State Key Laboratory of Proteomics, Beijing Proteome Research Center, Beijing Institute of Radiation Medicine, Beijing, China.
EMBO J. 2011 May 13;30(13):2675-89. doi: 10.1038/emboj.2011.155.
Smad ubiquitination regulatory factor 1 (Smurf1), an homologous to E6AP C-terminus (HECT)-type E3 ubiquitin ligase, performs a crucial role in the regulation of the bone morphogenetic protein (BMP) signalling pathway in both embryonic development and bone remodelling. How the stability and activity of Smurf1 are negatively regulated remains largely unclear. Here, we report that F-box and LRR domain-containing protein 15 (FBXL15), an F-box protein of the FBXL family, forms an Skp1-Cullin1-F-box protein-Roc1 (SCF)(FBXL15) ubiquitin ligase complex and targets Smurf1 for ubiquitination and proteasomal degradation. FBXL15, through its leucine-rich repeat domain, specifically recognizes the large subdomain within the N-lobe of the Smurf1 HECT domain and promotes the ubiquitination of Smurf1 on K355 and K357 within the WW-HECT linker region. In this way, FBXL15 positively regulates BMP signalling in mammalian cells. Knockdown of fbxl15 expression in zebrafish embryos by specific antisense morpholinos causes embryonic dorsalization phenocoping BMP-deficient mutants. Injection of FBXL15 siRNAs into rat bone tissues leads to a significant loss of bone mass and decrease in bone mineral density. Collectively, our results demonstrate that Smurf1 stability is suppressed by SCF(FBXL15)-mediated ubiquitination and that FBXL15 is a key regulator of BMP signalling during embryonic development and adult bone formation.
Smad 泛素化调节因子 1（Smurf1），一种同源的 E6AP C 端（HECT）-型 E3 泛素连接酶，在胚胎发育和骨重塑过程中骨形态发生蛋白（BMP）信号通路的调节中发挥着关键作用。Smurf1 的稳定性和活性如何受到负调控在很大程度上仍不清楚。在这里，我们报告 F-box 和富含亮氨酸重复序列的蛋白 15（FBXL15），FBXL 家族的一种 F-box 蛋白，形成 Skp1-Cullin1-F-box 蛋白-Roc1（SCF）（FBXL15）泛素连接酶复合物，并靶向 Smurf1 进行泛素化和蛋白酶体降解。FBXL15 通过其亮氨酸丰富重复结构域，特异性识别 Smurf1 HECT 结构域的 N-结构域内的大亚结构域，并促进 WW-HECT 连接区域内 K355 和 K357 上的 Smurf1 泛素化。通过这种方式，FBXL15 正向调节哺乳动物细胞中的 BMP 信号。通过特异性反义 morpholino 在斑马鱼胚胎中敲低 fbxl15 表达导致胚胎背化表型与 BMP 缺陷突变体相似。将 FBXL15 siRNAs 注射到大鼠骨组织中会导致骨量显著减少和骨密度降低。总之，我们的研究结果表明 Smurf1 的稳定性受 SCF（FBXL15）介导的泛素化抑制，FBXL15 是胚胎发育和成年骨形成过程中 BMP 信号的关键调节剂。
