Binding of beryllium to nuclear acidic proteins

Beryllium sulfate induces p21 CDKN1A expression and a senescence-like cell cycle arrest in susceptible cancer cell types

In fibroblasts, beryllium salt causes activation of the p53 transcription factor and induction of a senescence-like state. It is not known whether Be(2+) can affect the proliferation of cancer cells, which are generally unsusceptible to senescence. A172 glioblastoma and RKO colon carcinoma cell lines each have wildtype p53, so these cell types have the potential to be responsive to agents that activate p53. In A172 cells, BeSO(4) produced a G(0)/G(1)-phase cell cycle arrest and increased expression of senescence-associated β-galactosidase, an enzymatic marker of senescence. BeSO(4) caused phosphorylation of serine-15 of p53, accumulation of p53 protein, and expression of p21, the cyclin-dependent kinase inhibitor that is prominent during senescence. BeSO(4) inhibited A172 growth with an IC(50) = 4.7 μM in a 6-day proliferation assay. In contrast, BeSO(4) had no effect on RKO cells, even though Be(2+) uptake was similar for the two cell types. This differential responsiveness marks BeSO(4) as a reagent capable of activating a separable branch of the p53 signaling network. A172 and RKO cells are known to exhibit p53-dependent upregulation of p21 in response to DNA damage. The RKO cells produced high levels of p21 when exposed to DNA damaging agents, yet failed to express p21 when treated with BeSO(4). Conversely, BeSO(4) did not cause DNA damage in A172 cells, yet it was a potent inducer of p21 expression. These observations indicate that the growth control pathway affected by BeSO(4) is distinct from the DNA damage response pathway, even though both ultimately converge on p53 and p21.

Chronic beryllium disease: a model interaction between innate and acquired immunity

Beryllium (Be) is a lightweight and durable metal useful to a variety of manufacturing processes. With the use of Be in industrial settings, a number of health effects were noted including acute pneumonitis, sensitization to Be, interstitial lung disease and dermatological disease. Interstitial mononuclear cell inflammation and granuloma formation are the primary processes that occur in the lungs of Be-exposed workers, resulting in chronic beryllium disease (CBD). Recent studies have begun to describe the role of Be in the pathogenesis of CBD. These studies reveal that the host's response to Be involves components of the innate immune system or inflammatory responses. Inflammatory responses to Be can establish a state of acquired, Be antigen-specific, cell-mediated immunity. Despite triggering both the innate and acquired immune responses, Be is not eliminated from the host. Rather, it establishes pathways leading to chronic granulomatous inflammation. We will examine recent studies describing the host's cellular and molecular responses to Be, responses that promote granuloma formation.

The pathogenesis of beryllium-induced pulmonary granulomatosis. A scanning secondary ion analytical microscopy study

Chronic granulomatous pneumonitis was induced in rats with beryllium to study the pathogenesis of that disease, by identifying and localizing the beryllium in histological sections of the pulmonary tissues. This was done with scanning secondary ion mass spectrometry (SIMS). Thus, our observations suggest that the route of the Be from the site of injection into the lung, passes first by the blood, through the vascular wall and into the surrounding pulmonary tissues where Be was phagocytized by macrophages. There resulted in acute vasculitis throughout the lung. It was noted that the granuloma were focal inflammatory sites, solely observed within the vascular wall, distributed along the course of the affected vessel. These findings raise the question as to whether pulmonary granulomatous lesions of other origins are also localized within the vascular wall.

Beryllium-stimulated apoptosis in macrophage cell lines

In vitro stimulation of bronchoalveolar lavage cells from patients with chronic beryllium disease (CBD) induces the production of TNF-alpha. We tested the hypothesis that beryllium (Be)-stimulated TNF-alpha might induce apoptosis in mouse and human macrophage cell lines. These cell lines were selected because they produce a range of Be-stimulated TNF-alpha. The mouse macrophage cell line H36.12j produces high levels of Be-stimulated TNF-alpha. The mouse macrophage cell line P388D.1 produces low, constitutive, levels of TNF-alpha and does not up-regulate Be-stimulated TNF-alpha production. The DEOHS-1 human CBD macrophage cell line does not produce constitutive or Be-stimulated TNF-alpha. Apoptosis was determined by microscopic observation of propidium iodide stained fragmented nuclei in unstimulated and BeSO(4)-stimulated macrophage cell lines. BeSO(4) induced apoptosis in all macrophage cell lines tested. Beryllium-stimulated apoptosis was dose-responsive and maximal after 24 h of exposure to 100 microM BeSO(4). In contrast, unstimulated and Al(2)(SO(4))(3)-stimulated macrophage cell lines did not undergo apoptosis. The general caspase inhibitor BD-fmk inhibited Be-stimulated macrophage cell line apoptosis at concentrations above 50 microM. Our data show that Be-stimulated macrophage cell line apoptosis was caspase-dependent and not solely dependent on Be-stimulated TNF-alpha levels. We speculate that the release of Be-antigen from apoptotic macrophages may serve to re-introduce Be material back into the lung microenvironment, make it available for uptake by new macrophages, and thereby amplify Be-stimulated cytokine production, promoting ongoing inflammation and granuloma maintenance in CBD.

