Human T lymphocyte activation induces tyrosine phosphorylation of α‐tubulin and its association with the SH2 domain of the p59fyn protein tyrosine kinase

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Abstract
A glutathione‐S‐transferase‐src‐homology domain 2 (GST‐SH2) fusion protein was employed to identify molecules interacting with the protein tyrosine kinase p59fyn. Among several proteins which bound to the fyn SH2 domain in lysates of human Jurkat T lymphocytes, α‐ and β‐tubulin were identified by N‐terminal sequencing. Further analysis established that α‐tubulin exists as a tyrosine‐phosphorylated protein in Jurkat cells, where it interacts with p59fyn, but not with p56lck. By contrast, in untransformed resting human T lymphocytes α‐tubulin is not detectable as a tyrosine phosphorylated protein. However, following T cell activation, it becomes rapidly phosphorylated on tyrosine residues and subsequently associates with the SH2 domain of fyn. Interestingly, constitutively tyrosine‐phosphorylated α‐tubulin that is able to interact with the fyn‐SH2 domain is expressed in peripheral blood T lymphoblasts isolated from leukemic patients in the absence of external stimulation.