Tabas I, Zha X, Beatini N, Myers J N, Maxfield F R
Department of Medicine, Columbia University College of Physicians and Surgeons, New York, New York 10032.
J Biol Chem. 1994 Sep 9;269(36):22547-56.
Stimulation of intracellular cholesterol esterification, which is catalyzed by the enzyme acyl-coenzyme A: cholesterol O-acyltransferase (ACAT), by atherogenic lipoproteins in macrophages is a key step in the ability of these cells to store lipoprotein-cholesterol and in the eventual development of atheroma foam cells. Herein, we provide evidence that the actin cytoskeleton plays an important role in the stimulation of cholesterol esterification by atherogenic lipoproteins in macrophages. When the actin cytoskeleton of cultured mouse peritoneal macrophages was disrupted by treatment with cytochalasin D or Clostridial C2 toxin, the ability of beta very low density lipoprotein (beta-VLDL) to stimulate cholesterol esterification was decreased 3-6-fold, even under conditions in which beta-VLDL protein degradation, cholesteryl ester hydrolysis, or net cholesterol delivery to the cells was matched. Esterification of cellular phospholipids and triglycerides was not affected by this treatment. Cytochalasin D treatment of macrophages also inhibited the ability of acetyl-low density lipoprotein, another foam cell-forming lipoprotein, to stimulate cholesterol esterification, but stimulation of cholesterol esterification by 25-hydroxycholesterol was not inhibited by cytochalasin D. Cytochalasin D was found to inhibit neither the exit of beta-VLDL-derived cholesterol from lysosomes nor the ability of beta-VLDL to down-regulate endogenous cholesterol synthesis. From these data we conclude that an intact actin cytoskeleton is necessary for efficient stimulation of cholesterol esterification by atherogenic lipoproteins in macrophages. Although the exact function of actin in the cholesterol esterification pathway remains to be determined, our data rule out a general role for actin in intracellular cholesterol trafficking or maintenance of ACAT enzyme activity. Rather, we speculate that actin filaments play a role in specific cellular entry processes of atherogenic lipoproteins and/or in establishing transport or contact between the plasma membrane cholesterol substrate pool and the ACAT enzyme in macrophages.
动脉粥样硬化脂蛋白刺激巨噬细胞内由酰基辅酶A：胆固醇O-酰基转移酶（ACAT）催化的胆固醇酯化，是这些细胞储存脂蛋白胆固醇能力以及动脉粥样硬化泡沫细胞最终形成的关键步骤。在此，我们提供证据表明，肌动蛋白细胞骨架在动脉粥样硬化脂蛋白刺激巨噬细胞胆固醇酯化过程中发挥重要作用。当用细胞松弛素D或梭菌C2毒素处理使培养的小鼠腹腔巨噬细胞的肌动蛋白细胞骨架被破坏时，即使在β极低密度脂蛋白（β-VLDL）蛋白质降解、胆固醇酯水解或向细胞的净胆固醇递送相匹配的条件下，β-VLDL刺激胆固醇酯化的能力也降低了3至6倍。这种处理不影响细胞磷脂和甘油三酯的酯化。用细胞松弛素D处理巨噬细胞也抑制了另一种形成泡沫细胞的脂蛋白——乙酰低密度脂蛋白刺激胆固醇酯化的能力，但细胞松弛素D不抑制25-羟基胆固醇对胆固醇酯化的刺激。发现细胞松弛素D既不抑制β-VLDL衍生的胆固醇从溶酶体的流出，也不抑制β-VLDL下调内源性胆固醇合成的能力。根据这些数据我们得出结论，完整的肌动蛋白细胞骨架对于动脉粥样硬化脂蛋白有效刺激巨噬细胞胆固醇酯化是必需的。尽管肌动蛋白在胆固醇酯化途径中的具体功能仍有待确定，但我们的数据排除了肌动蛋白在细胞内胆固醇转运或ACAT酶活性维持中的一般作用。相反，我们推测肌动蛋白丝在动脉粥样硬化脂蛋白的特定细胞进入过程中以及/或者在巨噬细胞质膜胆固醇底物池与ACAT酶之间建立转运或接触中发挥作用。
