Senga Takeshi, Sivaprasad Umasundari, Zhu Wenge, Park Jong Hoon, Arias Emily E, Walter Johannes C, Dutta Anindya
Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, Virginia 22908, USA.
J Biol Chem. 2006 Mar 10;281(10):6246-52. doi: 10.1074/jbc.M512705200. Epub 2006 Jan 9.
Cdt1, a protein essential in G1 for licensing of origins for DNA replication, is inhibited in S-phase, both by binding to geminin and degradation by proteasomes. Cdt1 is also degraded after DNA damage to stop licensing of new origins until after DNA repair. Phosphorylation of Cdt1 by cyclin-dependent kinases promotes its binding to SCF-Skp2 E3 ubiquitin ligase, but the Cdk2/Skp2-mediated pathway is not essential for the degradation of Cdt1. Here we show that the N terminus of Cdt1 contains a second degradation signal that is active after DNA damage and in S-phase and is dependent on the interaction of Cdt1 with proliferating cell nuclear antigen (PCNA) through a PCNA binding motif. The degradation involves N-terminal ubiquitination and requires Cul4 and Ddb1 proteins, components of an E3 ubiquitin ligase implicated in protein degradation after DNA damage. Therefore PCNA, the matchmaker for many proteins involved in DNA and chromatin metabolism, also serves to promote the targeted degradation of associated proteins in S-phase or after DNA damage.
Cdt1是一种在G1期对DNA复制起点许可至关重要的蛋白质，在S期会因与geminin结合和被蛋白酶体降解而受到抑制。DNA损伤后，Cdt1也会被降解，以阻止新起点的许可，直到DNA修复之后。细胞周期蛋白依赖性激酶对Cdt1的磷酸化促进其与SCF-Skp2 E3泛素连接酶的结合，但Cdk2/Skp2介导的途径对Cdt1的降解并非必不可少。我们在此表明，Cdt1的N末端包含第二个降解信号，该信号在DNA损伤后和S期具有活性，并且依赖于Cdt1通过PCNA结合基序与增殖细胞核抗原（PCNA）的相互作用。这种降解涉及N末端泛素化，并且需要Cul4和Ddb1蛋白，这两种蛋白是一种E3泛素连接酶的组分，与DNA损伤后的蛋白质降解有关。因此，PCNA作为许多参与DNA和染色质代谢的蛋白质的媒介，也有助于促进S期或DNA损伤后相关蛋白质的靶向降解。
