Enhancement of TNF receptor p60-mediated cytotoxicity by TNF receptor p80: requirement of the TNF receptor-associated factor-2 binding site.
TNFR p60 (TNFR60) is the main mediator of TNF-induced apoptosis, although in some cells TNFR80 is also involved. TNFR80-dependent induction or enhancement of cytotoxicity has been explained by intracellular signaling, "ligand passing," or induction of endogenous TNF. Using HeLa transfectants expressing wild-type TNFR80 and deletion mutants derived from them, we have investigated the mechanism of TNFR80-mediated cytotoxicity. TNFR80 induces no cytotoxicity on its own, but is functional in these transfectants, as selective stimulation activates nuclear factor-kappaB (NF-kappaB) and induces NF-kappaB-dependent cellular responses (IL-6 and manganese superoxide dismutase). TNFR60-induced cytotoxicity, however, is enhanced about 1000-fold by costimulation of TNFR80, whereas only additive responses are observed with regard to NF-kappaB-dependent responses. Ligand passing is not critically involved, because a similar potentiation of TNFR60-mediated cytotoxicity was observed when agonistic Abs were used for stimulation of both receptors. In addition, in HeLa cells overexpressing a truncated form of TNFR80 lacking the cytoplasmic domain, no TNFR80-dependent potentiation of TNFR60-mediated cytotoxicity was detectable, emphasizing that intracellular signaling of TNFR80 is required for synergistic activity. The involvement of endogenously produced TNF can be ruled out by the use of TNF-neutralizing Abs. The ability of TNFR80 to cooperate with TNFR60 could be mapped to the binding site for the TNF receptor-associated factor-2. These results are in agreement with a differential cooperation of both TNFR; an additive effect is obtained in those responses that are initiated by both receptors via identical pathways, i.e., activation of NF-kappaB, whereas induction of cytotoxicity is most likely mediated by distinct signaling pathways, allowing positive cooperativity.
Weiss
T
T
Institute of Cell Biology and Immunology, University of Stuttgart, Germany.
Grell
M
M
Hessabi
B
B
Bourteele
S
S
Müller
G
G
Scheurich
P
P
Wajant
H
H
D001665:Binding Sites / Q000276:immunology; D003602:Cytotoxicity, Immunologic; D006367:HeLa Cells; D006801:Humans; D015850:Interleukin-6 / Q000096:biosynthesis; D016328:NF-kappa B / Q000378:metabolism; D018124:Receptors, Tumor Necrosis Factor / Q000276:immunology* / Q000502:physiology*; D015398:Signal Transduction / Q000276:immunology; D013482:Superoxide Dismutase / Q000096:biosynthesis
D015850:Interleukin-6; D016328:NF-kappa B; D018124:Receptors, Tumor Necrosis Factor; D013482:Superoxide Dismutase