Nuclear factor‐κB does not mediate the inhibitory effects of dexamethasone on granulocyte–macrophage colony‐stimulating factor expression

Summary Human granulocyte–macrophage colony‐stimulating factor (GM‐CSF) reporter constructs containing up to 3·3 kb of upstream promoter sequence were transiently transfected into both Jurkat and HUT78 human T‐cell lines. In Jurkat cells, stimulation with phorbol 12‐myristate 13‐acetate (PMA) plus phytohemaglutinin (PHA) produced robust increases in reporter activity, whereas HUT78 cells showed low levels of reporter induction attributable to constitutive nuclear factor (NF)‐κB activity. Following mutation of either the proximal NF‐κB site (−85/−76) or the activator protein1 (AP‐1) motif within the conserved lymphokine element 0 (CLE0) site (−54/−31), reporter activity was markedly reduced in both cell lines. Despite this dependence on NF‐κB and CLE0/AP‐1, GM‐CSF reporter activity was unaffected by dexamethasone in either cell line. Similarly, an NF‐κB‐dependent reporter was also not repressed by dexamethasone, yet GM‐CSF release from HUT78 T cells was inhibited. These data therefore confirm a critical role for both NF‐κB and CLE0 sites in GM‐CSF promoter activation and indicate that NF‐κB may not mediate glucocorticoid‐dependent repression of GM‐CSF in these cells.