scholarly journals The Role of Sphingomyelin (SM) in Tissue Factor (TF) Encryption: ATP-Induced Activation of Acid Sphingomyelinase in Macrophages Decrypts Tissue Factor By Hydrolysis of SM in the Outer Leaflet

Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 16-16
Author(s):  
Jue Wang ◽  
Usha R Pendurthi ◽  
L. Vijaya Mohan Rao
Keyword(s):  
Plasma Membrane ◽  
Cell Surface ◽  
Tissue Factor ◽  
Cell Injury ◽  
Critical Role ◽  
Inhibitory Effect ◽  
Amidolytic Activity ◽  
Anionic Phospholipids ◽  
Outer Leaflet ◽  
Hydrolysis Of

Abstract While tissue factor (TF)-mediated blood coagulation is essential for maintaining hemostasis, the aberrant activation of TF-mediated coagulation is a major determinant of thrombotic occlusions, the precipitating event in acute myocardial infarction, unstable angina, and ischemic stroke. Typically, TF on cell surfaces exists in inactive coagulant status (cryptic TF). Cell injury leads conversion of cryptic TF to coagulant active/prothrombotic TF. Molecular differences between cryptic and procoagulant TF and the mechanisms that are responsible for the conversion from one to the other form are poorly understood and often controversial. A majority of the evidence in the literature suggest that level of anionic phospholipids, such as phosphatidylserine (PS), in the outer leaflet of the plasma membrane plays a critical role in regulating TF procoagulant activity at the cell surface. However, other pathways, such as the thioredoxin system or thiol-disulfide exchange pathways involving protein-disulfide isomerase (PDI), were also shown to contribute to TF activation by inducing structural changes in TF. It is unknown at present whether TF on cell surfaces of naïve cells exists primarily in the cryptic state because of the limited availability of anionic phospholipids at the outer leaflet or phospholipids present in the outer leaflet play an active role in maintaining TF in the cryptic state. In the outer leaflet of mammalian plasma membrane, sphingomyelin (SM) constitutes up to 50% of the total phospholipids present on the cell surface. It is possible that a high SM content in the outer leaflet may be responsible for maintaining TF in its cryptic state at the cell surface in naïve cells, and the hydrolysis of SM on the outer leaflet mediated by factors released in cell injury contributes to TF activation. The present study was carried out to investigate this possibility. First, we tested the potential effect of SM on TF activity in a reconstituted system in which full-length TF was reconstituted into phospholipid vesicles composed of varying molar concentrations of SM with the remainder of the vesicle consisting of phosphatidylcholine (PC). SM, at 35 mol % or higher concentration in the proteoliposome, inhibited TF coagulant activity significantly as measured in factor X activation assay. Ceramide, having a similar sphingosine backbone as of SM, had no inhibitory effect on TF-FVIIa activation of FX. Measurement of FVIIa-TF amidolytic activity showed that SM does not inhibit the amidolytic activity of FVIIa-TF, indicating that SM neither affects FVIIa binding to TF nor TF-FVIIa cleavage of the small substrate peptide. SM also inhibited significantly TF activity of TF reconstituted in PC/PS (94%:6% mol/mol) vesicles. Next, human monocyte-derived macrophages (MDMs) were treated with varying concentrations of bacterial sphingomyelinase (b-SMase) to hydrolyze SM in the outer leaflet. b-SMase treatment increased cell surface TF activity in a dose-dependent manner. SMase treatment also enhanced the release of TF-bearing microparticles (MPs). SMase treatment had no significant effect on cell surface prothrombinase activity or annexin V binding to MDMs, indicating that b-SMase treatment did not increase PS availability at the cell surface under our experimental conditions. Similar to that observed in bone marrow-derived mouse macrophages, ATP (200 µM) stimulation of MDMs increased cell surface TF activity by about 3-fold and triggered the release of TF+ MPs. Immunofluorescence confocal microscopy revealed that ATP stimulation induced in the translocation of acid(a)-SMase from intracellular compartments to the outer leaflet of the plasma membrane. Treatment of MDMs with sphingomyelinase inhibitors, desipramine and imipramine (1 and 5 µM), or silencing a-SMase with siRNA markedly reduced the ATP-induced increased TF activity at the cell surface and TF+ MPs release. Finally, ATP stimulation was shown to increase the hydrolysis of SM in the outer leaflet of MDMs markedly. a-SMase inhibitors or silencing of a-SMase attenuated the ATP-induced SM hydrolysis. In summary, our data indicate that SM plays a critical role in maintaining TF in the cryptic state in resting cells. Activation/translocation of a-SMase to the outer leaflet following the activation of ATP receptor P2X7 leads to hydrolysis of SM and thus relieves the inhibitory effect of SM on TF, leading to TF decryption and the release of TF+ MPs. Disclosures No relevant conflicts of interest to declare.

