Inhaled asbestos exacerbates atherosclerosis in apolipoprotein E-deficient mice via CD4+ T cells

BACKGROUND

Associations between air pollution and morbidity/mortality from cardiovascular disease are recognized in epidemiologic and clinical studies, but the mechanisms by which inhaled fibers or particles mediate the exacerbation of atherosclerosis are unclear.

OBJECTIVE AND METHODS

To determine whether lung inflammation after inhalation of a well-characterized pathogenic particulate, chrysotile asbestos, is directly linked to exacerbation of atherosclerosis and the mechanisms involved, we exposed apolipoprotein E-deficient (ApoE(-/-)) mice and ApoE(-/-) mice crossed with CD4(-/-) mice to ambient air, NIEHS (National Institute of Environmental Health Sciences) reference sample of chrysotile asbestos, or fine titanium dioxide (TiO(2)), a nonpathogenic control particle, for 3, 9, or 30 days.

RESULTS

ApoE(-/-) mice exposed to inhaled asbestos fibers had approximately 3-fold larger atherosclerotic lesions than did TiO(2)-exposed ApoE(-/-) mice or asbestos-exposed ApoE(-/-)/CD4(-/-) double-knockout (DKO) mice. Lung inflammation and the magnitude of lung fibrosis assessed histologically were similar in asbestos-exposed ApoE(-/-) and DKO mice. Monocyte chemoattractant protein-1 (MCP-1) levels were increased in bronchoalveolar lavage fluid and plasma, and plasma concentrations correlated with lesion size (p < 0.04) in asbestos-exposed ApoE(-/-) mice. At 9 days, activator protein-1 (AP-1) and nuclear factor-kappaB (NF-kappaB), transcription factors linked to inflammation and found in the promoter region of the MCP-1 gene, were increased in aortas of asbestos-exposed ApoE(-/-) but not DKO mice.

CONCLUSION

Our findings show that the degree of lung inflammation and fibrosis does not correlate directly with cardiovascular effects of inhaled asbestos fibers and support a critical role of CD4(+) T cells in linking fiber-induced pulmonary signaling to consequent activation of AP-1- and NF-kappaB-regulated genes in atherogenesis.

Age affects ERK1/2 and NRF2 signaling in the regulation of GCLC expression

We previously reported that activator protein-1 (AP-1) DNA binding activity was increased in vascular smooth muscle cells (VSMC) from old rats when exposed to high glucose or tumor necrosis factor (TNF-alpha) (Li et al., 2003. J Cell Physiol 197:418-425). We have now examined the relationship between the age-dependent activation of the ERK1/2-AP-1 pathway and modulation of constitutive gene expression of the catalytic subunit of glutamate-cysteine ligase (GCLC) in response to high glucose and TNF-alpha. GCLC mRNA levels were higher in VSMC from old rats compared to young, a pattern consistent with its protein levels. To determine whether age-related activation of ERK1/2-AP-1 signaling is responsible for the up-regulation of GCLC, the MEK inhibitors, PD98059 and U0126, were used to block ERK1/2 in VSMC from old rats. An increase in GCLC with inhibitors was observed, diminishing the likelihood of ERK1/2-AP-1 activation as the up-regulating signal for GCLC. However, the transcription factor Nrf2 was higher in nuclei and accompanied by increased Nrf2-ARE binding in VSMC from old rats. Furthermore, MEK inhibitors increased nuclear Nrf2 and Nrf2/ARE binding. These data suggest opposing effects of Nrf2 and ERK1/2 signaling in the modulation of GCLC expression in old animals.

Age-related differences in MAP kinase activity in VSMC in response to glucose or TNF-alpha

Aortic vascular smooth muscle cells (VSMC) were used to study the effect of age on responses to high glucose concentrations or the cytokine, tumor necrosis factor-alpha (TNF-alpha). Activator protein-1 (AP-1) binding to DNA increased more in VSMC from old versus young rats (P < 0.02) and was related to increased expression of its components, c-Fos, Fra-1, and JunD. The relationship to upstream signals, i.e., activities of mitogen-activated protein kinases (MAPK), was studied using antibodies to total and phosphorylated forms of extracellular signal-regulated kinases (ERK), c-Jun N-terminal kinases (JNK) and p38. High glucose and TNF-alpha increased ERK phosphorylation more in old (P < 0.05); whereas only TNF-alpha induced JNK activation in young (P < 0.04). PD98059, a MEK inhibitor, attenuated AP-1 activation, lowered c-Fos and Fra-1 protein levels and reduced cell number and cells positive for proliferating cell nuclear antigen in old. We concluded that age differentially influenced activation of signaling pathways in VSMC exposed to high glucose or TNF-alpha. This may contribute to the increased risk for vascular disease associated with aging and diabetes mellitus (DM).

