Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, California, USA.
Institute for Immunology, University of California, Irvine, Irvine, California, USA.
mBio. 2021 Jan 26;12(1):e02031-20. doi: 10.1128/mBio.02031-20.
is an intracellular protozoan parasite that has the remarkable ability to infect and replicate in neutrophils, immune cells with an arsenal of antimicrobial effector mechanisms. We report that infection extends the life span of primary human peripheral blood neutrophils by delaying spontaneous apoptosis, serum starvation-induced apoptosis, and tumor necrosis alpha (TNF-α)-mediated apoptosis. blockade of apoptosis was associated with an inhibition of processing and activation of the apoptotic caspases caspase-8 and -3, decreased phosphatidylserine exposure on the plasma membrane, and reduced cell death. We performed a global transcriptome analysis of -infected peripheral blood neutrophils using RNA sequencing (RNA-Seq) and identified gene expression changes associated with DNA replication and DNA repair pathways, which in mature neutrophils are indicative of changes in regulators of cell survival. Consistent with the RNA-Seq data, infection upregulated transcript and protein expression of PCNA, which is found in the cytosol of human neutrophils, where it functions as a key inhibitor of apoptotic pro-caspases. Infection of neutrophils resulted in increased interaction of PCNA with pro-caspase-3. Inhibition of this interaction with an AlkB homologue 2 PCNA-interacting motif (APIM) peptide reversed the infection-induced delay in cell death. Taken together, these findings indicate a novel strategy by which manipulates cell life span in primary human neutrophils, which may allow the parasite to maintain an intracellular replicative niche and avoid immune clearance. is an obligate intracellular parasite that can cause life-threatening disease in immunocompromised individuals and in the developing fetus. Interestingly, has evolved strategies to successfully manipulate the host immune system to establish a productive infection and evade host defense mechanisms. Although it is well documented that neutrophils are mobilized during acute infection and infiltrate the site of infection, these cells can also be actively infected by and serve as a replicative niche for the parasite. However, there is a limited understanding of the molecular processes occurring within infected neutrophils. This study reveals that extends the life span of human neutrophils by inducing the expression of PCNA, which prevents activation of apoptotic caspases, thus delaying apoptosis. This strategy may allow the parasite to preserve its replicative intracellular niche.
刚地弓形虫是一种细胞内原生动物寄生虫，具有感染和在中性粒细胞中复制的显著能力，中性粒细胞是具有一系列抗菌效应机制的免疫细胞。我们报告称，感染通过延迟自发性细胞凋亡、血清饥饿诱导的细胞凋亡和肿瘤坏死因子-α（TNF-α）介导的细胞凋亡来延长原代人外周血中性粒细胞的寿命。凋亡的阻断与凋亡半胱氨酸蛋白酶 caspase-8 和 caspase-3 的加工和激活的抑制、质膜上磷脂酰丝氨酸暴露的减少以及细胞死亡的减少有关。我们使用 RNA 测序（RNA-Seq）对感染的外周血中性粒细胞进行了全转录组分析，并鉴定了与 DNA 复制和 DNA 修复途径相关的基因表达变化，这些变化在成熟中性粒细胞中表明细胞存活调节剂的变化。与 RNA-Seq 数据一致，感染上调了 PCNA 的转录和蛋白表达，PCNA 存在于人中性粒细胞的细胞质中，在那里它作为凋亡前半胱氨酸蛋白酶的关键抑制剂发挥作用。感染中性粒细胞导致 PCNA 与前半胱氨酸蛋白酶-3 的相互作用增加。用 AlkB 同源物 2 PCNA 相互作用模体（APIM）肽抑制这种相互作用可逆转感染诱导的细胞死亡延迟。总之，这些发现表明，弓形虫通过操纵原代人中性粒细胞的寿命来操纵细胞寿命，这可能使寄生虫能够维持细胞内复制龛并避免免疫清除。弓形虫是一种专性细胞内寄生虫，可在免疫功能低下的个体和发育中的胎儿中引起危及生命的疾病。有趣的是，弓形虫已经进化出策略来成功地操纵宿主免疫系统，以建立有性感染并逃避宿主防御机制。尽管众所周知，中性粒细胞在急性弓形虫感染期间被动员并浸润感染部位，但这些细胞也可以被弓形虫主动感染，并成为寄生虫的复制龛。然而，对于感染中性粒细胞中发生的分子过程知之甚少。这项研究表明，弓形虫通过诱导 PCNA 的表达来延长人中性粒细胞的寿命，从而防止凋亡半胱氨酸蛋白酶的激活，从而延迟细胞凋亡。这种策略可能使寄生虫能够维持其复制的细胞内龛。
