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Src42 binding activity regulates Drosophila RAF by a novel CNK-dependent derepression mechanism

Gino Laberge1, Mélanie Douziech, Marc Therrien

  • 1Institut de Recherche en Immunologie et en Cancérologie, Laboratory of Intracellular Signaling, Université de Montréal, Montréal, Québec, Canada.

The EMBO Journal
|January 22, 2005
PubMed

Insights

Connector enhancer of KSR (CNK) integrates RAS and Src42 signals to regulate RAF activation in Drosophila. Src42 binding to CNK, independent of its catalytic activity, counteracts RAF inhibition, revealing a two-component input mechanism.

Area of Science:

  • Molecular Biology
  • Cell Signaling
  • Genetics

Background:

  • Connector enhancer of KSR (CNK) is crucial for Drosophila receptor tyrosine kinase/mitogen-activated protein kinase (RTK/MAPK) pathways.
  • CNK exhibits bimodal regulation of RAF, stimulating it via RAS integration and inhibiting it through its RAF-inhibitory region (RIR).

Purpose of the Study:

  • To investigate how CNK's RAF inhibitory function is regulated.
  • To elucidate the role of Src42 in modulating CNK activity within RTK/MAPK signaling.

Main Methods:

  • Analysis of Drosophila cnk loss-of-function alleles.
  • Investigating the interaction between Src42 and CNK using biochemical assays.
  • Assessing the impact of mutations on Src42 binding and CNK function.

Main Results:

  • Src42 associates with CNK in an RTK-dependent manner, counteracting the RIR-mediated inhibition.
  • Mutations in a conserved region C-terminal to the RIR impair Src42 binding.
  • Src42's derepressing effect on CNK relies on its SH3 and SH2 domains, not its catalytic activity.

Conclusions:

  • CNK integrates both RAS and Src42 signals for RAF activation.
  • Src42 binding to CNK is essential for RAF activation, acting as a critical regulatory step.
  • This study reveals a novel two-component input mechanism for RAF activation in Drosophila.

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