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Assessment of Mitochondrial Functions and Cell Viability in Renal Cells Overexpressing Protein Kinase C Isozymes
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Activation of protein kinase C decreases phosphorylation of c-Jun at sites that negatively regulate its DNA-binding

W J Boyle1, T Smeal, L H Defize

  • 1Molecular Biology and Virology Laboratory, Salk Institute, La Jolla, California 92037.

Cell
|February 8, 1991
PubMed

Insights

In resting cells, c-Jun protein is inactive due to phosphorylation. Protein Kinase C activation triggers dephosphorylation, enhancing AP-1 binding activity and c-Jun

Area of Science:

  • Molecular biology
  • Cell signaling

Background:

  • c-Jun is a transcription factor regulating gene expression.
  • Phosphorylation of c-Jun affects its DNA-binding and trans-activation activities.

Purpose of the Study:

  • To investigate the role of c-Jun phosphorylation in regulating its activity.
  • To identify specific phosphorylation sites and their impact on DNA binding.

Main Methods:

  • In vitro phosphorylation assays using glycogen synthase kinase 3 (GSK-3).
  • Site-directed mutagenesis of c-Jun phosphorylation sites.
  • Analysis of AP-1 binding activity following protein kinase C activation.

Main Results:

  • GSK-3 phosphorylates c-Jun at three specific sites (residues 227-252).
  • Protein Kinase C activation causes dephosphorylation of c-Jun, increasing AP-1 binding.
  • Mutation of serine 243 to phenylalanine enhances c-Jun trans-activation by 10-fold.

Conclusions:

  • c-Jun exists in a latent, phosphorylated state in resting cells.
  • Site-specific dephosphorylation, triggered by Protein Kinase C, activates c-Jun.
  • Phosphorylation status is a key regulator of c-Jun's transcriptional function.

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