FK 506 and cyclosporin each block antigen-induced T cell receptor signalling that is dependent on CD4 co-receptor and operates in the absence of detectable cytoplasmic calcium fluxes.
The T cell hybridoma "171", which lacks CD4 but expresses T cell receptor (TCR) for hen egg white lysozyme, requires introduction of wild-type CD4 for antigen-mediated induction and secretion of interleukin-2 (IL-2). Mutant CD4, which fails to associate with the tyrosine kinase p56lck does not support IL-2 secretion, suggesting that a role of CD4 is to bring cytoplasmic p56lck into alignment for signal transduction to the IL-2 promotor. Using 171, 171-CD4 (wild-type) and 171-CD4 (mutant), we found that IL-2 secretion was inhibited by FK 506 and cyclosporin but not by rapamycin. However, this inhibition was not associated with calcium fluxes since no change in cytoplasmic free calcium levels ([Ca]i; resting level 80 nM) was detectable during antigen stimulation of the 171 or 171-CD4 cells. Thus, although FK 506 and cyclosporin inhibited calcium-dependent signalling to the IL-2 promoter via inhibition of the protein phosphatase calcineurin, it is possible that IL-2 induction via TCR/CD4 requires an FK 506 (and cyclosporin) sensitive step which is independent of cytoplasmic calcium changes.
Addenbrookes Hospital, Cambridge, UK.
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S
Metcalfe
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Alexander
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J
Turner
D000818:Animals; D015704:CD4 Antigens / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D002645:Chickens; D016572:Cyclosporine / Q000494:pharmacology*; D003593:Cytoplasm / Q000502:physiology; D007376:Interleukin-2 / Q000096:biosynthesis; D009113:Muramidase / Q000276:immunology; D011948:Receptors, Antigen, T-Cell / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects* / Q000276:immunology; D020123:Sirolimus / Q000494:pharmacology; D013601:T-Lymphocytes / Q000276:immunology*; D016559:Tacrolimus / Q000494:pharmacology*
D015704:CD4 Antigens; D007376:Interleukin-2; D011948:Receptors, Antigen, T-Cell; D016572:Cyclosporine; D009113:Muramidase; D002118:Calcium; D020123:Sirolimus; D016559:Tacrolimus