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Subcellular localization of 3 alpha, 7 alpha-dihydroxy- and 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoyl-coenzyme A ligase(s) in rat liver.

Liver peroxisomes from both rat and humans have previously been shown to contain enzymes that catalyze the oxidative cleavage of the C27-steroid side chain in the formation of bile acids. It has not been clear, however, whether the initial step, formation of the CoA-esters of the 5 beta-cholestanoic acids, also occurs in these organelles. In the present work the subcellular localization of 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoyl-CoA (THCA-CoA) ligase (THCA-CoA synthetase) and of 3 alpha,7 alpha-dihydroxy-5 beta-cholestanoyl-CoA (DHCA-CoA) ligase in rat liver has been investigated. Main subcellular fractions and peroxisome-rich density gradient fractions from rat liver were incubated with THCA or DHCA, CoA, ATP, and Mg2+. Formation of THCA-CoA and DHCA-CoA was determined after high pressure liquid chromatography of the incubation extracts. The microsomal fraction contained the highest specific (and also relative specific) activity both for the formation of THCA-CoA and DHCA-CoA. The rates of THCA-CoA formation were further increased from 124-159 nmol/mg.hr-1 in crude microsomal fractions to 184-220 nmol/mg.hr-1 when studied in purified rough endoplasmic reticulum fractions. Formation of THCA-CoA in peroxisomal fractions prepared in Nycodenz density gradients could be accounted for by a small contamination (3-7%) by microsomal protein. The distribution of THCA-CoA ligase was different from that of palmitoyl-CoA ligase that was found to be localized also to the peroxisomal fractions.

Animals

Subcellular localization of immunoreactive thyroid-stimulating hormone in the rat hypothalamus.

Hypothalamic tissue contains TSH-like material which is biologically, immunologically, and physicochemically similar to pituitary TSH. Immunoreactive thyroid-stimulating hormone (IR-TSH) is released from hypothalamic tissue in vitro by depolarizing concentrations of potassium or veratridine by a calcium-dependent mechanism. In the present study, we investigated the subcellular localization of IR-TSH using equilibrium density centrifugation. Tissue homogenates from intact, hypophysectomized or thyroidectomized rats were centrifuged at 150 g at 4 degrees C for 10 min and the supernatants were layered onto continuous sucrose gradients (1.00-1.27 g/ml) and centrifuged at 100,000 g (max) for 16 h. IR-TSH in pituitary supernatants from intact and thyroidectomized rats showed high equilibrium density peaks with a modal density around 1.2 g/ml. Fractionation of the supernatant from ventral or dorsal hypothalamic homogenates resulted in a bimodal distribution of IR-TSH. In supernatants from both tissues, IR-TSH containing particles were found at the top of the gradient in a low equilibrium density peak between 1.0 and 1.08 g/ml. In addition, IR-TSH containing particles were found in ventral and dorsal hypothalamic supernatants with modal densities at 1.16 and 1.25, respectively. These high density IR-TSH particles were present in tissue taken from hypophysectomized rats, and were not appreciably affected by thyroidectomy. Homogenization of the tissue in a hypo-osmotic medium disrupted the high density IR-TSH particles resulting in a single low density peak at the top of the gradient. These data suggest that hypothalamic IR-TSH is stored in membrane bound particles which have densities similar to that of secretory granules.

Animals

Subcellular localization of N-acetylglucosaminide beta 1----4 galactosyltransferase revealed by immunoelectron microscopy.

We prepared a monoclonal antibody (MAb) against N-acetylglucosaminide beta 1----4 galactosyltransferase purified from F9 embryonal carcinoma cells. The MAb recognized the protein portion of the enzyme, since it inhibited galactosyltransferase activity, reacted with the enzyme both from F9 cells and from bovine milk, and did not exhibit anti-carbohydrate activity. Using this MAb, we studied the subcellular localization of the enzyme by immunoelectron microscopy. Intense staining was observed in trans-Golgi stacks within testicular interstitial cells and mucous neck cells, confirming the specificity of the immunological reaction. Cell surface galactosyltransferase was detected in the following regions: cultured cells such as F9 embryonal carcinoma cells, testicular interstitial cells, seminiferous tubule epithelial cells, Sertoli cells, the head of the epididymal sperm, epididymal epithelial cells, and apical surfaces of epithelial cells in the fundic gland and of intestinal goblet cells. The use of Triton X-100 intensified the cell surface immunoreactivity, and in certain cases the mode of distribution of the cell surface enzyme was different from that described in previous reports. In addition, nuclear envelopes of cultured cells were distinctly stained. The possible significance of the latter finding is discussed in relation to recent advances in nuclear localization of glycoproteins.

