Hayashi Teruo, Su Tsung-Ping
Cellular Pathobiology Unit, Cellular Neurobiology Research Branch, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Department of Health and Human Services, Baltimore, MD 21224, USA.
J Pharmacol Exp Ther. 2003 Aug;306(2):718-25. doi: 10.1124/jpet.103.051284. Epub 2003 May 2.
The brain sigma-1 receptors can bind neurosteroids and psychotropic drugs, including neuroleptics and cocaine and are implicated in schizophrenia, depression, and drug dependence. In this study, we found that sigma-1 receptors specifically target lipid storage sites (lipid droplets) on the endoplasmic reticulum by forming a distinct class of lipid microdomains. Both endogenously expressing sigma-1 receptors and transfected C-terminally enhanced yellow fluorescent protein (EYFP)-tagged sigma-1 receptors (Sig-1R-EYFP) target unique "ring-like" structures associated with endoplasmic reticulum reticular networks in NG108-15 cells. The ring-like structures contain neutral lipids and are enlarged by the oleate treatment, indicating that they are endoplasmic reticulum-associated lipid droplets (ER-LDs). sigma-1 receptors colocalize with caveolin-2, a cholesterol-binding protein in lipid rafts on the ER-LDs, but not with adipocyte differentiation-related protein (ADRP), a cytosolic lipid droplet (c-LD)-specific protein. When the double-arginine ER retention signal on the N terminus of sigma-1 receptors is truncated, sigma-1 receptors no longer exist on ER-LDs, but predominantly target c-LDs, which contain ADRP. sigma-1 receptors on ER-LDs form detergent-resistant raft-like lipid microdomains, the buoyancy of which is different from that of plasma membrane lipid rafts. (+)-Pentazocine causes sigma-1 receptors to disappear from the microdomains. N-Terminally EYFP-tagged sigma-1 receptors (EYFP-Sig-1R) failed to target ER-LDs. EYFP-Sig-1R-transfected cells showed an unrestricted distribution of neutral lipids all over the endoplasmic reticulum network, decreases in c-LDs and cholesterol in plasma membranes, and the bulbous aggregation of endoplasmic reticulum. Thus, sigma-1 receptors are unique endoplasmic reticulum proteins that regulate the compartmentalization of lipids on the endoplasmic reticulum and their export from the endoplasmic reticulum to plasma membrane and c-LDs.
大脑中的σ-1受体可与神经甾体和精神药物结合，包括抗精神病药物和可卡因，并且与精神分裂症、抑郁症及药物依赖有关。在本研究中，我们发现σ-1受体通过形成一类独特的脂质微区，特异性地靶向内质网上的脂质储存位点（脂滴）。内源性表达的σ-1受体和转染的C末端增强型黄色荧光蛋白（EYFP）标记的σ-1受体（Sig-1R-EYFP）均靶向NG108-15细胞中与内质网网状网络相关的独特“环状”结构。这些环状结构含有中性脂质，并通过油酸盐处理而增大，表明它们是内质网相关脂滴（ER-LDs）。σ-1受体与小窝蛋白-2共定位，小窝蛋白-2是ER-LDs上脂筏中的一种胆固醇结合蛋白，但不与脂肪细胞分化相关蛋白（ADRP）共定位，ADRP是一种胞质脂滴（c-LD）特异性蛋白。当σ-1受体N末端的双精氨酸内质网保留信号被截断时，σ-1受体不再存在于ER-LDs上，而是主要靶向含有ADRP的c-LDs。ER-LDs上的σ-1受体形成抗去污剂的筏样脂质微区，其浮力与质膜脂筏不同。（+）-喷他佐辛使σ-1受体从这些微区消失。N末端EYFP标记的σ-1受体（EYFP-Sig-1R）未能靶向ER-LDs。EYFP-Sig-1R转染的细胞在内质网网络上显示中性脂质分布不受限制，质膜中的c-LDs和胆固醇减少，以及内质网的球状聚集。因此，σ-1受体是独特的内质网蛋白，可调节内质网上脂质的区室化及其从内质网到质膜和c-LDs的输出。
