Section of Molecular Biology, Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA.
Department of Biology, Georgia State University, Atlanta, GA 30303, USA.
Int J Mol Sci. 2020 Nov 29;21(23):9094. doi: 10.3390/ijms21239094.
In yeast, the selective autophagy of intracellular lipid droplets (LDs) or lipophagy can be induced by either nitrogen (N) starvation or carbon limitation (e.g., in the stationary (S) phase). We developed the yeast, (formerly ), as a new lipophagy model and compared the N-starvation and S-phase lipophagy in over 30 autophagy-related mutants using the Erg6-GFP processing assay. Surprisingly, two lipophagy pathways had hardly overlapping stringent molecular requirements. While the N-starvation lipophagy strictly depended on the core autophagic machinery (Atg1-Atg9, Atg18, and Vps15), vacuole fusion machinery (Vam7 and Ypt7), and vacuolar proteolysis (proteinases A and B), only Atg6 and proteinases A and B were essential for the S-phase lipophagy. The rest of the proteins were only partially required in the S-phase. Moreover, we isolated the (for the positive regulator of lipophagy 1) mutant affected in the S-phase lipophagy, but not N-starvation lipophagy. The defect was at a stage of delivery of the LDs from the cytoplasm to the vacuole, further supporting the mechanistically different nature of the two lipophagy pathways. Taken together, our results suggest that N-starvation and S-phase lipophagy have distinct molecular mechanisms.
在酵母中，细胞内脂滴（LDs）或脂噬的选择性自噬可以通过氮（N）饥饿或碳限制（例如在静止（S）期）来诱导。我们开发了酵母，（以前称为），作为一种新的脂噬模型，并使用 Erg6-GFP 处理测定法在 30 多个自噬相关突变体中比较了 N 饥饿和 S 期脂噬。令人惊讶的是，两种脂噬途径几乎没有重叠的严格分子要求。虽然 N 饥饿的脂噬严格依赖于核心自噬机制（Atg1-Atg9、Atg18 和 Vps15）、液泡融合机制（Vam7 和 Ypt7）和液泡蛋白水解（蛋白酶 A 和 B），但只有 Atg6 和蛋白酶 A 和 B 对 S 期脂噬是必需的。其余的蛋白质在 S 期只部分需要。此外，我们分离了（用于脂噬的正调控因子 1）突变体，该突变体影响 S 期脂噬，但不影响 N 饥饿的脂噬。缺陷发生在 LDs 从细胞质递送到液泡的阶段，这进一步支持了两种脂噬途径在机制上的不同性质。总之，我们的结果表明，N 饥饿和 S 期脂噬具有不同的分子机制。
