Mix D, Winslow G M
Wadsworth Center for Laboratories and Research, New York State Department of Health, Albany 12201-2002, USA.
J Exp Med. 1996 Oct 1;184(4):1549-54. doi: 10.1084/jem.184.4.1549.
Mouse mammary tumor virus (MMTV) superantigens (vSAg) undergo proteolytic processing at residues that have been demonstrated in vitro to be recognition sites for the endoprotease furin. To examine the role of furin in the presentation of vSAg7 to T cells, the vSAg7 and class II MHC IEk genes were introduced into Chinese Hamster Ovary (CHO) cells (furin-positive) and into a furin-negative CHO variant (FD11). Both transfected cell lines efficiently presented peptide antigen and bacterial superantigens to T cell hybridomas. However, while the furin-positive cells presented vSAg7 well, the furin-negative cells presented poorly. Transient transfection of the furin-negative cells with an expression plasmid containing the furin gene restored the ability to present vSAg7 efficiently. The marginal presentation of vSAg7 observed using the furin-negative transfectants was eliminated after culture with the protease inhibitor leupeptin, suggesting that one or more endoproteases other than furin have a detectable but limited capacity to proteolytically activate vSAg7. Biochemical analyses revealed that vSAg7 was largely unprocessed in the absence of furin. Thus, viral superantigens, unlike bacterial superantigens, require proteolytic processing to activate T cells.
小鼠乳腺肿瘤病毒（MMTV）超抗原（vSAg）在体外已被证明是内切蛋白酶弗林蛋白酶识别位点的残基处进行蛋白水解加工。为了研究弗林蛋白酶在向T细胞呈递vSAg7中的作用，将vSAg7和II类MHC IEk基因导入中国仓鼠卵巢（CHO）细胞（弗林蛋白酶阳性）和弗林蛋白酶阴性的CHO变体（FD11）中。两种转染细胞系都能有效地将肽抗原和细菌超抗原呈递给T细胞杂交瘤。然而，虽然弗林蛋白酶阳性细胞能很好地呈递vSAg7，但弗林蛋白酶阴性细胞的呈递效果较差。用含有弗林蛋白酶基因的表达质粒对弗林蛋白酶阴性细胞进行瞬时转染，恢复了其有效呈递vSAg7的能力。在用蛋白酶抑制剂亮肽素培养后，使用弗林蛋白酶阴性转染体观察到的vSAg7的少量呈递被消除，这表明除弗林蛋白酶外的一种或多种内切蛋白酶具有可检测但有限的蛋白水解激活vSAg7的能力。生化分析表明，在没有弗林蛋白酶的情况下，vSAg7基本未被加工。因此，与细菌超抗原不同，病毒超抗原需要蛋白水解加工来激活T细胞。
