scholarly journals The Sac1 Phosphoinositide Phosphatase Regulates Golgi Membrane Morphology and Mitotic Spindle Organization in Mammals

2008 ◽  
Vol 19 (7) ◽  
pp. 3080-3096 ◽  
Author(s):  
Yang Liu ◽  
Malika Boukhelifa ◽  
Emily Tribble ◽  
Elizabeth Morin-Kensicki ◽  
Andrea Uetrecht ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Mitotic Spindle ◽  
Mitotic Spindles ◽  
Lipid Phosphatases ◽  
Membrane Morphology ◽  
Golgi Membranes ◽  
Major Class ◽  
Phosphoinositide Phosphatase

Phosphoinositides (PIPs) are ubiquitous regulators of signal transduction events in eukaryotic cells. PIPs are degraded by various enzymes, including PIP phosphatases. The integral membrane Sac1 phosphatases represent a major class of such enzymes. The central role of lipid phosphatases in regulating PIP homeostasis notwithstanding, the biological functions of Sac1-phosphatases remain poorly characterized. Herein, we demonstrate that functional ablation of the single murine Sac1 results in preimplantation lethality in the mouse and that Sac1 insufficiencies result in disorganization of mammalian Golgi membranes and mitotic defects characterized by multiple mechanically active spindles. Complementation experiments demonstrate mutant mammalian Sac1 proteins individually defective in either phosphoinositide phosphatase activity, or in recycling of the enzyme from the Golgi system back to the endoplasmic reticulum, are nonfunctional proteins in vivo. The data indicate Sac1 executes an essential household function in mammals that involves organization of both Golgi membranes and mitotic spindles and that both enzymatic activity and endoplasmic reticulum localization are important Sac1 functional properties.

Katanin, the microtubule-severing ATPase, is concentrated at centrosomes

1996 ◽  
Vol 109 (3) ◽  
pp. 561-567 ◽  
Author(s):  
F.J. McNally ◽  
K. Okawa ◽  
A. Iwamatsu ◽  
R.D. Vale
Keyword(s):  
Mitotic Spindle ◽  
Dynamic Properties ◽  
Mitotic Spindles ◽  
Microtubule Severing ◽  
Spindle Microtubules ◽  
Gamma Tubulin ◽  
And Function ◽  
Poleward Flux

The assembly and function of the mitotic spindle involve specific changes in the dynamic properties of microtubules. One such change results in the poleward flux of tubulin in which spindle microtubules polymerize at their kinetochore-attached plus ends while they shorten at their centrosome-attached minus ends. Since free microtubule minus ends do not depolymerize in vivo, the poleward flux of tubulin suggests that spindle microtubules are actively disassembled at or near their centrosomal attachment points. The microtubule-severing ATPase, katanin, has the ability actively to sever and disassemble microtubules and is thus a candidate for the role of a protein mediating the poleward flux of tubulin. Here we determine the subcellular localization of katanin by immunofluorescence as a preliminary step in determining whether katanin mediates the poleward flux of tubulin. We find that katanin is highly concentrated at centrosomes throughout the cell cycle. Katanin's localization is different from that of gamma-tubulin in that microtubules are required to maintain the centrosomal localization of katanin. Direct comparison of the localization of katanin and gamma-tubulin reveals that katanin is localized in a region surrounding the gamma-tubulin-containing pericentriolar region in detergent-extracted mitotic spindles. The centrosomal localization of katanin is consistent with the hypothesis that katanin mediates the disassembly of microtubule minus ends during poleward flux.

