Faculty Opinions recommendation of Peroxisomes, lipid droplets, and endoplasmic reticulum "hitchhike" on motile early endosomes.

In canonical microtubule-based transport, adaptor proteins link cargos to dynein and kinesin motors. Recently, an alternative mode of transport known as ‘hitchhiking’ was discovered, where cargos achieve motility by hitching a ride on already-motile cargos, rather than attaching to a motor protein. Hitchhiking has been best-studied in two filamentous fungi, Aspergillus nidulans and Ustilago maydis. In U. maydis, ribonucleoprotein complexes, peroxisomes, lipid droplets, and endoplasmic reticulum hitchhike on early endosomes. In A. nidulans, peroxisomes hitchhike using a putative molecular linker, PxdA, which associates with early endosomes. However, whether other organelles use PxdA to hitchhike on early endosomes is unclear, as are the molecular mechanisms that regulate hitchhiking. Here we find that the proper distribution of lipid droplets, mitochondria and pre-autophagosomes do not require PxdA, suggesting that PxdA is a peroxisome-specific molecular linker. We identify two new pxdA alleles, including a point mutation (R2044P) that disrupts PxdA's ability to associate with early endosomes and reduces peroxisome movement. We also identify a novel regulator of peroxisome hitchhiking, the phosphatase DipA. DipA co-localizes with early endosomes and its early endosome-association relies on PxdA. Together, our data suggest that PxdA and the DipA phosphatase are specific regulators of peroxisome hitchhiking on early endosomes. [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text]

Download Full-text

Peroxisomes, lipid droplets, and endoplasmic reticulum “hitchhike” on motile early endosomes

The Journal of Cell Biology ◽

10.1083/jcb.201505086 ◽

2015 ◽

Vol 211 (5) ◽

pp. 945-954 ◽

Cited By ~ 72

Author(s):

Sofia C. Guimaraes ◽

Martin Schuster ◽

Ewa Bielska ◽

Gulay Dagdas ◽

Sreedhar Kilaru ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Molecular Motors ◽

Lipid Droplets ◽

Intracellular Transport ◽

Model System ◽

Directed Transport ◽

Intracellular Movement ◽

Early Endosomes ◽

Dependent Transport ◽

First Time

Intracellular transport is mediated by molecular motors that bind cargo to be transported along the cytoskeleton. Here, we report, for the first time, that peroxisomes (POs), lipid droplets (LDs), and the endoplasmic reticulum (ER) rely on early endosomes (EEs) for intracellular movement in a fungal model system. We show that POs undergo kinesin-3– and dynein-dependent transport along microtubules. Surprisingly, kinesin-3 does not colocalize with POs. Instead, the motor moves EEs that drag the POs through the cell. PO motility is abolished when EE motility is blocked in various mutants. Most LD and ER motility also depends on EE motility, whereas mitochondria move independently of EEs. Covisualization studies show that EE-mediated ER motility is not required for PO or LD movement, suggesting that the organelles interact with EEs independently. In the absence of EE motility, POs and LDs cluster at the growing tip, whereas ER is partially retracted to subapical regions. Collectively, our results show that moving EEs interact transiently with other organelles, thereby mediating their directed transport and distribution in the cell.

Download Full-text

Faculty Opinions recommendation of Peroxisomes, lipid droplets, and endoplasmic reticulum "hitchhike" on motile early endosomes.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.725975729.793512328 ◽

2015 ◽

Author(s):

Michael Roth

Keyword(s):

Endoplasmic Reticulum ◽

Lipid Droplets ◽

Early Endosomes

Download Full-text

STUDIES ON MICROPEROXISOMES II. A CYTOCHEMICAL METHOD FOR LIGHT AND ELECTRON MICROSCOPY

Journal of Histochemistry & Cytochemistry ◽

10.1177/20.12.1006 ◽

1972 ◽

Vol 20 (12) ◽

pp. 1006-1023 ◽

Cited By ~ 144

Author(s):

ALEX B. NOVIKOFF ◽

PHYLLIS M. NOVIKOFF ◽

CLEVELAND DAVIS ◽

NELSON QUINTANA

Keyword(s):

