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The post-translational modification of ras p21 is important for Raf-1 activation

A Kikuchi1, L T Williams

  • 1Cardiovascular Research Institute, University of California, San Francisco 94143-0130.

The Journal of Biological Chemistry
|August 5, 1994
PubMed

Insights

Post-translational modification of ras p21 is essential for activating Raf-1 kinase. While ras p21 binds to Raf-1, this association alone does not trigger Raf-1 activity, highlighting the importance of modifications like farnesylation.

Area of Science:

  • Cellular signaling pathways
  • Protein kinase regulation
  • Ras GTPase biology

Background:

  • Raf-1 kinase is crucial for mitogenic signaling mediated by ras p21.
  • Ras p21 undergoes C-terminal farnesylation and carboxyl methylation, essential for its function.
  • Direct association between ras p21 and Raf-1 has been previously established.

Purpose of the Study:

  • To investigate the role of ras p21 post-translational modifications in Raf-1 activation.
  • To determine if ras p21 association with Raf-1 is sufficient for kinase activation.

Main Methods:

  • Overexpression of Raf-1 and ras p21 (wild-type and mutants) in baculovirus/Sf9 insect cells.
  • Assay of Raf-1 autophosphorylating activity.
  • In vitro kinase assays measuring Raf-1's ability to activate MEK (mitogen-activated protein kinase kinase).
  • Analysis of Raf-1/ras p21 complex formation.

Main Results:

  • Coexpression of Raf-1 with wild-type v-ras p21 stimulated Raf-1 autophosphorylation and MEK activation.
  • Post-translationally modified v-ras p21 mutants failed to stimulate Raf-1 activity.
  • Raf-1 formed complexes with both wild-type v-ras p21 and its non-modified mutants.
  • These findings indicate that post-translational modification of ras p21 is a prerequisite for Raf-1 activation.

Conclusions:

  • Ras p21 post-translational modifications are necessary for Raf-1 activation.
  • The physical association between ras p21 and Raf-1 is not sufficient to induce Raf-1 kinase activity.
  • This study elucidates a critical regulatory step in ras-mediated signaling pathways.

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