scholarly journals Role of Cell Surface Lipids and Thiol-Disulphide Exchange Pathways in Regulating the Encryption and Decryption of Tissue Factor

2019 ◽  
Vol 119 (06) ◽  
pp. 860-870 ◽  
Author(s):  
Shabbir A. Ansari ◽  
Usha R. Pendurthi ◽  
L. Vijaya Mohan Rao
Keyword(s):  
Cell Surface ◽  
Tissue Factor ◽  
Cell Injury ◽  
Critical Role ◽  
The Body ◽  
Resting Cells ◽  
Aberrant Expression ◽  
Outer Leaflet ◽  
Coagulant Activity ◽  
Encryption And Decryption

AbstractTissue factor (TF), a transmembrane glycoprotein, is the cellular receptor of the coagulation factors VII (FVII) and VIIa (FVIIa). The formation of TF–FVIIa complex triggers the initiation of the blood coagulation pathway. TF plays an essential role in haemostasis, but an aberrant expression of TF activity contributes to thrombotic disorders. In health, TF pro-coagulant activity on cells is controlled tightly to allow sufficient coagulant activity to achieve haemostasis but not to cause thrombosis. It is achieved largely by selective localization of TF in the body and encryption of TF at the cell surface. A vast majority of TF on resting cells exists in an encrypted state with minimal pro-coagulant activity but becomes pro-thrombotic following cell injury or activation. At present, the mechanisms that are responsible for TF encryption and activation (decryption) are not entirely clear, but recent studies provide important mechanistic insights into these processes. To date, externalization of phosphatidylserine to the outer leaflet and thiol-disulphide exchange pathways that either turn on and off the allosteric disulphide bond in TF are shown to play a major role in regulating TF pro-coagulant activity on cell surfaces. Recent studies showed that sphingomyelin, a major phospholipid in the outer leaflet of plasma membrane, plays a critical role in the encryption of TF in resting cells. The present review provides an overview of recent literature on the above-described mechanisms of TF encryption and decryption with a particular emphasis on our recent findings.

scholarly journals Acid sphingomyelinase plays a critical role in LPS- and cytokine-induced tissue factor procoagulant activity

Blood ◽  
2019 ◽  
Vol 134 (7) ◽  
pp. 645-655
Author(s):  
Jue Wang ◽  
Usha R. Pendurthi ◽  
L. Vijaya Mohan Rao
Keyword(s):  
Plasma Membrane ◽  
Tissue Factor ◽  
Critical Role ◽  
Acid Sphingomyelinase ◽  
Procoagulant Activity ◽  
Model Systems ◽  
Resting Cells ◽  
Aberrant Expression ◽  
Outer Leaflet ◽  
Hydrolysis Of

Abstract Tissue factor (TF) is a cofactor for factor VIIa and the primary cellular initiator of coagulation. Typically, most TF on cell surfaces exists in a cryptic coagulant-inactive state but are transformed to a procoagulant form (decryption) following cell activation. Our recent studies in cell model systems showed that sphingomyelin (SM) in the outer leaflet of the plasma membrane is responsible for maintaining TF in an encrypted state in resting cells, and the hydrolysis of SM leads to decryption of TF. The present study was carried out to investigate the relevance of this novel mechanism in the regulation of TF procoagulant activity in pathophysiology. As observed in cell systems, administration of adenosine triphosphate (ATP) to mice enhanced lipopolysaccharide (LPS)-induced TF procoagulant activity in monocytes. Treatment of mice with pharmacological inhibitors of acid sphingomyelinase (ASMase), desipramine and imipramine, attenuated ATP-induced TF decryption. Interestingly, ASMase inhibitors also blocked LPS-induced TF procoagulant activity without affecting the LPS-induced de novo synthesis of TF protein. Additional studies showed that LPS induced translocation of ASMase to the outer leaflet of the plasma membrane and reduced SM levels in monocytes. Studies using human monocyte-derived macrophages and endothelial cells further confirmed the role of ASMase in LPS- and cytokine-induced TF procoagulant activity. Overall, our data indicate that LPS- or cytokine-induced TF procoagulant activity requires the decryption of newly synthesized TF protein by ASMase-mediated hydrolysis of SM. The observation that ASMase inhibitors attenuate TF-induced coagulation raises the possibility of their therapeutic use in treating thrombotic disorders associated with aberrant expression of TF.