Anchoring of FLT3 in the endoplasmic reticulum alters signaling quality

Blood ◽  
2009 ◽  
Vol 113 (15) ◽  
pp. 3568-3576 ◽  
Author(s):  
Dirk Schmidt-Arras ◽  
Sylvia-Annette Böhmer ◽  
Sina Koch ◽  
Jörg P. Müller ◽  
Lutz Blei ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Transformation ◽  
Intracellular Location ◽  
Er Retention ◽  
Transforming Activity ◽  
Signaling Quality

Abstract The mechanism of cell transformation by Fms-like tyrosine kinase 3 (FLT3) in acute myeloid leukemia (AML) is incompletely understood. The most prevalent activated mutant FLT3 ITD exhibits an altered signaling quality, including strong activation of the STAT5 transcription factor. FLT3 ITD has also been found partially retained as a high-mannose precursor in an intracellular compartment. To analyze the role of intracellular retention of FLT3 for transformation, we have generated FLT3 versions that are anchored in the perinuclear endoplasmic reticulum (ER) by appending an ER retention sequence containing a RRR (R3) motif. ER retention of R3, but not of corresponding A3 FLT3 versions, is shown by biochemical, fluorescence-activated cell sorting, and immunocytochemical analyses. ER anchoring reduced global autophosphorylation and diminished constitutive activation of ERK1/2 and AKT of the constitutively active FLT3 versions. ER anchoring was, however, associated with elevated signaling to STAT3. Transforming activity of the FLT3 D835Y mutant was suppressed by ER anchoring. In contrast, ER-anchored FLT3 ITD retained STAT5-activating capacity and was transforming in vitro and in vivo. The findings highlight another aspect of the different signaling quality of FLT3 ITD: It can transform cells from an intracellular location.

Incorporation in vivo of [32P]orthophosphate and [Me-3H]choline into rough microsomal, Golgi, and plasma membranes of rat liver

1977 ◽  
Vol 55 (8) ◽  
pp. 876-885 ◽  
Author(s):  
Patricia L. Chang ◽  
John R. Riordan ◽  
Mario A. Moscarello ◽  
Jennifer M. Sturgess
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Rat Liver ◽  
Plasma Membranes ◽  
Specific Activity ◽  
Specific Radioactivity ◽  
Marker Enzyme ◽  
Golgi Membranes ◽  
Endomembrane Flow

To study membrane biogenesis and to test the validity of the endomembrane flow hypothesis, incorporation of 32P and [Me-3H]choline in vivo into membranes of the rat liver was followed. Rough microsomal, Golgi-rich, and plasma membrane fractions were monitored with marker enzyme assays and shown with morphometric analysis to contain 82% rough microsomes, at least 70% Golgi complexes, and 88% plasma membranes, respectively. Membrane subfractions from the rough microsomal and Golgi-rich fractions were prepared by sonic disruption.At 5 to 30 min after 32P injection, the specific radioactivity of phosphatidylcholine was higher in the rough microsomal membranes than in the Golgi membranes. From 1 to 3 h, the specific activity of phosphatidylcholine in Golgi membranes became higher and reached the maximum at about 3 h. Although the plasma membrane had the lowest specific radioactivity throughout 0.25–3 h, it increased rapidly thereafter to attain the highest specific activity at 5 h. Both rough microsomal and plasma membranes reached their maxima at 5 h.The specific radioactivity of [32P]phosphatidylethanolamine in the three membrane fractions was similar to that of [32P]phosphatidylcholine except from 5 to 30 min, when the specific radioactivity of phosphatidylethanolamine in the Golgi membranes was similar to the rough microsomal membranes.At 15 min to 5 h after [Me-3H]choline injection, more than 90% of the radioactivity in all the membranes was acid-precipitable. The specific radioactivities of the acid-precipitated membranes, expressed as dpm per milligram protein, reached the maximum at 3 h. After [Me-3H]choline injection, the specific radioactivity of phosphatidylcholine separated from the lipid extract of the acid-precipitated membranes (dpm per micromole phosphorus) did not differ significantly in the three membrane fractions. The results indicated rapid incorporation of choline into membrane phosphatidylcholine by the rough endoplasmic reticulum, Golgi, and plasma membranes simultaneously.The data with both 32P and [Me-3H]choline precursors did not support the endomembrane flow hypothesis. The Golgi complexes apparently synthesized phosphatidylethanolamine and incorporated choline into phosphatidylcholine as well as the endoplasmic reticulum. The results are discussed with relevance to current hypotheses on the biogenesis and transfer of membrane phospholipids.

