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Constitutive phosphorylation of I kappa B alpha by casein kinase II

C F Barroga1, J K Stevenson, E M Schwarz

  • 1Molecular Biology and Virology Laboratory, Salk Institute, San Diego, CA 92186-5800, USA.

Proceedings of the National Academy of Sciences of the United States of America
|August 15, 1995
PubMed

Insights

This study identifies a cellular kinase that phosphorylates I kappa B alpha, a protein regulating NF-kappa B/Rel. This phosphorylation is crucial for controlling NF-kappa B/Rel protein activity.

Area of Science:

  • Molecular Biology
  • Cell Signaling
  • Protein Kinases

Background:

  • NF-kappa B/Rel proteins are key regulators of immune and inflammatory responses.
  • I kappa B alpha sequesters NF-kappa B/Rel in the cytoplasm, and its degradation precedes NF-kappa B activation.
  • Understanding the regulation of I kappa B alpha phosphorylation is critical for controlling NF-kappa B signaling.

Purpose of the Study:

  • To identify and characterize the cellular kinase responsible for phosphorylating I kappa B alpha.
  • To elucidate the role of this kinase in the regulation of NF-kappa B/Rel protein activity.

Main Methods:

  • Partial purification of a cellular kinase from murine cells.
  • In vitro kinase assays using I kappa B alpha as a substrate.
  • Site-directed mutagenesis of potential phosphorylation sites on I kappa B alpha.
  • Antibody inhibition assays using antibodies against casein kinase II (CKII).
  • Two-dimensional phosphopeptide mapping.

Main Results:

  • A cellular kinase specifically phosphorylates the C-terminus of I kappa B alpha.
  • The kinase activity is inhibited by antibodies against CKII alpha subunit.
  • Mutation of CKII consensus sites on I kappa B alpha abolished phosphorylation.
  • In vitro and in vivo phosphorylation patterns of I kappa B alpha were identical.

Conclusions:

  • Casein kinase II (CKII) is responsible for the constitutive phosphorylation of I kappa B alpha.
  • CKII-mediated phosphorylation of I kappa B alpha plays a role in regulating NF-kappa B/Rel protein activity.

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