Inactivation of Hdac3 in the cause, prevention, and treatment of HCC

描述（由申请人提供）：组蛋白去乙酰化酶调节染色质结构、转录、复制和DNA修复/重组。由于这些在细胞周期控制中的关键作用，hdac已成为多种肿瘤治疗干预的重要靶点，首个组蛋白去乙酰化酶抑制剂（HDI）已获得FDA批准。组蛋白去乙酰化酶3 （Hdac3）是染色质结构和基因表达的关键调节因子，我们的初步数据表明它可能是hdi的中心靶点。由于组蛋白去乙酰化酶的多方面作用，很难确定抑制这些酶是如何杀死癌细胞而不影响周围正常组织的。因此，我们开始通过改造含有“floxed”Hdac3的小鼠来了解Hdac3的作用。在种系中缺失Hdac3会导致早期胚胎死亡。此外，Hdac3缺失对体外培养的小鼠胚胎成纤维细胞甚至是致命的。尽管我们用“转录偏差”来进行分析，但基因表达阵列分析未能确定可能解释这种细胞凋亡的基因表达模式的诱导。相反，对细胞周期的仔细分析表明，凋亡需要S期进展，并且S期减慢。令人惊讶的是，在Hdac3缺失的情况下，S期DNA损伤检查点被激活。这一观察结果，再加上将Hdac3与DNA修复联系起来的数据，使我们发现Hdac3的缺失导致DNA损伤，这很可能是由于DNA双链断裂的修复效率低下，而DNA双链断裂发生在DNA复制分叉处。我们现在已经开始将这些信息转化为成年小鼠体内对Hdac3的需求。小鼠肝脏中Hdac3的去除导致了类似于非酒精性脂肪性肝病的表型，这可能是由于核激素受体功能的失调。最重要的是，与DNA修复缺陷和基因组不稳定性一致，肝脏特异性缺失Hdac3导致100%的浸润性肝细胞癌，平均发生时间为10.2个月。我们假设Hdac3是有效的DNA修复所必需的，Hdac3的缺失会导致基因组不稳定，从而导致癌症的发展，但我们可以利用DNA修复中的这些缺陷来治疗癌症。这一建议将进一步明确Hdac3失活影响DNA修复、调节染色质结构和导致肝细胞癌的机制。

DESCRIPTION (provided by applicant): Histone deacetylases regulate chromatin structure, transcription, replication, and DNA repair/recombination. Because of these key roles in cell cycle control, HDACs have become an important target for therapeutic intervention in a variety of tumors and the first Histone Deacetylase Inhibitor (HDI) has received FDA approval. Histone deacetylase 3 (Hdac3) is a key regulator of chromatin structure and gene expression and our preliminary data suggests that it may be a central target of HDIs. Because of the multi-faceted action of histone deacetylases, it has been difficult to pin down how inhibiting these enzymes acts to kill cancer cells while sparing surrounding normal tissues. Therefore, we set out to understand the action of Hdac3 by engineering mice containing a "floxed" Hdac3. Deletion of Hdac3 in the germ line caused early embryonic lethality. Moreover, Hdac3 deletion was even lethal to murine embryonic fibroblasts in vitro. Although we approached this analysis with a "transcription bias", gene expression array analysis failed to identify the induction of a gene expression pattern that might explain this apoptosis. By contrast, careful analysis of the cell cycle indicated that apoptosis required S phase progression and that S phase was slowed. Surprisingly, the S phase DNA damage checkpoint was activated in the absence of Hdac3. This observation, coupled with data linking Hdac3 to DNA repair, led us to the discovery that loss of Hdac3 caused DNA damage that was most likely due to inefficient repair of the DNA double strand breaks that occur at stalled DNA replication forks. We have now begun to translate this information to the in vivo requirements for Hdac3 in adult mice. Removal of Hdac3 in the mouse liver caused a phenotype similar to non-alcoholic fatty liver disease, which was likely due to de- regulated nuclear hormone receptor functions. Most importantly, consistent with defects in DNA repair and genomic instability, the liver-specific deletion of Hdac3 caused a 100% penetrant hepatocellular carcinoma with a mean time to HCC of 10.2 months. We hypothesize that Hdac3 is required for efficient DNA repair and that loss of Hdac3 causes genomic instability that leads to cancer development, but that we can take advantage of these defects in DNA repair to treat cancer. This proposal will further define the mechanisms by which inactivation of Hdac3 affects DNA repair, regulates chromatin structure, and causes hepatocellular carcinoma. PUBLIC HEALTH RELEVANCE: Histone deacetylase 3 (Hdac3) is a key factor controlling the expression of genes, which may be a therapeutic target for cancer therapy. This application addresses the role of this key gene in the cause, prevention, and treatment of hepatocellular carcinoma.