scholarly journals Inositol triphosphate-triggered calcium release blocks lipid exchange at endoplasmic reticulum-Golgi contact sites

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Mouhannad Malek ◽  
Anna M. Wawrzyniak ◽  
Peter Koch ◽  
Christian Lüchtenborg ◽  
Manuel Hessenberger ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Golgi Complex ◽  
Calcium Release ◽  
Inositol Triphosphate ◽  
Vesicular Traffic ◽  
Oxysterol Binding Protein ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Lipid Exchange ◽  
Membrane Contact

AbstractVesicular traffic and membrane contact sites between organelles enable the exchange of proteins, lipids, and metabolites. Recruitment of tethers to contact sites between the endoplasmic reticulum (ER) and the plasma membrane is often triggered by calcium. Here we reveal a function for calcium in the repression of cholesterol export at membrane contact sites between the ER and the Golgi complex. We show that calcium efflux from ER stores induced by inositol-triphosphate [IP3] accumulation upon loss of the inositol 5-phosphatase INPP5A or receptor signaling triggers depletion of cholesterol and associated Gb3 from the cell surface, resulting in a blockade of clathrin-independent endocytosis (CIE) of Shiga toxin. This phenotype is caused by the calcium-induced dissociation of oxysterol binding protein (OSBP) from the Golgi complex and from VAP-containing membrane contact sites. Our findings reveal a crucial function for INPP5A-mediated IP3 hydrolysis in the control of lipid exchange at membrane contact sites.

scholarly journals Inositol triphosphate-triggered calcium release blocks lipid exchange at endoplasmic reticulum-Golgi contact sites

2020 ◽  
Author(s):  
Charles Malek ◽  
Anna Maria Wawrzyniak ◽  
Peter Koch ◽  
Christian Lüchtenborg ◽  
Manuel Hessenberger ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Golgi Complex ◽  
Calcium Release ◽  
Inositol Triphosphate ◽  
Vesicular Traffic ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Lipid Exchange ◽  
Membrane Contact ◽  
Membrane Tethers

Abstract Vesicular traffic and membrane contact sites between organelles enable the exchange of proteins, lipids, and metabolites. Recruitment of membrane tethers to contact sites between the endoplasmic reticulum (ER) and the plasma membrane is often triggered by calcium. In contrast, we reveal here a function for calcium in the repression of cholesterol export at membrane contact sites between the ER and the Golgi complex. We show that calcium efflux from ER stores induced by inositol-triphosphate [IP3] accumulation upon loss of the inositol 5-phosphatase INPP5A or sustained receptor signaling triggers the depletion of cholesterol and associated complex glycosphingolipids from the cell surface, resulting in a blockade of clathrin-independent endocytosis (CIE) of bacterial toxins. This phenotype is caused by the calcium-induced dissociation of oxysterol binding protein (OSBP) from the Golgi complex and from VAP-containing membrane contact sites. Our findings reveal a crucial function for INPP5A-mediated IP3 hydrolysis in the control of lipid exchange at membrane contact sites.

scholarly journals SAC1 Degrades its Lipid Substrate PtdIns4P in the Endoplasmic Reticulum to Maintain a Steep Chemical Gradient with Donor Membranes

2018 ◽  
Author(s):  
James P. Zewe ◽  
Rachel C. Wills ◽  
Sahana Sangappa ◽  
Brady D. Goulden ◽  
Gerald R. V. Hammond
Keyword(s):  
Endoplasmic Reticulum ◽  
Lipid Homeostasis ◽  
Chemical Gradient ◽  
Vesicular Traffic ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Catalytic Domains ◽  
In Trans ◽  
Membrane Contact ◽  
And Function

AbstractGradients of PtdIns4P between organelle membranes and the endoplasmic reticulum (ER) are thought to drive counter-transport of other lipids via non-vesicular traffic. This novel pathway requires the SAC1 phosphatase to degrade PtdIns4P in a “cis” configuration at the ER to maintain the gradient. However, SAC1 has also been proposed to act in “trans” at membrane contact sites, which could oppose lipid traffic. It is therefore crucial to determine which mode SAC1 uses in living cells. We report that acute inhibition of SAC1 causes accumulation of PtdIns4P in the ER, that SAC1 does not enrich at membrane contact sites, and that SAC1 has little activity in “trans”, unless a linker is added between its ER-anchored and catalytic domains. The data reveal an obligate “cis” activity of SAC1, supporting its role in non-vesicular lipid traffic and implicating lipid traffic more broadly in inositol lipid homeostasis and function.

