Intracellular cholesterol transporter StarD4 binds free cholesterol and increases cholesteryl ester formation
Intracellular cholesterol transporter StarD4 binds free cholesterol and increases cholesteryl ester formation
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DOI：
10.1194/jlr.m700537-jlr200
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发表时间：
2008-07-01
影响因子：
6.5
通讯作者：
Pandak, William M.
中科院分区：
文献类型：
--
作者：
Rodriguez-Agudo, Daniel;Ren, Shunlin;Pandak, William M.
StarD 4蛋白是类固醇生成急性调节相关脂质转移（START）结构域蛋白的StarD 4亚家族的成员，其包括StarD 5和StarD 6，其功能仍然不清楚的蛋白质。本研究的目的是分离和表征StarD 4的甾醇结合，并在肝细胞培养模型中确定其甾醇转运能力。利用纯化的全长StarD 4，体外结合试验证明StarD 4对[C-14]胆固醇的浓度依赖性结合与胆固醇结合START结构域蛋白StarD 1和StarD 5的结合相似。其他测试的甾醇显示与StarD 4没有可检测的结合，除了7 α-羟基胆固醇，其StarD 4在脂质蛋白覆盖测定中显示弱结合。随后，使用分离的小鼠肝细胞模型来研究StarD 4结合/动员/分布细胞胆固醇的能力。原代小鼠肝细胞中StarD 4表达的增加导致细胞内胆固醇酯浓度和胆汁酸合成速率的显著增加。StarD 4结合胆固醇的能力和特异性，以及作为其表达水平的函数，指导内源性细胞胆固醇的能力和特异性表明，StarD 4在维持细胞胆固醇稳态中作为定向胆固醇转运蛋白发挥重要作用。
StarD4 protein is a member of the StarD4 subfamily of steroidogenic acute regulatory-related lipid transfer (START) domain proteins that includes StarD5 and StarD6, proteins whose functions remain poorly defined. The objective of this study was to isolate and characterize StarD4's sterol binding and to determine in a hepatocyte culture model its sterol transport capabilities. Utilizing purified full-length StarD4, in vitro binding assays demonstrated a concentration-dependent binding of [C-14] cholesterol by StarD4 similar to that of the cholesterol binding START domain proteins StarD1 and StarD5. Other tested sterols showed no detectable binding to StarD4, except for 7 alpha-hydroxycholesterol, for which StarD4 demonstrated weak binding on lipid protein overlay assays. Subsequently, an isolated mouse hepatocyte model was used to study the ability of StarD4 to bind/mobilize/distribute cellular cholesterol. Increased expression of StarD4 in primary mouse hepatocytes led to a marked increase in the intracellular cholesteryl ester concentration and in the rates of bile acid synthesis. The ability and specificity of StarD4 to bind cholesterol and, as a function of its level of expression, to direct endogenous cellular cholesterol suggest that StarD4 plays an important role as a directional cholesterol transporter in the maintenance of cellular cholesterol homeostasis.