Beryllium-stimulation does not activate transcription factors in a mouse hybrid macrophage cell line

We tested the hypothesis that beryllium (Be) could stimulate H36.12j cell (12j) TNF-alpha production by transcription factor-mediated pathways similar to those induced by either LPS- or IFN-gamma stimulation. Unstimulated 12j cells produce constitutive levels of TNF-alpha (175+/-18 pg/ml, mean +/- SEM) detected by ELISA of culture supernatants after 24 h. Beryllium-stimulated (100 microM BeSO4) 12j cell TNF-alpha (724+/-47 pg/ml) was observed after 24 h while LPS-stimulated (1 microg/ml) TNF-alpha (515+/-151 pg/ml) after 6 h. Recombinant-Mu-IFN-gamma (10 U) stimulated 12j cell TNF-alpha at lower levels (284+/-31 pg/ml) while rMu-IFN-gamma + Be-stimulated 12j cells produced 1195+/-225 pg/ml TNF-alpha. Constitutive levels of transcription factors were observed in unstimulated 12j cell nuclei. In LPS-stimulated 12j cells IkappaBalpha was degraded in the cytoplasm and increased levels of NF-kappaB were found in nuclei after 30 min. After 3 h there were increased levels of AP-1 and CREB, with increased amounts of Fos family, Jun B and Jun D transcription factors. In contrast, Be-stimulation failed to increase the levels of any transcription factor tested, NF-kappaB, AP-1, AP-2, CREB, C/EBP, Sp-1, Egr-1, Ets, NF-Y or Oct-1, in 12j cells. A pattern of increased transcription factors, similar to that observed for LPS-stimulation, was found in 12j cell nuclei after stimulation with rMu-IFN-gamma. However, NF-kappaB was increased at 3 h while AP-1 (Jun B and Jun D) and CREB were increased at 15 h. Co-stimulation of 12j cells with rMu-IFN-gamma + Be increased the levels of NF-KB in 12j cell nuclei at 3 h, and the levels of AP-1 and CREB at 15 h, however, only Jun B was increased. Our data show 12j cell TNF-alpha production was associated with increased levels of transcription factors present in nuclei with disparate kinetics and patterns of expression depending on the trigger. We reject our initial hypothesis and conclude that Be-stimulation signals 12j cell TNF-alpha synthesis via a transcription factor-independent pathway. Beryllium may induce novel pathways of macrophage cytokine gene regulation.

Beryllium-stimulated production of tumor necrosis factor-alpha by a mouse hybrid macrophage cell line

Chronic beryllium disease (CBD) results from exposure to the light-weight metal beryllium (Be). In vitro stimulation of bronchoalveolar lavage cells from CBD subjects causes the production of high levels of TNF-alpha, IFN-gamma and IL-6. We tested the hypothesis that Be-stimulation might induce the production of TNF-alpha by macrophage cell lines. We observed that H36.12j cells (12j), a mouse hybrid macrophage cell line, but not other mouse and human macrophage cell lines, produced TNF-alpha upon Be-stimulation. The response was maximal at 100 microM BeSO4 and did not occur when 12j cells were stimulated with either aluminum sulfate or cobalt sulfate. Beryllium-stimulated the production of 725+/-25 pg/ml (mean +/- SEM) TNF-alpha protein by 12j cells as measured by ELISA of culture supernatants after 24 h. As measured by RT-PCR, Be-stimulated 12j cell TNF-alpha protein production was accompanied by an increased intracellular TNF-alpha mRNA at 3 and 24 h. The addition of 10U or 100U of rMu-IFN-gamma to Be-stimulated 12j cells further increased TNF-alpha production 1.5-4 fold (1.6+/-0.1 ng/ml) respectively. Bacterial lipopolysaccharide (LPS, 1 microg/ml) stimulated production of TNF-alpha in 12j culture supernatants after 6 h (515+/-151 pg/ml). This early versus late TNF-alpha production suggests that LPS and Be both stimulate 12j cell TNF-alpha synthesis, but through different pathways. We report for the first time, the direct effects of Be stimulation on the ability of 12j cells to produce TNF-alpha. The 12j cell line, contrasted with other macrophage hybrids that do not respond to Be-stimulation, may provide a useful tool to evaluate the mechanisms by which Be stimulates macrophage cytokine production, and by which T cell derived IFN-gamma amplifies TNF-alpha production in granulomatous diseases.

