Hermansky Pudlak Syndrome & melanosome formation

描述（由申请人提供）：黑色素小体是组织特异性的细胞内细胞器，在眼睛色素细胞和皮肤黑色素细胞中的黑色素的生物合成、储存和运输中起作用。黑素体在这些细胞中通过早期内吞细胞器的特定蛋白质含量的有序递送，在渐进的发育阶段形成。黑色素小体形成缺陷导致眼皮肤白化病（OCA），这是一种与视力受损和皮肤和眼睛癌症易感性增强相关的疾病。OCA是与Hermansky-Pudlak综合征（HPS）相关的几种系统性疾病之一，HPS是一种遗传性疾病，其中黑素体和其他相关的组织特异性细胞器不能正常形成。在小鼠中，大多数形式的HPS和相关疾病是由编码参与黑素体形成的细胞质多亚基蛋白复合物亚基的基因突变引起的。其中三种复合物AP-3、block -1和block -2在早期核内体和黑素小体之间运输不同的跨膜蛋白。AP-3是一种将蛋白质包裹到内核体衍生囊泡中的外壳蛋白，但block -1和block -2的分子功能尚不清楚。我们将利用AP-3， block -1和block -2缺陷黑素细胞提供的遗传工具，以概括的术语定义内核体到黑素小体的顺行和逆行运输途径，并定义控制它们的分子相互作用。初步证据表明，VAMP7和syntaxin 13这两个SNARE家族成员在内体途径中介导膜对接和融合，以及小调节GTPase Rab11在block -1和/或AP-3途径中具有重要的功能。我们假设block -1、block -2和AP-3与Rab11协同作用，调节内核体的循环膜动力学和成熟黑素体与SNARE依赖的膜融合，并且syntaxin 13和VAMP7是必要的SNARE复合物的组成部分。我们将在以下具体目标中检验这一一般假设：为了验证SNARE蛋白syntaxin 13是SNARE复合体的一个组成部分的假设，该复合体通过block -1调节的途径将货物运送到黑素体。2. 为了验证SNARE蛋白VAMP7是SNARE复合体的一个组成部分的假设，该复合体将ap -3依赖性货物传递与block -1依赖性货物传递联系起来。3. 为了验证block -2在调节早期内体小管与黑素体的snare依赖性融合中的作用。4. 为了验证Rab11效应物通过调节内体和黑素小体之间的顺行和逆行运输平衡而作为黑素小体成熟传感器的假设。通过定义这些功能和途径，我们将进一步了解细胞器形成遗传疾病的病因学，并为HPS的治疗方案提供见解。公共卫生相关性：Hermansky-Pudlak综合征是一组常见于波多黎各的遗传性疾病，其特征是皮肤白化病、大出血，在许多情况下还会导致致命的肺纤维化和/或免疫缺陷。这些症状是由于在受影响的细胞类型中不能形成某些特殊的膜结构或细胞器而引起的。本研究利用色素细胞内的靶细胞器黑素小体作为模型系统，以了解Hermansky-Pudlak综合征患者中被破坏的基因产物如何正常地产生专门的细胞器。

DESCRIPTION (provided by applicant): Melanosomes are tissue-specific intracellular organelles that function in the biosynthesis, storage, and transport of melanins in pigment cells of the eye and skin melanocytes. Melanosomes form within these cells through progressive developmental stages by the ordered delivery of specific protein contents from early endocytic organelles. Defects in melanosome formation cause oculocutaneous albinism (OCA), a condition associated with impaired vision and enhanced cancer susceptibility in the skin and eye. OCA is one of several systemic conditions associated with the Hermansky-Pudlak syndromes (HPS), genetic disorders in which melanosomes and other related tissue-specific organelles fail to form properly. Most forms of HPS and related disorders in mice result from mutations in genes that encode subunits of cytoplasmic multisubunit protein complexes involved in melanosome formation. Three of these complexes, AP-3, BLOC-1 and BLOC-2, function in trafficking distinct sets of transmembrane proteins between early endosomes and melanosomes. AP-3 is a coat protein that packages protein cargoes into endosome-derived vesicles, but the molecular functions of BLOC-1 and BLOC-2 are not known. We will exploit the genetic tools afforded by AP-3-, BLOC-1- and BLOC-2-deficient melanocytes to define endosome-to-melanosome anterograde and retrograde trafficking pathways in generalizable terms and define the molecular interactions that govern them. Preliminary evidence implicates VAMP7 and syntaxin 13, two SNARE family members that mediate membrane docking and fusion in the endosomal pathway, and the small regulatory GTPase Rab11 as functionally important in the BLOC-1 and/or AP-3 pathways. We hypothesize that BLOC-1, BLOC-2 and AP-3 function in concert with Rab11 to regulating recycling endosome membrane dynamics and SNARE-dependent membrane fusion with maturing melanosomes, and that syntaxin 13 and VAMP7 are components of the requisite SNARE complexes. We will test this general hypothesis in the following specific aims: 1. To test the hypothesis that the SNARE protein, syntaxin 13, is a component of the SNARE complex that delivers cargo to melanosomes by the BLOC-1-regulated pathway. 2. To test the hypothesis that the SNARE protein, VAMP7, is a component of the SNARE complex that links AP-3-dependent cargo delivery to melanosomes with BLOC-1-dependent cargo delivery. 3. To test the hypothesis that BLOC-2 functions in regulating SNARE-dependent fusion of early endosomal tubules with melanosomes. 4. To test the hypothesis that Rab11 effectors function as sensors of melanosome maturation by regulating the balance of anterograde and retrograde transport between endosomes and melanosomes. By defining these functions and pathways, we will further our understanding of the etiology of genetic disorders of organelle formation and provide insights into treatment regimens for HPS. PUBLIC HEALTH RELEVANCE: Hermansky-Pudlak syndrome is a group of genetic disorders that are common in Puerto Rico and are characterized by oculocutaneous albinism, excessive bleeding, and in many cases a fatal lung fibrosis and/or immune deficiency. The symptoms result from the failure to form certain specialized membrane structures, or organelles, within affected cell types. This proposal uses the melanosome, a target organelle within pigment cells, as a model system to understand how the products of the genes that are disrupted in Hermansky-Pudlak syndrome patients normally function to generate specialized organelles.