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N Borregaard

Publications and source records attributed to N Borregaard.

At least 91 records · Page 5Linked to original sources
PubMed1994

Molecular cloning and expression of a cDNA encoding NGAL: a lipocalin expressed in human neutrophils.

NGAL, a protein recently isolated from human neutrophils, is a novel member of the lipocalins. NGAL binds a derivative of the bacterial chemotactic peptide formylmethionyl-leucyl-phenylalanine and may have important immunomodulatory functions. We here report the cloning of a cDNA for NGAL covering a 63 bp 5' untranslated region and the coding region of 591 bp. The cDNA encodes a protein of 197 amino acids, with a 19 amino acid leader sequence and a mature protein of 178 amino acids. Alignment of the cDNA sequence of NGAL to the rat analogue, alpha 2-microglobulin related protein, demonstrates a very high degree of conservation of this lipocalin. Northern blotting of a variety of tissues revealed that NGAL is mainly expressed in myeloid cells, where a signal of approximately 850 bp is observed. A faint signal was observed in fetal and adult human lung tissue. The molecular cloning of the NGAL cDNA allowed the recombinant production of NGAL in E. coli.

Acute-Phase Proteins↗
PubMed1994

Secretory vesicles are the intracellular reservoir of complement receptor 1 in human neutrophils.

The subcellular localization of complement receptor 1 (CR1) was investigated in human neutrophils. CR1 was located exclusively in the light membrane fractions containing secretory vesicles and plasma membranes in Percoll density gradients of unperturbed neutrophils. Separation of plasma membranes from secretory vesicles by high-voltage free-flow electrophoresis of the light membranes from the Percoll gradient revealed that more than 80% of the CR1 was located intracellularly in secretory vesicles. After weak stimulation of neutrophils, the increase in CR1 surface expression closely paralleled both surface increase of known secretory vesicle membrane Ags and the release of matrix proteins from secretory vesicles. More potent stimulation of the neutrophils did not enhance CR1 surface expression further, in agreement with the lack of CR1 in granules as demonstrated on Percoll gradient. CR3 (Mac-1), which has been shown to be located both in secretory vesicles and in neutrophil granules, was up-regulated in parallel with CR1 after weak stimuli, whereas a profound increase of CR3 was observed after more potent stimuli in accordance with granule mobilization. These results identify secretory vesicles as the reservoir of CR1, which translocates to the plasma membrane after weak stimulation, and underscore the functional significance of this recently identified organelle.

Cytoplasmic Granules↗
PubMed1994

Subcellular localization and translocation of the receptor for N-formylmethionyl-leucyl-phenylalanine in human neutrophils.

The subcellular localization of N-formylmethionyl-leucyl-phenylalanine (fMLP) receptors in human neutrophils was investigated. The fMLP receptor was detected with a high-affinity, photoactivatable, radioiodinated derivative of N-formyl-methionyl-leucyl-phenylalanyl-lysine (fMLFK). Neutrophils were disrupted by nitrogen cavitation and fractionated on Percoll density gradients. fMLP receptors were located in the beta-band containing gelatinase and specific granules, and in the gamma-band containing plasma membrane and secretory vesicles. Plasma membranes and secretory vesicles were separated by high-voltage free-flow electrophoresis, and secretory vesicles were demonstrated to be highly enriched in fMLP receptors. The receptors found in secretory vesicles translocated fully to the plasma membrane upon stimulation with inflammatory mediators. The receptor translocation from the beta-band indicated that the receptor present there was mainly located in gelatinase granules. A 25 kDa fMLP-binding protein was found in the beta-band. Immunoprecipitation revealed that this protein was identical with NGAL (neutrophil gelatinase-associated lipocalin), a novel protein found in specific granules. In summary, we demonstrate that the compartment in human neutrophils that is mobilized most easily and fastest, the secretory vesicle, is a major reservoir of fMLP receptors. This explains the prompt and extensive upregulation of fMLP receptors on the neutrophil surface in response to inflammatory stimuli.

