Tyrosine kinase activity of CD4-associated p56lck may not be required for CD4-dependent T-cell activation.
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 approximately 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.
Collins
T L
TL
Division of Pediatric Oncology, Dana-Farber Cancer Institute, Boston, MA 02115.
Burakoff
S J
SJ
D000818:Animals; D000906:Antibodies; D015704:CD4 Antigens / Q000378:metabolism*; D017931:DNA Primers; D015151:Immunoblotting; D007376:Interleukin-2 / Q000096:biosynthesis; D007700:Kinetics; D008213:Lymphocyte Activation; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D051379:Mice; D016297:Mutagenesis, Site-Directed; D004676:Myelin Basic Protein / Q000378:metabolism; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D011505:Protein-Tyrosine Kinases / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D013601:T-Lymphocytes / Q000201:enzymology / Q000276:immunology*; D014162:Transfection
D000906:Antibodies; D015704:CD4 Antigens; D017931:DNA Primers; D007376:Interleukin-2; D004676:Myelin Basic Protein; D011505:Protein-Tyrosine Kinases; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck)