Department of Medicine, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.
Sci Signal. 2010 May 18;3(122):ra38. doi: 10.1126/scisignal.2000500.
The activation and fusion of macrophages and of osteoclasts require the adaptor molecule DNAX-activating protein of 12 kD (DAP12), which contains immunoreceptor tyrosine-based activation motifs (ITAMs). TREM2 (triggering receptor expressed on myeloid cells-2) is the main DAP12-associated receptor in osteoclasts and, similar to DAP12 deficiency, loss of TREM2 in humans leads to Nasu-Hakola disease, which is characterized by bone cysts and dementia. Furthermore, in vitro experiments have shown that deficiency in DAP12 or TREM2 leads to impaired osteoclast development and the formation of mononuclear osteoclasts. Here, we demonstrate that the ligation of TREM2 activated phosphatidylinositol 3-kinase (PI3K), extracellular signal-regulated kinase 1 (ERK1) and ERK2, and the guanine nucleotide exchange factor Vav3; induced the mobilization of intracellular calcium (Ca(2+)) and the reorganization of actin; and prevented apoptosis. The signaling adaptor molecule DAP10 played a key role in the TREM2- and DAP12-dependent recruitment of PI3K to the signaling complex. Src homology 2 (SH2) domain-containing inositol phosphatase-1 (SHIP1) inhibited TREM2- and DAP12-induced signaling by binding to DAP12 in an SH2 domain-dependent manner and preventing the recruitment of PI3K to DAP12. These results demonstrate a previously uncharacterized interaction of SHIP1 with DAP12 that functionally limits TREM2- and DAP12-dependent signaling and identify a mechanism through which SHIP1 regulates key ITAM-containing receptors by directly blocking the binding and activation of PI3K.
巨噬细胞和破骨细胞的激活和融合需要衔接分子 DNAX 激活蛋白 12kD（DAP12），其包含免疫受体酪氨酸激活基序（ITAMs）。TREM2（髓样细胞触发受体-2）是破骨细胞中主要的与 DAP12 相关的受体，与 DAP12 缺乏相似，人类 TREM2 的缺失导致 Nasu-Hakola 病，其特征为骨囊肿和痴呆。此外，体外实验表明，DAP12 或 TREM2 的缺乏导致破骨细胞发育受损和单核破骨细胞的形成。在这里，我们证明 TREM2 的连接激活了磷脂酰肌醇 3-激酶（PI3K）、细胞外信号调节激酶 1（ERK1）和 ERK2，以及鸟嘌呤核苷酸交换因子 Vav3；诱导细胞内钙离子（Ca(2+)）的动员和肌动蛋白的重排；并阻止细胞凋亡。信号衔接分子 DAP10 在 TREM2 和 DAP12 依赖的 PI3K 向信号复合物募集中发挥关键作用。Src 同源 2（SH2）结构域含有肌醇磷酸酶-1（SHIP1）通过以 SH2 结构域依赖的方式与 DAP12 结合并阻止 PI3K 募集到 DAP12 来抑制 TREM2 和 DAP12 诱导的信号。这些结果证明了 SHIP1 与 DAP12 之间以前未被表征的相互作用，该相互作用通过直接阻断 PI3K 的结合和激活来功能上限制了 TREM2 和 DAP12 依赖性信号，并确定了 SHIP1 通过直接阻断 PI3K 的结合和激活来调节关键 ITAM 含有受体的机制。