Partial IL-10 Inhibition of the Cell-Mediated Immune Response in Chronic Beryllium Disease

Chronic beryllium disease (CBD) provides a human disorder in which to study the delayed type IV hypersensitivity response to persistent Ag that leads to noncaseating pulmonary granuloma formation. We hypothesized that, in CBD, failure of IL-10 to modulate the beryllium-specific, cell-mediated immune response would result in persistent, maximal cytokine production and T lymphocyte proliferation, thus contributing to the development of granulomatous lung disease. To test this hypothesis, we used bronchoalveolar lavage cells from control and CBD subjects to evaluate the beryllium salt-specific production of endogenous IL-10 and the effects of exogenous human rIL-10 (rhIL-10) on HLA expression, on the production of IL-2, IFN-γ, and TNF-α, and on T lymphocyte proliferation. Our data demonstrate that beryllium-stimulated bronchoalveolar lavage cells produce IL-10, and the neutralization of endogenous IL-10 does not increase significantly cytokine production, HLA expression, or T lymphocyte proliferation. Second, the addition of excess exogenous rhIL-10 partially inhibited the beryllium-stimulated production of IL-2, IFN-γ, and TNF-α; however, we measured no change in T lymphocyte proliferation or in the percentage of alveolar macrophages expressing HLA-DP. Interestingly, beryllium salts interfered with an IL-10-stimulated decrease in the percentage of alveolar macrophages expressing HLA-DR. We conclude that, in the CBD-derived, beryllium-stimulated cell-mediated immune response, low levels of endogenous IL-10 have no appreciable effect; exogenous rhIL-10 has a limited effect on cytokine production and no effect on T lymphocyte proliferation or HLA expression.

Beryllium-stimulated release of tumor necrosis factor-alpha, interleukin-6, and their soluble receptors in chronic beryllium disease

Chronic beryllium disease (CBD) provides a model system in which to evaluate the antigen-stimulated, cell-mediated, immune response that leads to granulomatous lung disease. We hypothesized that beryllium salts would stimulate bronchoalveolar lavage (BAL) cell release of tumor necrosis factor-alpha (TNF-alpha) and lnterleukin-6 (IL-6), and their soluble receptors, soluble TNF receptor I (sTNF RI), sTNF RII, and sIL-6R and that chronic exposure to antigen would increase production of soluble receptors in the serum and BAL fluid (BALF) of beryllium-sensitized and CBD patients. We have demonstrated (1) similar constitutive TNF-alpha, IL-6, and soluble receptor production by control subjects and CBD patients, (2) a BeSO4-stimulated increase in TNF-alpha and IL-6 production by CBD-derived BAL cells, and (3) a BeSO4-induced decrease in sTNF RII production by BAL cells from control subjects. We measured increased serum sTNF RI and serum and BALF sIL-6R in beryllium-sensitized subjects and increased sTNF RI and RII in serum and sIL-6R and sTNF RII and BALF in CBD patients. These changes correlated with pulmonary lymphocytosis and clinical measures of disease severity, indicating that soluble receptors may reflect disease status.

C-myc expression is maintained during the G1 phase cell cycle block produced by beryllium

Salts of the toxic metal beryllium have been shown previously to prevent the synthesis of several enzymes essential for DNA replication in proliferating rat hepatic cells in vivo, and to inhibit the division of rat liver-derived BL9L epithelial cells in vitro, specifically during the G1 phase of the cell cycle. The present study shows, however, that exposure of serum-stimulated sub-confluent monolayer cultures of synchronized BL9L cells to inhibitory concentrations of the beryllium salt BeSO4 (50 microM) did not impair expression of the cell proliferation associated nuclear proto-oncogene c-myc. On the contrary, the increased c-myc mRNA levels normally observed during the G1 phase were maintained by continuous exposure of the cells to BeSO4. This response was specific in that other colloid forming metal salts (ZnSO4 and ZrSO4), which did not inhibit cell division, had no affect on c-myc expression, and mRNA levels for the constantly expressed H-2Kb major histocompatibility complex gene (3'Kb) were unaltered by BeSO4 treatment of the cells. The prevention by Be2+ of the down-regulation of c-myc expression in serum-stimulated BL9L cells appears to result from a modulation of the endogenous transcriptional control process for c-myc, which allows a maintained expression of the gene.