Mesothelial cell transformation requires increased AP-1 binding activity and ERK-dependent Fra-1 expression

Mesothelioma is a unique and insidious tumor associated historically with occupational exposure to asbestos. The transcription factor, activator protein-1 (AP-1) is a major target of asbestos-induced signaling pathways. Here, we demonstrate that asbestos-induced mesothelial cell transformation is linked to increases in AP-1 DNA binding complexes and the AP-1 component, Fra-1. AP-1 binding to DNA was increased dramatically in mesothelioma cell lines in comparison to isolated rat pleural mesothelial (RPM) cells. Elevated levels of AP-1 complexes, including significant increases in c-Jun, JunB and Fra-1, were found in asbestos-exposed RPM cells, but only Fra-1 expression was significantly increased and protracted in both asbestos-exposed RPM cells and mesothelioma cell lines. Asbestos-induced Fra-1 expression in RPM cells was dependent on stimulation of the extracellular signal-regulated kinases (ERKs 1/2). Inhibition of ERK phosphorylation or transfection with dominant-negative fra-1 constructs reversed the transformed phenotype of mesothelioma cells and anchorage-independent growth in soft agar. In summary, we demonstrate that ERK-dependent Fra-1 is elevated in AP-1 complexes in response to asbestos fibers and is critical to the transformation of mesothelial cells.

In vitro and in vivo activation of extracellular signal-regulated kinases by coal dusts and quartz silica

Alveolar type II epithelial cells are the main precursor cells that develop into carcinomas after inhalation of poorly soluble particles (PSP) at overload concentrations, but the mechanisms leading to initial proliferative events in these cells are unclear. In studies here, cell cycle kinetics, mitogen-activated protein kinase (MAPK) signaling events, and gene expression of activator protein-1 family members were investigated in murine alveolar type II epithelial cells (C10) or rats in vivo after exposure to several coal mine dusts (CMDs) of high or low quartz content. In contrast to results using unexposed C10 cells or cells exposed to the nonpathogenic particle glass beads, flow cytometry showed increased numbers of hypodiploid cells and cells in S phase after addition of DQ12 quartz or CMDs. Using a ribonuclease protection assay, increased mRNA levels of fos and jun family members were seen in response to DQ12 quartz and CMD with high quartz content. Increased phosphorylation of extracellular signal regulated kinases (ERKs)1/2 occurred in DQ12- and CMD-exposed cells by Western blot analysis. The use of the hydroxyl radical scavenger tetramethylthiourea blocked S-phase entry by DQ12 and CMDs as well as the phosphorylation of ERKs. Immunohistochemistry on lung sections of CMD-exposed rats showed chronic activation of phosphorylated ERKs in epithelial cells, supporting the possible role of this signal cascade in proliferation of pulmonary epithelium by PSP in vivo.

A mutant epidermal growth factor receptor targeted to lung epithelium inhibits asbestos-induced proliferation and proto-oncogene expression

Asbestos is a ubiquitous naturally occurring fiber causing multiple cancers and fibroproliferativedisease. The mechanisms of epithelial cell hyperplasia, a hallmark of the initiation of lung cancers by asbestos, have been unclear. We demonstrate here that mice expressing a dominant-negative mutant epidermal growth factor receptor (EGFR) under the control of the human lung surfactant protein-C promoter exhibit decreased pulmonary epithelial cell proliferation without alterations in asbestos-induced inflammation. In contrast to transgene-negative littermates, inhalation of asbestos by mice expressing the mutant EGFR does not result in early and elevated expression of early response proto-oncogenes (fos/jun or activator protein 1 family members). Additionally, quantitative reverse transcriptase-PCR analysis for levels of c-jun and c-fos in bronchiolar epithelium isolated by laser capture microdissection demonstrates increases in expression of these genes in asbestos-exposed epithelial cells. Results show that the EGFR mediates both asbestos-induced proto-oncogene expression and epithelial cell proliferation, providing a rationale for modification of its phosphorylation in preventive and therapeutic approaches to lung cancers and mesothelioma.

