Regulated Proteolysis of Nonmuscle Myosin IIA Stimulates Osteoclast Fusion
Regulated Proteolysis of Nonmuscle Myosin IIA Stimulates Osteoclast Fusion
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DOI：
10.1074/jbc.m808621200
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发表时间：
2009-05-01
影响因子：
4.8
通讯作者：
Lee, Beth S.
中科院分区：
文献类型：
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作者：
McMichael, Brooke K.;Wysolmerski, Robert B.;Lee, Beth S.
非肌肉肌球蛋白IIA重链（Myh9）与破骨细胞的粘附结构密切相关。在这项研究中，我们证明，在破骨细胞生成，肌球蛋白IIA重链水平暂时抑制，刺激细胞融合的发病事件。这种抑制不是由mRNA或翻译水平的变化介导的，而是由于肌球蛋白IIA降解速率的暂时增加。破骨细胞前体融合开始时，细胞内组织蛋白酶B的活性显著增强，特异性抑制其活性可防止肌球蛋白IIA降解。此外，在分化过程中用组织蛋白酶B抑制剂处理正常细胞降低了细胞融合和骨吸收能力，而组织蛋白酶B的过表达增强了融合。通过RNA干扰持续抑制肌球蛋白IIA重链导致形成具有显著增加的细胞核数量的大破骨细胞，而肌球蛋白IIA过表达导致破骨细胞融合减少。肌球蛋白IIA抑制引起的多核化增加不需要RANKL。此外，肌球蛋白IIA的敲低增强细胞铺展并降低运动性。这些数据结合在一起强烈表明，基线表达的非肌肉肌球蛋白IIA抑制破骨细胞前体融合和临时，组织蛋白酶B介导的肌球蛋白IIA水平的降低触发破骨细胞生成过程中的前体融合。
The nonmuscle myosin IIA heavy chain (Myh9) is strongly associated with adhesion structures of osteoclasts. In this study, we demonstrate that during osteoclastogenesis, myosin IIA heavy chain levels are temporarily suppressed, an event that stimulates the onset of cell fusion. This suppression is not mediated by changes in mRNA or translational levels but instead is due to a temporary increase in the rate of myosin IIA degradation. Intracellular activity of cathepsin B is significantly enhanced at the onset of osteoclast precursor fusion, and specific inhibition of its activity prevents myosin IIA degradation. Further, treatment of normal cells with cathepsin B inhibitors during the differentiation process reduces cell fusion and bone resorption capacity, whereas overexpression of cathepsin B enhances fusion. Ongoing suppression of the myosin IIA heavy chain via RNA interference results in formation of large osteoclasts with significantly increased numbers of nuclei, whereas overexpression of myosin IIA results in less osteoclast fusion. Increased multinucleation caused by myosin IIA suppression does not require RANKL. Further, knockdown of myosin IIA enhances cell spreading and lessens motility. These data taken together strongly suggest that base-line expression of nonmuscle myosin IIA inhibits osteoclast precursor fusion and that a temporary, cathepsin B-mediated decrease in myosin IIA levels triggers precursor fusion during osteoclastogenesis.