精准调控DNA复制是细胞周期进程的核心事件，对维持基因组稳定性至关重要。由于DNA复制调控异常而导致的基因组不稳定性是人类肿瘤发生发展的关键驱动因素。为确保基因组在细胞周期中只复制一次，真核细胞仅在G1期组装DNA前复制复合体（prereplicative complex, pre-RC）。目前，关于细胞如何阻断pre-RC在S期和G2/M期组装的分子机制已较为清楚；但对在G1期如何促进pre-RC组装的调控机制尚不明了。本课题组在前期工作中以人类肿瘤样本高通量测序数据为切入点，发现CDK12/cyclin K通过抑制cyclin E1的活性而正调控G1期pre-RC组装过程。本项目将围绕这些新发现进行深入研究。由于cyclin E1基因是30%的高级别浆液性卵巢癌发生发展的驱动基因，我们提出CDK12抑制剂将有希望成为治疗这类高级别浆液性卵巢癌的新靶向。

The assembly of prereplicative complex (pre-RC) during G1 phase must be tightly controlled to sustain cell proliferation and maintain genomic stability. Mechanisms to prevent pre-RC formation in G2/M and S phases are well appreciated, whereas how cells ensure efficient pre-RC assembly during G1 is less clear. We report here that cyclin K regulates pre-RC formation. We find that cyclin K expression positively correlates with, and is required for cell proliferation in multiple biological contexts. Knockdown of cyclin K or its cognate kinase CDK12 prevents the assembly of pre-RC in G1 phase, and halts cell cycle progression. Mechanistically we uncover that cyclin K promotes pre-RC assembly by restricting cyclin E1 activity in G1. We identify a cyclin K-dependent, novel phosphorylation site in cyclin E1 that disrupts its interaction with CDK2. Importantly, this antagonistic relationship is largely recapitulated in cyclin E1-overexpressing tumors. Increased cyclin E1 activity is known to be detrimental to pre-RC formation, resulting in genomic instability. We discuss the implications of our findings in light of recent reports linking cyclin K and CDK12 to human tumorigenesis.