Cell Fractionation↗
PubMed1994

Isolation and characterization of gelatinase granules from human neutrophils.

We recently confirmed the existence of gelatinase granules as a subpopulation of peroxidase-negative granules by double-labeling immunogold electron microscopy on intact cells and by subcellular fractionation. Further characterization of gelatinase granules has been hampered by poor separation of specific and gelatinase granules on both two-layer Percoll gradients and sucrose gradients. We have developed a three-layer Percoll density gradient that allows separation of the different granules and vesicles from human neutrophils; in particular, it allows separation of specific and gelatinase granules. This allows us to characterize these two granule populations with regard to their content of membrane proteins, which become incorporated into the plasma membrane during exocytosis. We found that gelatinase granules, defined as peroxidase-negative granules containing gelatinase but lacking lactoferrin, contain 50% of total cell gelatinase, with the remaining residing in specific granules. Furthermore, we found that 20% to 25% of both the adhesion protein Mac-1 and the NADPH-oxidase component cytochrome b558 is localized in gelatinase granules. Although no qualitative difference was observed between specific granules and gelatinase granules with respect to cytochrome b558 and Mac-1, stimulation of the neutrophil with FMLP resulted in a selective mobilization of the least dense peroxidase-negative granules, ie, gelatinase granules, which, in concert with secretory vesicles, furnish the plasma membrane with Mac-1 and cytochrome b558. This shows that gelatinase granules are functionally important relative to specific granules in mediating early inflammatory responses.

Centrifugation, Density Gradient↗
PubMed1994

Identification of neutrophil gelatinase-associated lipocalin as a novel matrix protein of specific granules in human neutrophils.

Neutrophil gelatinase-associated lipocalin (NGAL) is a novel 25-kD protein of human neutrophils, that is in part covalently complexed with neutrophil gelatinase. However, both NGAL and gelatinase exist mainly in forms not associated with each other. An explanation for this phenomenon might be that the unassociated proteins reside in different subcellular compartments. The aim of the present study was to determine the subcellular localization of NGAL. An enzyme-linked immunosorbent assay (ELISA) for NGAL was developed using specific anti-NGAL antibodies. The assay was applied on subcellular fractions of neutrophils obtained after centrifugation of a postnuclear supernatant on a two-layer Percoll gradient. The distribution profile of NGAL was found to colocalize strictly with the distribution profile of lactoferrin. This was confirmed by immunogold double-labeling of frozen thin sections of neutrophils that showed a high degree of colocalization of NGAL and lactoferrin, and by exocytosis experiments, which showed lactoferrin, vitamin B12-binding protein, and NGAL to be similarly released upon stimulation. Therefore, NGAL is a novel matrix protein of specific granules and thus partly segregated from gelatinase, the major part of which is located in a separate compartment, the gelatinase granules. An ELISA specific for the NGAL/gelatinase complex was developed and the subcellular distribution and release of this complex was determined. The distribution and mobilization of the complex allowed us to confirm the existence of differentially mobilized granule subpopulations among peroxidase negative granules.

Acute-Phase Proteins↗
PubMed1994

Changes in subcellular localization and surface expression of L-selectin, alkaline phosphatase, and Mac-1 in human neutrophils during stimulation with inflammatory mediators.

The localization of the adhesion protein L-selectin in human neutrophils was determined by subcellular fractionation and immunoelectron microscopy and compared with the localization of Mac-1 (alpha m beta 2) and alkaline phosphatase, the marker for secretory vesicles. L-selectin was found to be localized exclusively on the plasma membrane of unstimulated cells and also of stimulated cells, although markedly diminished. This was in contrast to Mac-1, which was also localized in secretory vesicles and in specific/gelatinase granules as shown previously [Sengeløv, H., et al. J. Clin. Invest. (1993) 92, 1467-1476]. Stimulation of neutrophils with inflammatory mediators such as tumor necrosis factor (TNF), platelet-activating factor (PAF), or f-Met-Leu-Phe (fMLP), induced parallel up-regulation of the surface membrane content of alkaline phosphatase and Mac-1 and down-regulation of L-selectin, as evidenced by flow cytometry. Preimbedding immunoelectron microscopy confirmed that L-selectin was present mainly on tips of microvilli in unstimulated cells and showed that alkaline phosphatase and Mac-1 were randomly distributed on the surface membrane of fMLP-stimulated cells. These studies indicate that the transition of neutrophils from L-selectin-presenting cells to Mac-1-presenting cells induced by inflammatory mediators is mediated by incorporation of secretory vesicle membrane, rich in Mac-1 and devoid of L-selectin, into the plasma membrane.

