Role of Daxx in protein folding and tumorigenesis

摘要 这项应用的总体目标是阐明死亡结构域相关蛋白(DAXX)在肿瘤发生中的作用。Daxx最初被PI鉴定为与死亡受体Fas(CD95/Apo-1)的胞内结构域相互作用的接头蛋白。其他人和我们随后的研究表明，DAXX参与了各种不同的细胞凋亡场景，以及无数其他细胞过程。值得注意的是，胰腺神经内分泌肿瘤(PanNETs)经常存在DAXX和DAXX相关蛋白ATRX的突变。这些观察提出了一个关键问题，即是否存在一种明确的生化活性，这是DAXX总体上的不同功能以及其在PanNETs中的肿瘤抑制功能的基础。我们的初步数据表明，DAXX在蛋白质质量控制(PQC)中具有以前没有预料到的活性。在这里，我们计划检验中心假设，即DAXX是蛋白质折叠(折叠酶)的一种新型催化剂，并且该活性的失调有助于PanNETs的发病。我们提出了三个具体目标。首先，我们将确定DAXX蛋白折叠催化剂活性的分子机制，并阐明其通过相互作用伙伴和翻译后修饰来调节。其次，肿瘤抑制基因p53在绝大多数肿瘤中都是失活的，但在PanNETs中很少发生突变。基于我们的初步数据，我们将检验这一假设，即DAXX是P53的折叠催化剂，促进其稳定性和功能，并且DAXX的丢失有助于PanNETs中这一卓越的肿瘤抑制因子的失活。第三，DAXX和DAXX相互作用蛋白PML都参与了端粒交替延长(ALT)途径，在包括PanNETs在内的各种肿瘤中维持端粒长度。我们以前的研究揭示了PML在清除错误折叠的蛋白质中的重要作用。我们将研究DAXX和PML在ALT途径中的合作。此外，我们还将探讨DAXX在PanNETs发病机制中的作用。总而言之，这些目标将解决DAXX生物学中的关键问题，并将为开发有效的PanNETs和其他DAXX相关肿瘤的治疗方法提供有价值的信息。

ABSTRACT The overall goal of this application is to elucidate the role of the death domain-associated protein (DAXX) in tumorigenesis. DAXX was initially identified by the PI as an adaptor protein interacting with the intracellular domain of the death receptor Fas (CD95/Apo-1). Subsequent studies by others and us have implicated DAXX in various scenarios of apoptosis, as well as a myriad of other cellular processes. Of note, pancreatic neuroendocrine tumors (PanNETs) frequently harbor mutations in DAXX and the DAXX-associated protein ATRX. These observations raise a critical issue of whether there is a defined biochemical activity that underlies the diverse function of DAXX in general and its tumor suppressive function in PanNETs in particular. Our preliminary data suggests that DAXX possesses a previously unanticipated activity in protein quality control (PQC). Here we plan to test the central hypothesis that DAXX is a novel catalyst for protein folding (foldase) and that the dysregulation of this activity contributes to the pathogenesis of PanNETs. We propose three specific aims. First, we will define the molecular mechanism of the protein folding catalyst activity of DAXX, and elucidate its regulation by interacting partners and post-translational modifications. Second, the tumor suppressor p53, which is inactivated in the vast majority of tumors, is rarely mutated in PanNETs. Based on our preliminary data, we will test the hypothesis that DAXX is a folding catalyst for p53, promoting its stability and functionality, and that the loss of DAXX contributes to the inactivation of this preeminent tumor suppressor in PanNETs. Third, both DAXX and the DAXX-interacting protein PML are involved in the alternative lengthening of telomeres (ALT) pathway, which maintains telomere length in various tumors including PanNETs. Our previous studies reveal an important role of PML in the clearance of misfolded proteins. We will examine the cooperation of DAXX and PML in the ALT pathway. Moreover, we will investigate the role of DAXX in the pathogenesis of PanNETs. Collectively, these aims will address critical issues in DAXX biology and will provide valuable information for the development of effective therapies for PanNETs and other DAXX-associated tumors.