Department of Molecular Cell Biology, Cancer Genomics Centre Netherlands and Centre of Biomedical Genetics, Leiden University Medical Center, Leiden, RC, The Netherlands.
EMBO J. 2013 Apr 3;32(7):996-1007. doi: 10.1038/emboj.2013.38. Epub 2013 Mar 1.
SMAD6 is a crucial feedback inhibitory regulator of bone morphogenetic protein (BMP)/SMAD signalling. Although little is known regarding the post-transcriptional modification of inhibitory SMADs and the mechanism by which their function is regulated. In this study, using a whole proteomic interaction screen for SMAD6, we identified a large putative E2 ubiquitin-conjugating enzyme UBE2O (E2-230K) as a novel interacting protein of SMAD6. We showed that UBE2O functions as an E2-E3 hybrid to monoubiquitinate SMAD6 at lysine 174 and that the cysteine 885 residue of human UBE2O is necessary for SMAD6 monoubiquitination. Inactivation of the SMAD6 monoubiquitination site specially potentiates the inhibitory ability of SMAD6 against BMP7-induced SMAD1 phosphorylation and transcriptional responses. We also found that UBE2O potentiated BMP7 signalling in a SMAD6-dependent manner. Addressing the molecular mechanism by which UBE2O and monoubiquitinated SMAD6 potentiate BMP7 signalling, we demonstrated that monoubiquitinated SMAD6 impairs the binding affinity of non-modified SMAD6 to the BMP type I receptor. Moreover, UBE2O and SMAD6 cooperated in the regulation of BMP7-induced adipogenesis.
SMAD6 是骨形态发生蛋白（BMP）/SMAD 信号转导的关键反馈抑制调节因子。尽管人们对抑制性 SMAD 的转录后修饰以及其功能调节的机制知之甚少。在这项研究中，我们通过全蛋白质组相互作用筛选 SMAD6，鉴定出一个大的假定 E2 泛素连接酶 UBE2O（E2-230K）是 SMAD6 的一种新型相互作用蛋白。我们表明，UBE2O 作为 E2-E3 杂合体，在赖氨酸 174 处单泛素化 SMAD6，而人 UBE2O 的半胱氨酸 885 残基对于 SMAD6 单泛素化是必需的。SMAD6 单泛素化位点的失活特别增强了 SMAD6 对 BMP7 诱导的 SMAD1 磷酸化和转录反应的抑制能力。我们还发现 UBE2O 以 SMAD6 依赖的方式增强 BMP7 信号。为了解决 UBE2O 和单泛素化 SMAD6 增强 BMP7 信号的分子机制，我们证明单泛素化 SMAD6 降低了非修饰 SMAD6 与 BMP 型 I 受体结合的亲和力。此外，UBE2O 和 SMAD6 合作调节 BMP7 诱导的脂肪生成。
