Metabolomics,Unknown,Transcriptomics,Genomics,Proteomics

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Long-term exposure to low-concentrations of Cr(VI) induce DNA damage and disrupt the transcriptional response to benzo[a]pyrene

ABSTRACT: Living organisms are exposed on a daily basis to widespread mixtures of toxic compounds. Mixtures pose a major problem in the assessment of health effects because they often generate substance-specific effects that cannot be attributed to a single mechanism. Two compounds often found together in the environment are the heavy metal chromium and the polycyclic aromatic hydrocarbon benzo[a]pyrene (B[a]P). We have examined how long-term exposure to a low concentration of Cr(VI) affects the transcriptional response to B[a]P, a second toxicant with an unrelated mechanism of action. Growth of mouse hepatoma cells for 20 passages in medium with 0.1 or 0.5 uM Cr(VI) increases DNA damage and apoptosis and decreases clonogenic ability. These cells also show transcriptome changes indicative of increased expression of DNA damage response and repair genes. In them, B[a]P activates cancer progression pathways, unlike cells never exposed to Cr(VI), where B[a]P activates mostly xenobiotic metabolism pathways. Cells grown in Cr(VI) for 20 passages and then cultured for an additional 5 passages in the absence of Cr(VI) recover from some but not all the chromium effects. They show B[a]P-dependent transcriptome changes strongly weighted towards xenobiotic metabolism, similar to those in B[a]P-treated cells that had no previous Cr(VI) exposure, but retain a high level of Cr(VI)-induced DNA damage and silence the expression of DNA damage and cancer progression genes. We conclude that the combined effect of these two toxicants appears to be neither synergistic nor cumulative, generating a toxic/adaptive condition that cannot be predicted from the effect of each toxicant alone. Mouse Hepa-1 cells treated with Cr, Bap, Cr+Bap and untreated were profiled using RNAseq in duplicates.

ORGANISM(S): Mus musculus

SUBMITTER: Jing Chen

PROVIDER: E-GEOD-49571 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Although the consequences of genotoxic injury include cell cycle arrest and apoptosis, cell survival responses after genotoxic injury can produce intrinsic death-resistance and contribute to the development of a transformed phenotype. Protein tyrosine phosphatases (PTPs) are integral components of key survival pathways, and are responsible for their inactivation, while PTP inhibition is are often associated with enhanced cell proliferation. Our aim was to elucidate signaling events that modulate cell survival after genotoxin exposure. Diploid human lung fibroblasts (HLF) were treated with Cr(VI) (as Na2CrO4), a well known human respiratory carcinogen that induces a wide spectrum of DNA damage, in the presence and absence of a broad-range PTP inhibitor, sodium orthovanadate. Notably, PTP inhibition abrogated Cr(VI)-induced clonogenic lethality. The enhanced survival of Cr(VI)-exposed cells after PTP inhibition was predominantly due to a bypass of cell cycle arrest and was not due to decreased Cr uptake as evidenced by unchanged Cr-DNA adduct burden. Additionally, the bypass of Cr-induced growth arrest by PTP inhibition, was accompanied by a decrease in Cr(VI)-induced expression of cell cycle inhibiting genes, and an increase in the Cr(VI)-induced expression of cell cycle promoting genes. Importantly, PTP inhibition resulted in an increase in forward mutations at the HPRT locus, supporting the hypothesis that PTP inhibition in the presence of DNA damage may lead to genomic instability, via bypass of cell cycle checkpoints. Experiment Overall Design: Experimental factor was chemical treatment type (3 of them) Experiment Overall Design: (1) No: HLF 1-1, HLF 1-2, HLF 1-3, HLF 1-4 Experiment Overall Design: (2) 1uM Cr(VI): HLF 3-1, HLF 3-2, HLF 3-3, HLF 3-4 Experiment Overall Design: (3) 10uM SOV + 1uM Cr(VI): HLF 4-1, HLF 4-2, HLF 4-3, HLF 4-4 Experiment Overall Design: Biological replicates: 4 different RNA extractions from 4 different cell cultures=quadruplicate per chemical treatment type

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Long-term exposure to low-concentrations of Cr(VI) induce DNA damage and disrupt the transcriptional response to benzo[a]pyrene

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