Superfund Research Program

Genotoxic and Cell Signaling Pathways of Arsenic in Mammalian Cells

Project Leader: Tom K. Hei (Columbia University Mailman School of Public Health)
Grant Number: P42ES010349
Funding Period: 2000 - 2011

Project-Specific Links

Final Progress Reports

Year:   2010  2005 

1. The overall goals of this project remain unchanged.

2. During the current funding period, the research group examined the profile of pathway-specific phosphoproteins induced by arsenic in human cells. Human telomerase-immortalized human small airway epithelial cells (h-TERT SAEC) exposed to arsenite were used to identify phosphoproteins of two major signaling cascades, including the human phospho-receptor tyrosine kinase (Phospho-RTK) and the nitogen-activated protein kinases (MAPKs), which play an essential role in modulating genotoxic response of mammalian cells to arsenic. In arsenite-treated cells, phosphorylation of epidermal growth factor receptor (EGFR), InsulinR and Flt3R were significantly increased when compared to untreated controls. Inhibitors of these proteins further confirmed the involvement of these proteins in the neoplastic transformation of arsenite-treated human small airway epithelial cells as evidenced by changes in plating efficiency, anchorage-independent growth and proliferation rate. Their data provide further evidence that analysis of phosphoprotein induction can be very useful in understanding the carcinogenic mechanism of sodium arsenite.

   In mammalian cells, genomic instability is considered a predisposition factor for cancer. To determine whether arsenic induces genomic instability and how the effect correlates with the exposure conditions, h-TERT SAECs were treated with inorganic arsenic at different doses and for various treatment periods. Treated and non-treated control cells were analyzed for micronuclei formation, which was used as a surrogate marker for genomic instability. At a concentration of 1.4 μM, a two-month treatment resulted in a micronucleus incidence that was twice the basal level. The incidence further increased such that after 14 months exposure, the micronucleus incidence was 7 fold higher than the controls. These data show that arsenic is genotoxic and induces genomic instability among treated cells.

   In addition, to provide mechanistic insights on the role of the neurotoxicity of arsenic, researchers treated rat neuron-like PC12 cells with arsenite. They observed arsenite-induced apoptosis in both cancer (melanoma) cells and neuron-like PC12 cells 48 h after treatment with 2-4 μM arsenite. Both melanoma cells and PC12 cells were characterized by surface expression of neuron growth factor-receptor (NGF-R). However, NGF (ligand) added to the cell media suppressed arsenite-induced apoptosis only in neuron-like PC12 cells via induction of the PI3K-AKT pathway but not in arsenate-sensitive melanoma cells. This differential response to a combination of arsenite and NGF will allow the protection of neurons from cytotoxic effects of arsenite, which has been used as a therapeutic regimen in cancer therapy.

3. Arsenic is an important environmental carcinogen that affects millions of people worldwide through contaminated water supplies. A better understanding of the mutagenic/carcinogenic mechanism of arsenic should provide a basis for better interventional approaches in both treatment and prevention of arsenic-induced cancer.

4. In the current funding period, the researchers are not able to assess genomic instability in blood lymphocytes using the Bangladeshi cohort samples since all collected samples were pre-fixed in paraformaldehyde. In the coming year, they will resume their studies on mitochondrial DNA mutations in arsenic-induced skin lesions, with or without concurrent UV exposure, based on the Bangladeshi cohort.