Division of Biological Chemistry, Department of Pharmaceutical Sciences, School of Pharmacy, Showa University, 1-5-8 Hatanodai, Shinagawa, Tokyo 142-8555, Japan.
Int J Mol Sci. 2022 Jun 7;23(12):6366. doi: 10.3390/ijms23126366.
Lipid droplets (LDs) are intracellular organelles that are ubiquitous in many types of cells. The LD core consists of triacylglycerols (TGs) surrounded by a phospholipid monolayer and surface proteins such as perilipin 2 (PLIN2). Although TGs accumulate in the phospholipid bilayer of the endoplasmic reticulum (ER) and subsequently nascent LDs buds from ER, the mechanism by which LD proteins are transported to LD particles is not fully understood. Sar1 is a GTPase known as a regulator of coat protein complex Ⅱ (COPⅡ) vesicle budding, and its role in LD formation was investigated in this study. HuH7 human hepatoma cells were infected with adenoviral particles containing genes coding GFP fused with wild-type Sar1 (Sar1 WT) or a GTPase mutant form (Sar1 H79G). When HuH7 cells were treated with oleic acid, Sar1 WT formed a ring-like structure around the LDs. The transient expression of Sar1 did not significantly alter the levels of TG and PLIN2 in the cells. However, the localization of PLIN2 to the LDs decreased in the cells expressing Sar1 H79G. Furthermore, the effects of Sar1 on PLIN2 localization to the LDs were verified by the suppression of endogenous Sar1 using the short hairpin RNA technique. In conclusion, it was found that Sar1 has some roles in the intracellular distribution of PLIN2 to LDs in liver cells.
脂滴（LDs）是许多类型细胞中普遍存在的细胞内细胞器。LD 的核心由三酰甘油（TGs）组成，周围是一层磷脂单层和表面蛋白，如 perilipin 2（PLIN2）。尽管 TGs 在内质网（ER）的磷脂双层中积累，随后新生的 LD 从 ER 芽生，但 LD 蛋白如何转运到 LD 颗粒尚不完全清楚。Sar1 是一种 GTPase，被称为衣壳蛋白复合物 Ⅱ（COPⅡ）囊泡出芽的调节剂，本研究探讨了其在 LD 形成中的作用。HuH7 人肝癌细胞用含有 GFP 与野生型 Sar1（Sar1 WT）或 GTPase 突变体（Sar1 H79G）融合基因的腺病毒颗粒感染。当 HuH7 细胞用油酸处理时，Sar1 WT 在 LD 周围形成环状结构。Sar1 的瞬时表达并没有显著改变细胞中 TG 和 PLIN2 的水平。然而，在表达 Sar1 H79G 的细胞中，PLIN2 向 LD 的定位减少。此外，通过短发夹 RNA 技术抑制内源性 Sar1，验证了 Sar1 对 PLIN2 向 LD 定位的影响。总之，发现 Sar1 在肝细胞中 PLIN2 向 LD 的细胞内分布中具有一些作用。
