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PubMed1980

The origin of the dendritic reticulum cell. An experimental enzyme-histochemical and electron microscopic study on the rabbit spleen.

To obtain more information concerning the origin of dendritic reticulum cells, the development of germinal centers in the spleens of rabbits was investigated by conventional light microscopy, enzyme histochemistry, and electron microscopy. Washed sheep erythrocytes were used as antigen. Splenic tissue was examined on the 13th, 18th, 21st, 27th and 48th day after antigen administration. Electron microscopic investigations revealed transitional forms between typical fibroblastic reticulum cells, which formed the framework of the entire splenic white pulp, and typical dendritic reticulum cells. During this transformation, the enzyme histochemical pattern of alkaline phosphatase disappeared and a positive alpha-naphthylacetate esterase reaction appeared in the transformed cells. On the basis of these findings, it is highly likely that dendritic reticulum cells develop through transformation of fibroblastic reticulum cells during the development of germinal centers in rabbit spleens. The characteristic folding of the surface membrane of dendritic reticulum cells is probably caused by the conspicuous increase in size of the Golgi apparatus, the detachment of vesicles, and the uptake of such vesicles by the cell membrane observed electron microscopically during the cellular transformation. Receptors that are of significance in antigen trapping might reach the cell surface in this manner, i.e., with the Golgi vesicles.

Alkaline Phosphatase↗
PubMed1983

Heterogeneous distribution of glycosyltransferases in the endoplasmic reticulum of castor bean endosperm.

Endoplasmic reticulum membranes stripped of attached ribosomes were isolated from homogenates of germinating castor bean (Ricinus communis L.) endosperm by sucrose density gradient centrifugation. The isolated endoplasmic reticulum fraction was further separated into two major membrane subfractions by centrifugation on a flotation gradient. Both subfractions appeared to be derived from the endoplasmic reticulum inasmuch as they share several enzymic markers including cholinephosphotransferase, NADH-cytochrome c reductase, and glycoprotein fucosyl-transferase and phase separation of membrane polypeptides using Triton X-114 revealed a striking similarity in both their hydrophilic and hydrophobic protein components. The endoplasmic reticulum membrane subfractions contain glycoproteins which were readily labeled by incubating intact endosperm tissue with radioactive sugars prior to fractionation.Castor bean endosperm endoplasmic reticulum apparently exhibits a degree of enzymic heterogeneity, however, since the enzymes responsible for the synthesis of dolicholpyrophosphate N-acetylglucosamine and dolicholmonophosphate mannose together with their incorporation into the oligosaccharide-lipid precursor of protein N-glycosylation were largely recovered in a single endoplasmic reticulum subfraction.

Journal Article↗
PubMed1987

Calcium Transport in Sealed Vesicles from Red Beet (Beta vulgaris L.) Storage Tissue : I. Characterization of a Ca-Pumping ATPase Associated with the Endoplasmic Reticulum.

Calcium transport was examined in microsomal membrane vesicles from red beet (Beta vulgaris L.) storage tissue using chlorotetracycline as a fluorescent probe. This probe demonstrates an increase in fluorescence corresponding to calcium accumulation within the vesicles which can be collapsed by the addition of the calcium ionophore A23187. Calcium uptake in the microsomal vesicles was ATP dependent and completely inhibited by orthovanadate. Centrifugation of the microsomal membrane fraction on a linear 15 to 45% (w/w) sucrose density gradient revealed the presence of a single peak of calcium uptake which comigrated with the marker for endoplasmic reticulum. The calcium transport system associated with endoplasmic reticulum vesicles was then further characterized in fractions produced by centrifugation on discontinous sucrose density gradients. Calcium transport was insensitive to carbonylcyanide m-chlorophenylhydrazone indicating the presence of a primary transport system directly linked to ATP utilization. The endoplasmic reticulum vesicles contained an ATPase activity that was calcium dependent and further stimulated by A23187 (Ca(2+), A23187 stimulated-ATPase). Both calcium uptake and Ca(2+), A23187 stimulated ATPase demonstrated similar properties with respect to pH optimum, inhibitor sensitivity, substrate specificity, and substrate kinetics. Treatment of the red beet endoplasmic reticulum vesicles with [gamma-(32)P]-ATP over short time intervals revealed the presence of a rapidly turning over 96 kilodalton radioactive peptide possibly representing a phosphorylated intermediate of this endoplasmic reticulum associated ATPase. It is proposed that this ATPase activity may represent the enzymic machinery responsible for mediating primary calcium transport in the endoplasmic reticulum linked to ATP utilization.

