Silencing of the mRNA-binding protein HuR increases the sensitivity of colorectal cancer cells to ionizing radiation through upregulation of caspase-2. (1st May 2017)

• Record Type: Journal Article
• Authors: Badawi, Amel; Hehlgans, Stephanie; Pfeilschifter, Josef; Rödel, Franz; Eberhardt, Wolfgang
• Is Part Of: Cancer letters. Volume 393(2017)
• Page Start: 103
• Page End: 112
• Publication Date: 2017-05-01
• Subjects: Apoptosis -- Caspase-2 -- Colorectal carcinoma cells -- HuR -- Radiotherapy resistance; CRC colorectal cancer -- DDR DNA-damage response -- HuR human antigen R -- PARP poly ADP-ribose polymerase -- 5′UTR 5′-untranslated region; Cancer -- Periodicals; Neoplasms -- Periodicals; Cancer -- Périodiques; Electronic journals; 616.994
• DOI: 10.1016/j.canlet.2017.02.010
• Languages: English
• ISSNs: 0304-3835

Abstract

Abstract: 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-G1 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 γH2AX/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). Highlights: HuR silencing sensitizes colon carcinoma cells to irradiation-induced apoptosis. HuR deficiency increases radiation-induced DNA damage and impairs clonogenic survival. Irradiation enhances the constitutive HuR binding to the 5′UTR of caspase-2 mRNA. Caspase-2 is critical for the radiosensitization upon HuR knockdown.