Animals

Melanin-concentrating hormone-like immunoreactive material in the rat hypothalamus; characterization and subcellular localization.

Melanin-concentrating hormone (MCH) is a neurosecretory peptide that induces melanin concentration within teleost melanophores. Here, we characterized MCH-like substance in the rat brain by both an in vitro fish-scale melanophore bioassay and a radioimmunoassay with a salmon MCH antiserum that is directed toward the carboxy-terminus and requires the cyclic configuration for recognition. Furthermore, subcellular localization of the MCH in the rat brain was examined by immunocytochemistry using electron microscopy. We confirmed that MCH-immunoreactivity and MCH-bioactivity were present together in the same effluent fractions of the rat hypothalamic extracts by reverse-phase high-performance liquid chromatography (HPLC). At electron microscopic level, MCH-immunoreactivity was located specifically in secretory granules in MCH-positive cell bodies confined to the hypothalamus with their neuronal processes projecting widely in the rat brain. Although full characterization of substance must await its isolation, our results strongly support the notion that rat MCH-like substance may be homologous but not identical to salmon MCH, and simultaneously may serve some neurotransmitter and/or neuromodulator role in the brain of the rat.

Animals

Distribution and subcellular localization of surfactant-associated glycoproteins in human lung.

Human surfactant contains lung-specific, high molecular weight glycoproteins which are composed of disulfide-linked 34-kilodalton peptide subunits. We prepared antibodies to both isolated HMW glycoproteins and 34-kilodalton peptides and tested the antisera for specificity with immunochemical procedures. In the present study we have investigated the cellular distribution and subcellular localization of these glycoproteins in surgically excised human lung tissue with or without type II cell hyperplasia. An immunoperoxidase technique was used, and cytoplasmic staining reflecting labeling with antibodies to either high molecular weight glycoproteins or the 34-kilodalton peptide subunits was consistently observed in normal type II cells, Clara cells, and some alveolar macrophages and was more intense and diffuse in hyperplastic type II cells. The ultrastructural localization of surfactant-associated glycoproteins was investigated using the periodate-lysine-paraformaldehyde fixative and a peroxidase-labeled antibody technique. In both normal and proliferating type II cells the staining was localized in the rough endoplasmic reticulum, perinuclear cisternas, vesicles of the Golgi complex, vesicles and lamellar membranes of the multivesicular bodies, and some multivesicular body-lamellar body forms. In addition, staining was frequently found in peripheral portions of partially preserved lamellar bodies including those at the stage of secretion, as well as in association with of alveolar tubular myelin. Labeling was also observed in the rough endoplasmic reticulum of Clara cells. We conclude that antibodies against human surfactant-associated glycoproteins are markers for normal and regenerating type II cells, as well as for Clara cells which apparently retain limited ability to produce surfactant-associated glycoproteins independently of surfactant phospholipids. The results indicate that, in type II cells, synthesis and secretion of these glycoproteins involve the same cytoplasmic organelles that are responsible for synthesis, packaging, storage, and exocytosis of surfactant phospholipids. However, maturation of the lamellar bodies, known to be characterized by progressive accumulation of phospholipids, may not require parallel storage of surfactant-associated glycoproteins within the entire lamellar body compartment.

Aged

CDC46/MCM5, a yeast protein whose subcellular localization is cell cycle-regulated, is involved in DNA replication at autonomously replicating sequences.

