department of Chemistry & Biochemistry, University of California, San Diego, La Jolla, California, USA; Structural Biochemistry Laboratory, Department of Chemistry & Biochemistry, San Diego State University, San Diego, California, USA
| | - Samantha N Cohen
- Structural Biochemistry Laboratory, Department of Chemistry & Biochemistry, San Diego State University, San Diego, California, USA
| | - Smarajit Polley
- Department of Chemistry & Biochemistry, University of California, San Diego, La Jolla, California, USA
| | - Sushil K Mahata
- Department of Medicine, University of California, San Diego, La Jolla, California, USA; Medicine, VA San Diego Health Care System, San Diego, California, USA
| | - Tapan Biswas
- Department of Chemistry & Biochemistry, University of California, San Diego, La Jolla, California, USA
| | - Tom Huxford
- Structural Biochemistry Laboratory, Department of Chemistry & Biochemistry, San Diego State University, San Diego, California, USA
| | - Gourisankar Ghosh
- Department of Chemistry & Biochemistry, University of California, San Diego, La Jolla, California, USA.
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Ko MS, Biswas T, Mulero MC, Bobkov AA, Ghosh G, Huxford T. Structurally plastic NEMO and oligomerization prone IKK2 subunits define the behavior of human IKK2:NEMO complexes in solution. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2020; 1868:140526. [PMID: 32853772 DOI: 10.1016/j.bbapap.2020.140526] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2020] [Revised: 07/30/2020] [Accepted: 08/08/2020] [Indexed: 10/23/2022]
Abstract
The human IκB Kinase (IKK) is a multisubunit protein complex of two kinases and one scaffolding subunit that controls induction of transcription factor NF-κB activity. IKK behaves as an entity of aberrantly high apparent molecular weight in solution. Recent X-ray crystallographic and cryo-electron microscopy structures of individual catalytic subunits (IKK1/IKKα and IKK2/IKKβ) reveal that they are both stably folded dimeric proteins that engage in extensive homo-oligomerization through unique surfaces that are required for activation of their respective catalytic activities. The NEMO/IKKγ subunit is a predominantly coiled coil protein that is required for activation of IKK through the canonical NF-κB signaling pathway. Here we report size-exclusion chromatography, multi-angle light scattering, analytical centrifugation, and thermal denaturation analyses of full-length human recombinant NEMO as well as deletion and disease-linked variants. We observe that NEMO is predominantly a dimer in solution, although by virtue of its modular coiled coil regions NEMO exhibits complicated solution dynamics involving portions that are mutually antagonistic toward homodimerization. This behavior causes NEMO to behave as a significantly larger sized particle in solution. Analyses of NEMO in complex with IKK2 indicate that NEMO preserves this structurally dynamic character within the multisubuit complex and provides the complex-bound IKK2 further propensity toward homo-oligomerization. These observations provide critical information on the structural plasticity of NEMO subunit dimers which helps clarify its role in diseases and in IKK regulation through oligomerization-dependent phosphorylation of catalytic IKK2 subunit dimers.
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Affiliation(s)
- Myung Soo Ko
- Structural Biochemistry Laboratory, Department of Chemistry & Biochemistry, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182-1030, United States; Department of Chemistry & Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0357, United States
| | - Tapan Biswas
- Department of Chemistry & Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0357, United States
| | | | - Andrey A Bobkov
- Sanford Burnham Prebys Medical Discovery Institute, United States
| | - Gourisankar Ghosh
- Department of Chemistry & Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0357, United States.
| | - Tom Huxford
- Structural Biochemistry Laboratory, Department of Chemistry & Biochemistry, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182-1030, United States.
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Shoji S, Hanada K, Takahashi M, Watanabe K, Yonemochi M, Tomabechi Y, Shirouzu M. The NF-κB regulator IκBβ exhibits different molecular interactivity and phosphorylation status from IκBα in an IKK2-catalysed reaction. FEBS Lett 2020; 594:1532-1549. [PMID: 32017069 DOI: 10.1002/1873-3468.13752] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2019] [Revised: 01/06/2020] [Accepted: 01/21/2020] [Indexed: 12/13/2022]
Abstract
Activation of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) transcription factor, a central player in immune response regulation, is based on phosphorylation of inhibitor of kappaB alpha (IκBα) by the Inhibitor of kappaB kinase (IKK) that triggers IκBα degradation. Although inhibitor of kappaB beta (IκBβ) is structurally similar to IκBα, its precise characteristics remain undefined. Herein, we report that the molecular interactivity of IκBβ with the kinase-active region of IKK subunit 2 (IKK2), as well as its phosphorylation status, differs markedly from those of IκBα. A mass spectrometry analysis revealed that IκBβ phosphorylation sites are distributed in its C-terminal region, whereas IκBα phosphorylation sites are located in the N-terminal region. Furthermore, IKK2 phosphorylation sites in IκBβ are found in a region distinct from typical degradation signals, such as phosphodegron and proline/glutamic acid/serine/threonine-rich sequence (PEST) motifs. Mutation of the IκBβ phosphorylation sites enhances its resistance to homeostatic proteasomal degradation. These findings contribute a novel concept in NF-κB/IKK signalling research.
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Affiliation(s)
- Shisako Shoji
- RIKEN Center for Biosystems Dynamics Research, Yokohama, Japan
| | - Kazuharu Hanada
- RIKEN Center for Biosystems Dynamics Research, Yokohama, Japan
| | | | | | | | - Yuri Tomabechi
- RIKEN Center for Biosystems Dynamics Research, Yokohama, Japan
| | - Mikako Shirouzu
- RIKEN Center for Biosystems Dynamics Research, Yokohama, Japan
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