Signal Transduction of Paired Inhibitory Receptors of NK Cells and Macrophages

髓样细胞（TREM）上表达的触发受体在多种先天免疫细胞上表达，包括单核细胞、巨噬细胞、树突状细胞（DC）、中性粒细胞和破骨细胞。这些受体通过与信号链DAP12的关联将信号传递给宿主细胞。DAP12信号通路依赖于其细胞质尾部免疫受体酪氨酸激活基序（ITAM）的存在。在DAP12偶联受体的刺激下，DAP12被磷酸化并招募对下游信号传播至关重要的蛋白质。最近的研究表明，TREM家族的成员可以通过DAP12向单核细胞和巨噬细胞传递激活或抑制信号。然而，髓细胞内DAP12信号的生化性质在很大程度上未被表征，TREM基因簇的整体免疫学作用也未被表征。因此，我们采取了两方面的方法来了解TREM簇的免疫生物学。我们了解TREM在先天免疫和癌症调控中的作用的第二种方法是解剖骨髓细胞中的DAP12信号通路。我们的研究已经在巨噬细胞和单核细胞中发现了一个移动的、发育调节的信号盒。单核细胞表达两个关键的细胞内接头蛋白，T细胞活化接头（LAT）和B细胞活化接头（LAB，也称为非T细胞接头，NTAL）。我们发现，在体外单核细胞的DC或巨噬细胞成熟过程中，LAT水平下降，而LAB水平上升。我们之前的工作已经证明了LAB能够调节巨噬细胞中炎症细胞因子的产生。最近，我们已经证明树突状细胞（DC）通过LAB信号。多种DC木质素的筛选表明，真菌颗粒zymosan （Zy）可以引起强大的LAB磷酸化，而TLR刺激则不会。分离和转染研究表明，LAB磷酸化是由真菌来源的甘露侬信号通过DC细胞表面的Dectin-1引起的。有趣的是，我们发现由于核β连环蛋白水平升高，缺乏LAB的DC产生较低水平的炎症细胞因子。因此，LAB缺失小鼠的T细胞反应降低，这些小鼠更容易受到真菌感染。除了我们在先天免疫系统髓系室的信号研究外，我们还研究了TREM在与癌症相关的炎症中的作用。我们发现肿瘤相关的髓源性抑制细胞表达TREM1，并且携带4T1乳腺癌的小鼠血液中可溶性TREM1水平升高。此外，我们发现TREM2在肿瘤相关巨噬细胞上高表达，我们已经开始评估TREM2在炎症相关结肠癌中可能发挥的作用。

The Triggering Receptors Expressed on Myeloid Cells (TREM) are expressed on a variety of innate immune cells including monocytes, macrophages, dendritic cells (DC), neutrophils, and osteoclasts. These receptors deliver signals to their host cells via association with the signaling chain, DAP12. DAP12 signaling is dependent on the presence of an immunoreceptor tyrosine-based activation motif (ITAM) within its cytoplasmic tail. Upon stimulation of a DAP12-coupled receptor, DAP12 is phosphorylated and recruits proteins critical to the propagation of downstream signals. Recent work has demonstrated that members of the TREM family, via DAP12, can deliver either activation or inhibitory signals to monocytes and macrophages. However, the biochemical nature of DAP12 signaling within myeloid cells is largely uncharacterized as is the overall immunological role of the TREM gene cluster. Thus, we have taken a bipartite approach to understand the immunobiology of the TREM cluster. Our second approach to understanding the role of TREM in regulation of innate immunity and cancer is dissection of the DAP12 signaling pathway in myeloid cells. Our studies have identified a shifting, developmentally regulated signaling cassette in macrophages and monocytes. Monocytes express two key intracellular adaptor proteins, the Linker for Activation of T cells (LAT) and the Linker for Activation of B cells (LAB, also known as the Non-T cell Adaptor, NTAL). We find that during maturation of DC or macrophages from monocytes in vitro, the levels of LAT fall whereas the levels of LAB increase. Our previous work had demonstrated the ability of LAB to regulate inflammatory cytokine production in macrophages. More recently, we have demonstrated that dendritic cells (DC) signal via LAB. A screen of multiple DC lignads suggested that the fungal particle zymosan (Zy) could elicit robust LAB phosphorylation whereas TLR stimulation does not. Fractionation and transfection studies demonstrated that LAB phosphorylation was caused by fungal-derived mannons signaling via Dectin-1 on the DC cell surface. Interestingly, we found that DC lacking LAB produced lower levels of inflammatory cytokine due to increased levels of nuclear beta catenin. Accordingly, T cell responses are reduced in LAB null mice and these mice are more susceptible to fungal infection.In addition to our signaling studies in the myeloid compartment of the innate immune system we study the role of the TREM in the inflammation associated with cancer. We find that tumor associated myeloid-derived suppressor cells express TREM1 and that mice harboring 4T1 breast cancers have elevated levels of soluble (s)TREM1 in their blood. In addition, we find high expression of TREM2 on tumor associated macrophages and we have begun to assess the role that TREM2 may play in inflammation associated cancer of the colon.