Journal Article↗
PubMed1975

Ultrastructural study of erythrophagocytosis in the rat bone marrow. I. Red cell engulfment by reticulum cells.

Previous light microscopic studies have revealed the erythroclastic potential of the rat bone marrow reticulum cells, and call for ultrastructural study of the finer details of this process. Electron microscopy of rat bone marrow which had been stimulated to increase its erythrophagic activity, either by splenectomy or by transfusion of heat denatured erythrocytes, confirmed the central reticulum cell of erythroblastic islands as the main phagocytic cell in bone marrow erythroclasia. The early digestive vacuoles, which are formed by the fusion of erythrophagic vacuoles with lysosomes, correspond to the acidophilic, globular structures which characterize erythrophagocytosis as observed by light microscopy. By forming intrasinusoidal protrusions, the bone marrow reticulum cells engulf circulating effete red cells. The engulfed red cells are then transported intracellularly across the sinusoidal wall for final disintegration in the intraparenchymal part of the reticulum cell. This transmural mode of erythrophagocytosis by reticulum cells most probably demonstrates the fundamental phagocytic mechanism of the bone marrow part of the reticulo-endothelial system. Transmural transport of reticulocytes adherent to reticulum cells during the formation of protrusions illustrates a possible mechanism for liberation of red cells from the bone marrow.

Animals↗
PubMed1978

Ultrastructure of reticulum cells in the bone marrow.

In this study the attempt was made to classify the reticulum cells of the bone marrow on the basis of electron-microscopic findings. The basis of the differentiation was the ability of the cells to phagocytize substances or not. For two cell types the intracytoplasmic filaments were used as distinctive marks. The following classification resulted: (a) phagocytic reticulum cells, (b) undifferentiated reticulum cells, (c) fibrous reticulum cells of type I, which contain filaments of 4-8 nm diameter and are located near the blood sinus of the bone marrow, (d) fibrous reticulum cells of type II, which contain intracytoplasmic filaments of 10 nm diameter; since these cells contain neutral fat bodies, the possibility of a reversible conversion to fat cells has to be assumed and (e) fibroblasts, cells which synthesize the substance of the extracellular space. A connection of reticulum cells to haematopoietic functions or to stem cell functions could be found.

Animals↗
PubMed2002

Aggregation and retention of human urokinase type plasminogen activator in the yeast endoplasmic reticulum.

BACKGROUND: Secretion of recombinant proteins in yeast can be affected by their improper folding in the endoplasmic reticulum and subsequent elimination of the misfolded molecules via the endoplasmic reticulum associated protein degradation pathway. Recombinant proteins can also be degraded by the vacuolar protease complex. Human urokinase type plasminogen activator (uPA) is poorly secreted by yeast but the mechanisms interfering with its secretion are largely unknown. RESULTS: We show that in Hansenula polymorpha overexpression worsens uPA secretion and stimulates its intracellular aggregation. The absence of the Golgi modifications in accumulated uPA suggests that aggregation occurs within the endoplasmic reticulum. Deletion analysis has shown that the N-terminal domains were responsible for poor uPA secretion and propensity to aggregate. Mutation abolishing N-glycosylation decreased the efficiency of uPA secretion and increased its aggregation degree. Retention of uPA in the endoplasmic reticulum stimulates its aggregation. CONCLUSIONS: The data obtained demonstrate that defect of uPA secretion in yeast is related to its retention in the endoplasmic reticulum. Accumulation of uPA within the endoplasmic reticulum disturbs its proper folding and leads to formation of high molecular weight aggregates.

Journal Article↗
PubMed2004

Inositol trisphosphate producing agonists do not mobilize the thapsigargin-insensitive part of the endoplasmic-reticulum and Golgi Ca2+ store.