Sterol trafficking between the endoplasmic reticulum and plasma membrane in yeast

2006 ◽  
Vol 34 (3) ◽  
pp. 356-358 ◽  
Author(s):  
D.P. Sullivan ◽  
H. Ohvo-Rekilä ◽  
N.A. Baumann ◽  
C.T. Beh ◽  
A.K. Menon
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Wild Type Strain ◽  
Binding Pocket ◽  
Oxysterol Binding Protein ◽  
Sterol Transport ◽  
Transport Cycle ◽  
Independent Mechanism

We recently showed that transport of ergosterol from the ER (endoplasmic reticulum) to the sterol-enriched PM (plasma membrane) in yeast occurs by a non-vesicular (Sec18p-independent) mechanism that results in the equilibration of sterol pools in the two organelles [Baumann, Sullivan, Ohvo-Rekilä, Simonot, Pottekat, Klaassen, Beh and Menon (2005) Biochemistry 44, 5816–5826]. To explore how this occurs, we tested the role of proteins that might act as sterol transporters. We chose to study oxysterol-binding protein homologues (Osh proteins), a family of seven proteins in yeast, all of which contain a putative sterol-binding pocket. Recent structural analyses of one of the Osh proteins [Im, Raychaudhuri, Prinz and Hurley (2005) Nature (London) 437, 154–158] suggested a possible transport cycle in which Osh proteins could act to equilibrate ER and PM pools of sterol. Our results indicate that the transport of newly synthesized ergosterol from the ER to the PM in an OSH deletion mutant lacking all seven Osh proteins is slowed only 5-fold relative to the isogenic wild-type strain. Our results suggest that the Osh proteins are not sterol transporters themselves, but affect sterol transport in vivo indirectly by affecting the ability of the PM to sequester sterols.

scholarly journals Modifications of Golgi Complex in Chondrocytes from Osteoarthrotic (OA) Rat Cartilage

2002 ◽  
Vol 50 (10) ◽  
pp. 1333-1339 ◽  
Author(s):  
Juan B. Kourí ◽  
Lourdes Rojas ◽  
Elizabeth Pérez ◽  
Karin A. Abbud-Lozoya
Keyword(s):  
Monoclonal Antibody ◽  
Endoplasmic Reticulum ◽  
Golgi Complex ◽  
Normal Cartilage ◽  
Golgi Membranes ◽  
Significant Difference ◽  
The Status ◽  
Nuclear Changes ◽  
Oa Chondrocytes

The status of the Golgi complex in normal vs osteoarthrotic (OA) cartilage has not yet been studied. A monoclonal antibody, MAb 58-K-9, allowed scoring of Golgi labeling intensity. In addition, ultrastructural assessment enabled us to focus on the distribution and relation between the endoplasmic reticulum (ER) and Golgi membranes. The study was performed in both normal and partially menisectomized OA-induced rat cartilage 20 and 45 days after surgery. Comparing Golgi immunolabeling intensities (mean ± SEM) revealed a highly significant difference between normal (9.98 ± 1.25), 20-day (2.49 ± 0.34), and 45-day (0.82 ± 0.22) cartilage. Moreover, chondrocytes from normal cartilage displayed 71.18% of labeling intensity in contrast to OA cartilage, in which chondrocyte labeling intensities were 24.95% (20 days) and 8.11% (45 days). OA chondrocytes appeared to display an overall reduction in Golgi labeling intensity, suggesting disruption of this organelle as the OA damage progressed. Interestingly, many 20-day OA-induced chondrocytes exhibited bubble-like Golgi immunolabeling compartmentalizing the cytoplasm, concomitant with putative apoptotic nuclear changes. At the same time, OA chondrocytes with a typical ultrastructural apoptotic pattern revealed a prominent ER gathered together with Golgi vesicles and saccules, also appearing to compartmentalize chondrocyte cytoplasm. We speculate about the role of Golgi modifications and apoptosis in OA pathogenesis.

