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PubMed1992

Characterization of the mammary hyperplasia, dysplasia and neoplasia induced in athymic female adult mice by polyomavirus.

We have characterized mammary oncogenesis induced after polyomavirus infection of adult female nude mice regarding histopathogenesis, viral replication and viral and cellular oncogene expression. A unique transient generalized epithelial hyperplasia was observed (starting at 2 weeks post infection), preceding the development of dysplasias (onset 6 weeks post infection) and multiple neoplasias (onset 6 weeks post infection) in all glands. The ductal epithelium was the target for neoplastic transformation, and the occurrence of numerous ductal dysplasias coincided with the appearance of frank tumors. Stromal abnormalities were also seen. Tumor growth was not dependent upon ovarian hormones, and new tumors continued to develop in ovariectomized mice. Viral replication, high although variable, preceded but did not correlate with oncogenesis. Most but not all tumors contained high levels of unintegrated viral DNA. Tumors produced very low levels of live virus. Viral gene expression was markedly increased in the tumors compared with the infected but morphologically normal glands. The expression of c-myc was moderately increased (fourfold); changes in c-int-2 and c-Ha-ras expression were slight and inconsistent, while expression of c-neu and c-int-1 was unchanged.

Animals↗
PubMed1992

Novel leukocyte agonists are released by endothelial cells exposed to peroxide.

Reactive oxygen species do not activate isolated neutrophils, yet in vivo, such oxidants promote their adhesion to, and subsequent migration through, the vascular wall. We show human endothelial cells exposed to t-butylhydroperoxide shed large, sealed membrane vesicles that contained potent neutrophil agonists. This activity migrated on TLC like platelet-activating factor (PAF). Since neutrophils have a receptor for this phospholipid, which recognizes its unique characteristics including the short sn-2 acetyl residue, we examined the effect of PAF receptor antagonists and PAF acetylhydrolase on this activity. Structurally unrelated PAF receptor antagonists blocked neutrophil stimulation by vesicular phospholipids, and digestion with PAF acetylhydrolase, which is specific for short sn-2 residues, destroyed this activity. However, metabolic labeling, inhibition of synthesis, phospholipase A1 digestion, and high performance liquid chromatographic studies demonstrated that the vesicles did not contain PAF. Instead, the bioactivity migrated on high performance liquid chromatography like the phospholipids generated by oxidative fragmentation of synthetic arachidonoyl phosphatidylcholine that we have shown previously (Smiley, P. L., Stremler, K. E., Prescott, S. M., Zimmerman, G. A., and McIntyre, T. M. (1991) J. Biol. Chem. 266, 11104-11110) to stimulate neutrophils through their receptor for PAF. Thus, peroxide treatment of endothelial cells fragments cellular phosphatidylcholines, forming novel PAF-like phospholipids, and induces the shedding of membrane vesicles that contain these bioactive phospholipids.

Cell Adhesion↗
PubMed1992

Basic fibroblast growth factor modulates the mitogenic potency of the platelet-derived growth factor (PDGF) isoforms by specific upregulation of the PDGF alpha receptor in vascular smooth muscle cells.

Platelet-derived growth factor AA (PDGF AA), in contrast to PDGF AB and BB, is a poor mitogen for smooth muscle cells (SMC). However, together with basic fibroblast growth factor (bFGF) it acts synergistically on DNA synthesis of these cells. Northern blot analysis revealed that bFGF selectively increases the PDGF-receptor alpha subtype (PDGF-R alpha) mRNA level without a significant effect on the PDGF-R beta mRNA level. The amount of PDGF-R alpha protein is also selectively increased after stimulating SMC with bFGF as shown by immunoprecipitation of lysates from SMC with anti-PDGF-R alpha antibodies. The number of binding sites for 125I-PDGF AA is more than doubled after bFGF-treatment, whereas the specific binding for PDGF AB and BB increased only by approximately 30 and 20%, respectively. The increase in the number of PDGF-R alpha renders the SMC responsive for PDGF AA as demonstrated by the induction of the proto-oncogene c-fos as well as by an increased cell proliferation. The enhanced PDGF binding after bFGF treatment may in fact explain the observed synergistic behavior. These data are discussed with regard to a possible role of growth factor-induced transmodulation of receptor expression during atherogenesis.

Animals↗
PubMed1992

Regulation of the 5-hydroxytryptamine1B receptor in opossum kidney cells after exposure to agonists.

