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Molecular and Cellular Biology, August 2006, p. 6005-6015, Vol. 26, No. 16
0270-7306/06/$08.00+0     doi:10.1128/MCB.02067-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Negative Regulation of Interleukin-2 and p38 Mitogen-Activated Protein Kinase during T-Cell Activation by the Adaptor ALX

Claire E. Perchonock, Melissa C. Fernando, William J. Quinn III, Chau T. Nguyen, Jing Sun, Michael J. Shapiro, and Virginia Smith Shapiro*

Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104

Received 24 October 2005/ Returned for modification 19 November 2005/ Accepted 3 June 2006

Activation of naïve T cells requires synergistic signals produced by the T-cell receptor (TCR) and by CD28. We previously identified the novel adaptor ALX, which, upon overexpression in Jurkat T cells, inhibited activation of the interleukin-2 (IL-2) promoter by TCR/CD28, suggesting that it is a negative regulator of T-cell activation. To further understand the physiological role of ALX, ALX-deficient mice were generated. Purified T cells from ALX-deficient mice demonstrated increased IL-2 production, CD25 expression, and proliferation in response to TCR/CD28 stimulation. Enhanced IL-2 production and proliferation were also observed when ALX-deficient mice were primed in vivo with ovalbumin-complete Freund's adjuvant and then restimulated ex vivo. Consistent with our initial overexpression studies, these data demonstrate that ALX is a negative regulator of T-cell activation. While TCR/CD28-mediated activations of phosphotyrosine induction, extracellular signal-regulated kinase 1/2, Jun N-terminal protein kinase, I{kappa}B kinase {alpha}/ß, and Akt were unaltered, constitutive activation of p38 mitogen-activated protein kinase and its upstream regulators MKK3/6 were observed for ALX-deficient splenocytes. The phenotype of ALX-deficient mice resembled the phenotype of those deficient in the transmembrane adaptor LAX, and an association between ALX and LAX proteins was demonstrated. These results suggest that ALX, in association with LAX, negatively regulates T-cell activation through inhibition of p38.

* Corresponding author. Mailing address: 288 John Morgan Bldg., Dept. of Pathology and Laboratory Medicine, University of Pennsylvania, 3620 Hamilton Walk, Philadelphia, PA 19104. Phone: (215) 573-9260. Fax: (215) 898-4227. E-mail: shapirov{at}mail.med.upenn.edu.

Molecular and Cellular Biology, August 2006, p. 6005-6015, Vol. 26, No. 16
0270-7306/06/$08.00+0     doi:10.1128/MCB.02067-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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