Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, USA.
J Biol Chem. 2013 Jun 14;288(24):17399-407. doi: 10.1074/jbc.M112.440362. Epub 2013 Apr 23.
A critical step in the influenza virus replication cycle is the cleavage activation of the HA precursor. Cleavage activation of influenza HA enables fusion with the host endosome, allowing for release of the viral genome into the host cell. To date, studies have determined that HA activation is driven by trypsin-like host cell proteases, as well as yet to be identified bacterial proteases. Although the number of host proteases that can activate HA is growing, there is still uncertainty regarding which secreted proteases are able to support multicycle replication of influenza. In this study, we have determined that the kallikrein-related peptidases 5 and 12 are secreted from the human respiratory tract and have the ability to cleave and activate HA from the H1, H2, and H3 subtypes. Each peptidase appears to have a preference for particular influenza subtypes, with kallikrein 5 cleaving the H1 and H3 subtypes most efficiently and kallikrein 12 cleaving the H1 and H2 subtypes most efficiently. Cleavage analysis using HA cleavage site peptide mimics revealed that the amino acids neighboring the arginine cleavage site affect cleavage efficiency. Additionally, the thrombolytic zymogens plasminogen, urokinase, and plasma kallikrein have all been shown to cleave and activate influenza but are found circulating mainly as inactive precursors. Kallikrein 5 and kallikrein 12 were examined for their ability to activate the thrombolytic zymogens, and both resulted in activation of each zymogen, with kallikrein 12 being a more potent activator. Activation of the thrombolytic zymogens may therefore allow for both direct and indirect activation of the HA of human-adapted influenza viruses by kallikrein 5 and kallikrein 12.
流感病毒复制周期的一个关键步骤是 HA 前体的裂解激活。流感 HA 的裂解激活使融合与宿主内体，允许病毒基因组释放到宿主细胞中。迄今为止，研究已经确定，HA 的激活是由胰蛋白酶样宿主细胞蛋白酶以及尚未确定的细菌蛋白酶驱动的。尽管能够激活 HA 的宿主蛋白酶的数量在不断增加，但仍不确定哪些分泌蛋白酶能够支持流感的多轮复制。在这项研究中，我们已经确定激肽释放酶相关肽酶 5 和 12 从人类呼吸道分泌出来，并具有裂解和激活 H1、H2 和 H3 亚型 HA 的能力。每种肽酶似乎对特定的流感亚型都有偏好，其中激肽释放酶 5 最有效地裂解 H1 和 H3 亚型，而激肽释放酶 12 最有效地裂解 H1 和 H2 亚型。使用 HA 裂解位点肽模拟物进行的裂解分析表明，紧邻精氨酸裂解位点的氨基酸会影响裂解效率。此外，纤溶酶原、尿激酶和血浆激肽原等血栓溶解酶原已被证明可以裂解和激活流感，但主要以无活性前体形式循环。研究了激肽释放酶 5 和激肽释放酶 12 激活血栓溶解酶原的能力，结果都导致每个酶原的激活，激肽释放酶 12 是更有效的激活剂。因此，激肽释放酶 5 和激肽释放酶 12 可能允许纤溶酶原直接和间接激活适应人类的流感病毒的 HA。
