epidermal-growth-factor and sodium-arsenite

Inorganic arsenic (iAs) is a carcinogen and could increase the risks of bladder, lung, and skin cancer. Mining and smelting of non-ferrous metals are common occupational arsenic exposures. In this study, 125 individuals working in non-ferrous metal smelting plants were separated into two groups according to urinary total arsenic (TAs) levels: group 1, TAs < 100 μg/g Cr; group 2, TAs ≥ 100 μg/g Cr. Demographic characteristics of participants were obtained by questionnaire interview. Levels of E-cadherin soluble ectodomain fragment (sEcad) and epidermal growth factor (EGF) in workers urine were determined by ELISA test. We found that concentrations of sEcad and EGF present in urine were significantly elevated in the high urinary arsenic group 2 compared with the low urinary arsenic group 1. Urinary levels of the shedding of E-cadherin soluble ectodomain fragment (sEcad) and epidermal growth factor (EGF) were positively related to the concentrations of iAs in urine after adjusting for the confounding effects. A positive correlation between sEcad and EGF concentrations in urine was also observed. In order to verify the effects of iAs on sEcad and EGF, the human uroepithelial cell line (SV-HUC-1) was treated with NaAsO

Topics: Adult; Antigens, CD; Arsenic; Arsenites; Cadherins; Cell Line, Transformed; Epidermal Growth Factor; Female; Humans; Male; Metallurgy; Middle Aged; Mining; Occupational Exposure; Sodium Compounds; Urinary Bladder; Urothelium

Arsenic is an established lung carcinogen, however, the carcinogenic mechanisms are currently under investigation. Phosphorylation of the epidermal growth factor receptor (EGFR) has been reported with arsenic exposure in bladder cells. EGFR is a tyrosine kinase transmembrane receptor that regulates important processes in carcinogenesis, including cell survival, cell cycle progression, tumor invasion, and angiogenesis. We investigated the mechanisms of EGFR pathway activation by levels of arsenic relevant to human exposure scenarios both in vitro using cultured lung epithelial cells, and in lung tumors samples from New England Lung Cancer Study participants. Toenail arsenic levels were used as an internal biomarker of arsenic exposure. Our in vitro data suggest that arsenic increases levels of the EGFR ligand, heparin binding-EGF, and activate EGFR phosphorylation in the lung. Downstream of EGFR, arsenic exposure increased pERK and cyclin D1 levels. These effects were inhibited by treatment of cultured cells with the EGFR tyrosine kinase inhibitor, Tarceva (erlotinib). In a consecutive series of human lung tumor specimens, pEGFR protein levels were higher in subjects with elevated toenail arsenic levels compared to those with low exposure (odds ratio adjusted for other factors, OR 4.1 (95% confidence interval 1.1-15.6) (p = 0.04). These data suggest that arsenic exposure may stimulate EGFR pathway activation in the lung. Moreover, the tumors that arise in arsenic-exposed individuals also exhibit signs of EGFR pathway dysregulation. Further work is needed to assess the clinical utility of targeting the EGFR pathway in subgroups of lung cancer patients who have been exposed to elevated levels of arsenic.

Topics: Adult; Aged; Amphiregulin; Analysis of Variance; Arsenic; Arsenites; Biomarkers; Bronchi; Cells, Cultured; Cyclin D1; Cycloheximide; EGF Family of Proteins; Epidermal Growth Factor; Epithelial Cells; ErbB Receptors; Erlotinib Hydrochloride; Gene Expression; Glycoproteins; Heparin-binding EGF-like Growth Factor; Humans; Intercellular Signaling Peptides and Proteins; Lung; Lung Neoplasms; Middle Aged; Nails; Phosphorylation; Protein Kinase Inhibitors; Quinazolines; Reverse Transcriptase Polymerase Chain Reaction; Signal Transduction; Sodium Compounds

