A weak Lck tail bite is necessary for Lck function in T cell antigen receptor signaling.
Src family kinases are suppressed by a "tail bite" mechanism, in which the binding of a phosphorylated tyrosine in the C terminus of the protein to the Src homology (SH) 2 domain in the N-terminal half of the protein forces the catalytic domain into an inactive conformation stabilized by an additional SH3 interaction. In addition to this intramolecular suppressive function, the SH2 domain also mediates intermolecular interactions, which are crucial for T cell antigen receptor (TCR) signaling. To better understand the relative importance of these two opposite functions of the SH2 domain of the Src family kinase Lck in TCR signaling, we created three mutants of Lck in which the intramolecular binding of the C terminus to the SH2 domain was strengthened. The mutants differed from wild-type Lck only in one to three amino acid residues following the negative regulatory tyrosine 505, which was normally phosphorylated by Csk and dephosphorylated by CD45 in the mutants. In the Lck-negative JCaM1 cell line, the Lck mutants had a much reduced ability to transduce signals from the TCR in a manner that directly correlated with SH2-Tyr(P)(505) affinity. The mutant with the strongest tail bite was completely unable to support any ZAP-70 phosphorylation, mitogen-activated protein kinase activation, or downstream gene activation in response to TCR ligation, whereas other mutants had intermediate abilities. Lipid raft targeting was not affected. We conclude that Lck is regulated by a weak tail bite to allow for its activation and service in TCR signaling, perhaps through a competitive SH2 engagement mechanism.
Nika
Konstantina
K
Program on Inflammatory Disease Research, Infectious and Inflammatory Disease Center, The Burnham Institute for Medical Research, La Jolla, California 92037, USA. konstantina.nika@path.ox.ac.uk
Tautz
Lutz
L
Arimura
Yutaka
Y
Vang
Torkel
T
Williams
Scott
S
Mustelin
Tomas
T
D019943:Amino Acid Substitution; D000081247:CSK Tyrosine-Protein Kinase; D020134:Catalytic Domain / Q000235:genetics; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006801:Humans; D019169:Jurkat Cells; D017493:Leukocyte Common Antigens / Q000378:metabolism; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / Q000235:genetics / Q000378:metabolism*; D020125:Mutation, Missense; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D051746:ZAP-70 Protein-Tyrosine Kinase / Q000378:metabolism; D018909:src Homology Domains / Q000235:genetics; D019061:src-Family Kinases
D011518:Proto-Oncogene Proteins; D011948:Receptors, Antigen, T-Cell; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D051746:ZAP-70 Protein-Tyrosine Kinase; C497261:ZAP70 protein, human; D019061:src-Family Kinases; C000631346:CSK protein, human; D048049:Extracellular Signal-Regulated MAP Kinases; D017493:Leukocyte Common Antigens; C516769:PTPRC protein, human