Division of Cell Biology and Cancer Genomics Center, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
Cells. 2021 Mar 4;10(3):550. doi: 10.3390/cells10030550.
Most Cyclin-dependent kinases (Cdks) are redundant for normal cell division. Here we tested whether these redundancies are maintained during cell cycle recovery after a DNA damage-induced arrest in G1. Using non-transformed RPE-1 cells, we find that while Cdk4 and Cdk6 act redundantly during normal S-phase entry, they both become essential for S-phase entry after DNA damage in G1. We show that this is due to a greater overall dependency for Cdk4/6 activity, rather than to independent functions of either kinase. In addition, we show that inactivation of pocket proteins is sufficient to overcome the inhibitory effects of complete Cdk4/6 inhibition in otherwise unperturbed cells, but that this cannot revert the effects of Cdk4/6 inhibition in DNA damaged cultures. Indeed, we could confirm that, in addition to inactivation of pocket proteins, Cdh1-dependent anaphase-promoting complex/cyclosome (APC/C) activity needs to be inhibited to promote S-phase entry in damaged cultures. Collectively, our data indicate that DNA damage in G1 creates a unique situation where high levels of Cdk4/6 activity are required to inactivate pocket proteins and APC/C to promote the transition from G1 to S phase.
大多数细胞周期蛋白依赖性激酶（Cdks）在正常细胞分裂中是冗余的。在这里，我们测试了这些冗余性是否在 G1 期因 DNA 损伤引起的阻滞后细胞周期恢复期间得以维持。使用非转化的 RPE-1 细胞，我们发现虽然 Cdk4 和 Cdk6 在正常 S 期进入时表现出冗余性，但它们在 G1 期的 DNA 损伤后对 S 期进入都是必需的。我们表明，这是由于 Cdk4/6 活性的总体依赖性更高，而不是两种激酶的独立功能。此外，我们表明，失活 pocket 蛋白足以克服完全抑制 Cdk4/6 对未受干扰细胞的抑制作用，但这不能逆转 Cdk4/6 抑制在 DNA 损伤培养物中的作用。事实上，我们可以证实，除了失活 pocket 蛋白外，还需要抑制 Cdh1 依赖性后期促进复合物/细胞周期蛋白（APC/C）活性，以促进受损培养物中 S 期的进入。总的来说，我们的数据表明，G1 期的 DNA 损伤创造了一种独特的情况，需要高水平的 Cdk4/6 活性来失活 pocket 蛋白和 APC/C，以促进从 G1 到 S 期的转变。
