Knockdown of CAVEOLIN-1 Sensitizes Human Basal-Like Triple-Negative Breast Cancer Cells to Radiation
Background/Aims: Triple-negative breast cancer (TNBC) is a high-risk breast cancer phenotype without specific targeted therapy options and is significantly associated with increased local recurrence in patients treated with radiotherapy. CAVEOLIN-1 (CAV-1)-mediated epidermal growth factor receptor (EGFR) nuclear translocation following irradiation promotes DNA repair and thus induces radiation resistance. In this study, we aimed to determine whether knockdown of CAV-1 enhances the radiosensitivity of basal-like TNBC cell lines and to explore the possible mechanisms. Methods: Western blotting was used to compare protein expression in a panel of breast cancer cell lines. Nuclear accumulation of EGFR as well as DNA repair and damage at multiple time points following irradiation with or without CAV-1 siRNA pretreatment were investigated using western blotting and confocal microscopy. The radiosensitizing effect of CAV-1 siRNA was evaluated using a clonogenic assay. Flowcytometry was performed to analyse cell apoptosis and cell cycle alteration. Results: We found that CAV-1 is over-expressed in basal-like TNBC cell lines and barely expressed in HER-2-positive cells; additionally, we observed that HER-2-positive cell lines are more sensitive to irradiation than basal-like TNBC cells. Our findings revealed that radiation-induced EGFR nuclear translocation was impaired by knockdown of CAV-1. In parallel, radiation-induced elevation of DNA repair proteins was also hampered by pretreatment with CAV-1 siRNA before irradiation. Silencing of CAV-1 also promoted DNA damage 24 h after irradiation. Colony formation assays verified that cells could be radiosensitized after knockdown of CAV-1. Furthermore, G2/M cell cycle arrest and apoptosis enhancement may also contribute to the radiosensitizing effect of CAV-1 siRNA. Conclusion: Our results support the hypothesis that CAV-1 knockdown by siRNA causes increased radiosensitivity in basal-like TNBC cells. The mechanisms associated with this effect are reduced DNA repair through delayed CAV-1-associated EGFR nuclear accumulation and induction of G2/M arrest and apoptosis through the combined effects of CAV-1 siRNA and radiation.