scholarly journals Sphingomyelin encrypts tissue factor: ATP-induced activation of A-SMase leads to tissue factor decryption and microvesicle shedding

2017 ◽  
Vol 1 (13) ◽  
pp. 849-862 ◽  
Author(s):  
Jue Wang ◽  
Usha R. Pendurthi ◽  
L. Vijaya Mohan Rao
Keyword(s):  
Plasma Membrane ◽  
Tissue Factor ◽  
Outer Leaflet ◽  
Key Points ◽  
Hydrolysis Of

Key PointsSM in the outer leaflet of the plasma membrane is responsible for TF encryption. ATP-induced activation of A-SMase leads to hydrolysis of SM in the outer leaflet, which consequently activates TF and releases TF+ MVs.

scholarly journals Tissue factor activation: is disulfide bond switching a regulatory mechanism?

Blood ◽  
2007 ◽  
Vol 110 (12) ◽  
pp. 3900-3908 ◽  
Author(s):  
Usha R. Pendurthi ◽  
Samit Ghosh ◽  
Samir K. Mandal ◽  
L. Vijaya Mohan Rao
Keyword(s):  
Cell Surface ◽  
Cell Signaling ◽  
Tissue Factor ◽  
Disulfide Bond ◽  
Annexin V ◽  
Disulfide Exchange ◽  
Anionic Phospholipids ◽  
Coagulant Activity ◽  
Novel Concept ◽  
Cysteine Thiols

AbstractA majority of tissue factor (TF) on cell surfaces exists in a cryptic form (ie, coagulation function inactive) but retains its functionality in cell signaling. Recent studies have suggested that cryptic TF contains unpaired cysteine thiols and that activation involves the formation of the disulfide bond Cys186-Cys 209 and that protein disulfide isomerase (PDI) regulates TF coagulant and signaling activities by targeting this disulfide bond. This study was carried out to investigate the validity of this novel concept. Although treatment of MDA 231 tumor cells, fibroblasts, and stimulated endothelial cells with the oxidizing agent HgCl2 markedly increased the cell-surface TF coagulant activity, the increase is associated with increased anionic phospholipids at the cell surface. Annexin V, which binds to anionic phospholipids, attenuated the increased TF coagulant activity. It is noteworthy that treatment of cells with reducing agents also increased the cell surface TF activity. No evidence was found for either detectable expression of PDI at the cell surface or association of TF with PDI. Furthermore, reduction of PDI with the gene silencing had no effect on either TF coagulant or cell signaling functions. Overall, the present data undermine the recently proposed hypothesis that PDI-mediated disulfide exchange plays a role in regulating TF procoagulant and cell signaling functions.

scholarly journals Brefeldin A inhibits the endocytosis of plasma-membrane-associated heparan sulphate proteoglycans of cultured rat ovarian granulosa cells

1995 ◽  
Vol 310 (1) ◽  
pp. 271-278 ◽  
Author(s):  
L Uhlin-Hansen ◽  
M Yanagishita
Keyword(s):  
Plasma Membrane ◽  
Cell Surface ◽  
Granulosa Cells ◽  
Protein Transport ◽  
Heparan Sulphate ◽  
Brefeldin A ◽  
Inhibitory Effect ◽  
Surface Proteins ◽  
Gel Chromatography ◽  
Ovarian Granulosa Cells

Rat ovarian granulosa cells were labelled with [35S]sulphate for 0.5-20 h and chased in the presence or absence of 1-2 micrograms/ml of brefeldin A (BFA) for up to 21 h. Heparan [35S]sulphate (HS) proteoglycans from the culture medium, plasma membrane and intracellular fractions were then analysed by gel chromatography. In the absence of BFA, about 85% of the plasma membrane-associated HS proteoglycans were endocytosed and subsequently degraded intracellularly. Recirculation of the HS proteoglycans between the intracellular pool and the cell surface was not observed. Exposing the cells to BFA for less than 1 h did not influence the turnover of the HS proteoglycans, whereas the effect of the drug on the Golgi functions reached a maximum in approx. 10 min. When the cells were treated with BFA for more than 1-2 h, the rate of endocytosis of HS proteoglycans was reduced to about 50% of the control. The delivery of endocytosed HS proteoglycans to lysosomes were not affected by the drug. Cycloheximide also reduced the endocytosis of HS proteoglycans, but not as much as BFA, indicating that the inhibitory effect of BFA can be only partly accounted for by a block of protein transport from the endoplasmic reticulum to the plasma membrane. In contrast with the endocytosis of HS proteoglycans, neither that of 125I-transferrin, known to be mediated by clathrin-coated vesicles, nor that of 125I-ricin, a marker molecule for bulk endocytosis, was affected by BFA. The half-life of 125I-transferrin and 125I-ricin in the plasma membrane was about 10 and 25 min respectively compared with about 5 h for the HS proteoglycans. Altogether, these results indicate that the endocytosis of plasma-membrane-associated HS proteoglycans is mediated by different mechanisms than the endocytosis of most other cell-surface proteins. Further, the mechanisms involved in the endocytosis of HS proteoglycans are sensitive to BFA.

