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CaMKII targets Bc110 in T-cell receptor induced activation of NF-κB
Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine). Umeå University, Faculty of Medicine, Department of Medical Biosciences, Pathology.
Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
2011 (English)In: Molecular Immunology, ISSN 0161-5890, E-ISSN 1872-9142, Vol. 48, no 12-13, 1448-1460 p.Article in journal (Refereed) Published
Abstract [en]

Recognition of antigen by T- or B-cell receptors leads to formation of an immunological synapse and initiation of signalling events that collaborate to determine the nature of the adaptive immune response. Activation of NF-κB transcription factors has a key role in regulation of numerous genes with important functions in immune responses and inflammation and is of great importance for lymphocyte activation and differentiation. The activation of NF-κB depends on changes in intracellular Ca2+ levels, and both calmodulin (CaM) and a CaM-dependent kinase, CaMKII, help regulate NF-κB activation after T-cell receptor (TCR) stimulation, but the mechanisms are not well characterized. Here we have analyzed the functional role of CaMKII in the signalling pathway from the TCR to activation of IKK, the kinase that phosphorylates the NF-κB inhibitor IκB. We show that CaMKII is recruited to the immunological synapse where it interacts with and phosphorylates the signalling adaptor protein Bcl10. Furthermore, phosphorylation of the CARD domain of Bcl10 by CaMKII regulates the interactions within the important Carma1, Bcl10, Malt1 signalling complex and the essential signal induced ubiquitinations of Bcl10 and IKKγ. We propose a novel mechanism whereby Ca2+ signals can be integrated at the immunological synapse through CaMKII-dependent phosphorylation of Bcl10.

Place, publisher, year, edition, pages
Elsevier, 2011. Vol. 48, no 12-13, 1448-1460 p.
National Category
Biochemistry and Molecular Biology
Research subject
Molecular Biology
Identifiers
URN: urn:nbn:se:umu:diva-3572DOI: 10.1016/j.molimm.2011.03.020OAI: oai:DiVA.org:umu-3572DiVA: diva2:142338
Available from: 2008-10-29 Created: 2008-10-29 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Calmodulin mediated regulation of NF-kappaB in lymphocytes
Open this publication in new window or tab >>Calmodulin mediated regulation of NF-kappaB in lymphocytes
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

NF-κB transcription factors are regulators of a wide spectrum of genes involved in immune responses and inflammation as well as cellular proliferation and survival. Transcriptionally competent NF-κB dimers are retained in the cytoplasm of resting cells by binding to inhibitors of NF-κB (IκBs). Stimuli that activate NF-κB converge on the activation of the IκB kinase (IKK), resulting in phosphorylation and subsequent proteasomal degradation of IκB. This releases functional NF-κB dimers that rapidly move to the nucleus where they regulate transcription of NF-κB-dependent target genes. The study of signalling to NF-κB from T and B lymphocyte antigen receptors is a field of intense investigation, and much attention is focused on the complex of the molecular scaffolding proteins Carma1, Bcl10 and MALT1. Together, these are crucial for the organisation of a structure beneath the activated receptor, termed the immunological synapse. IKK is recruited to this structure and becomes activated, subsequently leading to activation of NF-κB.

Calcium (Ca2+) is a ubiquitous intracellular messenger that is involved in the regulation of numerous aspects of cellular function, including transcription. NF-κB activity is known to be regulated by changes in intracellular Ca2+ levels, such as those created by antigen receptor activation, but the mechanisms are to a large extent undefined. Ca2+ signals in cells are transmitted predominantly by the ubiquitous Ca2+ sensor protein calmodulin (CaM). Signalling that increases the intracellular Ca2+ concentration leads to binding of Ca2+ to CaM, which changes its structure, thereby allowing it to interact with a new range of target proteins.

The studies of NF-κB signalling in lymphocytes presented here reveal that CaM is involved, both directly and indirectly, in the regulation of NF-κB. CaM was found to interact directly and in a Ca2+-dependent manner with the NF-κB proteins RelA and c-Rel after their signal-induced release from IκB. The interaction of CaM with c-Rel, but not RelA, was found to be inhibitory for its nuclear accumulation and transcriptional activity on Ca2+-regulated IL-2 and GM-CSF promoters; thus, CaM binding was found to differentially regulate c-Rel and RelA in lymphocytes. CaM was also shown to interact directly and in a Ca2+-dependent manner with Bcl10. The interaction was mapped to the Carma1-interacting CARD domain of Bcl10 and was found to have a negative effect on the ability of Bcl10 to bind to Carma1. Binding of CaM to Bcl10 also had a negative effect on activation of NF-κB after T cell receptor stimulation, since a point mutant of Bcl10 with reduced binding to CaM showed increased activation of an NF-κB reporter in Jurkat T cells, which was further enhanced by TCR-activating stimuli.

