Analysis of the Function of a Novel Class of Mammalian Phospholipase C, PLCε

我们已经阐明了一类新的磷脂酶C的调节机制，即PLCε，并建立了PLDε作为小GTP酶RAS和PAP1的效应器。此外，还阐明了PLCε的生理功能。PLCε的CDC25同源结构域作为RAP1的鸟核苷酸交换因子，从而放大依赖于RAP1的信号。血小板衍生生长因子刺激细胞后，通过激活RAS和RAP1，诱导PLCε的双相激活。这种激活的快速和初始阶段是由质膜上的RAS介导的，而Rap1负责高尔基体的长时间激活。CDC25同源结构域是RAP1延长激活PCLε的关键。结论1.依赖RAS/RAP1激活的PLCε可阻止BaF3细胞发生凋亡并维持其增殖。对PLCε的时空表达模式的分析表明，在小鼠胚胎中，在神经干细胞向神经元分化的过程中观察到了PLCε表达的特异性诱导。在成人中，PLCε在心脏中大量表达。通过基因打靶创造的PLCε基因敲除小鼠被发现在4周大的时候就表现出以心脏肥大和心力衰竭标志物的过度表达为特征的表型。因此，PLCε可能通过将RAS通路与钙调神经磷酸酶-NFAT通路联系起来，在心肌细胞内信号传导中发挥重要作用。我们分离到一条缺失PLCε基因的秀丽线虫突变体蠕虫。它表现出一种不育的表型，这是由于卵子运输到子宫的障碍，这可能是由于受精囊的括约肌松弛缺陷引起的。有趣的是，哺乳动物和线虫都表现出相似的表型，携带着节律性肌肉收缩的缺陷。

We have clarified the regulation mechanism of a novel class of phospholipase C, PLCε, and established PLDε as an effector of small GTPases Ras and Pap1. Also, a physiological function of PlCε has been elucidated.1. The CDC25 homology domain of PLCε acts as a guanine nucleotide exchange factor for Rap1, thereby amplifying Rap1-dependent signaling. Stimulation of cells by platelet-derived growth factor (PDGF), induces two phase activation of PLCε through activation of Ras and Rap1. The rapid and initial phase of this activation is mediated by Ras at the plasma membrane, whereas Rap1 is responsible for the prolonged activation at the Golgi apparatus. The CDC25 homology domain is crucial for the prolonged activation of PCLε by Rap1. The Ras/Rap1-dependent activation of PLCε prevents BaF3 cells from undergoing apoptosis and sustains their proliferation.2. Analysis of the spatial and temporal expression patterns of PLCε indicates that in mouse embryos a specific induction of PLCε expression is observed during the course of differentiation of the neural stem cells into the neuronal lineage. In adult, PLCε is expressed abundantly in the heart. The PLCε gene-knockout mice, created by gene targeting, are found to exhibit a phenotype characterized by a market cardiomegaly as well as by overexpression of the heart failure markers as early as 4 weeks of age. Thus, PLCε may play a crucial function in intracellular signaling of the cardiomyocytes by linking the Ras pathway with the Ca^<2+>-calcineurin-NFAT pathway.3. We have isolated a Caenorhabditis elegans mutant worm lacking the PLCε gene. It exhibits a sterile phenotype due to a disorder in transporting the eggs to the uterus, which is presumably caused by defective relaxation of the sphincters of the spermatheca. It is interesting that both the mammals and the nematodes exhibit a similar phenotype carrying a defect in rhythmic muscular contraction.