Interleukin-2 inhibits glucocorticoid receptor transcriptional activity through a mechanism involving STATS (signal transducer and activator of transcription 5) but not AP-1

Cytokines and glucocorticoids (GCs) signaling pathways interfere with each other in the regulation of apoptosis and gene expression in the immune syst em. Interleukin-2 (IL-2), through the Janus kinase/signal transducers and a ctivators of transcription (Jak/STAT) and mitogen-activated protein kinase (MAPK) pathways, activates STAT5 and activated protein-1 (AP-1) transcripti on factors, respectively, which are known to repress glucocorticoid recepto r (GR) activity, at least in part, through protein-protein interactions. In this work, we have analyzed the mechanisms whereby IL-2 down-regulates the GC-induced transactivation of the mouse mammary tumor virus long terminal repeat (MMTV-LTR) in murine CTLL-2 T lymphocytes. Mutagenesis studies revea led that the MMTV-LTR STAT5 binding site (-923/-914) was not required for I L-2-mediated inhibition but identified both glucocorticoid response element s (GREs) and the -104/+1 region as critical elements for this negative resp onse. The DNA binding activities of transcription factors required for GC-m ediated activation of the MMTV-LTR promoter and that bind to the -104/+1 re gion (nuclear factor-1, Oct-1) were not affected by IL-2 treatment. Overexp ression of wild-type STAT5B enhanced the effect of IL-2 on MMTV-LTR activit y, and a dominant negative form of STAT5B (Y699F) abolished the IL-2-mediat ed MMTV-LTR inhibition, whereas AP-1 activation had no effect in this syste m. Direct interaction between liganded on and STAT5 was observed in CTLL-2 cells in a STAT5 phosphorylation-independent manner. Overexpression of nucl ear coactivators CBP (CREB-binding protein) or SRC-1a (steroid receptor coa ctivator 1a) did not blunt IL-2 inhibitory effects. We suggest that the STA TE-repressive activity on the GC-dependent transcription may involve direct interaction of STAT5 with GR, is dependent on the promoter context and STA T5 activation level, and occurs independently of coactivators levels in T c ells.