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Eric Barklis, August O Staubus, Andrew Mack, Logan Harper, Robin Lid Barklis, Ayna Alfadhli
The matrix (MA) domain of the HIV-1 precursor Gag protein (PrGag) has been shown interact with the HIV-1 envelope (Env) protein, and to direct PrGag proteins to plasma membrane (PM) assembly sites by virtue of its affinity to phosphatidylinositol-4,5-bisphosphate (PI[4,5]P2). Unexpectedly, HIV-1 viruses with large MA deletions (ΔMA) have been shown to be conditionally infectious as long as they are matched with Env truncation mutant proteins or alternative viral glycoproteins. To characterize the interactions of wild type (WT) and ΔMA Gag proteins with PI(4,5)P2 and other acidic phospholipids, we have employed a set of lipid biosensors as probes...
March 14, 2018: Virology
Daniel V Olivença, Inna Uliyakina, Luis L Fonseca, Margarida D Amaral, Eberhard O Voit, Francisco R Pinto
Phosphoinositides are signalling lipids that constitute a complex network regulating many cellular processes. We propose a computational model that accounts for all species of phosphoinositides in the plasma membrane of mammalian cells. The model replicates the steady-state of the pathway and most known dynamic phenomena. Sensitivity analysis demonstrates model robustness to alterations in the parameters. Model analysis suggest that the greatest contributor to phosphatidylinositol 4,5-biphosphate (PI(4,5)P2 ) production is a flux representing the direct transformation of PI into PI(4,5)P2 , also responsible for the maintenance of this pool when phosphatidylinositol 4-phosphate (PI(4)P) is decreased...
March 2, 2018: Scientific Reports
Mira Sohn, Marek Korzeniowski, James P Zewe, Rachel C Wills, Gerald R V Hammond, Jana Humpolickova, Lukas Vrzal, Dominika Chalupska, Vaclav Veverka, Gregory D Fairn, Evzen Boura, Tamas Balla
Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2 ) is a critically important regulatory lipid of the plasma membrane (PM); however, little is known about how cells regulate PM PI(4,5)P2 levels. Here, we show that the phosphatidylinositol 4-phosphate (PI4P)/phosphatidylserine (PS) transfer activity of the endoplasmic reticulum (ER)-resident ORP5 and ORP8 is regulated by both PM PI4P and PI(4,5)P2 Dynamic control of ORP5/8 recruitment to the PM occurs through interactions with the N-terminal Pleckstrin homology domains and adjacent basic residues of ORP5/8 with both PI4P and PI(4,5)P2...
February 22, 2018: Journal of Cell Biology
Hai H Bui, Phillip E Sanders, Diane Bodenmiller, Ming Shang Kuo, Gregory P Donoho, Anthony S Fischl
Phosphatidylinositol (3,4,5) trisphosphate (PIP3 ) is a biologically active membrane phospholipid that is essential for the growth and survival of all eukaryotic cells. We describe a new method that directly measures PIP3 and describe the HPLC separation and measurement of the positional isomers of phosphatidylinositol bisphosphate, PI(3,5)P2 , PI(3,4)P2 and PI(4,5)P2 . Mass spectrometric analyses were performed online using ultra-high performance liquid chromatography (UHPLC)-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) in the negative multiple-reaction monitoring (MRM) modes...
February 19, 2018: Analytical Biochemistry
Marina Besprozvannaya, Eamonn Dickson, Hao Li, Kenneth S Ginburg, Donald M Bers, Johan Auwerx, Jodi Nunnari
Endoplasmic reticulum (ER) membrane contact sites (MCSs) are crucial regulatory hubs in cells, playing roles in signaling, organelle dynamics, and ion and lipid homeostasis. Previous work demonstrated that the highly conserved yeast Ltc/Lam sterol transporters localize and function at ER MCSs. Our analysis of the human family members, GRAMD1a and GRAMD2a, demonstrates that they are ER-PM MCS proteins, which mark separate regions of the plasma membrane (PM) and perform distinct functions in vivo. GRAMD2a, but not GRAMD1a, co-localizes with the E-Syt2/3 tethers at ER-PM contacts in a PIP lipid-dependent manner and pre-marks the subset of PI(4,5)P2-enriched ER-PM MCSs utilized for STIM1 recruitment...