The density of 5-hydroxytryptamine (5-HT)1B receptors and their coupling to the inhibition of cAMP accumulation were investigated in opossum kidney cells maintained in culture. The density and properties of the receptor were determined using [125I] iodocyanopindolol as the radioligand. The pharmacological specificity of the binding site was consistent with that expected for a 5-HT1B receptor. Serotonin inhibited forskolin-stimulated cAMP accumulation with an EC50 of 4-8 nM. Compounds known to show selectivity at the 5-HT1B receptor, such as trifluoromethyl-phenylpiperazine and CGS-12066B, also inhibited forskolin-stimulated cAMP accumulation, acting as full agonists with efficacies comparable to that of serotonin. Other beta-adrenergic receptor antagonists, including (-)-pindolol and (-)-alprenolol, bound to the receptor with high affinity and acted as partial agonists capable of inhibiting forskolin-stimulated cAMP accumulation. Exposure of cells to 5-HT resulted in a time- and dose-dependent decrease in the density of 5-HT1B receptors that was not accompanied by a change in the Kd of the binding site for [125I] iodocyanopindolol. A maximum decrease of 60% in the number of 5-HT1B receptors was evident after a 16-hr treatment with 1 microM 5-HT. Concomitant with the observed decrease in the density of receptors was a marked increase in the EC50 for 5-HT-mediated inhibition of forskolin-stimulated cAMP accumulation. The EC50 was increased 4-5-fold after a 16-hr exposure to 1 microM 5-HT, and the maximal level of inhibition was markedly decreased. Whereas pretreatment with moderate concentrations of 5-HT (100-300 nM) for 16 hr produced significant decreases in the density of 5-HT1B receptors and increases in the EC50 for inhibition of forskolin-stimulated cAMP formation, there was little change in the maximal level of inhibition that could be attained. Such a combination of changes could be explained by the presence of "spare" 5-HT1B receptors on these cells.

Animals↗
PubMed1992

Seizures and the regulation of astroglial gene expression.

Seizures are known to induce dramatic alterations in neuronal gene expression. These changes may play a role in the genesis of an epileptic state. The present report describes another consequence of seizures-a dramatic induction of glial fibrillary acidic protein (GFAP) expression in astrocytes. Using a hippocampal kindling model, we demonstrate that kindled seizures lead to many fold increases in mRNA for GFAP in structures which experience electrographic seizures. The increases can be detected 1 day following a single seizure. If seizures are induced repetitively (every other day for many days), levels of GFAP mRNA remain elevated. However, when kindled seizures are not induced, levels of GFAP mRNA return to near control levels within a few days. The increases in GFAP mRNA levels are not in response to decreases in neuronal activity (as a result of postictal depression), because GFAP mRNA levels are unaffected when neuronal activity is decreased by blocking afferent drive (with tetrodotoxin). The induction of GFAP expression by seizures may reflect the first step in a process in which seizures induce astrocytic hypertrophy. The changes in astrocytes could in turn modify the way in which astrocytes maintain homeostasis in the extracellular microenvironment in ways that could contribute to the development of an epileptic state.

Animals↗
PubMedDate not supplied

Upregulation of HLA class II, but not intercellular adhesion molecule 1 (ICAM-1) by granulocyte-macrophage colony stimulating factor (GM-CSF) or interleukin-3 (IL-3) in synergy with dexamethasone.

In this study we have compared the effects of granulocyte macrophage colony stimulating factor (GM-CSF) on purified normal blood monocytes, with two other haemopoietic growth factors, Interleukin (IL-) 3 and Macrophage (M-)CSF on HLA class I, class II and intercellular adhesion molecule 1 (ICAM-1) expression in the presence and absence of dexamethasone (Dex). IL-3 alone, like GM-CSF, was a weak inducer of HLA class II expression but in combination with Dex markedly enhanced HLA-DR, DP and DQ expression. Similar changes were observed for HLA class I expression. The response to both IL-3 and GM-CSF was not additive in the presence of an optimal concentration of one cytokine and titrating concentrations of the other indicating that they may use common receptors and signal transduction mechanisms. Although IL-3 or GM-CSF alone also enhanced ICAM-1 expression, Dex inhibited both constitutive and the cytokine induced expression of this antigen. In contrast M-CSF, in the presence or absence of Dex, failed to enhance ICAM-1, HLA class I or II expression. These observations further highlight differences between the effects of the haemopoietic growth factors GM-CSF and IL-3 versus M-CSF in the regulation of monocyte function. Finally, the distinct effect of a combination of glucocorticoids with GM-CSF or IL-3 to induce high levels of HLA expression on human monocytes suggests they may have an important role during inflammatory conditions in vivo.

