In Vivo Evidence That Furin from Hepatocytes Inactivates PCSK9
In Vivo Evidence That Furin from Hepatocytes Inactivates PCSK9
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DOI：
10.1074/jbc.m110.192104
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发表时间：
2011-02-01
影响因子：
4.8
通讯作者：
Prat, Annik
中科院分区：
文献类型：
--
作者：
Essalmani, Rachid;Susan-Resiga, Delia;Prat, Annik
蛋白转化酶PCSK9通过结合LDL受体并使其降解，在胆固醇稳态中起关键作用。PCSK9在肝脏中强烈表达，在人和小鼠血浆中以成熟（类似于62 kDa）和灭活（类似于55 kDa）的形式存在。离体数据显示，人PCSK9在Arg218向下箭头处被过表达的转化酶furin和PC5/6A切割而失活。对R218S和F216L突变的人杂合子血浆的分析显示，与55-kDa形式相似的水平降低了50%。为了确定体内负责Arg（218）切割的转化酶，我们在肝细胞中特异性地灭活了furin和/或PC5/6基因。在肝细胞（Fur-hKO）缺乏furin的小鼠中，pcsk9灭活形式强烈减少，而在PC5/6-hKO血浆中仅轻微减少。与furin在体内调节PCSK9活性的关键作用一致，我们观察到Fur-hKO肝脏LDL受体蛋白水平总体下降26%，可能是由于PCSK9 mRNA水平增加35%和PCSK9切割缺失的复合作用，这表明PCSK9在这些小鼠中具有更高的活性。从这些小鼠获得的原代肝细胞中，PCSK9的过表达表明，只有全长的、膜结合的、但不溶的furin是同源转化酶。我们得出结论，在肝细胞中，furin调节PCSK9 mRNA水平，是体内循环PCSK9蛋白酶失活的关键。
The proprotein convertase PCSK9 plays a key role in cholesterol homeostasis by binding the LDL receptor and targeting it toward degradation. PCSK9 is strongly expressed in the liver and is found in human and mouse plasma as mature (similar to 62 kDa) and inactivated (similar to 55 kDa) forms. Ex vivo data showed that human PCSK9 is inactivated by cleavage at Arg218 down arrow by the overexpressed convertases furin and PC5/6A. Analysis of the plasma of human heterozygotes for R218S and F216L mutations revealed a similar to 50% reduction in the levels of the similar to 55-kDa form. To identify the convertase(s) responsible for cleavage at Arg(218) in vivo, we inactivated the genes of furin and/or PC5/6 specifically in hepatocytes. The PCSK9-inactivated form was strongly reduced in mice lacking furin in hepatocytes (Fur-hKO) and only slightly reduced in PC5/6-hKO plasma. In agreement with a key role of furin in regulating PCSK9 activity in vivo, we observed an overall 26% drop in the LDL receptor protein levels of Fur-hKO livers, likely due to the compound effects of a 35% increase in PCSK9 mRNA levels and the loss of PCSK9 cleavage, suggesting a higher activity of PCSK9 in these mice. Overexpression of PCSK9 in primary hepatocytes obtained from these mice revealed that only full-length, membrane-bound, but not soluble, furin is the cognate convertase. We conclude that in hepatocytes furin regulates PCSK9 mRNA levels and is the key in vivo-inactivating protease of circulating PCSK9.