Department of Pathology and Cell Biology, Columbia University, New York, NY 10032.
Mol Biol Cell. 2021 Dec 1;32(22):br12. doi: 10.1091/mbc.E21-04-0179. Epub 2021 Oct 20.
Microlipophagy (µLP), degradation of lipid droplets (LDs) by microautophagy, occurs by autophagosome-independent direct uptake of LDs at lysosomes/vacuoles in response to nutrient limitations and ER stressors in . In nutrient-limited yeast, liquid-ordered (L) microdomains, sterol-rich raftlike regions in vacuolar membranes, are sites of membrane invagination during LD uptake. The endosome sorting complex required for transport (ESCRT) is required for sterol transport during L formation under these conditions. However, ESCRT has been implicated in mediating membrane invagination during µLP induced by ER stressors or the diauxic shift from glycolysis- to respiration-driven growth. Here we report that ER stress induced by lipid imbalance and other stressors induces L microdomain formation. This process is ESCRT independent and dependent on Niemann-Pick type C sterol transfer proteins. Inhibition of ESCRT or L microdomain formation partially inhibits lipid imbalance-induced µLP, while inhibition of both blocks this µLP. Finally, although the ER stressors dithiothreitol or tunicamycin induce L microdomains, µLP in response to these stressors is ESCRT dependent and L microdomain independent. Our findings reveal that L microdomain formation is a yeast stress response, and stress-induced L microdomain formation occurs by stressor-specific mechanisms. Moreover, ESCRT and L microdomains play functionally distinct roles in LD uptake during stress-induced µLP.
微脂噬作用(µLP),即溶酶体/液泡通过微自噬作用降解脂滴(LDs),发生在营养限制和内质网应激时,通过自噬体独立的直接摄取 LDs。在营养限制的酵母中,液有序(L)微区是液泡膜中富含固醇的筏状区域,是 LD 摄取时膜内陷的部位。在这些条件下,形成 L 时需要内体分选复合物(ESCRT)来运输固醇。然而,ESCRT 已被牵连到 ER 应激或糖酵解到呼吸驱动生长的双相转变诱导的 µLP 中的膜内陷的过程中。在这里,我们报告脂质失衡和其他应激源诱导的 ER 应激诱导 L 微区形成。这个过程与 ESCRT 无关,而是依赖于尼曼-匹克 C 型固醇转移蛋白。ESCRT 或 L 微区形成的抑制部分抑制了由脂质失衡诱导的 µLP,而两者的抑制都阻止了这种 µLP。最后,尽管 ER 应激源二硫苏糖醇或衣霉素诱导 L 微区形成,但这些应激源诱导的 µLP 依赖于 ESCRT 且与 L 微区无关。我们的发现揭示了 L 微区形成是酵母应激反应的一种,应激诱导的 L 微区形成通过应激特异性机制发生。此外,在应激诱导的 µLP 期间,ESCRT 和 L 微区在 LD 摄取中发挥功能不同的作用。
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