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Tyrosine Kinase Activity of CD4-Associated p56lck May Not be Required for CD4-Dependent T-Cell Activation

Tassie L. Collins and Steven J. Burakoff
Proceedings of the National Academy of Sciences of the United States of America
Vol. 90, No. 24 (Dec. 15, 1993), pp. 11885-11889
Stable URL: http://www.jstor.org/stable/2363568
Page Count: 5
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Tyrosine Kinase Activity of CD4-Associated p56lck May Not be Required for CD4-Dependent T-Cell Activation
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Abstract

The lymphoid-specific tyrosine kinase p56lck (Lck) is critical for the development and activation of T lymphocytes, and Lck kinase activity has been implicated in both T-cell antigen receptor/CD3- and CD4-mediated signaling. CD4-dependent T-cell activation has been demonstrated to be dependent upon the association of CD4 with Lck. To examine the role of the kinase activity of Lck in CD4-dependent T-cell activation, we have generated several kinase-deficient mutants of Lck. When transfected into CD4+ murine T-cell hybridoma cells, these mutants cause ≈90% diminution in CD4-associated Lck kinase activity. Specifically, upon CD4 crosslinking there is decreased Lck autophosphorylation and decreased phosphorylation of an exogenous substrate. When CD4 is crosslinked to the T-cell antigen receptor-CD3 complex, decreased phosphorylation of associated substrates is also observed. In spite of this striking inhibition of Lck kinase function, cells expressing the kinase-deficient mutants demonstrate normal or enhanced CD4-dependent antigen responsiveness. These data demonstrate that the level of Lck kinase activity does not correlate with its CD4-associated function and suggest that the kinase activity of Lck may not be required for CD4-mediated signaling.

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