title: Degree of ERK activation influences both positive and negative thymocyte selection.
abstract: Considerable evidence suggests that the ERK pathway is required for positive but not negative thymocyte selection. Here, we report that ERK is highly activated in double-positive (DP) thymocytes expressing an MHC class I-restricted TCR (P14) in response to negatively selecting conditions, whereas ligands that trigger positive selection induced weaker ERK activation. Biochemical evidence also shows that death by neglect is associated with a further reduction in ERK activation. These findings are consistent with the affinity / avidity model of thymocyte selection. To further examine the role of ERK in negative selection we used the MEK-1 inhitibor, PD98059, a specific pharmacological inhibitor of the ERK pathway. Biochemical data demonstrated a reduction of ERK activity by PD98059 in the presence of the negatively selecting ligand. Analysis of P14 TCR-transgenic fetal thymic lobes cultured with PD98059 under negatively selecting conditions showed impaired clonal deletion of DP thymocytes and a concomitant increase in positive selection of functional mature, TCR(hi) transgenic T cells. This demonstrates that altering ERK activity switched negative to positive selection. Contrary to previous reports that show an exclusive role for ERK signaling in positive selection, our data demonstrate that negative selection is also sensitive to the degree of ERK activation.
authors.affiliation: Ontario Cancer Institute, Department of Medical Biophysics and Immunology, Toronto, Canada.
authors.forename: S
authors.initials: S
authors.lastname: Mariathasan
authors.forename: S S
authors.initials: SS
authors.lastname: Ho
authors.forename: A
authors.initials: A
authors.lastname: Zakarian
authors.forename: P S
authors.initials: PS
authors.lastname: Ohashi
mesh_terms: D000818:Animals; D018414:CD8-Positive T-Lymphocytes / Q000187:drug effects / Q000276:immunology; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D019070:Cell Lineage / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000235:genetics / Q000276:immunology; D004789:Enzyme Activation / Q000187:drug effects; D005419:Flavonoids / Q000494:pharmacology; D006183:H-2 Antigens / Q000235:genetics / Q000276:immunology; D008024:Ligands; D048369:MAP Kinase Kinase 1; D020935:MAP Kinase Signaling System / Q000187:drug effects; D051379:Mice; D008822:Mice, Transgenic; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009924:Organ Culture Techniques; D010455:Peptides / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell / Q000276:immunology; D013601:T-Lymphocytes / Q000201:enzymology* / Q000276:immunology*; D013950:Thymus Gland / Q000166:cytology / Q000187:drug effects / Q000276:immunology
chemical_list: D004268:DNA-Binding Proteins; D005419:Flavonoids; D006183:H-2 Antigens; D008024:Ligands; D010455:Peptides; C499308:Rag2 protein, mouse; D011948:Receptors, Antigen, T-Cell; C064655:V(D)J recombination activating protein 2; D017346:Protein Serine-Threonine Kinases; D020928:Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human; C482127:Map2k1 protein, mouse; D020929:Mitogen-Activated Protein Kinase Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one