scholarly journals A Ral GAP complex links PI 3-kinase/Akt signaling to RalA activation in insulin action

2011 ◽  
Vol 22 (1) ◽  
pp. 141-152 ◽  
Author(s):  
Xiao-Wei Chen ◽  
Dara Leto ◽  
Tingting Xiong ◽  
Genggeng Yu ◽  
Alan Cheng ◽  
...  
Keyword(s):  
Glucose Transporter ◽  
Critical Role ◽  
Inhibitory Effect ◽  
Small Gtpase ◽  
Regulatory Subunit ◽  
Hydrolysis Of ◽  
Identification And Characterization

Insulin stimulates glucose transport in muscle  and adipose tissue by translocation of glucose transporter 4 (GLUT4) to the plasma membrane. We previously reported that activation of the small GTPase RalA downstream of PI 3-kinase plays a critical role in this process by mobilizing the exocyst complex for GLUT4 vesicle targeting in adipocytes. Here we report the identification and characterization of a Ral GAP complex (RGC) that mediates the activation of RalA downstream of the PI 3-kinase/Akt pathway. The complex is composed of an RGC1 regulatory subunit and an RGC2 catalytic subunit (previously identified as AS250) that directly stimulates the guanosine triphosphate hydrolysis of RalA. Knockdown of RGC proteins leads to increased RalA activity and glucose uptake in adipocytes. Insulin inhibits the GAP complex through Akt2-catalyzed phosphorylation of RGC2 in vitro and in vivo, while activated Akt relieves the inhibitory effect of RGC proteins on RalA activity. The RGC complex thus connects PI 3-kinase/Akt activity to the transport machineries responsible for GLUT4 translocation.

Tissue Factor Activation: Is Disulfide Switching a General Regulatory Mechanism?.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 1747-1747 ◽  
Author(s):  
Usha Pendurthi ◽  
Samit Ghosh ◽  
Samir Mandal ◽  
L. Vijaya Mohan Rao
Keyword(s):  
Cell Surface ◽  
Cell Signaling ◽  
Tissue Factor ◽  
Factor Viia ◽  
Coagulation Cascade ◽  
Clotting Factor ◽  
Permeabilized Cells ◽  
Anionic Phospholipids ◽  
Cellular Expression ◽  
Coagulant Activity