Cell Adhesion Molecules↗
PubMed1992

T-cell activation is potentiated by cytokines released by lesional psoriatic, but not normal, epidermis.

BACKGROUND AND DESIGN: T-cell activation appears to be critical for the maintenance of psoriatic lesions. In this study, we determined whether cytokines released by epidermal cells from psoriatic lesions are providing signals that result in propagation of intralesional T-cell activation. Supernatants were obtained from epidermal cell cultures derived from skin biopsy specimens of psoriatic patients and normal subjects. These supernatants were added to purified normal CD4+ T cells activated via T-cell receptor (immobilized anti-CD3 and fibronectin) or via other activating pathways (anti-CDw60 or UM4D4). RESULTS: Psoriatic supernatants (n = 9), but not normal supernatants (n = 7, P < .0006), potentiated T-cell stimulation with anti-CD3 and fibronectin to 172% +/- 41% over control stimulation levels. The degree of lesional psoriatic epidermal cell potentiation correlated with the clinical severity of the lesion (r = .82, P = .007). Psoriatic epidermal cytokine potentiation of T-cell activation was not limited to T-cell receptor mediated stimulation; potentiation of anti-CDw60-stimulated CD4+ T cells was also observed. Neutralizing antisera to interleukin 1 and interleukin 8, but not interleukin 6, were found to reduce only partly the observed potentiation of T-cell activation. To determine whether cyclosporine is down modulating T-cell-potentiating cytokine activity in psoriasis, we compared samples obtained during a double-blind clinical trial of intralesional cyclosporine. T-cell-potentiating activity from psoriatic lesional sites treated with cyclosporine was not significantly modulated relative to the activity derived from vehicle-treated or untreated sites. CONCLUSION: These data demonstrate that lesional psoriatic epidermal cells release a balance of cytokines that potentiate T-cell activation. Because normal epidermal cells do not potentiate T-cell activation in this system, these findings demonstrate a mechanism by which the epidermis may non-specifically potentiate and perpetuate T-cell activation in psoriatic lesions.

CD4-Positive T-Lymphocytes↗
PubMed1992

Adhesion to vascular cell adhesion molecule 1 and fibronectin. Comparison of alpha 4 beta 1 (VLA-4) and alpha 4 beta 7 on the human B cell line JY.

Most mononuclear leukocytes and cell lines express the integrin alpha 4 beta 1 (VLA-4) heterodimer. In this study we have used Northern blotting and immunoprecipitation experiments to demonstrate that a B lymphoblastoid cell line (JY) expressed the integrin beta 7 subunit in association with alpha 4. These alpha 4 beta 7-positive JY cells bound poorly or not at all to VLA-4 ligands (soluble form of vascular cell adhesion molecule 1 (sVCAM-1) and the CS1 region of fibronectin). In contrast, a beta 1-positive variant of JY cells (selected to express a mixture of alpha 4 beta 1 and alpha 4 beta 7) bound avidly to VLA-4 ligands, and this binding was completely inhibitable by anti-alpha 4 and anti-beta 1 monoclonal antibodies. Thus, beta 1 expression appears to be a critically important component of VLA-4-mediated binding to its ligands. After either JY or JY-beta 1 cells were stimulated for 15 min with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate, the majority of adhesion to VCAM or fibronectin remained alpha 4- and beta 1-dependent, but a low amount of adhesion to sVCAM-1 or fibronectin became alpha 4-dependent, beta 1-independent, thus suggesting a role for alpha 4 beta 7. In summary, we have found (i) that alpha 4 beta 7 makes little or no contribution to fibronectin or VCAM-1 binding on unstimulated JY cells, (ii) that alpha 4 beta 7 perhaps makes a minor contribution to ligand binding on 12-O-tetradecanoyl-phorbol-13-acetate-stimulated cells, and (iii) that alpha 4 beta 1 is the functionally dominant VCAM-1 and fibronectin receptor even when expressed in relatively low amounts compared to alpha 4 beta 7.

Antibodies, Monoclonal↗
PubMed1992

Endogenous receptor-bound urokinase mediates tissue invasion of the human lung carcinoma cell lines A549 and Calu-1.

Macrophage colony-stimulating factor (CSF-1) increases the tissue invasive potential of the CSF-1 receptor-bearing lung carcinoma cell lines A549 and Calu-1 by increasing the number of endogenously bound urokinase-type plasminogen activators (u-PA)s on these cells. CSF-1, at concentrations which optimize invasion of A549 and Calu-1 cells into human amnion membranes (250 ng/ml), maximally augments the number of u-PA receptors occupied by endogenously produced urokinase. Preincubation of A549 and Calu-1 cells with the anti-u-PA monoclonal antibody MPW5UK (25 micrograms/ml) or with a 20- to 40-fold stoichiometric excess of fluid phase type 2 plasminogen activator inhibitor abrogates invasiveness, indicating that functionally active cell surface u-PA is essential for tissue invasion. In contrast, fluid phase type 1 plasminogen activator inhibitor (PAI-1, 5-15 units/ml) does not inhibit invasiveness unless preincubated with the amnion membranes. Inhibition of invasion by PAI-1 is abolished by presaturating the amnion membranes with antiitronectin monoclonal antibody (10 micrograms/ml) which prevents binding of PAI-1 to tissue-associated vitronectin. Binding of PAI-1 to tissue vitronectin is therefore a prerequisite for its inhibitory action. Thus, endogenously receptor-bound u-PA is the primary protease mediating CSF-1-induced tissue invasiveness of the lung carcinoma cell lines A549 and Calu-1.

Amnion↗
PubMed1992

Hematopoietic growth factors upregulate the p65 type II interleukin-1 receptor on bone marrow progenitor cells in vitro.

Having previously shown that interleukin-1 (IL-1) induces the expression of IL-1 receptors (IL-1Rs) on bone marrow (BM) cells in vivo through an indirect mechanism, we studied whether hematopoietic growth factors (HGFs) could induce the expression of IL-1R on BM cells in vitro. In vitro treatment of light-density murine BM (LDBM) cells with either IL-3, IL-6, granulocyte--colony-stimulating factor (CSF), or granulocyte-macrophage--CSF caused a 5- to 10-fold upregulation of IL-1R expression, whereas IL-1, IL-5, IL-7, and macrophage-CSF had no effect. Scatchard analysis showed one class of IL-1Rs on LDBM cells with an average of 66 +/- 20 sites per cells. After 24 hours of treatment with IL-3, the number of IL-1Rs increased to 413 +/- 125, without effecting the affinity. This effect required protein synthesis, but was independent of cell division. Purified lineage-negative progenitor cells (Lin-) did not express detectable levels of IL-1R, but 24 hours of treatment with IL-3, GM-CSF, and G-CSF stimulated IL-1--specific binding. Autoradiographic analysis of Lin- cells showed that IL-1R induction by IL-3 occurs on undifferentiated blast cells. Affinity labeling of Lin- cells treated with HGFs showed an increase in a 65-Kd IL-1 binding protein that did not bind or compete with an anti-type I IL-1R antibody, suggesting that these cells expressed type II IL-1R. These data suggest that IL-1 stimulation of myelopoiesis occurs by a mechanism involving IL-1R upregulation on hematopoietic progenitor cells by HGFs.

Animals↗
PubMed1992

Interferon-gamma increases the expression of the gene encoding the beta subunit of the granulocyte-macrophage colony-stimulating factor receptor.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) activates a broad range of myeloid cells through binding to high-affinity receptors (GM-CSF-R) consisting of at least two distinct subunits, GM-CSF-R alpha and GM-CSF-R beta. The genes of these GM-CSF-R subunits have been identified recently, but little is known about the regulation of their expression. In this study, we investigated the expression of the GM-CSF-R subunit genes in normal human monocytes. Out of a panel of various cytokines and factors tested, only interferon-gamma (IFN-gamma) affected the expression of one of the GM-CSF-R subunit genes by increasing the GM-CSF-R beta mRNA expression threefold to sixfold with no effect on GM-CSF-R alpha. Maximal effects occurred 2 to 4 hours after stimulation with 500 to 5,000 U/mL IFN-gamma. Nuclear run-on assays and mRNA half-life studies showed that IFN-gamma modestly enhanced the transcription of the GM-CSF-R beta gene and stabilized the GM-CSF-R beta mRNA, with the latter mechanism predominant. Pretreatment of the monocytes with cycloheximide did not abrogate the increase of GM-CSF-R beta mRNA expression induced by IFN-gamma, indicating that de novo protein synthesis was not required for this activity. When monocytes were exposed to IFN-gamma for 6 to 24 hours, the number of GM-CSF-R per cell was increased 79% as compared with controls, whereas the receptor affinity remained unchanged. These data indicate that the GM-CSF-R expression in monocytes may be upregulated by IFN-gamma via an increased expression of the beta subunit gene, involving both transcriptional and post-transcriptional mechanisms.

