scholarly journals ORP5 localizes to ER–lipid droplet contacts and regulates the level of PI(4)P on lipid droplets

2019 ◽  
Vol 219 (1) ◽  
Author(s):  
Ximing Du ◽  
Linkang Zhou ◽  
Yvette Celine Aw ◽  
Hoi Yin Mak ◽  
Yanqing Xu ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Protein ◽  
Lipid Droplets ◽  
Lipid Synthesis ◽  
Integral Membrane Protein ◽  
Normal Cells ◽  
Bilayer Membranes ◽  
Contact Sites ◽  
Evolutionarily Conserved ◽  
Phosphatidylinositol 4

Lipid droplets (LDs) are evolutionarily conserved organelles that play important roles in cellular metabolism. Each LD is enclosed by a monolayer of phospholipids, distinct from bilayer membranes. During LD biogenesis and growth, this monolayer of lipids expands by acquiring phospholipids from the endoplasmic reticulum (ER) through nonvesicular mechanisms. Here, in a mini-screen, we find that ORP5, an integral membrane protein of the ER, can localize to ER–LD contact sites upon oleate loading. ORP5 interacts with LDs through its ligand-binding domain, and ORP5 deficiency enhances neutral lipid synthesis and increases the size of LDs. Importantly, there is significantly more phosphatidylinositol-4-phosphate (PI(4)P) and less phosphatidylserine (PS) on LDs in ORP5-deficient cells than in normal cells. The increased presence of PI(4)P on LDs in ORP5-deficient cells requires phosphatidylinositol 4-kinase 2-α. Our results thus demonstrate the existence of PI(4)P on LDs and suggest that LD-associated PI(4)P may be primarily used by ORP5 to deliver PS to LDs.

scholarly journals The seipin complex Fld1/Ldb16 stabilizes ER–lipid droplet contact sites

2015 ◽  
Vol 211 (4) ◽  
pp. 829-844 ◽  
Author(s):  
Alexandra Grippa ◽  
Laura Buxó ◽  
Gabriel Mora ◽  
Charlotta Funaya ◽  
Fatima-Zahra Idrissi ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Protein ◽  
Neutral Lipid ◽  
Diffusion Barrier ◽  
Lipid Droplets ◽  
Lipid Binding ◽  
Contact Sites ◽  
Packing Defects ◽  
Specific Proteins ◽  
Lipid Binding Proteins

Lipid droplets (LDs) are storage organelles consisting of a neutral lipid core surrounded by a phospholipid monolayer and a set of LD-specific proteins. Most LD components are synthesized in the endoplasmic reticulum (ER), an organelle that is often physically connected with LDs. How LD identity is established while maintaining biochemical and physical connections with the ER is not known. Here, we show that the yeast seipin Fld1, in complex with the ER membrane protein Ldb16, prevents equilibration of ER and LD surface components by stabilizing the contact sites between the two organelles. In the absence of the Fld1/Ldb16 complex, assembly of LDs results in phospholipid packing defects leading to aberrant distribution of lipid-binding proteins and abnormal LDs. We propose that the Fld1/Ldb16 complex facilitates the establishment of LD identity by acting as a diffusion barrier at the ER–LD contact sites.

scholarly journals Seipin is required for converting nascent to mature lipid droplets

eLife ◽  
2016 ◽  
Vol 5 ◽  
Author(s):  
Huajin Wang ◽  
Michel Becuwe ◽  
Benjamin E Housden ◽  
Chandramohan Chitraju ◽  
Ashley J Porras ◽  
...  
Keyword(s):  
Lipid Droplets ◽  
Lipid Synthesis ◽  
Human Cells ◽  
Lipid Transfer ◽  
Cellular Lipid ◽  
Contact Sites ◽  
Discrete Step

How proteins control the biogenesis of cellular lipid droplets (LDs) is poorly understood. Using Drosophila and human cells, we show here that seipin, an ER protein implicated in LD biology, mediates a discrete step in LD formation—the conversion of small, nascent LDs to larger, mature LDs. Seipin forms discrete and dynamic foci in the ER that interact with nascent LDs to enable their growth. In the absence of seipin, numerous small, nascent LDs accumulate near the ER and most often fail to grow. Those that do grow prematurely acquire lipid synthesis enzymes and undergo expansion, eventually leading to the giant LDs characteristic of seipin deficiency. Our studies identify a discrete step of LD formation, namely the conversion of nascent LDs to mature LDs, and define a molecular role for seipin in this process, most likely by acting at ER-LD contact sites to enable lipid transfer to nascent LDs.

