Research Group Phagosome Biology, Helmholtz Centre for Infection Research, 38124 Braunschweig, Germany.
Proc Natl Acad Sci U S A. 2012 Dec 11;109(50):20485-90. doi: 10.1073/pnas.1206811109. Epub 2012 Nov 28.
Phagosome maturation is an essential part of the innate and adaptive immune response. Although it is well established that several Ras-related proteins in brain (Rab) proteins become associated to phagosomes, little is known about how these phagosomal Rab proteins influence phagosome maturation. Here, we show a specific role for Rab34 and mammalian uncoordinated 13-2 (Munc13-2) in phagolysosome biogenesis and cargo delivery. Rab34 knockdown impaired the fusion of phagosomes with late endosomes/lysosomes and high levels of active Rab34 promoted this process. We demonstrate that Rab34 enhances phagosome maturation independently of Rab7 and coordinates phagolysosome biogenesis through size-selective transfer of late endosomal/lysosomal cargo into phagosomes. More importantly, we show that Rab34 mediates phagosome maturation through the recruitment of the protein Munc13-2. Finally, we report that the alternative maturation pathway controlled by Rab34 is critical for mycobacterial killing because Rab34 silencing resulted in mycobacterial survival, and Rab34 expression led to mycobacterial killing. Altogether, our studies uncover Rab34/Munc13-2 as a critical part of an alternative Rab7-independent phagosome maturation machinery and lysosome-mediated killing of mycobacteria.
吞噬体成熟是先天和适应性免疫反应的重要组成部分。尽管已经确定大脑中的几种 Ras 相关蛋白（Rab）与吞噬体相关，但对于这些吞噬体 Rab 蛋白如何影响吞噬体成熟知之甚少。在这里，我们显示 Rab34 和哺乳动物协调蛋白 13-2（Munc13-2）在吞噬溶酶体发生和货物传递中具有特定作用。Rab34 敲低会损害吞噬体与晚期内体/溶酶体的融合，而高水平的活性 Rab34 促进了这一过程。我们证明 Rab34 可独立于 Rab7 增强吞噬体成熟，并通过大小选择性将晚期内体/溶酶体货物转移到吞噬体中来协调吞噬溶酶体的发生。更重要的是，我们表明 Rab34 通过募集蛋白 Munc13-2 来介导吞噬体成熟。最后，我们报告说，Rab34 控制的替代成熟途径对于分枝杆菌的杀伤至关重要，因为 Rab34 沉默导致分枝杆菌存活，而 Rab34 表达导致分枝杆菌杀伤。总之，我们的研究揭示了 Rab34/Munc13-2 是一种替代 Rab7 独立的吞噬体成熟机制和溶酶体介导的分枝杆菌杀伤的关键部分。
