Title:
Regulation of genome integrity by CRL4-Cdt2 ubiquitin ligase that ensures DNA replication once per cell cycle.

 

Speaker:
Hideo Nishitani
Graduate School of Life Science, University of Hyogo

 

Abstract:
During a cell division cycle, both genetic and epigenetic informations must be correctly transmitted into daughter cells. Control of DNA replication-licensing ensures that chromosomal DNA is replicated once-and-only once in a cell cycle. By the early G1 phase, Cdc6 and Cdt1 load DNA helicase, MCM2-7 on replication origins for licensing. We reported that high expression of Cdt1 and/or Cdc6 caused over-replication of DNA, demonstrating that control of licensing factors is essential for only once replication. When cells started S phase, PCNA is loaded on chromatin and connects Cdt1 to ubiquitin ligase CRL4(Cul4-DDB1)-Cdt2 for degradation, thus preventing the re-replication. Cdt1 associates through its PIP-box (PCNA interacting protein box) to PCNA and is recognized by Cdt2. When cells are exposed to DNA damaging agents including UV-irradiation, the same PCNA and CRL4-Cdt2 mediated pathway is activated in G1 phase to degrade Cdt1, which appears to be important for repair of DNA damages. In addition to Cdt1, several targets of CRL4-Cdt2 have been reported, including H4K20 monomethylase Set8, CDK inhibitor p21, and thymine DNA glycosylase (TDG); all these substrate proteins are directly or indirectly involved in replication licensing or genome integrity. Recently, we found that human Cdt2 has a PIP-box at its C-terminal end. This motif is important to recruiting CRL4-Cdt2 to PCNA sites for efficient Cdt1 degradation. We propose that direct binding of Cdt2 to PCNA is important for targeting the CRL4Cdt2 E3 ligase activity to substrates to maintain genome integrity.

 

References:
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