Saccharomyces cerevisiae cells containing mutations in the cell-division-cycle gene CDC46 arrest with a large bud and a single nucleus with unreplicated DNA at the non-permissive temperature. This G1/S arrest, together with the increased rates of mitotic chromosome loss and recombination phenotype, suggests that these mutants are defective in DNA replication. The subcellular localization of the CDC46 protein changes with the cell cycle; it is nuclear between the end of M phase and the G1/S transition but is cytoplasmic in other phases of the cell cycle. Here we show that CDC46 is identical to MCM5, based on complementation analysis of the mcm5-1 and cdc46-1 alleles, complementation of the minichromosome maintenance defect of mcm5-1 by CDC46, and the genetic linkage of these two genes. Like mcm5-1, cdc46-1 and cdc46-5 also show a minichromosome maintenance defect thought to be associated with DNA replication initiation at autonomously replicating sequences. Taken together, these observations suggest that CDC46/MCM5 acts during a very narrow window at the G1/S transition or the beginning of S phase by virtue of its nuclear localization to effect the initiation of DNA replication at autonomously replicating sequences.

Amino Acid Sequence

Chain elongation of fatty acids in rat small intestine: subcellular localization and effects of clofibrate and partially hydrogenated fish oil.

Clofibrate treatment was found to increase by a factor of two the activity of malonyl-CoA-dependent palmitic acid chain elongation in crude 'microsomal' fractions isolated from rat small intestine. A slight stimulation was indicated also after feeding a high fat diet containing partially hydrogenated fish oil (PHFO). This effect was, however, not statistically significant. Subcellular localization of this chain elongation activity was studied by Nycodenz gradient centrifugation. Chain elongation of palmitic acid was observed only in fractions containing high esterase activity, suggesting a microsomal localization. Similar distributions were seen after feeding the peroxisomal proliferators clofibrate and PHFO. Chain-shortening activity was found in the fractions containing high catalase activity, confirming our earlier studies suggesting a peroxisomal localization of this activity also in rat small intestine.

Acetyltransferases

Subcellular localization of monoamine oxidase in bovine thalamus tissue using immunoferritin conjugates.

A combination of discontinuous sucrose gradient analysis and polyacrylamide electrophoresis was used to isolate one of the multiple forms of monoamine oxidase (MAO) from bovine thalamus. This substance (the principle form and the most anodic of the five MAO forms observed) was used as a basis for an immunoferritin-electron microscope approach to determine the subcellular localization of MAO in thalamus. This form of MAO, as well as antigenically related forms, was found to reside mainly on the outer mitochondrial membrane. In addition, the action of SDS on solubilization and interconversion of MAO forms was studied and found to be dependent on the concentration and time of reaction of SDS with thalamus tissue.

Animals

Human platelet-derived mitogens. II. Subcellular localization of insulinlike growth factor I to the alpha-granule and release in response to thrombin.

Platelets contain mitogenic activities for MCF-7 human breast cancer cells when assayed under serum-free chemically defined conditions. Purification from outdated human platelets identified insulinlike growth factor I (IGF-I) as the most potent breast cancer cell mitogen in lysates (Karey KP, Sirbasku DA: see accompanying article, this issue). In this study the release and subcellular localization of IGF-I was investigated. Degranulation of platelets by thrombin treatment caused release of lysosomal enzymes (beta-glucuronidase and N-acetyl-D-glucosaminidase), alpha-granule proteins (beta-thromboglobulin and fibrinogen) as well as mitogenic activity for MCF-7 cells and IGF-I as measured by radioimmunoassay (RIA) and radioreceptor assay. Release of mitogenic activity and immunologically identified IGF-I was induced tenfold over controls by thrombin and was nearly complete as compared to platelets disrupted by repeated freezing and thawing. Disruption of platelets by nitrogen cavitation followed by separation of the organelles by sucrose density gradient sedimentation showed that IGF-I and mitogenic activity localized predominantly to fractions containing alpha-granules rather than soluble cellular components, lysosomes, or dense granules. The morphology of MCF-7 cells in serum-free medium supplemented with supernatants from thrombin-treated platelets also indicated the release of important cell-adhesion factors for human breast cancer cells.

Blood Platelets

Conversion of alkylacetylglycerol to platelet-activating factor in HL-60 cells and subcellular localization of the mediator.

