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，但其机制尚不清楚。我们将肾素基因调控的研究重点放在人类肾素启动子中独特的cAMP响应元件（huREN/CNRE， -135至-107）上。我们克隆了一种与这种独特的CNRE结合的蛋白质，并证明该蛋白质是肝脏X受体-α (LXRα)，是核受体家族的转录因子。LXRα在人肾素生成细胞Calu-6中的瞬时表达增加了人肾素启动子cAMP的诱导性。同样，lxr α-稳定转染的Calu-6细胞表现出增强的肾素启动子和内源性肾素基因的cAMP诱导能力。huREN/CNRE位点突变破坏了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LXRa来源于人肾小球旁细胞（肾脏中肾素的主要产生部位）与huREN/CNRE的体内结合。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发挥重要作用。在平行实验中，我们证明LXRα也可以结合c-myc启动子中的同源CNRE。cAMP在lxr α-瞬时转染的细胞中通过c-myc/CNRE: LXRa相互作用促进转录，在稳定转染的细胞中增加c-myc mRNA的表达。LXRα作为肾素和c-myc表达的新的cAMP响应性核调节剂的鉴定不仅具有心血管意义，而且可能在基因转录调控方面具有广泛的意义。

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.