Cross‐linking of CD26 by antibody induces tyrosine phosphorylation and activation of mitogen‐activated protein kinase

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Abstract
CD26, a T-cell activation antigen that has dipeptidyl peptidase IV activity in its extracellular domain and has also been shown to play an important role in T-cell activation. The earliest biochemical events seen in stimulated T lymphocytes activated through the engagement of the T-cell receptor (TCR) is the tyrosine phosphorylation of a panel of cellular proteins. In this study we demonstrate that antibody-induced cross-linking of CD26-in CD26-transfected Jurkat cells induced tyrosine phosphorylation of several intracellular proteins with a similar pattern to that seen after TCR/CD3 stimulation. Herbimycin A, an inhibitor of the src family protein tyrosine kinases dramatically inhibited this CD26-mediated effect on tyrosine phosphorylation. Major tyrosine phosphorylated proteins were identified by immunoblotting, and included p56lck, p59fyn, zeta associated protein-tyrosine kinase of 70,000 MW (ZAP-70), mitogen-activated protein (MAP) kinase, c-Cb1, and phospholipase C gamma. CD26-induced tyrosine phosphorylation of MAP kinase correlated with increased MAP kinase activity. In addition, CD26 was costimulatory to CD3 signal transduction since co-cross-linking of CD26 and CD3 antigens induced prolonged and increased tyrosine phosphorylation in comparison with CD3 activation alone. We therefore conclude that CD26 is a true costimulatory entity that can up-regulate the signal transducing properties of the TCR.