Elucidating the structural insights into the BMP receptor mutations in PAH

项目概要/摘要 肺动脉高压（PAH）是一种进行性疾病，如果不治疗，可导致3年内死亡。PAH 其特征是肺动脉重塑并最终闭塞，随后PA压力升高 和右心衰竭骨形态发生蛋白受体2型基因（BMPR 2）的杂合突变 是PAH的主要遗传原因。在BMPR 2突变的患者中，PAH的发生时间提前数年， 比BMPR 2正常的患者更严重。尽管最近在查明 BMPR 2突变的分子和细胞后果，不存在针对BMPR 2携带者的靶向治疗，也没有 满足了对新疗法的迫切需要。 一个得到充分支持的BMP信号传导模型始于配体与一组跨膜蛋白结合， 丝氨酸/苏氨酸受体激酶包括两种1型受体（BMRP 1）和两种2型受体（BMPR 2）。 异源四聚体活性BMP受体复合物磷酸化携带信号的Smad蛋白 到细胞核的下游。该模型的缺陷包括缺乏对受体为什么需要被 以异源四聚体构型组织以具有活性，以及受体激酶如何被激活。 因此，我们对定位于BMPR 2细胞内区域的普遍PAH突变的理解， 仍然不能令人满意，并且阻碍了PAH靶向治疗的发展。我们最近的研究导致了 发现BMPR 2的激酶结构域与1型BMP受体激酶形成异二聚体。形成 异二聚体不足以激活1型激酶但对于配体诱导的受体信号传导是必需的， 提示其在活性受体四聚体的组装中的重要作用。重要的是，一些BMPR 2突变体 连接到PAH映射到异二聚体界面并抑制配体诱导的下游Smad信号传导， 支持异二聚体界面的生理学意义。本申请的目的是阐明 BMP受体激酶激活的分子基础，并阐明对BMPR 2 突变通过以下方式触发PAH：（i）剖析1型/1型激酶寡聚化在PAH的催化代谢中的作用， BMP受体复合物的激活、下游信号传导和血管稳态，和（ii）获得BMP受体复合物， 结构的理解，活性1型/2型激酶结构域复合物单独和在全- 长度的BMP受体四聚体。完成后，这项研究将确定非催化的意义， 界面上存在的BMP受体激酶，并提供了深入了解BMPR 2突变如何扰乱类型 1/2型激酶相互作用导致PAH。这些知识将为发展提供平台， 创新的新型PAH疗法。

PROJECT SUMMARY/ABSTRACT Pulmonary Arterial Hypertension (PAH) is a progressive disease that leads to death in 3 years if untreated. PAH is characterized by remodeling and eventually occlusion of the pulmonary arteries, followed by high PA pressure and right heart failure. Heterozygous mutations in the bone morphogenetic protein receptor type 2 gene (BMPR2) are the leading genetic cause of PAH. In patients with BMPR2 mutations, PAH develops years earlier, and in a more severe form, than in patients with normal BMPR2. Notwithstanding the recent progress in identifying the molecular and cellular consequences of BMPR2 mutations, no targeted therapy for BMPR2 carriers exist, nor the dire need for novel therapies has been met. A well-supported model of BMP signaling starts with a ligand binding to a group of transmembrane serine/threonine receptor kinases comprised of two type 1 receptor (BMRPI) and two type 2 receptors (BMPR2). The heterotetrameric active BMP receptor complex phosphorylates Smad proteins that carry the signal downstream to the nucleus. Gaps in this model include lack of understanding why the receptors need to be organized in a heterotetramer configuration to be active, and how the receptor kinases are activated. Consequently, our understanding of prevalent PAH mutations that localize to the BMPR2 intracellular regions remains unsatisfactory and prohibitive from advancing PAH-targeted therapies. Our recent studies have led to a discovery that kinase domain of BMPR2 forms a heterodimer with a type 1 BMP receptor kinase. Formation of the heterodimer is not sufficient to activate the type 1 kinase but is essential for ligand-induced receptor signaling, suggesting its essential role in assembly of the active receptor tetramer. Importantly, several BMPR2 mutants linked to PAH map to the heterodimer interface and inhibit ligand-induced downstream Smad signaling, supporting the physiological significance of the heterodimer interface. The goal of this application is to elucidate the molecular underpinnings of BMP receptor kinase activation and elucidate how poorly understood BMPR2 mutations trigger PAH by: (i) dissecting the role of the type 1/type 1 kinase oligomerization in the catalytic activation of the BMP receptor complex, downstream signaling, and vascular homeostasis, and (ii) gaining the structural understanding of the active type 1/type 2 kinase domain complexes alone and in the context of full- length BMP receptor tetramers. Upon completion, this study will define the significance of the non-catalytic interfaces present on BMP receptor kinases and provide insights into how BMPR2 mutations perturb the type 1/type 2 kinase interactions resulting in PAH. This knowledge will provide platform for the development of innovative novel PAH therapies.