Activation of NF-kappaB-dependent gene expression by silica in lungs of luciferase reporter mice

Occupational exposure to crystalline silica is associated with the development of pulmonary inflammation and silicosis, yet how silica initiates pulmonary fibrosis and which cell types are involved are unclear. In studies here, we hypothesized that silica particles interact initially with pulmonary epithelial cells and alveolar macrophages (AMs) to cause transcriptional activation of nuclear factor (NF)-kappaB-regulated genes encoding inflammatory cytokines. Exposure of NF-kappaB luciferase reporter mice intratracheally to silica or lipopolysaccharide (LPS), but not the nonfibrogenic particle titanium dioxide (TiO(2)), increased immunoreactivity of luciferase protein in bronchiolar epithelial cells and AMs. Ribonuclease protection assays revealed significant (P < or = 0.05) increases in mRNA levels of inducible nitric oxide synthase, tumor necrosis factor-alpha, macrophage inflammatory protein-2, macrophage chemotactic protein-1 (MCP-1), interferon-gamma, interleukin (IL)-6, and IL-12 in lung homogenates of reporter mice after exposures to silica or LPS. Immunoreactivity of MCP-1 in these animals was localized to AMs and epithelial cells. These data are the first to show activation of NF-kappaB in situ by fibrogenic particles in pulmonary epithelial cells and AMs. Increased expression of NF-kappaB-related inflammatory cytokines by these cell types, which first encounter silica after inhalation, may be critical to the initiation of silica-associated lung diseases, thus providing a rationale for focusing on NF-kappaB in preventive and therapeutic strategies.

Ultrafine airborne particles cause increases in protooncogene expression and proliferation in alveolar epithelial cells

Exposure to ambient particulate matter (PM) is linked to increases in respiratory morbidity and exacerbation of cardiopulmonary diseases. However, the important components of PM and their mechanisms of action in lung disease are unclear. We demonstrate the development of dose-related proliferation and apoptosis after exposure of an alveolar epithelial cell line (C10) to PM or to ultrafine carbon black (ufCB), a component of PM. Ribonuclease protection assays demonstrated that increases in mRNA levels of the early response protooncogenes c-jun, junB, fra-1, and fra-2 accompanied cell proliferation at low concentrations of PM whereas apoptotic concentrations of PM caused transient increases in expression of fos and jun family members and dose responsive increases in mRNA levels of receptor-interacting protein, Fas-associated death domain, and caspase-8. Significant increases in steady-state mRNA levels of protooncogenes and apoptosis-associated genes, TNFR-associated death domain, and Fas were also observed after exposure of epithelial cells to ufCB, but not fine carbon black or glass beads, respectively, suggesting that the ultrafine particulate component of PM is critical to its biological activity.

Modulation of cell injury and survival by high glucose and advancing age

Old age is associated with a higher prevalence of cardiovascular disease and diabetes mellitus. Vascular smooth muscle cells (VSMC) play a role in the pathogenesis of vascular diseases, often a complication of diabetes mellitus. We examined in explanted aortic VSMC from young vs. older rats glucose-related activation of nuclear factor kappaB (NF-kappaB), a transcription factor induced by many oxidants. Data demonstrate that old age is associated with enhanced NF-kappaB activity in unstimulated VSMC that is further increased after exposure to high glucose medium. Furthermore, VSMC from old animals exhibit increased levels of protein carbonyls, an indicator of oxidative stress, and less apoptosis in response to glucose than VSMC isolated from young animals. These changes are accompanied by increased expression of NF-kappaB-related genes, gamma-glutamylcysteine synthetase, inhibitor of apoptosis protein-1 (IAP-1), and inducible nitric oxide synthase (iNOS). Results suggest that high glucose, a putative oxidative stress, causes apoptosis in VSMC from young animals and is associated with greater induction of NF-kappaB in VSMC from older animals. Increases in IAP-1 and decreased apoptosis implicate NF-kappaB as a survival factor in VSMC.

