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Nerve growth factor-stimulated B-Raf catalytic activity is refractory to inhibition by cAMP-dependent protein kinase

M C MacNicol1, A M MacNicol

  • 1Department of Medicine and the Committee on Cancer Biology, The University of Chicago, Chicago, Illinois 60637, USA.

The Journal of Biological Chemistry
|May 1, 1999
PubMed

Insights

The cAMP-dependent protein kinase (PKA) does not inhibit nerve growth factor-stimulated B-Raf activity. However, PKA inhibits a truncated B-Raf form, suggesting the N-terminal domain prevents PKA regulation.

Area of Science:

  • Cellular signaling pathways
  • Protein kinase regulation
  • Proto-oncogene research

Background:

  • The cAMP-dependent protein kinase (PKA) has dual roles in growth factor signaling via the mitogen-activated protein kinase pathway.
  • PKA inhibits Raf-1-mediated proliferation but potentiates nerve growth factor-stimulated PC12 cell differentiation, a B-Raf-mediated process.
  • The conserved kinase domains of Raf-1 and B-Raf suggest PKA should inhibit both.

Purpose of the Study:

  • To investigate PKA's regulation of B-Raf kinase activity.
  • To understand why B-Raf-mediated differentiation is potentiated by PKA, contrasting with PKA's inhibition of Raf-1.

Main Methods:

  • In vitro kinase assays.
  • Transfection of PC12 cells with B-Raf constructs.
  • Analysis of PKA's effect on wild-type and truncated B-Raf activity.

Main Results:

  • Nerve growth factor-stimulated B-Raf activity was not inhibited by PKA.
  • A constitutively active, N-terminally truncated B-Raf was inhibited by PKA both in vitro and in transfected cells.
  • These findings indicate the N-terminal regulatory domain of B-Raf interferes with PKA modulation.

Conclusions:

  • B-Raf-dependent processes are resistant to PKA inhibition due to interference by its N-terminal regulatory domain.
  • This provides a molecular explanation for the differential regulation of B-Raf and Raf-1 by PKA.
  • PKA's regulatory role in cell signaling is complex and context-dependent.

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