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Molecular and Cellular Biology, September 2000, p. 6945-6957, Vol. 20, No. 18
0270-7306/00/$04.00+0

Deficiency of PTEN in Jurkat T Cells Causes Constitutive Localization of Itk to the Plasma Membrane and Hyperresponsiveness to CD3 Stimulation

Xiaochuan Shan,1 Michael J. Czar,2 Stephen C. Bunnell,3 Pinghu Liu,1 Yusen Liu,1 Pamela L. Schwartzberg,2 and Ronald L. Wange1,*

Laboratory of Biological Chemistry, Gerontology Research Center, National Institute on Aging, National Institutes of Health, Baltimore, Maryland 21224-6825,1 and Genetic Disease Research Branch, National Human Genome Research Institute,2 and Laboratory of Cellular and Molecular Biology, National Cancer Institute,3 National Institutes of Health, Bethesda, Maryland 20892

Received 16 March 2000/Returned for modification 24 April 2000/Accepted 16 June 2000

Pleckstrin homology (PH) domain binding to D3-phosphorylated phosphatidylinositides (PI) provides a reversible means of recruiting proteins to the plasma membrane, with the resultant change in subcellular localization playing a key role in the activation of multiple intracellular signaling pathways. Previously we found that the T-cell-specific PH domain-containing kinase Itk is constitutively membrane associated in Jurkat T cells. This distribution was unexpected given that the closely related B-cell kinase, Btk, is almost exclusively cytosolic. In addition to constitutive membrane association of Itk, unstimulated JTAg T cells also exhibited constitutive phosphorylation of Akt on Ser-473, an indication of elevated basal levels of the phosphatidylinositol 3-kinase (PI3K) products PI-3,4-P2 and PI-3,4,5-P3 in the plasma membrane. Here we describe a defect in expression of the D3 phosphoinositide phosphatase, PTEN, in Jurkat and JTAg T cells that leads to unregulated PH domain interactions with the plasma membrane. Inhibition of D3 phosphorylation by PI3K inhibitors, or by expression of PTEN, blocked constitutive phosphorylation of Akt on Ser-473 and caused Itk to redistribute to the cytosol. The PTEN-deficient cells were also hyperresponsive to T-cell receptor (TCR) stimulation, as measured by Itk kinase activity, tyrosine phosphorylation of phospholipase C-gamma 1, and activation of Erk compared to those in PTEN-replete cells. These data support the idea that PH domain-mediated association with the plasma membrane is required for Itk activation, provide evidence for a negative regulatory role of PTEN in TCR stimulation, and suggest that signaling models based on results from Jurkat T-cell lines may underestimate the role of PI3K in TCR signaling.

* Corresponding author. Mailing address: Gerontology Research Center, MSC-12, 5600 Nathan Shock Dr., Baltimore, MD 21224-6825. Phone: (410) 558-8054. Fax: (410) 558-8107. E-mail: wanger{at}grc.nia.nih.gov.

Molecular and Cellular Biology, September 2000, p. 6945-6957, Vol. 20, No. 18
0270-7306/00/$04.00+0


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