Biomedical subjects

O Bakke

Publications and source records attributed to O Bakke.

At least 55 records · Page 3Linked to original sources

PubMed1993

Intracellular distribution of the MHC class II molecules and the associated invariant chain (Ii) in different cell lines.

Intracellular localization and routing of MHC class II molecules and the associated invariant chain (Ii) were studied using rat-2 cells and HeLa cells stably transfected with the murine class II genes A alpha kA beta k (Ak) alone or supertransfected with human Ii or a truncated delta 20Ii lacking the endosomal sorting signal within Ii. We show that Ii and delta 20Ii are able to bind the class II molecules and replace the highly homologous murine Ii in class II sorting. Expression of transfected Ii or delta 20Ii also result in more efficient transport of class II molecules from the ER. There are, however, cell type specific differences in the intracellular routing of the class II molecules. The endosomal sorting signal within Ii is required to target class II molecules to endosomes in HeLa cells, whereas class II molecules alone enter endosomes in rat-2 cells. Class II molecules cannot direct the associated delta 20Ii to endosomes, suggesting that they follow a direct route to the cell surface and the majority of class II may enter endosomes by internalization. This is also supported by the long lived presence of class II molecules in endosomes after arresting protein transport with cycloheximide or brefeldin A. Class II molecules expressed alone or together with Ii are located in the whole endosomal pathway in rat-2 cells. However, full length Ii is required to target the class II molecules to vesicles that are more chloroquine sensitive than vesicles containing class II molecules alone. Our results thus indicate that Ii is responsible for endosomal sorting of class II molecules in HeLa cells, whereas in rat-2 cells the presence of Ii leads to an altered endosomal distribution.

Animals↗

PubMed1993

Common peptide epitope in mumps virus nucleocapsid protein and MHC class II-associated invariant chain.

The present study describes a 7 amino acid-long sequence (YQQQGRL) which is identical in HLA-associated invariant chain and mumps virus nucleocapsid protein and is additionally followed by one conservative amino acid pair. As such a long amino acid homology is extremely rare in two evolutionarily unrelated proteins the possibility that it could induce immunological cross-reactivity was evaluated. Several antigenicity indices suggested high antigen potential within this region. Synthetic peptides containing this sequence were reactive with 31% of monoclonal antibodies specific for mumps virus nucleocapsid protein in ELISA. High antibody levels against this epitope were found in 7% of mumps-seropositive human sera and antibody levels clearly increased after natural mumps infections and mumps vaccinations. Rabbit antibodies raised against a synthetic invariant chain peptide AYF-LYQQQGRLDKL-C reacted with corresponding nucleocapsid peptide RFAKYQQQGRLEAR-C and antibodies against the nucleocapsid peptide reacted with the invariant chain peptide. Rabbit antibodies against the invariant chain peptide also reacted with nucleocapsid molecules in formaldehyde-fixed mumps virus-infected cells, and antibodies against the nucleocapsid peptide reacted with invariant chains expressed in methanol-fixed cells. One monoclonal antibody specific for the nucleocapsid molecule also reacted with cells expressing invariant chains. In immunoprecipitation rabbit antibodies against the invariant chain peptide bound to invariant chains while antibodies against the nucleocapsid peptide did not. The results suggest that there is antigenic similarity in mumps virus nucleocapsid molecule and HLA-associated invariant chain which may cause immunological cross-reactivity between these molecules.

Amino Acid Sequence↗

PubMed1993

The MHC class II-associated invariant chain contains two endosomal targeting signals within its cytoplasmic tail.

The oligomeric complex formed by major histocompatibility complex (MHC) class II alpha and beta chains and invariant chain (Ii) assembles in the endoplasmic reticulum and is then transported via the Golgi complex to compartments of the endocytic pathway. When Ii alone is expressed in CV1 cells it is sorted to endosomes. The Ii cytoplasmic tail has been found to be essential for targeting to these compartments. In order to characterize further the signals responsible for endosomal targeting, we have deleted various segments of the cytoplasmic tail. The Ii mutants were transiently expressed and the cellular location of the proteins was analyzed biochemically and morphologically. The cytoplasmic tail of Ii was found to contain two endosomal targeting sequences within its cytoplasmic tail; one targeting sequence was present within amino acid residues 12-29 and deletion of this segment revealed the presence of a second endosomal targeting sequence, located within the first 11 amino acid residues. The presence of a leucine-isoleucine pair at positions 7 and 8 within this sequence was found to be essential for endosomal targeting. In addition, the presence of this L-I motif lead to accumulation of Ii molecules in large endosomal vacuoles containing lysosomal marker proteins. Both wild type Ii and Ii mutant molecules containing only one endosomal targeting sequence were rapidly internalized from the plasma membrane. When the Ii cytoplasmic tail was fused to the membrane-spanning region of neuraminidase, a resident plasma membrane protein, the resulting chimera (INA) was found in endocytic compartments containing lysosomal marker proteins. Thus the cytoplasmic tail of Ii is sufficient for targeting to the endocytic/lysosomal pathway.

Amino Acid Sequence↗

PubMed1992

Stable surface expression of invariant chain prevents peptide presentation by HLA-DR.

Class II major histocompatibility complex (MHC) molecules are cell surface glycoproteins that bind and present immunogenic peptides to T cells. Intracellularly, class II molecules associate with a polypeptide referred to as the invariant (Ii) chain. Ii is proteolytically degraded and dissociates from the class II complex prior to cell surface expression of the mature class II alpha beta heterodimer. Using human fibroblasts transfected with HLA-DR1 and Ii cDNAs, we now demonstrate that truncation of the cytoplasmic domain of Ii results in the failure of Ii to dissociate from the alpha beta Ii complex and leads to stable expression of class II alpha beta Ii complexes on the cell surface. Furthermore, biochemical analysis and peptide presentation assays demonstrated that transfectants with stable surface alpha beta Ii complexes expressed very few free alpha beta heterodimers at the surface and were very inefficient in their ability to present immunogenic peptides to T cells. These results support the hypothesis that the cytoplasmic domain of Ii is responsible for endosomal targeting of alpha beta Ii and directly demonstrate that association with Ii interferes with the antigen presentation function of class II molecules.

Antigens, Differentiation, B-Lymphocyte↗

PubMed1991

Intracellular transport and localization of major histocompatibility complex class II molecules and associated invariant chain.

The intracellular transport and location of major histocompatibility complex (MHC) class II molecules and associated invariant chain (Ii) were investigated in a human melanoma cell line. In contrast to the class II molecules, which remain stable for greater than 4 h after synthesis, the associated Ii is proteolytically processed within 2 h. During or shortly after synthesis the NH2-terminal cytoplasmic and membrane-spanning segment is in some of the Ii molecules cleaved off; during intracellular transport, class II associated and membrane integrated Ii is processed from its COOH terminus in distinct steps in endocytic compartments. Immunocytochemical studies at the light and electron microscopic level revealed the presence of class II molecules, but not of Ii on the cell surface. Intracellularly both Ii and class II molecules were localized in three morphologically and kinetically distinct compartments, early endosomes, multivesicular bodies, and prelysosomes. This localization in several distinct endosomal compartments contrasts with the localization of class II molecules in mainly one endocytic compartment in B lymphoblastoid cell lines. As in these lymphoblastoid cell lines Ii is known to be rapidly degraded it is conceivable that the rate of proteolysis of the class II associated Ii and its dissociation from class II molecules modulates the retention of the oligomeric complex in endocytic compartments, and as a consequence the steady-state distribution of these molecules within the endosomal system.

Biological Transport↗

PubMed1990

MHC class II-associated invariant chain contains a sorting signal for endosomal compartments.

The invariant chain (Ii) is a transmembrane protein that associates with the MHC class II molecules in the endoplasmic reticulum. Expression of Ii in MHC class II-negative CV1 cells showed that it acquired complex-type oligosaccharide side chains and was retained in endosomal compartments. To search for a sorting signal, we made progressive deletions from the cytoplasmic N-terminus of Ii. Deleting 11 amino acid residues resulted in a protein that was still sorted and retained in endosomal vesicles, whereas deletion of 15 or more amino acid residues resulted in a protein that became resident in the plasma membrane. Amino acids 12-15 are thus essential for intracellular transport to endosomal compartments. As Ii is intracellularly associated with the MHC class II molecules, it is proposed that Ii determines the intracellular transport route of these molecules.

Amino Acid Sequence↗

PubMed1989

A flow cytometric and immunofluorescence microscopic study of tumor necrosis factor production and localization in human monocytes.

The production and localization of tumor necrosis factor (TNF) in human monocytes were investigated by using monoclonal and polyclonal antibodies against recombinant human TNF together with flow cytometry and immunofluorescence microscopy. Lipopolysaccharide (LPS) induced a rapid and transient accumulation of TNF in perinuclear vesicles which was detected 20 min after the addition of LPS. The fluorescence intensity of the vesicles peaked at 40 min of LPS exposure, concomitantly with the release of TNF into the medium. Thus, our results indicate that the secretion of TNF is typical for secretory proteins as it involves passage through the secretory apparatus. Additional studies demonstrated that plasma membrane-associated TNF could not be detected in live monocytes not exposed to LPS. However, after 90 min with LPS, a small population of monocytes expressed membrane-associated TNF, and by 24 hr approximately 50% of the monocytes displayed TNF on the plasma membrane. Furthermore, our results indicate that plasma membrane-associated TNF does not represent released TNF bound back to its own receptor. Thus, our findings support the view that TNF exists as a surface trans-membrane protein in LPS-stimulated monocytes.

Cell Compartmentation↗

PubMed1989

Retinoic acid induces a specific membrane glycoprotein in human epithelial cell lines.

Retinoic acid (RA) inhibits growth, increases the cytokeratin content, and alters the cytoskeleton of the human cervical cell line NHIK 3025. Using RA-treated NHIK 3025 cells as immunogen we prepared murine monoclonal antibodies (IgG1) which recognized an RA-induced cell-surface antigen which could not be detected in untreated NHIK 3025 cells. Analysis of the Triton soluble proteins by SDS-gel electrophoresis and immunoblotting revealed that the cell-surface antigen is a 140-kDa glycoprotein (gp140). gp140 was also shown to be induced by RA in HeLa S3 cells and constitutively expressed in the human trophoblast cell line BeWo. gp140 was also detected in other human epithelial cell lines, but not in human hematopoietic cells. Expression of gp140 was induced in HeLa S3 cells by nanomolar concentrations of RA, and in NHIK 3025 cells by micromolar amounts (1-10 microM). The glycoprotein was detectable 3-6 h following exposure to RA and its expression was reversible upon removal of RA from the medium. Our results indicate that gp140 is a newly identified RA-inducible epithelial membrane glycoprotein which may represent a phenotypic differentiation marker for epithelial cells.

Animals↗

PubMed1988

Glucocorticoids suppress the production of tumour necrosis factor by lipopolysaccharide-stimulated human monocytes.

We have investigated the modulating effect of steroids on the in vitro production of tumour necrosis factor (TNF) by lipopolysaccharide (LPS)-stimulated human monocytes. Dexamethasone, at concentrations ranging from 10(-8) to 10(-6) M, and cortisol, at concentrations 10(-7) and 10(-6) M, suppressed the TNF production in a dose-dependent manner. The highest concentrations of dexamethasone or cortisol reduced the TNF production to 21 +/- 2% and 48 +/- 8% of the control value, respectively. The effect of dexamethasone was time dependent, and an incubation time of 48 hr was required to reduce the TNF production to 21% of control. The effect of dexamethasone decreased when the incubation time became shorter, and the mean TNF production ranged from 49% to 72% of control when dexamethasone was added later than 8 hr before LPS addition, at the time of LPS addition, or within 1 hr after LPS addition. The magnitude of the TNF-suppressing effect of dexamethasone varied greatly from donor to donor. Only the glucocorticoids, and not the sex steroids or the mineralocorticoids, significantly reduced the TNF production.

