Journal
CANCER LETTERS
Volume 393, Issue -, Pages 103-112Publisher
ELSEVIER IRELAND LTD
DOI: 10.1016/j.canlet.2017.02.010
Keywords
Apoptosis; Caspase-2; Colorectal carcinoma cells; HuR; Radiotherapy resistance
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Funding
- Deutsche Forschungsgemeinschaft [EB 257/6-1, EXC 147/1]
- German Federal Ministry of Education and Research (BMBF) [GREWIS: 02NUK017F]
- DAAD [91541525]
- University of Khartoum
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Increased abundance of the mRNA-binding protein human antigen R (HuR) is a characteristic feature of many cancers and frequently associated with a high grade malignancy and therapy resistance. HuR elicits a broad cell survival program mainly by stabilizing or increasing the translation of mRNAs coding for anti-apoptotic effector proteins. Conversally, we previously identified the pro-apoptotic caspase-2 as a novel HuR target which is mainly regulated at the level of translation. In this study, we investigated whether siRNA-mediated HuR knockdown interferes with cell survival and radiation sensitivity by monitoring apoptosis, DNA repair and three-dimensional (3D) clonogenic survival. We observed a significant elevation in caspase-2 upon HuR depletion and in turn, a sensitization of colorectal DLD-1 and HCT-15 cells to radiation-induced apoptosis as implicated by the dose-dependent elevation of sub-G(1) phase cell entry and increased caspase-2,-3 and poly ADP-ribose polymerase (PARP)-cleavage, respectively. Coincidentally, HuR deficiency significantly elevated the number of radiation-induced gamma H2AX/53BP1-positive foci indicating an increase in DNA damage. Accordingly, the irradiation-dependent reduction in clonogenic cell survival was further impaired after knockdown of HuR. Importantly, HuR knockdown remained ineffective to radiation-induced cell responses after additional knockdown of caspase-2. Furthermore, by using RNA-pull down assay we demonstrate that irradiation (6 Gy) robustly increased HuR binding to caspase-2 mRNA. Collectively, sensitization of colon carcinoma cells to radiation-induced cell death and DNA-damage by HuR knockdown critically depends on caspase-2 and may represent a valuable approach to intervene with therapy resistance of colorectal cancer (CRC). (C) 2017 Elsevier B.V. All rights reserved.
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