Mitogen treatment of permeabilized human T lymphocytes stimulates rapid tyrosine and serine phosphorylation of a 42 kDa protein.

Three agents which are mitogenic for T lymphocytes (phytohaemagglutinin, monoclonal antibody UCHT 1 and 12-O-tetradecanoylphorbol-13-acetate) stimulated rapid phosphorylation of a 42 kDa protein in permeabilized T lymphocytes. Phosphorylation occurred on tyrosine and serine residues. A non-mitogenic monoclonal antibody (RFT11) did not stimulate phosphorylation of this protein. Furthermore, the dose response of 42 kDa protein phosphorylation and of mitogenesis to increasing amounts of phytohaemagglutinin were closely similar. We therefore propose that mitogen-stimulated phosphorylation of the 42 kDa protein is part of the mechanism for transduction of mitogenic signals in lymphocytes. To our knowledge, this is the first report of rapid, ligand-stimulated tyrosine protein phosphorylation in T lymphocytes.