The cellular trafficking of the secretory proprotein convertase PCSK9 and its dependence on the LDLR
The cellular trafficking of the secretory proprotein convertase PCSK9 and its dependence on the LDLR
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DOI：
10.1111/j.1600-0854.2007.00562.x
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发表时间：
2007-06-01
期刊：
影响因子：
4.5
通讯作者：
Seidah, Nabil G.
中科院分区：
文献类型：
--
作者：
Nassoury, Nasha;Blasiole, Daniel A.;Seidah, Nabil G.
前蛋白转化酶PCSK 9基因突变与常染色体显性遗传家族性高胆固醇血症或低胆固醇血症相关。这些表型是由前蛋白转化酶枯草杆菌蛋白酶kexin 9（PCSK 9）引起低密度脂蛋白受体（LDLR）蛋白降解的功能获得或丧失引起的。在此，我们询问野生型PCSK 9或PCSK 9突变体和LDLR的亚细胞定位是否可以提供对PCSK 9依赖性LDLR降解机制的深入了解。我们发现LDLR是调节PCSK 9细胞运输的主要伙伴。在缺乏LDLR的细胞中，PCSK 9定位于内质网（ER）中。在表达LDLR的细胞中，PCSK 9分选至ER后区室（即细胞系中的内体和原代肝细胞中的高尔基体），在那里与LDLR共定位。在细胞系中，PCSK 9还与细胞表面的LDLR共定位，需要存在PCSK 9的C末端Cys/His富集结构域。我们提供的证据表明，PCSK 9通过内吞机制促进LDLR降解，因为小干扰RNA介导的网格蛋白重链敲低降低了PCSK 9的功能活性。我们还比较了PCSK 9的天然突变体与人肝细胞（HuH 7）中的野生型酶的亚细胞定位。与高胆固醇血症相关的突变体（S127 R、F216 L和R218 S）定位于内体/溶酶体，而与低胆固醇血症相关的突变体则未到达该隔室。我们得出结论，PCSK 9分选到细胞表面和内体是PCSK 9完全促进LDLR降解所需的，并且保留在ER中会阻止这种活性。影响这种转运的突变可导致高胆固醇血症或低胆固醇血症。
Mutations in the proprotein convertase PCSK9 gene are associated with autosomal dominant familial hyper- or hypocholesterolemia. These phenotypes are caused by a gain or loss of function of proprotein convertase subtilisin kexin 9 (PCSK9) to elicit the degradation of the low-density lipoprotein receptor (LDLR) protein. Herein, we asked whether the subcellular localization of wild-type PCSK9 or mutants of PCSK9 and the LDLR would provide insight into the mechanism of PCSK9-dependent LDLR degradation. We show that the LDLR is the dominant partner in regulating the cellular trafficking of PCSK9. In cells lacking the LDLR, PCSK9 localized in the endoplasmic reticulum (ER). In cells expressing the LDLR, PCSK9 sorted to post-ER compartments (i.e. endosomes in cell lines and Golgi apparatus in primary hepatocytes), where it colocalized with the LDLR. In cell lines, PCSK9 also colocalized with the LDLR at the cell surface, requiring the presence of the C-terminal Cys/His-rich domain of PCSK9. We provide evidence that PCSK9 promotes the degradation of the LDLR by an endocytic mechanism, as small interfering RNA-mediated knockdown of the clathrin heavy chain reduced the functional activity of PCSK9. We also compared the subcellular localization of natural mutants of PCSK9 with that of the wild-type enzyme in human hepatic (HuH7) cells. Whereas the mutants associated with hypercholesterolemia (S127R, F216L and R218S) localized to endosomes/lysosomes, those associated with hypocholesterolemia did not reach this compartment. We conclude that the sorting of PCSK9 to the cell surface and endosomes is required for PCSK9 to fully promote LDLR degradation and that retention in the ER prevents this activity. Mutations that affect this transport can lead to hyper- or hypocholesterolemia.