Non-mitochondrial intracellular Ca2+ stores contain both thapsigargin-sensitive sarco(endo)plasmic-reticulum Ca2+-ATPases (SERCA) and thapsigargin-insensitive secretory-pathway Ca2+-ATPases (SPCA1). We now have studied the Ca2+-release properties of the compartments associated with these pumps in intact, i.e. non-permeabilized, cells of different origin (HeLa, keratinocytes, 16HBE14o-, COS-1, A7r5) and with different approaches (45Ca2+ fluxes, Ca2+ imaging and measurements of the free luminal [Ca2+] in the endoplasmic-reticulum and the Golgi apparatus using targeted aequorin). Application of an extracellular agonist in the absence of thapsigargin induced in all cells a Ca2+ release from both the endoplasmic-reticulum and the Golgi apparatus. The agonists were not able to release Ca2+ in the presence of 10 microM thapsigargin, except in COS-1 cells overexpressing SPCA1, where this pump not only appeared in the Golgi compartment but also overflowed into the agonist-sensitive part of the endoplasmic-reticulum. We conclude that the subcompartments of the endoplasmic-reticulum and of the Golgi complex that endogenously express SPCA1 are insensitive to agonist stimulation.

Animals↗
PubMed2001

Human brain carboxypeptidase B, which cleaves beta-amyloid peptides in vitro, is expressed in the endoplasmic reticulum of neurons.

Intracellular localization of novel human brain carboxypeptidase B (HBCPB) was investigated in human hippocampus, using immunohistochemistry by confocal laser microscopy and biochemical purification of the homogenate by density gradient ultracentrifugation. The former revealed that the majority of HBCPB was expressed in the endoplasmic reticulum, in which the HBCPB-specific C14-module immunoreactivity was colocalized with GRP78 immunoreactivity, a stress 70 heat shock protein specifically expressed in the endoplasmic reticulum. The latter showed that anti-C14-module immunoreactivity and prepro-HBCPB immunoreactivity were both enriched in the microsome fraction, especially in that of the endoplasmic reticulum-density fraction of normal human hippocampal homogenates from various sources. However, HBCPB prepared from human hippocampus showed exopeptidase activity for synthetic beta-amyloid 1-42 peptide, in which Abeta X-42 C-terminus immunoreactivity was decreased in a fashion dose-dependent of the amount of the protease added. These findings indicate that HBCPB, which is expressed in the endoplasmic reticulum of a group of neuronal perikarya, may play an important physiological role in degradation of beta-amyloid 1-42, which is specifically generated in the endoplasmic reticulum of human and rodent neurons and is also regarded as the most pathogenic and aggregatable species among all beta-amyloid peptides.

Alzheimer Disease↗
PubMed2002

Joint participation of mitochondria and sarcoplasmic reticulum in the formation of tubular aggregates in gastrocnemius muscle of CK-/- mice.

Tubular aggregates are specific subcellular structures that appear in skeletal muscle fibres under different pathological conditions. The origin of the tubular aggregates is generally ascribed to proliferating membranes of sarcoplasmic reticulum. There are, however, histochemical indications for the presence of mitochondrial enzymes in tubular aggregates suggesting contribution of mitochondria to the genesis of tubular aggregates. In this study we used an immunocytochemical detection technique to assess participation of mitochondria and of sarcoplasmic reticulum in derivation of tubular aggregates. The fast skeletal muscle fibres (m. gastrocnemius) of mice bearing the double invalidation for both the mitochondrial and the cytosolic isoforms of creatine kinase (CK), an enzyme involved in energetics of muscle cells, were employed as a model muscle with tubular aggregates (Steeghs et al., Cell 89, 93-103, 1997). Immunogold labelling of the bc1 complex, a specific integral protein of the inner mitochondrial membrane, provided strong signals in both the mitochondria and tubular aggregates but not in other ultrastructural components of muscle fibres. A similar strong immunogold signal was obtained when labelling for SERCA1, a specific enzyme of the sarcoplasmic reticulum membrane, in regions of typical occurrence of the sarcoplasmic reticulum and in tubular aggregates. In double labelling experiments, we found simultaneous labelling of tubular aggregates with both the bc1 and SERCA1 antibodies. It is concluded, that in CK-/- mouse both the inner mitochondrial membrane and the membrane of the sarcoplasmic reticulum participate in the formation of tubular aggregates.

Animals↗
PubMed1997

Dietary energy tissue-specifically regulates endoplasmic reticulum chaperone gene expression in the liver of mice.

A number of putative molecular chaperones seem to play essential roles in the correct folding, assembly and glycosylation of membrane and secreted proteins in the endoplasmic reticulum. We have shown that life span-extending dietary energy restriction significantly and specifically reduces GRP78 mRNA and protein by 50-75% in mice. Here, 5-mo-old female C3B10RF1 mice were given free access to food after being fed 50% less dietary energy since weaning. Hepatic GRP78 mRNA increased linearly, reaching the same level after 2 wk as was found in the liver of 20-mo-old mice with free access to food. This increase took place with no change in body weight. The mRNA levels of endoplasmic reticulum, cytosolic and mitochondrial chaperones were determined in young (7-mo-old) and old (21- or 28-mo-old) female C3B10RF1 mice. Each age group was either 50% energy restricted or was fed approximately 10% less energy than consumed by mice given free access to food. In young and old energy-restricted mice, hepatic expression of the endoplasmic reticulum chaperones ERp57 (37%), GRP170 (51%), ERp72 (43%), calreticulin (54%) and calnexin (23%) was significantly and specifically reduced. The GRP78, GRP94, GRP170, ERp57 and calnexin mRNA response to diet occurred reproducibly only in liver, and not in adipose, brain, heart, kidney, lung, muscle or small intestine. The mRNA for GRP75, a mitochondrial chaperone, HSC70, a cytoplasmic chaperone, protein disulfide isomerase, an endoplasmic reticulum chaperone, and C/EBPalpha, a transcription factor, was not regulated. Hepatic C/EBPbeta was 15% higher in old energy-restricted mice. Thus the expression of nearly all endoplasmic reticulum chaperones responded rapidly and specifically to dietary energy in mice.

Aging↗
PubMed1998

Enhanced binding to the molecular chaperone BiP slows thyroglobulin export from the endoplasmic reticulum.

To examine how binding of BiP (a molecular chaperone of the hsp70 family that resides in the endoplasmic reticulum) influences the conformational maturation of thyroglobulin (Tg, the precursor for thyroid hormone synthesis), we have developed a system of recombinant Tg stably expressed in wild-type Chinese hamster ovary (CHO) cells and CHO-B cells genetically manipulated for selectively increased BiP expression. The elevation of immunoreactive BiP in CHO-B cells is comparable to that seen during the unfolded protein response in the thyrocytes of certain human patients and animals suffering from congenital hypothyroid goiter with defective Tg. However, in CHO-B cells, we expressed Tg containing no mutations that induce misfolding (i.e. no unfolded protein response), so that levels of all other endoplasmic reticulum chaperones were normal. Increased availability of BiP did not accelerate Tg secretion; rather, the export of newly synthesized Tg was delayed. Tg detained intracellularly was concentrated in the endoplasmic reticulum. By coimmunoprecipitation, BiP exhibited enhanced binding to Tg in CHO-B cells. Moreover, two-dimensional gel analysis showed that BiP associated especially well with intracellular Tg containing mispaired disulfide bonds, thought to represent early Tg folding intermediates. An endoplasmic reticulum chaperone of the hsp90 family, GRP94, was also associated in Tg-chaperone complexes. The results suggest that increased binding of BiP to Tg leads to its delayed conformational maturation in the endoplasmic reticulum.

Animals↗
PubMed1992

Characterization of endoplasmic reticulum by co-localization of BiP and dicarbocyanine dyes.

The original concept of endoplasmic reticulum derived from the observation of a reticular network in cultured fibroblasts by electron microscopy of whole cells. It was previously reported that the fluorescent dye, DiOC6(3), stains a similar network as well as mitochondria and other organelles in living cells. Here, we investigate the significance of the structures labeled by DiO6(3) in CV-1 cells, a monkey epithelial cell line. First, we show that the network stained in living CV-1 cells is preserved by glutaraldehyde fixation and then we co-label it with an antibody against BiP (immunoglobulin binding protein), a protein commonly accepted to be present in the endoplasmic reticulum. Anti-BiP labeled the same network as that labeled by DiOC6(3), so this network now is identified as being part of the endoplasmic reticulum. DiOC6(3) labels many other membrane compartments in addition to the endoplasmic reticulum. This, along with its lipophilic properties, suggests that DiOC6(3) stains all intracellular membranes. However, the extensive reticular network in the thin peripheral regions of cultured cells is easily distinguished from these other membranes. Thus, staining by DiOC6(3) is a useful method for localizing the endoplasmic reticulum, particularly in thin peripheral regions of cultured cells.