A human promyelocytic leukemia (HL-60) cell line was used to investigate the conversion of 1-alkyl-2-acetyl-sn-glycerol (alkylacetyl-G) to platelet-activating factor (PAF; 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine) by intact cells and in subcellular fractions in order to examine the fate of PAF synthesized de novo. Lipid extracts obtained from undifferentiated HL-60 cells incubated with [3H]alkylacetyl-G contained 2-4% of the label as [3H]PAF; several related metabolites were also detected. The yield of [3H]PAF could be dramatically increased by pretreating the cells with either oleic acid, an activator of CTP:phosphocholine cytidylyltransferase, or phenylmethylsulfonyl fluoride, an inhibitor of PAF acetylhydrolase. These results, together with a kinetic study of [3H]alkylacetyl-G metabolism, indicate the sequential participation of a cholinephosphotransferase for the conversion of [3H]-alkylacetyl-G to PAF and acetylhydrolase and transacylase activities in the remodeling pathway that metabolize the newly formed [3H]PAF to 1-[3H]alkyl-2-acyl(long chain)-sn-glycero-3-phosphocholine. The dithiothreitol-insensitive cholinephosphotransferase activity capable of converting alkylacetyl-G to PAF was localized in subcellular fractions that contain CDP-choline:1,2-dioleoyl-sn-glycerol cholinephosphotransferase (dithiothreitol-sensitive), as well as marker enzyme activities for the endoplasmic reticulum and Golgi membranes. Subcellular localization analyses also indicated that the majority of newly formed [3H]PAF and a large portion of its deacetylated metabolite were associated with the plasma membrane-containing fractions, whereas most of the 1-[3H]alkyl-2-acyl(long chain)-sn-glycero-3- phosphocholine was present in the intracellular organelles. Incubations of HL-60 cells with exogenous [3H]PAF produced a similar subcellular distribution of metabolites. Very little (less than 10%) of the [3H]PAF produced from [3H]alkylacetyl-G was released from intact cells under a variety of incubation conditions but 50% of the de novo-derived mediator was recovered in the medium of cells that were permeabilized with saponin. Our results indicate that PAF is rapidly translocated from its intracellular site of enzymatic synthesis to the plasma membrane where it is apparently sequestered in a pool that is not accessible to extracellular acceptors in contact with intact cells.

Cell Line

Subcellular localization and dynamics of components of the respiratory burst oxidase.

Membrane and cytosolic factors cooperate to generate NADPH-oxidase. The study of the syndrome of NADPH-oxidase deficiencies, chronic granulomatous disease, has enabled the identification of two membrane factors: a flavin adenine dinucleotide flavoprotein and a b cytochrome. The nature of the cytosolic components is still unknown, but a 47-kD protein, whose phosphorylation occurs in parallel with the generation of a respiratory burst in intact cells, seems to be one of the cytosolic factors. The subcellular localization of the membrane-bound NADPH-oxidase components has been studied in neutrophils: In unstimulated cells, only a minute fraction of the NADPH-oxidase components is localized in the plasma membrane, whereas approximately 80% is localized in the membrane of the specific granules and the majority of the rest is in a newly described membrane-bound compartment, the secretory granules, identified by latent alkaline phosphatase. During stimulation, these NADPH-oxidase components are translocated to the plasma membrane as a result of fusion of granule membrane with plasma membrane. Only the NADPH-oxidase components present in the plasma membrane are incorporated in the respiratory burst oxidase generated in intact cells.

Animals

Subcellular localization of rev-gene product in visna virus-infected cells.

The 1.4-kb mRNA of visna lentivirus is expressed early during the lytic infection of sheep choroid plexus cell cultures. It encodes for visna early gene 1 (VEG1) product, since renamed rev gene product (or Rev), based on significant amino acid sequence homologies between this protein and the proteins of simian immunodeficiency virus of macaque and human immunodeficiency virus type 2. In this report, we examined the subcellular localization and time course appearance of the Rev protein in visna virus-infected cells. Immunoprecipitation assays of [35S]methionine-labeled cell lysates with antisera raised against the Rev protein revealed a polypeptide of 19 kDa (p19rev). This protein was predominant early in the viral replication cycle and accumulated preferentially in the cytoplasmic/membrane fraction of infected cells. Indirect immunofluorescence staining of infected cells confirmed the cytoplasmic location of visna Rev protein and could reveal in some stained cells a higher concentration of Rev at the cellular plasma membrane. The regulating protein, still present late in the viral lytic cycle, is packaged into mature viral particles along with the structural gag and env gene products.