Endoplasmic Reticulum ◽

Guinea Pig ◽

Lipid Droplets ◽

Smooth Endoplasmic Reticulum ◽

Light And Electron Microscopy ◽

Distal Tubule ◽

Striking Difference ◽

High Concentration ◽

Electron Microscopic ◽

Pig Kidney

A modification of the Novikoff-Goldfischer alkaline 3,3'-diaminobenzidine medium for visualizing peroxisomes is described. It makes possible light microscopic as well as electron microscopic studies of a recently described class of peroxisomes, the microperoxisomes. Potassium cyanide (5 x 10–3 M) is included in the medium to inhibit mitochondrial staining, the pH is 9.7 and there is a high concentration of H2O2 (0.05%). Two cell types have been chosen to illustrate the advantages of the new procedure for demonstrating the microperoxisomes: the absorptive cells in the human jejunum and the distal tubule cells in the guinea pig kidney. Suggestive relations of microperoxisomes and lipid are described in the human jejunum. The microperoxisomes are strategically located between smooth endoplasmic reticulum that radiates toward the organelles and contains lipid droplets and "central domains" of highly specialized endoplasmic reticulum which do not show the lipid droplets. The microperoxisomes are also present at the periphery of large lipid-like drops. In the guinea pig kidney tubule there is a striking difference between the thick limb of Henle and distal tubule. The distal tubule has a population of cells with large numbers of microperoxisomes readily visible by light microscopy; these cells are not present in the thick limb of Henle. Other differences between the two are also described.

Download Full-text

The endosomal transcriptional regulator RNF11 integrates degradation and transport of EGFR

The Journal of Cell Biology ◽

10.1083/jcb.201601090 ◽

2016 ◽

Vol 215 (4) ◽

pp. 543-558 ◽

Cited By ~ 25

Author(s):

Sandra Scharaw ◽

Murat Iskar ◽

Alessandro Ori ◽

Gaelle Boncompain ◽

Vibor Laketa ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Plasma Membrane ◽

Egf Receptor ◽

Regulatory Mechanism ◽

Transcriptional Regulator ◽

Transport Efficiency ◽

Early Endosomes ◽

Epidermal Growth ◽

Partial Degradation ◽

Stimulation Of

Stimulation of cells with epidermal growth factor (EGF) induces internalization and partial degradation of the EGF receptor (EGFR) by the endo-lysosomal pathway. For continuous cell functioning, EGFR plasma membrane levels are maintained by transporting newly synthesized EGFRs to the cell surface. The regulation of this process is largely unknown. In this study, we find that EGF stimulation specifically increases the transport efficiency of newly synthesized EGFRs from the endoplasmic reticulum to the plasma membrane. This coincides with an up-regulation of the inner coat protein complex II (COPII) components SEC23B, SEC24B, and SEC24D, which we show to be specifically required for EGFR transport. Up-regulation of these COPII components requires the transcriptional regulator RNF11, which localizes to early endosomes and appears additionally in the cell nucleus upon continuous EGF stimulation. Collectively, our work identifies a new regulatory mechanism that integrates the degradation and transport of EGFR in order to maintain its physiological levels at the plasma membrane.

Download Full-text

Ultrastructural studies of the hemocytes of Panstrongylus megistus (Hemiptera: Reduvidae)

Memórias do Instituto Oswaldo Cruz ◽

10.1590/s0074-02761989000200005 ◽

1989 ◽

Vol 84 (2) ◽

pp. 171-188 ◽

Cited By ~ 1

Author(s):

Margherita A. Barracco ◽

Clarice T. Loch

Keyword(s):

Endoplasmic Reticulum ◽

Light Microscopy ◽

Rough Endoplasmic Reticulum ◽

Lipid Droplets ◽

Panstrongylus Megistus ◽

Ultrastructural Studies ◽

Hemocyte Count

Ultrastructural analyses revealed the presence of six hemocyte types in the hemolymph of Panstrogylus megistus, partially confirming our previous results obtained through light microscopy. Prohemocytes: small, round hemocytes with a thin cytoplasm layer, espcieally rich in free ribosomes and poor in membranous systems. Plasmatocytes: polymorphic cells, whose cytoplasm contains many lysosomes and a well developed rough endoplasmic reticulum (RER).They are extremely phagocytic. Sometimes, they show a large vacuolation. Granulocytes: granular hemocytes whose granules show different degrees of electrondensity. Most of them, have an internal structuration. Coagulocytes: oval or elongated hemocytes, which show pronounced perinuclear cisternae as normally observed in coagulocytes. The cytoplasm is usually electrondense, poor in membranous systems and contains many labile granules. Oenocytoids: large and very stable hemocytes, whose homogeneous cytoplasme is rich in loose ribosomes and poor in membranous systems. Adipohemocytes: large cells, containing several characteristic lipid droplets. The cytoplasm is also rich in glycogen, RER and large mitochondria. The total and differential hemocyte count (THC and DHC) were also calculated for this reduviid. THC increases from 2,900 hemocytes/cubic millimeter of hemolymph in the 4th intar to 4,350 in the 5th and then, decreases to 1,950 in the adults. Plasmatocytes and coagulocytes are the predominant hemocyte types.

