Cathepsin-L can resist lysis by human serum in Trypanosoma brucei brucei.
Cathepsin-L can resist lysis by human serum in Trypanosoma brucei brucei.
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DOI：
10.1371/journal.ppat.1004130
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发表时间：
2014-05
期刊：
影响因子：
6.7
通讯作者：
Horn D
中科院分区：
文献类型：
--
作者：
Alsford S;Currier RB;Guerra-Assunção JA;Clark TG;Horn D
密切相关的非洲锥虫引起致命的疾病，但显示不同的宿主范围。具体来说，布氏锥虫引起家畜的长角病，但不会感染人类，而冈比亚锥虫和罗得西亚锥虫引起人类的昏睡病。T. B.布氏杆菌不能感染人类，因为它对正常人血清中发现的称为锥虫溶解因子（TLF）1和2的先天免疫复合物敏感;两种TLF中的溶解组分是载脂蛋白-L1。T. B. gambiense和T. B.罗得西亚人现在知道，通过获得或丧失功能，但我们的理解，使T。B.对人血清裂解敏感的布氏杆菌仍然不完全。我们进行了基因组规模的RNA干扰（RNAi）文库筛选，以降低对人血清的敏感性。在仅有的四个高可信度的“命中”中，所有三个基因都是先前显示的致敏T。B.布鲁氏菌对人血清、触珠蛋白-血红蛋白受体（HpHbR）、半胱氨酸肽酶（ICP）抑制剂和溶酶体蛋白p67的作用，从而证明这些因子发挥的关键作用。鉴定的第四个基因编码具有11个跨膜结构域的预测蛋白。使用化学和遗传学方法，我们表明，ICP敏化T。B.通过调节必需的组织蛋白酶CATL（一种溶酶体半胱氨酸肽酶）将布氏杆菌转化为人血清。第二种组织蛋白酶，CATB，可能在体外培养中被抑制生长，对人血清敏感性几乎没有影响。我们的研究结果揭示了T. B.布鲁塞。他们还揭示了溶酶体蛋白质-蛋白质相互作用，使T。B.布氏杆菌对人血清中的溶解因子非常敏感，这表明CATL，一个重要的潜在药物靶点，具有抵抗这些因子的能力。非洲锥虫宿主先天免疫和抗性机制之间的相互作用对这些采采蝇传播的寄生虫的宿主范围产生了重大影响，确定了它们在人类中引起疾病的能力。基因组规模的RNAi筛选确定了一组高度限制的四个基因，使锥虫对人血清敏感：那些编码触珠蛋白-血红蛋白受体，预测的跨膜通道，溶酶体膜蛋白和半胱氨酸肽酶抑制剂。半胱氨酸肽酶的分析揭示了组织蛋白酶-L作为受抑制剂调节的蛋白酶-并且具有使寄生虫对人血清裂解具有抗性的能力。这些发现强调了寄生虫因子对宿主毒素的传递和稳定性的重要性。它们还阐明了寄生虫对蛋白水解的控制以及靶向寄生虫蛋白酶的治疗的潜在意外后果。
Closely related African trypanosomes cause lethal diseases but display distinct host ranges. Specifically, Trypanosoma brucei brucei causes nagana in livestock but fails to infect humans, while Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense cause sleeping sickness in humans. T. b. brucei fails to infect humans because it is sensitive to innate immune complexes found in normal human serum known as trypanolytic factor (TLF) 1 and 2; the lytic component is apolipoprotein-L1 in both TLFs. TLF resistance mechanisms of T. b. gambiense and T. b. rhodesiense are now known to arise through either gain or loss-of-function, but our understanding of factors that render T. b. brucei susceptible to lysis by human serum remains incomplete. We conducted a genome-scale RNA interference (RNAi) library screen for reduced sensitivity to human serum. Among only four high-confidence ‘hits’ were all three genes previously shown to sensitize T. b. brucei to human serum, the haptoglobin-haemoglobin receptor (HpHbR), inhibitor of cysteine peptidase (ICP) and the lysosomal protein, p67, thereby demonstrating the pivotal roles these factors play. The fourth gene identified encodes a predicted protein with eleven trans-membrane domains. Using chemical and genetic approaches, we show that ICP sensitizes T. b. brucei to human serum by modulating the essential cathepsin, CATL, a lysosomal cysteine peptidase. A second cathepsin, CATB, likely to be dispensable for growth in in vitro culture, has little or no impact on human-serum sensitivity. Our findings reveal major and novel determinants of human-serum sensitivity in T. b. brucei. They also shed light on the lysosomal protein-protein interactions that render T. b. brucei exquisitely sensitive to lytic factors in human serum, and indicate that CATL, an important potential drug target, has the capacity to resist these factors. The interplay among host innate immunity and resistance mechanisms in African trypanosomes has a major impact on the host range of these tsetse-fly transmitted parasites, defining their ability to cause disease in humans. A genome-scale RNAi screen identified a highly restricted set of four genes that sensitise trypanosomes to human serum: those encoding the haptoglobin-haemoglobin receptor, a predicted trans-membrane channel, a lysosomal membrane-protein and the cysteine peptidase inhibitor. An analysis of the cysteine peptidases revealed cathepsin-L as the protease regulated by the inhibitor – and with the capacity to render the parasite resistant to lysis by human serum. These findings emphasise the importance of parasite factors for the delivery and stability of host toxins. They also shed light on the control of proteolysis by parasites and potential unanticipated consequences of therapies that target the parasite proteases.
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