The endosomal sorting complexes required for transport (ESCRT) mediate evolutionarily conserved membrane remodeling processes. Here, we used budding yeast (Saccharomyces cerevisiae) to explore how the ESCRT machinery contributes to plasma membrane (PM) homeostasis. We found that in response to reduced membrane tension and inhibition of TOR complex 2 (TORC2), ESCRT-III/Vps4 assemblies form at the PM and help maintain membrane integrity. In turn, the growth of ESCRT mutants strongly depended on TORC2-mediated homeostatic regulation of sphingolipid (SL) metabolism. This was caused by calcineurin-dependent dephosphorylation of Orm2, a repressor of SL biosynthesis. Calcineurin activity impaired Orm2 export from the endoplasmic reticulum (ER) and thereby hampered its subsequent endosome and Golgi-associated degradation (EGAD). The ensuing accumulation of Orm2 at the ER in ESCRT mutants necessitated TORC2 signaling through its downstream kinase Ypk1, which repressed Orm2 and prevented a detrimental imbalance of SL metabolism. Our findings reveal compensatory cross-talk between the ESCRT machinery, calcineurin/TORC2 signaling, and the EGAD pathway important for the regulation of SL biosynthesis and the maintenance of PM homeostasis.

中文翻译：

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TOR 复合物 2 (TORC2) 信号传导和 ESCRT 机制协同保护酵母质膜的完整性。

运输所需的内体分选复合物（ESCRT）介导进化保守的膜重塑过程。在这里，我们使用芽殖酵母（酿酒酵母）来探索 ESCRT 机制如何促进质膜 (PM) 稳态。我们发现，作为对膜张力降低和 TOR 复合物 2 (TORC2) 抑制的反应，ESCRT-III/Vps4 组件在 PM 处形成，有助于维持膜完整性。反过来，ESCRT突变体的生长强烈依赖于TORC2介导的鞘脂（SL）代谢的稳态调节。这是由 Orm2 的钙调神经磷酸酶依赖性去磷酸化引起的，Orm2 是 SL 生物合成的抑制因子。钙调神经磷酸酶活性损害 Orm2 从内质网 (ER) 的输出，从而阻碍其随后的内体和高尔基体相关降解 (EGAD)。随后 ESCRT 突变体中 Orm2 在 ER 处积累，需要通过其下游激酶 Ypk1 进行 TORC2 信号传导，从而抑制 Orm2 并防止 SL 代谢的有害失衡。我们的研究结果揭示了 ESCRT 机制、钙调神经磷酸酶/TORC2 信号传导和 EGAD 通路之间的代偿性串扰对于调节 SL 生物合成和维持 PM 稳态非常重要。