Hermansky Pudlak Syndrome & melanosome formation

描述(申请人提供)：黑素小体是组织特有的细胞内细胞器，在眼睛和皮肤黑素细胞的色素细胞中黑色素的生物合成、储存和运输中起作用。在这些细胞中，黑素小体通过早期内吞细胞器中特定蛋白质内容的有序递送，在逐渐发育的阶段形成。黑素小体形成缺陷会导致眼皮肤白化病(OCA)，这是一种与视力受损和皮肤和眼睛的癌症易感性增加有关的疾病。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，在这种疾病中，黑素体和其他相关的组织特异性细胞器无法正确形成。小鼠大多数形式的HPS和相关疾病是由编码参与黑素小体形成的细胞质多亚单位蛋白质复合体的亚单位的基因突变引起的。其中三个复合体，AP-3，BLOC-1和BLOC-2，功能是在早期内小体和黑素小体之间运输不同组的跨膜蛋白。AP-3是一种外壳蛋白，将蛋白质包装成内体衍生的小泡，但BLOC-1和BLOC-2的分子功能尚不清楚。我们将利用AP-3、BLOC-1和BLOC-2缺陷的黑素细胞所提供的遗传工具，以概括的术语定义内小体到黑素小体的顺行和逆行运输途径，并定义支配它们的分子相互作用。初步证据表明，VAMP7和Synaxin 13，两个SNARE家族成员，在内体途径中介导膜对接和融合，以及小的调节GTP酶Rab11，在BLOC-1和/或AP-3途径中具有重要的功能。我们推测，BLOC-1、BLOC-2和AP-3与Rab11共同调节循环内吞体膜动力学和SNARE依赖的膜与成熟黑素体膜的融合，而Synaxin 13和VAMP7是必需的SNARE复合体的组成部分。我们将在以下特定目标上检验这一一般假说：1.检验SNARE蛋白--Synaxin 13是SNARE复合体的组成部分的假说，SNARE复合体通过BLOC-1调节的途径向黑素体运送货物。2.验证SNARE蛋白VAMP7是SNARE复合体的一个组成部分，该复合体将AP-3依赖的货物传递与黑素体与BLOC-1依赖的货物传递联系起来。3.验证BLOC-2在调节早期内小管与黑素小体依赖的融合中的作用。4.验证Rab11效应器通过调节黑素小体与黑素小体之间的顺行和逆行转运平衡，发挥黑素小体成熟感受器的作用。通过定义这些功能和途径，我们将进一步了解细胞器形成的遗传障碍的病因学，并为HPS的治疗方案提供见解。公共卫生相关性：Hermansky-Pudlak综合征是一组在波多黎各常见的遗传性疾病，其特征是眼皮肤白化，大量出血，在许多情况下是致命的肺纤维化和/或免疫缺陷。这些症状是由于未能在受影响的细胞类型中形成特定的膜结构或细胞器。这项建议使用黑素小体作为模型系统，黑素小体是色素细胞中的一个目标细胞器，以了解在Hermansky-Pudlak综合征患者中被破坏的基因产物通常如何发挥功能来产生专门的细胞器。

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.