Liu J, Grove R I, Vestal R E
Molecular Pharmacology Research Laboratory, Department of Veterans Affairs Medical Center, Boise, Idaho 83702.
Cell Growth Differ. 1994 Dec;5(12):1333-8.
Oncostatin M (OM), a cytokine produced by macrophages and activated T cells, has been shown to be a potent inducer of liver low density lipoprotein receptor (LDLR) activity by increasing LDL uptake and cell surface LDLR number in HepG2 cells. To investigate whether OM regulates the transcription of the LDLR gene and if the effect is independent of the sterol pathway, we examined the effects of OM on the promoter activity of the LDLR gene and the expression of LDLR mRNA. HepG2 cells were transfected with hybrid genes containing three different lengths of DNA fragments from the 5' flanking region of the LDLR gene that were fused to the coding region of the chloramphenicol acetyltransferase (CAT) gene. OM induced an approximately 3-fold increase in CAT activities in pLDLR-CAT vector-transfected cells that were incubated in lipoprotein-depleted medium and a 6-fold increase in CAT activities when the transfected cells were treated with sterols. OM stimulated similar increases in CAT activities in HepG2 cells transfected with pLDLR-CAT 234, pLDLR-CAT 1563, and pLDLR-CAT 6500, suggesting that the essential cis-acting element that mediates the OM effect is located within the 177 base pairs upstream of the transcription start site of the LDLR gene. Examination of the regulation of the endogenous LDLR mRNA expression by OM gave results similar to those in transfected cells. OM increased the levels of mRNA of LDLR, regardless of the presence or absence of lipoprotein and sterols. These data suggest that the up-regulation of the LDLR by OM is at the transcriptional level through a nonsterol mediated mechanism.
抑瘤素M（OM）是一种由巨噬细胞和活化T细胞产生的细胞因子，已被证明可通过增加低密度脂蛋白（LDL）摄取和HepG2细胞表面LDL受体（LDLR）数量，成为肝脏LDLR活性的有效诱导剂。为了研究OM是否调节LDLR基因的转录，以及该效应是否独立于固醇途径，我们检测了OM对LDLR基因启动子活性和LDLR mRNA表达的影响。用含有来自LDLR基因5'侧翼区三种不同长度DNA片段的杂交基因转染HepG2细胞，这些片段与氯霉素乙酰转移酶（CAT）基因的编码区融合。在脂蛋白缺乏培养基中培养的pLDLR-CAT载体转染细胞中，OM诱导CAT活性增加约3倍，当转染细胞用固醇处理时，CAT活性增加6倍。在转染了pLDLR-CAT 234、pLDLR-CAT 1563和pLDLR-CAT 6500的HepG2细胞中，OM刺激CAT活性有类似增加，表明介导OM效应的必需顺式作用元件位于LDLR基因转录起始位点上游177个碱基对内。对OM对内源性LDLR mRNA表达的调节研究结果与转染细胞中的结果相似。无论有无脂蛋白和固醇，OM均可增加LDLR的mRNA水平。这些数据表明，OM对LDLR的上调作用是通过非固醇介导的机制在转录水平上实现的。