Aldosterone↗

PubMed1987

Characterization and sequence-specific binding to mouse mammary tumor virus DNA of purified activated human glucocorticoid receptor.

Activated glucocorticoid receptor (GR) from the human cell line HeLa S3 was purified by differential chromatography on DNA-cellulose followed by DEAE-Sepharose chromatography to 50-60% homogeneity according to sodium dodecyl sulfate gel electrophoresis and densitometric scanning of silver-stained gels. These gels routinely demonstrated a main band of Mr 94,000 (94K band) and two minor bands of Mr 79,000 (79K band) and 39,000 (39K band), respectively. Photoaffinity labeling indicated that the hormone was bound to the 94K and 79K components. In some preparations, a 72K band was observed. Further characterization of the purified receptor by gel permeation chromatography on Sephadex G-200 revealed a receptor complex with a Stokes radius of 5.8 nm. The sedimentation coefficient of the purified receptor was 4.4 Sw. In analogy to the rat hepatic GR, limited proteolysis of the purified GR with trypsin or alpha-chymotrypsin led to degradation of the 94K and 79K components and appearance of 28K and 39K fragments, respectively. In addition, no difference in the protease digestion pattern using Staphylococcus aureus V8 protease was observed. Immunoblotting using a monoclonal antibody raised against the 94K GR from rat liver demonstrated cross-reactivity with the human 94K and 79K proteins from HeLa S3 cells, indicating similar antigenic characteristics between rat and human GR. In our study, five out of nine tested monoclonal antibodies against the rat liver GR cross-reacted with human GR. DNase I and exonuclease III protection experiments demonstrated binding of the purified human GR to specific GR binding regions in mouse mammary tumor virus DNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Cellulose↗

PubMed1987

Inhibition of in vitro lysozyme release from human granulocytes and monocytes by non-steroidal anti-inflammatory agents.

A selective zymosan-induced release of lysozyme from freshly prepared human blood granulocytes and monocytes was inhibited by indomethacin, sulindac, piroxicam and ibuprofen. This effect was slightly more marked for granulocytes than for monocytes. Salicylic acid, acetylsalicylic acid and naproxen, even at high concentrations, did not inhibit the enzyme release from either cell type. Since all these nonsteroidal anti-inflammatory agents are cyclooxygenase inhibitors, these findings suggest that lysozyme release is independent of prostaglandin biosynthesis.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed1987

Intracellular localization of the glucocorticoid receptor: evidence for cytoplasmic and nuclear localization.

Using a monospecific, monoclonal antibody against the glucocorticoid receptor (GR), an immunocytochemical study was performed to investigate the intracellular localization of GR both in the presence or absence of ligand. With all fixation methods tested (paraformaldehyde, acetic acid in ethanol, Bouin's fixative, and bensochinone in PBS), it was possible to obtain specific GR staining. Fixation with paraformaldehyde was chosen for further studies on the effect of permeabilization, using several concentrations of Triton X-100 or saponin. A rat Rueber hepatoma (H-4-II-E) and a human uterus carcinoma (NHIK 3025) cell line were used as well as cultured hepatocytes from normal rat. The accessibility of the different cell compartments after fixation and permeabilization was tested for by using antibodies against cellular constituents with known locations (i.e. core-nucleosome proteins and tubulin), in combination with the anti-GR antibody in double immunofluorescence staining experiments. The specific GR stain obtained with the indirect peroxidase antiperoxidase technique or with fluorescein isothiocyanate-labeled second antibodies was shown to be present both in the cytoplasm and in the nucleus. Staining of all cellular compartments was abolished (peroxidase antiperoxidase) or diminished (fluorescein isothiocyanate) if the monoclonal antibody was preincubated with a 90% pure GR preparation. These findings are in contrast to recently reported immunocytochemical studies, where a strict nuclear existence of the estrogen and progestin receptors has been reported. Consequently, generalizations with regard to steroid receptor localization cannot be made. Furthermore, an in vitro model is described, where the effect of dexamethasone administration upon the localization of receptor staining in H-4-II-E cells can be studied.

