Department of Microbiology and Immunology, University of Arkansas for Medical Sciences, Little Rock, Arkansas, USA.
Infect Immun. 2014 Jun;82(6):2229-38. doi: 10.1128/IAI.01236-13. Epub 2014 Mar 18.
Coxiella burnetii is an intracellular Gram-negative bacterium that causes human Q fever, a flu-like disease that can progress to chronic, life-threatening endocarditis. In humans, C. burnetii infects alveolar macrophages and promotes phagosomal fusion with autophagosomes and lysosomes, establishing a unique parasitophorous vacuole (PV) in which to replicate. The pathogen uses a Dot/Icm type IV secretion system (T4SS) to deliver effector proteins to the host cytoplasm, where they alter cellular processes to benefit the pathogen. The T4SS is required for PV expansion and prevention of apoptosis, but little else is known about the role of the system during intracellular growth. Recent reports suggest that C. burnetii actively recruits autophagosomes to the PV to deliver nutrients to the pathogen and provide membrane for the expanding vacuole. In this study, we examined the role of the T4SS in mediating PV interactions with autophagosomes. We found that the autophagy-related proteins LC3 and p62 localized to wild-type PV but not to T4SS mutant organism-containing phagosomes in human macrophage-like cells, primary human alveolar macrophages, and Chinese hamster ovary cells. However, while lipidated LC3 levels were elevated regardless of T4SS activity, no p62 turnover was observed during C. burnetii growth in macrophages, suggesting that the pathogen recruits preformed autophagosomes. When the T4SS was activated 24 h after infection, autophagosome recruitment ensued, indicating that autophagosome interactions are dispensable for initial PV maturation to a phagolysosome-like compartment but are involved in vacuole expansion. Together, these results demonstrate that C. burnetii actively directs PV-autophagosome interactions by using the Dot/Icm T4SS.
贝氏考克斯氏体是一种细胞内革兰氏阴性细菌，可引起人类 Q 热，即类似流感的疾病，可进展为慢性、危及生命的心内膜炎。在人类中，C. burnetii 感染肺泡巨噬细胞，并促进吞噬体与自噬体和溶酶体融合，在其中建立一个独特的寄生空泡（PV）进行复制。病原体利用 Dot/Icm 型 IV 型分泌系统（T4SS）将效应蛋白输送到宿主细胞质，在那里它们改变细胞过程以利于病原体。该 T4SS 对于 PV 的扩张和防止细胞凋亡是必需的，但对于该系统在细胞内生长过程中的作用知之甚少。最近的报告表明，C. burnetii 积极将自噬体募集到 PV 中，以向病原体输送营养物质并为扩张的空泡提供膜。在这项研究中，我们研究了 T4SS 在介导 PV 与自噬体相互作用中的作用。我们发现，自噬相关蛋白 LC3 和 p62 定位于野生型 PV 中，但不在人类巨噬样细胞、原代人肺泡巨噬细胞和中国仓鼠卵巢细胞中含 T4SS 突变体的吞噬体中。然而，尽管脂质化 LC3 水平升高与 T4SS 活性无关，但在巨噬细胞中 C. burnetii 生长过程中未观察到 p62 周转，这表明病原体招募了预先形成的自噬体。当 T4SS 在感染后 24 小时被激活时，自噬体的募集随之发生，这表明自噬体相互作用对于初始 PV 成熟为类似吞噬溶酶体的隔室是 dispensable 的，但参与了空泡的扩张。总之，这些结果表明，C. burnetii 通过使用 Dot/Icm T4SS 主动指导 PV-自噬体相互作用。
