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Indirect induction of a clastogenic effect in epidermal cells by a tumor promoter
Abstract:
The mechanisms by which tumor promoters exert their effects on target tissues are not clearly understood. Recent studies have demonstrated that phorbol ester tumor promoters induce an oxidative burst in phagocytes and DNA single-strand breaks (SSB) in leukocytes. The purpose of the research presented here was to investigate the clastogenic effects of tumor promoters in the target cell population, primary mouse epidermal cells co-incubated with leukocytes. Using the alkaline elution assay to detect DNA SSB, it was demonstrated that tumor promoters induce DNA SSB in primary mouse epidermal cells incubated in the presence of leukocytes. By increasing the ratio of leukocytes to epidermal cells from 1:2 to 10:1, in the presence of 1.6 X 10(-6) M 12-O-tetradecanoylphorbol-13-acetate (TPA), a ratio dependent increase in DNA SSB was observed (from 9 X 10(-2) to 121 DNA SSB per 10(6) nucleotides). A dose response in DNA SSB was seen with TPA over a concentration range of 4 X 10(-9)-1.6 X 10(-6) M. Mezerein, a second stage tumor promoter, induced similar levels of DNA SSB to that of TPA. 4-O-Methyl TPA, a first stage tumor promoter, induced significantly fewer DNA SSB than either TAP or mezerein at similar concentrations. The induction of DNA SSB in epidermal cells treated with TPA and co-incubated with leukocytes was inhibited by catalase but not superoxide dismutase. These data indicate that tumor promoters can act indirectly on target epidermal cells by stimulating the release of a clastogenic factor from leukocytes through a mechanism involving H2O2.
Insights
Tumor promoters induce DNA damage in skin cells indirectly via leukocytes. Hydrogen peroxide released from leukocytes causes these DNA single-strand breaks (SSB), highlighting a novel mechanism in tumor promotion.
Area of Science:
- Oncology
- Cell Biology
- Toxicology
Background:
- Tumor promoter mechanisms remain unclear.
- Phorbol esters induce oxidative stress and DNA damage in immune cells.
- Leukocytes may play a role in tumor promoter-induced DNA damage in target tissues.
Purpose of the Study:
- Investigate tumor promoter clastogenic effects on primary mouse epidermal cells.
- Determine if leukocytes mediate tumor promoter-induced DNA damage in epidermal cells.
- Elucidate the role of reactive oxygen species in this process.
Main Methods:
- Co-incubation of primary mouse epidermal cells with leukocytes.
- Alkaline elution assay to detect DNA single-strand breaks (SSB).
- Varying leukocyte:epidermal cell ratios and tumor promoter concentrations.
- Inhibition studies using catalase and superoxide dismutase.
Main Results:
- Tumor promoters induced DNA SSB in epidermal cells co-incubated with leukocytes.
- A dose- and ratio-dependent increase in DNA SSB was observed with 12-O-tetradecanoylphorbol-13-acetate (TPA).
- Catalase inhibited TPA-induced DNA SSB, while superoxide dismutase did not, implicating hydrogen peroxide (H2O2).
Conclusions:
- Tumor promoters can indirectly cause DNA damage in epidermal cells via leukocytes.
- Leukocyte-derived hydrogen peroxide is a key mediator of this clastogenic effect.
- This suggests a novel pathway for tumor promotion involving oxidative stress and intercellular communication.