Costet P, Luo Y, Wang N, Tall A R
Division of Molecular Medicine, Department of Medicine, Columbia University, New York, New York 10032, USA.
J Biol Chem. 2000 Sep 8;275(36):28240-5. doi: 10.1074/jbc.M003337200.
Tangier disease, a condition characterized by low levels of high density lipoprotein and cholesterol accumulation in macrophages, is caused by mutations in the ATP-binding cassette transporter ABC1. In cultured macrophages, ABC1 mRNA was induced in an additive fashion by 22(R)-hydroxycholesterol and 9-cis-retinoic acid (9CRA), suggesting induction by nuclear hormone receptors of the liver X receptor (LXR) and retinoid X receptor (RXR) family. We cloned the 5'-end of the human ABC1 transcript from cholesterol-loaded THP1 macrophages. When transfected into RAW macrophages, the upstream promoter was induced 7-fold by 22(R)-hydroxycholesterol, 8-fold by 9CRA, and 37-fold by 9CRA and 22(R)-hydroxycholesterol. Furthermore, promoter activity was increased in a sterol-responsive fashion when cotransfected with LXRalpha/RXR or LXRbeta/RXR. Further experiments identified a direct repeat spaced by four nucleotides (from -70 to -55 base pairs) as a binding site for LXRalpha/RXR or LXRbeta/RXR. Mutations in this element abolished the sterol-mediated activation of the promoter. The results show sterol-dependent transactivation of the ABC1 promoter by LXR/RXR and suggest that small molecule agonists of LXR could be useful drugs to reverse foam cell formation and atherogenesis.
丹吉尔病是一种以高密度脂蛋白水平低和巨噬细胞中胆固醇蓄积为特征的疾病，由ATP结合盒转运体ABC1的突变引起。在培养的巨噬细胞中，22(R)-羟基胆固醇和9-顺式视黄酸（9CRA）以累加方式诱导ABC1 mRNA表达，提示由肝脏X受体（LXR）和类视黄醇X受体（RXR）家族的核激素受体诱导。我们从胆固醇负载的THP1巨噬细胞中克隆了人ABC1转录本的5'端。当转染到RAW巨噬细胞中时，上游启动子被22(R)-羟基胆固醇诱导7倍，被9CRA诱导8倍，被9CRA和22(R)-羟基胆固醇共同诱导37倍。此外，当与LXRα/RXR或LXRβ/RXR共转染时，启动子活性以固醇反应性方式增加。进一步的实验确定了一个由四个核苷酸间隔的直接重复序列（从-70到-55碱基对）作为LXRα/RXR或LXRβ/RXR的结合位点。该元件中的突变消除了启动子的固醇介导的激活。结果显示LXR/RXR对ABC1启动子有固醇依赖性反式激活作用，并提示LXR的小分子激动剂可能是逆转泡沫细胞形成和动脉粥样硬化的有用药物。
