Trypanosome Lysis by Human Haptoglobin Related Protein

描述(由申请人提供)：布鲁氏锥虫引起牛Nagana病，但由于其对正常人类血清的细胞溶解活性敏感，对人类不具传染性。这种活性归功于人结合珠蛋白相关蛋白(HPR)。HPR在人血清中以高密度脂蛋白相关的载脂蛋白、锥虫裂解因子-I(TLF-L)或称为TLF-2的大蛋白复合体的形式存在。TLF-L介导的布氏支原体裂解的细胞途径包括受体介导的与锥虫表面结合、内吞和溶酶体靶向。TLF-L通过铁依赖反应使溶酶体膜不稳定，导致溶酶体破坏和细胞溶解，从而杀死布鲁氏支原体。人类昏睡病寄生虫布氏锥虫对TLF介导的裂解具有抵抗力。罗氏锥虫对TLf-L的抗性机制与TLf-L摄取和胞内转运减少有关。血清耐药相关蛋白(SRA)的表达足以在体外和体内产生对TLF-L的抗性。该蛋白是一种59 kDa的膜蛋白，属于VSG基因家族成员。SRA的表达仅限于人类昏睡病锥体，其表达受转录调控。在拟议的研究中，我们将继续研究J-IPR杀灭锥虫的生化和分子机制，以及SRA保护TLF-L杀灭罗氏锥虫的机制。本建议的具体目的如下：(1)确定hPR杀伤锥虫的结构和生化要求；(2)建立人hPR的转基因小鼠模型；(3)确定SRA抑制hPR杀伤布鲁氏锥虫的细胞和生化机制。 我们的长期目标仍然是探索HPR的修饰或其被人类昏睡病锥体摄取的可能性，可能导致基于这种强大的先天杀伤因子发现治疗这种日益重要的人类疾病的新方法。

DESCRIPTION (provided by the applicant): Trypanosoma brucei brucei causes the bovine disease Nagana but is non-infectious to humans because of its susceptibility to the cytolytic activity of normal human serum. This activity is due to human haptoglobin related protein (HPR). HPR is found in human sera either as an HDL associated apolipoprotein, trypanosome Lytic factor-i (TLF-l), or as a large protein complex termed TLF-2. The cellular pathway of TLF-l mediated lysis of T b. brucei includes receptor mediated binding to the trypanosome surface, endocytosis and lysosomal targeting. TLF-l kills T b. brucei by destabilization of the lysosomal membrane in an iron dependent reaction that leads to lysosome disruption and cell lysis. The human sleeping sickness parasite Trypanosoma brucei rhodesiense is resistant to TLF-mediated lysis. The mechanism of T b. rhodesiense resistance to TLF-l is associated with a reduction in TLF-l uptake and intracellular trafficking. Expression of a single protein, Serum Resistance Associated (SRA) is sufficient to confer resistance to TLF-l in vitro and in vivo. This protein is a 59 kDa membrane protein that is a member of the VSG gene family. SRA expression is restricted to human sleeping sickness trypanosomes and its expression is transcriptionally regulated. In the proposed studies we will continue to investigate the biochemical and molecular mechanism of J-IPR killing of trypanosomes and the mechanism of SRA protection from TLF-l killing in T b. rhodesiense. The specific aims of this proposal are the following: (1) Determine the structural and biochemical requirements for HPR killing of trypanosomes; (2) Develop a transgenic mouse model for human HPR; (3) Determine the cellular and biochemical mechanisms of SRA inhibition of HPR killing of T b. brucei. Our long-term goals remain to explore the possibilities that modification of HPR or its uptake byhuman sleeping sickness trypanosomes may lead to the identification of novel approaches for treatment of this increasingly important human disease based on this potent innate killing factor.