Con A activates an Akt/PKB dependent survival mechanism to modulate TCR induced cell death in double positive thymocytes.
While low avidity ligation of the T cell receptor (TCR) leads to positive selection and further maturation of developing thymocytes providing the immune system with mature CD4(+) and CD8(+) (single positive) T cells, high avidity ligation triggers negative selection by apoptotic cell death and therefore the TCR repertoire is purged of autoreactive T cells. On peripheral T cells, however, high avidity ligation of the TCR triggers activation and survival not death. In the present study we used concanavalin A (Con A) and alpha-CD3 epsilon antibody to investigate a possible survival mechanism in connection with TCR ligation. Con A and alpha-CD3 epsilon were used in the study for the following reasons: (1) they both mimic the effects of high avidity TCR ligation by activating peripheral T cells, and (2) they trigger distinctively different physiological changes in developing thymocytes. While Con A supports events associated with cellular survival, alpha-CD3 epsilon induces apoptotic cell death. In our experimental system the TCR was cross-linked by Con A and alpha-CD3 epsilon in thymocytes of major histocompatibility complex (MHC) deficient thymus organ cultures, where signals from the TCR can be triggered on zero background signal level. We have found that TCR cross-linking by Con A and not by alpha-CD3 epsilon decreases the gene and protein expression of the pro-apoptotic molecule, Bad; and that Con A is capable of the activation of the survival signalling pathway including protein kinase B (Akt/PKB) independently of phosphatidyl inositol kinase (PI3K).
Department of Anatomy, Medical School, University of Birmingham, Edgbaston, B15 2TT, Birmingham, UK. j.pongracz@bham.ac.uk
Judit
J
Pongracz
Sonia
S
Parnell
Graham
G
Anderson
Jean-Pierre
JP
Jaffrézou
Eric
E
Jenkinson
D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D017209:Apoptosis; D015496:CD4-Positive T-Lymphocytes / Q000145:classification / Q000187:drug effects / Q000201:enzymology; D018414:CD8-Positive T-Lymphocytes / Q000145:classification / Q000187:drug effects / Q000201:enzymology; D002352:Carrier Proteins / Q000378:metabolism; D002470:Cell Survival; D003208:Concanavalin A / Q000494:pharmacology*; D004789:Enzyme Activation; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D009924:Organ Culture Techniques; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D017260:Receptor-CD3 Complex, Antigen, T-Cell / Q000276:immunology*; D015398:Signal Transduction; D016176:T-Lymphocyte Subsets / Q000145:classification / Q000187:drug effects / Q000201:enzymology*; D013950:Thymus Gland / Q000166:cytology / Q000276:immunology*; D051025:bcl-Associated Death Protein
D000906:Antibodies; D002352:Carrier Proteins; D003208:Concanavalin A; D019869:Phosphatidylinositol 3-Kinases; D010749:Phosphoprotein Phosphatases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2; D017260:Receptor-CD3 Complex, Antigen, T-Cell; D051025:bcl-Associated Death Protein; C494820:Bad protein, mouse