HUMAN T-LYMPHOCYTE ACTIVATION INDUCES TYROSINE PHOSPHORYLATION OF ALPHA-TUBULIN AND ITS ASSOCIATION WITH THE SH2 DOMAIN OF THE P59(FYN) PROTEIN-TYROSINE KINASE

A glutathione-S-transferase-src-homology domain 2 (GST-SH2) fusion pro tein was employed to identify molecules interacting with the protein t yrosine kinase p59(fyn). Among several proteins which bound to the fyn SH2 domain in lysates of human Jurkat T lymphocytes, alpha- and beta- tubulin were identified by N-terminal sequencing. Further analysis est ablished that alpha-tubulin exists as a tyrosine-phosphorylated protei n in jurkat cells, where it interacts with p59(fyn), but not with p56( lck). By contrast, in untransformed resting human T lymphocytes alpha- tubulin is not detectable as a tyrosine phosphorylated protein. Howeve r, following T cell activation, it becomes rapidly phosphorylated on t yrosine residues and subsequently associates with the SH2 domain of fy n. Interestingly, constitutively tyrosine-phosphorylated alpha-tubulin that is able to interact with the fyn-SH2 domain is expressed in peri pheral blood T lymphoblasts isolated from leukemic patients in the abs ence of external stimulation.