Shimamoto Yoko, Hirota Keiko, Fukamizu Akiyoshi
Center for Tsukuba Advanced Research Alliance, Aspect of Functional Genomic Biology, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan.
Int J Mol Med. 2004 May;13(5):729-33.
The renin-angiotensin system plays a key role in the regulation of blood pressure. Angiotensinogen (ANG), mainly synthesized in the liver, is the first substrate of renin-angiotensin system. We had previously found that hepatocyte nuclear factor 4 (HNF-4) dramatically activates the human ANG promoter. It is generally known that HNF-4 and peroxisome proliferator-activated receptor alpha (PPARalpha) bind to response elements composed of two core motifs, RG(G/T)TCA, or a closely related sequence separated by 1 nucleotide (DR1 element). To examine whether or not PPARalpha activates the human ANG promoter, we used the reporter gene containing the sequence from -1222 to +44 of the human ANG gene promoter. PPARalpha and RXR heterodimer activated this promoter, and the PPARalpha responsive region was the same site that we had previously mapped as a binding site for HNF-4. Although the human ANG promoter was not induced by PPARalpha ligand bezafibrate in HepG2 cells, this reporter gene was inducible by bezafibrate treatment in HeLa cells, which do not express endogenous HNF-4. We suspected that the high level expression of HNF-4 in HepG2 cells might interfere with the effect of bezafibrate on the human ANG promoter. To confirm this model, we cotransfected HNF-4 expression vector with PPARalpha expression vector into HeLa cells. The bezafibrate-dependent activation of the ANG promoter was inhibited by HNF-4. These results suggest that PPARalpha and HNF-4 competitively affect the human ANG promoter through the C region.
肾素-血管紧张素系统在血压调节中起关键作用。血管紧张素原（ANG）主要在肝脏中合成，是肾素-血管紧张素系统的首个底物。我们之前发现肝细胞核因子4（HNF-4）能显著激活人ANG启动子。众所周知，HNF-4和过氧化物酶体增殖物激活受体α（PPARα）与由两个核心基序RG(G/T)TCA或被1个核苷酸隔开的密切相关序列（DR1元件）组成的反应元件结合。为了检测PPARα是否激活人ANG启动子，我们使用了包含人ANG基因启动子从-1222至+44序列的报告基因。PPARα和RXR异源二聚体激活了该启动子，且PPARα反应区域与我们之前确定为HNF-4结合位点的是同一位点。尽管在HepG2细胞中PPARα配体苯扎贝特未诱导人ANG启动子，但在不表达内源性HNF-4的HeLa细胞中，该报告基因经苯扎贝特处理可被诱导。我们怀疑HepG2细胞中HNF-4的高水平表达可能干扰了苯扎贝特对人ANG启动子的作用。为了证实该模型，我们将HNF-4表达载体与PPARα表达载体共转染至HeLa细胞。HNF-4抑制了苯扎贝特依赖的ANG启动子激活。这些结果表明PPARα和HNF-4通过C区域竞争性地影响人ANG启动子。