Animals

Surfactant protein D: subcellular localization in nonciliated bronchiolar epithelial cells.

Surfactant protein D (SP-D, CP4) is a collagenous surfactant-associated carbohydrate binding protein that was initially characterized as a biosynthetic product of type II pneumocytes. Immunoperoxidase studies of formaldehyde solution-fixed and paraffin-embedded rat lung demonstrated staining for SP-D in the cytoplasm of a subpopulation of bronchiolar epithelial cells as well as type II cells. Accordingly, immunogold-labeling techniques were used to further examine the cellular distribution and subcellular localization of SP-D in the small airways. Lung tissues were fixed with 0.5% glutaraldehyde-3% paraformaldehyde and embedded in LR White resin. Sections were reacted with affinity purified polyclonal antibodies to SP-D, and sites of antibody binding were demonstrated using a biotinylated secondary antibody-streptavidin-gold detection system. Anti-SP-D selectively decorated secretory compartments of nonciliated bronchiolar cells (Clara cells) with strong and specific labeling of apical electron-dense secretory granules. Almost all of the granules in nonciliated columnar cells were labeled; however, labeling was typically nonuniform, with preferential decoration of the periphery of the granule. The largest numbers of immunoreactive epithelial cells were observed in the distal membranous bronchioles, with progressively smaller numbers of cells in more proximal bronchioles. There was no detectable labeling of cells lining the large cartilagenous airways or trachea. These studies provide evidence that SP-D is a secretory product of nonciliated bronchiolar cells. We suggest that Clara cell-derived SP-D is a component of bronchiolar lining material, consistent with our hypothesis that SP-D contributes to surfactant metabolism and/or host defense within small airways.

Animals

Subcellular localization of [3H]-nitrendipine binding sites in guinea-pig ileal smooth muscle.

The binding of [3H]-nitrendipine was studied in microsomal fractions isolated from guinea-pig ileal smooth muscle. Only one class of specific binding sites was detected, with a KD of 0.4 nM. For various dihydropyridine derivatives, including the stereoisomers of nimodipine and the 'Ca agonist' Bay K 8644, the potency for inhibition of [3H]-nitrendipine binding correlated well with the reported pharmacological potency in smooth muscle preparations. To establish the subcellular localization of [3H]-nitrendipine binding sites, untreated and digitonin-treated microsomal fractions were subfractionated by isopycnic density gradient centrifugation. The density distribution of [3H]-nitrendipine binding was markedly shifted by digitonin towards higher densities, as were the distributions of 5'-nucleotidase and [3H]-ouabain binding, whereas the distributions of NADPH:cytochrome c reductase and NADH:cytochrome c reductase were hardly modified by digitonin. It is concluded that most, if not all, [3H]-nitrendipine binding sites in guinea-pig ileal smooth muscle are present in the plasma membrane, in agreement with the postulated mode of action of dihydropyridines as inhibitors of plasmalemmal Ca channels.

5'-Nucleotidase

Subcellular localization and immunological detection of proteins encoded by the vir locus of Bordetella pertussis.

The DNA sequence of the central regulatory locus vir of Bordetella pertussis predicts that three gene products, BvgA, BvgB, and BvgC, are encoded. Features of the predicted primary structures of these proteins and their homology to other two-component systems suggest that BvgA is located in the cytoplasm, BvgB is located in the periplasm, and BvgC spans the inner membrane. We have used gene fusions to the phoA and lacZ genes of Escherichia coli to investigate the subcellular localization and membrane topology of these proteins. PhoA fusion proteins were also purified and used to raise antibodies that allowed visualization of the vir-encoded polypeptides by Western immunoblotting. Our results have largely confirmed the predictions of the DNA sequence, with the exception that BvgB and BvgC were found to constitute one larger protein that was homologous to the sensor class of two-component systems. We propose that this protein be named BvgS (for sensor) and that its gene be named bvgS.

