Singapore Bioimaging Consortium.
Hum Mol Genet. 2014 Jan 15;23(2):502-13. doi: 10.1093/hmg/ddt444. Epub 2013 Sep 10.
Seipin regulates lipid homeostasis by preventing lipid droplet (LD) formation in non-adipocytes but promoting it in developing adipocytes. Here, we report that seipin interacts with 14-3-3β through its N- and C-termini. Expression of 14-3-3β is upregulated during adipogenesis, and its deletion results in defective adipogenesis without affecting key adipogenic transcription factors. We further identified the actin-severing protein cofilin-1 as an interacting partner to 14-3-3β. Cofilin-1 was spatiotemporally recruited by 14-3-3β in the cytoplasm during adipocyte differentiation. Extensive actin cytoskeleton remodelling, from stress fibres to cortical structures, was apparent during adipogenesis, but not under lipogenic conditions, indicating that actin cytoskeleton remodelling is only required for adipocyte development. Similar to seipin and 14-3-3β, cofilin-1 knockdown led to impaired adipocyte development. At the cellular level, differentiated cells with knockdown of cofilin-1, 14-3-3β or seipin continued to maintain relatively intact stress fibres, in contrast to cortical actin structure in control cells. Finally, 3T3-L1 cells expressing a severing-resistant actin mutant exhibited impaired adipogenesis. We propose that seipin regulates adipogenesis by recruiting cofilin-1 to remodel actin cytoskeleton through the 14-3-3β protein.
Seipin 通过防止非脂肪细胞中脂滴 (LD) 的形成，同时促进正在发育的脂肪细胞中 LD 的形成，从而调节脂质稳态。在这里，我们报告 seipin 通过其 N 端和 C 端与 14-3-3β 相互作用。14-3-3β 的表达在脂肪生成过程中上调，其缺失导致脂肪生成缺陷，而不影响关键的脂肪生成转录因子。我们进一步鉴定了肌动蛋白切割蛋白 cofilin-1 为 14-3-3β 的相互作用伙伴。在脂肪细胞分化过程中，cofilin-1 被 14-3-3β 在细胞质中时空募集。在脂肪生成过程中，广泛的肌动蛋白细胞骨架重塑，从应力纤维到皮质结构，是明显的，但在脂生成条件下则不然，这表明肌动蛋白细胞骨架重塑仅适用于脂肪细胞发育。与 seipin 和 14-3-3β 相似，cofilin-1 的敲低导致脂肪细胞发育受损。在细胞水平上，与对照细胞中的皮质肌动蛋白结构不同，敲低 cofilin-1、14-3-3β 或 seipin 的分化细胞继续保持相对完整的应力纤维。最后，表达切割抗性肌动蛋白突变体的 3T3-L1 细胞表现出脂肪生成受损。我们提出，seipin 通过募集 cofilin-1 通过 14-3-3β 蛋白重塑肌动蛋白细胞骨架来调节脂肪生成。