Abstract Tissue factor (TF) is the cellular receptor for plasma clotting factor VIIa, and the formation of TF-VIIa complexes on cell surfaces trigger the coagulation cascade and cell signaling. It is a well-known fact that only a small fraction of TF at the cell surface is coagulantly active whereas a majority of TF on the cell surface is non-functional (cryptic). However, it is unclear, at present, how the coagulant active TF differs from the cryptic form, and mechanisms involved in TF activation. Recent studies show that a thiol oxidizing agent, HgCl2, increases TF coagulant activity on the surface of HL-60 cells by several fold (Chen et al., Blood vol 106, abstract #684, 2005). Further, TF is shown to associate with protein disulfide isomerase (PDI) in HaCaT cells (Ahamed et al., Blood vol 106, abstract #685, 2005). Based on these and other observations, it has been proposed that switching between cryptic and coagulant TF involves cleavage and formation of allosteric disulfide bond (Cys186-Cys209) and PDI has been implicated in controlling the conversion of cryptic TF to the coagulant form and to act as a switch between TF-mediated signaling and coagulation. Although these data are interesting and novel, there is no fail-proof evidence that disulfide switching alone and not other potential changes, such as exposure of anionic phospholipids, at the cell surface is responsible for the TF activation associated with various treatments. Therefore we have examined the effect of HgCl2 and other treatments on TF activation in MDA 231 cells in relation to anionic phospholipids and also characterized the cellular expression of PDI in this and other cell types. As reported earlier, the HgCl2 treatment increased the cell surface TF coagulant activity (5-fold or higher). However, the HgCl2 treatment also increased the prothombinase activity by 3-fold. More importantly, annexin V, which binds to anionic phospholipids, markedly reduced the increased TF coagulant activity associated with the HgCl2 treatment whereas it had only minimal and insignificant effect on TF activity of the control cells. Further, pretreatment of cells with 5,5′-dithio-bis(2-nitronezoic acid) (DTNB), a sulfhydryl reagent that reacts with thiol groups and thus can block disulfide switching, failed to prevent the increase in TF activity associated with the HgCl2 treatment. Interestingly, we found that treatment of MDA 231 cells with glutathione (5 to 100 mM), a cell impermeable reducing agent, also increased the surface TF activity by about 2- to 3-fold. In additional studies, we found that PDI antibodies had no effect on either the TF coagulant activity or TF-mediated cell signaling. Further, we found no evidence for the expression of PDI at the cell surface in immunofluorescence confocal microscopy as both monoclonal and polyclonal PDI antibodies failed to stain nonpermeabilized cells whereas they brightly stained intracellular PDI in permeabilized cells. In contrast, TF antibodies stained intensely the surface of both nonpermeabilized and permeabilized cells. Exposure of tumor cells to various proteases failed to transport the intracellular PDI to the cell surface. The present data raise a valid question whether disulfide switching by PDI plays the predominant and general regulatory role in controlling the TF coagulant activity and signaling functions. Our data also suggest that other cellular changes, including increase in anionic phospholipids, may be responsible for increased TF coagulant activity associated with the thiol oxidizers and other treatments.

Plasmin Enhances Cell Surface Tissue Factor Activity without Increasing Tissue Factor Antigen Levels at the Cell Surfaces of Mesothelial and Endothelial Cells.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 1758-1758 ◽  
Author(s):  
Hema Kothari ◽  
L. Vijaya Mohan Rao ◽  
Steven Idell ◽  
Usha R. Pendurthi
Keyword(s):  
Endothelial Cells ◽  
Cell Surface ◽  
Tissue Factor ◽  
De Novo ◽  
Mesothelial Cells ◽  
Model Systems ◽  
Pleural Effusions ◽  
De Novo Synthesis ◽  
Anionic Phospholipids ◽  
Activation Assay

Abstract Mesothelial cells that line the thoracic and peritoneal cavities play an important role in protecting the heart, lungs and internal organs and keeping the surfaces free of friction and non-adhesive. Although human mesothelial cells in culture express low levels of tissue factor (TF), TF expression was not detected in vivo in the mesothelial lining of normal pleura but was detected in the mesothelium overlying injured or inflamed lung tissue. Inflammation in the lung parenchyma predisposes to the development of inflammatory exudative pleural effusions and pleural loculation, but the mechanism(s) responsible for TF expression in mesothelial cells under such conditions remains unclear. In the present study, we investigated whether plasmin and thrombin, two major proteases present in exudative pleural effusions, induce TF expression in cultured primary human pleural mesothelial cells (HMC). Confluent monolayers of HMC were treated with plasmin (50 nM) and thrombin (5 nM) for varying time periods. TF expression was analyzed by measurement of cell surface TF activity in FX activation assay, TF antigen by Western blotting and TF mRNA by Northern blot analysis. Both plasmin and thrombin increased cell surface TF activity by 3–4 fold. Thrombin markedly increased TF antigen levels. Surprisingly, only a minimal increase in TF antigen levels was seen in the plasmin-treated cells and no increase in TF mRNA was observed in these cells. Interestingly, 75% of the increase in TF activity was observed within 30 min of plasmin treatment. In thrombin-stimulated cells, TF activity increased slowly, reaching maximum at 4–6 h. Treatment of HMC with actinomycin-D or cycloheximide prior to the addition of the protease failed to inhibit the plasmin-induced TF activity whereas they completely attenuated the thrombin-induced TF activity. These data suggest that plasmin and thrombin enhance TF activity in HMC by different mechanisms, and that plasmin-induced TF activity is independent of de novo synthesis of TF. We also examined the effect of plasmin on TF activity in human umbilical vein endothelial cells (HUVEC). Although plasmin had a minimal effect on naive HUVEC, 30 min plasmin treatment increased cell surface TF activity of thrombin-stimulated endothelial cells by more than two-fold. In our earlier studies, we showed that proteases could mobilize intracellular TF to the cell surface of fibroblasts and thus enhance TF activity independent of de novo synthesis of TF. However, FACS analysis and 125I-FVIIa binding to cell surface TF revealed no significant differences in TF antigen levels at the surfaces of control and plasmin-stimulated HMC. Since exposure of anionic phospholipids at the outer cell surface membrane can increase cell surface TF activity, we next sought to determine if plasmin increases anionic phospholipids on the outer bilayer of the HMC cell membrane. Prothrombin activation assays showed no increase in anionic phospholipids at the surface in plasmin-treated cells. Although recent studies suggest that disulfide bond formation of cysteines in TF enhances TF procoagulant activity, our recent studies in other cell model systems suggest that this mechanism is unlikely to account for plasmin-mediated induction of cell surface TF activity in HMC. While further studies are required to exclude this possibility, our present data indicate that plasmin enhances cell surface TF activity of HMC and HUVEC by a novel mechanism that is yet to be elucidated.

