ppat.1013974.t001 -

As a first line of host defense, macrophages must be able to effectively sense and respond to diverse types of pathogens, and while a particular response may be beneficial in some circumstances, it can be detrimental in others. Upon infection, Mycobacterium tuberculosis (Mtb) induces proinflammatory cytokines and activates antibacterial responses. Surprisingly, Mtb also triggers antiviral responses that actually hinder the ability of macrophages to restrict Mtb growth. In Mtb-infected macrophages, the ubiquitin ligase CBL suppresses antiviral responses and preserves the antibacterial capacity of the macrophage. However, the mechanisms by which CBL regulates immune signaling are unknown. We found that CBL controls responses to multiple immune stimuli and broadly suppresses the expression of antiviral response genes. We used mass spectrometry to identify potential CBL substrates, and found, in total, over 46,000 ubiquitylated peptides in Mtb-infected macrophages, including roughly 400 peptides with CBL-dependent ubiquitylation. We then performed genetic interaction analysis of CBL and its putative substrates, and identified the Fas-associated factor 2 (FAF2) adapter protein as a key signaling molecule downstream of CBL. Together, these analyses reveal thousands of new ubiquitin-mediated signaling events and identify an important new regulator of immune signaling.作为宿主防御的第一道防线，巨噬细胞必须能够有效感知并响应多种病原体。尽管特定的免疫应答在某些情境下有益，但在另一些情境下却可能产生有害影响。当宿主巨噬细胞感染结核分枝杆菌（Mycobacterium tuberculosis, Mtb）后，会诱导促炎细胞因子产生并激活抗菌应答。令人意外的是，Mtb还会触发抗病毒应答，而这类应答实际上会削弱巨噬细胞限制Mtb增殖的能力。在感染Mtb的巨噬细胞中，泛素连接酶CBL（ubiquitin ligase CBL）可抑制抗病毒应答，并维持巨噬细胞的抗菌能力。然而，CBL调控免疫信号转导的具体机制仍未阐明。本研究发现，CBL可调控机体对多种免疫刺激的应答，并广泛抑制抗病毒应答基因的表达。我们采用质谱法（mass spectrometry）鉴定了潜在的CBL底物，总计在感染Mtb的巨噬细胞中检出超过46000条泛素化肽段，其中约400条肽段的泛素化修饰依赖CBL。随后，我们针对CBL及其推定底物开展了遗传互作分析，并鉴定出Fas相关因子2（Fas-associated factor 2, FAF2）衔接蛋白为CBL下游的关键信号分子。综上，本系列分析揭示了数千种全新的泛素介导信号转导事件，并鉴定出一类重要的免疫信号转导新型调控因子。