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Methods to Study Endothelium-Dependent Responses
Published in Thomas F. Lüscher, Paul M. Vanhoutte, The Endothelium: Modulator of Cardiovascular Function, 2020
Thomas F. Lüscher, Paul M. Vanhoutte
The enzyme phospholipase C catalyzes the breakdown of phosphatidylinositol 4,5-biphosphate, phosphatidylinositol-4-phosphate, and phosphatidylinositol and leads to the formation of inositol 1,4,5-trisphosphate and diacylglycerol.428,484,790,998,1006–1008,1019 The formation of the second messengers inositol trisphosphate and diacylglycerol can be measured by incubating the cells either with labeled phospholipids (3H-myoinositol or 14C-glycerol) or with labeled phosphorus (32Pi).12,428,1019,1020
Ion Transport and Left Ventricular Hypertrophy in Essential Hypertension
Published in Antonio Coca, Ricardo P. Garay, Ionic Transport in Hypertension: New Perspectives, 2019
Antonio Coca, Alejandro De la Sierra, Alvaro Urbano-Márquez
A major recent advance in the understanding of how the Ca2+ messenger system operates followed the demonstration that receptor function in this system is linked to a specific enzyme, phospholipase C. This phosphodiesterase of the plasma membrane catalyzes the hydrolysis of a specific class of membrane phospholipids located in its inner leaflet, the phosphatidylinositols, thereby generating two intracellular messengers, inositol triphosphate (IP3) and DAG. The phosphatidylinositides exist in three forms: phosphatidylinositol, phosphatidylinositol 4-phosphate, and phos-phatidylinositol 4,5-bisphosphate, at a ratio of approximately 90:5:5. These forms are rapidly interconvertible by appropriate kinases and phosphatases.
The Role of Protein Phosphorylation in the Mechanism of Action of α-Msh
Published in Mac E. Hadley, The Melanotropic Peptides, 2018
Pierre N. E. De Graan, Alex N. Eberle
The degree of B-50 phosphorylation is thought to be an important factor in the regulation of the activity of the enzyme, phosphatidylinositol 4-phosphate kinase (PIP kinase), the rate-limiting enzyme in the synthesis of phosphatidylinositol 4,5-bisphosphate (PIP2). Receptor-mediated PIP2 hydrolysis is known to result in the formation of the second messengers diacylglycerol and inositol 1,4,5-bisphosphate.17,18 Since diacylglycerol stimulates PKC, thus increasing B-50 phosphorylation, the B-50 protein is thought to be part of a negative feedback loop in receptor-mediated hydrolysis of polyphosphoinositides. The inhibition of B-50 phosphorylation by ACTH and MSH-like peptides would temporarily attenuate the feedback regulation, thus rendering more PIP2 available for receptor-mediated hydrolysis. The precise mechanism by which the neuropeptides inhibit PKC activity has not yet been resolved. However, these data show that a role of ACTH and MSH-like peptides in receptor-mediated hydrolysis of polyphosphoinositides has to be considered. This notion is further substantiated by data on the effects of ACTH on adrenal cells.
The participation of non-canonical autophagic proteins in the autophagy process and their potential as therapeutic targets
Published in Expert Opinion on Therapeutic Targets, 2023
Yiming Yin, Yourong Zhou, Xiaochun Yang, Zhifei Xu, Bo Yang, Peihua Luo, Hao Yan, Qiaojun He
Zhao et al. reported that VAPs contribute to the autophagy process mainly by contributing to the formation of the isolation membrane of the autophagosome [127]. In the same study, they also found that the FFAT motifs of VAPs can directly interact with FIP200 and ULK1 to stabilize the ULK1/FIP200 complex at the autophagosome formation sites in the ER. In adition, VAPs can enhance the tethering between WIPI2/FIP200 and the isolation membrane, the precursor of the autophagosome, by interacting with WIPI2 [127]. Moreover, VAPs depletion significantly reduced the ULK1 puncta, and the VAPB P56S mutation impairs ULK1/FIP200 interaction and reduces autophagy as a consequence [127]. Mao et al. [128] noticed that the depletion of VAPs can cause the accumulation of aberrant lysosomes and impairs lysosomal degradation indicating the disrupted autophagy function. The mechanism is that VAPs mediate the transfer of phosphatidylinositol-4-phosphate (PtdIns4P) to the ER and Golgi, therefore affecting the formation of the autophagosome. All these studies show that VAPs play a crucial role in the formation of autophagosomes.
Type II phosphatidylinositol 4-kinase regulates nerve terminal growth and synaptic vesicle recycling
Published in Journal of Neurogenetics, 2018
Kristyn C. Cantarutti, Jason Burgess, Julie A. Brill, Jeffrey S. Dason
Phosphoinositides affect a vast array of processes at synapses (reviewed in Frere, Chang-Ileto, & Di Paolo, 2012; Lauwers, Goodchild, & Verstreken, 2016). Phosphatidylinositol (4,5)-bisphosphate (PI(4,5)P2) regulates axonal growth (Khuong, Habets, Slabbaert, & Verstreken, 2010), ion channel function (Suh, Leal, & Hille, 2010; Suh & Hille, 2002) and several steps of the synaptic vesicle (SV) cycle (Di Paolo et al., 2004; Verstreken et al., 2009; Walter et al., 2017). The role of the PI(4,5)P2 precursor phosphatidylinositol 4-phosphate (PI4P) at the synapse is less clear. Mounting evidence suggests that PI4P is functionally important and not simply a precursor for PI(4,5)P2 ( reviewed in D'Angelo, Vicinanza, Di Campli, & De Matteis, 2008; De Matteis, Wilson, & D'Angelo, 2013; Tan & Brill, 2014 ). Phosphatidylinositol 4-kinase (PI4K) is responsible for the synthesis of PI4P, which is subsequently converted to PI(4,5)P2 by phosphatidylinositol 4-phosphate 5-kinase (PI4P5K).
Roles of membrane lipids in the organization of epithelial cells: Old and new problems
Published in Tissue Barriers, 2018
Interestingly, we found that Podocalyxin-1 has an intrinsic affinity to sphingomyelin-enriched membrane domain, irrespective of binding to EBP50. In addition, we found that EBP 50 directly binds to the type I phosphatidylinositol phosphate kinase isoform-beta (PIP5Kbeta) which is responsible for the production of PtdIns(4,5)P2 and forms a tripartite complex of Podocalyxin-1-EBP50-PIPK5Kbeta. Therefore, clustering of Podocalyxin-1-EBP50-PIPK5Kbeta occurs in the sphingomyelin enriched membrane domains, which results in the local accumulation of PtdIns(4,5)P2. We proposed that the local accumulation of PtdIns(4,5)P2 mediated by this protein complex promotes the activation of ERM family proteins and the formation of microvilli (Fig. 1B).8 Thus, we revealed that the two apically-enriched membrane lipids – sphingomyelin and PtdIns(4,5)P2 – are accumulated in the microvilli of the apical membrane and involved in the formation of microvilli.