Alkaline Phosphatase↗
PubMed1993

Structural and functional heterogeneity among peroxidase-negative granules in human neutrophils: identification of a distinct gelatinase-containing granule subset by combined immunocytochemistry and subcellular fractionation.

The existence of separate gelatinase granules in human neutrophils has been a matter of debate in recent years. We have demonstrated that the 135-kD form of neutrophil gelatinase is a complex of 92-kD gelatinase and a novel 25-kD protein termed neutrophil gelatinase-associated lipocalin (NGAL) that, in addition to being complexed with part of the gelatinase, is localized in free form in peroxidase-negative specific granules. Because this association was not appreciated in earlier studies, we decided to reassess the ultrastructural localization of gelatinase using specific antibodies without immunoreactivity towards NGAL. Double-labeling immunogold electron microscopy was performed on frozen thin sections of human neutrophils. Twenty-four percent of all peroxidase-negative granules were labeled with antigelatinase antibody, but not with antilactoferrin antibody. These granules are defined as gelatinase granules. Sixteen percent reacted with antilactoferrin antibody but not with antigelatinase antibody. The rest (60%) reacted with both antibodies. All granules labeling for lactoferrin are defined as specific granules. Gelatinase granules were observed as round and oval forms of considerably smaller size than specific granules, and were less electron dense. Isolated granules obtained by subcellular fractionation were also examined by immunoelectron microscopy. This demonstrated that peroxidase-negative granules comprise a continuum from the most dense granules that contain lactoferrin but no gelatinase to the lightest that contain gelatinase but no lactoferrin. Thus, gelatinase granules do exist as a subpopulation of peroxidase-negative granules and may allow for exocytosis of gelatinase during neutrophil diapedesis without substantial mobilization of other peroxidase-negative granules, ie, specific granules.

Cytoplasmic Granules↗
PubMed1993

Evidence for small intracellular vesicles in human blood phagocytes containing cytochrome b558 and the adhesion molecule CD11b/CD18.

Human neutrophils contain a rapidly mobilizable pool of so-called secretory vesicles distinct from the azurophil granules and specific granules. Using human albumin as a marker for these intracellular vesicles in immuno-electron microscopy, we found that part of the cytochrome b558 in non-purified whole blood neutrophils colocalized in these vesicles. This was detected with monoclonal antibody (MoAb) CLB-48, binding to the high molecular weight subunit of cytochrome b558. Approximately 65% of the albumin-containing vesicles showed MoAb CLB-48 labeling. This was also found in eosinophilic granulocytes and in monocytes. Cytofluorimetric determination of cytochrome b558 expression on the plasma membrane of intact, nonpurified granulocytes (and monocytes) with MoAb 7D5, which is directed against an extracellular epitope of cytochrome b558, did not show any binding. However, granulocytes (and monocytes) significantly bound 7D5 after density centrifugation. The positive binding of 7D5 to purified neutrophilic granulocytes correlated with a strongly reduced labeling of cytochrome b558 in the albumin-positive vesicles. Binding of CD11b MoAb CLB-B2.12 to the alpha subunit of the complement receptor type 3 (CR3) on the surface of intact, nonpurified neutrophils was detected to a limited extent in whole blood samples, but was strongly increased upon density gradient centrifugation of the cells, as we have described before. Investigation at the ultrastructural level showed that the CD11b antigen codistributed with albumin in vesicular structures in nonpurified phagocytes, especially in neutrophils and eosinophils. Together, these data substantiate the idea of an intracellular store that can be easily mobilized (even under the simple stress condition of density gradient centrifugation). Such mobilization may result in the expression of cytochrome b558 on the plasma membrane, as was indicated in this study. Apart from cytochrome b558, several other surface membrane molecules, as we show here for the integrin CD11b/CD18 (CR3), are probably also located in these rapidly mobilizable intracellular vesicles.

Antibodies, Monoclonal↗
PubMed1993

Isolation and primary structure of NGAL, a novel protein associated with human neutrophil gelatinase.

A 25-kDa protein was found to be associated with purified human neutrophil gelatinase. Polyclonal antibodies raised against gelatinase not only recognized gelatinase but also this 25-kDa protein. Specific antibodies against the 25-kDa protein were obtained by affinity purification of the gelatinase antibodies. Immunoblotting and immunoprecipitation studies demonstrated the 135-kDa form of gelatinase to be a complex of 92-kDa gelatinase and the 25-kDa protein, and the 220-kDa form was demonstrated to be a homodimer of the 92-kDa protein, thus explaining the 220-, 135-, and 92-kDa forms characteristic of neutrophil gelatinase. The 25-kDa protein was purified to apparent homogeneity from exocytosed material from phorbol myristate acetate-stimulated neutrophils. The primary structure of the 25-kDa protein was determined as a 178-residue protein. It was susceptible to treatment with N-glycanase, and one N-glycosylation site was identified. The sequence did not match any known human protein, but showed a high degree of similarity with the deduced sequences of rat alpha 2-microglobulin-related protein and the mouse protein 24p3. It is thus a new member of the lipocalin family. The function of the 25-kDa protein, named neutrophil gelatinase-associated lipocalin (NGAL), remains to be determined.

Acute-Phase Proteins↗
PubMed1993

Control of exocytosis in early neutrophil activation.

Exocytosis of human neutrophil secretory vesicles, gelatinase granules, specific granules, and azurophil granules was measured during modulation of the intracellular free calcium concentration. A strict rank order of exocytosis of the four compartments was observed when cytosolic calcium was elevated by an ionophore in Fura-2-loaded cells. The rank order was: secretory vesicles, gelatinase granules, specific granules, and azurophil granules. Secretory vesicles were exceptionally sensitive to cytosolic free calcium, being completely mobilized after small cytosolic calcium transients. Kinetic studies with FMLP or ionomycin as stimulus showed that the same rank order was valid concerning the rate of exocytosis. In contrast to the other granules, a major part of the secretory vesicles were exocytosed after FMLP stimulation when intracellular calcium was chelated with bis-(2-amino-5-methylphenoxy)-ethane-N,N,N',N'-tetraacetic acid tetraacetoxymethyl ester. These data indicate that, in contrast to other neutrophil granules, secretory vesicles are mobilized completely after small isolated elevations of cytosolic calcium. On the other hand, complete elimination of the FMLP-derived calcium transient does not inhibit exocytosis of secretory vesicles markedly. Thus, the effect of FMLP on secretory vesicles is signaled via cytosolic free calcium and an alternative pathway activated in parallel. This may be the basis for the unique position of this compartment as a readily mobilizable store of components important in early neutrophil activation.

Calcium↗
PubMed1993

Human neutrophil granules and secretory vesicles.

The traditional classification of neutrophil granules as peroxidase-positive (azurophil, or primary) and peroxidase-negative (specific or secondary) has proven to be too simple to explain the differential exocytosis of granule proteins and incorporation of granule membrane into the plasma membrane which is an important aspect of neutrophil activation. Combined subcellular fractionation and immunoelectron microscopy has revealed heterogeneity among both peroxidase-positive and peroxidase-negative granules with regard to their content, mobilization and time of formation. Peroxidase-negative granules may be classified according to their content of lactoferrin and gelatinase: 15% of peroxidase-negative granules contain lactoferrin, but no gelatinase. 60% contain both lactoferrin and gelatinase. The term specific or secondary granule should be reserved for these two subsets. In addition, 25% of peroxidase-negative granules contain gelatinase but no lactoferrin. These should be termed gelatinase granules or tertiary granules. Gelatinase granules are formed later than specific granules and mobilized more readily. In addition, a distinct, highly mobilizable intracellular compartment, the secretory vesicle, has now been recognized as an important store of surface membrane-bound receptors. This compartment is formed in band cells and segmented cells by endocytosis. This heterogeneity among the neutrophil granules is of functional significance, and may also be reflected in the dysmaturation which is an important feature of myeloproliferative and myelodysplastic disorders.