Animals↗
PubMed1992

Product of the Steel locus can replace leukemic cell interaction.

Mutations in the Steel locus, encoding a growth factor (Steel factor or SF) or c-kit, the gene encoding its receptor, result in severe anemia in the mouse. In the present study, we have addressed the mechanism of synergistic growth activation, at the cellular level, by SF and GM-CSF using the blast cells of acute myeloblastic leukemia (AML blasts). Our data indicate that SF drastically alleviates the requirement in cell interaction for blast colony formation in most of the samples tested. Analysis of cultures performed in the presence of SF and GM-CSF at different cell concentrations, ranging from 1,000 to 20,000 cells, suggested a single limiting element, i.e., the blast clonogenic cell, while 2 or more limiting elements were found in cultures stimulated with GM-CSF alone, suggesting interacting cell populations. The presence of membrane-bound SF was detected by immunofluorescence, suggesting the possibility that secreted or membrane-bound SF may, at least in part, contribute to the density-dependent growth of AML blasts. In all samples tested, SF appears to increase the responsiveness of AML blasts to GM-CSF, as demonstrated by a 3-fold decrease of GM-CSF half efficient concentration on addition of SF to the cultures. Exposure of AML blasts to SF did not affect GM-CSF receptor expression, suggesting that this increase in GM-CSF responsiveness is likely to occur at the postreceptor level. Interestingly, 2 of 15 AML samples surveyed did not respond to SF, and were both of the myelomonocytic or monocytic subtype, classified as M4 and M5, respectively.

Cell Communication↗
PubMed1992

Activation of the Na(+)-K(+)-2Cl- cotransporter in rat parotid acinar cells by aluminum fluoride and phosphatase inhibitors.

The bumetanide-sensitive component of pHi recovery from an NH4Cl-induced acute alkaline load was used as a measure of Na(+)-K(+)-2Cl- cotransport activity in rat parotid acini. Acinar treatment with NaF/AlCl3 (15 mM NaF plus 10 microM AlCl3) induced a 5-fold stimulation in the initial rate of bumetanide-sensitive pHi recovery. This effect was dependent on NaF concentration (K1/2 approximately 7 mM) and was blunted in the presence of the Al3+ chelator desferal mesylate suggesting that it might be due to the aluminofluoride ion, AlF-4. NaF/AlCl3 treatment did not increase acinar intracellular cAMP levels but did result in an increase in intracellular calcium concentration (from 87 +/- 5 to 181 +/- 2 nM) and in acinar cell shrinkage (12 +/- 1%). But the stimulation of the Na(+)-K(+)-2Cl- cotransporter by NaF/AlCl3 persisted in acini which had been depleted of their intracellular Ca2+ stores. In these acini no effect of NaF/AlCl3 on intracellular calcium or cell volume was observed, indicating that stimulation of the cotransporter was not secondary to either of these phenomena. The effect of NaF/AlCl3 on the cotransporter was blocked by the protein kinase inhibitor K252a indicating the involvement of a protein phosphorylation event. This result is consistent with either NaF/AlCl3-dependent protein kinase activation or phosphatase inhibition. The stimulation of the cotransporter by NaF/AlCl3 was mimicked by the protein phosphatase inhibitor calyculin A; however, this effect was not blocked by K252a suggesting that a different protein kinase from that associated with NaF/AlCl3 may be involved. The data indicate that the Na(+)-K(+)-2Cl- cotransporter in this tissue is under tight regulatory control, in all likelihood via multiple protein kinase/phosphatase systems. The physiological roles of these regulatory events in modulating acinar fluid secretion driven by the Na(+)-K(+)-2Cl- cotransporter remain to be elucidated.

Aluminum↗