P. Ghosh et al., ACTIVATION OF NUCLEAR FACTOR OF ACTIVATED T-CELLS IN A CYCLOSPORINE A-RESISTANT PATHWAY, The Journal of biological chemistry, 271(13), 1996, pp. 7700-7704
The mechanism of action of the immunosuppressive drug cyclosporin A (C
sA) is the inactivation of the Ca2+/calmodulin-dependent serine-threon
ine phosphatase calcineurin by the drug-immunophilin complex, Inactive
calcineurin is unable to activate the nuclear factor of activated T c
ells (NFAT), a transcription factor required for expression of the int
erleukin 2 (IL-2) gene. IL-2 production by CsA-treated cells is theref
ore dramatically reduced, We demonstrate here, however, that NFAT can
be activated, and significant levels of IL-2 can be produced by the Cs
A-resistant CD28-signaling pathway. In transient transfection assays,
both multicopy NFAT- and IL-2 promoter-beta-galactosidase reporter gen
e constructs could be activated by phorbol 12-myristate 13-acetate (PM
A)/alpha CD28 stimulation, and this activation was resistant to CsA. E
lectrophoretic mobility shift assay showed the induction of a CsA-resi
stant NFAT complex in the nuclear extracts of peripheral blood T cells
stimulated with PMA plus alpha CD28. Peripheral blood T cells stimula
ted with PMA/alpha CD28 produced IL-2 in the presence of CsA. Collecti
vely, these data suggest that NFAT can be activated and IL-2 can be pr
oduced in a calcineurin independent manner.