Download Full-text

The Torsin/ NEP1R1-CTDNEP1/ Lipin axis regulates nuclear envelope lipid metabolism for nuclear pore complex insertion

10.1101/2020.07.05.188599 ◽

2020 ◽

Author(s):

Julie Jacquemyn ◽

Joyce Foroozandeh ◽

Katlijn Vints ◽

Jef Swerts ◽

Patrik Verstreken ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Nuclear Envelope ◽

Nuclear Pore Complex ◽

Lipid Droplets ◽

Nuclear Pore ◽

List Type ◽

Unknown Mechanism ◽

Structure Lipid ◽

Cellular Events ◽

Upstream Regulator

AbstractTorsin ATPases of the endoplasmic reticulum (ER) and nuclear envelope (NE) lumen inhibit Lipin-mediated phosphatidate (PA) to diacylglycerol (DAG) conversion by an unknown mechanism. This excess PA metabolism is implicated in TOR1A/TorsinA diseases, but it is unclear whether it explains why Torsin concomitantly affects nuclear structure, lipid droplets (LD), organelle and cell growth. Here a fly miniscreen identified that Torsins affect these events via the NEP1R1-CTDNEP1 phosphatase complex. Further, Torsin homo-oligomerization rather than ATPase activity was key to function. NEP1R1-CTDNEP1 activates Lipin by dephosphorylation. We show that Torsin prevents CTDNEP1 from accumulating in the NE and excludes Lipin from the nucleus. Moreover, this repression of nuclear PA metabolism is required for interphase nuclear pore biogenesis. We conclude that Torsin is an upstream regulator of the NEP1R1-CTDNEP1/ Lipin pathway. This connects the ER/NE lumen with PA metabolism, and affects numerous cellular events including it has a previously unrecognized role in nuclear pore biogenesis.HighlightsNuclear envelope PA-DAG-TAG synthesis is independently regulated by Torsin and Torip/LAP1Torsin removes CTDNEP1 from the nuclear envelope and excludes Lipin from the nucleusExcess nuclear envelope NEP1R1-CTDNEP1/ Lipin activity impairs multiple aspects of NPC biogenesisNEP1R1-CTDNEP1/ Lipin inhibition prevents cellular defects associated with TOR1A and TOR1AIP1 / LAP1 disease

Download Full-text

Life and Death of Fungal Transporters Under the Challenge of Polarity

10.20944/preprints202007.0601.v1 ◽

2020 ◽

Author(s):

Sofia Dimou ◽

George Diallinas

Keyword(s):

Endoplasmic Reticulum ◽

Plasma Membrane ◽

Membrane Proteins ◽

Cell Polarity ◽

Secretory Pathway ◽

Fungal Growth ◽

Present Evidence ◽

Life And Death ◽

Early Endosomes ◽

Stress Signals

Eukaryotic plasma membrane (PM) transporters face critical challenges that are not widely present in prokaryotes. The two most important issues are proper subcellular traffic and targeting to the PM, and regulated endocytosis in response to physiological, developmental or stress signals. Sorting of transporters from their site of synthesis, the Endoplasmic Reticulum (ER), to the PM has been long thought, but not formally shown, to occur via the conventional Golgi-dependent vesicular secretory pathway. Endocytosis of specific eukaryotic transporters has been studied more systematically and shown to involve ubiquitination, internalization, and sorting to early endosomes, followed by turnover in the MVB/lysosomes/vacuole system. In specific cases internalized transporters have been shown to recycle back to the PM. However, the mechanisms of transporter forward trafficking and turnover have been overturned recently through systematic work in the model fungus Aspergillus nidulans. In this review we present evidence that shows that transporter traffic to the PM takes place through Golgi-bypass and transporter endocytosis operates via a mechanism that is distinct from that of recycling membrane cargoes essential for fungal growth. We discuss these findings in relation to adaptation to challenges imposed by cell polarity in fungi as well as in other eukaryotes and provide a rationale why transporters and possibly other housekeeping membrane proteins ‘avoid’ routes of polar trafficking.

Download Full-text

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

Journal of Virology ◽

10.1128/jvi.01904-16 ◽

2017 ◽

Vol 91 (6) ◽

Cited By ~ 13

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.

Download Full-text