Department of Physiology and Cell Biology, The Ohio State University College of Medicine, Columbus, Ohio 43210, USA.
J Biol Chem. 2010 Aug 20;285(34):26641-51. doi: 10.1074/jbc.M110.119909. Epub 2010 Jun 14.
Osteoclasts resorb bone through the formation of a unique attachment structure called the sealing zone. In this study, a role for thyroid hormone receptor-interacting protein 6 (TRIP6) in sealing zone formation and osteoclast activity was examined. TRIP6 was shown to reside in the sealing zone through its association with tropomyosin 4, an actin-binding protein that regulates sealing dimensions and bone resorptive capacity. Suppression of TRIP6 in mature osteoclasts by RNA interference altered sealing zone dimensions and inhibited bone resorption, whereas overexpression of TRIP6 increased the sealing zone perimeter and enhanced bone resorption. Treatment of osteoclasts with lysophosphatidic acid (LPA), which phosphorylates TRIP6 at tyrosine 55 through a c-Src-dependent mechanism, caused increased association of TRIP6 with the sealing zone, as did overexpression of a TRIP6 cDNA bearing a phosphomimetic mutation at tyrosine 55. Further, LPA treatment caused increases in osteoclast fusion, sealing zone perimeter, and bone resorptive capacity. In contrast, overexpression of TRIP6 containing a nonphosphorylatable amino acid residue at position 55 severely diminished sealing zone formation and bone resorption and suppressed the effects of LPA on the cytoskeleton. LPA effects were mediated through its receptor isoform LPA(2), as indicated by treatments with receptor-specific agonists and antagonists. Thus, these studies suggest that TRIP6 is a critical downstream regulator of c-Src signaling and that its phosphorylation is permissive for its presence in the sealing zone where it plays a positive role in osteoclast bone resorptive capacity.
破骨细胞通过形成一种独特的附着结构——封闭区来吸收骨骼。在这项研究中，研究了甲状腺激素受体相互作用蛋白 6（TRIP6）在封闭区形成和破骨细胞活性中的作用。研究表明，TRIP6 通过与肌球蛋白 4 结合而存在于封闭区中，肌球蛋白 4 是一种肌动蛋白结合蛋白，可调节封闭区的大小和骨吸收能力。通过 RNA 干扰抑制成熟破骨细胞中的 TRIP6 会改变封闭区的大小并抑制骨吸收，而过表达 TRIP6 会增加封闭区的周长并增强骨吸收。溶血磷脂酸（LPA）处理破骨细胞，通过 c-Src 依赖性机制使 TRIP6 酪氨酸 55 磷酸化，会导致 TRIP6 与封闭区的结合增加，而过表达含有酪氨酸 55 磷酸模拟突变的 TRIP6 cDNA 也会导致这种情况。此外，LPA 处理会导致破骨细胞融合、封闭区周长和骨吸收能力增加。相比之下，在位置 55 处含有不可磷酸化氨基酸残基的 TRIP6 的过表达严重削弱了封闭区的形成和骨吸收，并抑制了 LPA 对细胞骨架的作用。LPA 的作用是通过其受体亚型 LPA(2)介导的，这是通过使用受体特异性激动剂和拮抗剂进行治疗来表明的。因此，这些研究表明 TRIP6 是 c-Src 信号的关键下游调节剂，其磷酸化使其能够存在于封闭区中，在那里它在破骨细胞的骨吸收能力中发挥积极作用。
