Molecular functions of the shelterin component ACD/TPP1 in somatic stem cells and tissue homeostasis

 描述(申请人提供)：六种蛋白质的保护素复合体与端粒酶协同作用，以维持染色体末端的完整性。作为保护素的一部分，ACD/TPP1蛋白保护端粒末端不受DNA损伤反应机制的影响。此外，ACD/TPP1通过一种被称为TEL补丁的专用蛋白质表面，参与将端粒酶招募到端粒中。末端保护和末端延长对于衰老组织中体细胞的维持和功能都是重要的。我们发现ACD/TPP1在造血干细胞和其他组织中具有重要的上下文特异性功能。最近的工作在先天性角化不良患者中发现了候选的ACD/TPP1突变，这是一种以骨髓和其他器官的躯体干细胞功能受损为特征的人类疾病，具有过早衰老的特征。这是首次在人类疾病中发现ACD/TPP1突变。我们的初步数据显示，这些突变可以扰乱细胞系中端粒酶的募集和端粒的稳态。然而，由于ACD/TPP1突变导致的细胞端粒维持缺陷如何转化为体内特定干细胞隔间的功能障碍，以及它们如何促进组织衰老和疾病，目前尚不清楚。我们假设ACD/TPP1突变可以在先天性角化不良和相关的躯体干细胞疾病中起到致病作用。此外，我们假设，当在哺乳动物组织中建模时，影响ACD/TPP1与其蛋白质伙伴的界面的点突变可以揭示Shelterin复合体的独特功能。为了详细探讨这一假说，我们将研究候选突变和其他影响ACD/TPP1与端粒酶或其掩蔽蛋白TIN2结合的变异，使用现代基因组编辑技术来评估它们在整个有机体中的作用。我们的具体目标是：1)评估候选人类ACD/TPP1 TEL斑块突变对造血干细胞和骨髓稳态的影响；2)确定ACD/TPP1与TIN2相互作用的结构要求以及TIN2-ACD/TPP1结合缺陷的功能后果；3)研究候选ACD/TPP1致病变异体如何影响组织稳态和寿命，这些变异破坏了与关键蛋白质伙伴的相互作用。我们的多学科方法将确定ACD/TPP1的不同功能表面，并确定它们对干细胞、组织动态平衡和衰老的影响。我们预计，我们将揭示ACD/TPP1和保护素/端粒酶复合体的突变失调如何最终导致人类疾病。

 DESCRIPTION (provided by applicant): The six-protein shelterin complex cooperates with telomerase to maintain the integrity of chromosomal ends. As part of shelterin, the protein ACD/TPP1 protects telomeric ends from the DNA damage response machinery. Additionally, ACD/TPP1 is uniquely involved in recruiting telomerase to telomeres through a dedicated protein surface known as the TEL patch. Both end-protection and end-elongation are important for the maintenance and function of somatic stem cells in aging tissues. We showed that ACD/TPP1 has essential context- specific functions in hematopoietic stem cells and in other tissues. Recent work identified candidate ACD/TPP1 mutations in patients with Dyskeratosis congenita, a human disorder characterized by impaired somatic stem cell function in the bone marrow and other organs, with features of premature aging. This is the first identification of ACD/TPP1 mutations in human disease. Our preliminary data show that these mutations can disrupt telomerase recruitment and telomere homeostasis in cell lines. However, how telomere maintenance defects in cells due to ACD/TPP1 mutations translate to dysfunction of specific stem cell compartments in vivo and how they contribute to tissue aging and disease is not understood. We hypothesize that ACD/TPP1 mutations can play a causative role in Dyskeratosis congenita and related somatic stem cell disorders. Furthermore, we postulate that point mutations affecting the interface of ACD/TPP1 with its protein partners can reveal unique functions of the shelterin complex when modeled in mammalian tissues. To explore this hypothesis in detail, we will study candidate mutations and other variants affecting binding of ACD/TPP1 with telomerase or with its shelterin partner TIN2, using modern genome-editing technology to assess their in vivo effects in the entire organism. Our Specific Aims are to: 1) Evaluate the impact of candidate human ACD/TPP1 TEL patch mutations on hematopoietic stem cells and bone marrow homeostasis; 2) Determine the structural requirements for the interaction of ACD/TPP1 with TIN2 and the functional consequences of defective TIN2- ACD/TPP1 binding; 3) Investigate how tissue homeostasis and longevity are affected by candidate ACD/TPP1 pathogenic variants that disrupt interaction with key protein partners. Our multidisciplinary approach will identify distinct functional surfaces of ACD/TPP1 and determine their impact on stem cells, tissue homeostasis and aging. We anticipate that we will uncover how mutational dysregulation of ACD/TPP1 and the shelterin/telomerase complex can ultimately result in human disease.