Department of Cell Signaling, Graduate School of Medical and Dental Science, Tokyo Medical and Dental University, Yushima 1-5-45, Bunkyo-ku, Tokyo 113-8549, Japan.
Biochem Biophys Res Commun. 2010 Mar 12;393(3):432-8. doi: 10.1016/j.bbrc.2010.02.013. Epub 2010 Feb 12.
Osteoclasts, multinucleated cells that resorb bone, play a key role in bone remodeling. Although immunoreceptor tyrosine-based activation motif (ITAM)-mediated signaling is critical for osteoclast differentiation, the significance of immunoreceptor tyrosine-based inhibitory motif (ITIM) has not been well understood. Here we report the function of Ly49Q, an Ly49 family member possessing an ITIM motif, in osteoclastogenesis. Ly49Q is selectively induced by receptor activator of nuclear factor-kappaB (NF-kappaB) ligand (RANKL) stimulation in bone marrow-derived monocyte/macrophage precursor cells (BMMs) among the Ly49 family of NK receptors. The knockdown of Ly49Q resulted in a significant reduction in the RANKL-induced formation of tartrate-resistance acid phosphatase (TRAP)-positive multinucleated cells, accompanied by a decreased expression of osteoclast-specific genes such as Nfatc1, Tm7sf4, Oscar, Ctsk, and Acp5. Osteoclastogenesis was also significantly impaired in Ly49Q-deficient cells in vitro. The inhibitory effect of Ly49Q-deficiency may be explained by the finding that Ly49Q competed for the association of Src-homology domain-2 phosphatase-1 (SHP-1) with paired immunoglobulin-like receptor-B (PIR-B), an ITIM-bearing receptor which negatively regulates osteoclast differentiation. Unexpectedly, Ly49Q deficiency did not lead to impaired osteoclast formation in vivo, suggesting the existence of a compensatory mechanism. This study provides an example in which an ITIM-bearing receptor functions as a positive regulator of osteoclast differentiation.
破骨细胞是一种多核细胞，负责吸收骨骼，在骨骼重塑中发挥着关键作用。尽管免疫受体酪氨酸激活基序 (ITAM) 介导的信号通路对于破骨细胞分化至关重要，但免疫受体酪氨酸抑制基序 (ITIM) 的意义尚未得到充分理解。在这里，我们报告了 Ly49Q（一种具有 ITIM 基序的 Ly49 家族成员）在破骨细胞生成中的功能。在核因子-κB 受体激活剂（RANKL）刺激下，骨髓来源的单核细胞/巨噬细胞前体细胞（BMM）中的 Ly49 家族 NK 受体中，Ly49Q 被选择性诱导。Ly49Q 的敲低导致 RANKL 诱导的抗酒石酸盐酸性磷酸酶（TRAP）阳性多核细胞形成显著减少，同时破骨细胞特异性基因如 Nfatc1、Tm7sf4、Oscar、Ctsk 和 Acp5 的表达降低。体外 Ly49Q 缺陷细胞中的破骨细胞生成也受到显著抑制。Ly49Q 缺陷的抑制作用可能是由于发现 Ly49Q 与 Src 同源结构域-2 磷酸酶-1（SHP-1）竞争结合配对免疫球蛋白样受体-B（PIR-B），PIR-B 是一种具有 ITIM 的受体，可负向调节破骨细胞分化。出乎意料的是，Ly49Q 缺陷并不导致体内破骨细胞形成受损，这表明存在代偿机制。本研究提供了一个例证，即具有 ITIM 的受体可作为破骨细胞分化的正调控因子。
