Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “APPARATUS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 631 records · Page 35Linked to original sources
PubMed1998

Leptin receptor immunoreactivity is associated with the Golgi apparatus of hypothalamic neurons and glial cells.

Leptin has emerged as a major peripheral hormone, controlling central mechanisms of metabolism and related autonomic and endocrine functions. In the regulation of hypothalamic neurones, leptin is suggested to affect different second messenger systems and transcription regulating factors. The present study reports the predominant localization of leptin receptor immunoreactivity in the cis and trans cisternae of the Golgi apparatus in hypothalamic neuronal and glial cells. In these hypothalamic cells, translocation of leptin receptor immunoreactivity from the Golgi apparatus to the perikaryal membrane, nucleus or to the cytoplasm was not apparent after manipulation of the metabolic state either by fasting or suppression of the thyroid axis. On the other hand, leptin receptor immunoreactivity was associated with the perikaryal membrane of neurones in other parts of the central nervous system, including the dentate gyrus and the cingulate cortex. These data indicate an extremely high turnover of leptin receptors in hypothalamic target sites, but also raise the possibility that leptin may interact with the Golgi apparatus-related mechanisms to alter intracellular mechanisms.

Animals↗
PubMed2001

Cholesterol depletion by methyl-beta-cyclodextrin blocks cholera toxin transport from endosomes to the Golgi apparatus in hippocampal neurons.

We recently demonstrated that although cholera toxin (CT) is found in detergent-insoluble domains/rafts at the cell surface of cultured hippocampal neurons, it is internalized via a raft-independent mechanism. Thus, cholesterol depletion by methyl-beta-cyclodextrin (MbetaCD) did not affect the rate of CT internalization from the plasma membrane, but did affect the rate of CT degradation, which occurs in lysosomes. In the current study, we analyze which step of CT intracellular transport is inhibited by MbetaCD. Whereas pre-incubation with MbetaCD completely blocked CT degradation, it had no effect on the degradation of wheat germ agglutinin (WGA) or bovine serum albumin (BSA), which are internalized by receptor-mediated and fluid phase endocytosis, respectively. Brefeldin A also completely blocked CT degradation but had no effect on WGA or BSA degradation. In contrast, MbetaCD did not affect CT degradation, or CT-mediated cAMP generation, when added to neurons after CT had been transported to the Golgi apparatus. We conclude that CT transport from endosomes to the Golgi apparatus is cholesterol-dependent, whereas CT transport from the Golgi apparatus to lysosomes is cholesterol-independent.

Anti-Bacterial Agents↗
PubMed1981

Heterogeneous distribution of filipin--cholesterol complexes across the cisternae of the Golgi apparatus.

The Golgi apparatus is a key element in the ordered movement of secretory polypeptides from the rough endoplasmic reticulum to the plasma membrane during secretion. It has been shown that cisternae that receive membranes from the reticulum are morphologically similar to the latter and that cisternae liberating secretory granules resemble that plasma membrane. By using an ultrastructural probe for membrane cholesterol, filipin, on freeze-fractured and thin-sectioned exocrine and endocrine pancreatic cells, we have shown that an enrichment in filipin-cholesterol complexes takes places across the stacked cisternae of the Golgi apparatus; the reticulum-related (forming) cisternae are poor in such complexes, but the secretory granule-related (maturing) cisternae contain numerous complexes. Secretory granule membrane is also richly labeled with filipin-cholesterol complexes. The heterogeneous cholesterol distribution in the membranes of the Golgi apparatus, as shown by filipin, emphasizes the polarity of this organelle, in agreement with its role in organizing the traffic of the secretory polypeptides from the rough endoplasmic reticulum to the plasma membrane.

Animals↗
PubMed1983

Subfractionation of rat liver Golgi apparatus: separation of enzyme activities involved in the biosynthesis of the phosphomannosyl recognition marker in lysosomal enzymes.

