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Regulation of NF-κB by Calmodulin
Umeå University, Faculty of Medicine, Molecular Biology.
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Cells experience numerous external signals which they must respond to. Such signals arriving at the cell surface are transduced via various signal transduction pathways and often ultimately result in regulation of transcription. NF-κB is a family of transcription factors involved in the regulation of genes important for processes such as immune and inflammatory responses, cell growth, development and cell survival. NF-κB proteins are normally kept inactive in the cytoplasm due to masking of their nuclear localisation signal (NLS) by inhibitory IκB proteins. A large number of stimuli lead to the activation of IκB-kinase (IKK). Active IKK phosphorylates IκB and thereby labels it for ubiquitination and, subsequently, degradation by the proteasome. Liberated NF-κB enters the nucleus, where it takes part in the regulation of its target genes.

Calmodulin (CaM) is a ubiquitous Ca2+-binding protein which is considered to be the predominant intracellular Ca2+ sensor. CaM plays a major role in the Ca2+-dependent regulation of a wide variety of cellular processes, including transcription. CaM regulates transcription both indirectly through CaM-dependent kinases and phosphatases and directly through interaction with transcription factors.

CaM was found to bind directly and in a Ca2+-dependent fashion to the two NF-κB family members c-Rel and RelA. The CaM-NF-κB interactions were strongly enhanced by NF-κB activating stimuli and this enhancement was blocked by the addition of IκB, suggesting that c-Rel and RelA can bind CaM after their signal-induced release from IκB. Compared to wild-type c-Rel, CaM binding-deficient mutants were shown to exhibit an increased nuclear accumulation and transcriptional activity on Ca2+-regulated cytokine promoters. The results suggest that CaM can inhibit transport of c-Rel, but not of RelA, to the nucleus and thereby differentially regulate the activation of NF-κB proteins following cell stimulation. CaM was also found to affect NF-κB activity indirectly through the action of a CaM-dependent kinase (CaMK). Studies of the events leading to IκBα phosphorylation revealed that CaM and CaMKII inhibitors blocked phorbol ester induced activation of IKK. Furthermore, CaM and CaMKII inhibitors also blocked T cell receptor/CD3 induced IκBα degradation, and expression of an inhibitor-resistant derivative of the γ isoform of CaMKII caused the inhibitors lose their effect on phorbol ester induced IκBα degradation. Finally, expression of a constitutively active CaMKII resulted in the activation of NF-κB. These results identify CaMKII as a mediator of IKK activation, specifically in response to T cell receptor/CD3 and phorbol ester stimulation.

In conclusion, this thesis describes the identification of CaM as a dual regulator of NF-κB proteins, acting both directly and indirectly to affect the activity of this family of transcription factors.

Place, publisher, year, edition, pages
2003. , 69 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; ISSN 0346-6612; 864
Keyword [en]
Molecular biology, NF-κB, calmodulin, transcription, calcium
Keyword [sv]
Molekylärbiologi
National Category
Biochemistry and Molecular Biology
Research subject
Molecular Biology
Identifiers
URN: urn:nbn:se:umu:diva-158ISBN: 91-7305-549-2 (print)OAI: oai:DiVA.org:umu-158DiVA: diva2:141434
Public defence
2003-12-05, Major Groove, 6L, NUS, Umeå, 12:00
Opponent
Supervisors
Available from: 2003-11-25 Created: 2003-11-25Bibliographically approved
List of papers
1. Regulation of c-Rel Nuclear Localization by Binding of Ca2+/Calmodulin
Open this publication in new window or tab >>Regulation of c-Rel Nuclear Localization by Binding of Ca2+/Calmodulin
2003 (English)In: Molecular and Cellular Biology, ISSN 0270-7306, E-ISSN 1098-5549, Vol. 23, no 4, 1418-1427 p.Article in journal (Refereed) Published
Abstract [en]

