The Phosphoinositide-Gated Lysosomal Ca2+ Channel, TRPML1, Is Required for Phagosome Maturation
The Phosphoinositide-Gated Lysosomal Ca2+ Channel, TRPML1, Is Required for Phagosome Maturation
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DOI：
10.1111/tra.12303
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发表时间：
2015-09-01
期刊：
影响因子：
4.5
通讯作者：
Botelho, Roberto J.
中科院分区：
文献类型：
--
作者：
Dayam, Roya M.;Saric, Amra;Botelho, Roberto J.
巨噬细胞内化并隔离病原体进入吞噬体。吞噬体然后依次与内体和溶酶体融合，转化为降解性吞噬溶酶体。吞噬体成熟是一个复杂的过程，需要包括磷酸肌醇脂质在内的内体途径的调节剂。分别控制早期内体和晚期内溶酶体的磷脂酰肌醇-3-磷酸和磷脂酰肌醇-3，5-二磷酸（PtdIns（3，5）P-2）都是吞噬体成熟所必需的。抑制PIKfyve（其合成PtdIns（3，5）P-2）阻断吞噬体-溶酶体融合并减弱吞噬体的降解能力。然而，尚不清楚PIKfyve和PtdIns（3，5）P-2如何参与吞噬体成熟。TRPML 1是PtdIns（3，5）P-2门控的溶酶体钙通道。由于Ca 2+触发膜融合，我们假设TRPML 1有助于介导吞噬体-溶酶体融合。使用Fc受体介导的吞噬作用作为模型，我们描述了我们的研究表明，沉默的TRPML 1阻碍吞噬体收购溶酶体标志物，并降低了吞噬体的杀菌性能。具体而言，从TRPML 1沉默细胞分离的吞噬体用停靠但不融合的溶酶体装饰。我们可以拯救吞噬体成熟TRPML 1沉默和PIKfyve抑制细胞通过强制钙离子释放离子霉素。我们还提供了证据表明，胞浆Ca 2+浓度增加后，吞噬作用的方式依赖于TRPML 1和PIKfyve。总之，我们提出了一个模型，其中PIKfyve和PtdIns（3，5）P-2激活TRPML 1以诱导吞噬体-溶酶体融合。
Macrophages internalize and sequester pathogens into a phagosome. Phagosomes then sequentially fuse with endosomes and lysosomes, converting into degradative phagolysosomes. Phagosome maturation is a complex process that requires regulators of the endosomal pathway including the phosphoinositide lipids. Phosphatidylinositol-3-phosphate and phosphatidylinositol-3,5-bisphosphate (PtdIns(3,5)P-2), which respectively control early endosomes and late endolysosomes, are both required for phagosome maturation. Inhibition of PIKfyve, which synthesizes PtdIns(3,5)P-2, blocked phagosome-lysosome fusion and abated the degradative capacity of phagosomes. However, it is not known how PIKfyve and PtdIns(3,5)P-2 participate in phagosome maturation. TRPML1 is a PtdIns(3,5)P-2-gated lysosomal Ca2+ channel. Because Ca2+ triggers membrane fusion, we postulated that TRPML1 helps mediate phagosome-lysosome fusion. Using Fc receptor-mediated phagocytosis as a model, we describe our research showing that silencing of TRPML1 hindered phagosome acquisition of lysosomal markers and reduced the bactericidal properties of phagosomes. Specifically, phagosomes isolated from TRPML1-silenced cells were decorated with lysosomes that docked but did not fuse. We could rescue phagosome maturation in TRPML1-silenced and PIKfyve-inhibited cells by forcible Ca2+ release with ionomycin. We also provide evidence that cytosolic Ca2+ concentration increases upon phagocytosis in a manner dependent on TRPML1 and PIKfyve. Overall, we propose a model where PIKfyve and PtdIns(3,5)P-2 activate TRPML1 to induce phagosome-lysosome fusion.