Hernández-Pérez Santiago, Cabrera Elisa, Amoedo Hugo, Rodríguez-Acebes Sara, Koundrioukoff Stephane, Debatisse Michelle, Méndez Juan, Freire Raimundo
Unidad de Investigación, Hospital Universitario de Canarias, Instituto de Tecnologías Biomédicas, Ofra s/n, La Laguna, Tenerife, Spain.
DNA Replication Group, Spanish National Cancer Research Centre (CNIO), E-28029 Madrid, Spain.
Mol Oncol. 2016 Oct;10(8):1196-206. doi: 10.1016/j.molonc.2016.05.008. Epub 2016 Jun 3.
DNA replication control is a key process in maintaining genomic integrity. Monitoring DNA replication initiation is particularly important as it needs to be coordinated with other cellular events and should occur only once per cell cycle. Crucial players in the initiation of DNA replication are the ORC protein complex, marking the origin of replication, and the Cdt1 and Cdc6 proteins, that license these origins to replicate by recruiting the MCM2-7 helicase. To accurately achieve its functions, Cdt1 is tightly regulated. Cdt1 levels are high from metaphase and during G1 and low in S/G2 phases of the cell cycle. This control is achieved, among other processes, by ubiquitination and proteasomal degradation. In an overexpression screen for Cdt1 deubiquitinating enzymes, we isolated USP37, to date the first ubiquitin hydrolase controlling Cdt1. USP37 overexpression stabilizes Cdt1, most likely a phosphorylated form of the protein. In contrast, USP37 knock down destabilizes Cdt1, predominantly during G1 and G1/S phases of the cell cycle. USP37 interacts with Cdt1 and is able to de-ubiquitinate Cdt1 in vivo and, USP37 is able to regulate the loading of MCM complexes onto the chromatin. In addition, downregulation of USP37 reduces DNA replication fork speed. Taken together, here we show that the deubiquitinase USP37 plays an important role in the regulation of DNA replication. Whether this is achieved via Cdt1, a central protein in this process, which we have shown to be stabilized by USP37, or via additional factors, remains to be tested.
DNA复制控制是维持基因组完整性的关键过程。监测DNA复制起始尤为重要，因为它需要与其他细胞事件协调，并且每个细胞周期仅应发生一次。DNA复制起始的关键参与者是标记复制起点的ORC蛋白复合物，以及通过招募MCM2-7解旋酶使这些起点获得复制许可的Cdt1和Cdc6蛋白。为了准确实现其功能，Cdt1受到严格调控。Cdt1水平在中期和G1期较高，而在细胞周期的S/G2期较低。这种调控是通过泛素化和蛋白酶体降解等过程实现的。在一项针对Cdt1去泛素化酶的过表达筛选中，我们分离出了USP37，它是迄今为止第一个控制Cdt1的泛素水解酶。USP37过表达使Cdt1稳定，很可能是该蛋白的磷酸化形式。相反，敲低USP37会使Cdt1不稳定，主要在细胞周期的G1期和G1/S期。USP37与Cdt1相互作用，能够在体内使Cdt1去泛素化，并且USP37能够调节MCM复合物加载到染色质上。此外，下调USP37会降低DNA复制叉速度。综上所述，我们在此表明去泛素化酶USP37在DNA复制调控中起重要作用。这是通过Cdt1（此过程中的核心蛋白，我们已证明其可被USP37稳定）实现，还是通过其他因素实现，仍有待测试。