Silica-induced activation of c-Jun-NH2-terminal amino kinases, protracted expression of the activator protein-1 proto-oncogene, fra-1, and S-phase alterations are mediated via oxidative stress

Crystalline silica has been classified as a group 1 human carcinogen in the lung. However, its mechanisms of action on pulmonary epithelial cells which give rise to lung cancers are unclear. Using a nontransformed alveolar type II epithelial cell line (C10), we show that alpha-quartz silica causes persistent dose-related increases in phosphorylation of c-Jun-NH2-terminal amino kinases (JNKs) that are inhibited by antioxidants (P < or = 0.05). Increases in activator protein-1 (AP-1) binding to DNA and transactivation of AP-1-dependent gene expression by silica were accompanied by increases in steady-state mRNA levels of the AP-1 family members, c-jun, junB, fra-1, and c-fos at 8 h and elevated mRNA levels of fra-1 at 24 h (P < or = 0.05). Addition of tetramethylthiourea inhibited silica-associated increases infra-1 and proportions of cells in S-phase (P < or = .05). Our findings indicate that silica induces JNK activity, AP-1-dependent gene expression, ie., fra-1, and DNA synthesis via oxidative stress. Moreover, they suggest that silica may act mechanistically as a mitogen or tumor promoter, rather than a genotoxic carcinogen, in the development of lung cancers.

Strategies for evaluation of signaling pathways and transcription factors altered in aging

Aging is characterized by an accumulation of oxidative injury to DNA, RNA, proteins, lipids, and carbohydrates. In addition to damage, oxidative stress can initiate cell signaling cascades that modulate cell function, growth, and death. Aging and two common age-related diseases, diabetes mellitus and atherosclerosis, may share common oxidant-related signaling pathways that lead to abnormal transcription factor activation and ultimately to cellular dysfunction, degeneration, or death. This review will focus on approaches to evaluate key redox-sensitive signaling pathways and the transcription factors altered by diabetes, atherosclerosis, and aging.

Asbestos-induced phosphorylation of epidermal growth factor receptor is linked to c-fos and apoptosis

We examined the mechanisms of interaction of crocidolite asbestos fibers with the epidermal growth factor (EGF) receptor (EGFR) and the role of the EGFR-extracellular signal-regulated kinase (ERK) signaling pathway in early-response protooncogene (c-fos/c-jun) expression and apoptosis induced by asbestos in rat pleural mesothelial (RPM) cells. Asbestos fibers, but not the nonfibrous analog riebeckite, abolished binding of EGF to the EGFR. This was not due to a direct interaction of fibers with ligand, inasmuch as binding studies using fibers and EGF in the absence of membranes showed that EGF did not adsorb to the surface of asbestos fibers. Exposure of RPM cells to asbestos caused a greater than twofold increase in steady-state message and protein levels of EGFR (P < 0.05). The tyrphostin AG-1478, which inhibits the tyrosine kinase activity of the EGFR, but not the tyrphostin A-10, which does not affect EGFR activity, significantly ameliorated asbestos-induced increases in mRNA levels of c-fos but not of c-jun. Pretreatment of RPM cells with AG-1478 significantly reduced apoptosis in cells exposed to asbestos. Our findings suggest that asbestos-induced binding to EGFR initiates signaling pathways responsible for increased expression of the protooncogene c-fos and the development of apoptosis. The ability to block asbestos-induced elevations in c-fos mRNA levels and apoptosis by small-molecule inhibitors of EGFR phosphorylation may have therapeutic implications in asbestos-related diseases.

Modulation of mitochondrial gene expression in pulmonary epithelial cells exposed to oxidants

Oxidants are important in the regulation of signal transduction and gene expression. Multiple classes of genes are transcriptionally activated by oxidants and are implicated in different phenotypic responses. In the present study, we performed differential mRNA display to elucidate genes that are induced or repressed after exposure of rat lung epithelial (RLE) cells to H2O2 or crocidolite asbestos, a pathogenic mineral that generates oxidants. After 8 or 24 hr of exposure, RNA was extracted, reverse transcribed, and amplified by polymerase chain reaction with degenerate primers to visualize alterations in gene expression. The seven clones obtained were sequenced and encoded the mitochondrial genes, NADH dehydrogenase subunits ND5 and ND6, and 16S ribosomal RNA. Evaluation of their expression by Northern blot analysis revealed increased expression of 16S rRNA after 1 or 2 hr of exposure to H2O2. At later time periods (4 and 24 hr), mRNA levels of 16S rRNA and NADH dehydrogenase were decreased in H2O2-treated RLE cells when compared to sham controls. Crocidolite asbestos caused increases in 16S rRNA levels after 8 hr of exposure, whereas after 24 hr of exposure to asbestos, 16S rRNA levels were decreased in comparison to sham controls. In addition to these oxidants, the nitric oxide generator spermine NONOate caused similar decreases in NADH dehydrogenase mRNA levels after 4 hr of exposure. The present data and previous studies demonstrated that all oxidants examined resulted in apoptosis in RLE cells during the time frame where alterations of mitochondrial gene expression were observed. As the mitochondrion is a major organelle that controls apoptosis, alterations in expression of mitochondrial genes may be involved in the regulation of apoptosis.

