title: Tyrosine phosphorylation of a novel 100-kDa protein coupled to CD28 in resting human T cells is enhanced by a signal through TCR/CD3 complex.
abstract: For T cell activation, two signals are required, i.e., a T cell receptor (TCR)/CD3-mediated main signal and a CD28-mediated costimulatory signal. CD28 binds to its ligand (CD80 or CD86) and transduces the most important costimulatory signal. The cytoplasmic domain of the CD28 molecule, composed of 41 amino acids, does not contain any intrinsic enzyme activity. The cytoplasmic domain of CD28 is remarkably conserved among species and is associated with a number of signaling molecules that affect the main signal. We report here that a tyrosine phosphorylated 100-kDa protein (ppl00) was coupled to the CD28 cytoplasmic domain in Jurkat and human peripheral T cells. The pp100 was distinguished from other CD28 associated molecules such as Vav, STAT5, PI 3-kinase, Valosin-containing protein (VCP), Nucleolin, Gab2 (Grb2-associated binding protein 2), and STAT6. The tyrosine phosphorylation of pp100 coprecipitated with CD28 was enhanced by CD3 stimulation by the specific antibody, tyrosine phosphatase inhibitor and PKC activator. Tyrosine phosphorylation of pp100 was attenuated by the prior addition of PKC inhibitor. These findings indicate that pp100 is a novel tyrosine phosphorylated protein coupled to CD28 under continuous control of tyrosine phosphatases and might play a role in T cell activation augmented by a TCR/CD3-mediated main signal.
authors.affiliation: First Department of internal Medicine, Kagawa Medical University, Kita-gun, Kagawa 761-0793, Japan.
authors.forename: Aki
authors.initials: A
authors.lastname: Matsumoto
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Dobashi
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Ohnishi
authors.forename: Terukazu
authors.initials: T
authors.lastname: Tanaka
authors.forename: Yoshitsugu
authors.initials: Y
authors.lastname: Kubota
authors.forename: Akira
authors.initials: A
authors.lastname: Kitanaka
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ishida
authors.forename: Michiaki
authors.initials: M
authors.lastname: Tokuda
authors.forename: Masato
authors.initials: M
authors.lastname: Waki
authors.forename: Akihito
authors.initials: A
authors.lastname: Kubo
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Ishida
mesh_terms: D018106:CD28 Antigens / Q000276:immunology* / Q000378:metabolism; D000001:Calcimycin / Q000276:immunology; D004791:Enzyme Inhibitors / Q000276:immunology; D006801:Humans; D015151:Immunoblotting; D019169:Jurkat Cells; D008213:Lymphocyte Activation / Q000276:immunology*; D009281:Naphthalenes / Q000494:pharmacology; D010750:Phosphoproteins / Q000096:biosynthesis* / Q000276:immunology; D010766:Phosphorylation; D011233:Precipitin Tests; D011948:Receptors, Antigen, T-Cell / Q000276:immunology*; D015398:Signal Transduction / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology*; D013755:Tetradecanoylphorbol Acetate / Q000276:immunology; D014443:Tyrosine / Q000276:immunology / Q000378:metabolism; D014638:Vanadates / Q000276:immunology
chemical_list: D018106:CD28 Antigens; D004791:Enzyme Inhibitors; D009281:Naphthalenes; D010750:Phosphoproteins; D011948:Receptors, Antigen, T-Cell; C076715:pervanadate; D000001:Calcimycin; D014638:Vanadates; D014443:Tyrosine; C058819:calphostin C; D013755:Tetradecanoylphorbol Acetate