DBF4-dependent kinase (DDK) is a two-subunit kinase required for initiating DNA replication at individual origins and is composed of CDC7 kinase and its regulatory subunit DBF4. Both subunits are highly expressed in many diverse tumor cell lines and primary tumors, and this is correlated with poor prognosis. Inhibiting DDK causes apoptosis of tumor cells, but not normal cells, through a largely unknown mechanism. Firstly, to understand why DDK is often overexpressed in tumors, we identified gene expression signatures that correlate with DDK high- and DDK low-expressing lung adenocarcinomas. We found that increased DDK expression is highly correlated with inactivation of RB1-E2F and p53 tumor suppressor pathways. Both CDC7 and DBF4 promoters bind E2F, suggesting that increased E2F activity in RB1 mutant cancers promotes increased DDK expression. Surprisingly, increased DDK expression levels are also correlated with both increased chemoresistance and genome-wide mutation frequencies. Our data further suggest that high DDK levels directly promote elevated mutation frequencies. Secondly, we performed an RNAi screen to investigate how DDK inhibition causes apoptosis of tumor cells. We identified 23 kinases and phosphatases required for apoptosis when DDK is inhibited. These hits include checkpoint genes, G2/M cell cycle regulators, and known tumor suppressors leading to the hypothesis that inhibiting mitotic progression can protect against DDKi-induced apoptosis. Characterization of one novel hit, the LATS2 tumor suppressor, suggests that it promotes apoptosis independently of the upstream MST1/2 kinases in the Hippo signaling pathway.

中文翻译：

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DDK通过多种途径促进肿瘤化学耐药性和生存。

DBF4依赖性激酶（DDK）是在各个起源处启动DNA复制所需的两个亚基激酶，由CDC7激酶及其调节性亚基DBF4组成。这两个亚基在许多不同的肿瘤细胞系和原发性肿瘤中高表达，这与不良预后相关。抑制DDK会通过很大程度上未知的机制导致肿瘤细胞凋亡，但不会导致正常细胞凋亡。首先，为了了解为什么DDK在肿瘤中经常过表达，我们鉴定了与DDK高表达和DDK低表达肺腺癌相关的基因表达特征。我们发现增加的DDK表达与RB1-E2F和p53肿瘤抑制途径的失活高度相关。CDC7和DBF4启动子都结合E2F，这表明RB1突变型癌症中E2F活性的增加促进了DDK表达的增加。令人惊讶地，增加的DDK表达水平也与增加的化学抗性和全基因组突变频率相关。我们的数据进一步表明，高DDK水平直接促进突变频率升高。其次，我们进行了RNAi筛选，以研究DDK抑制如何导致肿瘤细胞凋亡。当DDK被抑制时，我们确定了凋亡所需的23种激酶和磷酸酶。这些命中因素包括检查点基因，G2 / M细胞周期调节剂和已知的肿瘤抑制因子，导致抑制有丝分裂进程可以防止DDKi诱导的凋亡的假说。LATS2肿瘤抑制因子是一种新型命中基因的特征，表明它可以独立于Hippo信号通路中的上游MST1 / 2激酶而促进细胞凋亡。DDK表达水平的增加也与化学抗药性和全基因组突变频率增加相关。我们的数据进一步表明，高DDK水平直接促进突变频率升高。其次，我们进行了RNAi筛选，以研究DDK抑制如何导致肿瘤细胞凋亡。当DDK被抑制时，我们确定了凋亡所需的23种激酶和磷酸酶。这些命中包括检查点基因，G2 / M细胞周期调节剂，以及已知的肿瘤抑制因子，导致抑制有丝分裂进程可以防止DDKi诱导的细胞凋亡的假说。LATS2肿瘤抑制因子是一种新型命中基因的特征，表明它可以独立于Hippo信号通路中的上游MST1 / 2激酶而促进细胞凋亡。DDK表达水平的增加也与化学抗药性和全基因组突变频率增加相关。我们的数据进一步表明，高DDK水平直接促进突变频率升高。其次，我们进行了RNAi筛选，以研究DDK抑制如何导致肿瘤细胞凋亡。当DDK被抑制时，我们确定了凋亡所需的23种激酶和磷酸酶。这些命中因素包括检查点基因，G2 / M细胞周期调节剂和已知的肿瘤抑制因子，导致抑制有丝分裂进程可以防止DDKi诱导的凋亡的假说。LATS2肿瘤抑制因子是一种新型命中基因的特征，表明它可以独立于Hippo信号通路中的上游MST1 / 2激酶而促进细胞凋亡。