CDK12 in Ovarian Cancer

 描述(申请人提供)：细胞周期蛋白依赖性激酶12(CDK12)基因是高级别浆液性卵巢癌中最常见的自发突变基因之一，是最致命的妇科恶性肿瘤。正如我们所展示的，这些突变破坏了该激酶的功能。此外，CDK12在卵巢肿瘤中常表现为拷贝数丢失。综上所述，这些发现表明CDK12在卵巢癌中通常是无效的。与其他CDK不同，CDK12不调节细胞周期进程。相反，CDK12调节包括BRCA1在内的人类基因的子集的表达，从而使CDK12失活会降低BRCA1的水平，从而促进同源重组(HR)修复。与BRCA1的减少一致，在卵巢癌细胞系中禁用CDK12会扰乱HR，使细胞对诱导HR修复的损害的药物敏感，并使细胞对聚(ADP-核糖)聚合酶(PARP)抑制剂敏感，后者对HR丧失的细胞具有选择性毒性。然而，目前尚不清楚CDK12突变或CDK12水平降低是否会影响人卵巢肿瘤对目前处于第三阶段临床试验的PARP抑制剂的反应。此外，我们对CDK12的调节和生化作用的了解仍然不完整。最近的研究表明，CDK12在RNAPII的最大亚基RBP1的C末端结构域(CTD)的七肽重复序列中磷酸化Ser2。这种磷酸化通过招募染色质修饰物和重构体来调节转录的多个方面，并促进mRNA剪接、3‘端切割和多聚腺苷化。尽管取得了这些进展，但目前尚不清楚CDK12是如何调控的，也不知道CDK12是仅通过磷酸化RBP1的CTD中的Ser2还是通过磷酸化其他底物来调节基因表达。在这项应用中，我们将研究CDK12是如何调控的(目标1)，评估CDK12如何调控前-mRNA剪接(目标2)，并确定CDK12通路组件的表达水平是否与接受铂类药物治疗的高级别浆液性卵巢癌患者的预后相关(目标3)。影响和相关性：总的来说，这些研究是相关的，因为它们将1)为CDK12的调节和生化作用提供新的机械性见解，CDK12是一种对肿瘤生物学有重大影响但其作用机制尚不清楚的蛋白激酶；2)确定CDK12途径是否与卵巢癌的标准护理治疗和新疗法的反应有关。

 DESCRIPTION (provided by applicant): The cyclin-dependent kinase 12 (CDK12) gene is among the most frequent spontaneously mutated genes in high-grade serous ovarian cancers, the most lethal gynecological malignancy. As we have shown, these mutations disrupt the function of the kinase. Additionally, CDK12 often show loss of copy number in ovarian tumors. Taken together, these findings suggest that CDK12 is often disabled in ovarian cancer. Unlike other CDKs, CDK12 does not regulate cell cycle progression. Instead, CDK12 regulates the expression of a subset of human genes, including BRCA1 such that disabling CDK12 reduces the levels of BRCA1, which facilitates homologous recombination (HR) repair. Consistent with a decrease in BRCA1, disabling CDK12 in ovarian cancer cell lines disrupts HR, sensitizes cells to agents that induce lesions repaired by HR, and sensitizes cells to poly(ADP-ribose) polymerase (PARP) inhibitors, which are selectively toxic to cells with disabled HR. It remains unclear, however, whether CDK12 mutations or reduced CDK12 levels affect the responses of human ovarian tumors to PARP inhibitors that are currently in Phase 3 clinical trials. Additionally, our understanding of the regulation and biochemical roles of CDK12 remains incomplete. Recent studies showed that CDK12 phosphorylates Ser2 in the heptapeptide repeats of the C-terminal domain (CTD) of RBP1, the largest subunit of RNA polymerase II (RNAPII). This phosphorylation regulates multiple aspects of transcription by recruiting chromatin modifiers and remodelers, and facilitating mRNA splicing, 3' end cleavage, and polyadenylation. Despite this progress, however, it is not currently known how CDK12 is regulated, nor do we know whether CDK12 regulates gene expression solely by phosphorylation of Ser2 in the CTD of RBP1 or by phosphorylating other substrates. In this application we will to examine how CDK12 is regulated (Aim 1), evaluate how CDK12 regulates pre-mRNA splicing (Aim 2), and determine whether the expression levels of CDK12 pathway components correlates with patient outcomes in women with high-grade serous ovarian cancer treated with platinum-based therapy (Aim 3). Impact and Relevance: Collectively, these studies are relevant because they will 1) provide novel mechanistic insights into the regulation and biochemical roles of CDK12, a protein kinase with major impacts on tumor biology but whose mechanisms of action remain obscure; and 2) determine whether the CDK12 pathway is associated with responses to standard-of-care therapy and novel therapies for ovarian cancer.