tailieunhanh - Báo cáo Y học: Repression of FasL expression by retinoic acid involves a novel mechanism of inhibition of transactivation function of the nuclear factors of activated T-cells

Retinoids are potent immune modulators that inhibit Fas ligand (FasL) expression and thereby repress the activationinduced apoptosis of immature thymocytes and T-cell hybridomas. In this study, we demonstrate that all-transretinoic acid (all-trans-RA) directly represses the transcriptional activity of the nuclear factors of activated T-cells (NFAT), which is an important transactivator of the FasL promoter. The analysis of reporter constructs containing the FasL promoter and wild-type or mutant NFAT bindingsites indicated that all-trans-RA repression was mediated via an NFAT binding element located in the promoter. A reporter construct comprising the NFAT binding sequence linked to a heterologous SV-40 promoter showed that. | Eur. J. Biochem. 269 1162-1170 2002 FEBS 2002 Repression of FasL expression by retinoic acid involves a novel mechanism of inhibition of transactivation function of the nuclear factors of activated T-cells Mi-Ock Lee1 Hyo-Jin Kang1 Young Mi Kim1 Ji-Hyun Oum2 and Jungchan Park2 1 Department of Bioscience and Biotechnology Institute of Bioscience Sejong University Seoul Korea 2Department of Bioscience and Biotechnology Hankuk University of Foreign Studies Kyounggi-do Korea Retinoids are potent immune modulators that inhibit Fas ligand FasL expression and thereby repress the activation-induced apoptosis of immature thymocytes and T-cell hybridomas. In this study we demonstrate that all-transretinoic acid all-trans-RA directly represses the transcriptional activity of the nuclear factors of activated T-cells NFAT which is an important transactivator of the FasL promoter. The analysis of reporter constructs containing the FasL promoter and wild-type or mutant NFAT bindingsites indicated that all-trans-RA repression was mediated via an NFAT binding element located in the promoter. A reporter construct comprising the NFAT binding sequence linked to a heterologous SV-40 promoter showed that NFAT transcriptional activity was significantly inhibited by all-trans-RA. Furthermore all-trans-RA inhibited activa tion of the distal NFAT binding motif present in the interleukin IL -2 promoter suggesting that the inhibition of NFAT function by all-trans-RA was not specific to the FasL promoter. Gel shift assays corroborated the results of the gene reporter studies by showing that all-trans-RA decreased the NFAT binding to DNA. All-trans-RA blocked translocation of NFATp from the cytosol into the nucleus which was induced by PMA ionomycin treatment in HeLa cells transfected with a Flag-tagged NFATp. Taken together our results indicate that FasL inhibition by all-trans-RA involves a novel mechanism whereby the transcriptional function of NFAT is blocked. Keywords retinoic acid NFAT .