Ray E, Bellini F, Stoudt G, Hemperly S, Rothblat G
Biochim Biophys Acta. 1980 Feb 22;617(2):318-34. doi: 10.1016/0005-2760(80)90174-5.
Cholesterol content and synthesis were measured in rabbit hepatocytes and rat hepatoma cells (Fu5AH) incubated in rabbit serum at concentrations ranging from 2.5% to 50%. Values were compared to controls grown in delipidized serum protein. Cellular cholesterol content varied inversely with the serum concentration, whereas cholesterol synthesis was elevated as serum concentration in the incubation medium was raised. The reduction in cellular cholesterol content and the elevation in synthesis observed with the cells incubated in high concentrations of fresh serum could be correlated with the extent of serum lipoprotein modification by lecithin:cholesterol acyltransferase. Unmodified serum in which LCAT had been inactivated depressed cholesterol synthesis and increased cellular cholesterol content at all concentrations. The presence of active LCAT was not required for the cellular responses, since serum which had been modified before LCAT inactivation also stimulated cholesterol synthesis and decreased content. Qualitatively similar results were obtained with human, rat and rabbit sera. Fractionation of serum demonstrated that the stimulatory activity of LCAT-modified serum was associated primarily with the high-density lipoprotein fraction. Comparative cholesterol flux studies using prelabeled hepatoma cells exposed to either normal or modified high-density lipoproteins demonstrated that cellular cholesterol efflux was somewhat depressed in the presence of the modified lipoprotein whereas cholesterol influx was markedly reduced. These data indicate that LCAT modification of serum lipoproteins alters the relative rates of cholesterol flux with the major effect being on cholesterol uptake. This results in a net loss of cholesterol from the cells accompanied by a stimulation of cholesterol synthesis.
在浓度范围为2.5%至50%的兔血清中孵育的兔肝细胞和大鼠肝癌细胞（Fu5AH）中测量胆固醇含量和合成情况。将这些值与在脱脂血清蛋白中生长的对照进行比较。细胞胆固醇含量与血清浓度呈反比，而随着孵育培养基中血清浓度的升高，胆固醇合成增加。在高浓度新鲜血清中孵育的细胞中观察到的细胞胆固醇含量降低和合成增加，可能与卵磷脂胆固醇酰基转移酶对血清脂蛋白的修饰程度有关。在所有浓度下，已使卵磷脂胆固醇酰基转移酶失活的未修饰血清会抑制胆固醇合成并增加细胞胆固醇含量。细胞反应并不需要活性卵磷脂胆固醇酰基转移酶的存在，因为在卵磷脂胆固醇酰基转移酶失活之前已被修饰的血清也会刺激胆固醇合成并降低含量。用人、大鼠和兔血清获得了定性相似的结果。血清分级分离表明，卵磷脂胆固醇酰基转移酶修饰血清的刺激活性主要与高密度脂蛋白部分有关。使用预先标记的肝癌细胞暴露于正常或修饰的高密度脂蛋白进行的比较胆固醇通量研究表明，在存在修饰脂蛋白的情况下，细胞胆固醇流出有所降低，而胆固醇流入则明显减少。这些数据表明，血清脂蛋白的卵磷脂胆固醇酰基转移酶修饰改变了胆固醇通量的相对速率，主要影响胆固醇摄取。这导致细胞内胆固醇净损失，同时刺激胆固醇合成。