scholarly journals Adenovirus Modulates Toll-Like Receptor 4 Signaling by Reprogramming ORP1L-VAP Protein Contacts for Cholesterol Transport from Endosomes to the Endoplasmic Reticulum

2017 ◽  
Vol 91 (6) ◽  
Author(s):  
Nicholas L. Cianciola ◽  
Stacey Chung ◽  
Danny Manor ◽  
Cathleen R. Carlin
Keyword(s):  
Innate Immunity ◽  
Endoplasmic Reticulum ◽  
Membrane Protein ◽  
Lipid Droplets ◽  
Cholesterol Transport ◽  
Toll Like Receptor ◽  
Toll Like Receptor 4 ◽  
Human Adenoviruses ◽  
Early Region ◽  
Early Region 3

ABSTRACT Human adenoviruses (Ads) generally cause mild self-limiting infections but can lead to serious disease and even be fatal in high-risk individuals, underscoring the importance of understanding how the virus counteracts host defense mechanisms. This study had two goals. First, we wished to determine the molecular basis of cholesterol homeostatic responses induced by the early region 3 membrane protein RIDα via its direct interaction with the sterol-binding protein ORP1L, a member of the evolutionarily conserved family of oxysterol-binding protein (OSBP)-related proteins (ORPs). Second, we wished to determine how this interaction regulates innate immunity to adenovirus. ORP1L is known to form highly dynamic contacts with endoplasmic reticulum-resident VAP proteins that regulate late endosome function under regulation of Rab7-GTP. Our studies have demonstrated that ORP1L-VAP complexes also support transport of LDL-derived cholesterol from endosomes to the endoplasmic reticulum, where it was converted to cholesteryl esters stored in lipid droplets when ORP1L was bound to RIDα. The virally induced mechanism counteracted defects in the predominant cholesterol transport pathway regulated by the late endosomal membrane protein Niemann-Pick disease type C protein 1 (NPC1) arising during early stages of viral infection. However, unlike NPC1, RIDα did not reconstitute transport to endoplasmic reticulum pools that regulate SREBP transcription factors. RIDα-induced lipid trafficking also attenuated proinflammatory signaling by Toll-like receptor 4, which has a central role in Ad pathogenesis and is known to be tightly regulated by cholesterol-rich “lipid rafts.” Collectively, these data show that RIDα utilizes ORP1L in a way that is distinct from its normal function in uninfected cells to fine-tune lipid raft cholesterol that regulates innate immunity to adenovirus in endosomes. IMPORTANCE Early region 3 proteins encoded by human adenoviruses that attenuate immune-mediated pathology have been a particularly rich source of information regarding intracellular protein trafficking. Our studies with the early region 3-encoded RIDα protein also provided fundamental new information regarding mechanisms of nonvesicular lipid transport and the flow of molecular information at membrane contacts between different organelles. We describe a new pathway that delivers cholesterol from endosomes to the endoplasmic reticulum, where it is esterified and stored in lipid droplets. Although lipid droplets are attracting renewed interest from the standpoint of normal physiology and human diseases, including those resulting from viral infections, experimental model systems for evaluating how and why they accumulate are still limited. Our studies also revealed an intriguing relationship between lipid droplets and innate immunity that may represent a new paradigm for viruses utilizing these organelles.

scholarly journals Pex24 and Pex32 are required to tether peroxisomes to the ER for organelle biogenesis, positioning and segregation in yeast

2020 ◽  
Vol 133 (16) ◽  
pp. jcs246983 ◽  
Author(s):  
Fei Wu ◽  
Rinse de Boer ◽  
Arjen M. Krikken ◽  
Arman Akşit ◽  
Nicola Bordin ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Protein ◽  
Matrix Protein ◽  
Protein Import ◽  
Hansenula Polymorpha ◽  
Major Effect ◽  
Organelle Biogenesis ◽  
Peroxisomal Membrane ◽  
Contact Sites ◽  
Membrane Growth

