CTLA-4 . FasL induces early apoptosis of activated T cells by interfering with anti-apoptotic signals.
The fusion protein CTLA-4 . FasL, a paradigmatic "trans signal converter protein", can attach to APC surfaces and in effect convert B7-activating costimulator signals into inhibitory Fas receptor-generated signals. The present study investigates CTLA-4 . FasL's mechanism of action. A combination of p27(kip) and proliferating cell nuclear Ag Western blot and propidium iodide flow cytometric analysis showed no CTLA-4 . FasL effect on cell cycle entry and progression, pointing away from the kind of classical anergy associated with CTLA-4 . Ig. Significantly, CTLA-4 . FasL elicited apoptosis (as detected by annexin-V/propidium iodide costaining) as early as 24 h after T cell activation, suggesting that some coordinate signaling might be capacitating the Fas receptor. Significantly, CTLA-4 . FasL, but not CTLA-4 . Ig, anti-Fas mAb, or the two in combination, abrogated the usual increase in expression of the anti-apototic protein, cFLIP. Furthermore, activation of caspases 8 and 3 were not affected by CTLA-4 . FasL. These findings suggest a model for CTLA-4 . FasL action wherein there is coordinate triggering of a death receptor and suppression of a proapoptotic protein.
Orbach
Ariel
A
Nephrology and Hypertension Services, Hadassah-Hebrew University Medical Center, Jerusalem, Israel.
Rachmilewitz
Jacob
J
Parnas
Miram
M
Huang
Jui-Han
JH
Tykocinski
Mark L
ML
Dranitzki-Elhalel
Michael
M
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000818:Animals; D015703:Antigens, CD / Q000187:drug effects / Q000276:immunology*; D000943:Antigens, Differentiation / Q000187:drug effects / Q000276:immunology*; D017209:Apoptosis / Q000276:immunology*; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000276:immunology; D060908:CTLA-4 Antigen; D002453:Cell Cycle / Q000276:immunology; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D053222:Fas Ligand Protein / Q000037:antagonists & inhibitors / Q000276:immunology*; D005260:Female; D051379:Mice; D008810:Mice, Inbred C57BL; D011993:Recombinant Fusion Proteins / Q000037:antagonists & inhibitors / Q000276:immunology*; D015398:Signal Transduction / Q000276:immunology*; D013601:T-Lymphocytes / Q000276:immunology*; D015854:Up-Regulation / Q000276:immunology
D000590:Amino Acid Chloromethyl Ketones; D015703:Antigens, CD; D000943:Antigens, Differentiation; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D060908:CTLA-4 Antigen; C556707:Ctla4 protein, mouse; D053222:Fas Ligand Protein; D011993:Recombinant Fusion Proteins; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone