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PubMed1990

Ultrastructural and immunocytochemical characterization of cultured cells from rat molar stellate reticulum.

By scanning electron microscopy, the cultured cells were stellate and had numerous filipodia--characteristics of stellate reticulum cells in vivo. By transmission electron microscopy, they contained bundles of intermediate filaments, numerous mitochondria, large electron-dense granules and desmosomes--all features of the stellate reticulum in vivo. Moreover, the stellate reticulum was the only region of the enamel organ in vivo that contained large, electron-dense granules. By immunocytochemistry, the cultured cells contained cytokeratins, confirming their epithelial nature, and stellate reticulum cells in vivo and in vitro did not have an EGF receptor. Thus, these combined ultrastructural and immunocytochemical findings suggest that the cell culture was of stellate reticulum.

Alkaline Phosphatase↗

PubMed1990

Effect of diabetes on the rat hepatic glucose-6-phosphatase system in endoplasmic reticulum subfractions.

Diabetes-induced alterations in the activities of the components of the glucose-6-phosphatase system (i.e., the enzyme, the glucose-6-P translocase (T(1)), and the phosphate translocase (T(2)) were examined in smooth and rough subfractions of hepatic endoplasmic reticulum from streptozotocin-injected rats. A significant effect of diabetes on the maximal velocity of glucose-6-P hydrolysis by the enzyme was present in both endoplasmic reticulum subfractions (3.1-fold increase in rough endoplasmic reticulum; 3.8-fold increase in smooth endoplasmic reticulum). Based on latency values, diabetes did not result in a proportional increase in capacity of T(1) or T(2). In contrast to the control condition, the relationship between transport capacity and hydrolytic capacity was not significantly different in the two subfractions from diabetic animals. Elucidation of the effects of diabetes on the components of the glucose-6-phosphatase system associated with smooth and rough endoplasmic reticulum membranes enhances our understanding of the hepatic contribution to diabetic hyperglycemia.

Journal Article↗

PubMed1969

Osmotic responses demonstrating the extracellular character of the sarcoplasmic reticulum.

1. Changes in the dimensions of the sarcoplasmic reticulum in frog sartorius muscles exposed to hypertonic and hypotonic solutions have been studied with the electron microscope.2. The volume of the sarcoplasmic reticulum has been found to be linearly related with a negative slope to the reciprocal of the osmotic pressure. Over the range 0.75 to 3.5 x normal osmotic pressure the reticulum volume has been calculated to change from 11.5 to 18.5% of normal cell volume.3. These changes in sarcoplasmic reticulum volume correspond to the calculated changes in the volume of the intra-fibre sucrose compartment, postulated by earlier workers on the basis of studies on changes in cell volume with changes in osmotic pressure in living muscles.4. To explain these and other related findings on the distribution of electrolytes in muscle, it is proposed that the sarcoplasmic reticulum of skeletal muscle is an extracellular compartment.5. The significance of this hypothesis for the mechanism of excitation-contraction coupling is discussed.

Animals↗

PubMed1966

Paraproteinemia and reticulum cell sarcoma in an inbred mouse strain.

Mice of the inbred SJL/J strain have a high incidence of a proliferative disease affecting several cell types, including reticulum cells and plasma cells, which is frequently accompanied by gamma(1) and gamma(2) paraproteinemia. In only some instances can seriallytransplantable lines of neoplastic cells be obtained; these are reticulum cell sarcomas. Mice with transplanted reticulum cell e arcomas do not have paraproteinemia and may develop profound hypogammaglobulinemia. The disease may be viewed as an abnormal proliferation of reticulum cells which differentiate into plasma cells with consequent paraproteinemia; the subsequent emergence of transplantable reticulum cell sarcoma appears as an end stage in which this capacity to differentiate is lost.

Animals↗

PubMed1969

Calcium transport by skeletal muscle sarcoplasmic reticulum in the hypothyroid rat.

The rate of calcium transport by isolated sarcoplasmic reticulum from rat skeletal muscle increases markedly during the first 4 wk of life and thereafter remains relatively constant. When animals are made hypothyroid during the first 3 wk of life, there is a marked inhibition of the increase in calcium transport by the sarcoplasmic reticulum. Production of hypothyroidism after 4 wk of age, at which time the calcium transport by sarcoplasmic reticulum has reached maximum levels, results in a depression in the rate of calcium transport. There is no clear alteration in ATPase activity of the sarcoplasmic reticulum to account for the low calcium transport in hypothyroidism. It is proposed that the decrease in calcium transport by sarcoplasmic reticulum may account for observed alterations in the intrinsic contractile properties of muscle in the hypothyroid animal.

Adenosine Triphosphatases↗

PubMed1992

Immunocytochemical demonstration of dopamine-beta-hydroxylase and cytochrome B561 on the axonal reticulum in bovine sympathetic neurons.

In sympathetic neurons the axonal reticulum can be considered an extension of the secretory pole of the Golgi apparatus. If this tubular system indeed represents the neurosecretory apparatus, it would likely contain on its membranes the enzymes involved in catecholamine synthesis. To test this hypothesis, we investigated the distribution of dopamine-beta-hydroxylase and cytochrome b561 in bovine splenic nerve and nerve terminals in the vas deferens with an immunogold procedure after glycolmethacrylate embedding. Counterstaining with phosphotungstic acid at low pH selectively revealed the axonal reticulum elements. With antibodies against both enzymes, gold labeling was observed over the large dense-cored vesicles, the Golgi-associated axonal reticulum, the reticulum within axons, and the tubular complex at the nerve terminal. From our results it can be concluded that in sympathetic neurons the axonal reticulum represents a tubular neurosecretory system, extending from the Golgi apparatus in the cell soma to the nerve terminal. This concept emphasizes the local production of neurosecretory vesicles and may be of importance in the interpretation of neuronal transmission in normal and diseased states.

Animals↗

PubMed1989

Differentiation of interdigitating reticulum cells and Langerhans cells in the human skin with T-lymphoid infiltrate. An immunocytochemical and ultrastructural study.

The differentiation of two types of T-lymphocyte accessory cells, i.e., interdigitating reticulum cells and Langerhans cells, was studied immunocytochemically and ultrastructurally on cutaneous lesions from patients with mycosis fungoides, a neoplasm of mature T-lymphocytes. In such a condition the lymphoid infiltrate creates, adjacent to the epidermis, a microenvironment in the dermis similar to that of T-cell areas of lymphoid organs. Immunocytochemistry revealed that CD11c+ CD1a- putative monocytic cells co-exist with CD11c+ CD1a+ putative mature accessory cells. By electron microscopy, large numbers of interdigitating reticulum cells in the dermal infiltrate and Langerhans cells in the epidermis were found. Furthermore, monocytes were frequently observed, at times with cells showing intermediate features between monocytes and interdigitating reticulum cells on the one hand and Langerhans cells on the other. In the absence of proliferative phenomena of the above cells, it is conceivable that both interdigitating reticulum cells and Langerhans cells originate from locally migrated monocytes. A possible role of the local tissue micro-environment--namely the T-lymphoid microenvironment for interdigitating reticulum cells and the epidermal microenvironment for Langerhans cells--in inducing the differentiation of monocytes into the two kinds of accessory cells is proposed.

Cell Differentiation↗

PubMed1977

Intraocular reticulum cell sarcoma: its dramatic response to systemic chemotherapy and its angiogenic potential.

A 77-year-old woman with reticulum cell sarcoma in apparent remission presented with neovascular glaucoma. Ultrasonography demonstrated a 360 degree ring tumor of the ciliary body which totally regressed in 3 weeks after reinsitution of systemic chemotherapy. This appears to be a ring reticulum cell sarcoma of the ciliary body and is apparently the first reported case of an intraocular reticulum cell sarcoma which has undergone such a dramatic response to combined chemotherapy. A review of the English literature of all published cases of ocular reticulum cell sarcoma (16 cases) discloses no similar case, and emphasizes for the first time the angiogenic potential of this tumor. Secondary glaucoma was found to be associated with intraocular reticulum cell sarcoma in approximately two-thirds of the reported cases, and neovascular glaucoma in about one-quarter of these cases.

Aged↗

PubMed1983

Electrophoretic mobility profiles of mouse leukemias. II. Electrophoresis of thymic lymphoma, myeloid leukemia and reticulum sarcoma cells.

Electrophoretic mobility of cells from 21 primary mouse leukemias was investigated and compared with that of various normal mouse reference cells. Six thymic lymphomas, nine reticulum cell sarcomas, five myeloid leukemias and one stem-cell leukemia were examined. The mean AEM of cells from the group of primary thymic lymphomas (1.13 microns s-1 V-1 cm) was similar to that of reticulum cell sarcomas (1.15 microns s-1 V-1 cm) and significantly lower than that of the myeloid leukemias (1.20 microns s-1 V-1 cm). Since the examined cell suspensions were prepared from leukemic lymph nodes, the analysis was performed to investigate the possible admixture of normal LNC in the cell populations. Electrophoretograms of normal and leukemic lymph nodes were compared and the AEM of cells from leukemic lymph nodes was considered separately for two cell populations, one corresponding in size to normal LNC (6-9 microns in diameter) and the other to leukemic blast cells (10-16 microns in diameter). In the 6-9 microns cell subpopulations from leukemic lymph nodes, electrophoretically slow cells corresponding to B LNC were almost totally depleted (1%); also electrophoretically fast cells with the mean AEM of T LNC were fewer (45-57%) than in normal LNC populations. The leukemic cells 10-16 microns in diameter displayed mean AEM of 1.09 (thymic lymphomas), 1.12 (reticulum cell sarcomas) and 1.21 (myeloid leukemia) micron s-1 V-1 cm. The mean AEM of blast cells from thymic lymphomas and reticulum cell sarcomas was not significantly different; it was similar to that of blast cells prepared from normal mouse thymus (1.09 microns s-1 V-1 cm) on a density gradient. In contrast, the 10-16 microns cell populations from lymph nodes of mice with myeloid leukemias were significantly faster than blast cells from thymic lymphomas and reticulum cell sarcomas.

Animals↗

PubMed1989

Dynamics of the endoplasmic reticulum in living non-muscle and muscle cells.

The dynamic changes of the endoplasmic reticulum (ER) in interphase and mitotic cells was detected by the vital fluorescent dye 3,3'-dihexyloxacarbocyanine iodide. Two types of arrays characterize the continuous ER system in the non-muscle PtK2 cell: 1) a lacy network of irregular polygons and 2) long strands of ER that are found aligned along stress fibers. In cross-striated myotubes there was a periodic localization of fluorescence over each I-band corresponding to the positions of the terminal cisternae of the sarcoplasmic reticulum (SR). In contrast to the arrangement in muscle cells, the alignment of the long strands of ER alon stress fibers showed no strict periodicity that could be correlated with the sarcomeric units of the stress fibers. The ER and SR arrays seen in living cells were also detected in fixed cells stained with antibodies directed against proteins of the endoplasmic reticulum and sarcoplasmic reticulum, respectively. Observations of vitally stained PtK2 cells at 1 to 2 minute intervals using low light level video cameras and image processing techniques enabled us to see the polygonal ER units form and undergo changes in their shapes. During cell division, the ER, rhodamine 123-stained mitochondria, and phagocytosed fluorescent beads were excluded from the mitotic spindle while soluble proteins were not. No obvious concentration or alignment of membranes could be found associated with the contractile proteins in the cleavage furrow. After completion of cell division there was a redeployment of the ER network in each daughter cell.

Animals↗

PubMed2001

Targeting of calsequestrin to the sarcoplasmic reticulum of skeletal muscle upon deletion of its glycosylation site.

The glycoprotein calsequestrin (CS) is segregated to the junctional sarcoplasmic reticulum (jSR) and is responsible for intraluminal Ca(2+) binding. A chimeric CS-hemoagglutinin 1 (HA1), obtained by adding the nine amino acid viral epitope hemoagglutinin to the carboxy terminal of CS and shown to be correctly segregated to skeletal muscle jSR [A. Nori, K. A. Nadalini, A. Martini, R. Rizzuto, A. Villa, and P. Volpe (1997). Chimeric calsequestrin and its targeting to the junctional sarcoplasmic reticulum of skeletal muscle. Am. J. Physiol. 272, C1420-C1428] lends itself as a molecular tool to investigate the targeting domains of CS. A putative targeting mechanism of CS to jSR implies glycosylation-dependent steps in the endoplasmic reticulum (ER) and Golgi complex. To test this hypothesis, CS-HA1DeltaGly, a mutant in which the unique N-glycosylation site Asn316 was changed to Ile, was engineered by site-directed mutagenesis. The mutant cDNA was transiently transfected in either HeLa cells, myoblasts of rat skeletal muscle primary cultures, or regenerating soleus muscle fibers of adult rats. The expression and intracellular localization of CS-HA1DeltaGly was studied by double-labeling epifluorescence by means of antibodies against either CS, HA1, or the ryanodine receptor calcium release channel. CS-HA1DeltaGly was expressed and retained to ER and ER/sarcoplasmic reticulum of HeLa cells and myotubes, respectively, and expressed, sorted, and correctly segregated to jSR of regenerating soleus muscle fibers. Thus, the targeting mechanism of CS in vivo appears not to be affected by glycosylation-that is, the sorting, docking, and segregation of CS are independent of cotranslational and posttranslational glycosylation or glycosylations.

Animals↗

PubMed1992

Calcium binding proteins in the sarcoplasmic/endoplasmic reticulum of muscle and nonmuscle cells.

In this paper we review some of the large quantities of information currently available concerning the identification, structure and function of Ca(2+)-binding proteins of endoplasmic and sarcoplasmic reticulum membranes. The review places particular emphasis on identification and discussion of Ca2+ 'storage' proteins in these membranes. We believe that the evidence reviewed here supports the contention that the Ca(2+)-binding capacity of both calsequestrin and calreticulin favor their contribution as the major Ca(2+)-binding proteins of muscle and nonmuscle cells, respectively. Other Ca(2+)-binding proteins discovered in both endoplasmic reticulum and sarcoplasmic reticulum membranes probably contribute to the overall Ca2+ storage capacity of these membrane organelles, and they also play other important functional role such as posttranslational modification of newly synthesized proteins, a cytoskeletal (structural) function, or movement of Ca2+ within the lumen of the sarcoplasmic/endoplasmic reticulum towards the storage sites.

Calcium↗

PubMed2005

Rearrangement of the endoplasmic reticulum and calcium transient formation: the computational approach.

Experiments affecting calcium signaling often lead to changes in the calcium transient height. The present work is designed to approach this effect theoretically. Use of computational model let us to follow results of precisely designed changes in the endoplasmic reticulum distribution as a possible cause of cytoplasmic free calcium ion level. Obtained results suggest that indeed, rearrangement of the endoplasmic reticulum elements may be responsible for modulation of calcium signal's strength. We have also noticed that even if the endoplasmic reticulum concentration levels are local, the resulting changes in free calcium concentration are global and evenly distributed throughout the cell. The used mathematical method proved to be a powerful tool which made us understand the chemical dynamics of nonequilibrium processes of calcium transient formation. Presented data show how Ca2+ signal resulting from IP3 provoked release of calcium from the endoplasmic reticulum may depend on the cytoskeleton structure.

Calcium Signaling↗

PubMed1990

Molecular cloning and chromosomal localization of a sarco/endoplasmic reticulum-type Ca2(+)-ATPase of Drosophila melanogaster.

We report here the characterization of a Drosophila melanogaster cDNA that encodes a sarco/endoplasmic reticulum-type Ca2(+)-ATPase. Previously we amplified the phosphorylation site - FITC-binding site fragment of this cDNA by Polymerase Chain Reaction utilizing homology primers (Váradi, A., Gilmore-Hebert, M. and Benz, E. J. Jr. (1989) FEBS Letters 258 203-207) and in the present work we used this fragment as probe for isolation of a cDNA clone with the intire coding region. The isolated 3.3 kb clone has been sequenced and the primary structure of the encoded protein has been deduced. It consists of 1002 amino acids with all the characteristic features of the P-type ATPases. It shows 67-71% amino acid identity and an apparently identical hydropathy profile with the mammalian sarco/endoplasmic reticulum-type Ca2(+)-ATPases. On basis of sequence similarity we suggest that the first transmembrane segment of sarco/endoplasmic reticulum type Ca2(+)-ATPases may be responsible for targeting of these transport proteins into the organellar membrane. The gene of this sarco/endoplasmic reticulum-type Ca2(+)-ATPase has been mapped on the right arm of chromosome 2, in section 60A.

Amino Acid Sequence↗

PubMed1996

Disturbances of calcium homeostasis within the endoplasmic reticulum may contribute to the development of ischemic-cell damage.

It is widely accepted that disturbances of calcium homeostasis play a key role in the development of cell damage produced by transient cerebral ischemia. It is believed that the sharp increase in cytosolic calcium activity during ischemia activates a cascade of calcium-dependent metabolic processes which ultimately destroy the integrity of the cell. However, it has never been taken into account that ischemic cell damage may, at least in part, be caused by a disturbance of calcium homeostasis within the endoplasmic reticulum after transient cerebral ischemia. In fact, depletion of the endoplasmic reticulum from calcium induces metabolic changes resembling, in many respects, those produced by transient cerebral ischemia: it causes an inhibition of the activity of the eucaryotic initiation factor elF-2 alpha (by phosphorylation), a disaggregation of polyribosomes and thus an inhibition of global protein synthesis, and an increased expression of certain genes such as transcription factors (c-fos and c-jun) and the glucose-related protein grp78. Finally, a depletion of calcium in the endoplasmic reticulum induces tissue damage within the brain and triggers apoptosis in neuronal and non-neuronal cells. It is therefore concluded that cell damage induced by transient ischemia may, at least in part, be caused by a disturbance of calcium homeostasis within the endoplasmic reticulum.

Animals↗

PubMed1994

Sequential interaction of the chaperones BiP and GRP94 with immunoglobulin chains in the endoplasmic reticulum.

During their transit through the endoplasmic reticulum, newly synthesized light and heavy chains of immunoglobulins associate with two endoplasmic reticulum stress proteins. BiP/GRP78, a member of the HSP70 family, binds these polypeptides, presumably through promiscuously exposed hydrophobic sequences, soon after their translocation into the endoplasmic reticulum. GRP94, another endoplasmic reticulum stress protein homologous to HSP90, also associates with unassembled immunoglobulin chains, but its interaction is biochemically, kinetically and structurally distinct from BiP's. We report here that whereas BiP preferentially binds an early disulphide intermediate of light chain and dissociates within a few minutes, GRP94 exclusively binds fully oxidized molecules and dissociates with a half-time of 50 min. These results indicate that GRP94 is itself a chaperone which acts after BiP.

Brefeldin A↗

PubMed2004

Anti-apoptotic protein Bcl-2 interacts with and destabilizes the sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (SERCA).

The anti-apoptotic effect of Bcl-2 is well established, but the detailed mechanisms are unknown. In the present study, we show in vitro a direct interaction of Bcl-2 with the rat skeletal muscle SERCA (sarcoplasmic/endoplasmic reticulum Ca2+-ATPase), leading to destabilization and inactivation of the protein. Recombinant human Bcl-2D21, a truncated form of Bcl-2 with a deletion of 21 residues at the C-terminal membrane-anchoring region, was expressed and affinity-purified as a glutathione S-transferase fusion protein. Bcl-2D21 co-immunoprecipitated and specifically interacted with SERCA in an in vitro-binding assay. The original level of Bcl-2 in sarcoplasmic reticulum vesicles was very low, i.e. hardly detectable by immunoblotting with specific antibodies. The addition of Bcl-2D21 to the sarcoplasmic reticulum resulted in the inhibition of the Ca2+-ATPase activity dependent on the Bcl-2D21/SERCA molar ratio and incubation time. A complete inactivation of SERCA was observed after 2.5 h of incubation at approx. 2:1 molar ratio of Bcl-2D21 to SERCA. In contrast, Bcl-2D21 did not significantly change the activity of the plasma-membrane Ca2+-ATPase. The redox state of the single Cys158 residue in Bcl-2D21 and the presence of GSH did not affect SERCA inhibition. The interaction of Bcl-2D21 with SERCA resulted in a conformational transition of SERCA, assessed through a Bcl-2-dependent increase in SERCA thiols available for the labelling with a fluorescent reagent. This partial unfolding of SERCA did not lead to a higher sensitivity of SERCA towards oxidative inactivation. Our results suggest that the direct interaction of Bcl-2 with SERCA may be involved in the regulation of apoptotic processes in vivo through modulation of cytoplasmic and/or endoplasmic reticulum calcium levels required for the execution of apoptosis.

Animals↗

PubMed2002

Regulation of calreticulin expression during induction of differentiation in human myeloid cells. Evidence for remodeling of the endoplasmic reticulum.

Induction of differentiation of HL-60 human myeloid cells profoundly affected expression of calreticulin, a Ca(2+)-binding endoplasmic reticulum chaperone. Induction with Me(2)SO or retinoic acid reduced levels of calreticulin protein by approximately 60% within 4 days. Pulse-chase studies indicated that labeled calreticulin decayed at similar rates in differentiated and undifferentiated cells (t(12) approximately 4.6 days), but the biosynthetic rate was <10% of control after 4 days. Differentiation also induced a rapid decline in calreticulin mRNA levels (90% reduction after 1 day) without a decrease in transcript stability (t(12) approximately 5 h). Nuclear run-on analysis demonstrated rapid down-regulation of gene transcription (21% of control at 2 h). Differentiation also greatly reduced the Ca(2+) content of the cells (25% of control), although residual Ca(2+) pools remained sensitive to thapsigargin, ionomycin, and inositol trisphosphate. Progressive decreases were also observed in levels of calnexin and ERp57, whereas BiP/GRP78 and protein disulfide isomerase were only modestly affected. Ultrastructural studies showed a substantial reduction in endoplasmic reticulum content of the cells. Thus, terminal differentiation of myeloid cells was associated with decreased endoplasmic reticulum content, selective reductions in molecular chaperones, and diminished intracellular Ca(2+) stores, perhaps reflecting an endoplasmic reticulum remodeling program as a prominent feature of granulocytic differentiation.

Calcium-Binding Proteins↗