MOLECULAR MECHANISM OF HUMAN RENIN AND C-MYC, GENES REGULATION THROUGH NUCLEAR RECEPTOR LXR

cAMP信号通路在肾素基因的调节中起着至关重要的作用，但所涉及的机制仍然知之甚少。我们将我们的研究集中在人肾素启动子中独特的cAMP反应元件（huREN/CNRE，-135到-107）上。我们已经克隆了一个与这种独特的CNRE结合的蛋白质，并证明该蛋白质是肝X受体-α（LXRα），核受体家族的转录因子。LXRα在人肾素产生细胞Calu-6中的瞬时表达增加了人肾素启动子的cAMP诱导。类似地，LXRα稳定转染的Calu-6细胞表现出增加的cAMP诱导的肾素启动子以及内源性肾素基因。huREN/CNRE的定点突变破坏了LXRα的结合，降低了cAMP诱导的人肾素启动子的转录活性。此外，我们证明了来源于人肾小球细胞（肾脏中肾素的主要产生部位）的LXR a与体内huREN/CNRE的结合。这些结果表明LXRα通过与CNRE结合在cAMP介导的人肾素基因转录调控中起重要作用。在平行实验中，我们证明LXRα也可以与c-myc启动子中的同源CNRE结合。在LXRα瞬时转染细胞中，cAMP通过c-myc/CNRE：LXR α相互作用促进转录，并增加稳定转染细胞中c-myc mRNA的表达。LXRα被鉴定为一种新型的cAMP响应性血管紧张素II和c-myc表达核调节剂，不仅具有心血管意义，而且可能对基因转录的调节具有普遍意义。

The cAMP-signaling pathway plays a crucial role in the regulation of the renin gene, but the mechanism involved remains poorly understood. We have focused our studies of renin gene regulation on the unique cAMP responsive element (huREN/CNRE, -135 to -107) in the human renin promoter. We have cloned a protein that binds to this unique CNRE and demonstrated that this protein is liver X receptor-α (LXRα), a transcriptional factor of the nuclear receptor family. Transient expression of LXRα in human renin-producing Calu-6 cells increased cAMP inducibility of human renin promoter. Similarly, LXRα-stably transfected Calu-6 cells exhibited increased cAMP inducibility of renin promoter as well as the endogenous renin gene. Site-directed mutation of huREN/CNRE, which disrupted LXRα binding, decreased cAMP-induced transcriptional activity of human renin promoter. Furthermore, we demonstrated that the binding of LXRa derived from human juxtaglomerular cells, the main production site of renin in the kidney, to the huREN/CNRE in vivo. These results suggest that LXRα plays an important role in the cAMP-mediated regulation of human renin gene transcription by binding to CNRE. In parallel experiments, we demonstrated that LXRα can also bind to the homologous CNRE in the c-myc promoter. cAMP promotes transcription through c-myc/CNRE : LXRa interaction in LXRα-transiently transfected cells and increases c-myc mRNA expression in stably transfected cells. Identification of LXRα as a novel cAMP responsive nuclear modulator of renin and c-myc expression not only has cardiovascular significance but may have generalized implication in the regulation of gene transcription.