title: Co-ligation of alpha4beta1 integrin and TCR rescues human thymocytes from steroid-induced apoptosis.
abstract: Maturation of thymocytes represents a sequence of events during which thymocytes expressing TCR with moderate avidity for self antigen/MHC are positively selected, whereas those with high or insufficient TCR avidity die. Glucocorticoids are produced intrathymically and can contribute to apoptosis of unselected thymocytes. Thymocytes differentiate in a close contact with epithelial cells, expressing vascular adhesion molecule-1 (VCAM-1) and secreting glucocorticoids, with bone marrow-derived macrophages, and with extracellular matrix containing fibronectin (FN) and collagen. Their contact with FN is mediated by alpha4beta1 and alpha5beta1 integrins. We examined the contribution of TCR and integrin signaling to the survival of thymocytes from dexamethasone (Dex)-induced apoptosis. We demonstrate that FN and VCAM-1 (both of which bind alpha4beta1 integrin), but not collagen, considerably augment TCR-mediated protection of thymocytes from Dex-induced apoptosis. This 'survival' signal is transduced through the alphabeta1, but not through the alpha5beta1 integrin. The observed protection from Dex-induced apoptosis correlated with an increase in bcl-2 protein levels. FN-alpha4beta1 and VCAM-1-alpha4beta1 engagement induced up-regulation bcl-2 protein, while alpha5beta1 binding to FN induced a negative signal that was blocked by anti-alpha5beta1 antibody. These data suggest that alpha4beta1 integrin may contribute to protection of thymocytes with moderate avidity TCR from glucocorticoid-induced death during intrathymic maturation.
authors.affiliation: Division of Viral Products, Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, MD 20892, USA.
authors.forename: M B
authors.initials: MB
authors.lastname: Zaitseva
authors.forename: C F
authors.initials: CF
authors.lastname: Mojcik
authors.forename: D R
authors.initials: DR
authors.lastname: Salomon
authors.forename: E M
authors.initials: EM
authors.lastname: Shevach
authors.forename: H
authors.initials: H
authors.lastname: Golding
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D002675:Child, Preschool; D003907:Dexamethasone / Q000494:pharmacology*; D005353:Fibronectins / Q000494:pharmacology; D006801:Humans; D007223:Infant; D039041:Integrin alpha4beta1; D016023:Integrins / Q000378:metabolism* / Q000502:physiology; D015759:Ionomycin / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis; D011948:Receptors, Antigen, T-Cell / Q000276:immunology / Q000378:metabolism*; D017469:Receptors, Fibronectin / Q000502:physiology; D016201:Receptors, Lymphocyte Homing / Q000378:metabolism* / Q000502:physiology; D011994:Recombinant Proteins / Q000494:pharmacology; D015398:Signal Transduction / Q000502:physiology; D013601:T-Lymphocytes / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D019010:Vascular Cell Adhesion Molecule-1 / Q000494:pharmacology
chemical_list: D000911:Antibodies, Monoclonal; D005353:Fibronectins; D039041:Integrin alpha4beta1; D016023:Integrins; D019253:Proto-Oncogene Proteins c-bcl-2; D011948:Receptors, Antigen, T-Cell; D017469:Receptors, Fibronectin; D016201:Receptors, Lymphocyte Homing; D011994:Recombinant Proteins; D019010:Vascular Cell Adhesion Molecule-1; D015759:Ionomycin; D003907:Dexamethasone; D013755:Tetradecanoylphorbol Acetate