ABSTRACTThe yeast Hansenula polymorpha contains four members of the Pex23 family of peroxins, which characteristically contain a DysF domain. Here we show that all four H. polymorpha Pex23 family proteins localize to the endoplasmic reticulum (ER). Pex24 and Pex32, but not Pex23 and Pex29, predominantly accumulate at peroxisome–ER contacts. Upon deletion of PEX24 or PEX32 – and to a much lesser extent, of PEX23 or PEX29 – peroxisome–ER contacts are lost, concomitant with defects in peroxisomal matrix protein import, membrane growth, and organelle proliferation, positioning and segregation. These defects are suppressed by the introduction of an artificial peroxisome–ER tether, indicating that Pex24 and Pex32 contribute to tethering of peroxisomes to the ER. Accumulation of Pex32 at these contact sites is lost in cells lacking the peroxisomal membrane protein Pex11, in conjunction with disruption of the contacts. This indicates that Pex11 contributes to Pex32-dependent peroxisome–ER contact formation. The absence of Pex32 has no major effect on pre-peroxisomal vesicles that occur in pex3 atg1 deletion cells.

scholarly journals Systematic Prediction of FFAT Motifs Across Eukaryote Proteomes Identifies Nucleolar and Eisosome Proteins With the Predicted Capacity to Form Bridges to the Endoplasmic Reticulum

Contact ◽  
2019 ◽  
Vol 2 ◽  
pp. 251525641988313 ◽  
Author(s):  
John A. Slee ◽  
Timothy P. Levine
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Protein ◽  
Common Mechanism ◽  
Linear Motif ◽  
Membrane Contact Sites ◽  
Contact Sites ◽  
Cytoplasmic Proteins ◽  
Eukaryotic Proteins ◽  
Minimum Number ◽  
Membrane Contact

The endoplasmic reticulum (ER), the most pervasive organelle, exchanges information and material with many other organelles, but the extent of its interorganelle connections and the proteins that form bridges are not well known. The integral ER membrane protein vesicle-associated membrane protein-associated protein (VAP) is found in multiple bridges, interacting with many proteins that contain a short linear motif consisting of “two phenylalanines in an acidic tract” (FFAT). The VAP-FFAT interaction is the most common mechanism by which cytoplasmic proteins, particularly interorganelle bridges, target the ER. Therefore, predicting new FFAT motifs may both find new individual peripheral ER proteins and identify new routes of communication involving the ER. Here, we searched for FFAT motifs across whole proteomes. The excess of eukaryotic proteins with FFAT motifs over background was ≥0.8%, suggesting that this is the minimum number of peripheral ER proteins. In yeast, where VAP was previously known to bind 4 proteins with FFAT motifs, a detailed analysis of a subset of proteins predicted 20 FFAT motifs. Extrapolating these findings to the whole proteome estimated the number of FFAT motifs in yeast at approximately 50 to 55 (0.9% of proteome). Among these previously unstudied FFAT motifs, most have known functions outside the ER, so could be involved in interorganelle communication. Many of these can target well-characterized membrane contact sites; however, some are in nucleoli and eisosomes, organelles previously unknown to have molecular bridges to the ER. We speculate that the nucleolar and eisosomal proteins with predicted motifs may function while bridging to the ER, indicating novel ER–nucleolus and ER–eisosome routes of interorganelle communication.

Protein 4.2 is critical to CD47-membrane skeleton attachment in human red cells

Blood ◽  
2004 ◽  
Vol 103 (3) ◽  
pp. 1131-1136 ◽  
Author(s):  
Kris Noel Dahl ◽  
Ranganath Parthasarathy ◽  
Connie M. Westhoff ◽  
D. Mark Layton ◽  
Dennis E. Discher
Keyword(s):  
Membrane Protein ◽  
Blood Cells ◽  
Significant Variation ◽  
Integral Membrane Protein ◽  
Membrane Skeleton ◽  
Band 3 ◽  
Normal Cells ◽  
Human Red Blood Cells ◽  
Protein 4.2 ◽  
Human Red Cells

Abstract The reduction in expression of the integral membrane protein CD47 in human red blood cells (RBCs) deficient in protein 4.2 suggests that protein 4.2 may mediate a linkage of CD47 to the membrane skeleton. We compared the fractions of membrane skeleton-attached CD47, Rh-associated glycoprotein (RhAG), Rh, and band 3 in normal and protein 4.2-deficient cells using fluorescence-imaged microdeformation. We found that CD47 attachment decreases from 55% in normal cells to 25% to 35% in 4.2-deficient cells. RhAG, which has been shown to have no significant variation in expression among the cells studied, shows a significant decrease in membrane skeleton attachment in 4.2-deficient cells from 60% to 40%. Both Rh and band 3, which have also been shown to have no change in expression, show a smaller decrease from 75% attached in normal RBCs to 55% attached in 4.2-deficient cells. In normal cells, Rh phenotype influences CD47 expression but not the level of membrane skeleton attachment of CD47. In contrast, the results indicate that protein 4.2 strongly influences CD47 levels as well as the extent of membrane skeleton attachment in the RBC, whereas protein 4.2 affects membrane skeletal attachment of RhAG, Rh, and band 3 to a lesser extent. (Blood. 2004;103:1131-1136)

scholarly journals Infectious Bronchitis Virus 3a Protein Localizes to a Novel Domain of the Smooth Endoplasmic Reticulum