A blotting method for monitoring the formation of chemically induced DNA-protein complexes

The formation and identification of DNA-protein crosslinks are usually detected by filter binding assays such as alkaline elution. We describe a modified blotting method to selectively identify DNA-protein complexes (DPCs) formed in vitro by either Cr3+ ion or formaldehyde. This protocol allows DPC formation in vitro to be assayed with various chemical agents, requires minimal usage of radioactivity, and is performed in a shorter time frame than that commonly used to resolve DPCs from free proteins and unbound DNA.

In vivo crosslinking of nuclear proteins to DNA by cis-diamminedichloroplatinum (II) in differentiating rat myoblasts

When cells are briefly exposed to cis-diamminedichloroplatinum (II) before lysis in high sodium dodecyl sulfate-urea solutions, the high molecular-weight nucleic acids pelleted by ultracentrifugation contain an increased level of bound proteins when compared to a similar fraction from untreated cells. Subsequent shearing of the pelleted DNA followed by treatment with DNase permits electrophoretic and immunoblot analysis of the crosslinked proteins. In the present study such experiments were carried out with reference to nuclear envelope pore complex proteins in the differentiating L8 rat skeletal muscle cells. The results show that (i) whereas the major lamin proteins crosslinked to DNA in both myoblast and myotubes, lamin B is crosslinked to a greater extent to DNA in myotubes; (ii) a 62-kDa lectin-binding glycoprotein is apparently situated differently with respect to DNA in myotube nuclei; and (iii) the crosslinking pattern of the nuclear matrix proteins to DNA is qualitatively similar in myoblast and myotubes. In addition, lamin C', a modified form of lamin C, not observed in intact nonmuscle cells previously [Glass et al. (1985) J. Biol. Chem. 260, 1895-1900], exists as a native component of the nuclear lamina in rat skeletal myotubes but not in myoblasts. These results point to significant structural alterations in the proteins of the nuclear lamina-pore complex during myogenesis.

Specific G1-S phase cell cycle block by beryllium as demonstrated by cytofluorometric analysis

Inhibition of cell division by beryllium (Be2+) has been examined in synchronized cultures of a liver-derived cell line (BL9L cells) using cytofluorometric cell cycle analysis. Results show that a selective dose-related block of the G1-pre-S transition is produced, with other periods of the cell cycle appearing relatively insensitive.

Inhibition of nuclear-protein phosphorylation in vitro by beryllium

Endogenous cyclic-nucleotide-independent protein phosphorylation by ATP at pH 6.5 in adult rat liver nuclei in vitro is inhibited by beryllium (Be2+), but under the same conditions nuclear-protein dephosphorylation appears to be insensitive to Be2+. Prior incubation of nuclei with Be2+ is necessary to demonstrate the inhibition of phosphorylation, which increases as the pH is decreased from pH 8.0 to 6.5. The extent of inhibition can be related to the level of nuclear Be2+ binding and, evidence suggests, may be caused by direct or indirect interference by Be2+ with Mg2+ binding sites normally required to facilitate protein phosphorylation.

Beryllium toxicity. The selective inhibition of casein kinase 1

1. Cyclic AMP-independent casein kinase 1 in liver cytoplasm and nuclei was inhibited by Be2+ in vitro (Ki 2.5 microM and 29 microM respectively). Casein kinase 2 (phosvitin kinase) and cyclic AMP-dependent protein kinase were unaffected. 2. The inhibition of casein kinase 1 by Be2+ was competitive with respect to the protein substrate; at non-saturating concentrations of casein, inhibition was non-competitive with respect to ATP. 3. In rats given LD50 doses of Be2+ 24 h before death, the activities of cytoplasmic and nuclear casein kinase 1 in livers from partially hepatectomized animals were diminished approx. 50%; with intact rats, nuclear casein kinase 1 was inhibited at concentrations of casein less than the Km.