Two regions in the CD80 cytoplasmic tail regulate CD80 redistribution and T cell costimulation.
CD28 is a major T cell costimulatory molecule, delivering signals distinct from those of the CD3/TCR complex, which regulate cytokine and cytokine receptor expression, cell proliferation, and cell viability. CD28 needs to be cross-linked to initiate signals, yet both of its ligands, CD80 and CD86, are expressed as monomers. Previously, we determined the cytoplasmic tail of CD80 is required for CD28-mediated costimulation and subcellular relocalization of CD80 in lymphocytes. In this study, we report that Reh B cell transfectants expressing CD80 with mutations in the cytoplasmic tail region either at 275-278 (RRNE-->AAAA, CD80/4A) or serine 284 (S-->A, CD80/SA) can bind ligand similar to transfectants expressing wild-type CD80, yet are unable to costimulate T cell proliferation. These mutant CD80 molecules are expressed on the surface of the Reh cells in small clusters or foci indistinguishable from those of wild-type CD80 molecules. However, mutant CD80 molecules unlike wild-type CD80 cannot be readily induced by ligand into caps. Thus, small clusters of CD80 found on APC are insufficient to initiate CD28-mediated signals, and the formation of CD80 caps appears to be a critical factor regulating the initiation of T cell costimulation. A 30-kDa phosphoprotein that associates with the cytoplasmic tail of CD80 in activated cells may play a role in CD80 redistribution and thus CD28-mediated costimulation. These results indicate two distinct regions of the CD80 cytoplasmic tail regulate its costimulatory function, and both regions are required for CD80 function.
Doty
R T
RT
Department of Immunology, University of Washington, Seattle 98195, USA.
Clark
E A
EA
D000595:Amino Acid Sequence; D018122:B7-1 Antigen / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D003593:Cytoplasm / Q000276:immunology*; D006801:Humans; D008024:Ligands; D008213:Lymphocyte Activation / Q000276:immunology*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D010750:Phosphoproteins / Q000276:immunology / Q000378:metabolism; D011485:Protein Binding / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology*
D018122:B7-1 Antigen; D008024:Ligands; D010446:Peptide Fragments; D010750:Phosphoproteins