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Activation of CD4 T cells by Raf-independent effectors of Ras

Jan Czyzyk1, Jennifer L Brogdon, Abdallah Badou

  • 1Section of Immunobiology, Department of Pathology, and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06510, USA.

Proceedings of the National Academy of Sciences of the United States of America
|May 2, 2003
PubMed

Insights

Small GTPase Ras activates T cells via Raf kinase. However, alternative Ras pathways exist, with phospholipase C epsilon significantly boosting T cell responses independently of Raf.

Area of Science:

  • Immunology
  • Molecular Biology
  • Cell Signaling

Background:

  • Small GTPase Ras is a key regulator of T lymphocyte activation.
  • The Raf kinase-dependent pathway is a known Ras effector in T cells.
  • Alternative Ras effectors may also influence T cell functions.

Purpose of the Study:

  • To investigate Ras effector pathways beyond Raf in T cell activation.
  • To identify specific Ras effectors that contribute to T cell responses.
  • To elucidate the role of non-Raf Ras signaling in T lymphocyte function.

Main Methods:

  • Utilized a Ras(V12G37) mutant that does not bind Raf.
  • Overexpressed known Ras effectors including phospholipase C epsilon, RIN1, and Ral guanine nucleotide exchange factors.
  • Measured intracellular calcium concentration and cytokine production in primary antigen-stimulated T cells.
  • Assessed T cell responses using a nuclear factor-activated T cell reporter assay.

Main Results:

  • The Ras(V12G37) mutant potently increased intracellular calcium and cytokine production.
  • Overexpression of phospholipase C epsilon, but not RIN1 or Ral GEFs, enhanced T cell responses.
  • This suggests a Raf-independent Ras pathway mediated by phospholipase C epsilon.

Conclusions:

  • T cell activation is critically regulated by Ras effector pathways independent of Raf.
  • Phospholipase C epsilon acts as a key mediator in this alternative Ras signaling pathway.
  • These findings reveal a novel mechanism for T cell activation control.

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