Abstract
BackgroundColorectal cancer (CRC) is a leading cause of cancer-related death. The biologic response of CRC to standard of care adjuvant therapies such as chemotherapy and radiation are poorly understood. MicroRNAs (miRs) have been shown to affect CRC progression and metastasis. Therefore, we hypothesized that specific miRs modulate CRC response to chemoradiation.MethodsIn this study, we used miR expression profiling and discovered a set of microRNAs upregulated rapidly in response to either a single 2 Gy dose fraction or a 10 Gy dose of γ-radiation in mouse colorectal carcinoma models. We used gain and loss-of-function studies in 2D and 3Dcell proliferation assays and colony formation assays to understand the role of the top miR candidate from our profiling. We used Student’s T-tests for simple comparisons and two-factor ANOVA for evaluating significance.ResultsThe most upregulated candidate at early time points in our signature, miR-451a inhibited tumor cell proliferation and attenuated surviving fraction in longer-term cultures. Conversely, inhibition of miR-451a increased proliferation, tumorsphere formation, and surviving fraction of tumor cells. Using a bioinformatics approach, we identified four genes, CAB39, EMSY, MEX3C, and EREG, as targets of miR-451a. Transfection of miR-451a decreased both mRNA and protein levels of these targets. Importantly, we found miR-451a expression was high and CAB39, EMSY levels were low in a small subset of rectal cancer patients who had a partial response to chemoradiation when compared to patients that had no response. Finally, analysis of a TCGA colorectal cancer dataset revealed that CAB39 and EMSY are upregulated at the protein level in a significant number of CRC patients. Higher levels of CAB39 and EMSY correlated with poorer overall survival.ConclusionsTaken together, our data indicates miR-451a is induced by radiation and may influence colorectal carcinoma proliferation via CAB39 and EMSY pathways.
Highlights
Colorectal cancer (CRC) is a leading cause of cancer-related death
Through gain and loss-of-function studies, we show that miR-451a is a negative regulator of proliferation in CRC and likely mediates its effects by targeting Calcium binding protein 39 (CAB39) and EMSY
We chose these two cell lines because they have been well-characterized and grow well in vitro and in xenograft studies [13, 14]. They provide a contrast of sorts with HCT-116 being microsatellite unstable (MSI), PIK3CA H1047R mutated and p53 WT whereas SW480 is microsatellite stable (MSS), PIK3CA WT but p53 R237H mutated
Summary
Colorectal cancer (CRC) is a leading cause of cancer-related death. The biologic response of CRC to standard of care adjuvant therapies such as chemotherapy and radiation are poorly understood. Emerging evidence suggests that microRNAs (miRs) modulate gene expression programs in response to radiation and confer variable sensitivity and efficacy to modern high dose ionizing radiation therapy [9, 10]. In this context, we have identified miR-451a as an antiproliferative microRNA in colorectal adenocarcinoma whose presence correlates with increased radiation efficacy. We believe our work highlights the potential for using miRs and their target genes in predicting radiation responsiveness of CRC while illustrating potential avenues for restoring radiation sensitivity in poorly responding tumors
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