Project 2: Role of ACER2 in Liver Cancer

摘要 肝细胞癌是一种主要的肝癌，是世界范围内癌症死亡的主要原因。 肝细胞癌对大多数治疗方案仍然难以奏效；因此，迫切需要新的治疗方式。我们的 长期目标是在深入了解其发病机制的基础上开发新的肝癌治疗方法。这个 本申请的特定目标是确定碱性神经酰胺酶2的新的肿瘤抑制作用 (ACER2)通路在肝癌发生发展中的作用ACER2是碱性神经酰胺酶家族的成员 我们最初从酿酒酵母中鉴定出这种物质，然后从哺乳动物中鉴定出来。ACER2催化 神经酰胺的水解产生鞘氨醇(SPH)，这是一种与细胞程序性死亡有关的生物活性脂质 (PCD)和自噬。我们发现ACER2是P53的一个新的转录靶点，并证明了ACER2 ACER2/SPH通路是一个新的信号轴，它在P53下游调节PCD DNA损伤。根据TCGA数据库，ACER2在几种癌症中发生突变或缺失抑制。 先前的一项研究发现，ACER2在肝癌中受到表观遗传抑制，我们的初步结果显示 与患者配对的邻近非肿瘤肝组织相比，ACER2在肝脏肿瘤中表达下调。 值得注意的是，我们发现缺乏碱性神经酰胺酶2(Acer2)基因的小鼠更容易受到年龄的影响。 包括肝肿瘤在内的各种自发性肿瘤类型的相关发展，表明ACER2是一种 新型肿瘤抑制药。根据这些令人兴奋的发现，我们假设ACER2是一种新的肿瘤 抑制物可促进肝细胞癌的发生、发展和对DNA损伤的抵抗 化疗药物。作为进一步的推论，我们假设纠正ACER2/SPH途径将抑制 并克服肝癌对化疗药物的耐药性。这些假说将在三个方面进行检验 相关的特定目标：目标1确定ACER2在使用肝脏的肝细胞癌中发挥关键的肿瘤抑制作用 小鼠致癌模型和肝脏器官模型，目的2通过以下方式确定细胞和分子机制 其中抑制ACER2/SPH通路促进肝肿瘤的发生，目的3确定其作用 ACER2通路在提高肝细胞癌放化疗效果中的作用成功完成这些目标将1) 验证新发现的肿瘤抑制基因ACER2的肿瘤抑制作用；2)提供新的见解 新发现的P53/ACER2/SPH信号轴介导DNA损伤的机制 反应和肿瘤抑制；以及3)提供了将ACER2/SPH途径发展为 肝癌的新治疗靶点。鉴于肝细胞癌患者的临床结果不佳，这些研究可能已经 对这些患者的临床管理产生了广泛影响。

Abstract Hepatocellular carcinoma (HCC), a major type of liver cancer, is a leading cause of cancer deaths worldwide. HCC remains refractory to most treatment options; hence, new therapeutic modalities are urgently needed. Our long-term goal is to develop novel HCC therapeutics based on a deep understanding of its pathogenesis. The specific goal of this application is to define a novel tumor suppressive role for the alkaline ceramidase 2 (ACER2) pathway in HCC development and progression. ACER2 is a member in the alkaline ceramidase family that we identified initially from the yeast Saccharomyces cerevisiae and then from mammals. ACER2 catalyzes the hydrolysis of ceramides to generate sphingosine (SPH), a bioactive lipid implicated in programmed cell death (PCD) and autophagy. We identify ACER2 as a novel transcriptional target of p53 and demonstrate that the ACER2/SPH pathway is a novel signaling axis that operates downstream of p53 to mediate PCD in response to DNA damage. According to the TCGA database, ACER2 is mutated or deleted suppressed in several cancers. A previous study finds that ACER2 is epigenetically repressed in HCC and our preliminary results reveal that ACER2 is downregulated in liver tumors compared to patient-matched adjacent non-tumor liver tissues. Remarkably, we find that mice deficient in the alkaline ceramidase 2 (Acer2) gene are more susceptible to age- related development of various spontaneous tumor types including liver tumors, suggesting that ACER2 is a novel tumor suppressor. According to these exciting findings, we hypothesize that ACER2 is a novel tumor suppressor whose suppression promotes HCC development, progression, and resistance to DNA-damaging chemotherapeutics. As a further corollary, we hypothesize that rectifying the ACER2/SPH pathway will inhibit HCC and overcome the resistance of HCC to chemotherapeutics. These hypotheses will be tested in three interrelated specific aims: Aim 1 Establish that ACER2 plays a key tumor suppressive role in HCC using a liver carcinogenesis mouse model and liver organoid model, Aim 2 Define the cellular and molecular mechanisms by which the repression of the ACER2/SPH pathway promotes liver tumorigenesis, and Aim 3 Establish the role of the ACER2 pathway in improving the radio/chemotherapy of HCC. Successful completion of these aims will 1) validate the tumor suppressive role of the newly-identified tumor suppressor ACER2; 2) offer novel insights into the mechanisms by which the newly identified p53/ACER2/SPH signaling axis mediates the DNA damage response and tumor suppression; and 3) provide a proof of concept to develop the ACER2/SPH pathway into a novel therapeutic target for HCC. Given the poor clinical outcome of patients with HCC, these studies may have widespread impact on the clinical management of these patients.