Animals↗

PubMed1986

Effect of oral high-dose progestins on the disposition of antipyrine, digitoxin, and warfarin in patients with advanced breast cancer.

The influence of two progestins, medroxyprogesterone acetate (MPA) and megestrol acetate (MA), given orally in high doses, on the pharmacokinetics of antipyrine, digitoxin, and warfarin were studied in patients with advanced breast cancer. Antipyrine and warfarin were given as a single test dose before and after 5 weeks of progestin treatment. The pharmacokinetics of digitoxin was investigated at steady state in patients receiving this drug therapeutically before and during treatment with progestins. Small changes in clearance rates for antipyrine, warfarin, and digitoxin were found. A minor decrease observed in warfarin clearance however may be of clinical importance. Half-lives decreased by 13% for antipyrine and increased by 71% for warfarin. High-dose progestins given orally do not seem to have a major influence on drug metabolism, probably reflecting a minor effect on drug and steroid-metabolizing microsomal mono-oxygenases in the liver.

Administration, Oral↗

PubMed1986

Glucocorticoid mechanism of action: monoclonal antibodies as experimental tools.

In order to provide a further insight into glucocorticoid receptor (GR)-mediated action of glucocorticoid hormones, we produced ten monoclonal antibodies against rat GR. In studies combining physicochemical separation methods with antibody methodology, we established that the molybdate-stabilised GR contains one steroid-binding monomer. Using a monoclonal anti-GR antibody-based immunoaffinity chromatographic procedure, we purified two non-ligand-binding proteins, with molecular weights of 80,000 and 90,000, present in the molybdate-stabilised GR complex. These proteins are not recognised by monoclonal antibodies directed against GR. The possible relation of these two proteins to heat shock proteins remains to be established. Immunohistochemical studies of GR in the central nervous system of the rat provided new information on the distribution of GR, particularly in the hypothalamus. Studies of intracellular receptor localisation in rat brain after endocrine manipulations gave results in support of the classical concept of translocation of GR from cytoplasm to cell nucleus. Studies with a cell culture system also supported the existence of GR in the cytoplasm as well as in the cell nucleus.

Animals↗

PubMed1986

Cell-mediated inhibition of proliferation and activation of alloreactive cytotoxic lymphocytes: maintenance of response potential of precursors and dissociation between proliferation and effector function of activated cytotoxic lymphocytes.

Adherent layers of macrophages (M phi-c) generated in vitro from splenic precursors inhibit lymphoproliferative responses to mitogen and to alloantigen without inhibiting the production of interleukin-2 (IL-2). Analysis of spleen cells stimulated for 48 hr in the presence of M phi-c indicated that both blastogenesis (increased cell mass) and expression of IL-2 receptors (7D4 determinants) were reduced. Analysis of BrdU incorporation (frequency of S-phase cells) and total cellular DNA revealed that the M phi-c inhibited the progression from G1 to S phase of cell cycle. The M phi-c not only inhibited the proliferative response to alloantigen but also prevented the generation of alloreactive cytotoxic T cells. The M phi-c were shown not to inhibit CTL responses by eliminating the stimulators or by inactivating precursors or inducing suppressors. The M phi-c were affecting the induction of CTL activity since the M phi-c did not affect the expression of cytolytic activity by activated CTL. The M phi-c did inhibit the proliferation of the activated CTL, suggesting that although cytolytic activity can be expressed in G1 phase of cell cycle, the activation of cytolytic activity in CTL-P may require a G1 to S phase transition. The cells recovered from 5-day MLC incubated in the presence of M phi-c were fully capable of generating a subsequent CTL response. This is in contrast to cells recovered from unstimulated cultures (no M phi-c) which have lost the ability to generate CTL responses. The M phi-c therefore prevent the generation of CTL responses in a totally reversible fashion, so as to allow activation and proliferation of CTL-P which have been removed from the influence of the M phi-c. These observations are discussed in the context of the currently hypothesized role of tissue macrophages in microenvironmental regulation.