A highly purified Golgi apparatus preparation from rat liver was subfractionated on a Percoll gradient into two major protein peaks of similar size that migrated at densities of 1.028 and 1.051 g/ml. The lighter protein peak contained 70--80% of the total activities of the oligosaccharide-processing enzymes alpha-1,2-mannosidase and mannosidase II and of UDP-N-acetylglucosamine:glycoprotein N-acetylglucosaminyl-1-phosphotransferase (alpha-N-acetylglucosaminylphosphotransferase), an enzyme involved in the biosynthesis of the mannose 6-phosphate recognition marker of lysosomal enzymes. These enzyme activities were enriched 2-fold in specific activity over that of the heavy protein peak. In contrast, 80% of the alpha-N-acetylglucosaminylphosphodiesterase, an enzyme that exposes 6-phosphomonoesters of mannose on the oligosaccharide chains of lysosomal enzymes, migrated in a region of slightly higher density than did the protein peak of density 1.051 g/ml. Sialyltransferase (SiaTase) and galactosyltransferase (Gal-Tase) activities distributed almost equally among the two protein peaks. Controls rule out that the two protein peaks were the result of aggregation/deaggregation and that enzyme activities were altered by Percoll per se. Lysosomal enzyme activities migrated in a region essentially devoid of Golgi apparatus-associated enzyme activities. These results suggest a physical separation within the Golgi apparatus of some of the enzymes involved in the biosynthesis and processing of the oligosaccharides on glycoproteins, including those responsible for the formation of the mannose 6-phosphate recognition marker on lysosomal enzymes.

Animals↗
PubMed1983

Role of microtubules in the distribution of the Golgi apparatus: effect of taxol and microinjected anti-alpha-tubulin antibodies.

Immunofluorescence microscopy reveals that both microtubule organizing center (MTOC) and Golgi apparatus are contained in the same perinuclear area of A549 cells in interphase. The cells display long microtubules stretching radially from the MTOC to the plasma membrane. Treatment of cells with taxol results in polymerization of microtubules without relation to the MTOC and formation of microtubule bundles predominantly localized in the cell periphery. After incubation with taxol, the Golgi apparatus is fragmented and is conspicuously present in areas of the cytoplasm enriched in microtubules. Incubation of cells with Colcemid results in complete depolymerization of microtubules and fragmentation of the Golgi into elements randomly distributed throughout the cytoplasm. Cells treated with taxol before being incubated with Colcemid contain large numbers of Golgi-derived elements in close association with Colcemid-resistant microtubules. Microtubule depolymerization by vinblastine also is followed by fragmentation of the Golgi apparatus. These Golgi-derived elements show no association with the atypical polymers of tubulin induced by vinblastine. The codistribution of Golgi-derived elements with taxol-induced microtubule bundles can be reversed by microinjection of a monoclonal (YL 1/2) antibody reacting specifically with the tyrosylated form of alpha-tubulin.

Alkaloids↗
PubMed1983

Polarization of the Golgi apparatus and the microtubule-organizing center within cloned natural killer cells bound to their targets.

In cell couples formed between a cloned murine natural killer (NK) cell and either of two target cells, we have obtained evidence by immunofluorescence observations for a rapid coordinate repositioning of two organelles, the microtubule organizing center and the perinuclear Golgi apparatus, inside the NK cell to face the region of contact with the target cell. With microtubule-disrupting drugs, which also cause a dispersion of the Golgi apparatus throughout the periphery of the NK cell, it was found that target cell lysis is reversibly inhibited. It is proposed that the coordinate repositioning of the two organelles serves the function of directing secretory vesicles derived from the Golgi apparatus to the bound target cells, the secretory vesicles containing components that induce target cell lysis.

Animals↗
PubMed1994

Disruption of the Golgi apparatus by brefeldin A blocks cell polarization and inhibits directed cell migration.

The role of the Golgi apparatus in the motile activity of fibroblasts was examined with brefeldin A (BFA), which disrupts the Golgi apparatus in a variety of cells. Upon incubation with BFA, Swiss mouse 3T3 fibroblasts lost their typical polarized morphology, in which the leading edge is characterized by intensive lamellipodia formation. BFA affected cell asymmetry as demonstrated by a decrease in the morphometric indices, dispersion, and elongation. After BFA treatment, cells showed little protrusional activity and did not form a dense actin network at the leading edge, and consequently the rate of cell migration into an experimental wound was significantly reduced. In addition, BFA prevented an increase in pseudopodial activity and prevented the formation of long processes induced by phorbol 12-myristate 13-acetate. The effects of BFA on cell shape and protrusional activity were quantitatively similar to those observed with the microtubule-disrupting agent nocodazole, although BFA had no effect on microtubule integrity. These results suggest that the integrity of both the Golgi apparatus and microtubules is necessary for the generation and maintenance of fibroblast asymmetry, which is a prerequisite for directed cell migration.

3T3 Cells↗
PubMed1997

Functional protein prenylation is required for the brefeldin A-dependent retrograde transport from the Golgi apparatus to the endoplasmic reticulum.

