Glucocorticoid receptor-mediated suppression of the interleukin 2 gene expression through impairment of the cooperativity between nuclear factor of activated T cells and AP-1 enhancer elements.
The immunosuppressant hormone dexamethasone (Dex) interferes with T cell-specific signals activating the enhancer sequences directing interleukin 2 (IL-2) transcription. We report that the Dex-dependent downregulation of 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and calcium ionophore-induced activity of the IL-2 enhancer are mediated by glucocorticoid receptor (GR) via a process that requires intact NH2- and COOH-terminal and DNA-binding domains. Functional analysis of chloramphenicol acetyltransferase (CAT) vectors containing internal deletions of the -317 to +47 bp IL-2 enhancer showed that the GR-responsive elements mapped to regions containing nuclear factor of activated T cells protein (NFAT) (-279 to -263 bp) and AP-1 (-160 to -150 bp) motifs. The AP-1 motif binds TPA and calcium ionophore-induced nuclear factor(s) containing fos protein. TPA and calcium ionophore-induced transcriptional activation of homo-oligomers of the NFAT element were not inhibited by Dex, while AP-1 motif concatemers were not stimulated by TPA and calcium ionophore. When combined, NFAT and AP-1 motifs significantly synergized in directing CAT transcription. Such a synergism was impaired by specific mutations affecting the trans-acting factor binding to either NFAT or AP-1 motifs. In spite of the lack of hormone regulation of isolated cis elements, TPA/calcium ionophore-mediated activation of CAT vectors containing a combination of the NFAT and the AP-1 motifs became suppressible by Dex. Our results show that the IL-2-AP-1 motif confers GR sensitivity to a flanking region containing a NFAT element and suggest that synergistic cooperativity between the NFAT and AP-1 sites allows GR to mediate the Dex inhibition of IL-2 gene transcription. Therefore, a Dex-modulated second level of IL-2 enhancer regulation, based on a combinatorial modular interplay, appears to be present.
Vacca
A
A
Department of Experimental Medicine, University La Sapienza, Rome, Italy.
Felli
M P
MP
Farina
A R
AR
Martinotti
S
S
Maroder
M
M
Screpanti
I
I
Meco
D
D
Petrangeli
E
E
Frati
L
L
Gulino
A
A
D001483:Base Sequence; D003907:Dexamethasone / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects; D004357:Drug Synergism; D004742:Enhancer Elements, Genetic / Q000502:physiology; D015870:Gene Expression / Q000187:drug effects; D007108:Immune Tolerance / Q000187:drug effects; D007375:Interleukin-1 / Q000276:immunology; D007376:Interleukin-2 / Q000235:genetics*; D008213:Lymphocyte Activation; D008211:Lymphocyte Cooperation; D008969:Molecular Sequence Data; D011965:Receptors, Glucocorticoid / Q000502:physiology*; D013601:T-Lymphocytes / Q000276:immunology*; D014158:Transcription, Genetic
D007375:Interleukin-1; D007376:Interleukin-2; D011965:Receptors, Glucocorticoid; D003907:Dexamethasone