PI4P and PI(4,5)P-2 Are Essential But Independent Lipid Determinants of Membrane Identity

Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1PD, UK.
Science (Impact Factor: 33.61). 06/2012; 337(6095):727-30. DOI: 10.1126/science.1222483
Source: PubMed


The quantitatively minor phospholipid phosphatidylinositol (4,5)-bisphosphate [PI(4,5)P(2)] fulfills many cellular functions in the plasma membrane (PM), whereas its synthetic precursor, phosphatidylinositol 4-phosphate (PI4P), has no assigned PM roles apart from PI(4,5)P(2) synthesis. We used a combination of pharmacological and chemical genetic approaches to probe the function of PM PI4P, most of which was not required for the synthesis or functions of PI(4,5)P(2). However, depletion of both lipids was required to prevent PM targeting of proteins that interact with acidic lipids or activation of the transient receptor potential vanilloid 1 cation channel. Therefore, PI4P contributes to the pool of polyanionic lipids that define plasma membrane identity and to some functions previously attributed specifically to PI(4,5)P(2), which may be fulfilled by a more general polyanionic lipid requirement.

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Available from: Michael J.M. Fischer, Dec 17, 2013
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    • "In contrast to the PM, which contains levels of PI4P far in excess of those needed to support basal PI(4,5)P2 synthesis (Hammond et al., 2012), in primary cilia it appears that ciliary PI(4,5)P2 hydrolysis by INPP5E is the likely source of PI4P. Indeed, upon INPP5E inactivation, PI(4,5)P2 accumulates in cilia along with depletion of PI4P from the ciliary compartment (Figures 2B, 3A, and 3B), thus suggesting that PI(4,5)P2 is unable to be dephosphorylated to PI4P. "
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    ABSTRACT: Ciliary transport is required for ciliogenesis, signal transduction, and trafficking of receptors to the primary cilium. Mutations in inositol polyphosphate 5-phosphatase E (INPP5E) have been associated with ciliary dysfunction; however, its role in regulating ciliary phosphoinositides is unknown. Here we report that in neural stem cells, phosphatidylinositol 4-phosphate (PI4P) is found in high levels in cilia whereas phosphatidylinositol (4,5)-bisphosphate (PI(4,5)P2) is not detectable. Upon INPP5E inactivation, PI(4,5)P2 accumulates at the ciliary tip whereas PI4P is depleted. This is accompanied by recruitment of the PI(4,5)P2-interacting protein TULP3 to the ciliary membrane, along with Gpr161. This results in an increased production of cAMP and a repression of the Shh transcription gene Gli1. Our results reveal the link between ciliary regulation of phosphoinositides by INPP5E and Shh regulation via ciliary trafficking of TULP3/Gpr161 and also provide mechanistic insight into ciliary alterations found in Joubert and MORM syndromes resulting from INPP5E mutations. Copyright © 2015 Elsevier Inc. All rights reserved.
    Developmental Cell 07/2015; DOI:10.1016/j.devcel.2015.06.016 · 9.71 Impact Factor
    • "A known player is INPP5E, which is able to convert PtdIns(4,5)P 2 into PtdIns(4)P (Fig. 1). Consistently, depletion of this phosphatase decreases TfR internalization rate [42]. Similarly, down-modulation of INPP4A (type I a "
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    ABSTRACT: The spatial restriction of phosphorylated phosphoinositides generated downstream activated membrane receptors is critical for proper cell response to environmental cues. The α isoform of class II PI3Ks, PI3K-C2α, has emerged as a modulator of receptor localization, acting both in the control of receptor endocytosis and resensitization. This unexpectedly versatile enzyme was found to differentially produce two distinct 3-phosphorylated phosphoinositides and to selectively control distinct steps of vesicular traffic such as endocytosis and recycling. This review focuses on the latest discoveries regarding PI3K-C2α function in vesicle trafficking and its impact on cell biology and mammalian embryonic development. Copyright © 2015. Published by Elsevier B.V.
    FEBS letters 05/2015; 589(14). DOI:10.1016/j.febslet.2015.05.001 · 3.17 Impact Factor
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    • "Thus, we infer that the 2e subunit binds PI(4)P and PIP 2 , and that depleting both lipids allows dissociation of the 2e subunit from the membrane. These results are reminiscent of findings that PI(4)P and PIP 2 activate TRPV1 channels with similar potency (Hammond et al., 2012; Lukacs et al., 2013). Membrane PI(4)P can be involved in scaffolding, recruiting peripheral proteins to the membrane, activation of ion channels, and as a precursor for PIP 2 synthesis (Suh and Hille, 2008; Korzeniowski et al., 2009; Balla, 2013). "
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    ABSTRACT: High voltage-activated Ca(2+) (CaV) channels are protein complexes containing pore-forming α1 and auxiliary β and α2δ subunits. The subcellular localization and membrane interactions of the β subunits play a crucial role in regulating CaV channel inactivation and its lipid sensitivity. Here, we investigated the effects of membrane phosphoinositide (PI) turnover on CaV2.2 channel function. The β2 isoform β2e associates with the membrane through electrostatic and hydrophobic interactions. Using chimeric β subunits and liposome-binding assays, we determined that interaction between the N-terminal 23 amino acids of β2e and anionic phospholipids was sufficient for β2e membrane targeting. Binding of the β2e subunit N terminus to liposomes was significantly increased by inclusion of 1% phosphatidylinositol 4,5-bisphosphate (PIP2) in the liposomes, suggesting that, in addition to phosphatidylserine, PIs are responsible for β2e targeting to the plasma membrane. Membrane binding of the β2e subunit slowed CaV2.2 current inactivation. When membrane phosphatidylinositol 4-phosphate and PIP2 were depleted by rapamycin-induced translocation of pseudojanin to the membrane, however, channel opening was decreased and fast inactivation of CaV2.2(β2e) currents was enhanced. Activation of the M1 muscarinic receptor elicited transient and reversible translocation of β2e subunits from membrane to cytosol, but not that of β2a or β3, resulting in fast inactivation of CaV2.2 channels with β2e. These results suggest that membrane targeting of the β2e subunit, which is mediated by nonspecific electrostatic insertion, is dynamically regulated by receptor stimulation, and that the reversible association of β2e with membrane PIs results in functional changes in CaV channel gating. The phospholipid-protein interaction observed here provides structural insight into mechanisms of membrane-protein association and the role of phospholipids in ion channel regulation. © 2015 Kim et al.
    The Journal of General Physiology 05/2015; 145(6). DOI:10.1085/jgp.201411349 · 4.79 Impact Factor
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