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Cover image for Vol. 15 Issue 10

Edited By: Michael S. Marks, Mark C. P. Marsh, Trina A. Schroer, Tom H. Stevens

Online ISSN: 1600-0854

Highlights

  • ORIGINAL ARTICLE: The Large GTPase Mx1 Is Involved in Apical Transport in MDCK Cells

    ORIGINAL ARTICLE: The Large GTPase Mx1 Is Involved in Apical Transport in MDCK Cells

    Mx1 is localized on p75-GFP-positive vesicular structures in MDCK cells.MDCKp75-GFP (A) and MDCKSI-YFP (B) were cultured for 5 days; newly synthesized proteins were accumulated in the TGN at 20°C and released for 10 min at 37°C. Cells were fixed and immunostained with mAb anti-Mx1/Alexa Fluor 647 and analyzed by confocal microscopy. Vesicular structures co-labeled with endogenous Mx1 and p75-GFP (A) or SI-YFP (B) are indicated by arrows. C) MDCK cells were transfected with Mx1-GFP and p75-DsRed, fixed in steady state after polarization and analyzed by microscopy. Vesicular structures co-stained by Mx1-GFP and p75-DsRed are indicated by arrows. Nucleus staining (Hoechst 33342) is indicated in blue, scale bars: 10 µm. D) Colocalized vesicles either positive for endogenous Mx1 and p75-GFP (n = 12), endogenous Mx1 and SI-YFP (n = 16) or Mx1-GFP and p75-DsRed (n = 9) as depicted in (A–C) were quantified and normalized to the sum of each population. Data are represented as means ± SD, p < 0.001.

  • ORIGINAL ARTICLE: Mpl Traffics to the Cell Surface Through Conventional and Unconventional Routes

    ORIGINAL ARTICLE: Mpl Traffics to the Cell Surface Through Conventional and Unconventional Routes

    The complex intracellular trafficking of Mpl. Mature Mpl reaches the surface through the conventional ER-Golgi pathway and bears fully processed N-linked carbohydrate. Immature Mpl appears to be routed through an autophagic pathway for unconventional secretion, providing an alternate pathway for membrane expression of core-glycosylated Mpl. Once delivered to the cell surface, both forms of Mpl can be recycled or stored in calcium-dependent and independent compartments capable of fusion with the plasma membrane. In some cells, such as K562 cells, Mpl is packaged into exosomes and secreted.

  • ORIGINAL ARTICLE: Cytokine-Induced Slowing of STAT3 Nuclear Import; Faster Basal Trafficking of the STAT3β Isoform

    ORIGINAL ARTICLE: Cytokine-Induced Slowing of STAT3 Nuclear Import; Faster Basal Trafficking of the STAT3β Isoform

    Differential intranuclear mobility of STAT3α and β in the absence and presence of cytokine. HeLa cells transfected to express GFP-STAT3α or -STAT3β were stimulated with OSM (10 ng/mL) for 0–60 min as indicated prior to FRAP analysis, where a small area of the nucleus (position indicated by the white dotted circles) was photobleached (2000 milliseconds, 100% laser power, at 0 seconds post-bleach) and fluorescence recovery monitored at 5-second intervals for 100 seconds. Ai–Ci) Images of representative FRAP experiments are shown. Aii–Cii) Plots of the percentage recovery of specific intranuclear fluorescence (Fin–b value at respective time intervals divided by the pre-bleach Fin–b value set as a 100%) from experiments such as those in (Ai–Ci). Insets represent percentage recovery for the first 10 seconds as indicated, with the line of best fit used for the calculation of initial import rate. D–F) Pooled results for experiments as per (A–C); results are for the mean ± SEM (n ≥ 25) for the initial rate of recovery of Fin, derived as per the legend to Figure , t1/2, and for the maximal percentage recovery of Fin derived from curve fitting. Asterisks denote values that are statistically significant compared with untreated cells (*p ≤ 0.05;**p ≤ 0.01; ***p ≤ 0.001).

  • ORIGINAL ARTICLE: Phospholipid Transport via Mitochondria

    ORIGINAL ARTICLE: Phospholipid Transport via Mitochondria

    The ERMES complex physically connects the ER to the OM. A) Schematic of the tethering between the ER and OM by the ERMES complex. Mmm1 is N-glycosylated. B) Mitochondria-targeted GFP is expressed in wild-type or mutant cells lacking ERMES components (mmm1Δ, mmm2Δ, mdm10Δ and mdm12Δ) and observed by fluorescence microscopy. C) Mitochondria in cells expressing C-terminally GFP-tagged Mmm1 are stained with Mitotracker and observed under a fluorescence microscope.

