Endosomal trafficking and proprotein convertase cleavage of cis Golgi protein GP73 produces marker for hepatocellular carcinoma
Endosomal trafficking and proprotein convertase cleavage of cis Golgi protein GP73 produces marker for hepatocellular carcinoma
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DOI：
10.1111/j.1600-0854.2007.00621.x
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发表时间：
2007-10-01
期刊：
影响因子：
4.5
通讯作者：
Linstedt, Adam D.
中科院分区：
文献类型：
--
作者：
Bachert, Collin;Fimmel, Claus;Linstedt, Adam D.
肝细胞癌（HCC）患者血清GP73水平显著升高，可能为早期检测提供标志物。然而，GP73是一个整合的膜蛋白定位于顺式高尔基体，并不知道被分泌。基于其在血清中的存在，我们试图确定GP73是否可以正常地从细胞中释放，并阐明这种释放的机制。事实上，可溶形式的GP73从培养的细胞中释放出来，与高尔基体定位的全长蛋白质相比，分子量略有降低，表明切割释放了GP73胞外域。序列分析揭示了前蛋白转化酶（PC）的共识网站，而且，事实上，无处不在的PC弗林蛋白酶能够切割纯化的GP73。此外，PC位点中的丙氨酸取代阻断了GP73的体外和体内切割。使用切割特异性抗体，切割的GP73中发现的反高尔基体网络和内体，表明GP73切割发生的GP73周期远端的早期高尔基体。我们的结论是，GP73的内体运输允许PC介导的切割，导致GP73分泌，并提供了其作为HCC的血清生物标志物存在的分子机制。
Serum GP73 levels are significantly increased in patients with hepatocellular carcinoma (HCC), potentially providing a marker for early detection. However, GP73 is an integral membrane protein localized to the cis Golgi and is not known to be secreted. Based on its presence in sera, we sought to determine whether GP73 might normally be released from cells and to elucidate the mechanism of this release. Indeed, a soluble form of GP73 was released from cultured cells and compared with the Golgi-localized full-length protein, the molecular weight was slightly reduced, suggesting that cleavage releases the GP73 ectodomain. Sequence analysis revealed a proprotein convertase (PC) consensus site, and, indeed, the ubiquitous PC furin was capable of cleaving purified GP73. Further, alanine substitutions in the PC site blocked both the in vitro and the in vivo cleavage of GP73. Using a cleavage-specific antibody, cleaved GP73 was found in the trans Golgi network and endosomes, suggesting that GP73 cleavage occurs as GP73 cycles distal to the early Golgi. We conclude that the endosomal trafficking of GP73 allows for PC-mediated cleavage, resulting in GP73 secretion, and provides a molecular mechanism for its presence as a serum biomarker for HCC.