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DNA damage signals induction of fas ligand in tumor cells
1Division of Developmental Therapeutics, Cancer Center, University of Illinois at Chicago, Chicago, Illinois, USA.
Abstract:
Many anticancer agents exert their cytotoxicity through DNA damage and induction of apoptosis. Fas ligand (FasL), a key component of T lymphocytes, has been shown to be induced by some of those agents. To address what is an early signal for this induction, we constructed a FasL promoter-luciferase reporter gene to investigate effects of DNA topoisomerase (Topo) II inhibitors on FasL promoter activity. Transient transfection assays in HeLa and other tumor cell lines demonstrated that induction of FasL promoter activity in response to Topo II inhibitors such as VM-26 mimicked endogenous FasL expression under the same conditions. The ability of these agents to induce FasL expression correlated with their ability to cause DNA damage. For instance, complex-stabilizing Topo II inhibitors such as etoposide, teniposide, and doxorubicin, which cause DNA damage, strongly induce FasL expression; by contrast, non-DNA-damaging catalytic Topo II inhibitors such as ICRF-187 and merbarone do not do this. In support of the notion that DNA damage triggers FasL induction, we found that DNA-damaging irradiation also induced FasL promoter activity in a dose-dependent manner. Finally, the catalytic Topo II inhibitor ICRF-187 suppressed VM-26-induced-FasL expression. This suppression correlated with the ability of this drug to inhibit VM-26-induced DNA strand breaks. Together, our results suggest that DNA damage in response to agents such as etoposide and teniposide might serve as an early signal to induce FasL expression.
Insights
DNA damage from anticancer drugs like etoposide and teniposide may trigger Fas ligand (FasL) expression. This study used reporter genes to show DNA damage, not just Topoisomerase II inhibition, signals FasL induction in cancer cells.
Area of Science:
- Molecular Biology
- Cancer Research
- Immunology
Background:
- Anticancer agents often induce cell death via DNA damage and apoptosis.
- Fas ligand (FasL) is crucial for T-cell-mediated immune responses and can be induced by some anticancer drugs.
- The precise early signaling mechanism for FasL induction by these agents remains unclear.
Purpose of the Study:
- To investigate the role of DNA damage as an early signal for Fas ligand (FasL) induction by DNA topoisomerase (Topo) II inhibitors.
- To analyze the impact of Topo II inhibitors on FasL promoter activity using a reporter gene system.
Main Methods:
- Construction of a FasL promoter-luciferase reporter gene.
- Transient transfection assays in HeLa and other tumor cell lines.
- Treatment with various Topo II inhibitors (e.g., VM-26, etoposide, doxorubicin, ICRF-187) and DNA-damaging irradiation.
Main Results:
- Topo II inhibitors that cause DNA damage (e.g., etoposide, teniposide, doxorubicin) strongly induced FasL promoter activity, mimicking endogenous FasL expression.
- Non-DNA-damaging Topo II inhibitors (e.g., ICRF-187, merbarone) did not induce FasL expression.
- DNA-damaging irradiation also induced FasL promoter activity in a dose-dependent manner.
- The catalytic Topo II inhibitor ICRF-187 suppressed VM-26-induced FasL expression, correlating with inhibition of DNA strand breaks.
Conclusions:
- DNA damage, rather than Topoisomerase II inhibition alone, appears to be a critical early signal for FasL induction.
- Anticancer agents like etoposide and teniposide may induce apoptosis partly through DNA damage-mediated FasL expression.
- These findings provide insights into the mechanisms of anticancer drug action and immune system engagement.