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Published on: June 26, 2020
PTEN Loss Enhances Error-Prone DSB Processing and Tumor Cell Radiosensitivity by Suppressing RAD51 Expression and
Xile Pei1,2, Emil Mladenov1,2, Aashish Soni1,2
1Division of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany.
Abstract:
PTEN has been implicated in the repair of DNA double-strand breaks (DSBs), particularly through homologous recombination (HR). However, other data fail to demonstrate a direct role of PTEN in DSB repair. Therefore, here, we report experiments designed to further investigate the role of PTEN in DSB repair. We emphasize the consequences of PTEN loss in the engagement of the four DSB repair pathways-classical non-homologous end-joining (c-NHEJ), HR, alternative end-joining (alt-EJ) and single strand annealing (SSA)-and analyze the resulting dynamic changes in their utilization. We quantitate the effect of PTEN knockdown on cell radiosensitivity to killing, as well as checkpoint responses in normal and tumor cell lines. We find that disruption of PTEN sensitizes cells to ionizing radiation (IR). This radiosensitization is associated with a reduction in RAD51 expression that compromises HR and causes a marked increase in SSA engagement, an error-prone DSB repair pathway, while alt-EJ and c-NHEJ remain unchanged after PTEN knockdown. The G2-checkpoint is partially suppressed after PTEN knockdown, corroborating the associated HR suppression. Notably, PTEN deficiency radiosensitizes cells to PARP inhibitors, Olaparib and BMN673. The results show the crucial role of PTEN in DSB repair and show a molecular link between PTEN and HR through the regulation of RAD51 expression. The expected benefit from combination treatment with Olaparib or BMN673 and IR shows that PTEN status may also be useful for patient stratification in clinical treatment protocols combining IR with PARP inhibitors.
Insights
PTEN loss sensitizes cells to radiation by impairing homologous recombination (HR) DNA repair. This disruption increases reliance on error-prone pathways and enhances sensitivity to PARP inhibitors, suggesting PTEN status aids patient stratification for combined treatments.
Area of Science:
- Molecular Biology
- Cancer Research
- DNA Repair Mechanisms
Background:
- PTEN's role in DNA double-strand break (DSB) repair, particularly homologous recombination (HR), is debated.
- Understanding PTEN's precise function in DSB repair is crucial for cancer therapy.
Purpose of the Study:
- To investigate the role of PTEN in the four major DSB repair pathways: c-NHEJ, HR, alt-EJ, and SSA.
- To quantify the impact of PTEN loss on cell radiosensitivity and checkpoint responses.
- To explore the therapeutic implications of PTEN status in combination treatments.
Main Methods:
- PTEN knockdown in normal and tumor cell lines.
- Quantification of cell radiosensitivity to ionizing radiation (IR).
- Analysis of DSB repair pathway engagement and G2-checkpoint responses.
- Assessment of sensitivity to PARP inhibitors (Olaparib, BMN673).
Main Results:
- PTEN disruption sensitizes cells to IR, linked to reduced RAD51 expression and compromised HR.
- PTEN loss significantly increases single-strand annealing (SSA) pathway engagement.
- Classical non-homologous end-joining (c-NHEJ) and alternative end-joining (alt-EJ) pathways remain unaffected.
- PTEN deficiency leads to partial suppression of the G2-checkpoint and radiosensitization to PARP inhibitors.
Conclusions:
- PTEN plays a critical role in maintaining HR fidelity by regulating RAD51 expression.
- PTEN loss shifts DSB repair towards error-prone SSA, contributing to radiosensitization.
- PTEN status is a potential biomarker for stratifying patients for combined IR and PARP inhibitor therapies.
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