组蛋白H3.3伴侣DAXX驱动乳腺癌起始、进程和转移

Breast cancer is the most common malignancy in women, and metastatic lesions are the leading cause of death in patients. The molecular insights and potential specific biomarkers, particularly regarding the tumor-initiating and invasion and migration, is critical to improve current treatment options. Death-associated protein 6 (DAXX) is a ubiquitous protein implicated in various cellular processes such as apoptosis, tumorigenesis, development and transcription. To date, the role of DAXX as an H3.3-specific histone chaperone has been investigated primarily using biochemical approaches which provide genome-wide views on cell populations and information on changes in local chromatin structures. The complex which deposits H3.3 at heterochromatin is comprised of DAXX, an H3.3 specific chaperone, and a chromatin remodeller, ATRX. This chaperone complex both targets H3.3 to specific heterochromatic sites and interacts with histone modifiers to maintain the K9me3 heterochromatin mark. Although, genome sequencing efforts in a variety of cancers have revealed mutations and/or structural alterations in ATRX and DAXX . It is not yet known whether Daxx act separately or functionally role in breast cancer. Here, we assessed the expression of DAXX in human breast cancer tissue, and found Daxx played an intrinsic role in the cellular response to damage induced by UV irradiation in human breast cancer cells. Further, we examined the role of Daxx in breast tumor initiation and progression of primary tumor and metastasis by conditionally ablating Daxx in mammary epithelium of the MMTV-PyMT breast cancer mouse model. Depletion of Daxx caused a delay in primary tumor initiation, inhibited tumor progression, and reduced metastasis to lung. Thus, we hypothesis that Daxx driving carcinogenesis is believed to result from a succession of epigenetic alterations and selection steps leading to the emergence of cells accumulating survival and proliferation advantages. Interestingly, we also found not all of mammary tumor development and metastatasis were delayed and inhibited, which should be independent Daxx regulation. Both type of mammary carcinomas will be investigated. It should be help to understanding of the mechanisms that contribute to intratumoral heterogeneity in breast tumors. In this study, we not only investigate the epigenetic function of Daxx regulating mammary tumor development and metastasis, also we integrate and analyze the expression and epigenetic modification profiling, combined with reported breast cancer data and our results, to constitute a novel target for diagnosis biomarker and therapeutic intervention.

乳腺癌是女性最常见的恶性肿瘤，复发和转移导致患者死亡。探寻肿瘤起始、侵袭和迁移的特异标记对于改善治疗尤为重要。Daxx参与细胞凋亡、转录调控和肿瘤发生等多种事件。近年来发现Daxx作为组蛋白H3.3伴侣与ATRX掺入异染色质，维持H3k9me3修饰调控基因组功能。Atrx/Daxx在不同肿瘤中出现突变，但Daxx在乳腺癌的作用尚未明确。前期研究我们发现Daxx促进人乳腺癌细胞抵抗DNA损伤的作用。进一步在乳腺癌小鼠模型（MMTV-PyMT）中条件性敲除Daxx，发现Daxx缺失能够延迟肿瘤发生、抑制肿瘤进程和肺转移。因此，我们认为Daxx通过表观遗传修饰的调控驱动肿瘤的发展，促进癌细胞存活和增殖。但是，部分乳腺癌的发展和转移并未完全推迟和抑制，说明有不依赖于Daxx调控的机制，这有助于理解乳腺癌的异质性。我们不仅研究Daxx促进乳腺癌发生和转移的表观调控，还整合数据挖掘新的诊断和治疗靶点。

乳腺癌是女性最常见的恶性肿瘤，复发和转移导致患者死亡。探寻肿瘤起始、侵袭和迁移的特异标记对于改善治疗尤为重要。本研究中利用小鼠乳腺癌模型系统全面研究Daxx对乳腺癌发生、进展和转移的贡献，为乳腺癌发生机制提供新的理论基础。DAXX作为组蛋白H3.3伴侣的表观调控染色质结构维持基因组功能稳定，通过这一视角阐明Daxx在乳腺癌发生和转移中的机制，这对丰富肿瘤发生和转移的机制功能研究具有重要意义，并为寻求新的诊断和治疗靶点提供帮助。.1、重要结果.（1）开展利用乳腺癌细胞系和多种实验技术手段证明Daxx具有促进乳腺癌细胞的增殖、迁移和存活的作用。过表达Daxx发现可显著提高乳腺癌细胞的迁移速度，而敲低则受到抑制，证明Daxx可以促进乳腺癌细胞的增殖和迁移。并且DAXX高表达也可以对抗DNA损伤引起的凋亡，为乳腺癌的临床治疗的预后提供参考。.（2）已构建Daxx模型小鼠，证实了体内敲除DAXX延迟小鼠乳腺肿瘤发生的起始和进程，并提高小鼠生存率，且抑制乳腺癌发生，发展和转移。同时敲除与DAXX相互作用的蛋白，也出现抑制肿瘤发生和发展的表型。.（3）获得Daxx敲除小鼠胚胎成纤维细胞（MEF）来源的iPSCs，结合转录组分析，证实了缺失DAXX抑制重编程过程，并具有抑制iPSCs的外胚层分化和神经分化能力。在神经分化过程中可诱导凋亡通路增加，并通过表观修饰导致rRNA转录增加。.（4）开展了公共数据库收录的乳腺癌和iPSCs转录组学数据的比较工作，鉴定与临床病理特征和预后显著相关的30个共同差异表达基因，将为新的潜在标志物进一步帮助研究者们理解肿瘤发生进展机制和提高治疗效率。.（5）本项目研究期间满足原计划SCI收录论文2-4篇的任务，均已按规定标注基金资助。主要结果发表在杂志：《Cell Reprogram》和《Cell Cycle》。.2、科学意义.本项目的完成将有助于理解Daxx在肿瘤发生和转移的机制，从基因组表观调控角度揭示了肿瘤发生的复杂因素及乳腺癌的异质性，为DAXX传统的功能研究进行新的注释，为发展乳腺癌诊断和治疗新靶点提供线索。