Patterns of c-fos and c-jun proto-oncogene expression, apoptosis, and proliferation in rat pleural mesothelial cells exposed to erionite or asbestos fibers

Erionite, a naturally occurring fibrous zeolite, is associated with the development of nonmalignant and malignant lung diseases and is more carcinogenic than asbestos fibers in man and rodent inhalation models of disease. To investigate the possible molecular mechanisms of erionite-induced toxicity and carcinogenesis and whether cationic content of erionite fibers was important, we examined c-fos and c-jun mRNA levels, activator protein-1 (AP-1) binding to DNA, and changes in cell proliferation and apoptosis in rat pleural mesothelial (RPM) cells exposed to different cation-substituted erionite fibers or crocidolite asbestos at various concentrations (1, 5, or 10 microg/cm2 dish) at time periods from 8 to 48 h after addition of minerals. c-fos mRNA levels in cells exposed to equal weight concentrations of various erionites and crocidolite fibers were increased comparably. When compared to other fibers, Na-erionite caused significantly increased levels of c-jun mRNA at lower mass concentrations (1 and 5 microg/cm2) than crocidolite asbestos, but comparable AP-1 binding to DNA. In comparison to untreated controls, numbers of RPM cells incorporating 5'-bromodeoxyuridine (BrdU) were increased dramatically after exposure to asbestos or Na-erionite at 5 and 10 microg/cm2. Significant dose-dependent increases in apoptosis were observed with asbestos at all time points, whereas erionites failed to induce apoptosis at 8 or 24 h, with minimal induction at higher concentrations than asbestos at 48 h. These data suggest that erionite increases the balance between cell proliferation (and/or abnormal DNA repair) and apoptosis, a normal mechanism of elimination of transformed or proliferating cells.

Mechanisms of asbestos-induced nitric oxide production by rat alveolar macrophages in inhalation and in vitro models

To evaluate the contribution of reactive nitrogen species to inflammation by asbestos, Fischer 344 rats were exposed to crocidolite or chrysotile asbestos by inhalation to determine whether increases occurred in nitric oxide (NO.) metabolites from alveolar macrophages (AMs). AMs from animals inhaling asbestos showed significant elevations (p < .05) in nitrite/nitrate levels which were ameliorated by NG-monomethyl-L-arginine (NMMA), an inhibitor of inducible nitric oxide synthase (iNOS) activity. Temporal patterns of NO. generation from AMs correlated with neutrophil influx in bronchoalveolar lavage samples after asbestos inhalation or bleomycin instillation, another model of pulmonary fibrosis. To determine the molecular mechanisms and specificity of iNOS promoter activation by asbestos, RAW 264.7 cells, a murine macrophage-like line, and AMs isolated from control rats were exposed to crocidolite asbestos in vitro. These cells showed increases in steady-state levels of iNOS mRNA in response to asbestos and more dramatic increases in both iNOS mRNA and immunoreactive protein after addition of lipopolysaccharide (LPS). After transfection of an iNOS promoter/luciferase reporter construct, RAW 264.7 cells exposed to LPS, crocidolite asbestos and its nonfibrous analog, riebeckite, revealed increases in luciferase activity whereas cristobalite silica had no effects. Studies suggest that NO. generation may be important in cell injury and inflammation by asbestos.

GRP78, HSP72/73, and cJun stress protein levels in lung epithelial cells exposed to asbestos, cadmium, or H2O2