scholarly journals Sialidase NEU3 is a peripheral membrane protein localized on the cell surface and in endosomal structures

2007 ◽  
Vol 408 (2) ◽  
pp. 211-219 ◽  
Author(s):  
Gabriele Zanchetti ◽  
Paolo Colombi ◽  
Marta Manzoni ◽  
Luigi Anastasia ◽  
Luigi Caimi ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Membrane Protein ◽  
Cell Surface ◽  
Surface Protein ◽  
Experimental Conditions ◽  
Cellular Processes ◽  
Endosomal Compartment ◽  
Outer Leaflet ◽  
Peripheral Membrane Protein ◽  
The Moment

Sialidase NEU3 is also known as the plasma-membrane-associated form of mammalian sialidases, exhibiting a high substrate specificity towards gangliosides. In this respect, sialidase NEU3 modulates cell-surface biological events and plays a pivotal role in different cellular processes, including cell adhesion, recognition and differentiation. At the moment, no detailed studies concerning the subcellular localization of NEU3 are available, and the mechanism of its association with cellular membranes is still unknown. In the present study, we have demonstrated that sialidase NEU3, besides its localization at the plasma membrane, is present in intracellular structures at least partially represented by a subset of the endosomal compartment. Moreover, we have shown that NEU3 present at the plasma membrane is internalized and locates then to the recycling endosomal compartment. The enzyme is associated with the outer leaflet of the plasma membrane, as shown by selective cell-surface protein biotinylation. This evidence is in agreement with the ability of NEU3 to degrade gangliosides inserted into the plasma membrane of adjacent cells. Moreover, the mechanism of the protein association with the lipid bilayer was elucidated by carbonate extraction. Under these experimental conditions, we have succeeded in solubilizing NEU3, thus demonstrating that the enzyme is a peripheral membrane protein. In addition, Triton X-114 phase separation demonstrates further the hydrophilic nature of the protein. Overall, these results provide important information about the biology of NEU3, the most studied member of the mammalian sialidase family.

scholarly journals Phospholipid flipping facilitates annexin translocation across membranes

2018 ◽  
Author(s):  
Sarah E Stewart ◽  
Avraham Ashkenazi ◽  
Athena Williamson ◽  
David C Rubinsztein ◽  
Kevin Moreau
Keyword(s):  
Plasma Membrane ◽  
Cell Migration ◽  
Cell Surface ◽  
Binding Proteins ◽  
Annexin A2 ◽  
Plasminogen Activation ◽  
Anoctamin 6 ◽  
Outer Leaflet ◽  
Membrane Cell ◽  
Plasma Membrane Phospholipid

AbstractAnnexins are phospholipid binding proteins that somehow translocate from the inner leaflet of the plasma membrane to the outer leaflet. For example, Annexin A2 is known to localise to the outer leaflet of the plasma membrane (cell surface) where it is involved in plasminogen activation leading to fibrinolysis and cell migration, among other functions. Despite having well described extracellular functions, the mechanism of annexin transport from the cytoplasmic inner leaflet to the extracellular outer leaflet of the plasma membrane remains unclear. Here, we show that phospholipid flipping activity is crucial for the transport of annexins A2 and A5 across membranes in cells and in liposomes. We identified TMEM16F (anoctamin-6) as a lipid scramblase required for transport of these annexins to the outer leaflet of the plasma membrane. This work reveals a mechanism for annexin translocation across membranes which depends on plasma membrane phospholipid flipping.

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