Palmer G H, Machado J, Fernandez P, Heussler V, Perinat T, Dobbelaere D A
Institute of Animal Pathology, University of Bern, Bern 3012, Switzerland.
Proc Natl Acad Sci U S A. 1997 Nov 11;94(23):12527-32. doi: 10.1073/pnas.94.23.12527.
Infection of cattle with the protozoan Theileria parva results in uncontrolled T lymphocyte proliferation resulting in lesions resembling multicentric lymphoma. Parasitized cells exhibit autocrine growth characterized by persistent translocation of the transcriptional regulatory factor nuclear factor kappaB (NFkappaB) to the nucleus and consequent enhanced expression of interleukin 2 and the interleukin 2 receptor. How T. parva induces persistent NFkappaB activation, required for T cell activation and proliferation, is unknown. We hypothesized that the parasite induces degradation of the IkappaB molecules which normally sequester NFkappaB in the cytoplasm and that continuous degradation requires viable parasites. Using T. parva-infected T cells, we showed that the parasite mediates continuous phosphorylation and proteolysis of IkappaBalpha. However, IkappaBalpha reaccumulated to high levels in parasitized cells, which indicated that T. parva did not alter the normal NFkappaB-mediated positive feedback loop which restores cytoplasmic IkappaBalpha. In contrast, T. parva mediated continuous degradation of IkappaBbeta resulting in persistently low cytoplasmic IkappaBbeta levels. Normal IkappaBbeta levels were only restored following T. parva killing, indicating that viable parasites are required for IkappaBbeta degradation. Treatment of T. parva-infected cells with pyrrolidine dithiocarbamate, a metal chelator, blocked both IkappaB degradation and consequent enhanced expression of NFkappaB dependent genes. However treatment using the antioxidant N-acetylcysteine had no effect on either IkappaB levels or NFkappaB activation, indicating that the parasite subverts the normal IkappaB regulatory pathway downstream of the requirement for reactive oxygen intermediates. Identification of the critical points regulated by T. parva may provide new approaches for disease control as well as increase our understanding of normal T cell function.
牛被原生动物小泰勒虫感染会导致T淋巴细胞不受控制地增殖，从而产生类似于多中心淋巴瘤的病变。被寄生的细胞表现出自分泌生长，其特征是转录调节因子核因子κB（NFκB）持续易位至细胞核，进而导致白细胞介素2和白细胞介素2受体的表达增强。小泰勒虫如何诱导T细胞活化和增殖所需的NFκB持续活化尚不清楚。我们推测，该寄生虫诱导IκB分子降解，而IκB分子通常将NFκB隔离在细胞质中，且持续降解需要存活的寄生虫。利用感染小泰勒虫的T细胞，我们发现该寄生虫介导IκBα的持续磷酸化和蛋白水解。然而，IκBα在被寄生的细胞中重新积累到高水平，这表明小泰勒虫并未改变正常的NFκB介导的正反馈回路，该回路可恢复细胞质中的IκBα。相反，小泰勒虫介导IκBβ的持续降解，导致细胞质IκBβ水平持续较低。只有在小泰勒虫被杀死后，IκBβ水平才恢复正常，这表明IκBβ降解需要存活的寄生虫。用金属螯合剂吡咯烷二硫代氨基甲酸盐处理感染小泰勒虫的细胞，可阻断IκB降解以及随之而来的NFκB依赖性基因的表达增强。然而，使用抗氧化剂N -乙酰半胱氨酸进行处理对IκB水平或NFκB活化均无影响，这表明该寄生虫在活性氧中间体需求的下游破坏了正常的IκB调节途径。确定受小泰勒虫调节的关键点可能为疾病控制提供新方法，同时增进我们对正常T细胞功能的理解。
