K. Wakizaka et al., A NOVEL 90-KDA TYROSINE-PHOSPHORYLATED PROTEIN ASSOCIATED WITH TCR COMPLEX IN THYMOCYTES, European Journal of Immunology, 28(2), 1998, pp. 636-645
Ligation of the TCR-CD3 complex initiates a cascade of tyrosine phosph
orylation that results in T cell activation. Initial activation of tyr
osine kinases depends on the phosphorylation of activation motifs on C
D3 chains. We previously found that a 90-kDa protein was tyrosine phos
phorylated upon TCR cross-linking and the induction of the phosphoryla
tion was dependent on the structure of the CD3 complex. In this study,
we further characterized p90 phosphorylation. Phosphorylation of p90
was induced only by stimulation through the TCR-CD3 complex but not by
other kinds of stimulation including CD28- or hydrogen peroxide-media
ted activation and was dynamically regulated. Phosphorylated p90 was a
ssociated with the TCR-CD3 complex upon T cell activation. In a normal
T cell population, thymocytes but not splenic T cells induced the tyr
osine phosphorylation of p90 upon TCR cross-linking. These results sug
gest that p90 is a novel phosphoprotein associated with the TCR-CD3 co
mplex and may play a role in TCR signaling during thymocyte differenti
ation.