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Casein kinase II is a negative regulator of c-Jun DNA binding and AP-1 activity

A Lin1, J Frost, T Deng

  • 1Department of Pharmacology, University of California, San Diego School of Medicine, La Jolla 92093-0636.

Cell
|September 4, 1992
PubMed

Insights

Casein kinase II (CKII) phosphorylates c-Jun, inhibiting its DNA binding and AP-1 activity. This study reveals CKII

Area of Science:

  • Molecular Biology
  • Cell Signaling
  • Biochemistry

Background:

  • c-Jun is a key component of the AP-1 transcription factor, regulating gene expression.
  • Phosphorylation of c-Jun inhibits its DNA-binding activity, impacting AP-1 transcriptional function.
  • The specific kinases responsible for c-Jun phosphorylation and their regulatory roles were not fully understood.

Purpose of the Study:

  • To identify the kinase responsible for phosphorylating inhibitory sites on c-Jun.
  • To elucidate the role of casein kinase II (CKII) in regulating AP-1 activity.
  • To investigate how CKII-mediated phosphorylation of c-Jun affects AP-1 transcriptional function.

Main Methods:

  • Site-directed mutagenesis of c-Jun phosphorylation sites.
  • In vitro kinase assays using purified casein kinase II.
  • In vivo studies involving microinjection of peptides and CKII into cells.
  • Analysis of AP-1 activity and c-Jun expression levels.

Main Results:

  • Casein kinase II (CKII) was identified as the kinase phosphorylating Thr-231 and Ser-249 on c-Jun.
  • Substitution of Ser-243 with Phenylalanine impaired c-Jun phosphorylation by CKII.
  • Microinjection of CKII inhibitors induced AP-1 activity and c-Jun expression.
  • Microinjection of CKII suppressed AP-1 induction by phorbol ester or inhibitory peptides.

Conclusions:

  • Casein kinase II (CKII) plays a crucial role in attenuating AP-1 activity by phosphorylating c-Jun.
  • CKII acts as a negative regulator of AP-1 transcriptional activity.
  • These findings uncover a novel function for CKII in cellular signaling pathways.

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