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The T-cell receptor regulates Akt (protein kinase B) via a pathway involving Rac1 and phosphatidylinositide 3-kinase

E M Genot1, C Arrieumerlou, G Ku

  • 1Department of Immunology, Imperial College, London W12 0NN, United Kingdom. e.genot@croissance.u-bordeaux.fr

Molecular and Cellular Biology
|July 13, 2000
PubMed

Insights

The small GTPase Rac1 links T-cell antigen receptor (TCR) engagement to Akt/PKB activation by acting upstream of phosphatidylinositide 3-kinase (PI3K). This study reveals Rac1

Area of Science:

  • Molecular Biology
  • Cell Signaling
  • Immunology

Background:

  • The serine/threonine kinase Akt (also known as protein kinase B) (Akt/PKB) is crucial in T-cell activation.
  • T-cell receptor (TCR) engagement and phosphatidylinositide 3-kinase (PI3K) activation are key events in T-lymphocyte signaling.

Purpose of the Study:

  • To investigate the role of the small GTPase Rac1 in the TCR-induced Akt/PKB activation pathway.
  • To elucidate the signaling hierarchy connecting TCR, Rac1, and PI3K in T lymphocytes.

Main Methods:

  • Utilized Jurkat T-cell lines.
  • Employed activated forms of Rac1 and Cdc42, dominant-negative mutants, and PI 3-kinase inhibitors (LY294002, wortmannin).
  • Assessed Akt/PKB activity and GTP-Rac content following TCR triggering.

Main Results:

  • Activated Rac1, but not Rho or Cdc42, stimulated Akt/PKB activity in Jurkat cells.
  • TCR-induced Akt/PKB activation was inhibited by PI3K inhibitors and dominant-negative Rac1, but not Cdc42.
  • Rac1 acts upstream of PI3K in the TCR-Akt/PKB signaling pathway, distinct from its role in cytoskeleton rearrangements.

Conclusions:

  • Rac1 is a novel upstream transducer linking TCR engagement to Akt/PKB activation via PI3K.
  • This study identifies a previously unrecognized role for Rac1 in T-cell signaling cascades.
  • The findings highlight a unique mechanism where a membrane receptor utilizes Rac1 for downstream Akt/PKB activation.

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