In addition, CaM was found to positively regulate NF-κB activation indirectly through CaM-dependent kinase II (CaMKII). Inhibitors of CaM and CaMKII were shown to inhibit IκBα degradation in lymphocytes induced by phorbol ester or T cell receptor stimulation. The actions of CaMKII were mapped to a point upstream of IKK activation and further studies revealed that CaMKII is recruited to the immunological synapse, where it inducibly interacts with and phosphorylates Bcl10 at multiple sites. Phosphorylation of Bcl10 by CaMKII was shown to be important for the ability of Bcl10 to activate NF-κB, since mutation of the phosphorylation sites of Bcl10 inhibited Bcl10-induced transcriptional activity of NF-κB, in part by preventing signalinduced ubiquitination and degradation of Bcl10.

Place, publisher, year, edition, pages
Umeå: Molekylärbiologi (Medicinska fakulteten), 2008. 63 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1217
Keyword
calcium, CaM, CaMKII, NF-kappaB, Bc110, immunological synapse
National Category
Cell and Molecular Biology
Identifiers
urn:nbn:se:umu:diva-1895 (URN)978-91-7264-659-9 (ISBN)
Public defence
2008-11-14, Major Groove, 6L, Umeå Universitet, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2008-10-29 Created: 2008-10-29 Last updated: 2010-01-18Bibliographically approved
2. Regulation of activation of NF-κB by Calmodulin in T-lymphocytes
Open this publication in new window or tab >>Regulation of activation of NF-κB by Calmodulin in T-lymphocytes
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nuclear factor kappa B (NF-kB) is a widely expressed family of transcription factors that are involved in a diverse number of processes. These include inflammation or differentiation, survival or apoptosis, and proliferation or cell cycle arrest. NF-kB is usually associated with inhibitory kB proteins (IkB), which mask the nuclear localisation sequence (NLS) of NF-kB and renders it in the cytoplasm. Various stimuli result in the activation of the I kappa B kinase (IKK) protein complex, which phosphorylates IκB proteins and thereby marks them for degradation by the ubiquitin-proteasome pathway. Thereby NF-kB enters the nucleus and acts on its target genes. The study of T- and B-lymphocyte antigen receptor signalling to NF-kB is a field of intense investigation, with much attention being focused on the molecular scaffolding proteins Carma1, Bcl10 and MALT1 and their post-translational modifications. These have been shown to be crucial for the organization of the immunological synapse structure under the activated receptor, to which IKK is recruited and becomes activated, which subsequently leads to the activation of NF-kB.

T cell receptor (TCR) activation results in a rapid increase in the intracellular Ca2+ level and NF-kB activation is known to be regulated by those increases, but the mechanisms have remained unclear. Calmodulin (CaM) is a calcium sensory protein that responds to increases in intracellular Ca2+ levels. When CaM binds Ca2+ ions, it leads to structural changes that directly as well as indirectly, through CaM dependent kinases (CaMKs), phosphatases and other enzymes, alters a variety of cellular processes, among them transcriptional regulation. Here CaM is shown to interact directly with Bcl10 in a Ca2+ dependent manner. Increases in the intracellular Ca2+ level are shown to induce the proximity of Bcl10 and CaM in vivo. Carma1 associates with Bcl10 through a CARD-CARD domain interaction that is known to be crucial for TCR signalling to NF-kB. The interaction of CaM with Bcl10 was mapped to the CARD domain and was shown to be a negative regulator for the Bcl10-Carma1 interaction. Inhibition of the CaM interaction by a point mutation within the CaM binding site of Bcl10 results in decreased binding of CaM to Bcl10 in vivo, as well as an increased ability of Bcl10 to induce NF-kB transcriptional activity, which is further enhanced by TCR activating stimuli.

NF-kB activation is also shown here to be regulated by CaM indirectly through actions of CaMKII. The CaMKII is recruited to the immunological synapse where it interacts with Bcl10 in an inducible fashion and phosphorylates Bcl10. Phosphorylations of Bcl10 by CaMKII are shown to be important for the ability of Bcl10 to induce NF-κB transcriptional activity. Upon mutation of its most important CaMKII site, Bcl10 fails to activate an NF-kB reporter and an NF-kB target gene (IL-2). This mutated Bcl10 also fails to induce activating phosphorylations of IKKa/b and the kinase JNK2 but not JNK1. Furthermore, phosphorylation of Bcl10 by CaMKII regulates the interactions within the important Carma1, Bcl10, Malt1 signaling complex and the essential signal induced ubiquitinations of Bcl10 and IKKg. Phosphorylation of IKK by TAK1 is also regulated by CaMKII, and serine 82 is a putative CaMKII target site of TAK1 that appears to be important for IκBα degradation.

In summary, this thesis explores that not only NF-kB but also CaM is a double-edged sword, since the multi-functional NF-kB family of transcription factors is regulated by CaM both negatively and positively.

Place, publisher, year, edition, pages
Umeå: Umeå university, 2011. 75 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1445
Keyword
Calcium, Calmodulin, CaMKII, TCR, Bcl10, NF-κB
Identifiers
urn:nbn:se:umu:diva-46561 (URN)978-91-7459-278-8 (ISBN)
Public defence
2011-09-27, Major Groove, Byggnad 6L, Umeå University, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2011-09-06 Created: 2011-09-05 Last updated: 2011-09-06Bibliographically approved

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