2005 ◽  
Vol 79 (10) ◽  
pp. 6142-6151 ◽  
Author(s):  
Amanda R. Pendleton ◽  
Carolyn E. Machamer
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Protein ◽  
Infectious Bronchitis Virus ◽  
Smooth Endoplasmic Reticulum ◽  
Integral Membrane Protein ◽  
Open Reading Frames ◽  
Infectious Bronchitis ◽  
Infected Cells ◽  
Group 3 ◽  
Small Open Reading Frames

ABSTRACT All coronaviruses possess small open reading frames (ORFs) between structural genes that have been hypothesized to play important roles in pathogenesis. Infectious bronchitis virus (IBV) ORF 3a is one such gene. It is highly conserved among group 3 coronaviruses, suggesting that it has an important function in infection. IBV 3a protein is expressed in infected cells but is not detected in virions. Sequence analysis predicted that IBV 3a was a membrane protein; however, only a fraction behaved like an integral membrane protein. Microscopy and immunoprecipitation studies demonstrated that IBV 3a localized to the cytoplasm in a diffuse pattern as well as in sharp puncta in both infected and transfected cells. These puncta did not overlap cellular organelles or other punctate structures. Confocal microscopy demonstrated that IBV 3a puncta lined up along smooth endoplasmic reticulum (ER) tubules and, in a significant number of instances, were partially surrounded by these tubules. Our results suggest that IBV 3a is partially targeted to a novel domain of the smooth ER.

scholarly journals Immunoisolaton of the Yeast Golgi Subcompartments and Characterization of a Novel Membrane Protein, Svp26, Discovered in the Sed5-Containing Compartments

2005 ◽  
Vol 25 (17) ◽  
pp. 7696-7710 ◽  
Author(s):  
Hironori Inadome ◽  
Yoichi Noda ◽  
Hiroyuki Adachi ◽  
Koji Yoda
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Endoplasmic Reticulum ◽  
Membrane Proteins ◽  
Golgi Apparatus ◽  
Membrane Protein ◽  
Considerable Portion ◽  
Marker Proteins ◽  
Evolutionarily Conserved ◽  
Golgi Compartment

ABSTRACT The Golgi apparatus consists of a set of vesicular compartments which are distinguished by their marker proteins. These compartments are physically separated in the Saccharomyces cerevisiae cell. To characterize them extensively, we immunoisolated vesicles carrying either of the SNAREs Sed5 or Tlg2, the markers of the early and late Golgi compartments, respectively, and analyzed the membrane proteins. The composition of proteins was mostly consistent with the position of each compartment in the traffic. We found six uncharacterized but evolutionarily conserved proteins and named them Svp26 (Sed5 compartment vesicle protein of 26 kDa), Tvp38, Tvp23, Tvp18, Tvp15 (Tlg2 compartment vesicle proteins of 38, 23, 18, and 15 kDa), and Gvp36 (Golgi vesicle protein of 36 kDa). The localization of Svp26 in the early Golgi compartment was confirmed by microscopic and biochemical means. Immunoprecipitation indicated that Svp26 binds to itself and a Golgi mannosyltransferase, Ktr3. In the absence of Svp26, a considerable portion of Ktr3 was mislocalized in the endoplasmic reticulum. Our data suggest that Svp26 has a novel role in retention of a subset of membrane proteins in the early Golgi compartments.

scholarly journals UDP-Galactose:Ceramide Galactosyltransferase Is a Class I Integral Membrane Protein of the Endoplasmic Reticulum

1998 ◽  
Vol 273 (40) ◽  
pp. 25880-25888 ◽  
Author(s):  
Hein Sprong ◽  
Boudewijn Kruithof ◽  
Richtje Leijendekker ◽  
Jan Willem Slot ◽  
Gerrit van Meer ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Protein ◽  
Integral Membrane Protein ◽  
Class I
Sign in / Sign up

Export Citation Format

Share Document