The Gamma Interferon (IFN-γ)-Inducible GTP-Binding Protein IGTP Is Necessary for Toxoplasma Vacuolar Disruption and Induces Parasite Egression in IFN-γ-Stimulated Astrocytes
The Gamma Interferon (IFN-γ)-Inducible GTP-Binding Protein IGTP Is Necessary for Toxoplasma Vacuolar Disruption and Induces Parasite Egression in IFN-γ-Stimulated Astrocytes
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DOI：
10.1128/iai.01288-07
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发表时间：
2008-11-01
影响因子：
3.1
通讯作者：
Halonen, S. K.
中科院分区：
文献类型：
--
作者：
Melzer, T.;Duffy, A.;Halonen, S. K.
弓形虫是一种常见的中枢神经系统感染，发生在免疫系统免疫受损的人中，如艾滋病患者。干扰素是介导弓形虫免疫保护的主要细胞因子。我们以前的研究发现，干扰素通过干扰素诱导的GTP结合蛋白(IGTP)依赖的机制显著抑制星形胶质细胞中的弓形虫。IGTP依赖的、干扰素-γ刺激的抑制作用尚不清楚，但最近的研究发现，IGTP可诱导巨噬细胞内寄生虫空泡(PV)的破坏。在本研究中，我们进一步研究了干扰素-γ抑制的机制以及IGTP在小鼠星形胶质细胞空泡破裂中的作用。空泡破裂依赖于IGTP，因为在IGTP缺陷(-/-)星形胶质细胞中没有观察到PV破裂，而在IGTP(-/-)星形胶质细胞中可以诱导PV破裂。使用绿色荧光蛋白-IGTP进行的活细胞成像研究发现，IGTP在入侵后早期通过宿主细胞内质网(ER)传递到PV，并且IGTP在PV破坏之前在液泡上浓缩成囊泡状结构，这表明IGTP参与了PV破坏。寄生虫的空泡内运动恰好发生在PV中断之前。在某些情况下，干扰素-伽马可诱导寄生虫外泄。电子显微镜和免疫荧光研究表明，宿主细胞内质网在空泡破裂之前与PV融合。在这些结果的基础上，我们假设了ER/PV融合是PV破坏中的一个关键事件的机制。ER与PV的融合，释放钙到空泡中，也可能是空泡内寄生虫移动和干扰素-γ诱导的寄生虫外泄的机制。
Toxoplasma gondii is a common central nervous system infection in individuals with immunocompromised immune systems, such as AIDS patients. Gamma interferon (IFN-gamma) is the main cytokine mediating protection against T. gondii. Our previous studies found that IFN-gamma significantly inhibits T. gondii in astrocytes via an IFN-gamma-inducible GTP-binding protein (IGTP)-dependent mechanism. The IGTP-dependent-, IFN-gamma-stimulated inhibition is not understood, but recent studies found that IGTP induces disruption of the parasitophorous vacuole (PV) in macrophages. In the current study, we have further investigated the mechanism of IFN-gamma inhibition and the role of IGTP in the vacuolar disruption in murine astrocytes. Vacuolar disruption was found to be dependent upon IGTP, as PV disruption was not observed in IGTP-deficient (IGTP(-/-)) astrocytes and PV disruption could be induced in IGTP(-/-) astrocytes transfected with IGTP. Live-cell imaging studies using green fluorescent protein-IGTP found that IGTP is delivered to the PV via the host cell endoplasmic reticulum (ER) early after invasion and that IGTP condenses into vesicle-like structures on the vacuole just prior to PV disruption, suggesting that IGTP is involved in PV disruption. Intravacuolar movement of the parasite occurred just prior to PV disruption. In some instances, IFN-gamma induced parasite egression. Electron microscopy and immunofluorescence studies indicate that the host cell ER fuses with the PV prior to vacuolar disruption. On the basis of these results, we postulate a mechanism by which ER/PV fusion is a crucial event in PV disruption. Fusion of the ER with the PV, releasing calcium into the vacuole, may also be the mechanism by which intravacuolar parasite movement and IFN-gamma-induced parasite egression occur.