CEACAM1 negatively regulates IL-1β production in LPS activated neutrophils by recruiting SHP-1 to a SYK-TLR4-CEACAM1 complex.
CEACAM1 negatively regulates IL-1β production in LPS activated neutrophils by recruiting SHP-1 to a SYK-TLR4-CEACAM1 complex.
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DOI：
10.1371/journal.ppat.1002597
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发表时间：
2012
期刊：
影响因子：
6.7
通讯作者：
Shively JE
中科院分区：
文献类型：
--
作者：
Lu R;Pan H;Shively JE
LPS 激活的中性粒细胞通过激活 TLR-4 分泌 IL-1β。根据对巨噬细胞的研究，Syk 激活调节的 ROS 和溶酶体不稳定也可能参与其中。由于中性粒细胞富含含有 ITIM 的辅助受体 CEACAM1 表达，并且革兰氏阴性菌（例如奈瑟菌）利用 CEACAM1 作为抑制炎症的受体，因此我们假设 LPS 处理的中性粒细胞中 IL-1β 的总体产生可能受到 CEACAM1 的负调节。我们发现 LPS 处理的中性粒细胞诱导 Syk 磷酸化，导致形成包括 TLR4、p-Syk 和 p-CEACAM1 的复合物，该复合物反过来又招募抑制性磷酸酶 SHP-1。 LPS 处理会导致中性粒细胞中 ROS 产生、溶酶体损伤、caspase-1 激活和 IL-1β 分泌。 Ceacam1−/− 中性粒细胞中缺乏这种调节导致对 LPS 的反应导致 IL-1β 的过度产生。 IL-1β 的过度产生可以通过体内重建野生型而非 ITIM 突变的 CEACAM1 骨髓干细胞来消除。通过激酶抑制剂或 RNAi 阻断 Syk 激活可减少 Ceacam1−/− 中性粒细胞中的 Syk 磷酸化、溶酶体不稳定、ROS 产生和 caspase-1 激活。我们得出的结论是，LPS 处理中性粒细胞会触发 TLR4 与 pSyk 和 pCEACAM1 形成复合物，该复合物在将 SHP-1 募集到 pCEACAM1 的 ITIM 后，抑制炎症小体产生 IL-1β。因此，CEACAM1 可以微调 LPS 处理的中性粒细胞中 IL-1β 的产生，这解释了为什么额外利用 CEACAM1 作为病原体受体会进一步抑制炎症。病原体通常通过直接结合并抑制中性粒细胞（感染部位积聚的大量白细胞）来逃避免疫系统。例如，引起淋病或脑膜炎的革兰氏阴性奈瑟菌病原体与中性粒细胞受体 CEACAM1 结合。革兰氏阴性细菌表达脂多糖 (LPS)，可与中性粒细胞上的 Toll 样受体 4 (TLR4) 相互作用。由于 CEACAM1 是一种抑制性受体，我们假设 LPS 对 TLR4 的激活会受到抑制。在本文中，我们证明了这种情况，并且 LPS 抑制机制涉及诱导 LPS 受体 TLR4、CEACAM1 和称为 Syk 的激活激酶之间的复合物。在 CEACAM1 存在的情况下，抑制性磷酸酶（对抗激酶）被招募到复合物中，从而阻止 Syk 的激活。净效应是抑制通常导致促炎细胞因子 IL-1β 产生的途径。我们发现这种抑制作用在 CEACAM1 缺陷的中性粒细胞中消失，导致 IL-1β 的过度产生。我们认为 CEACAM1 可以微调感染部位的正常炎症反应，防止过度炎症，但在革兰氏阴性病原体实际与中性粒细胞结合的情况下，炎症会进一步减弱，有利于感染过程。
LPS-activated neutrophils secrete IL-1β by activation of TLR-4. Based on studies in macrophages, it is likely that ROS and lysosomal destabilization regulated by Syk activation may also be involved. Since neutrophils have abundant expression of the ITIM-containing co-receptor CEACAM1 and Gram-negative bacteria such as Neisseria utilize CEACAM1 as a receptor that inhibits inflammation, we hypothesized that the overall production of IL-1β in LPS treated neutrophils may be negatively regulated by CEACAM1. We found that LPS treated neutrophils induced phosphorylation of Syk resulting in the formation of a complex including TLR4, p-Syk, and p-CEACAM1, which in turn, recruited the inhibitory phosphatase SHP-1. LPS treatment leads to ROS production, lysosomal damage, caspase-1 activation and IL-1β secretion in neutrophils. The absence of this regulation in Ceacam1−/− neutrophils led to hyper production of IL-1β in response to LPS. The hyper production of IL-1β was abrogated by in vivo reconstitution of wild type but not ITIM-mutated CEACAM1 bone marrow stem cells. Blocking Syk activation by kinase inhibitors or RNAi reduced Syk phosphorylation, lysosomal destabilization, ROS production, and caspase-1 activation in Ceacam1−/− neutrophils. We conclude that LPS treatment of neutrophils triggers formation of a complex of TLR4 with pSyk and pCEACAM1, which upon recruitment of SHP-1 to the ITIMs of pCEACAM1, inhibits IL-1β production by the inflammasome. Thus, CEACAM1 fine-tunes IL-1β production in LPS treated neutrophils, explaining why the additional utilization of CEACAM1 as a pathogen receptor would further inhibit inflammation. Pathogens often evade the immune system by directly binding to and inhibiting neutrophils, abundant white cells that accumulate at the site of infection. For example Gram-negative Neisseria pathogens, such as those that cause gonorrhea or meningitis, bind the neutrophil receptor CEACAM1. Gram-negative bacteria express lipopolysaccharide (LPS) that interacts with toll-like receptor-4 (TLR4) on neutrophils. Since CEACAM1 is an inhibitory receptor, we hypothesized that LPS activation of TLR4 would be inhibited. In this paper we show that this is the case and that the mechanism of LPS inhibition involves induction of a complex between the LPS receptor TLR4, CEACAM1 and an activating kinase called Syk. In the presence of CEACAM1, an inhibitory phosphatase (opposes the kinase) is recruited to the complex that prevents the activation of Syk. The net effect is the inhibition of the pathway that normally leads to the production of the pro-inflammatory cytokine IL-1β. We show that this inhibition is lost in CEACAM1 deficient neutrophils leading to hyper production of IL-1β. We think that CEACAM1 fine-tunes the normal inflammatory response at the site of infection preventing hyper-inflammation, but in the case of Gram-negative pathogens that actually bind to neutrophils, inflammation is further blunted, favoring the infectious process.
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