GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR GENE-TRANSCRIPTION IS DIRECTLY REPRESSED BY THE VITAMIN-D-3 RECEPTOR - IMPLICATIONS FOR ALLOSTERIC INFLUENCES ON NUCLEAR RECEPTOR STRUCTURE AND FUNCTION BY A DNA ELEMENT

The primary function of activated T lymphocytes is to produce various cytokines necessary to elicit an immune response; these cytokines incl ude interleukin-a (IL-2), interleukin-4, and granulocyte-macrophage co lony-stimulating factor (GMCSF). Steroid hormones and vitamin A and D- 3 metabolites act to repress the expression of cytokines. 1,25-Dihydro xyvitamin D-3 (1,25-(OH)(2)D-3) down-modulates activated IL-2 expressi on at the level transcription, through direct antagonism of the transa ctivating complex NFAT-1/AP-1 by the vitamin D-3 receptor (VDR). We re port here that GMCSF transcription in Jurkat T cells is also directly repressed by 1,25-(OH)(2)D-3 and VDR. Among four NFAT/AP-1 elements in the GMCSF enhancer, we have focused on one such element that when mul timerized, is sufficient in mediating both activation by NFAT-1 and AP -1 and repression in response to 1,25-(OH)(2)D-3. Although this elemen t does not contain any recognizable vitamin D response elements (VDREs ), high affinity DNA binding by recombinant VDR is observed. In contra st to VDR interactions with positive VDREs, this binding is independen t of VDR's heterodimeric partner, the retinoid X receptor. Moreover, V DR appears to bind the GMCSF element as an apparent monomer in vitro. Protease digestion patterns of bound VDR, and receptor mutations affec ting DNA binding and dimerization, demonstrate that the receptor binds to the negative site in a distinct conformation relative to a positiv e VDRE, suggesting that the DNA element itself acts as an allosteric e ffector of VDR function. This altered conformation may account for VDR 's action as a repressing rather than activating factor at this locus.