Role of myristoylation in membrane attachment and function of G alpha i-3 on Golgi membranes

1996 ◽  
Vol 270 (5) ◽  
pp. C1362-C1369 ◽  
Author(s):  
S. H. Brand ◽  
E. J. Holtzman ◽  
D. A. Scher ◽  
D. A. Ausiello ◽  
J. L. Stow
Keyword(s):  
Secretory Pathway ◽  
Vesicle Trafficking ◽  
Regulatory Element ◽  
Metabolic Labeling ◽  
Cytosol Fraction ◽  
Golgi Membranes ◽  
Gamma Subunits

Heterotrimeric G protein alpha-subunits localized on the cytoplasmic face of Golgi membranes are involved in regulating vesicle trafficking and protein secretion. We investigated the role of myristoylation in attachment of the G alpha i-3 subunit to Golgi membranes. G alpha i-3 was epitope-tagged by insertion of a FLAG sequence at an NH2-terminal site predicted to interfere with myristoylation, and the resulting NT-alpha i-3 construct was stably transfected and expressed in polarized epithelial LLC-PK1 cells. Metabolic labeling confirmed that the translation product of NT-alpha i-3 was not myristoylated. In contrast to endogenous G alpha 1-3, which is tightly bound to Golgi membranes, the unmyristoylated FLAG-tagged NT-alpha i-3 did not attach to membranes; it was localized by immunofluorescence in the cytoplasm of LLC-PK1 cells and was detected only in the cytosol fraction of cell homogenates. Pertussis toxin-dependent ADP-ribosylation was used to test the ability of NT-alpha i-3 to interact with membrane-bound beta gamma-subunits. In both in vitro and in vivo assays, cytosolic NT-alpha i-3 alone was not ADP-ribosylated, although in the presence of membranes it could interact with G beta gamma-subunits to form heterotrimers. The expression of NT-alpha i-3 in LLC-PK1 cells altered the rate of basolateral secretion of sulfated proteoglycans, consistent with the demonstrated function of endogenous G alpha i-3. These data are consistent with a model in which G alpha i-3 utilizes NH2-terminal myristoylation to bind to Golgi membranes and to maximize its interaction with G beta gamma-subunits. Furthermore, our results show that stable attachment of G alpha i-3 to Golgi membranes is not required for it to participate as a regulatory element in vesicle trafficking in the secretory pathway.

scholarly journals Bring it back, bring it back, don't take it away from me – the sorting receptor RER1

2020 ◽  
Vol 133 (17) ◽  
pp. jcs231423
Author(s):  
Wim Annaert ◽  
Christoph Kaether
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Biology ◽  
Mammalian Cells ◽  
Future Directions ◽  
Binding Motifs ◽  
Sorting Receptor ◽  
Intermediate Compartment ◽  
The Brain

ABSTRACTThe quote “bring it back, bring it back, don't take it away from me” from Queen's Love of my life describes the function of the sorting receptor RER1, a 23 kDa protein with four transmembrane domains (TMDs) that localizes to the intermediate compartment and the cis-Golgi. From there it returns escaped proteins that are not supposed to leave the endoplasmic reticulum (ER) back to it. Unique about RER1 is its ability to recognize its ligands through binding motifs in TMDs. Among its substrates are ER-resident proteins, as well as unassembled subunits of multimeric complexes that are retrieved back into the ER, this way guarding the full assembly of their respective complexes. The basic mechanisms for RER1-dependent retrieval have been already elucidated some years ago in yeast. More recently, several important cargoes of RER1 have been described in mammalian cells, and the in vivo role of RER1 is being unveiled by using mouse models. In this Review, we give an overview of the cell biology of RER1 in different models, discuss its controversial role in the brain and provide an outlook on future directions for RER1 research.

scholarly journals ATG9 regulates autophagosome progression from the endoplasmic reticulum in Arabidopsis

2017 ◽  
Vol 114 (3) ◽  
pp. E426-E435 ◽  
Author(s):  
Xiaohong Zhuang ◽  
Kin Pan Chung ◽  
Yong Cui ◽  
Weili Lin ◽  
Caiji Gao ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Functional Relationship ◽  
Electron Tomography ◽  
Dependent Manner ◽  
Tubular Structures ◽  
Autophagosome Formation ◽  
Cytoplasmic Material ◽  
Dynamic Analyses