The NF-κB/Rel family of transcription factors participates in the control of a wide array of genes, including genes involved in embryonic development and regulation of immune, inflammation, and stress responses. In most cells, inhibitory IκB proteins sequester NF-κB/Rel in the cytoplasm. Cellular stimulation results in the degradation of IκB and modification of NF-κB/Rel proteins, allowing NF-κB/Rel to translocate to the nucleus and act on its target genes. Calmodulin (CaM) is a highly conserved, ubiquitously expressed Ca2+ binding protein that serves as a key mediator of intracellular Ca2+ signals. Here we report that two members of the NF-κB/Rel family, c-Rel and RelA, interact directly with Ca2+-loaded CaM. The interaction with CaM is greatly enhanced by cell stimulation, and this enhancement is blocked by addition of IκB. c-Rel and RelA interact with CaM through a similar sequence near the nuclear localization signal. Compared to the wild-type protein, CaM binding-deficient mutants of c-Rel exhibit increases in both nuclear accumulation and transcriptional activity on the interleukin 2 and granulocyte macrophage colony-stimulating factor promoters in the presence of a Ca2+ signal. Conversely, for RelA neither nuclear accumulation nor transcriptional activity on these promoters is increased by mutation of the sequence interacting with CaM. Our results suggest that CaM binds c-Rel and RelA after their release from IκB and can inhibit nuclear import of c-Rel while letting RelA translocate to the nucleus and act on its target genes. CaM can therefore differentially regulate the activation of NF-κB/Rel proteins following stimulation.

Place, publisher, year, edition, pages
American Society for Microbiology, 2003
National Category
Microbiology
Identifiers
urn:nbn:se:umu:diva-3008 (URN)10.1128/MCB.23.4.1418-1427.2003 (DOI)
Available from: 2003-11-25 Created: 2003-11-25 Last updated: 2012-05-10Bibliographically approved
2. Calmodulin dependence of NFκB activation
Open this publication in new window or tab >>Calmodulin dependence of NFκB activation
1998 (English)In: FEBS Letters, ISSN 0014-5793, E-ISSN 1873-3468, Vol. 441, no 1, 132-136 p.Article in journal (Refereed) Published
Abstract [en]

The NF kappa B family of transcription factors is regulated by inhibitory I kappa B proteins. A diversity of stimuli leads to the phosphorylation and subsequent degradation of I kappa B, releasing NF kappa B to act on its target genes. Calmodulin (CaM) is a key regulator of numerous cellular processes and is the predominant intracellular receptor for Ca2+ signals. Here me report that several CaM antagonists inhibit the activation of NF kappa B, and that this is due to the prevention of inducible I kappa B phosphorylation. Our results suggest that CaM is involved in the phosphorylation of I kappa B, a finding that may help in elucidating the mechanism of this critical step of NF kappa B activation.

Place, publisher, year, edition, pages
Elsevier, 1998
Keyword
calmodulin, I kappa B, nuclear factor kappa B, phosphorylation, transcriptional regulation
National Category
Medical Biotechnology (with a focus on Cell Biology (including Stem Cell Biology), Molecular Biology, Microbiology, Biochemistry or Biopharmacy)
Identifiers
urn:nbn:se:umu:diva-3009 (URN)10.1016/S0014-5793(98)01537-3 (DOI)000077631800028 ()
Available from: 2003-11-25 Created: 2003-11-25 Last updated: 2015-01-19Bibliographically approved
3. Calmodulin-dependent Kinase II Mediates T Cell Receptor/CD3- and Phorbol Ester-induced Activation of IκB Kinase
Open this publication in new window or tab >>Calmodulin-dependent Kinase II Mediates T Cell Receptor/CD3- and Phorbol Ester-induced Activation of IκB Kinase
2001 (English)In: Journal of Biological Chemistry, ISSN 1083-351X, Vol. 276, no 38, 36008 - 36013 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-3010 (URN)
Available from: 2003-11-25 Created: 2003-11-25 Last updated: 2009-04-03Bibliographically approved

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