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RAF inhibitors activate the MAPK pathway by relieving inhibitory autophosphorylation

Matthew Holderfield1, Hanne Merritt, John Chan

  • 1Novartis Institutes for Biomedical Research, Emeryville, CA 94608, USA.

Cancer Cell
|May 18, 2013
PubMed

Insights

ATP-competitive inhibitors paradoxically activate wild-type BRAF (BRAF(WT)) signaling. This activation is ATP-dependent, linked to RAF kinase activity, and involves disrupting inhibitory autophosphorylation, explaining BRAF oncogenesis.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Oncology

Background:

  • ATP-competitive inhibitors targeting BRAF(V600E) paradoxically activate downstream signaling in cells with wild-type BRAF (BRAF(WT)).
  • Understanding the mechanism of this paradoxical activation is crucial for cancer therapy and understanding BRAF oncogenesis.

Purpose of the Study:

  • To investigate the biochemical mechanism of wild-type RAF (RAF(WT)) activation by multiple catalytic inhibitors.
  • To elucidate the role of ATP and RAF kinase activity in this activation process.

Main Methods:

  • Kinetic analysis of purified BRAF(V600E) and RAF(WT) enzymes.
  • Investigated the effect of pharmacologic and genetic alterations on RAF activation.

Main Results:

  • RAF(WT) activation by inhibitors is ATP-dependent and directly linked to RAF kinase activity.
  • A mechanism involving inhibitory autophosphorylation of RAF's phosphate-binding loop was identified.
  • Disruption of this autophosphorylation leads to RAF activation and mitogen-activated protein kinase (MAPK) pathway activation.

Conclusions:

  • The study reveals a biochemical mechanism for paradoxical RAF(WT) activation by inhibitors.
  • This mechanism explains compound-mediated MAPK pathway activation in BRAF(WT) cells.
  • The findings offer insights into the biochemical basis of BRAF oncogenesis.

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