Transcriptional activation of c-fos protooncogene by 17β-estradiol:: Mechanism of aryl hydrocarbon receptor-mediated inhibition
Transcriptional activation of c-fos protooncogene by 17β-estradiol:: Mechanism of aryl hydrocarbon receptor-mediated inhibition
复制标题
DOI：
10.1210/me.13.9.1511
复制
发表时间：
1999-09-01
影响因子：
--
通讯作者：
Safe, S
中科院分区：
文献类型：
--
作者：
Duan, RQ;Porter, W;Safe, S
17 β-雌二醇（E-2）诱导MCF-7人乳腺癌细胞中c-fos原癌基因mRNA的表达，在处理后1 h内观察到最大诱导。2，3，7，8-四氯二苯并-对-二恶英（TCDD）在2 h内抑制E-2诱导的反应。使用pFC 2-CAT进一步研究了这种反应的分子机制，pFC 2-CAT是一种含有与细菌氯霉素乙酰转移酶（CAT）报告基因连接的人c-fos原癌基因的-1400至+41序列的构建体。在瞬时转染pFC 2-CAT的MCF-7细胞中，10 nM E-2诱导CAT活性增加8.5倍，与10 nM TCDD共处理使该反应降低45%以上。α-萘啶酮，一种芳香烃受体（AhR）拮抗剂，阻断TCDD的抑制作用;此外，在变体Ah-nonresponsive MCF-7细胞中未观察到抑制反应，表明AhR复合物是雌激素受体串扰所必需的。c-fos基因启动子中的E-2应答序列（-1220至-1155）包含两个推定的核心五核苷酸二恶英应答元件（DRES），位于-1206至-1202和-1163至-1159。在使用野生型和核心DRE突变体构建体的瞬时转染测定中，下游核心DRE（在-1163至-1159处）被鉴定为功能性抑制性DRE。光诱导交联、凝胶迁移率变化和体外DNA足迹分析的结果表明，AhR复合物与核心DRE相互作用，该核心DRE也与E-2响应性GC富集位点（-1168至-1161）重叠，这表明AhR介导的抑制作用的机制可能是由于Sp1结合位点的淬灭或掩蔽。
17 beta-Estradiol (E-2) induced c-fos protooncogene mRNA levels in MCF-7 human breast cancer cells, and maximal induction was observed within 1 h after treatment. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) inhibited the E-2-induced response within 2 h. The molecular mechanism of this response was further investigated using pFC2-CAT, a construct containing a -1400 to +41 sequence from the human c-fos protooncogene linked to a bacterial chloramphenicol acetyltransferase (CAT) reporter gene. In MCF-7 cells transiently transfected with pFC2-CAT, 10 nM E-2 induced an 8.5-fold increase of CAT activity, and cotreatment with 10 nM TCDD decreased this response by more than 45%. alpha-Naphthoflavone, an aryl hydrocarbon receptor (AhR) antagonist, blocked the inhibitory effects of TCDD; moreover, the inhibitory response was not observed in variant Ah-nonresponsive MCF-7 cells, suggesting that the AhR complex was required for estrogen receptor cross-talk. The E-2-responsive sequence (-1220 to -1155) in the c-fos gene promoter contains two putative core pentanucleotide dioxin-responsive elements (DREs) at -1206 to -1202 and -1163 to -1159. In transient transfection assays using wild-type and core DRE mutant constructs, the downstream core DRE (at -1163 to -1159) was identified as a functional inhibitory DRE. The results of photo-induced cross-linking, gel mobility shift, and in vitro DNA footprinting assays showed that the AhR complex interacted with the core DRE that also overlapped the E-2-responsive GC-rich site (-1168 to -1161), suggesting that the mechanism for AhR-mediated inhibitory effects may be due to quenching or masking at the Sp1-binding site.