Amino Acid Sequence

Identification, subcellular localization, and estrogen regulation of peroxidase in 7,12-dimethylbenz(a)anthracene-induced rat mammary tumors.

An estrogen-induced, intensely staining peroxidase 3,3-diaminobenzidine-positive reaction product is found to be characteristic of hormone-dependent, 7,12-dimenthylbenz(a)anthracene-induced mammary tumors of the rat. This product is demonstrated in thick sections of such tumors from intact or estrogen-treated castrate rats but is not seen in tumors that are in regression due to castration or estrogen deprivation. It is, furthermore, absent from tumors whose growth is unaffected by castration. The subcellular localization of this enzyme activity is restricted mainly to the nuclear envelope and cisternae of the granular endoplasmic reticulum in addition to secretory granules. This provides the first evidence for a criterion that would allow differentiation of hormone-dependent and hormone-independent mammary cancer on histological sections and, as such, may have considerable potential as an aid in the classification of human breast cancer.

Animals

Subcellular localization of hematoporphyrin derivative in bladder tumor cells in culture.

Mitochondria have been implicated as a primary subcellular site of porphyrin localization and photodestruction. However, other organelles including the cell membrane, lysosomes and nucleus have been shown to be damaged by hematoporphyrin derivative (HpD) photosensitized destruction as well. In this study we attempted to follow the translocation of the fluorescent components of HpD in human bladder tumor cells (MGH-U1) in culture to determine whether specific subcellular localization occurs over time. Following a 30 min exposure to HpD the cellular fluorescence was examined immediately and 1, 2, 4, and 24 h after HpD removal using fluorescence microscopy and an interactive laser cytometer. The in vitro translocation of dye appeared to be fairly rapid with fluorescence present at the cell membrane and later (1-2 h) within a perinuclear area of the cytoplasm. To determine whether HpD had become concentrated into a specific subcellular organelle, these fluorescence distribution patterns were compared with fluorescent marker dyes specific for mitochondria, endoplasmic reticulum and other membranous organelles. The HpD fluorescence did not appear to be as discrete as the dyes specific for mitochondria or endoplasmic reticulum but appeared similar to the diffuse cytomembrane stain. Finally, the interaction between the fluorescent components of HpD and the cellular constituents was evaluated using a "fluorescence redistribution after photobleaching" technique. The results indicated that the mean lateral diffusion for HpD in MGH-U1 cells was 1.05 x 10(-8) cm2/s, a rate closer to that of lipid diffusion (10(-8)) than that of protein diffusion (10(-10)).(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Line

Purification, characterization, and subcellular localization of an acid phosphatase from black mustard cell-suspension cultures: comparison with phosphoenolpyruvate phosphatase.

An acid phosphatase from Brassica nigra (black mustard) leaf petiole cell-suspension cultures has been purified 1633-fold to a final specific activity of 1225 (mumols orthophosphate produced/min)/mg protein and near homogeneity. The native protein was a glycosylated monomer having a molecular mass of 60 kDa and a pI of 4.5. The enzyme displayed a broad pH optimum of about pH 5.6 and was heat stable. The final preparation hydrolyzed a wide variety of phosphate esters. The highest specificity constants were obtained with 3-phosphoglycerate, 2,3-diphosphoglycerate, PPi, and phosphoenolpyruvate (PEP). The enzyme was activated 1.4-fold by 4 mM Mg2+ or Mn2+, but was strongly inhibited by Mo, Pi, F, and several phosphorylated compounds. Subcellular localization experiments revealed that this nonspecific acid phosphatase is probably a secreted enzyme, localized in the cell wall. By contrast, B. nigra PEP phosphatase appeared to be localized in the cell vacuole. Peptide mapping via CNBr fragmentation was employed to investigate the structural relatedness of the two phosphatases. Their respective CNBr cleavage patterns were dissimilar, suggesting that B. nigra acid and PEP phosphatases are distinct polypeptides. Putative metabolic functions of these two phosphatases are discussed in relation to the biochemical adaptations of B. nigra cell-suspension cultures to nutritional phosphate deprivation.

Acid Phosphatase