Immunobiology Laboratory, Department of Zoology, University of Delhi, Delhi, 110007, India.
Department of Zoology, University of Delhi, Delhi, 110007, India.
Cell Death Dis. 2019 Feb 15;10(3):161. doi: 10.1038/s41419-019-1420-9.
Recent studies have documented the diverse role of host immunity in infection by the protozoan parasite, Toxoplasma gondii. However, the contribution of the β-catenin pathway in this process has not been explored. Here, we show that AKT-mediated phosphorylated β-catenin supports T. gondii multiplication which is arrested in the deficiency of its phosphorylation domain at S552 position. The β-catenin-TCF4 protein complex binds to the promoter region of IRF3 gene and initiates its transcription, which was also abrogated in β-catenin knockout cells. TBK-independent phosphorylation of STING(S366) and its adaptor molecule TICAM2 by phospho-AKT(T308S473) augmented downstream IRF3-dependent IDO1 transcription, which was also dependent on β-catenin. But, proteasomal degradation of IDO1 by its tyrosine phosphorylation (at Y115 and Y253) favoured parasite replication. In absence of IDO1, tryptophan was catabolized into melatonin, which supressed cellular reactive oxygen species (ROS) and boosted parasite growth. Conversely, when tyrosine phosphorylation was abolished by phosphosite mutations, IDO1 escaped its ubiquitin-mediated proteasomal degradation system (UPS) and the stable IDO1 prevented parasite replication by kynurenine synthesis. We propose that T. gondii selectively utilizes tryptophan to produce the antioxidant, melatonin, thus prolonging the survival of infected cells through functional AKT and β-catenin activity for better parasite replication. Stable IDO1 in the presence of IFN-γ catabolized tryptophan into kynurenine, promoting cell death by suppressing phospho-AKT and phospho-β-catenin levels, and circumvented parasite replication. Treatment of infected cells with kynurenine or its analogue, teriflunomide suppressed kinase activity of AKT, and phosphorylation of β-catenin triggering caspase-3 dependent apoptosis of infected cells to inhibit parasite growth. Our results demonstrate that β-catenin regulate phosphorylated STING-TICAM2-IRF3-IDO1 signalosome for a cell-intrinsic pro-parasitic role. We propose that the downstream IRF3-IDO1-reliant tryptophan catabolites and their analogues can act as effective immunotherapeutic molecules to control T. gondii replication by impairing the AKT and β-catenin axis.
最近的研究记录了宿主免疫在原生动物寄生虫弓形虫感染中的多种作用。然而，β-连环蛋白途径在这个过程中的贡献尚未被探索。在这里，我们表明 AKT 介导的磷酸化β-连环蛋白支持弓形虫的增殖，而在 S552 位置磷酸化结构域缺失的情况下，其增殖被阻断。β-连环蛋白-TCF4 蛋白复合物结合到 IRF3 基因的启动子区域并启动其转录，而在β-连环蛋白敲除细胞中，该转录也被阻断。磷酸化 AKT（T308S473）磷酸化 STING（S366）及其衔接分子 TICAM2 导致下游 IRF3 依赖性 IDO1 转录增加，这也依赖于β-连环蛋白。但是，磷酸化 AKT（T308S473）磷酸化 STING（S366）及其衔接分子 TICAM2 导致下游 IRF3 依赖性 IDO1 转录增加，这也依赖于β-连环蛋白。但是，磷酸化 AKT（T308S473）磷酸化 STING（S366）及其衔接分子 TICAM2 导致下游 IRF3 依赖性 IDO1 转录增加，这也依赖于β-连环蛋白。但是，磷酸化 AKT（T308S473）磷酸化 STING（S366）及其衔接分子 TICAM2 导致下游 IRF3 依赖性 IDO1 转录增加，这也依赖于β-连环蛋白。但是，磷酸化 AKT（T308S473）磷酸化 STING（S366）及其衔接分子 TICAM2 导致下游 IRF3 依赖性 IDO1 转录增加，这也依赖于β-连环蛋白。
由非典型蛋白激酶 TBK1 独立磷酸化的 STING（S366）和其衔接分子 TICAM2 通过磷酸化 AKT（T308S473）增强下游 IRF3 依赖性 IDO1 转录，这也依赖于β-连环蛋白。但是，由磷酸化 AKT（T308S473）磷酸化的 IDO1（在 Y115 和 Y253 处的酪氨酸磷酸化）促进寄生虫复制。在 IDO1 缺失的情况下，色氨酸被代谢为褪黑素，这抑制了细胞内活性氧物种（ROS）并促进了寄生虫的生长。相反，当通过磷酸化位点突变消除酪氨酸磷酸化时，IDO1 逃脱了其泛素介导的蛋白酶体降解系统（UPS），稳定的 IDO1 通过犬尿氨酸合成防止寄生虫复制。我们提出，弓形虫选择性地利用色氨酸产生抗氧化剂褪黑素，从而通过 AKT 和β-连环蛋白活性延长感染细胞的存活时间，以更好地复制寄生虫。IFN-γ 存在时稳定的 IDO1 将色氨酸代谢为犬尿氨酸，通过抑制磷酸化 AKT 和磷酸化β-连环蛋白水平来促进细胞死亡，并避免寄生虫复制。用犬尿氨酸或其类似物（特立氟胺）处理感染细胞可抑制 AKT 的激酶活性，并触发依赖半胱天冬酶-3 的细胞凋亡，从而抑制寄生虫的生长。我们的研究结果表明，β-连环蛋白调节磷酸化 STING-TICAM2-IRF3-IDO1 信号体，以发挥细胞内有利于寄生虫的作用。我们提出，下游 IRF3-IDO1 依赖的色氨酸代谢物及其类似物可以作为有效的免疫治疗分子，通过破坏 AKT 和β-连环蛋白轴来控制弓形虫的复制。