In cells exposed to brefeldin A (BFA), enzymes of the Golgi apparatus are redistributed to the endoplasmic reticulum (ER) by retrograde membrane flow, where they may cause modifications on resident ER proteins. We have used a truncated form of the rough ER-specific type I transmembrane glycoprotein ribophorin I as a probe to detect Golgi glycosyltransferases relocated to the ER in a BFA-dependent fashion. This polypeptide (RI332) comprises the 332 amino-terminal amino acids of ribophorin I and behaves like a luminal ER protein when expressed in HeLa cells. Upon treatment of the cells with BFA, RI332 becomes quantitatively O-glycosylated by Golgi glycosyltransferases that are transported back to the ER. Here we demonstrate that pretreatment of the cells with lovastatin, an inhibitor of HMG-CoA reductase, abrogates this modification and that mevalonate, the product formed in the step inhibited by the drug, is able to counteract the effect of lovastatin. We also show by immunofluorescence using mannosidase II as a Golgi marker that the BFA-induced retrograde transport of Golgi enzymes is blocked by lovastatin, although electron microscopy indicates that BFA causes disassembly of the Golgi apparatus into swollen vesicles and tubules. Our observations support the role of a prenylated protein, such as the geranylgeranylated small G protein Rab6, in the retrograde transport from the Golgi apparatus to the ER, since lovastatin acts by inhibiting its prenylation.

Animals↗
PubMed1997

Possible involvement of heterotrimeric G proteins in the organization of the Golgi apparatus.

Nordihydroguaiaretic acid (NDGA) caused disassembly of the Golgi apparatus of NRK cells in a dose-, time-, and energy-dependent manner but not in a microtubule-dependent manner. In contrast to brefeldin A, NDGA did not cause release of beta-COP, a component of Golgi-derived vesicles. However, NDGA-induced disassembly was blocked by AlF4-, an activator of the heterotrimeric but not the small GTP-binding proteins. In digitonin-permeabilized cells, guanosine 5'-3-O-(thio)triphosphate (GTPgammaS) as well as AlF4- blocked the NDGA-promoted disassembly of the Golgi apparatus, and Gbetagamma (betagamma subunits of heterotrimeric G proteins) reversed this effect. Our present results suggest the possible involvement of heterotrimeric G proteins in the organization of the Golgi apparatus.

Animals↗
PubMed2000

Inhibition of phosphatidic acid synthesis alters the structure of the Golgi apparatus and inhibits secretion in endocrine cells.

In mammalian cells, activation of a Golgi-associated phospholipase D by ADP-ribosylation factor results in the hydrolysis of phosphatidylcholine to form phosphatidic acid (PA). This reaction stimulates the release of nascent secretory vesicles from the trans-Golgi network of endocrine cells. To understand the role of PA in mediating secretion, we have exploited the transphosphatidylation activity of phospholipase D. Rat anterior pituitary GH3 cells, which secrete growth hormone and prolactin, were treated with 1-butanol resulting in the synthesis of phosphatidylbutanol rather than PA. Under these conditions transport from the ER through the Golgi apparatus and secretion of polypeptide hormones were inhibited quantitatively. Furthermore, the in vitro synthesis of phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P(2)) by Golgi membranes was inhibited quantitatively. Most significantly, in the presence of 1-butanol the architecture of the Golgi apparatus was disrupted, resulting in its disassembly and fragmentation. Removal of the alcohol resulted in the rapid restoration of Golgi structure and secretion of growth hormone and prolactin. Our results suggest that PA stimulation of PtdIns(4,5)P(2) synthesis is required for maintaining the structural integrity and function of the Golgi apparatus.

1-Butanol↗
PubMed2002

ZnT7, a novel mammalian zinc transporter, accumulates zinc in the Golgi apparatus.

ZnT7, a novel member of the zinc transporter (ZnT) family, was identified by searching the expressed sequence tag (EST) databases with the amino acid sequence of ZnT1. Like the other ZnT proteins, the protein (387 amino acids) predicted from this gene contains six transmembrane domains and a histidine-rich loop between transmembrane domains IV and V. We show that Znt7 is widely transcribed in mouse tissues with abundant expression in the liver and small intestine and moderate expression in the kidney, spleen, brain, and lung. An affinity-purified antibody raised against the amino acids 299-315 of mouse ZnT7 specifically reacted with the proteins with apparent molecular masses of 85, 43, and 65 kDa in small intestine and lung tissues by Western blot analysis. Immunofluorescence microscope analysis reveals that ZnT7 is localized in the Golgi apparatus and cytoplasmic vesicles. Exposure of the ZnT7-expressing Chinese hamster ovary (CHO) cells to zinc causes an accumulation of zinc in the Golgi apparatus, suggesting that ZnT7 facilitates zinc transport from the cytoplasm into the Golgi apparatus.

Amino Acid Sequence↗
PubMed2002

Fragmentation of the Golgi apparatus. A role for beta III spectrin and synthesis of phosphatidylinositol 4,5-bisphosphate.

Phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P(2)) synthesis has been implicated in maintaining the function of the Golgi apparatus. Here we demonstrate that the inhibition of PtdIns(4,5)P(2) synthesis in vitro in response to primary alcohol treatment and the kinetics of Golgi fragmentation in vivo were very rapid and tightly coupled. Preloading Golgi membranes with short chain phosphatidic acid abrogated the alcohol-mediated inhibition of PtdIns(4,5)P(2) synthesis in vitro. We also show that fragmentation of the Golgi apparatus in response to diminished PtdIns(4,5)P(2) synthesis correlated with both the phosphorylation of a Golgi form of beta III spectrin, a PtdIns(4,5)P(2)-interacting protein, and changes in its intracellular redistribution. The data are consistent with a model suggesting that the decreased PtdIns(4,5)P(2) synthesis and the phosphorylation state of beta III spectrin modulate the structural integrity of the Golgi apparatus.

Animals↗
PubMed2005

The ZIP7 gene (Slc39a7) encodes a zinc transporter involved in zinc homeostasis of the Golgi apparatus.

It has been suggested that ZIP7 (Ke4, Slc39a7) belongs to the ZIP family of zinc transporters. Transient expression of the V5-tagged human ZIP7 fusion protein in CHO cells led to elevation of the cytoplasmic zinc level. However, the precise function of ZIP7 in cellular zinc homeostasis is not clear. Here we report that the ZIP7 gene is ubiquitously expressed in human and mouse tissues. The endogenous ZIP7 was associated with the Golgi apparatus and was capable of transporting zinc from the Golgi apparatus into the cytoplasm of the cell. Moreover, by using the yeast mutant strain Deltazrt3 that was defective in release of stored zinc from vacuoles, we found that ZIP7 was able to decrease the level of accumulated zinc and in the meantime to increase the nuclear/cytoplasmic labile zinc level in the ZIP7-expressing zrt3 mutant. We showed that the protein expression of ZIP7 was repressed under zinc-rich condition, whereas there were no effects of zinc on ZIP7 gene expression and intracellular localization. Neither did zinc deficiency affect the intracellular distribution of ZIP7 in mammalian cells. Our study demonstrates that ZIP7 is a functional zinc transporter that acts by transporting zinc from the Golgi apparatus to the cytoplasm of the cell.

Animals↗
PubMed2006

Localization of the phosphoethanolamine methyltransferase of the human malaria parasite Plasmodium falciparum to the Golgi apparatus.

Phosphatidylcholine is the most abundant phospholipid in the membranes of Plasmodium falciparum, the agent of severe human malaria. The synthesis of this phospholipid occurs via two routes, the CDP-choline pathway, which uses host choline as a precursor, and the plant-like serine decarboxylase-phosphoethanolamine methyltransferase (SDPM) pathway, which uses host serine as a precursor. Although various components of these pathways have been identified, their cellular locations remain unknown. We have previously reported the identification and characterization of the phosphoethanolamine methyltransferase, Pfpmt, of P. falciparum and shown that it plays a critical role in the synthesis of phosphatidylcholine via the SDPM pathway. Here we provide the first evidence that the transmethylation step of the SDPM pathway occurs in the parasite Golgi apparatus. We show that the level of Pfpmt protein in the infected erythrocyte is regulated in a stage-specific fashion, with high levels detected during the trophozoite stage at the peak of parasite membrane biogenesis. Confocal microscopy revealed that Pfpmt is not cytoplasmic. Immunoelectron microscopy revealed that Pfpmt localizes to membrane structures that extend from the nuclear membrane but that it only partially co-localizes with the endoplasmic reticulum marker BiP. Using transgenic parasites expressing green fluorescent protein targeted to different cellular compartments, a complete co-localization was detected with Rab6, a marker of the Golgi apparatus. Together these studies provide the first evidence that the transmethylation step of the SDPM pathway of P. falciparum occurs in the Golgi apparatus and indicate an important role for this organelle in parasite membrane biogenesis.

Animals↗
PubMed1999

The discovery of the Golgi apparatus.

The existence of the cell organelle which is now known as Golgi apparatus or Golgi complex, or simply as 'the Golgi", was first reported by Camillo Golgi in 1898, when he described in nerve cells an 'internal reticular apparatus' impregnated by a variant of his chromoargentic staining. It soon became clear that the newly-identified cytoplasmic structure occurred in a variety of cell types. However, the reality of the organelle was questioned for decades, until it was finally ascertained with electron microscopy. The Golgi apparatus was destined to become a protagonist of the research in cytology and cell biology pursued in the second half of the twentieth century.

