title: Rapid phosphorylation and modulation of the T4 antigen on cloned helper T cells induced by phorbol myristate acetate or antigen.
abstract: A cell surface protein known as T4 (CD4, Leu3), Mr = 55,000, is expressed on the subset of human T lymphocytes which provides helper function for B cell and cytotoxic T cell activities. We show that T4 is constitutively phosphorylated and that phorbol myristate acetate (PMA) induces a rapid serine phosphorylation which is followed by a fast dephosphorylation. Within 5 min after PMA treatment, there is a 24% reduction of T4 on the cell surface, by 4 h the loss is nearly complete, and by 20 h T4 is re-expressed. Addition of antigen to a T4+ antigen-reactive T cell clone induces both phosphorylation and dephosphorylation with kinetics similar to that described for PMA. Antigen also causes reduction of cell surface T4, although to a lesser degree than stimulation with PMA. The rapid phosphorylation/dephosphorylation of T4 as well as its movement from the cell surface suggest that T4 functions as a receptor for an unknown ligand.
mesh_terms: D000595:Amino Acid Sequence; D000941:Antigens / Q000276:immunology*; D000945:Antigens, Differentiation, T-Lymphocyte; D000954:Antigens, Surface / Q000032:analysis / Q000378:metabolism*; D002478:Cells, Cultured; D002999:Clone Cells; D006678:HIV / Q000378:metabolism; D006684:HLA-DR Antigens / Q000276:immunology; D006801:Humans; D008213:Lymphocyte Activation; D010766:Phosphorylation; D011991:Receptors, Virus / Q000378:metabolism; D006377:T-Lymphocytes, Helper-Inducer / Q000276:immunology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
chemical_list: D000941:Antigens; D000945:Antigens, Differentiation, T-Lymphocyte; D000954:Antigens, Surface; D006684:HLA-DR Antigens; D011991:Receptors, Virus; D013755:Tetradecanoylphorbol Acetate