Fucosylation of N-glycans regulates the secretion of hepatic glycoproteins into bile ducts
Fucosylation of N-glycans regulates the secretion of hepatic glycoproteins into bile ducts
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DOI：
10.1074/jbc.m605697200
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发表时间：
2006-10-06
影响因子：
4.8
通讯作者：
Miyoshi, Eiji
中科院分区：
文献类型：
--
作者：
Nakagawa, Tsutomu;Uozumi, Naofumi;Miyoshi, Eiji
岩藻糖基化甲胎蛋白（AFP）是肝细胞癌（HCC）的高度特异性肿瘤标志物。然而，HCC患者血清岩藻糖基化AFP水平升高的分子机制仍不清楚。在这里，我们报告说，岩藻糖基化的糖蛋白可能是一个可能的信号分泌到胆管中的肝脏。我们通过几种类型的凝集素印迹分析比较了人胆汁和血清中糖蛋白的寡糖结构。与血清糖蛋白相比，在较宽的分子量范围内观察到胆汁糖蛋白与识别岩藻糖残基的凝集素的结合增强。通过二维图谱高效液相色谱和基质辅助激光解吸电离飞行时间质谱对寡糖进行结构分析，证实胆汁糖蛋白岩藻糖基化增加。纯化后对肝脏中合成的α 1-抗胰蛋白酶、α 1-酸性糖蛋白和触珠蛋白进行结构分析，结果表明胆汁中的岩藻糖基化程度高于血清。为了找到岩藻糖基化和分选信号进入胆管的直接证据，我们使用α 1 - 6岩藻糖基转移酶（Fut 8）缺陷小鼠，因为小鼠肝脏中产生的糖蛋白的岩藻糖基化主要是α 1 - 6键。有趣的是，与野生型小鼠相比，Fut 8缺陷小鼠胆汁中α 1-抗胰蛋白酶和α 1-酸性糖蛋白的水平相当低.免疫组织化学研究显示，这些糖蛋白在Fut 8缺陷小鼠肝脏中的定位发生了巨大变化。总之，这些结果表明，岩藻糖基化是一个可能的信号，糖蛋白分泌到胆管中的肝脏。该系统的不稳定可能涉及HCC患者血清中岩藻糖基化AFP的增加。
Fucosylated alpha-fetoprotein (AFP) is a highly specific tumor marker for hepatocellular carcinoma (HCC). However, the molecular mechanism by which serum level of fucosylated AFP increases in patients with HCC remains largely unknown. Here, we report that the fucosylation of glycoproteins could be a possible signal for secretion into bile ducts in the liver. We compared oligosaccharide structures on glycoproteins in human bile with those in serum by several types of lectin blot analyses. Enhanced binding of biliary glycoproteins to lectins that recognize a fucose residue was observed over a wide range of molecular weights compared with serum glycoproteins. A structural analysis of oligosaccharides by two-dimensional mapping high performance liquid chromatography and matrix- assisted laser desorption ionization time-of flight mass spectrometry confirmed the increases in the fucosylation of biliary glycoproteins. Purification followed by structural analysis on alpha 1- antitrypsin, alpha 1- acid glycoprotein and haptoglobin, which are synthesized in the liver, showed higher fucosylation in bile than in serum. To find direct evidence for fucosylation and sorting signal into bile ducts, we used alpha 1 - 6 fucosyltransferase (Fut8)- deficient mice because fucosylation of glycoproteins produced in mouse liver was mainly an alpha 1 - 6 linkage. Interestingly, the levels of alpha 1- antitrypsin and alpha 1- acid glycoprotein were quite low in bile of Fut8- deficient mice as compared with wild- type mice. An immunohistochemical study showed dramatic changes in the localization of these glycoproteins in the liver of Fut8- deficient mice. Taken together, these results suggest that fucosylation is a possible signal for the secretion of glycoproteins into bile ducts in the liver. Adisruption in this system might involve an increase in fucosylated AFP in the serum of patients with HCC.