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Lymphocyte antigen receptor activation of a focal adhesion kinase-related tyrosine kinase substrate
S B Kanner1, A Aruffo, P Y Chan
1Bristol-Myers Squibb Pharmaceutical Research Institute, Seattle, WA 98121.
Abstract:
One of the earliest responses of T and B lymphocytes to stimulation through their antigen receptors is the activation of protein tyrosine kinases and the tyrosine phosphorylation of multiple cellular substrates. Here we describe a tyrosine kinase substrate, fakB, a putative homologue of the focal adhesion kinase pp125FAK. Tyrosine phosphorylation of fakB was rapidly augmented in human T and B cells following antigen receptor cross-linking with antibody, while pp125FAK was nonresponsive. Costimulation of the T-cell antigen receptor (TCR/CD3) with either the CD2 or CD4 costimulatory receptors induced synergistic fakB tyrosine phosphorylation in normal human T cells. Engagement of TCR/CD3 induced the stable association of fakB with ZAP-70, the TCR/CD3 sigma-chain-associated tyrosine kinase involved in antigen receptor-induced T-cell activation. In addition, preformed complexes of fakB and ZAP-70 were observed in T-cell leukemia lines. Phosphorylation of fakB on serine, threonine, and tyrosine residues was observed both in vivo and in vitro, where a functional increase of in vitro kinase activity was observed following TCR/CD3 stimulation. fakB is thus a focal adhesion kinase-related tyrosine kinase substrate that is differentially regulated from that of pp125FAK and likely plays a role in antigen-induced lymphocyte signaling.
Insights
Researchers identified fakB, a novel tyrosine kinase substrate, crucial for lymphocyte signaling. FakB phosphorylation increases upon antigen receptor stimulation, unlike pp125FAK, suggesting a key role in T and B cell activation.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Lymphocyte activation via antigen receptors involves protein tyrosine kinase signaling.
- Multiple cellular substrates undergo tyrosine phosphorylation upon T and B cell stimulation.
Purpose of the Study:
- To identify and characterize novel tyrosine kinase substrates involved in lymphocyte activation.
- To investigate the role of fakB, a homologue of focal adhesion kinase pp125FAK, in T and B cell signaling.
Main Methods:
- Utilized human T and B cells, antigen receptor cross-linking with antibodies.
- Employed costimulation with T-cell receptor (TCR/CD3) and CD2 or CD4 receptors.
- Analyzed protein tyrosine phosphorylation, complex formation with ZAP-70, and in vitro kinase activity.
Main Results:
- Tyrosine phosphorylation of fakB was rapidly augmented in T and B cells after antigen receptor stimulation, while pp125FAK remained unresponsive.
- Costimulation of TCR/CD3 with CD2 or CD4 synergistically enhanced fakB tyrosine phosphorylation in T cells.
- fakB formed stable complexes with ZAP-70, a key tyrosine kinase in T-cell activation, and showed increased in vitro kinase activity post-TCR/CD3 stimulation.
Conclusions:
- fakB is a focal adhesion kinase-related tyrosine kinase substrate differentially regulated compared to pp125FAK.
- fakB likely plays a significant role in antigen-induced lymphocyte signaling pathways.