We have investigated the role of the different classes of MAPKs, i.e. ERKs, c-Jun N-terminal kinases (JNKs), and p38 MAPK in the proliferation of dog and human thyroid epithelial cells (thyrocytes) in primary cultures. In these cells, TSH, acting through cAMP, epidermal growth factor, hepatocyte growth factor (HGF), and phorbol 12-myristate 13-acetate induce DNA synthesis. With the exception of HGF, all of these factors require the presence of insulin for mitogenic effects to be expressed. We found that TSH and forskolin are without effect on the phosphorylation and activity of the different classes of MAPKs. In contrast, all the cAMP-independent growth factors, whereas without effect on the phosphorylation and activity of JNKs and p38 MAPK, stimulated the ERKs. This effect was strong and sustained in response to HGF, epidermal growth factor and 12-myristate 13-acetate but weak and transient in response to insulin. Moreover, whereas in stimulated cells DNA synthesis was inhibited by PD 098059, an inhibitor of MAPK kinase 1 and consequently of ERKs, it was not modified by SB 203580, an inhibitor of p38 MAPK. Taken together, these data 1) exclude a role of JNKs and p38 MAPK in the proliferation of dog and human thyrocytes; 2) suggest that the mitogenic action of the cAMP-independent agents requires a strong and sustained activation of both ERKs and phosphatidylinositol 3-kinase/protein kinase B as realized by HGF alone or by the other agents together with insulin; and 3) show that TSH and cAMP do not activate ERKs but that the weak activation of ERKs by insulin is nevertheless necessary for DNA synthesis to occur.

Topics: Animals; Arsenites; Carcinogens; Cell Division; Cells, Cultured; Colforsin; Cyclic AMP; Dogs; Enzyme Inhibitors; Epidermal Growth Factor; Epithelial Cells; Flavonoids; Hepatocyte Growth Factor; Humans; Hypoglycemic Agents; Imidazoles; Insulin; MAP Kinase Signaling System; Mitogen-Activated Protein Kinases; p38 Mitogen-Activated Protein Kinases; Phosphorylation; Pyridines; Sodium Compounds; Tetradecanoylphorbol Acetate; Thyroid Gland; Thyrotropin

It is well accepted that arsenic is a human carcinogen, yet its mechanism of action is not defined. Arsenic cannot be classified as an initiating agent or as a promoter, although altered proliferative responsiveness has been proposed as a mechanism by which arsenic exerts its carcinogenic effects. Based on the hypothesis that arsenic exposure results in modulation of both positive and negative regulators of cell proliferation, this study examined physiological and biochemical changes in the proliferative response of murine fibroblasts grown long-term in the maximum tolerated concentration of sodium arsenite. In response to EGF stimulation, DNA synthesis and the proportion of cells entering S phase of the cell cycle both were increased in cells grown long-term in arsenic compared to control cells. Analysis of positive proliferative regulators revealed an increase in the expression of c-myc and E2F-1, thereby supporting the hypothesis that arsenic increases activity of positive growth modulators. In contrast, the activity and expression of ERK-2 were unchanged, as was the expression of EGF-receptor and mSOS. When negative regulators of proliferation were examined, expression levels of MAP kinase phosphatase-1 and p27(Kip1) were found to be lower in arsenic-treated cells compared to control cells; this result supports a model in which arsenic disinhibits normal regulation of cell proliferation. Taken together, these data indicate that long-term exposure to sodium arsenite creates conditions within the cell consistent with sensitization to mitogenic stimulation. It is further postulated that the observed changes in mitogenic signaling proteins contribute to the carcinogenic property of arsenic.

Topics: Analysis of Variance; Animals; Arsenites; Cell Cycle; Cells, Cultured; DNA; Enzyme Inhibitors; Epidermal Growth Factor; Fibroblasts; Mice; Mitogen-Activated Protein Kinase Kinases; Proto-Oncogene Proteins c-myc; Signal Transduction; Sodium Compounds

Pretreatment of cells with 0.5 mM sodium arsenite (but not other activators of stress-activated MAP kinase cascades) prevents the activation of p21Ras and strongly suppresses the activation of c-Raf and the MAP kinase cascade by a variety of growth factors. Arsenite appears to exert its effect by preventing the guanine nucleotide exchange factor mSos from converting Ras to its active GTP-bound state. Exposure to arsenite may be a simple way of assessing whether Ras plays an essential role in mediating activation of the MAP kinase cascade by extracellular signals.

Topics: 3T3 Cells; Adaptor Proteins, Signal Transducing; Animals; Arsenites; Calcium-Calmodulin-Dependent Protein Kinases; Enzyme Activation; Enzyme Inhibitors; Epidermal Growth Factor; GRB2 Adaptor Protein; Guanine Nucleotide Exchange Factors; Mice; Platelet-Derived Growth Factor; Proteins; ras Guanine Nucleotide Exchange Factors; ras Proteins; Sodium Compounds; Tumor Cells, Cultured