Cell Biology↗
PubMed1961

The direct isolation of the mitotic apparatus.

A method for isolating the mitotic apparatus from dividing sea urchin eggs without the use of ethyl alcohol or of detergents is described. In the present method, the eggs are dispersed directly in a medium containing 1 M (to 1.15 M) sucrose, 0.15 M dithiodiglycol, and 0.001 M Versene at pH 6, releasing the visibly intact mitotic apparatus. The method is designed for studies of enzyme activities, lipid components, and the variables affecting the stability of the apparatus.

Animals↗
PubMed1985

Intracellular translocation of fluorescent sphingolipids in cultured fibroblasts: endogenously synthesized sphingomyelin and glucocerebroside analogues pass through the Golgi apparatus en route to the plasma membrane.

When monolayer cultures of Chinese hamster lung fibroblasts are briefly incubated at 2 degrees C with the fluorescent sphingolipid analogue, C6-NBD-ceramide (N- [7-(4-nitrobenzo-2-oxa-1,3-diazole)] aminocaproyl sphingosine), fluorescent labeling of the mitochondria, endoplasmic reticulum, and nuclear envelope occur. During further incubation at 37 degrees C, the Golgi apparatus, and later the plasma membrane, become intensely fluorescent. Within this period, the C6-NBD-ceramide is converted to equal amounts of fluorescent sphingomyelin and glucocerebroside (Lipsky, N. G., and R. E. Pagano, 1983, Proc. Natl. Acad. Sci. USA., 80:2608-2612). In the present study, the intracellular translocation of these metabolites and their subsequent appearance at the plasma membrane were investigated by fluorescence microscopy, the addition of the ionophore monensin, and the technique of "back exchange," in which the amounts and types of fluorescent lipids present at the cell surface are identified after their transfer from the cell surface into recipient vesicles. In control cells, the amount of fluorescent glucocerebroside and sphingomyelin that could be removed from the cell surface by back exchange increased during incubation at 37 degrees C, correlating with the increased fluorescence of the plasma membrane observed by microscopy. In the presence of 10 microM monensin, visible labeling of the plasma membrane was greatly diminished, whereas the Golgi apparatus became highly fluorescent and distended. The ability to remove fluorescent metabolites from the cell surface by back exchange was significantly but reversibly inhibited by monensin. Monensin also increased the total amount of fluorescent sphingomyelin, but not the glucocerebroside found in cells. Subcellular fractions were assayed for their ability to convert radiolabeled and fluorescent ceramides to the corresponding sphingomyelins and glucocerebrosides. The activities of parallel fractions coincided, suggesting that the presence of the NBD moiety did not affect the cellular metabolism of ceramide. Furthermore, the major peak of sphingomyelin- and glucocerebroside-synthesizing activity appeared to coincide with an enriched Golgi fraction. These results strongly suggest that fluorescent sphingomyelin was not synthesized at the plasma membrane as has recently been suggested for endogenous sphingomyelin. Rather, both the sphingomyelin and glucocerebroside analogues were synthesized intracellularly from C6-NBD-ceramide and translocated through the Golgi apparatus to the cell surface.

Animals↗
PubMed1988

A membrane glycoprotein, Sec12p, required for protein transport from the endoplasmic reticulum to the Golgi apparatus in yeast.

SEC12, a gene that is required for secretory, membrane, and vacuolar proteins to be transported from the endoplasmic reticulum to the Golgi apparatus, has been cloned from a genomic library by complementation of a sec12 ts mutation. Genetic analysis has shown that the cloned gene integrates at the SEC12 locus and that a null mutation at the locus is lethal. The DNA sequence predicts a protein of 471 amino acids containing a hydrophobic stretch of 19 amino acids near the COOH terminus. To characterize the gene product (Sec12p) in detail, a lacZ-SEC12 gene fusion has been constructed and a polyclonal antibody raised against the hybrid protein. The antibody recognizes Sec12p as a approximately 70-kD protein that sediments in a mixed membrane fraction that includes endoplasmic reticulum. Sec12p is not removed from the membrane fraction by treatment at high pH and high salt and is not degraded by exogenous protease unless detergent is present. Glycosylation of Sec12p during biogenesis is indicated by an electrophoretic mobility shift of the protein that is influenced by tunicamycin and by imposition of an independent secretory pathway block. We suggest that Sec12p is an integral membrane glycoprotein with a prominent domain that faces the cytoplasm where it functions to promote protein transport to the Golgi apparatus. In the process of transport, Sec12p itself may migrate to the Golgi apparatus and function in subsequent transport events.

Amino Acid Sequence↗