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Molecular and Cellular Biology, August 2000, p. 5469-5478, Vol. 20, No. 15
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

The T-Cell Receptor Regulates Akt (Protein Kinase B) via a Pathway Involving Rac1 and Phosphatidylinositide 3-Kinase

Elisabeth M. Genot,1,2,* Cecile Arrieumerlou,3 Gregory Ku,4 Boudewijn M. T. Burgering,5 Arthur Weiss,4 and Ijsbrand M. Kramer2

Department of Immunology, Imperial College, London W12 0NN, United Kingdom1; Growth Factors and Differentiation Laboratory, University of Bordeaux I, 33 405 Talence Cedex,2 and Laboratoire d'Immunologie Cellulaire, CERVI, UMR 7627 CNRS, 75013 Paris,3 France; Department of Medicine, Microbiology and Immunology, Howard Hughes Medical Institute, University of California at San Francisco, San Francisco, California 94143-07954; and Laboratory for Physiological Chemistry, Utrecht University, 3584 CG Utrecht, The Netherlands5

Received 3 February 2000/Returned for modification 7 March 2000/Accepted 8 May 2000

The serine/threonine kinase Akt (also known as protein kinase B) (Akt/PKB) is activated upon T-cell antigen receptor (TCR) engagement or upon expression of an active form of phosphatidylinositide (PI) 3-kinase in T lymphocytes. Here we report that the small GTPase Rac1 is implicated in this pathway, connecting the receptor with the lipid kinase. We show that in Jurkat cells, activated forms of Rac1 or Cdc42, but not Rho, stimulate an increase in Akt/PKB activity. TCR-induced Akt/PKB activation is inhibited either by PI 3-kinase inhibitors (LY294002 and wortmannin) or by overexpression of a dominant negative mutant of Rac1 but not Cdc42. Accordingly, triggering of the TCR rapidly stimulates a transient increase in GTP-Rac content in these cells. Similar to TCR stimulation, L61Rac-induced Akt/PKB kinase activity is also LY294002 and wortmannin sensitive. However, induction of Akt/PKB activity by constitutive active PI 3-kinase is unaffected when dominant negative Rac1 is coexpressed, placing Rac1 upstream of PI 3-kinase in the signaling pathway. When analyzing the signaling hierarchy in the pathway leading to cytoskeleton rearrangements, we found that Rac1 acts downstream of PI 3-kinase, a finding that is in accordance with numerous studies in fibroblasts. Our results reveal a previously unrecognized role of the GTPase Rac1, acting upstream of PI 3-kinase in linking the TCR to Akt/PKB. This is the first report of a membrane receptor employing Rac1 as a downstream transducer for Akt/PKB activation.

* Corresponding author. Mailing address: Growth Factors and Differentiation Laboratory, Batiment de Biologie Animale, University of Bordeaux I, Avenue des facultés, 33 405 Talence Cedex, France. Phone: (33) 5 56 84 89 25. Fax: (33) 5 56 84 87 05. E-mail: e.genot{at}croissance.u-bordeaux.fr.

Molecular and Cellular Biology, August 2000, p. 5469-5478, Vol. 20, No. 15
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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