Department of Cell and Developmental Biology, BK21 and DRI, Seoul National University, Seoul, Korea.
J Biol Chem. 2012 Aug 24;287(35):29620-6. doi: 10.1074/jbc.M112.351239. Epub 2012 Jul 3.
Triggering receptor expressed on myeloid cells (TREM)-like transcript-1 (TLT-1) is an immunoreceptor tyrosine-based inhibitory motif (ITIM)-baring TREM family protein. In this study, we identified an alternative transcript form of TLT-1, namely TLT-1s, which has very short extracellular immunoglobulin domain consisting of only 202 amino acids. TLT-1s was mainly expressed in macrophages and osteoclast precursor cells. Upon receptor activator of nuclear factor-κB ligand stimulation, TLT-1s mRNA and protein levels were gradually decreased in BMMs. We also showed the TLT-1s is localized to the cytoplasmic membrane in osteoclast precursor cells. TLT-1s silencing strongly enhanced the formation and resorption activity of osteoclast. In addition, forced expression of TLT-1s showed reduced formation of osteoclast. Because ITIM-baring proteins inhibit immunoreceptor tyrosine-based activation motif (ITAM)-mediated receptor signaling, we tested whether TLT-1s physically interacted with TREM-2, the ITAM-associated co-stimulatory receptor essential for osteoclast differentiation. We showed that TLT-1s is associated with TREM-2 in osteoclast precursor cells. TLT-1s is also associated with tyrosine Src homology 2 domain-containing phosphatase-1 and SH2 domain-containing inositol phosphatase-1 and recruited them to the TREM2-ITAM signaling complex. In addition, knockdown of TLT-1s markedly elevated the intracellular calcium concentration and oscillation in osteoclast precursor cells. In addition, calcium-mediated induction of nuclear factor of activated T cells was also increased by TLT-1s silencing. Furthermore, TREM-2-mediated Akt activation and proliferation of osteoclast precursor cells were also enhanced in TLT-1s silenced cells. In this paper, we found the noble ITIM-baring inhibitory membrane protein; TLT-1s, which regulates ITAM-mediated signaling on osteoclastogenesis.
触发受体表达在髓样细胞（TREM）样转录本-1（TLT-1）是一种免疫受体酪氨酸的基于抑制基序（ITIM）的TREM 家族蛋白。在这项研究中，我们鉴定了 TLT-1 的一种替代转录本形式，即 TLT-1s，其具有非常短的细胞外免疫球蛋白结构域，仅由 202 个氨基酸组成。TLT-1s 主要在巨噬细胞和破骨细胞前体细胞中表达。在核因子-κB 受体激活剂配体刺激下，TLT-1s mRNA 和蛋白水平在 BMMs 中逐渐降低。我们还表明 TLT-1s 在破骨细胞前体细胞中定位于质膜。TLT-1s 的沉默强烈增强了破骨细胞的形成和吸收活性。此外，TLT-1s 的强制表达显示出破骨细胞形成减少。因为 ITIM 携带蛋白抑制免疫受体酪氨酸的基于激活基序（ITAM）的受体信号，我们测试了 TLT-1s 是否与 TREM-2 物理相互作用，TREM-2 是破骨细胞分化所必需的 ITAM 相关共刺激受体。我们表明 TLT-1s 在破骨细胞前体细胞中与 TREM-2 相关。TLT-1s 也与酪氨酸 Src 同源 2 结构域含有磷酸酶-1 和 SH2 结构域含有肌醇磷酸酶-1 相关，并将它们募集到 TREM2-ITAM 信号复合物中。此外，TLT-1s 的敲低显著增加了破骨细胞前体细胞中的细胞内钙浓度和振荡。此外，TLT-1s 的敲低也增加了钙介导的活化 T 细胞核因子的诱导。此外，TREM-2 介导的 Akt 激活和破骨细胞前体细胞的增殖也在 TLT-1s 敲低的细胞中增强。在本文中，我们发现了一种高尚的 ITIM 携带抑制性膜蛋白；TLT-1s，它调节破骨细胞发生中的 ITAM 介导的信号。
