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控中起着至关重要的作用，但其中涉及的机制仍然知之甚少。我们对肾素基因调控的研究集中在人肾素启动子中独特的cAMP反应元件(huREN/CNRE，-135至-107)。我们已经克隆了一个与这种独特的CNRE结合的蛋白，并证明该蛋白是肝X受体-α(LXRα)，是核受体家族的转录因子。在产生肾素的CALU-6细胞中瞬时表达LXRα可增加人肾素启动子的cAMP诱导性。同样，LXRα稳定转染的CALU-6细胞显示肾素启动子和内源性肾素基因的cAMP诱导性增加。HuREN/CNRE的定点突变破坏了LXRα结合，降低了cAMP诱导的人肾素启动子的转录活性。此外，我们还在体内证明了肾素的主要产生部位--人肾小球旁细胞的LXRa与huREN/CNRE的结合。这些结果表明，LXRα通过与cAMP结合，在cAMP介导的人肾素基因转录调控中发挥重要作用。在平行实验中，我们证明了LXRα也可以与c-myc启动子中的同源CNRE结合。CAMP通过c-myc/CNRE：LXRa相互作用促进LXRα瞬时转染细胞的转录，并增加稳定转染细胞中c-myc基因的表达。发现LXRα是一种新的cAMP反应的肾素和c-myc表达的核调节剂，不仅具有心血管意义，而且可能在基因转录调控中具有普遍意义。

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.