February 22, 2018: ELife
Julia P Steringer, Walter Nickel
As illustrated by a diverse set of examples in this special issue, multiple mechanisms of protein secretion have been identified in eukaryotes that do not involve the endoplasmic reticulum (ER) and the Golgi apparatus. Here we focus on the type I pathway with Fibroblast Growth Factor 2 (FGF2) being the most prominent example. Unconventional secretion of FGF2 from cells is mediated by direct protein translocation across the plasma membrane. A unique feature of this process is the ability of FGF2 to form its own membrane translocation intermediate through oligomerization and membrane insertion...
February 16, 2018: Seminars in Cell & Developmental Biology
Chun Liu, Sanghamitra Deb, Vinicius S Ferreira, Eric Xu, Tobias Baumgart
Phosphatidylinositides play important roles in cellular signaling and migration. Phosphatidylinositol-3,4,5-trisphosphate (PI(3,4,5)P3) is an important phosphatidylinositide because it acts as a secondary messenger to trigger cell movement and proliferation. A high level of PI(3,4,5)P3 at the plasma membrane is known to contribute to tumorigenesis. One key enzyme that regulates PI(3,4,5)P3 levels at the plasma membrane is phosphatase and tensin homologue deleted on chromosome 10 (PTEN), which dephosphorylates PI(3,4,5)P3 through hydrolysis to form phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2)...
2018: PloS One
Xiaofan Chen, Jun Wan, Bo Yu, Yarui Diao, Wei Zhang
BACKGROUND: Skeletal muscle satellite cell-derived myoblasts are mainly responsible for postnatal muscle growth and injury-induced regeneration. Many intracellular signaling pathways are essential for myogenic differentiation, while a number of kinases are involved in this modulation process. Type I phosphatidylinositol 4-phosphate 5-kinase (PIP5KI) was identified as one of the key kinases involved in myogenic differentiation, but the underlying molecular mechanism is still unclear. METHODS: PIP5K1α was quantified by quantitative reverse transcriptase PCR and western blot assay...
February 9, 2018: Stem Cell Research & Therapy
Markku Hakala, Maria Kalimeri, Giray Enkavi, Ilpo Vattulainen, Pekka Lappalainen
Membrane phosphoinositides control organization and dynamics of the actin cytoskeleton by regulating the activities of several key actin-binding proteins. Twinfilin is an evolutionarily conserved protein, which contributes to cytoskeletal dynamics by interacting with actin monomers, filaments, and the heterodimeric capping protein. Twinfilin also binds phosphoinositides, which inhibit its interactions with actin, but the underlying mechanism has remained unknown. Here we show that the high-affinity binding site of twinfilin for phosphoinositides is located at the carboxy-terminal tail-region, while the two ADF/cofilin like ADF-H domains of twinfilin bind phosphoinositides only with low affinity...
February 7, 2018: Journal of Biological Chemistry
Thomas Stanislas, Matthieu Pierre Platre, Mengying Liu, Léa E S Rambaud-Lavigne, Yvon Jaillais, Olivier Hamant
BACKGROUND: In plants, the shoot apical meristem (SAM) has two main functions, involving the production of all aerial organs on the one hand and self-maintenance on the other, allowing the production of organs during the entire post-embryonic life of the plant. Transcription factors, microRNA, hormones, peptides and forces have been involved in meristem function. Whereas phosphatidylinositol phosphates (PIPs) have been involved in almost all biological functions, including stem cell maintenance and organogenesis in animals, the processes in meristem biology to which PIPs contribute still need to be delineated...
