Division of Immunology, Infection, and Inflammation, University of Glasgow, Glasgow G12 8TA, Scotland, United Kingdom.
J Biol Chem. 2010 Apr 2;285(14):10508-18. doi: 10.1074/jbc.M109.067298. Epub 2010 Jan 22.
Many Gram-negative bacteria possess a type III secretion system (TTSS( paragraph sign)) that can activate the NLRC4 inflammasome, process caspase-1 and lead to secretion of mature IL-1beta. This is dependent on the presence of intracellular flagellin. Previous reports have suggested that this activation is independent of extracellular K(+) and not accompanied by leakage of K(+) from the cell, in contrast to activation of the NLRP3 inflammasome. However, non-flagellated strains of Pseudomonas aeruginosa are able to activate NLRC4, suggesting that formation of a pore in the cell membrane by the TTSS apparatus may be sufficient for inflammasome activation. Thus, we set out to determine if extracellular K(+) influenced P. aeruginosa inflammasome activation. We found that raising extracellular K(+) prevented TTSS NLRC4 activation by the non-flagellated P. aeruginosa strain PA103DeltaUDeltaT at concentrations above 90 mm, higher than those reported to inhibit NLRP3 activation. Infection was accompanied by efflux of K(+) from a minority of cells as determined using the K(+)-sensitive fluorophore PBFI, but no formation of a leaky pore. We obtained exactly the same results following infection with Salmonella typhimurium, previously described as independent of extracellular K(+). The inhibitory effect of raised extracellular K(+) on NLRC4 activation thus reflects a requirement for a decrease in intracellular K(+) for this inflammasome component as well as that described for NLRP3.
许多革兰氏阴性菌都拥有一种 III 型分泌系统（TTSS），它可以激活 NLRC4 炎症小体，切割半胱天冬酶-1 并导致成熟的 IL-1β分泌。这依赖于细胞内鞭毛蛋白的存在。之前的报道表明，这种激活与细胞外 K+无关，也不会伴随 K+从细胞中泄漏，这与 NLRP3 炎症小体的激活不同。然而，非鞭毛型铜绿假单胞菌能够激活 NLRC4，这表明 TTSS 装置在细胞膜上形成孔可能足以激活炎症小体。因此，我们着手确定细胞外 K+是否影响铜绿假单胞菌炎症小体的激活。我们发现，在高于 90mM 的浓度下，升高细胞外 K+会阻止非鞭毛型铜绿假单胞菌 PA103DeltaUDeltaT 菌株 TTSS NLRC4 的激活，这一浓度高于抑制 NLRP3 激活的报道浓度。感染伴随着少数细胞中 K+的外流，这可以通过 K+敏感荧光探针 PBFI 来确定，但没有形成渗漏孔。我们在感染鼠伤寒沙门氏菌时得到了完全相同的结果，之前的研究表明该菌的激活不依赖于细胞外 K+。因此，升高的细胞外 K+对 NLRC4 激活的抑制作用反映了细胞内 K+的减少对该炎症小体成分的要求，这与 NLRP3 的描述相同。
