Department of Clinical and Biological Sciences, University of Turin, AOU S. Luigi, Reg. Gonzole 10, 10043 Orbassano, Torino, Italy.
J Cell Sci. 2010 Dec 1;123(Pt 23):4039-51. doi: 10.1242/jcs.072124. Epub 2010 Nov 2.
Membrane phosphatidylinositides recruit cytosolic proteins to regulate phagocytosis, macropinocytosis and endolysosomal vesicle maturation. Here, we describe effects of inactivation of PI3K, PTEN or PLC on Escherichia coli and Legionella pneumophila uptake by the professional phagocyte Dictyostelium discoideum. We show that L. pneumophila is engulfed by macropinocytosis, a process that is partially sensitive to PI3K inactivation, unlike phagocytosis of E. coli. Both processes are blocked by PLC inhibition. Whereas E. coli is rapidly digested, Legionella proliferates intracellularly. Proliferation is blocked by constitutively expressing Nramp1, an endolysosomal iron transporter that confers resistance against invasive bacteria. Inactivation of PI3K, but not PTEN or PLC, enhances Legionella infection and suppresses the protective effect of Nramp1 overexpression. PI3K activity is restricted to early infection and is not mediated by effects on the actin cytoskeleton; rather L. pneumophila, in contrast to E. coli, subverts phosphoinositide-sensitive fusion of Legionella-containing macropinosomes with acidic vesicles, without affecting Nramp1 recruitment. A model is presented to explain how Legionella escapes fusion with acidic vesicles and Nramp1-induced resistance to pathogens.
膜磷脂酰肌醇 3-激酶（PI3K）招募胞质蛋白以调节吞噬作用、巨胞饮作用和内溶酶体囊泡成熟。在此，我们描述了 PI3K、PTEN 或 PLC 失活对专业吞噬细胞变形虫（Dictyostelium discoideum）摄取大肠杆菌和嗜肺军团菌的影响。我们表明，军团菌通过巨胞饮作用被吞噬，这一过程对 PI3K 失活部分敏感，而不像大肠杆菌的吞噬作用。这两个过程都被 PLC 抑制所阻断。虽然大肠杆菌被迅速消化，但军团菌在细胞内增殖。增殖被组成型表达 Nramp1 阻断，Nramp1 是一种内溶酶体铁转运蛋白，赋予其对侵袭性细菌的抗性。PI3K 的失活，但不是 PTEN 或 PLC 的失活，增强了军团菌的感染，并抑制了 Nramp1 过表达的保护作用。PI3K 活性仅限于早期感染，不受肌动蛋白细胞骨架效应的影响；相反，与大肠杆菌不同，嗜肺军团菌会破坏含有军团菌的巨胞饮体与酸性囊泡的磷酯酰肌醇 3-激酶（PI3K）敏感融合，而不影响 Nramp1 的募集。提出了一个模型来解释军团菌如何逃避与酸性囊泡和 Nramp1 诱导的抗病原体融合。