February 7, 2018: BMC Biology
Samsuzzoha Mondal, Amitava Chandra, Ravindra Venkatramani, Ankona Datta
We present a systematic experimental and computational study of phospholipid induced peptide coil-helix transitions which are relevant in the context of proteins mediating cytoskeletal rearrangement via membrane binding. We developed a sensitive Förster resonance energy transfer (FRET) based assay to address whether coil-helix transitions in phospholipid binding motifs of actin-binding proteins can be induced by physiologically-relevant concentrations (1-20 μM) of phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) phospholipids...
January 24, 2018: Faraday Discussions
Justyna M Meissner, Jay M Bhatt, Eunjoo Lee, Melanie Styers, Anna A Ivanova, Richard A Kahn, Elizabeth Sztul
ARF GTPases are activated by guanine nucleotide exchange factors (GEFs) to support cellular homeostasis. Key to understanding spatio-temporal regulation of ARF signaling is the mechanism of GEF recruitment to membranes. Small GEFs are recruited through phosphoinositide (PIP) binding by a pleckstrin homology (PH) domain downstream from the catalytic Sec7 domain (Sec7d). The large GEFs lack PH domains, and their recruitment mechanisms are poorly understood. We probed Golgi recruitment of GBF1, a GEF catalyzing ARF activation required for Golgi homeostasis...
December 19, 2017: Journal of Cell Science
Thanh Kha Phan, Fung T Lay, Mark D Hulett
Host defense peptides (HDPs) are well-characterized for their antimicrobial activities but also variously display potent immunomodulatory effects. Human β-defensin 3 (HBD-3) belongs to a well-known HDP family known as defensins and is able to induce leukocyte chemotactic recruitment, leukocyte activation/maturation, proinflammatory cytokine release, and co-stimulatory marker expression. HBD-3-stimulated cytokine induction is NF-κB-dependent and was initially suggested to act via G protein-coupled C-C chemokine receptor phospholipase C (PLC) and/or Toll-like receptor signaling...
January 2018: Immunology and Cell Biology
Ao Hu, Xue-Tong Zhao, Heng Tu, Ting Xiao, Ting Fu, Yan Wang, Yong Liu, Xiong-Jie Shi, Jie Luo, Bao-Liang Song
The transport of LDL-derived cholesterol from lysosomes to peroxisomes is mediated by membrane contacts, which are facilitated by the lysosomal protein synaptotagmin VII and the peroxisomal lipid phosphatidylinositol 4, 5-bisphosphate (PI(4,5)P2). Here, we used RNA interference to search for regulators of PI(4,5)P2 and to study the effects of altered PI(4,5)P2 homeostasis on cholesterol transport. We found that knockdown of phosphatidylinositol 5-phosphate 4-kinase type-2 alpha (PIP4K2A) reduced peroxisomal PI(4,5)P2 levels, decreased lysosome-peroxisome membrane contacts, and increased accumulation of lysosomal cholesterol in human SV-589 fibroblasts...
January 20, 2018: Journal of Lipid Research
Zachary T Graber, Joseph Thomas, Emily Johnson, Arne Gericke, Edgar E Kooijman
The phosphoinositide, phosphatidylinositol-3,4,5-trisphosphate (PI(3,4,5)P3), is a key signaling lipid in the inner leaflet of the cell plasma membrane, regulating diverse signaling pathways including cell growth and migration. In this study we investigate the impact of the hydrogen-bond donor lipids phosphatidylethanolamine (PE) and phosphatidylinositol (PI) on the charge and phase behavior of PI(3,4,5)P3. PE and PI can interact with PI(3,4,5)P3 through hydrogen-bond formation, leading to altered ionization behavior and charge distribution within the PI(3,4,5)P3 headgroup...