Animals↗
PubMed1976

Ultrastructure of sarcoplasmic reticulum in atrial myocardium of patients with mitral valvular disease.

Alterations observed in the sarcoplasmic reticulum of muscle cells in left and right atrial myocardium from 10 patients with mitral valvular disease consisted of: a) proliferation of rough-surfaced endoplasmic reticulum, which formed large cisterns in perinuclear areas of hypertrophied cells and was considered indicative of increased protein synthesis; b) proliferation of free sarcoplasmic reticulum, a change that occurred in degenerated cells and appeared to be related to loss of contractile elements; c) two types of aggregates of tubules of free SR--one type was associated wtih abnormal Z-band material and was found only in cells showing loss of myofibrils and proliferation of free SR, whereas the other was not associated with either of these changes and occurred in less severely altered cells; and d) proliferation and enlargement of cisterns of extended junctional sarcoplasmic reticulum, which formed two distinct types of complexes: the first of these consisted of large, convoluted (Type A) cisterns that were wide (550 to 650 A in thickness) and did not have a central dense lamina; the second was composed of stacks of concentric or parallel (Type B) cisterns that were narrower (220 to 300 A in thickness), had a central dense lamina, and were separated from one another by layers of glycogen granules. The formation of these complexes of cisterns was regarded as an extreme form of overdevelopment of extended junctional sarcoplasmic reticulum in atrial muscle cells.

Adult↗
PubMed1977

Properties of passive binding of calcium to endoplasmic reticulum from adipocytes.

Calcium binding to isolated adipocyte microsomes enriched in endoplasmic reticulum has been characterized. Binding was concentration-dependent, saturable, and totally dissociable. Steady state was reached within 20 min at all calcium concentrations tested. Three apparent classes of binding sites were identified in kinetic and steady state studies using calcium concentrations from 1 muM to 10 mM. The affinity constants (and maximum binding capacities) as determined by computer analysis for the three classes were 2.1 X 10(5) M-1 (0.28 nmol of calcium/mg of protein), 1.3 X 10(4) M-1 (1.1 nmol/mg), and 1.3 X 10(2) M-1 (35 nmol/mg). The dissociation rate constants for the high and intermediate affinity classes of sites were 1.6 X 10(-3) S-1, respectively, and the association rate constant for the high affinity sites was 8 X 10(2) M-1 S-1. The affinity constant calculated from the rate constants was 5.0 X 10(5) M-1 for the high affinity sites in agreement with the value obtained in studies at steady state. The three classes of binding sites were specific for calcium. Magnesium was a noncompetitive inhibitor of calcium binding to all three classes of sites with a Ki of 9 to 12 mM. Calcium binding at 1 muM calcium was 50% inhibited by 18 muM La3+, 600 muM Sr2+, or 2.7 mM Ba2+. These data represent the first analysis of passive calcium binding to endoplasmic reticulum from nonmuscular cells and the first report of corresponding rate constants for either endoplasmic or sarcoplasmic reticulum. The characteristics of the binding are consistent with the properties of calcium transport by endoplasmic reticulum of adipocytes. The characteristics and specificity of the calcium binding constitute further evidence that endoplasmic reticulum plays an important role in cellular calcium homeostasis.

Adipose Tissue↗
PubMed1990

Effects of temperature and buffer composition on calcium sequestration by sarcoplasmic reticulum and plasma membrane of rabbit renal artery.