Autophagy is a conserved pathway for bulk degradation of cytoplasmic material by a double-membrane structure named the autophagosome. The initiation of autophagosome formation requires the recruitment of autophagy-related protein 9 (ATG9) vesicles to the preautophagosomal structure. However, the functional relationship between ATG9 vesicles and the phagophore is controversial in different systems, and the molecular function of ATG9 remains unknown in plants. Here, we demonstrate that ATG9 is essential for endoplasmic reticulum (ER)-derived autophagosome formation in plants. Through a combination of genetic, in vivo imaging and electron tomography approaches, we show that Arabidopsis ATG9 deficiency leads to a drastic accumulation of autophagosome-related tubular structures in direct membrane continuity with the ER upon autophagic induction. Dynamic analyses demonstrate a transient membrane association between ATG9 vesicles and the autophagosomal membrane during autophagy. Furthermore, trafficking of ATG18a is compromised in atg9 mutants during autophagy by forming extended tubules in a phosphatidylinositol 3-phosphate–dependent manner. Taken together, this study provides evidence for a pivotal role of ATG9 in regulating autophagosome progression from the ER membrane in Arabidopsis.

scholarly journals p31 Deficiency Influences Endoplasmic Reticulum Tubular Morphology and Cell Survival

2009 ◽  
Vol 29 (7) ◽  
pp. 1869-1881 ◽  
Author(s):  
Takefumi Uemura ◽  
Takashi Sato ◽  
Takehiro Aoki ◽  
Akitsugu Yamamoto ◽  
Tetsuya Okada ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Er Stress ◽  
Nuclear Translocation ◽  
Marked Change ◽  
Conditional Knockout ◽  
Induced Apoptosis ◽  
Factor C ◽  
Er Membrane

ABSTRACT p31, the mammalian orthologue of yeast Use1p, is an endoplasmic reticulum (ER)-localized soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP) receptor (SNARE) that forms a complex with other SNAREs, particularly syntaxin 18. However, the role of p31 in ER function remains unknown. To determine the role of p31 in vivo, we generated p31 conditional knockout mice. We found that homozygous deletion of the p31 gene led to early embryonic lethality before embryonic day 8.5. Conditional knockout of p31 in brains and mouse embryonic fibroblasts (MEFs) caused massive apoptosis accompanied by upregulation of ER stress-associated genes. Microscopic analysis showed vesiculation and subsequent enlargement of the ER membrane in p31-deficient cells. This type of drastic disorganization in the ER tubules has not been demonstrated to date. This marked change in ER structure preceded nuclear translocation of the ER stress-related transcription factor C/EBP homologous protein (CHOP), suggesting that ER stress-induced apoptosis resulted from disruption of the ER membrane structure. Taken together, these results suggest that p31 is an essential molecule involved in the maintenance of ER morphology and that its deficiency leads to ER stress-induced apoptosis.

The role of expansion segment of human ribosomal protein L35 in nuclear entry, translation activity, and endoplasmic reticulum docking

2008 ◽  
Vol 86 (3) ◽  
pp. 271-277 ◽  
Author(s):  
In-Jay Chen ◽  
I-Ann Wang ◽  
Lin-Ru Tai ◽  
Alan Lin
Keyword(s):  
Endoplasmic Reticulum ◽  
Ribosomal Protein ◽  
Nuclear Import ◽  
Large Subunit ◽  
Amino Acid Residues ◽  
Nuclear Entry ◽  
Contact Sites ◽  
Expansion Segment

The phylogenic alignment of homologous L35 protein suggests that human large subunit ribosomal protein L35 carries a 54 aa eukaryotic expansion segment (ES) at the C-terminal end. Within this ES, the first 25 amino acid residues were found to be essential for the nuclear import of the protein. The last 29 residues of the ES were shown to be uninvolved in the ribosome’s structural and translational functions, although this region proved to be one of the contact sites for ribosomal docking to endoplasmic reticulum, as evident from the results of an in vivo recombinant ribosome analysis.

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