Exposure of HepG2 cells to low levels of PAH-containing extracts from contaminated soils results in unpredictable genotoxic stress responses.
Contaminated soil is a serious environmental problem, constituting a risk to humans and the environment. Polycyclic aromatic hydrocarbons (PAHs) are often present at contaminated sites. However, risk levels are difficult to estimate because of the complexity of contaminants present. Here, we compare cellular effects of extracts from contaminated soils collected at six industrial settings in Sweden. Chemical analysis showed that all soils contained complex mixtures of PAHs and oxy-PAHs. Western blotting and immunocytochemistry were used to investigate DNA damage signaling in HepG2 cells exposed to extracts from these soils. The effects on phosphorylated Mdm2, p53, Erk, H2AX, 53BP1, and Chk2, cell cycle regulating proteins (cyclin D1 and p21), and cell proliferation were compared. We found that most soil extracts induced phosphorylation of Mdm2 at the 2A10 epitope at low concentrations. This is in line with previous studies suggesting that this endpoint reflects readily repaired DNA-damage. However, we found concentration- and time-dependent gammaH2AX and 53BP1 responses that were sustained for 48 hr. These endpoints may reflect the presence of different types of persistent DNA-damage. High concentrations of soil extracts decreased cyclin D1 and increased p21 response, indicating cell cycle arrest. Phosphorylation of Mdm2 at Ser166, which attenuates the p53 response and is induced by many tumor promoters, was induced in a time-dependent manner and was associated with Erk phosphorylation. Taken together, the PAH extracts elicited unpredictable signaling responses that differed between samples. More polar compounds, i.e., oxy-PAHs, also contributed to the complexity.
Mattsson
Ase
A
Institute of Environmental Medicine, Division of Biochemical Toxicology, Karolinska Institutet, S-171 77 Stockholm, Sweden.
Lundstedt
Staffan
S
Stenius
Ulla
U
D001564:Benzo(a)pyrene / Q000633:toxicity; D006528:Carcinoma, Hepatocellular; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor / Q000187:drug effects; D004784:Environmental Monitoring / Q000379:methods; D006801:Humans; D008113:Liver Neoplasms; D009153:Mutagens / Q000633:toxicity*; D010766:Phosphorylation; D011084:Polycyclic Aromatic Hydrocarbons / Q000302:isolation & purification / Q000633:toxicity*; D051736:Proto-Oncogene Proteins c-mdm2 / Q000187:drug effects / Q000378:metabolism; D012989:Soil Pollutants / Q000633:toxicity*; D013548:Sweden; D016159:Tumor Suppressor Protein p53 / Q000187:drug effects / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000633:toxicity
D009153:Mutagens; D011084:Polycyclic Aromatic Hydrocarbons; D012989:Soil Pollutants; D016159:Tumor Suppressor Protein p53; D014874:Water Pollutants, Chemical; D001564:Benzo(a)pyrene; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2