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Abstract
Although chemotherapy for treating colorectal cancer has had some success, drug resistance and metastasis remain the major causes of death for colorectal cancer patients. MicroRNA-21-5p (hereafter denoted as miR-21) is one of the most abundant miRNAs in human colorectal cancer. A Kaplan–Meier survival analysis found a negative prognostic correlation of miR-21 and metastasis-free survival in colorectal cancer patients (The Cancer Genome Atlas Colon Adenocarcinoma/TCGA-COAD cohort). To explore the role of miR-21 overexpression in drug resistance, a stable miR-21-overexpressing clone in a human DLD-1 colorectal cancer cell line was established. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) cell viability assay found that miR-21 overexpression induced drug resistance to topoisomerase inhibitors (SN-38, doxorubicin, and etoposide/VP-16). Mechanistically, we showed that miR-21 overexpression reduced VP-16-induced apoptosis and concomitantly enhanced pro-survival autophagic flux without the alteration of topoisomerase expression and activity. Bioinformatics analyses suggested that miR-21 overexpression induced genetic reprogramming that mimicked the gene signature of topoisomerase inhibitors and downregulated genes related to the proteasome pathway. Taken together, our results provide a novel insight into the role of miR-21 in the development of drug resistance in colorectal cancer.
Highlights
According to the global cancer statistics in 2018, colorectal cancer (CRC) is still the second essential contributor of cancer-related deaths in males and females worldwide [1]
Bioinformatics analyses further provided in silico mechanistic insights into miR-21-mediated drug resistance
3 beta (MAP1LC3B; GTX127375), Beclin 1 (GTX113039), Autophagy related 12 (ATG12; GTX124181), Lysosomal associated membrane protein 2 (LAMP2; GTX103214), and Glyceraldehyde-3-phosphate dehydrogenase (GAPDH; GTX100118) antibodies were from GeneTex (Hsinchu, Taiwan)
Summary
According to the global cancer statistics in 2018, colorectal cancer (CRC) is still the second essential contributor of cancer-related deaths in males and females worldwide [1]. Several molecular-targeted therapies have been developed, such as cetuximab and bevacizumab, which are monoclonal antibodies specific to epidermal growth factor receptor (EGFR) and vascular endothelial growth factor (VEGFR), respectively [2]. The acquisition of anticancer drug resistance remains the major challenge in treating CRC. A better characterization of the molecular mechanisms that are involved will provide clinical benefits for controlling and preventing the development of drug resistance. MicroRNAs (miRNAs), approximately 19 to 25 nucleotide-long small noncoding RNAs, could suppress mRNA translation or stability through interacting with the 3’-untranslated region (3’-UTR) of target mRNAs. The alteration of miRNA expressions is frequently observed in human cancers, and these altered miRNAs have been shown to display either oncogenic or tumor-suppressive functions [3]
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