HuR silencing elicits oxidative stress and DNA damage and sensitizes human triple-negative breast cancer cells to radiotherapy
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Meghna Mehta1,*, Kanthesh Basalingappa1,*, James N. Griffith1, Daniel Andrade1, Anish Babu2,3, Narsireddy Amreddy2,3, Ranganayaki Muralidharan2,3, Myriam Gorospe4, Terence Herman1, Wei-Qun Ding2, Rajagopal Ramesh2,3,5 and Anupama Munshi1,3
1 Department of Radiation Oncology, The University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA
2 Department of Pathology, The University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA
3 Stephenson Cancer Center, The University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA
4 National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA
5 Graduate Program in Biomedical Sciences, The University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA
* These authors contributed equally to this manuscript
Anupama Munshi, email:
Keywords: HuR, breast cancer, DNA repair, radiation, siRNA
Received: July 25, 2016 Accepted: August 24, 2016 Published: August 30, 2016
HuR is an mRNA-binding protein whose overexpression in cancer cells has been associated with poor prognosis and resistance to therapy. While reports on HuR overexpression contributing to chemoresistance exist, limited information is available on HuR and radioresistance especially in triple-negative breast cancer (TNBC).
In this study we investigated the role of HuR in radiation resistance in three TNBC (MDA-MB-231, MDA-MB-468 and Hs578t) cell lines. Endogenous HuR expression was higher in TNBC cells compared to normal cells. siRNA mediated knockdown of HuR (siHuR) markedly reduced HuR mRNA and protein levels compared to scrambled siRNA (siScr) treatment. Further, siHuR treatment sensitized TNBC cells to ionizing radiation at 2 Gy compared to siScr treatment as evidenced by the significant reduction in clonogenic cell survival from 59%, 49%, and 65% in siScr-treated cells to 40%, 33%, and 46% in siHuR-treated MDA-MB-231, MDA-MB-468 and Hs578t cells, respectively. Molecular studies showed increased ROS production and inhibition of thioredoxin reductase (TrxR) in HuR knockdown cells contributed to radiosensitization. Associated with increased ROS production was evidence of increased DNA damage, demonstrated by a significant increase (p < 0.05) in γ-H2AX foci that persisted for up to 24 h in siHuR plus radiation treated cells compared to control cells. Further, comet assay revealed that HuR-silenced cells had larger and longer-lasting tails than control cells, indicating higher levels of DNA damage. In conclusion, our studies demonstrate that HuR knockdown in TNBC cells elicits oxidative stress and DNA damage resulting in radiosensitization.
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