Animals↗

PubMed1986

Antagonistic effect of glucocorticoids on retinoic acid induced growth inhibition and morphological alterations of a human cell line.

When the human cell line NHIK 3025 was exposed to retinoic acid (1 nM; 10 microM), the cell cycle time was prolonged. Experiments using cells synchronized by mitotic selection showed that the retinoic acid induced growth delay was barely seen within the first cell cycle after exposure to 10 microM retinoic acid, whereas the next cell cycle durations were increased 30-60%. The effect was reversible as normal growth rate was restored after removal of the drug. DNA histograms indicated a prolongation of G1 of the cell cycle. We have shown earlier that glucocorticoid steroids also induce a prolongation of the cell cycle, located within G1. When the cells were exposed to the synthetic glucocorticoid, dexamethasone, in addition to retinoic acid, no additive effect was found; on the contrary, growth inhibition was less than that with retinoic acid alone. Dexamethasone from 1 nM upwards antagonized the growth inhibitory effect of retinoic acid. This glucocorticoid mediated effect seemed to be mediated via the glucocorticoid receptor, as no effect was seen when the receptor was blocked by the antagonist 17 beta hydroxy-11 beta, 4-dimethylaminophenyl-17 alpha-propynyl estra 4,9 diene-3-one [RU 38486]. The growth inhibition studies were supported by morphological observations showing that dexamethasone induced cytoskeletal alterations dominated when the cells were exposed to both drugs simultaneously. These findings might be of importance in cancer therapy where both drugs are used.

Cell Cycle↗

PubMed1985

Human monocyte-released cytotoxic factor. Modulation of cytotoxic activity by inhibitors of cellular DNA, RNA, and protein synthesis.

Human lymphokine-activated monocytes release a cytotoxic protein factor (CF). The cytostatic activity of CF was potentiated by the DNA and RNA synthesis inhibitors actinomycin D, daunomycin, and mitomycin C. These inhibitors increased the sensitivity for detecting CF approximately 10-fold, and this is of great practical value when assaying CF. The CF-potentiating inhibitors had a similar effect on the cell cycle distribution in that they all induced an accumulation of cells in the S and G2 phases of the cell cycle. Cytolytic activity was shown to be associated with CF, and this activity was also greatly potentiated by daunomycin and actinomycin D. The two other inhibitors studied, cycloheximide and 5-fluorouracil (5-FU), had an adverse effect on the cytostatic activity of CF. These two inhibitors reduced the sensitivity of the assay for CF about fivefold. Cycloheximide had no apparent effect on the relative cell cycle distribution, whereas 5-FU induced an accumulation of cells in the G1 phase. Of the inhibitors studied, only those that induced an accumulation of cells in the S and G2 phases of the cell cycle potentiated the cytotoxic activity of CF, suggesting that CF may preferentially act in these parts of the cell cycle.

Cell Cycle↗

PubMed1984

Concentration-dependent effects of potassium dichromate on the cell cycle.

Hexavalent chromium is found to be a strong mutagen, and it also is a potential carcinogen in man. DNA flow cytometry, growth measurements, and determinations of mitotic index show that 1-2 microM K2Cr2O7 produces a prolongation of the G2 phase of the cell cycle in NHIK 3025 cells. By increasing the chromate concentrations (greater than 2 microM K2Cr2O7) the cells are also arrested in G2 phase. We have found, using synchronized cells and measuring cell cycle time, that the most chromate-sensitive part of the cell cycle is S phase. This phase is also somewhat prolonged, and the cells became arrested in early S phase at high toxic K2Cr2O7 concentrations (8 microM). Our results thus indicate that K2Cr2O7 has an effect within S phase--maybe on DNA/RNA synthesis--and also interferes with processes necessary for progression through the G2 phase.

Cell Cycle↗