Regulation and Role of Phosphatidate Phosphatase in Lipid Metabolism

总结 磷脂酸（PA）磷酸酶（PAP）是一种进化上保守的酶，在脂质代谢中起着关键作用。 通过控制其底物PA及其产物甘油二酯的细胞水平来维持体内平衡。这些脂质是 三酰甘油和膜磷脂合成的必要中间体;它们也在 磷脂合成基因表达、脂滴形成和囊泡运输。PAP的重要性 对脂质稳态和细胞生理学的影响，在酵母、小鼠和人类中， 以及与酶功能丧失或过度表达相关的脂质性疾病。在酵母中，失去Pah1 PAP 导致核膜/内质网膜的大量扩张;这归因于PA含量的增加， 磷脂的合成是以三酰甘油合成为代价的。磷脂的增加 合成与磷脂合成基因表达的去抑制有关，而减少 在三酰甘油的合成中的减少与脂滴形成的减少有关。Lipin PAP缺乏症 在小鼠和人中引起横纹肌溶解，并且在小鼠中缺乏的特征还在于肝硬化。 新生儿期脂肪变性、脂肪营养不良、胰岛素抵抗和周围神经病变。的 Lipin1PAP在小鼠中的过表达导致脂肪生成增加和肥胖。人Lipin 2 PAP 缺乏引起慢性复发性多灶性骨髓炎和先天性红细胞生成不良性贫血，而 人LPIN2PAP基因的遗传变异与2型糖尿病有关。PAP是一种外周血管 膜蛋白，必须从胞质转移到核膜/ER膜，以将PA转化为 甘油二酯这个保守的过程由酶的磷酸化/去磷酸化控制。在 细胞溶质PAP被多种蛋白激酶磷酸化，导致其在细胞内滞留， 车厢PAP的膜结合需要一个保守的蛋白质去磷酸化 磷酸酶复合物（例如，酵母中的Nem1-Spo 7，小鼠和人中的CTDNEP 1-NEP 1-R1）。除了其 磷酸化PAP抑制其活性，但使其稳定于蛋白酶体降解; 去磷酸化具有相反的作用。在这个MIRA应用程序中提出的工作，建立在我们的 通过酵母模型的优点，先前的工作成为可能，将获得对结构的理解- Pah1 PAP的功能、作用方式和磷酸化/去磷酸化介导的调节， Nem1-Spo7蛋白磷酸酶复合物。我们将采用严格的实验方法，将联合收割机 生物化学和分子遗传学来阐明三酰甘油的比例合成， 膜磷脂被控制。基于Nem1-Spo7/Pah1磷酸酶的保守性， 级联，从我们的酵母研究中获得的信息预计与人类相关。

SUMMARY Phosphatidate (PA) phosphatase (PAP) is an evolutionarily conserved enzyme that plays a key role in lipid homeostasis by controlling the cellular levels of its substrate, PA, and its product, diacylglycerol. These lipids are essential intermediates for the synthesis of triacylglycerol and membrane phospholipids; they also function in phospholipid synthesis gene expression, lipid droplet formation, and vesicular trafficking. The importance of PAP to lipid homeostasis and cell physiology is exemplified in yeast, mouse, and human by a host of cellular defects and lipid-based diseases associated with loss or overexpression of enzyme function. In yeast, loss of Pah1 PAP results in a massive expansion of the nuclear/ER membrane; this is ascribed to increases in PA content and phospholipid synthesis that occur at the expense of triacylglycerol synthesis. The increase in phospholipid synthesis is associated with the derepression of phospholipid synthesis gene expression, whereas the reduction in the synthesis of triacylglycerol is associated with a decrease in lipid droplet formation. Lipin PAP deficiency in mouse and human causes rhabdomyolysis, and deficiency in the mouse is also characterized by hepatic steatosis during the neonatal period, lipodystrophy, insulin resistance and peripheral neuropathy. The overexpression of lipin 1 PAP in mouse results in increased lipogenesis and obesity. Human lipin 2 PAP deficiency causes chronic recurrent multifocal osteomyelitis and congenital dyserythropoietic anemia, whereas genetic variations in the human LPIN2 PAP gene are associated with type 2 diabetes. PAP is a peripheral membrane protein that must translocate from the cytosol to the nuclear/ER membrane in order to convert PA to diacylglycerol. This conserved process is governed by phosphorylation/dephosphorylation of the enzyme. In the cytosol, PAP is phosphorylated by multiple protein kinases that causes its retention in this cellular compartment. The membrane association of PAP requires is dephosphorylation by a conserved protein phosphatase complex (e.g., Nem1-Spo7 in yeast, CTDNEP1-NEP1-R1 in mouse and human). Besides its location, the phosphorylation of PAP inhibits its activity but stabilizes it to proteasomal degradation; dephosphorylation has the opposite effects. The work proposed in this MIRA application, which builds on our prior work made possible by the advantages of the yeast model, will gain understanding into the structure- function, mode of action and phosphorylation/dephosphorylation-mediated regulations of Pah1 PAP and the Nem1-Spo7 protein phosphatase complex. We will pursue rigorous experimental approaches that combine biochemistry and molecular genetics to shed light on how the proportional synthesis of triacylglycerol and membrane phospholipids is controlled. Based on the conserved nature of the Nem1-Spo7/Pah1 phosphatase cascade, the information gained from our studies with yeast is expected to be relevant in human.