Zarkik S, Decroly E, Wattiez R, Seidah N G, Burny A, Ruysschaert J M
Laboratoire de Chimie Physique des Macromolécules aux Interfaces (LCPMI) CP206/2, Université Libre de Bruxelles, Brussels, Belgium.
FEBS Lett. 1997 Apr 7;406(1-2):205-10. doi: 10.1016/s0014-5793(97)00275-5.
Intracellular proteolytic processing of bovine leukemia virus (BLV) envelope glycoprotein precursor (gp72) at the C-terminal end of the RVRR268 / site is an essential step for virus infectivity. Subtilisin/kexin-like convertases cleave proproteins at preferred RX(K/R)R / sites, including those commonly found in viral envelope glycoprotein precursors. We first demonstrated that gp72 is processed into gp51/gp30 in both CV1 cells and the furin-deficient LoVo cells, leading us to compare the ability of mammalian convertases to cleave BLV gp72 in vitro. In contrast to the inability of the neuroendocrine PC1 to cleave gp72, the convertases furin, PACE4, PC5-A and PC5-B, which process constitutively secreted precursors, can effectively cleave gp72 into gp51/gp30. N-terminal sequence analysis of the convertase-generated gp30 demonstrated that cleavage occurs at the in vivo-utilized RVRR / SPV site. Such furin-, PACE4- and PC5-mediated processing was completely inhibited by the alpha1-antitrypsin variant alpha1-PDX. Mutagenesis of the gp72 cleavage site into RVRG-TPV resulted in complete abrogation of gp72 processing by endogenous CV-1 cells and by convertases in vitro. Since our in vitro data suggest a redundancy in the ability of the convertases to cleave gp72, RT-PCR analysis was used to define the convertases expressed in B-lymphocytes, representing one of the major targets of BLV infection. Our data revealed that only furin and the newly discovered PC7 mRNAs are expressed in Raji, B-Jab and LG2 cell lines.
牛白血病病毒（BLV）包膜糖蛋白前体（gp72）在RVRR268 /位点的C末端进行细胞内蛋白水解加工是病毒感染性的关键步骤。枯草杆菌蛋白酶/克新样转化酶在优选的RX（K / R）R /位点切割前体蛋白，包括在病毒包膜糖蛋白前体中常见的那些位点。我们首先证明，gp72在CV1细胞和弗林蛋白酶缺陷型LoVo细胞中均被加工成gp51 / gp30，这使我们能够比较哺乳动物转化酶在体外切割BLV gp72的能力。与神经内分泌PC1无法切割gp72不同，加工组成型分泌前体的转化酶弗林蛋白酶、PACE4、PC5-A和PC5-B可以有效地将gp72切割成gp51 / gp30。对转化酶产生的gp30进行N末端序列分析表明，切割发生在体内利用的RVRR / SPV位点。α1-抗胰蛋白酶变体α1-PDX完全抑制了这种弗林蛋白酶、PACE4和PC5介导的加工。将gp72切割位点突变为RVRG-TPV导致内源性CV-1细胞和体外转化酶对gp72的加工完全消除。由于我们的体外数据表明转化酶切割gp72的能力存在冗余，因此使用RT-PCR分析来确定在B淋巴细胞中表达的转化酶，B淋巴细胞是BLV感染的主要靶标之一。我们的数据显示，只有弗林蛋白酶和新发现的PC7 mRNA在Raji、B-Jab和LG2细胞系中表达。
