Role of Nucleostemin in Conferring The Drug Resistance of Hepatocellular Carcinoma

 描述(申请人提供)：高级别肿瘤对DNA损伤诱导的化疗药物(C/TS)的耐药性是癌症死亡的主要原因。肝细胞癌以其对C/Ts的先天耐药而著称，但其潜在的机制尚不清楚。最近的研究开始认识到晚期乳腺癌和卵巢癌的进展和耐药性可能取决于同源重组(HR)修复途径。我的团队研究了一种由干细胞和癌细胞丰富的蛋白质控制的自我更新机制，这种蛋白质被称为核干素(NS)。我们最近发现了NS在促进HR修复和保护癌细胞免受复制诱导的DNA损伤方面的一个关键活性。我们还发现NS在Hep3B(人肝癌细胞)和晚期二乙基亚硝胺(DEN)诱导的小鼠肝癌细胞中高表达。此R03应用的目的是获得数据，以支持人类肝细胞癌标本中NS的临床相关性及其通过HR修复在增加肝细胞癌耐药性方面的潜在作用。我们假设NS的表达与人肝细胞癌的恶性程度相关，并且NS的缺失将损害肝细胞癌细胞基于HR的双链断裂(DSB)修复和化疗耐药特性。这一假说是基于以下原因提出的：1)NS在Hep3B细胞和DEN诱导的晚期肝癌中的表达显著上调；2)NS是维持Hep3B细胞持续增殖所必需的；3)NS促进基于HR的修复并防止乳腺(MDA-MB-231)和骨(U2OS)肿瘤细胞的基因组损伤；以及4)HR缺乏已知会使乳腺癌、卵巢癌、前列腺癌和胰腺癌对C/ts敏感。为了验证我们的假设，我们将追求三个具体目标。目标#1将描述与临床相关的 人肝细胞癌中的NS。目的#2将确定NS耗竭对肝癌细胞基于HR的DSB修复的影响。目的#3确定NS在介导肝癌耐药中的作用。作为这项应用的结果，我们将通过显示NS在人肝癌样本中表达的增加或异常来确定NS的临床重要性，确定NS表达与患者临床结局之间的关系，并提供功能证据支持NS在促进肝癌细胞基于HR的修复和化疗耐药中的作用，所有这些都是我们未来R01提交的重要初步数据。如果我们的假设被证明是正确的，这将影响我们对肝癌细胞如何适应过度活跃的有丝分裂状态和避免晚期致命的基因组不稳定的认识，肝癌如何发展先天的化疗耐药特性，以及是否可以通过NS消融使肝癌对C/Ts重新敏感。鉴于肝癌发生的复杂性和肝细胞癌的异质性，将C/TS与一种针对癌细胞共同适应机制的治疗相结合，为提高C/TS的疗效和耐受性提供了一个有吸引力的策略。

 DESCRIPTION (provided by applicant): Resistance of high-grade tumors to DNA damage-inducing chemotherapeutic agents (C/Ts) is a major cause of cancer mortality. Hepatocellular carcinoma (HCC) is well known for its innate resistance to C/Ts, but the underlying mechanisms remain unclear. Recent studies are beginning to home in on the notion that the progression and drug resistance of late-stage breast and ovarian cancers may depend on the homologous recombination (HR) repair pathway. My group studies a self-renewal mechanism controlled by a stem and cancer cell-enriched protein called nucleostemin (NS). We recently discovered a key activity of NS in promoting HR repair and protecting cancer cells from replication-induced DNA damage. We also found that NS is highly expressed in Hep3B (human HCC) cells and late-stage diethylnitrosamine (DEN)-induced mouse HCC. The objective of this R03 application is to obtain data to support the clinical relevance of NS in human HCC samples and its potential role in conferring HCC drug resistance via HR repair. We hypothesize that NS expression correlates with the malignancy of human HCC and that NS depletion will compromise the HR- based double-strand break (DSB) repair and chemoresistant property of HCC cells. This hypothesis is formulated based on the following reasons: 1) NS expression is significantly up-regulated in Hep3B cells and in DEN-induced HCC at the late carcinoma stage; 2) NS is required to maintain the continuous proliferation of Hep3B cells; 3) NS promotes HR-based repair and prevents genomic damage in breast (MDA-MB-231) and bone (U2OS) tumor cells; and 4) HR deficiency is known to sensitize breast, ovarian, prostate, and pancreatic cancers to C/Ts. To test our hypothesis, three specific aims will be pursued. Aim #1 will characterize the clinical relevance of NS in human HCC. Aim #2 will determine the effect of NS depletion on HR-based DSB repair in HCC cells. Aim #3 will determine the role of NS in mediating HCC drug resistance. As the outcome of this application, we will establish the clinical importance of NS by showing an increased or dysregulated NS expression in human HCC samples, define the relationship between NS expression and patients' clinical outcome, and provide functional evidence to support the role of NS in promoting the HR-based repair and chemoresistance in HCC cells, all of which are important preliminary data for our future R01 submission. If our hypothesis is proven true, it will impact on our knowledge of how HCC cells adapt to the hyperactive mitotic state and avoid fatal genomic instability at late stage, how HCC develop the innate property of chemoresistance, and whether HCC can be re-sensitized to C/Ts by NS ablation. Given the complexity of hepatocarcinogenesis and heterogeneity of HCC, combining C/Ts with a treatment that targets a common adaptive mechanism used by cancer cells offers an appealing strategy to improve the efficacy and tolerability of C/Ts.