Occupational exposure to crocidolite asbestos is associated with the development of nonmalignant and malignant pulmonary disease. Considerable evidence indicates that the mechanisms of asbestos-induced toxicity involve the production of active oxygen species (AOS). Production of AOS in excess of cellular defenses creates an environment of oxidative stress and stimulates the expression of a number of different genes whose products may be involved in mediating responses from oxidant injury. To further investigate the mechanisms of asbestos-induced pathogenicity, we have examined by Western blot analyses the induction of the stress response proteins GRP78 and HSP72/73 in rat lung epithelial cells (RLE) exposed to crocidolite asbestos. In comparative studies, we also examined GRP78, HSP72/73, and cJun expression in RLE cells exposed to equitoxic concentrations of cadmium chloride (CdCl2) and hydrogen peroxide (H2O2). Our results demonstrate that asbestos and H2O2 do not alter GRP78 or HSP72/73 protein levels in RLE cells, but do increase levels of cJun protein. Increases by asbestos and H2O2 were not accompanied by alterations in cellular glutathione levels in this cell type, but asbestos caused elevations in protein levels of manganese-containing superoxide dismutase (MnSOD), an indirect indicator of oxidant stress. In contrast, exposure of cells to CdCl2 led to no changes in MnSOD protein levels, but increases in GRP78, HSP72/73, and cJun proteins as well as significant increases in oxidized and reduced thiol pools. Results suggest that environmental agents causing oxidative injury to lung epithelium elicit different patterns of stress responses.

Novel cell imaging techniques show induction of apoptosis and proliferation in mesothelial cells by asbestos

We developed in situ dual-fluorescence detection techniques for measuring apoptosis and proliferation simultaneously in single dishes of cells. The deoxyribonucleic acid (DNA)-specific labeling method, terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate nick-end labeling (TUNEL), first was used in conjunction with a 4',6-diamidino-2-phenylindole (DAPI) counterstain to detect and measure morphologic characteristics of apoptotic rat pleural mesothelial (RPM) cells isolated from Fischer 344 rats and exposed to 300 microM hydrogen peroxide (H2O2). For this purpose, 100 TUNEL-positive nuclei were measured while being viewed with DAPI counterstaining for area, perimeter, longest diameter, and average diameter, using imaging software and an image-collection apparatus. We then exposed cells to a range of concentrations of crocidolite asbestos and putative apoptotic and mitogenic agents. Exposure to crocidolite asbestos (5 microg/cm2) caused a striking dose-dependent apoptotic response at 24 h, 48 h, and 72 h. The nonfibrous crocidolite analogue riebeckite failed to induce apoptosis. At 24 h, tumor necrosis factor-alpha (TNF-alpha) (10 ng/ml) caused an increase in apoptotic nuclei. A second method, utilizing an antibody to 5'-bromodeoxyridine (BrdU) and oxazole yellow homodimer (YOYO), showed a dose-dependent increase in proliferation occurring in cells exposed to asbestos (5 microg/cm2) at 48 h and 72 h. In addition, increased numbers of rat pleural mesothelial (RPM) cells exposed to 12-O-tetradecanoylphorbol-13-acetate (TPA), TNF-alpha, and epidermal growth factor (EGF) exhibited incorporation of BrdU at these time points, although total numbers of cells per unit area were unchanged. Results indicate a dynamic balance between apoptosis and increased DNA synthesis after exposure of mesothelial cells to asbestos.

Inhibition of protein kinase C prevents asbestos-induced c-fos and c-jun proto-oncogene expression in mesothelial cells

Asbestos and the phorbol ester tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), increase c-fos and c-jun mRNA levels and AP-1 DNA binding activity in rat pleural mesothelial (RPM) cells, a target cell of asbestos-induced mesotheliomas (N. H. Heintz et al., Proc. Natl. Acad. Sci. USA, 90: 3299-3303, 1993). Because protein kinase C (PKC) is the intracellular receptor of phorbol ester tumor promoters and asbestos is a putative tumor promoter in the respiratory tract, we hypothesized that PKC might play a critical role in asbestos-induced cell signaling pathways associated with regulation of proto-oncogenes. Using a panel of PKC antibodies, we identified PKC alpha as the major PKC isozyme in RPM cells. We then pretreated cells with phorbol ester dibutyrate to down-modulate PKC or with calphostin C, a specific PKC inhibitor, to determine if depletion of PKC alpha could block asbestos-induced c-fos/c-jun expression. Quantitation of Northern blots showed that fiber-associated c-fos/c-jun mRNA levels were significantly lower either after PKC alpha down-modulation or pretreatment with calphostin C. In addition, to determine whether tyrosine kinases also were involved in proto-oncogene activation by asbestos, tyrphostin AG82 or herbimycin A was added to RPM cells before exposure to asbestos. These inhibitors decreased crocidolite-induced c-fos but not c-jun levels, suggesting that tyrosine kinases have different regulatory roles in asbestos-induced c-fos versus c-jun signaling pathways. The ability to block induction of asbestos-induced proto-oncogene expression using pharmacological intervention may be important in prevention and treatment of asbestos-induced proliferative diseases including lung cancers, mesothelioma, and pulmonary fibrosis.

