title: CD28 ligation costimulates cell death but not maturation of double-positive thymocytes due to defective ERK MAPK signaling.
abstract: The differentiation of double-positive (DP) CD4(+)CD8(+) thymocytes to single-positive CD4(+) or CD8(+) T cells is regulated by signals that are initiated by coengagement of the Ag (TCR) and costimulatory receptors. CD28 costimulatory receptors, which augment differentiation and antiapoptotic responses in mature T lymphocytes, have been reported to stimulate both differentiation and apoptotic responses in TCR-activated DP thymocytes. We have used artificial APCs that express ligands for TCR and CD28 to show that CD28 signals increase expression of CD69, Bim, and cell death in TCR-activated DP thymocytes but do not costimulate DP thymocytes to initiate the differentiation program. The lack of a differentiation response is not due to defects in CD28-initiated TCR proximal signaling events but by a selective defect in the activation of ERK MAPK. To characterize signals needed to initiate the death response, a mutational analysis was performed on the CD28 cytoplasmic domain. Although mutation of all of CD28 cytoplasmic domain signaling motifs blocks cell death, the presence of any single motif is able to signal a death response. Thus, there is functional redundancy in the CD28 cytoplasmic domain signaling motifs that initiate the thymocyte death response. In contrast, immobilized Abs can initiate differentiation responses and cell death in DP thymocytes. However, because Ab-mediated differentiation occurs through CD28 receptors with no cytoplasmic domain, the response may be mediated by increased adhesion to immobilized anti-TCR Abs.
authors.affiliation: Department of Immunology, Mayo Clinic College of Medicine,301 Guggenheim Building, Rochester, MN 55905, USA.
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Graham
authors.forename: Michael P
authors.initials: MP
authors.lastname: Bell
authors.forename: Catherine J
authors.initials: CJ
authors.lastname: Huntoon
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Griffin
authors.forename: Xuguang
authors.initials: X
authors.lastname: Tai
authors.forename: Alfred
authors.initials: A
authors.lastname: Singer
authors.forename: David J
authors.initials: DJ
authors.lastname: McKean
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D000938:Antigen-Presenting Cells / Q000276:immunology; D015703:Antigens, CD / Q000378:metabolism; D000945:Antigens, Differentiation, T-Lymphocyte / Q000378:metabolism; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D000072224:Bcl-2-Like Protein 11; D018106:CD28 Antigens / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology / Q000276:immunology*; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology / Q000276:immunology*; D016923:Cell Death / Q000235:genetics; D002454:Cell Differentiation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000235:genetics / Q000378:metabolism; D005260:Female; D037181:Lectins, C-Type; D008024:Ligands; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008817:Mice, Mutant Strains; D008969:Molecular Sequence Data; D009154:Mutation; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell / Q000037:antagonists & inhibitors / Q000378:metabolism; D015398:Signal Transduction; D013950:Thymus Gland / Q000166:cytology / Q000276:immunology*; D000099192:CD69 Antigens
chemical_list: D000906:Antibodies; D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; D051017:Apoptosis Regulatory Proteins; D000072224:Bcl-2-Like Protein 11; D018106:CD28 Antigens; D048049:Extracellular Signal-Regulated MAP Kinases; D037181:Lectins, C-Type; D008024:Ligands; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D011948:Receptors, Antigen, T-Cell; D000099192:CD69 Antigens; C000606776:Bcl2l11 protein, mouse