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 activation-induced apoptosis of immature thymocytes and T-cell hybridomas. In this study, we demonstrate that all-trans-retinoic 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 binding-sites 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 activation 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.
Lee
Mi-Ock
MO
Department of Bioscience and Biotechnology, Institute of Bioscience, Sejong University, Seoul, Korea. molee@sejong.ac.kr
Kang
Hyo-Jin
HJ
Kim
Young Mi
YM
Oum
Ji-Hyun
JH
Park
Jungchan
J
D001665:Binding Sites; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors*; D053222:Fas Ligand Protein; D006367:HeLa Cells; D006801:Humans; D007536:Isomerism; D019169:Jurkat Cells; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000235:genetics*; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D011401:Promoter Regions, Genetic; D011485:Protein Binding / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D020218:Response Elements; D014157:Transcription Factors / Q000037:antagonists & inhibitors*; D015533:Transcriptional Activation; D014212:Tretinoin / Q000494:pharmacology*
D004268:DNA-Binding Proteins; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D008562:Membrane Glycoproteins; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D014157:Transcription Factors; D014212:Tretinoin