Farshbaf Mozhgan, Lindberg Mikael J, Truong Anh, Bevens Zachery, Chambers Elaina, Pournara Angeliki, Wallberg Annika E, White J Brandon
From the Department of Biological Sciences, San José State University, San José, California, United States of America.
From the Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
PLoS One. 2015 Jul 30;10(7):e0134013. doi: 10.1371/journal.pone.0134013. eCollection 2015.
Early studies demonstrated the involvement of ubiquitination of the Notch intracellular domain for rapid turnover of the transcriptional complex at Notch target genes. It was shown that this ubiquitination was promoted by the co-activator Mastermind like 1 (MAML1). MAML1 also contains numerous lysine residues that may also be ubiquitinated and necessary for protein regulation. In this study, we show that over-expressed MAML1 is ubiquitinated and identify eight conserved lysine residues which are required for ubiquitination. We also show that p300 stimulates ubiquitination and that Notch inhibits ubiquitination. Furthermore, we show that a mutant MAML1 that has decreased ubiquitination shows increased output from a HES1 reporter gene assay. Therefore, we speculate that ubiquitination of MAML1 might be a mechanism to maintain low levels of the protein until needed for transcriptional activation. In summary, this study identifies that MAML1 is ubiquitinated in the absence of Notch signaling to maintain low levels of MAML1 in the cell. Our data supports the notion that a precise and tight regulation of the Notch pathway is required for this signaling pathway.
早期研究表明，Notch细胞内结构域的泛素化参与了Notch靶基因转录复合物的快速周转。研究表明，这种泛素化是由共激活因子主调控分子样蛋白1（MAML1）促进的。MAML1还含有许多赖氨酸残基，这些残基也可能被泛素化，并且对蛋白质调节是必需的。在本研究中，我们表明过表达的MAML1被泛素化，并鉴定出八个泛素化所需的保守赖氨酸残基。我们还表明，p300刺激泛素化，而Notch抑制泛素化。此外，我们表明泛素化减少的突变型MAML1在HES1报告基因检测中显示出增加的输出。因此，我们推测MAML1的泛素化可能是一种在转录激活需要之前维持低水平蛋白质的机制。总之，本研究确定MAML1在没有Notch信号的情况下被泛素化，以维持细胞中低水平的MAML1。我们的数据支持这样一种观点，即该信号通路需要对Notch通路进行精确而严格的调控。
