Molecular Biology of Acyl-coenzyme A : cholesterol Acyltransferase

本文制备了抗人酰基辅酶A胆固醇酰基转移酶（ACAT）的特异性抗体（DM 10），并应用免疫组化方法对人体组织进行了分析。ACAT在各种人体组织中表达，包括肾上腺皮质、巨噬细胞及其相关细胞（如朗格汉斯细胞和肺泡巨噬细胞）、神经细胞（如许旺细胞和神经节细胞）和皮脂腺。在病理条件下，ACAT在主动脉粥样硬化病变中显著表达，尤其是在巨噬细胞源性泡沫细胞中，提示ACAT在动脉粥样硬化形成中的重要作用。Western blotting显示ACAT蛋白在单核细胞分化过程中表达显著增加，这部分解释了ACAT在动脉粥样硬化病变中的显著表达。在四种组织中，ACAT活性在肾上腺中最高，其次是肝脏，而肠和主动脉的活性较低。肾上腺中mRNA水平也最高。然而，与高ACAT活性相反，肝脏中的mRNA水平极低。免疫组织化学染色显示ACAT在肾上腺中有显著表达，但在肝脏中表达可忽略不计。提示大鼠肝脏中存在ACAT同工酶。用化学交联剂处理大鼠肾上腺微粒体组分，发现ACAT形成二聚体和四聚体，从而为ACAT的寡聚化提供了生化证据。

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.