When stressed, eukaryotic cells produce triacylglycerol (TAG) to store nutrients and mobilize autophagy to combat internal damage. We and others previously reported that in yeast, elimination of TAG synthesizing enzymes inhibits autophagy under nitrogen starvation, yet the underlying mechanism has remained elusive. Here, we show that disruption of TAG synthesis led to diacylglycerol (DAG) accumulation and its relocation from the vacuolar membrane to the endoplasmic reticulum (ER). We further show that, beyond autophagy, ER-accumulated DAG caused severe defects in the endomembrane system, including disturbing the balance of ER-Golgi protein trafficking, manifesting in bulging of ER and loss of the Golgi apparatus. Genetic or chemical manipulations that increase consumption or decrease supply of DAG reversed these defects. In contrast, increased amounts of precursors of glycerolipid synthesis, including phosphatidic acid and free fatty acids, did not replicate the effects of excess DAG. We also provide evidence that the observed endomembrane defects do not rely on Golgi-produced DAG, Pkc1 signaling, or the unfolded protein response. This work identifies DAG as the critical lipid molecule responsible for autophagy inhibition under condition of defective TAG synthesis and demonstrates the disruption of ER and Golgi function by excess DAG as the potential cause of the autophagy defect.

中文翻译：

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内质网中过量的二酰基甘油会破坏内膜稳态和自噬。

当受到压力时，真核细胞会产生三酰甘油（TAG）来存储营养并动员自噬以对抗内部损伤。我们和其他人以前曾报道过，在酵母中，消除TAG合成酶会抑制氮饥饿下的自噬，但其潜在机制仍然难以捉摸。在这里，我们表明TAG合成的破坏导致二酰基甘油（DAG）积累和其从液泡膜到内质网（ER）的重新定位。我们进一步表明，除自噬外，ER积累的DAG引起内膜系统的严重缺陷，包括扰乱ER-高尔基体蛋白运输的平衡，表现为ER膨胀和高尔基体丧失。遗传或化学处理增加了DAG的消耗或减少了其供应，从而扭转了这些缺陷。相反，增加的甘油脂合成前体（包括磷脂酸和游离脂肪酸）的量不能复制过量DAG的作用。我们还提供证据表明观察到的内膜缺陷不依赖于高尔基体产生的DAG，Pkc1信号传导或未折叠的蛋白质反应。这项工作确定DAG是在有缺陷的TAG合成条件下负责自噬抑制的关键脂质分子，并证明过量的DAG破坏ER和高尔基体功能是自噬缺陷的潜在原因。