Molecular Biology of Acyl-coenzyme A : cholesterol Acyltransferase

制备了一种针对人酰基酶a：胆固醇酰基转移酶（ACAT）的特异性抗体DM10，并采用免疫组化方法对人体组织进行了分析。ACAT在肾上腺皮质、巨噬细胞及其相关细胞如朗格汉斯细胞、肺泡巨噬细胞、神经细胞如雪旺细胞、神经节细胞、皮脂腺等多种人体组织中均有表达。病理条件下，ACAT在主动脉粥样硬化病变，特别是巨噬细胞来源的泡沫细胞中显著表达，提示ACAT在动脉粥样硬化中起重要作用。培养的人单核细胞的Western blotting显示，在单核细胞分化过程中，ACAT蛋白的表达明显增加，这在一定程度上解释了ACAT在人动脉粥样硬化病变中的显著表达。我们克隆了与人ACAT同源的大鼠ACAT cDNA，并对其在大鼠组织中的分布进行了研究。在4个组织中，ACAT活性最高的是肾上腺，其次是肝脏，而小肠和主动脉的ACAT活性较低。mRNA水平在肾上腺中也最高。然而，与高ACAT活性相比，肝脏mRNA水平极低。DM10免疫组化染色显示ACAT在肾上腺中有明显表达，而在肝脏中表达不明显。这些结果提示ACAT同工酶在大鼠肝脏中存在。用化学交联剂处理大鼠肾上腺微粒体片段可形成ACAT二聚体和四聚体。因此，我们提供了ACAT寡聚化的生化证据。

We prepared a specific antiboty (DM10) against human acyl-conzyme A : cholesterol acyltransnferase (ACAT) and analyzed human tissues by immunohistochemical methods. ACAT was expressed in various human tissues including adrenal cortex, macrophages and their related cells such as Langerhans cells and alveolar macrophages, nervous cells such as Schwann cells and ganglion cells, and sebaceous glands. Under pathological conditions, ACAT was markedly expressed in aortic atherosclerotic lesions particularly in macrophage-derived foam cells, suggesting an important role of ACAT in atherogenesis. Western blotting of cultured human monocytics showed that expression of ACAT protein was markedly increased during monocyte differentiation, which explains, in part, marked expression of ACAT in human atherosclerotic lesions.We cloned rat ACAT cDNA as a homologue of human ACAT and examined its tissue distribution in rat. Among four tissues examined, ACAT activity was highest in adrenal followed by liver while those of intestine and aorta were low. The level of mRNA was also highest in adrenal. However, in contrast to high ACAT activity, the level of mRNA in liver was extremely low. Immunohistochemical staining with DM10 showed marked expression of ACAT in adrenal but negligible expression in liver. These results suggest the presence of ACAT isozyme in rat liver. Treatment of microsomal fraction of rat adrenal with chemical cross-linkers showed formation of dimer and tetramer of ACAT.Thus, we provided biochemical evidence for oligomerization of ACAT.