Replication defects in the absence of the APC/C cofactor CDH1

Abstract

The anaphase promoting complex/cyclosome (APC/C) is an E3 ubiquitin ligase that promotes the degradation of different substrates by the proteasome. Its activity is limited to the cell cycle period comprised between anaphase and the end of the G1 phase, and is controlled by the regulated binding of two co-factors: Cdc20 or Cdh1. APC/C-Cdc20 is active during anaphase, while APC/C-Cdh1 is active from anaphase until the end of G1. APC/C-Cdh1 is known to play an important role in cell cycle progression, controling the levels of mitotic cyclins and other critical cell-cycle regulators. To get further insight into the biological function of Cdh1 in mammals, our group has generated a Cdh1 knockout mouse model (García-Higuera et al, 2008) that we are characterising at the cellular as well as the organismal level. Our results indicate that cells derived from mutant embryos (MEFs) accumulation of DNA damage, and activation of the DNA damage response, suggesting the presence of replication stress in Cdh1 deficient cells. To verify that this was the case, we performed a direct analysis of the DNA replication process and found altered replication dynamics in Cdh1 mutant cells. In particular, Cdh1 deficiency reduces the rate of replication fork progression while increasing the frequency of origing firing. These observations further confirm the importance of the APC/C-Cdh1 complex in preventing replication defects. We are now trying to understand at the molecular level how the absence of Cdh1 triggers these defects.