  • ORIGINAL ARTICLE: Lipid Trafficking in Plant Cells

    ORIGINAL ARTICLE: Lipid Trafficking in Plant Cells

    Subcellular locations of lipid synthesis and transport proteins for the major chloroplast lipids. The subcellular locations of the chloroplast envelope-associated enzymes for final assembly of the major chloroplast lipids are depicted along with known lipid transport proteins. Presumed movement of lipid precursors for the synthesis of major thylakoid lipids between and through the envelope membranes is indicated as necessitated by the location of the respective enzymes. All proteins represented have been studied in Arabidopsis except for PGD1, which was discovered in Chlamydomonas but has orthologs in Arabidopsis. ER, endoplasmic reticulum; oEM, outer envelope membrane; iEM, inner envelope membrane; G3P, glycerol 3-phosphate; ACP, acyl carrier protein; L-PtdOH, lysophosphatidic acid; PtdOH, phosphatidic acid; DAG, diacylglycerol; SQDG, sulfoquinovosyldiacylglycerol; L-MGDG, lysomonogalactosyldiacylglycerol; MGDG, monogalactosyldiacylglycerol; DGDG, digalactosyldiacylglycerol.

  • ORIGINAL ARTICLE:Binding Domain-Driven Intracellular Trafficking of Sterols for Synthesis of Steroid Hormones, Bile Acids and Oxysterols

    ORIGINAL ARTICLE:Binding Domain-Driven Intracellular Trafficking of Sterols for Synthesis of Steroid Hormones, Bile Acids and Oxysterols

    Schematics of cholesterol behavior within the membranes and their interactions with phospholipids and proteins. A) Schematic depiction of cholesterol lipid's lateral and transverse movement within a phospholipid membrane. Cholesterol has a high degree of mobility within the lipid environment of the membrane, with lateral diffusion times on the millisecond timescale observed in model and cellular membranes. Transverse movement within the membrane (flip-flop) is also rapid, with theoretical and experimental measurements on the millisecond to minute timescale. However, transverse movement out of the membrane (escape activity) is quite slow, as it takes place on the timescale of hours to days in the absence of proximal acceptors, whether they are proteins or other membranes. B) Stepwise schematic of LBP-mediated sterol transfer. Cholesterol in the membranes (yellow rectangles; red circle denotes 3′ OH group) is recognized (1) by a soluble LBP, which binds to the sterol and (2) extracts it from the donor membrane. The association of the LBP with an acceptor membrane (3) results in the release of the sterol, which begins the cycle anew (4). C) Simplified illustration of a condensed complex model of the cholesterol–phospholipid association and sterol escape activity. At low sterol-to-phospholipid ratios, cholesterol is able to associate stoichiometrically with the acyl chains of the surrounding phospholipids. When local cholesterol concentration exceeds the capacity of the membrane to form stoichiometric complexes, the excess cholesterol looks to move (either laterally or transversely), increasing its activity and possible association with molecules outside of its membrane. D) Simplified illustration of the umbrella model of the cholesterol–phospholipid association in sterol escape activity. Phospholipids with a high degree of acyl chain unsaturation (left, unsaturated acyl chains in orange) will sterically clash with cholesterol in the membranes, which is in contrast to phospholipids with a high degree of acyl chain saturation (right, saturated acyl chains in purple). Moreover, phospholipids with small headgroups (left) will insufficiently shield the hydrophobic cholesterol molecule from the aqueous media, making the escape of the cholesterol molecule to a more hydrophobic environment energetically favorable. In contrast, phospholipids with large headgroups (right) shield the smaller cholesterol molecule from the aqueous surroundings, reducing the degree of accessibility and activity of the cholesterol.

  • ORIGINAL ARTICLE: The Large GTPase Mx1 Is Involved in Apical Transport in MDCK Cells
  • ORIGINAL ARTICLE: Mpl Traffics to the Cell Surface Through Conventional and Unconventional Routes
  • ORIGINAL ARTICLE: Cytokine-Induced Slowing of STAT3 Nuclear Import; Faster Basal Trafficking of the STAT3β Isoform
  • ORIGINAL ARTICLE: Phospholipid Transport via Mitochondria
  • ORIGINAL ARTICLE: Lipid Trafficking in Plant Cells
  • ORIGINAL ARTICLE:Binding Domain-Driven Intracellular Trafficking of Sterols for Synthesis of Steroid Hormones, Bile Acids and Oxysterols

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Depending on its localization, Pten (the central antagonist of PI3K signaling in the cytoplasm) is involved in many diverse cellular functions including controlling mitosis and DNA repair, cellular homeostasis, cell migration and/or cell proliferation. Balancing the cellular distribution of Pten is crucial to the function of the cell. Li and colleagues provide evidence that sorting of Pten to various organelles occurs in endosomes. Using bimolecular fluorescence complementation and dominant negative Rab5, they demonstrate that Rab5 and the E3 ligase adaptor protein Ndfip1 work together in to ubiquitinate Pten, which is required for its trafficking to the nucleus.


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