Transcriptional activation of the proto-oncogene c-jun by asbestos and H2O2 is directly related to increased proliferation and transformation of tracheal epithelial cells

Asbestos causes persistent increases in c-jun mRNA and AP-1 DNA binding activity in hamster tracheal epithelial (HTE) cells, the progenitor cell type of asbestos-induced bronchogenic carcinoma. Studies here were designed to determine mechanisms of c-jun induction by asbestos and the phenotypic consequences of Jun expression in HTE cells. To examine whether asbestos or H2O2 induced transcription of c-jun, we transiently transfected HTE cells with a plasmid containing a fragment of the c-jun promoter coupled to a luciferase reporter gene. In addition, c-jun was overexpressed in cells using a full-length human c-jun construct, and effects on proliferation and transformation were examined. HTE cells transfected with the jun-luciferase construct showed increased luciferase activity when exposed to crocidolite asbestos or H2O2. These results demonstrate that asbestos and H2O2 activate AP-1-dependent gene transcription. Overexpression of c-jun led to increased proliferation and enhanced ability of HTE cells to grow in soft agar, an indication of cellular transformation. Data suggest that overexpression of c-jun may contribute to asbestos and oxidant-induced proliferation and carcinogenesis.

Sequence and expression of murine cDNAs encoding Xlr3a and Xlr3b, defining a new X-linked lymphocyte-regulated Xlr gene subfamily

Using a subtractive cDNA approach we have identified two nearly identical genes, Xlr3a and Xlr3b (X-linked lymphocyte regulated), expressed at a consistently high level in 14 out of 14 murine plasmacytoma cell lines, at a high level in 1 out of 8 B-lymphoma cell lines, and at a very low level in 2 out of the 8 B-lymphoma cell lines. The messages are not detected in 10 pre-B-lymphoma cell lines. These genes express 2.0-kb mRNAs that encode 226-amino-acid proteins that are extremely basic, with an estimated pI of 8.1 and 9.0, respectively. By sequence comparison they are homologous to Xlr1, an acidic nuclear protein that is produced in lymphoid cell lines corresponding to the late stages of lymphocyte differentiation. Xlr2 is a highly homologous gene that is expressed in differentiating male germ cells. Xlr3a and Xlr3b are members of a new subfamily in the Xlr multigene family. Like Xlr1, they are up-regulated during B-cell terminal differentiation in normal and neoplastic B-cells, and cross-hybridize with a message in testis RNA. Also, like Xlr1, they do not cross-hybridize with human genomic DNA.

Sequence and expression of a murine cDNA encoding PC326, a novel gene expressed in plasmacytomas but not normal plasma cells

Using a subtractive cDNA approach we have identified a gene, PC326, expressed in 13 of 14 murine plasmacytoma cell lines, but not in any B- or pre-B-lymphoma cell lines. It expresses 4.6-kb and 5.2-kb mRNAs that encode a 747 amino acid protein containing two highly acidic domains flanking a novel, moderately acidic 20 amino acid sequence that is repeated 7.5 times. Sequence comparison identifies an additional 43 amino acid domain that is homologous to a repeated sequence found in the members of the beta-transducin gene family. The PC326 mRNA is detectable in testis but in no other murine tissues, including plasma cells induced by lipopolysaccharide stimulation of splenocytes. Somatic cell hybrids derived from plasmacytomas and fibroblast or T-cell lines have a fibroblastic or T-cell phenotype respectively. Unlike B-cell-specific genes (e.g. immunoglobulin), the expression of which is extinguished in these hybrids, PC326 mRNA appears to be irreversibly turned on in these hybrids. Since PC326 is not expressed in normal plasma cells, it appears that its expression is a cause or consequence of the tumorigenic process that generates murine plasmacytomas.