PI4P/PS countertransport by ORP10 at ER–endosome membrane contact sites regulates endosome fission

2021 ◽  
Vol 221 (1) ◽  
Author(s):  
Asami Kawasaki ◽  
Akiko Sakai ◽  
Hiroki Nakanishi ◽  
Junya Hasegawa ◽  
Tomohiko Taguchi ◽  
...  
Keyword(s):  
Membrane Trafficking ◽  
Binding Protein ◽  
Dependent Manner ◽  
Oxysterol Binding Protein ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Lipid Exchange ◽  
Membrane Contact ◽  
Phosphatidylinositol 4

Membrane contact sites (MCSs) serve as a zone for nonvesicular lipid transport by oxysterol-binding protein (OSBP)-related proteins (ORPs). ORPs mediate lipid countertransport, in which two distinct lipids are transported counterdirectionally. How such lipid countertransport controls specific biological functions, however, remains elusive. We report that lipid countertransport by ORP10 at ER–endosome MCSs regulates retrograde membrane trafficking. ORP10, together with ORP9 and VAP, formed ER–endosome MCSs in a phosphatidylinositol 4-phosphate (PI4P)-dependent manner. ORP10 exhibited a lipid exchange activity toward its ligands, PI4P and phosphatidylserine (PS), between liposomes in vitro, and between the ER and endosomes in situ. Cell biological analysis demonstrated that ORP10 supplies a pool of PS from the ER, in exchange for PI4P, to endosomes where the PS-binding protein EHD1 is recruited to facilitate endosome fission. Our study highlights a novel lipid exchange at ER–endosome MCSs as a nonenzymatic PI4P-to-PS conversion mechanism that organizes membrane remodeling during retrograde membrane trafficking.

scholarly journals OSBP-Related Protein Family in Lipid Transport over Membrane Contact Sites

2015 ◽  
Vol 8s1 ◽  
pp. LPI.S31726 ◽  
Author(s):  
Vesa M. Olkkonen
Keyword(s):  
Endoplasmic Reticulum ◽  
Mammalian Cells ◽  
Binding Protein ◽  
High Capacity ◽  
Retrograde Transport ◽  
Protein Family ◽  
Oxysterol Binding Protein ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Membrane Contact

Increasing evidence suggests that oxysterol-binding protein-related proteins (ORPs) localize at membrane contact sites, which are high-capacity platforms for inter-organelle exchange of small molecules and information. ORPs can simultaneously associate with the two apposed membranes and transfer lipids across the interbilayer gap. Oxysterol-binding protein moves cholesterol from the endoplasmic reticulum to trans-Golgi, driven by the retrograde transport of phosphatidylinositol-4-phosphate (PI4P). Analogously, yeast Osh6p mediates the transport of phosphatidylserine from the endoplasmic reticulum to the plasma membrane in exchange for PI4P, and ORP5 and -8 are suggested to execute similar functions in mammalian cells. ORPs may share the capacity to bind PI4P within their ligand-binding domain, prompting the hypothesis that bidirectional transport of a phosphoinositide and another lipid may be a common theme among the protein family. This model, however, needs more experimental support and does not exclude a function of ORPs in lipid signaling.

scholarly journals SAC1 degrades its lipid substrate PtdIns4P in the endoplasmic reticulum to maintain a steep chemical gradient with donor membranes

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
James P Zewe ◽  
Rachel C Wills ◽  
Sahana Sangappa ◽  
Brady D Goulden ◽  
Gerald RV Hammond
Keyword(s):  
Endoplasmic Reticulum ◽  
Lipid Homeostasis ◽  
Chemical Gradient ◽  
Vesicular Traffic ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Catalytic Domains ◽  
In Trans ◽  
Membrane Contact ◽  
And Function

Gradients of PtdIns4P between organelle membranes and the endoplasmic reticulum (ER) are thought to drive counter-transport of other lipids via non-vesicular traffic. This novel pathway requires the SAC1 phosphatase to degrade PtdIns4P in a ‘cis’ configuration at the ER to maintain the gradient. However, SAC1 has also been proposed to act in ‘trans’ at membrane contact sites, which could oppose lipid traffic. It is therefore crucial to determine which mode SAC1 uses in living cells. We report that acute inhibition of SAC1 causes accumulation of PtdIns4P in the ER, that SAC1 does not enrich at membrane contact sites, and that SAC1 has little activity in ‘trans’, unless a linker is added between its ER-anchored and catalytic domains. The data reveal an obligate ‘cis’ activity of SAC1, supporting its role in non-vesicular lipid traffic and implicating lipid traffic more broadly in inositol lipid homeostasis and function.

scholarly journals Synaptotagmins at the endoplasmic reticulum–plasma membrane contact sites maintain diacylglycerol homeostasis during abiotic stress

2021 ◽  
Author(s):  
Noemi Ruiz-Lopez ◽  
Jessica Pérez-Sancho ◽  
Alicia Esteban del Valle ◽  
Richard P Haslam ◽  
Steffen Vanneste ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Abiotic Stress ◽  
Fluorescent Protein ◽  
Mechanical Damage ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Membrane Contact ◽  
Green Fluorescent

