Adenovirus RIDα uncovers a novel pathway requiring ORP1L for lipid droplet formation independent of NPC1.
Adenovirus RIDα uncovers a novel pathway requiring ORP1L for lipid droplet formation independent of NPC1.
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DOI：
10.1091/mbc.e12-10-0760
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发表时间：
2013-11
影响因子：
3.3
通讯作者：
Carlin CR
中科院分区：
文献类型：
--
作者：
Cianciola NL;Greene DJ;Morton RE;Carlin CR
腺病毒蛋白RIDα的表达通过诱导脂滴的形成来挽救NPC 1缺陷细胞中的胆固醇储存表型。RIDα的功能不依赖于NPC 1，但依赖于NPC 2和氧固醇结合蛋白ORP 1 L。这项研究提供了第一个证据表明，ORP 1 L在甾醇转运和LD形成中发挥作用。C型尼曼-匹克病（NPC）是由NPC 1或NPC 2的突变引起的，NPC 1或NPC 2协调低密度脂蛋白（LDL）-胆固醇从晚期内体的排出。我们先前报道了腺病毒编码的蛋白RIDα挽救了NPC 1突变成纤维细胞中的胆固醇储存表型。我们在这里发现，RIDα重建了缺乏的内体-内质网（ER）转运，使过量的LDL-胆固醇被酰基辅酶A：胆固醇酰基转移酶酯化，并储存在NPC 1缺陷细胞的脂滴（LD）中。此外，RIDα途径受氧固醇结合蛋白ORP 1 L调节。研究已将ORP 1 L分类为参与GTP-Rab 7下游LE定位的固醇传感器。然而，我们的数据表明，ORP 1 L可能在LDL-胆固醇转运到指定用于LD形成的特定ER池中发挥作用。与NPC 1不同，RIDα/ORP 1 L依赖性途径需要功能性NPC 2。虽然NPC 1/NPC 2构成了主要途径，但放大LDL-胆固醇次要外出途径的疗法可显著改善NPC 1突变功能丧失患者的临床管理。然而，推定的替代途径的分子身份，是很差的特点。我们提出RIDα作为一个模型系统，用于理解使用ORP 1 L激活参与LD形成的ER反馈反应的生理出口途径。
Expression of the adenovirus protein RIDα rescues the cholesterol storage phenotype in NPC1-deficient cells by inducing formation of lipid droplets. The function of RIDα is independent of NPC1 but dependent on NPC2 and the oxysterol-binding protein ORP1L. This study provides the first evidence that ORP1L plays a role in sterol transport and LD formation. Niemann–Pick disease type C (NPC) is caused by mutations in NPC1 or NPC2, which coordinate egress of low-density-lipoprotein (LDL)-cholesterol from late endosomes. We previously reported that the adenovirus-encoded protein RIDα rescues the cholesterol storage phenotype in NPC1-mutant fibroblasts. We show here that RIDα reconstitutes deficient endosome-to-endoplasmic reticulum (ER) transport, allowing excess LDL-cholesterol to be esterified by acyl-CoA:cholesterol acyltransferase and stored in lipid droplets (LDs) in NPC1-deficient cells. Furthermore, the RIDα pathway is regulated by the oxysterol-binding protein ORP1L. Studies have classified ORP1L as a sterol sensor involved in LE positioning downstream of GTP-Rab7. Our data, however, suggest that ORP1L may play a role in transport of LDL-cholesterol to a specific ER pool designated for LD formation. In contrast to NPC1, which is dispensable, the RIDα/ORP1L-dependent route requires functional NPC2. Although NPC1/NPC2 constitutes the major pathway, therapies that amplify minor egress routes for LDL-cholesterol could significantly improve clinical management of patients with loss-of-function NPC1 mutations. The molecular identity of putative alternative pathways, however, is poorly characterized. We propose RIDα as a model system for understanding physiological egress routes that use ORP1L to activate ER feedback responses involved in LD formation.