A murine cDNA encodes a pan-epithelial glycoprotein that is also expressed on plasma cells

Using a subtractive cDNA approach, we have identified a number of genes expressed in murine plasmacytomas, but not B or pre-B lymphomas. One of these genes, 289A, expresses a 1.8-kb microsomally localized mRNA that encodes a 314-amino-acid protein containing a signal sequence and a hydrophobic transmembrane domain. Sequence comparison suggests that the predicted protein is the murine homologue of a human cell surface pan-epithelial glycoprotein known variously as EGP, GA733-2, KSA, and KS1/4, recognized by mAb HEA125, GA733, KS1/4, CO17-1A, M74, and 323/A3. The 289A mRNA is highly expressed in normal murine tissues containing epithelial cells, and at a low level in plasma cells induced by LPS stimulation of spleen B lymphocytes. It is expressed in 15 of 16 plasmacytomas, but at a much lower level, if at all, in pre-B or B lymphomas. In human B cell lines, 289A detects a 1.5-kb mRNA in the myeloma cell line 8226, but not in Burkitt's lymphoma or lymphoblastoid cell lines. Subsequent FACS analysis of human cell lines with the mAb GA733 and KS1/4 demonstrated concordant expression of the mRNA and the protein. We conclude that 289A is the murine homologue of EGP, GA733-2, KSA, and KS1/4 Ag. Although its expression was previously thought to be restricted to epithelial cells, it is also expressed in plasma cells and is a B lymphocyte differentiation Ag. Because of the multiplicity of names, we propose calling the human gene hEGP314, and the murine gene mEGP314.

A murine cDNA encodes a pan-epithelial glycoprotein that is also expressed on plasma cells

Using a subtractive cDNA approach, we have identified a number of genes expressed in murine plasmacytomas, but not B or pre-B lymphomas. One of these genes, 289A, expresses a 1.8-kb microsomally localized mRNA that encodes a 314-amino-acid protein containing a signal sequence and a hydrophobic transmembrane domain. Sequence comparison suggests that the predicted protein is the murine homologue of a human cell surface pan-epithelial glycoprotein known variously as EGP, GA733-2, KSA, and KS1/4, recognized by mAb HEA125, GA733, KS1/4, CO17-1A, M74, and 323/A3. The 289A mRNA is highly expressed in normal murine tissues containing epithelial cells, and at a low level in plasma cells induced by LPS stimulation of spleen B lymphocytes. It is expressed in 15 of 16 plasmacytomas, but at a much lower level, if at all, in pre-B or B lymphomas. In human B cell lines, 289A detects a 1.5-kb mRNA in the myeloma cell line 8226, but not in Burkitt's lymphoma or lymphoblastoid cell lines. Subsequent FACS analysis of human cell lines with the mAb GA733 and KS1/4 demonstrated concordant expression of the mRNA and the protein. We conclude that 289A is the murine homologue of EGP, GA733-2, KSA, and KS1/4 Ag. Although its expression was previously thought to be restricted to epithelial cells, it is also expressed in plasma cells and is a B lymphocyte differentiation Ag. Because of the multiplicity of names, we propose calling the human gene hEGP314, and the murine gene mEGP314.

Lactose inhibits the growth of Rhizobium meliloti cells that contain an actively expressed Escherichia coli lactose operon

Expression of the Escherichia coli lactose operon in Rhizobium meliloti 104A14 made the cells sensitive to the addition of the beta-galactosides lactose, phenyl-beta-D-galactoside, and lactobionic acid. Growth stopped when the beta-galactoside was added and viability decreased modestly during the next few hours, but little cell lysis was observed and the cells appeared normal. Protein synthesis was not inhibited. Growth was inhibited only when beta-galactosidase expression was greater than 160 U. Lactose-resistant mutants had defects in the plasmid-carried E. coli beta-galactosidase or beta-galactoside permease and in the R. meliloti genome. We speculate that uncontrolled production of galactose by the action of the lactose operon proteins was responsible for growth inhibition.

Gene fusion vehicles for the analysis of gene expression in Rhizobium meliloti

A set of plasmid cloning vehicles was developed to facilitate the construction of gene or operon fusions in Rhizobium meliloti. The vehicles also contain a broad-host-range replicon and could be introduced into bacteria either by transformation or by transduction, using bacteriophage P2. Insertion of foreign DNA into a unique restriction endonuclease cleavage site promotes the synthesis of either the Escherichia coli lactose operon or the kanamycin phosphotransferase gene from transposon Tn5. Expression of the lactose operon could be detected by observing the color of Rhizobium colonies on medium that contained a chromogenic indicator. We also determined the growth conditions that make it possible to select either for or against the expression of the E. coli lactose operon in R. meliloti. Recombinant plasmids were constructed by inserting MboI restriction fragments of R. meliloti DNA into one of the vehicles, pMK353 . Expression of beta-galactosidase by a number of these recombinants was measured in both R. meliloti and E. coli.