title: Phosphorylation of Ku70 subunit by cell cycle kinases modulates the replication related function of Ku heterodimer.
abstract: The Ku protein, a heterodimer of Ku70 and Ku80, binds to chromosomal replication origins maximally at G1-phase and plays an essential role in assembly of origin recognition complex. However, the mechanism regulating such a critical periodic activity of Ku remained unknown. Here, we establish human Ku70 as a novel target of cyclin B1-Cdk1, which phosphorylates it in a Cy-motif dependent manner. Interestingly, cyclin E1- and A2-Cdk2 also phosphorylate Ku70, and as a result, the protein remains in a phosphorylated state during S-M phases of cell cycle. Intriguingly, the phosphorylation of Ku70 by cyclin-Cdks abolishes the interaction of Ku protein with replication origin due to disruption of the dimer. Furthermore, Ku70 is dephosphorylated in G1-phase, when Ku interacts with replication origin maximally. Strikingly, the over-expression of Ku70 with non-phosphorylable Cdk targets enhances the episomal replication of Ors8 origin and induces rereplication in HeLa cells, substantiating a preventive role of Ku phosphorylation in premature and untimely licensing of replication origin. Therefore, periodic phosphorylation of Ku70 by cyclin-Cdks prevents the interaction of Ku with replication origin after initiation events in S-phase and the dephosphorylation at the end of mitosis facilitates its participation in pre-replication complex formation.
authors.affiliation: Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Kolkata 700064, India.
authors.forename: Soumita
authors.initials: S
authors.lastname: Mukherjee
authors.affiliation: Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Kolkata 700064, India.
authors.forename: Prabal
authors.initials: P
authors.lastname: Chakraborty
authors.affiliation: Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Kolkata 700064, India Homi Bhaba National Institute, Mumbai 400094, India partha.saha@saha.ac.in.
authors.forename: Partha
authors.initials: P
authors.lastname: Saha
mesh_terms: D002453:Cell Cycle; D056744:Cyclin B1 / Q000378:metabolism; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D004261:DNA Replication; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D000072200:Ku Autoantigen / Q000378:metabolism*; D008938:Mitosis; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D010766:Phosphorylation; D011485:Protein Binding; D055503:Protein Multimerization; D021122:Protein Subunits / Q000378:metabolism*; D018741:Replication Origin
chemical_list: D056744:Cyclin B1; D021122:Protein Subunits; D018844:Cyclin-Dependent Kinases; D000072200:Ku Autoantigen