January 9, 2018: Biophysical Journal
José J De Jesús-Pérez, Silvia Cruz-Rangel, Ángeles E Espino-Saldaña, Ataúlfo Martínez-Torres, Zhiqiang Qu, H Criss Hartzell, Nancy E Corral-Fernandez, Patricia Pérez-Cornejo, Jorge Arreola
The TMEM16A-mediated Ca2+-activated Cl- current drives several important physiological functions. Membrane lipids regulate ion channels and transporters but their influence on members of the TMEM16 family is poorly understood. Here we have studied the regulation of TMEM16A by phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2), cholesterol, and fatty acids using patch clamp, biochemistry and fluorescence microscopy. We found that depletion of membrane PI(4,5)P2 causes a decline in TMEM16A current that is independent of cytoskeleton, but is partially prevented by removing intracellular Ca2+...
December 22, 2017: Biochimica et Biophysica Acta
Joshua A Lees, Yixiao Zhang, Michael S Oh, Curtis M Schauder, Xiaoling Yu, Jeremy M Baskin, Kerry Dobbs, Luigi D Notarangelo, Pietro De Camilli, Thomas Walz, Karin M Reinisch
Plasma membrane (PM) phosphoinositides play essential roles in cell physiology, serving as both markers of membrane identity and signaling molecules central to the cell's interaction with its environment. The first step in PM phosphoinositide synthesis is the conversion of phosphatidylinositol (PI) to PI4P, the precursor of PI(4,5)P2 and PI(3,4,5)P3 This conversion is catalyzed by the PI4KIIIα complex, comprising a lipid kinase, PI4KIIIα, and two regulatory subunits, TTC7 and FAM126. We here report the structure of this complex at 3...
December 26, 2017: Proceedings of the National Academy of Sciences of the United States of America
Isaac Jardín, Letizia Albarran, Ginés M Salido, Jose J López, Stewart O Sage, Juan A Rosado
Store-operated Ca2+ entry (SOCE) is a functionally relevant mechanism for Ca2+ influx present in electrically excitable and non-excitable cells. Regulation of Ca2+ entry through store-operated channels is essential to maintain an appropriate intracellular Ca2+ homeostasis and prevent cell damage. Calcium-release activated channels exhibit Ca2+ -dependent inactivation mediated by two temporally separated mechanisms: fast Ca2+ -dependent inactivation takes effect in the order of milliseconds and involves the interaction of Ca2+ with residues in the channel pore while slow Ca2+ -dependent inactivation (SCDI) develops over tens of seconds, requires a global rise in [Ca2+ ]cyt and is a mechanism regulated by mitochondria...
March 2018: Biochimica et Biophysica Acta
Xin Bian, Yasunori Saheki, Pietro De Camilli
The extended synaptotagmins (E-Syts) are endoplasmic reticulum (ER) proteins that bind the plasma membrane (PM) via C2 domains and transport lipids between them via SMP domains. E-Syt1 tethers and transports lipids in a Ca2+ -dependent manner, but the role of Ca2+ in this regulation is unclear. Of the five C2 domains of E-Syt1, only C2A and C2C contain Ca2+ -binding sites. Using liposome-based assays, we show that Ca2+ binding to C2C promotes E-Syt1-mediated membrane tethering by releasing an inhibition that prevents C2E from interacting with PI(4,5)P2 -rich membranes, as previously suggested by studies in semi-permeabilized cells...
January 17, 2018: EMBO Journal
Justyna Sobocińska, Paula Roszczenko-Jasińska, Monika Zaręba-Kozioł, Aneta Hromada-Judycka, Orest V Matveichuk, Gabriela Traczyk, Katarzyna Łukasiuk, Katarzyna Kwiatkowska
Lipopolysaccharide (LPS) is a component of the outer membrane of Gram-negative bacteria that induces strong proinflammatory reactions of mammals. These processes are triggered upon sequential binding of LPS to CD14, a GPI-linked plasma membrane raft protein, and to the TLR4/MD2 receptor complex. We have found earlier that upon LPS binding, CD14 triggers generation of phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2 ], a lipid controlling subsequent proinflammatory cytokine production. Here we show that stimulation of RAW264 macrophage-like cells with LPS induces global changes of the level of fatty-acylated, most likely palmitoylated, proteins...
February 2018: Molecular & Cellular Proteomics: MCP
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