Regulation of Bim by TCR signals in CD4/CD8 double-positive thymocytes.
Bim, a BH3-only Bcl-2 family member, is required for apoptosis of thymocytes in response to negative selection signals. Regulation of the apoptotic activity of Bim during negative selection is not understood. In this study we demonstrate that in murine thymocytes undergoing apoptosis in response to anti-CD3epsilon injection, levels of Bim protein expression do not change. In immature thymocytes, Bim is associated with mitochondria before stimulation and is not regulated by a change in subcellular localization during apoptosis. We also show that Bim(EL) is rapidly phosphorylated in thymocytes in response to CD3epsilon cross-linking both in vivo and in vitro, and that phosphorylation is sustained for at least 24 h. Analysis of MHC-deficient mice shows that phosphorylation of Bim occurs in CD4/CD8 double-positive thymocytes and does not depend on activation of mature T cells. We also find that TCR cross-linking on thymocytes induces an increase in the proportion of Bcl-x(L) bound to Bim at late time points. Our results favor a model in which strong TCR signals regulate the apoptotic activity of Bim by phosphorylation and subsequent changes in binding to Bcl-x(L) in immature thymocytes.
Bunin
Anna
A
Department of Pathology and Laboratory Medicine, Emory University School of Medicine, Atlanta, GA 30322, USA.
Khwaja
Fatima W
FW
Kersh
Gilbert J
GJ
D000818:Animals; D000911:Antibodies, Monoclonal / Q000008:administration & dosage; D017209:Apoptosis / Q000276:immunology*; D051017:Apoptosis Regulatory Proteins; D000072224:Bcl-2-Like Protein 11; D017252:CD3 Complex / Q000276:immunology; D015704:CD4 Antigens / Q000096:biosynthesis*; D016827:CD8 Antigens / Q000096:biosynthesis*; D002352:Carrier Proteins / Q000096:biosynthesis / Q000378:metabolism*; D003432:Cross-Linking Reagents / Q000378:metabolism; D003907:Dexamethasone / Q000008:administration & dosage; D004306:Dose-Response Relationship, Immunologic; D007275:Injections, Intravenous; D008565:Membrane Proteins / Q000096:biosynthesis / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008870:Microtubules / Q000378:metabolism; D018448:Models, Immunological; D010766:Phosphorylation; D011485:Protein Binding / Q000187:drug effects / Q000276:immunology; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell / Q000276:immunology / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction / Q000276:immunology*; D016176:T-Lymphocyte Subsets / Q000166:cytology / Q000276:immunology* / Q000378:metabolism; D013950:Thymus Gland / Q000166:cytology / Q000276:immunology* / Q000378:metabolism; D051020:bcl-X Protein
D000911:Antibodies, Monoclonal; D051017:Apoptosis Regulatory Proteins; D000072224:Bcl-2-Like Protein 11; C494812:Bcl2l1 protein, mouse; C000606776:Bcl2l11 protein, mouse; D017252:CD3 Complex; D015704:CD4 Antigens; D016827:CD8 Antigens; D002352:Carrier Proteins; C485468:Cd3e protein, mouse; D003432:Cross-Linking Reagents; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011948:Receptors, Antigen, T-Cell; D051020:bcl-X Protein; D003907:Dexamethasone