title: TNFR1-induced sphingomyelinase activation modulates TCR signaling by impairing store-operated Ca2+ influx.
abstract: Tumor necrosis factor alpha (TNF-alpha) is a potent, pleiotrophic cytokine, which is proinflammatory but can also suppress T lymphocyte function. In chronic inflammatory disease such as rheumatoid arthritis, exposure of T cells to TNF-alpha alters their ability to mount a response by modulating the T cell receptor (TCR) signaling pathway, but the mechanisms involved remain obscure. Here, we investigated the specific role of TNF receptor 1 (TNFR1) signaling in the modulation of the TCR signaling pathway. We observed a down-regulation of the intracellular calcium ([Ca(2+)](i)) signal in Jurkat T cells after just 30 min exposure to TNF-alpha, and maximum suppression was reached after 3 h. This effect was transient, and signals returned to normal after 12 h. This depression of [Ca(2+)](i) was also observed in human CD4+ T lymphocytes. The change in Ca(2+) signal was related to a decrease in the plasma membrane Ca(2+) influx, which was apparent even when the TCR signal was bypassed using thapsigargin to induce a Ca(2+) influx. The role of TNF-alpha-induced activation of the sphingolipid cascade in this pathway was examined. The engagement of TNFR1 by TNF-alpha led to a time-dependent increase in acid sphingomyelinase (SMase; ASM) activity, corresponding with a decrease in cellular sphingomyelin. In parallel, there was an increase in cellular ceramide, which correlated directly with the decrease in the magnitude of the Ca(2+) response to phytohemagglutinin. Exogenous addition of SMase or ceramide mimicked the effects of TNFR1 signals on Ca(2+) responses in Jurkat T cells. Direct evidence for the activation of ASM in this pathway was provided by complete abrogation of the TNF-alpha-induced inhibition of the Ca(2+) influx in an ASM-deficient murine T cell line (OT-II(+/+)ASM(-/-)). This potent ability of TNF-alpha to rapidly modulate the TCR Ca(2+) signal via TNFR1-induced ASM activation can explain its suppressive effect on T cell function. This TNFR1 signaling pathway may play a role as an important regulator of T cell responses.
authors.affiliation: Department of Rheumatology, Division of Immunity and Infection, University of Birmingham, Edgbaston, UK. L.D.Church@Bham.ac.uk
authors.forename: Leigh D
authors.initials: LD
authors.lastname: Church
authors.forename: Gabriele
authors.initials: G
authors.lastname: Hessler
authors.forename: John E
authors.initials: JE
authors.lastname: Goodall
authors.forename: David A
authors.initials: DA
authors.lastname: Rider
authors.forename: Creg J
authors.initials: CJ
authors.lastname: Workman
authors.forename: Dario A A
authors.initials: DA
authors.lastname: Vignali
authors.forename: Paul A
authors.initials: PA
authors.lastname: Bacon
authors.forename: Erich
authors.initials: E
authors.lastname: Gulbins
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Young
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology; D017252:CD3 Complex / Q000276:immunology / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000276:immunology*; D002518:Ceramides / Q000494:pharmacology; D004789:Enzyme Activation / Q000276:immunology; D006801:Humans; D019169:Jurkat Cells; D008246:Lysophospholipids / Q000378:metabolism; D010835:Phytohemagglutinins / Q000494:pharmacology; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism*; D047888:Receptors, Tumor Necrosis Factor, Type I / Q000378:metabolism*; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism* / Q000494:pharmacology; D013110:Sphingosine / Q000031:analogs & derivatives / Q000378:metabolism; D013601:T-Lymphocytes / Q000187:drug effects / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
chemical_list: D000911:Antibodies, Monoclonal; D017252:CD3 Complex; D015220:Calcium Channels; D002518:Ceramides; D008246:Lysophospholipids; D010835:Phytohemagglutinins; D011948:Receptors, Antigen, T-Cell; D047888:Receptors, Tumor Necrosis Factor, Type I; D014409:Tumor Necrosis Factor-alpha; C060506:sphingosine 1-phosphate; D013108:Sphingomyelin Phosphodiesterase; D013110:Sphingosine; D002118:Calcium