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Regulatory network of mitomycin C action in human colon cancer cells
K Suzuki1, W Yamamoto, J S Park
1Department of Biochemistry and Biophysics, Research Institute for Radiation Biology and Medicine, Hiroshima.
Abstract:
A network composed of activation and inactivation pathways to regulate mitomycin C (MMC) action is suggested to exist in human cancer cells. COLO201 colon cancer cells were stably transfected with human NQO1 cDNA that encodes NAD(P)H:quinone oxidoreductase (DT-diaphorase, DTD), and a clonal cell line with about 57-fold elevated DTD activity was obtained. Northern analysis revealed that expression of the NADPH:cytochrome P450 reductase (P450 reductase) gene was decreased in the transfectant, COLO201/NQO1, associated with the increase of NQO1 expression. Biochemical characterization of the cells showed a significant increase of the glutathione (GSH) content concomitantly with the decrease of the P450 reductase activity. As a result of these coordinated modulations, sensitivity of COLO201/NQO1 to MMC was not increased as compared to the parent cells. Analyses of inhibition by specific inhibitors of DTD, P450 reductase and glutathione S-transferase (GST) in 5 human colon cancer cell lines including the transfectant showed that DTD and P450 reductase play significant roles in MMC activation in cells with sufficiently high DTD activity and with marginal DTD activity, respectively. In contrast, GST appeared to participate in MMC inactivation in cells with a high level of GST activity. These results indicated that DTD, P450 reductase, GSH and GST may act together compensatively or competitively, depending on their levels in cells, to determine the cellular sensitivity to MMC.
Insights
Cellular sensitivity to mitomycin C (MMC) depends on a complex network of enzymes. NAD(P)H:quinone oxidoreductase (DTD) and other factors interact to regulate MMC activation and inactivation in cancer cells.
Area of Science:
- Cancer Biology
- Pharmacology
- Biochemistry
Background:
- Mitomycin C (MMC) is an anticancer drug whose efficacy is modulated by cellular metabolic pathways.
- A regulatory network involving enzyme activation and inactivation pathways is proposed to influence MMC action in human cancer cells.
Purpose of the Study:
- To investigate the roles of NAD(P)H:quinone oxidoreductase (DT-diaphorase, DTD) and other enzymes in determining cellular sensitivity to mitomycin C (MMC).
- To characterize the interplay between DTD, NADPH:cytochrome P450 reductase, glutathione (GSH), and glutathione S-transferase (GST) in modulating MMC response.
Main Methods:
- Stable transfection of COLO201 colon cancer cells with human NQO1 cDNA to elevate DT-diaphorase (DTD) activity.
- Northern analysis to assess gene expression changes (NQO1, P450 reductase).
- Biochemical assays to measure enzyme activities (DTD, P450 reductase, GST) and glutathione (GSH) content.
- Inhibition studies using specific enzyme inhibitors in multiple colon cancer cell lines.
Main Results:
- Transfection led to significantly increased DTD activity, decreased P450 reductase gene expression and activity, and increased GSH content.
- Despite elevated DTD, the transfected cells (COLO201/NQO1) did not show increased sensitivity to MMC compared to parent cells.
- DTD and P450 reductase were crucial for MMC activation, with roles varying based on DTD activity levels.
- Glutathione S-transferase (GST) appeared to be involved in MMC inactivation, particularly in cells with high GST activity.
Conclusions:
- Cellular sensitivity to MMC is determined by a dynamic interplay between DTD, P450 reductase, GSH, and GST.
- These enzymes can act compensatively or competitively, depending on their cellular levels, to regulate MMC efficacy.
- Understanding this complex network is crucial for optimizing mitomycin C-based cancer therapies.