title: Death or survival: membrane ceramide controls the fate and activation of antigen-specific T-cells depending on signal strength and duration.
abstract: Sphingomyelinase (SMase)-mediated release of ceramide in the plasma membrane of T-lymphocytes induced by different stimuli such as ligation of Fas/CD95, irradiation, stress, inflammation or anticancer drugs primarily involves mitochondrial apoptosis signaling, but under specific conditions non-apoptotic Fas-signaling was also reported. Here we investigated, using a quantitative simulation model with exogenous C2-ceramide (and SMase), the dependence of activation and fate of T-cells on the strength and duration of ceramide accumulation. A murine, influenza virus hemagglutinin-specific T-helper cell (IP12-7) alone or together with interacting antigen presenting B-cells (APC) was used. C2-ceramide induced apoptosis of TH cells above a 'threshold' stimulus (>25 microM in 'strength' or >30 min in duration), while below the threshold C2-ceramide was non-apoptotic, as confirmed by early and late apoptotic markers (PS-translocation, mitochondrial depolarization, caspase-3 activation, DNA-fragmentation). The modest ceramide stimuli strongly suppressed the calcium response and inhibited several downstream signal events (e.g. ERK1/2-, JNK-phosphorylation, CD69 expression or IL-2 production) in TH cells during both anti-CD3 induced and APC-triggered activation. Ceramide moderately affected the Ca2+ -release from internal stores upon antigen-specific engagement of TCR in immunological synapses, while the influx phase was remarkably reduced in both amplitude and rate, suggesting that the major target(s) of ceramide-effects are membrane-proximal. Ceramide inhibited Kv1.3 potassium channels, store operated Ca2+ -entry (SOC) and depolarized the plasma membrane to which contribution of spontaneously formed ceramide channels is possible. The impaired function of these transporters may be coupled to the quantitative, membrane raft-remodeling effect of ceramide and responsible, in a concerted action, for the suppressed activation. Our results suggest that non-apoptotic Fas stimuli, received from previously activated, FasL+ interacting lymphocytes in the lymph nodes, may negatively regulate subsequent antigen-specific T-cell activation and thus modulate the antigen-specific T-cell response.
authors.affiliation: Department of Immunology, Eötvös Lorand University, Pázmány P. sétány 1/C, 1117, Budapest, Hungary.
authors.forename: Cynthia
authors.initials: C
authors.lastname: Detre
authors.forename: Endre
authors.initials: E
authors.lastname: Kiss
authors.forename: Zoltán
authors.initials: Z
authors.lastname: Varga
authors.forename: Katalin
authors.initials: K
authors.lastname: Ludányi
authors.forename: Katalin
authors.initials: K
authors.lastname: Pászty
authors.forename: Agnes
authors.initials: A
authors.lastname: Enyedi
authors.forename: Dorottya
authors.initials: D
authors.lastname: Kövesdi
authors.forename: György
authors.initials: G
authors.lastname: Panyi
authors.forename: Eva
authors.initials: E
authors.lastname: Rajnavölgyi
authors.forename: János
authors.initials: J
authors.lastname: Matkó
mesh_terms: D000818:Animals; D017209:Apoptosis; D001402:B-Lymphocytes / Q000502:physiology; D053148:Caspase 3; D020169:Caspases / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism / Q000502:physiology; D002470:Cell Survival; D053938:DNA Fragmentation; D006801:Humans; D007376:Interleukin-2 / Q000378:metabolism; D051664:Kv1.3 Potassium Channel / Q000502:physiology; D008213:Lymphocyte Activation; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D011948:Receptors, Antigen, T-Cell / Q000502:physiology; D015398:Signal Transduction; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D006377:T-Lymphocytes, Helper-Inducer / Q000276:immunology / Q000502:physiology*; D013997:Time Factors; D019014:fas Receptor / Q000378:metabolism
chemical_list: D007376:Interleukin-2; D051664:Kv1.3 Potassium Channel; C064769:N-acetylsphingosine; D011948:Receptors, Antigen, T-Cell; D019014:fas Receptor; D013108:Sphingomyelin Phosphodiesterase; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases; D013110:Sphingosine