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Ras-independent activation of ERK signaling via the torso receptor tyrosine kinase is mediated by Rap1

Snigdha Mishra1, Sarah M Smolik, Michael A Forte

  • 1Vollum Institute, Oregon Health and Science University, Portland, OR 97201, USA.

Current Biology : CB
|February 23, 2005
PubMed

Insights

Drosophila Rap1 (D-Rap1) activates the ERK pathway and is crucial for embryonic development. This study provides the first genetic evidence that Rap1, independent of Ras, directly activates the MAP kinase cascade in eukaryotes.

Area of Science:

  • Cellular signaling pathways
  • Developmental biology
  • Genetics

Background:

  • Receptor tyrosine kinases (RTKs) like Torso activate ERK signaling for embryonic development.
  • While Ras is known to activate ERK, RTKs can also activate ERK independently of Ras.
  • The role of Rap1 in coupling RTKs to ERK signaling is debated due to a lack of direct genetic evidence.

Purpose of the Study:

  • To investigate the role of Drosophila Rap1 (D-Rap1) in activating the ERK pathway.
  • To provide direct genetic evidence for Rap1-mediated activation of the MAP kinase cascade.

Main Methods:

  • Biochemical assays to demonstrate D-Rap1 binding to D-Raf.
  • Genetic disruption of D-Rap1 expression in Drosophila embryos.
  • Analysis of Torso-dependent ERK activation and downstream gene expression (tailless, huckebein).

Main Results:

  • D-Rap1 directly binds and activates D-Raf and ERK in a GTP- and D-Raf-dependent manner.
  • Disrupting D-Rap1 reduced Torso-dependent ERK activation and gene expression, similar to D-Ras1 mutants.
  • Combined D-Ras1 and D-Rap1 deficiencies abolished gene expression, mimicking D-Raf mutants.

Conclusions:

  • Drosophila Rap1 (D-Rap1) is a key activator of the D-Raf/ERK signaling pathway.
  • This study provides the first direct genetic evidence for Rap1-mediated activation of the MAP kinase cascade in eukaryotes.
  • D-Rap1 functions alongside D-Ras1 in Torso-mediated developmental signaling.

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