Volume 271, Number 30, Issue of July 26, 1996 pp. 17896-17902
©1996 by The American Society for Biochemistry and Molecular Biology, Inc.

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An Activated Epidermal Growth Factor Receptor/Lck Chimera Restores Early T Cell Receptor-mediated Calcium Response in a CD45-deficient T Cell Line

(Received for publication, February 22, 1996, and in revised form, May 7, 1996)

Pascale Duplay , Andrés Alcover ^¶ , Christine Fargeas , Rafick P. Sékaly and Philip E. Branton

From the  Department of Biochemistry, McIntyre Medical Sciences Building, McGill University, Montréal, Québec H3G 1Y6, Canada, ^¶ Institut Pasteur, Unité de Biologie des Interactions Cellulaires, CNRS URA 1960, Institut Pasteur, 25 rue du Dr. Roux, 75724 Paris Cedex 15, France, and  IRCM, Immunology Laboratory, Montréal, Québec H2W 1R7, Canada

In T cells, cell surface expression of CD45, a transmembrane tyrosine phosphatase, is required for T cell receptor (TCR) signal transduction. Indirect evidence suggests that CD45 function in TCR signaling involves the dephosphorylation of the C-terminal negative regulatory site of p56^lck, Tyr-505. To evaluate the importance of CD45-mediated dephosphorylation of p56^lck Tyr-505 in TCR signaling, we established CD45 Jurkat cell lines expressing various forms of a chimera containing the extracellular and transmembrane domains of the epidermal growth factor receptor (EGFR) fused to p56^lck. We report that an activated EGFR/Lck chimera is able to reconstitute a Ca²⁺ response after CD3 stimulation in the absence of CD45 expression. In addition, the wild-type and kinase inactive versions of the EGFR/Lck chimera fail to restore early signaling. Restoration of the response by EGFR/LckF505 required EGF binding to the chimeric kinase. Altogether, these results provide the first direct evidence that the lack of efficient dephosphorylation of p56^lck Tyr-505 is, in part, responsible for the unresponsiveness of CD45 cells. They also indicate that a second event is required for p56^lck function in TCR signaling in addition to its dephosphorylation at Tyr-505.

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