Engdahl Ryan, Monroy M Alexandra, Daly John M
Temple University School of Medicine, Department of Surgery, 3400 North Broad Street, Philadelphia, PA 19140, USA.
Biochem Biophys Res Commun. 2007 Jul 20;359(1):88-93. doi: 10.1016/j.bbrc.2007.05.057. Epub 2007 May 21.
Prostaglandin metabolite 15-Deoxy-Delta(12,14)-prostaglandin J2 (15d-PGJ2) is known to inhibit a number of pro-inflammatory cytokines as well as being a ligand for nuclear receptor PPARgamma. We investigated the ability of 15d-PGJ2 to inhibit TNF-alpha gene expression through mechanisms that involve histone modification. Pretreatment with 15d-PGJ2 (10 microM) inhibited LPS-stimulated TNF-alpha mRNA in THP-1 monocytes or PMA-differentiated cells to nearly basal levels. A specific PPARgamma ligand, GW1929, failed to inhibit LPS-induced TNF-alpha mRNA expression nor did a PPARgamma antagonist, GW9662, alter the repression of TNF-alpha mRNA in LPS-stimulated cells pretreated with 15d-PGJ2 suggesting a PPARgamma-independent inhibition of TNF-alpha mRNA in THP-1 cells. Transfection studies with a reporter construct and subsequent treatment with 15d-PGJ2 demonstrated a dose-dependent inhibition of the TNF-alpha promoter. Additional studies demonstrated that inhibition of histone deacetylases with trichostatin A (TSA) or overexpression of histone acetyltransferase CBP could overcome 15d-PGJ2-mediated repression of the TNF-alpha promoter, suggesting that an important mechanism whereby 15d-PGJ2 suppresses a cytokine is through factors that regulate histone modifications. To examine the endogenous TNF-alpha promoter, chromatin immunoprecipitations (ChIP) were performed. ChIP assays demonstrated that LPS stimulation induced an increase in histone H3 and H4 acetylation at the TNF-alpha promoter, which was reduced in cells pretreated with 15d-PGJ2. These results highlight the ability of acetylation and deacetylation factors to affect the TNF-alpha promoter and demonstrate that an additional important mechanism whereby 15d-PGJ2 mediates TNF-alpha transcriptional repression by altering levels of acetylated histone H3 and H4 at its promoter.
前列腺素代谢产物15-脱氧-Δ(12,14)-前列腺素J2（15d-PGJ2）已知可抑制多种促炎细胞因子，并且是核受体PPARγ的配体。我们研究了15d-PGJ2通过涉及组蛋白修饰的机制抑制肿瘤坏死因子-α（TNF-α）基因表达的能力。用15d-PGJ2（10微摩尔）预处理可将LPS刺激的THP-1单核细胞或PMA分化细胞中的TNF-α mRNA抑制至接近基础水平。一种特异性PPARγ配体GW1929未能抑制LPS诱导的TNF-α mRNA表达，PPARγ拮抗剂GW9662也未改变在用15d-PGJ2预处理的LPS刺激细胞中TNF-α mRNA的抑制作用，这表明在THP-1细胞中对TNF-α mRNA的抑制不依赖于PPARγ。用报告基因构建体进行转染研究并随后用15d-PGJ2处理，结果显示对TNF-α启动子有剂量依赖性抑制作用。进一步的研究表明，用曲古抑菌素A（TSA）抑制组蛋白脱乙酰酶或组蛋白乙酰转移酶CBP的过表达可克服15d-PGJ2介导的TNF-α启动子抑制，这表明15d-PGJ2抑制细胞因子的一个重要机制是通过调节组蛋白修饰的因子来实现的。为了检测内源性TNF-α启动子，进行了染色质免疫沉淀（ChIP）实验。ChIP分析表明，LPS刺激可诱导TNF-α启动子处组蛋白H3和H4乙酰化增加，在用15d-PGJ2预处理的细胞中这种增加有所减少。这些结果突出了乙酰化和去乙酰化因子影响TNF-α启动子的能力，并证明了15d-PGJ2通过改变其启动子处乙酰化组蛋白H3和H4的水平介导TNF-α转录抑制的另一个重要机制。