Abstract Endoplasmic reticulum-plasma membrane contact sites (ER-PM CS) play fundamental roles in all eukaryotic cells. Arabidopsis thaliana mutants lacking the ER-PM protein tether synaptotagmin1 (SYT1) exhibit decreased plasma membrane (PM) integrity under multiple abiotic stresses such as freezing, high salt, osmotic stress and mechanical damage. Here, we show that, together with SYT1, the stress-induced SYT3 is an ER-PM tether that also functions in maintaining PM integrity. The ER-PM CS localization of SYT1 and SYT3 is dependent on PM phosphatidylinositol-4-phosphate and is regulated by abiotic stress. Lipidomic analysis revealed that cold stress increased the accumulation of diacylglycerol at the PM in a syt1/3 double mutant relative to wild type while the levels of most glycerolipid species remain unchanged. Additionally, the SYT1-green fluorescent protein (GFP) fusion preferentially binds diacylglycerol in vivo with little affinity for polar glycerolipids. Our work uncovers a SYT-dependent mechanism of stress adaptation counteracting the detrimental accumulation of diacylglycerol at the PM produced during episodes of abiotic stress.

scholarly journals Sigma 1 Receptor, Cholesterol and Endoplasmic Reticulum Contact Sites

Contact ◽  
2021 ◽  
Vol 4 ◽  
pp. 251525642110265
Author(s):  
Vladimir Zhemkov ◽  
Jen Liou ◽  
Ilya Bezprozvanny
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Composition ◽  
Sigma 1 Receptor ◽  
Functional Roles ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Sigma 1 ◽  
Membrane Contact ◽  
Organelle Communication ◽  
Cellular Organelles

Recent studies indicated potential importance of membrane contact sites (MCS) between the endoplasmic reticulum (ER) and other cellular organelles. These MCS have unique protein and lipid composition and serve as hubs for inter-organelle communication and signaling. Despite extensive investigation of MCS protein composition and functional roles, little is known about the process of MCS formation. In this perspective, we propose a hypothesis that MCS are formed not as a result of random interactions between membranes of ER and other organelles but on the basis of pre-existing cholesterol-enriched ER microdomains.

scholarly journals An Interorganellar Bidding War: Vps13 Localization by Competitive Organelle-Specific Adaptors

Contact ◽  
2018 ◽  
Vol 1 ◽  
pp. 251525641881462
Author(s):  
Samantha K. Dziurdzik ◽  
Björn D.M. Bean ◽  
Elizabeth Conibear
Keyword(s):  
Endoplasmic Reticulum ◽  
Recent Work ◽  
Protein Sorting ◽  
Repeat Region ◽  
Vacuolar Protein Sorting ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Prospore Membrane ◽  
Membrane Contact ◽  
Vacuolar Protein

Membrane contact sites are regulated through the controlled recruitment of constituent proteins. Yeast vacuolar protein sorting 13 (Vps13) dynamically localizes to membrane contact sites at endosomes, vacuoles, mitochondria, and the endoplasmic reticulum under different cellular conditions and is recruited to the prospore membrane during meiosis. Prior to our recent work, the mechanism for localization at contact sites was largely unknown. We identified Ypt35 as a novel Vps13 adaptor for endosomes and the nucleus-vacuole junction. Furthermore, we discovered a conserved recruitment motif in Ypt35 and found related motifs in the prospore membrane and mitochondrial adaptors, Spo71 and Mcp1, respectively. All three adaptors compete for binding to a six-repeat region of Vps13, suggesting adaptor competition regulates Vps13 localization. Here, we summarize and discuss the implications of our work, highlighting key outstanding questions.

scholarly journals Mitochondria Endoplasmic Reticulum Contact Sites (MERCs): Proximity Ligation Assay as a Tool to Study Organelle Interaction

2021 ◽  
Vol 9 ◽  
Author(s):  
Sara Benhammouda ◽  
Anjali Vishwakarma ◽  
Priya Gatti ◽  
Marc Germain
Keyword(s):  
Endoplasmic Reticulum ◽  
Fluorescence Probes ◽  
Proximity Ligation Assay ◽  
Proximity Ligation ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Membrane Contact ◽  
Endogenous Proteins ◽  
Underlying Mechanisms

Organelles cooperate with each other to regulate vital cellular homoeostatic functions. This occurs through the formation of close connections through membrane contact sites. Mitochondria-Endoplasmic-Reticulum (ER) contact sites (MERCS) are one of such contact sites that regulate numerous biological processes by controlling calcium and metabolic homeostasis. However, the extent to which contact sites shape cellular biology and the underlying mechanisms remain to be fully elucidated. A number of biochemical and imaging approaches have been established to address these questions, resulting in the identification of a number of molecular tethers between mitochondria and the ER. Among these techniques, fluorescence-based imaging is widely used, including analysing signal overlap between two organelles and more selective techniques such as in-situ proximity ligation assay (PLA). While these two techniques allow the detection of endogenous proteins, preventing some problems associated with techniques relying on overexpression (FRET, split fluorescence probes), they come with their own issues. In addition, proper image analysis is required to minimise potential artefacts associated with these methods. In this review, we discuss the protocols and outline the limitations of fluorescence-based approaches used to assess MERCs using endogenous proteins.

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