title: CTLA-4 activation of phosphatidylinositol 3-kinase (PI 3-K) and protein kinase B (PKB/AKT) sustains T-cell anergy without cell death.
abstract: The balance of T-cell proliferation, anergy and apoptosis is central to immune function. In this regard, co-receptor CTLA-4 is needed for the induction of anergy and tolerance. One central question concerns the mechanism by which CTLA-4 can induce T-cell non-responsiveness without a concurrent induction of antigen induced cell death (AICD). In this study, we show that CTLA-4 activation of the phosphatidylinositol 3-kinase (PI 3-K) and protein kinase B (PKB/AKT) sustains T-cell anergy without cell death. CTLA-4 ligation induced PI 3K activation as evidenced by the phosphorylation of PKB/AKT that in turn inactivated GSK-3. The level of activation was similar to that observed with CD28. CTLA-4 induced PI 3K and AKT activation also led to phosphorylation of the pro-apoptotic factor BAD as well as the up-regulation of BcL-XL. In keeping with this, CD3/CTLA-4 co-ligation prevented apoptosis under the same conditions where T-cell non-responsiveness was induced. This effect was PI 3K and PKB/AKT dependent since inhibition of these enzymes under conditions of anti-CD3/CTLA-4 co-ligation resulted in cell death. Our findings therefore define a mechanism by which CTLA-4 can induce anergy (and possibly peripheral tolerance) by preventing the induction of cell death.
authors.affiliation: Cell Signalling Section, Department of Pathology, University of Cambridge, Cambridge, UK.
authors.forename: Helga
authors.initials: H
authors.lastname: Schneider
authors.forename: Elke
authors.initials: E
authors.lastname: Valk
authors.forename: Rufina
authors.initials: R
authors.lastname: Leung
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Rudd
mesh_terms: D015703:Antigens, CD / Q000378:metabolism*; D017209:Apoptosis; D060908:CTLA-4 Antigen; D016923:Cell Death / Q000502:physiology; D049109:Cell Proliferation; D002478:Cells, Cultured; D017635:Clonal Anergy / Q000502:physiology*; D007376:Interleukin-2 / Q000096:biosynthesis; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D013601:T-Lymphocytes / Q000201:enzymology*
chemical_list: D015703:Antigens, CD; D060908:CTLA-4 Antigen; D007376:Interleukin-2; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt