Guiney Evan L, Goldman Aaron R, Elias Joshua E, Cyert Martha S
Department of Biology, Stanford University, Stanford, CA 94305.
Department of Chemical and Systems Biology, Stanford University, Stanford, CA 94305.
Mol Biol Cell. 2015 Feb 15;26(4):769-85. doi: 10.1091/mbc.E14-05-1019. Epub 2014 Dec 17.
During hyperosmotic shock, Saccharomyces cerevisiae adjusts to physiological challenges, including large plasma membrane invaginations generated by rapid cell shrinkage. Calcineurin, the Ca(2+)/calmodulin-dependent phosphatase, is normally cytosolic but concentrates in puncta and at sites of polarized growth during intense osmotic stress; inhibition of calcineurin-activated gene expression suggests that restricting its access to substrates tunes calcineurin signaling specificity. Hyperosmotic shock promotes calcineurin binding to and dephosphorylation of the PI(4,5)P2 phosphatase synaptojanin/Inp53/Sjl3 and causes dramatic calcineurin-dependent reorganization of PI(4,5)P2-enriched membrane domains. Inp53 normally promotes sorting at the trans-Golgi network but localizes to cortical actin patches in osmotically stressed cells. By activating Inp53, calcineurin repolarizes the actin cytoskeleton and maintains normal plasma membrane morphology in synaptojanin-limited cells. In response to hyperosmotic shock and calcineurin-dependent regulation, Inp53 shifts from associating predominantly with clathrin to interacting with endocytic proteins Sla1, Bzz1, and Bsp1, suggesting that Inp53 mediates stress-specific endocytic events. This response has physiological and molecular similarities to calcineurin-regulated activity-dependent bulk endocytosis in neurons, which retrieves a bolus of plasma membrane deposited by synaptic vesicle fusion. We propose that activation of Ca(2+)/calcineurin and PI(4,5)P2 signaling to regulate endocytosis is a fundamental and conserved response to excess membrane in eukaryotic cells.
在高渗休克期间，酿酒酵母会对生理挑战做出调整，包括因细胞快速收缩而产生的大量质膜内陷。钙调神经磷酸酶是一种依赖于Ca(2+)/钙调蛋白的磷酸酶，通常位于细胞质中，但在强烈的渗透胁迫下会集中在点状结构和极性生长位点；抑制钙调神经磷酸酶激活的基因表达表明，限制其与底物的接触可调节钙调神经磷酸酶信号传导的特异性。高渗休克促进钙调神经磷酸酶与PI(4,5)P2磷酸酶突触结合蛋白/Inp53/Sjl3结合并使其去磷酸化，并导致富含PI(4,5)P2的膜结构域发生显著的钙调神经磷酸酶依赖性重组。Inp53通常促进反式高尔基体网络的分选，但在渗透胁迫的细胞中定位于皮质肌动蛋白斑。通过激活Inp53，钙调神经磷酸酶使肌动蛋白细胞骨架重新极化，并在突触结合蛋白受限的细胞中维持正常的质膜形态。响应高渗休克和钙调神经磷酸酶依赖性调节，Inp53从主要与网格蛋白结合转变为与内吞蛋白Sla1、Bzz1和Bsp1相互作用，这表明Inp53介导应激特异性内吞事件。这种反应在生理和分子上与神经元中钙调神经磷酸酶调节的活性依赖性批量内吞作用相似，后者可回收由突触小泡融合沉积的大量质膜。我们提出，激活Ca(2+)/钙调神经磷酸酶和PI(4,5)P2信号传导以调节内吞作用是真核细胞对过量膜的一种基本且保守的反应。