45Ca electron microscopic autoradiography was used to examine the effects of buffer composition and temperature on the distribution of calcium in rabbit renal artery smooth muscle cells. The results show that the relative distribution of calcium is dependent on both the buffer used (Tris or Krebs) and the temperature of the bathing solution (25 degrees C or 34 degrees C). Krebs buffer at 34 degrees C gave the highest relative activity in the plasma membrane, sarcoplasmic reticulum, and mitochondria. Buffer and temperature had little effect on the relative activity of the nucleus or cytoplasm. Next, we identified the cellular sites of calcium accumulation after 5, 15, 30, or 60 min exposure to 45Ca in Krebs buffer at 34 degrees C. The results show that sarcoplasmic reticulum and plasma membrane are the primary sites of calcium accumulation during influx into these cells. Although the amount of 45Ca in the cell continues to increase with longer exposure, the relative distribution of calcium is essentially the same after 5 or 60 min. The data also indicate that the relative activity of plasma membrane + sarcoplasmic reticulum (a combination site that includes sarcoplasmic reticulum within a mean distance of 275 nm of the plasma membrane) is similar to the membrane alone and is lower than the sarcoplasmic reticulum alone.

Animals↗
PubMedDate not supplied

Anti-liver-kidney microsome antibody is a marker for the rat hepatocyte endoplasmic reticulum.

Human sera, containing anti-liver-kidney microsome antibody as demonstrated by indirect immunofluorescence, were obtained from a subgroup of young patients with autoimmune chronic hepatitis. The anti-liver-kidney microsome antibody-positive sera were used to study the localization of the liver-kidney microsome antigen in hepatocytes. Immunoblot analysis of microsomal subfractions, lysosomal membranes, plasma membranes, mitochondria and purified ribosomes obtained from rat liver demonstrated that this antibody recognizes a protein of 50 kD present only in endoplasmic reticulum membranes. Immunogold labeling of ultrathin frozen sections and immunoperoxidase staining of 11 to 15 micron cryostat sections were used to detect the liver-kidney microsome antigen in rat liver tissue. The anti-liver-kidney microsome antibody binds to antigenic domains on the cytoplasmic face of smooth and rough endoplasmic reticulum membranes of hepatocytes. No labeling was observed of the Golgi apparatus, peroxisomes, mitochondria, lysosomes, nuclei or plasma membranes. Not only was the antigen recognized by the anti-liver-kidney microsome antibody specific for endoplasmic reticulum membranes, but it was also specific for the endoplasmic reticulum of hepatocytes only, since no labeling was observed in any organelle of Kupffer or endothelial cells. Therefore, the anti-liver-kidney microsome antibody can be considered as a marker for endoplasmic reticulum in rat hepatocytes.

Antigens↗
PubMed1993

Activation of Ca2+ release from sarcoplasmic reticulum vesicles by 4-alkylphenols.

4-Alkylphenols induce Ca2+ release from junctional (terminal cisternae) sarcoplasmic reticulum vesicles, but not from nonjunctional sarcoplasmic reticulum vesicles. The 4-alkylphenol concentration required to induce Ca2+ release decreases about threefold for every methylene carbon increase in the alkyl chain length, indicating that the Ca(2+)-releasing potency of 4-alkylphenols is related to their ability to partition into the membrane. The rate and amount of Ca2+ release induced by relatively low 4-octylphenol concentrations (25 nmol/mg protein) are altered by the sarcoplasmic reticulum Ca2+ channel activators, Ca2+ and ATP, and the Ca2+ channel inhibitors, Mg2+ and ruthenium red. Ca2+ release induced by 250 nmol 4-octylphenol/mg protein is much less influenced by Ca2+ channel activators and inhibitors; however, even at this high 4-octylphenol concentration, Ca2+ release is not induced from nonjunctional sarcoplasmic reticulum vesicles. The data indicate that 4-alkylphenols induce Ca2+ release by activating the sarcoplasmic reticulum Ca2+ channel.

Animals↗
PubMed1994

Carp parvalbumin binds to and directly interacts with the sarcoplasmic reticulum for Ca2+ translocation.

Interaction between two relaxing factors, the sarcoplasmic reticulum and parvalbumin, in carp fast skeletal muscle was investigated. Immunoblotting using an anti-parvalbumin antibody revealed that parvalbumin bound to the light sarcoplasmic reticulum isolated from carp fast skeletal muscle in the presence of Ca2+. Parvalbumin enhanced Ca2+ uptake activity of the light sarcoplasmic reticulum. Furthermore, using a photoreactive cross-linker, we detected a protein in the light sarcoplasmic reticulum which bound to parvalbumin in a Ca(2+)-dependent manner. These results suggest that parvalbumin may directly interact with the sarcoplasmic reticulum in contraction-relaxation cycle of carp fast skeletal muscle.

Animals↗