Calcium↗
PubMed1993

Mobilization of granules in neutrophils from patients with myeloproliferative disorders.

Neutrophil granule subsets and dynamics were studied in 4 patients with polycythemia vera/myelofibrosis and 2 patients with chronic myelogenous leukemia. Alkaline phosphatase, a marker for the membrane of secretory vesicles (the most readily mobilizable pool of intracellular membranes in neutrophils) was highly elevated in the PV/MF patients and significantly reduced in the CML patients. In spite of this, the amount of secretory vesicles was normal as judged by the content of albumin, and of the membrane protein cytochrome b-245 and CD11b, both partially localized in secretory vesicles. Gelatinase granules were present in all patients. The azurophil granules were lighter than normal in both CML patients. SDS-PAGE protein profiles indicated absence of defensins from azurophil granules from 1 CML patient. In addition, a 41-42 kD doublet protein band was absent from 2 PV and 1 CML patient, and reduced in the other CML patient. No difference in mobilization of granules was observed between patient neutrophils and control neutrophils. Also, stimulation with 10(-8) mol/l N-formyl-methionyl-leucyl-phenylalanine induced normal increases in intracellular Ca2+ in patient neutrophils. These results indicate that stimulus-response coupling leading to granule exocytosis is intact in neutrophils from patients with myeloproliferative disorders.

Aged↗
PubMed1993

Subcellular localization and dynamics of Mac-1 (alpha m beta 2) in human neutrophils.

The subcellular localization of Mac-1 was determined in resting and stimulated human neutrophils after disruption by nitrogen cavitation and fractionation on two-layer Percoll density gradients. Light membranes were further separated by high voltage free flow electrophoresis. Mac-1 was determined by an ELISA with monoclonal antibodies that were specific for the alpha-chain (CD11b). In unstimulated neutrophils, 75% of Mac-1 colocalized with specific granules including gelatinase granules, 20% with secretory vesicles and the rest with plasma membranes. Stimulation with nanomolar concentrations of FMLP resulted in the translocation of Mac-1 from secretory vesicles to the plasma membrane, and only minimal translocation from specific granules and gelatinase granules. Stimulation with PMA or Ionomycin resulted in full translocation of Mac-1 from secretory vesicles and gelatinase granules to the plasma membrane, and partial translocation of Mac-1 from specific granules. These findings were corroborated by flow cytometry, which demonstrated a 6-10-fold increase in the surface membrane content of Mac-1 in response to stimulation with FMLP, granulocyte-macrophage colony stimulating factor, IL-8, leukotriene B4, platelet-activating factor, TNF-alpha, and zymosan-activated serum, and a 25-fold increase in response to Ionomycin. Thus, secretory vesicles constitute the most important reservoir of Mac-1 that is incorporated into the plasma membrane during stimulation with inflammatory mediators.

Cell Compartmentation↗
PubMed1992

Activation of the oxygen-radical-generating system in granules of intact human neutrophils by a calcium ionophore (ionomycin).

Subcellular fractionation studies were performed on human neutrophils stimulated with ionomycin (a Ca(2+)-specific ionophore). The results of these studies revealed NADPH-oxidase activity, without any additive, both in the plasma membrane and in the specific granule fractions. After comparing these results with the NADPH oxidase activity induced by the ionophore in intact neutrophils, in differentiated HL-60 cells and in neutrophil cytoplasts, we conclude that ionomycin preferentially activates the NADPH oxidase pool located in the membrane of specific granules. Furthermore, we suggest that incorporation of granule membrane into the plasma membrane makes the associated NADPH oxidase less sensitive to activation induced by a rise in [Ca(2+)]i.

