Molecular characterization of hepatocystin, the protein that is defective in autosomal dominant polycystic liver disease
Molecular characterization of hepatocystin, the protein that is defective in autosomal dominant polycystic liver disease
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DOI：
10.1053/j.gastro.2004.02.023
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发表时间：
2004-06-01
期刊：
影响因子：
29.4
通讯作者：
Bonifacino, JS
中科院分区：
文献类型：
--
作者：
Drenth, JPH;Martina, JA;Bonifacino, JS
背景和目的：常染色体显性多囊肝病的特征是存在遍布整个肝实质的大量囊肿。最近，我们发现多囊肝病是由蛋白激酶C底物80K-H基因突变引起的，该基因编码一种名为肝囊素的蛋白质。先前的研究已将肝囊素鉴定为蛋白激酶 C 底物、胞质信号转导复合物的组成部分、晚期糖基化终产物的受体、液泡蛋白和内质网葡萄糖苷酶 H 的 P 亚基。因此，肝囊素的确切定位和细胞功能仍不清楚。方法：通过结合免疫荧光显微镜、免疫印迹、代谢标记、免疫沉淀和碳水化合物分析，检查正常和多囊肝病突变型肝囊肿的定位和生化特性。结果：正常肝囊素定位于内质网，在那里与葡萄糖苷酶 II α 亚基组装。在一些多囊肝病患者中观察到的肝囊肿素中的 1338-2A-->G 截短突变产生的蛋白质不保留在内质网中，而是分泌到培养基中。该突变蛋白无法与葡萄糖苷酶 II α 亚基组装。因此，在肝囊肿中检测不到突变型肝囊肿素。此外，多囊肝病患者的肝脏和 Epstein-Barr 病毒永生化 B 淋巴母细胞中正常肝囊素和葡萄糖苷酶 II α 亚基的水平显着降低。结论：这些发现与肝囊肿素在内质网中碳水化合物加工和新合成糖蛋白的质量控制中的作用一致。因此，细胞增殖的一些关键调节因子的内质网处理过程的改变可能是多囊肝病的基础。
Background & Aims: Autosomal dominant polycystic liver disease is characterized by the presence of numerous cysts spread throughout the liver parenchyma. Recently, we discovered that polycystic liver disease is caused by mutations in the protein kinase C substrate 80K-H gene, which encodes a protein named hepatocystin. Previous studies have identified hepatocystin as a protein kinase C substrate, a component of a cytosolic signal transduction complex, a receptor for advanced glycation end products, a vacuolar protein, and the P subunit of endoplasmic reticulum glucosidase H. Thus, the exact localization and cellular function of hepatocystin remain unclear. Methods: The localization and biochemical properties of normal and polycystic liver disease mutant forms of hepatocystin were examined by using a combination of immunofluorescence microscopy, immunoblotting, metabolic labeling, immuno-precipitation, and carbohydrate analyses. Results: Normal hepatocystin localizes to the endoplasmic reticulum, where it assembles with the glulcosidase II alpha subunit. The 1338-2A-->G truncating mutation in hepatocystin observed in some polycystic liver disease patients produces a protein that is not retained in the endoplasmic reticulum but is secreted into the medium. This mutant protein fails to assemble with the glucosidase II alpha subunit. As a consequence, mutant hepatocystin is undetectable in liver cysts. In addition, levels of normal hepatocystin and of the glucosidase II alpha subunit are substantially reduced in liver and Epstein-Barr virus-immortalized B lymphoblasts from patients with polycystic liver disease. Conclusions: These findings are consistent with a role of hepatocystin in carbohydrate processing and quality control of newly synthesized glycoproteins in the endoplasmic reticulum. Therefore, altered endoplasmic reticulum processing of some key regulator of cell proliferation may underlie polycystic liver disease.