title: Silencing BMI1 radiosensitizes human breast cancer cells by inducing DNA damage and autophagy.
abstract: Overexpression of BMI1 in human cancer cells, a member of the polycomb group of repressive complexes, correlates with advanced stage of disease, aggressive clinico-pathological behavior, poor prognosis, and resistance to radiation and chemotherapy. Studies have shown that experimental reduction of BMI1 protein level in tumor cells results in inhibition of cell proliferation, induction of apoptosis and/or senescence, and increased susceptibility to cytotoxic agents and radiation therapy. Although a role for BMI1 in cancer progression and its importance as a molecular target for cancer therapy has been established, information on the impact of silencing BMI1 in triple-negative breast cancer (TNBC) and its consequence on radiotherapy have not been well studied. Therefore, in the present study we investigated the potential therapeutic benefit of radiation therapy in BMI1-silenced breast cancer cells and studied the mechanism(s) of radiosensitization. Human MDA-MB-231 and SUM159PT breast cancer cells that were either stably transfected with a lentiviral vector expressing BMI1 shRNA (shBMI1) or control shRNA (shControl) or transient transfection with a BMI1-specific siRNA were used. Silencing of BMI1 resulted in marked reduction in BMI1 both at the mRNA and protein level that was accompanied by a significant reduction in cell migration compared to control cells. Further, BMI1 knockdown produced a marked enhancement of DNA damage as evidenced by Comet Assay and γH2AX foci, resulting in a dose-dependent radiosensitization effect. Molecular studies revealed modulation of protein expression that is associated with the DNA damage response (DDR) and autophagy pathways. Our results demonstrate that BMI1 is an important therapeutic target in breast cancer and suppression of BMI1 produces radiation sensitivity. Further, combining BMI1-targeted therapeutics with radiation might benefit patients diagnosed with TNBC.
authors.affiliation: Department of Radiation Oncology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.
authors.forename: James
authors.initials: J
authors.lastname: Griffith
authors.affiliation: Department of Radiation Oncology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Andrade
authors.affiliation: Department of Radiation Oncology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.
authors.forename: Meghna
authors.initials: M
authors.lastname: Mehta
authors.affiliation: Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.
authors.forename: William
authors.initials: W
authors.lastname: Berry
authors.affiliation: Department of Obstetrics and Gynecology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.
authors.forename: Doris M
authors.initials: DM
authors.lastname: Benbrook
authors.affiliation: Department of Radiation Oncology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.
authors.forename: Natarajan
authors.initials: N
authors.lastname: Aravindan
authors.affiliation: Department of Radiation Oncology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.
authors.forename: Terence S
authors.initials: TS
authors.lastname: Herman
authors.affiliation: Department of Pathology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.
authors.forename: Rajagopal
authors.initials: R
authors.lastname: Ramesh
authors.affiliation: Department of Radiation Oncology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.
authors.forename: Anupama
authors.initials: A
authors.lastname: Munshi
mesh_terms: D001343:Autophagy; D045744:Cell Line, Tumor; D002465:Cell Movement; D049109:Cell Proliferation / Q000187:drug effects; D004249:DNA Damage; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D063150:Polycomb Repressive Complex 1 / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000494:pharmacology*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D064726:Triple Negative Breast Neoplasms / Q000235:genetics* / Q000532:radiotherapy
chemical_list: C069077:BMI1 protein, human; D034741:RNA, Small Interfering; D011838:Radiation-Sensitizing Agents; D063150:Polycomb Repressive Complex 1