Activation of Cdh1-dependent APC is required for G₁ cell cycle arrest and DNA damage-induced G₂ checkpoint in vertebrate cells

Anaphase-promoting complex (APC) is activated by two regulatory proteins, Cdc20 and Cdh1. In yeast and Drosophila, Cdh1-dependent APC (Cdh1-APC) activity targets mitotic cyclins from the end of mitosis to the G₁ phase. To investigate the function of Cdh1 in vertebrate cells, we generated clones of chicken DT40 cells disrupted in their Cdh1 loci. Cdh1 was dispensable for viability and cell cycle progression. However, similarly to yeast and Drosophila, loss of Cdh1 induced unscheduled accumulation of mitotic cyclins in G₁, resulting in abrogation of G₁, arrest caused by treatment with rapamycin, an inducer of p27^Kipl. Furthermore, we found that Cdh1^-1- cells fail to maintain DNA damage-induced G₂ arrest and that Cdh1-APC is activated by X-irradiation-induced DNA damage. Thus, activation of Cdh1-APC plays a crucial role in both cdk inhibitor-dependent G₁ arrest and DNA damage-induced G₂ arrest.