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Cell type-specific regulation of B-Raf kinase by cAMP and 14-3-3 proteins

W Qiu1, S Zhuang, F C von Lintig

  • 1Department of Medicine and Cancer Center, University of California, San Diego, La Jolla, California 92093-0652, USA.

The Journal of Biological Chemistry
|August 10, 2000
PubMed

Insights

Cyclic AMP differentially regulates the mitogen-activated protein kinase (MAPK) pathway, with 14-3-3 proteins mediating cell-type specific responses by protecting B-Raf from inhibition.

Area of Science:

  • Cellular signaling
  • Molecular biology
  • Signal transduction

Background:

  • Cyclic AMP (cAMP) exhibits dual roles in modulating the mitogen-activated protein kinase (MAPK) pathway.
  • MAPK pathway activation is linked to B-Raf in some cells, while inhibition is associated with protein kinase A (PKA) in others.

Purpose of the Study:

  • To investigate the cell-type specific mechanisms underlying cAMP's opposing effects on the MAPK pathway.
  • To elucidate the role of 14-3-3 proteins in regulating B-Raf kinase activity in response to cAMP.

Main Methods:

  • Comparative analysis of MAPK activity in response to cAMP across four distinct cell lines (CHO-K1, PC12, C6, NB2A).
  • Assessment of Rap1 activation, B-Raf expression, and B-Raf kinase activity.
  • Investigation of 14-3-3 protein association with B-Raf and the impact of 14-3-3 overexpression or inhibition.

Main Results:

  • cAMP stimulated MAPK activity in CHO-K1 and PC12 cells but inhibited it in C6 and NB2A cells.
  • 14-3-3 protein association with B-Raf was significantly lower in cell types where cAMP inhibited MAPK activity.
  • Overexpression of 14-3-3 isoforms prevented cAMP-mediated B-Raf inhibition, while a dominant-negative mutant impaired B-Raf activity.

Conclusions:

  • 14-3-3 proteins play a critical role in protecting B-Raf from PKA-mediated inhibition.
  • The differential association of 14-3-3 with B-Raf explains the tissue-specific effects of cAMP on B-Raf kinase activity and subsequent MAPK signaling.

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