Adult↗
PubMed1992

Subcellular localization and release of human neutrophil gelatinase, confirming the existence of separate gelatinase-containing granules.

An e.l.i.s.a. was developed using specific polyclonal rabbit antibodies against human neutrophil gelatinase. This assay, in contrast to the functional assay, is independent of activation of gelatinase, and is specific for the detection of gelatinase in both its reduced and unreduced forms. Using this assay, we were able to demonstrate a difference between the subcellular localization of gelatinase on the one hand, and the subcellular localization of vitamin B-12-binding protein, lactoferrin and cytochrome b558 on the other hand. The latter three co-localized in fractions of slightly higher density than gelatinase on a two-layer Percoll density gradient. Furthermore, the release of gelatinase exceeded the release of vitamin B-12-binding protein as well as lactoferrin by a factor of 3-6 following stimulation with formylmethionyl-leucyl-phenylalanine, leukotriene B4 and other soluble stimuli. Thus, although gelatinase has previously been found to co-localize with lactoferrin on immuno-electron microscopy, we confirm the existence of gelatinase-rich and lactoferrin- and vitamin B-12-binding-protein-poor granules, that are lighter and mobilized more easily than specific granules. These gelatinase-containing granules are not the store of cytochrome b558.

Cytoplasmic Granules↗
PubMed1992

Separation of human neutrophil plasma membrane from intracellular vesicles containing alkaline phosphatase and NADPH oxidase activity by free flow electrophoresis.

A putative reservoir of functional plasma membrane proteins, the secretory vesicle identified by latent alkaline phosphatase and tetranectin, has previously been demonstrated based on indirect evidence (Borregaard, N., Miller, L. J., and Springer, T. A. (1987) Science 237, 1204-1206; Borregaard, N., Christensen, L., Bjerrum, O. W., Birgens, H. S., and Clemmesen, I. (1990) J. Clin. Invest. 85, 408-416). Difficulties in separating plasma membranes from this entity by density gradient centrifugation has prohibited discriminative dynamic and quantitative studies of secretory vesicles and plasma membranes. By combining density centrifugation with free flow electrophoresis we overcame this obstacle. Freshly prepared unperturbed human neutrophils were subjected to nitrogen cavitation followed by density centrifugation on Percoll gradients. Light membrane fractions containing plasma membranes and secretory vesicles were applied to high voltage free flow electrophoresis on an Elphor VaP 22. Plasma membrane vesicles, identified by HLA class I antigen mixed enzyme-linked immunosorbent assay (Bjerrum, O. W., and Borregaard, N. (1990) Scand. J. Immunol. 31, 305-313) and 125I applied to cells before cavitation, were clearly separated from secretory vesicles. Electron microscopy revealed a morphology typical of plasma membranes in the former fraction and a population of vesicles with markedly different appearance in the latter. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles demonstrated distinct differences in protein patterns between the two fractions. Superoxide generating capacity induced by sodium dodecyl sulfate and cytosol, an entity traditionally ascribed to the plasma membrane, was largely confined to fractions containing secretory vesicles. Thus, the majority of membrane-bound NADPH oxidase components of light membranes of human neutrophils colocalize with secretory vesicles.

Alkaline Phosphatase↗
PubMed1992

Ca(2+)-dependent translocation of cytosolic proteins to isolated granule subpopulations and plasma membrane from human neutrophils.

In order to identify cytosolic proteins involved in control of granule exocytosis in human neutrophils, subcellular fractions enriched in each of the 3 major granule subsets were incubated with cytosol from neutrophils in the presence or absence of Ca2+. After washing, proteins were eluted from the organelles by EGTA. Annexins I, II, IV and VI were found to bind to all organelles studied. In addition, a 28-kDa protein was found to bind exclusively to plasma membranes and secretory vesicles, the most readily exocytosed organelle of neutrophils. Ca(2+)-dependent association of cytosolic proteins to different granule subsets may control differential exocytosis of granules.

Biological Transport, Active↗