Abstract
Chemoresistance is a major obstacle to cancer therapy including that of colon cancer (CC). Although the dysregulation of many miRNAs has been implicated in 5-fluorouracil (5-FU) resistance in CC cells, the specific role of miR-20b in chemoresistance has not been documented. In the present study, we first determined the expression of miR-20b by RT-PCR and the levels of adisintegrin and metalloprotease9 (ADAM9) and epidermal growth factor receptor (EGFR) by western blotting in CC and adjacent non-cancerous tissues from 5-FU-sensitive or -resistant CC patients. Subsequently, 5-FU-sensitive (HCT116) and -resistant (HCT116-R) cells were obtained, and the levels of miR-20b, ADAM9 and EGFR were detected. Meanwhile, the 5-FU resistance of the cells was examined by assessing cell viability (by MTT assay) and apoptosis (by flow cytometry). After transfection of miR-20b into HCT116-R cells, drug resistance was reexamined. We then confirmed the relationship between miR-20b and ADAM9 by luciferase reporter assay. Finally, 5-FU resistance in HCT116 and HCT116-R cells was compared after transfection with miR-20b. Our results showed that miR-20b was expressed at lower levels in the 5-FU-resistant tissues and cells than in the 5-FU-sensitive tissues and cells. The opposite was the case for expression of ADAM9 and EGFR. In addition, we demonstrated that ADAM9 is a direct target of miR-20b and that miR-20b decreased the 5-FU resistance of HCT116-R cells. Our findings suggest that miR-20b reduces 5-FU resistance to induce apoptosis invitro by suppressing ADAM9/EGFR in CC cells.
Highlights
Colon cancer (CC) is a common neoplasm and presents a considerable disease burden worldwide
Results miR-20b is downregulated, while a disintegrin and metalloprotease 9 (ADAM9) and epidermal growth factor receptor (EGFR) are upregulated in tissues of the 5-FU-resistant CC patients
Our results showed that miR-20b expression was markedly downregulated in the CC tissues compared to the level in the corresponding adjacent non-cancerous tissues (Fig. 1A)
Summary
Colon cancer (CC) is a common neoplasm and presents a considerable disease burden worldwide. The phosphorylation of EGFR leads to the activation of extracellular signal-regulated kinase (ERK) and the phosphatidylinositol 3-kinase (PI3K)/Ser/Thr kinase (AKT) pathways [7] These two pathways are correlated with cell migration and apoptosis. A recent study found that ADAM9 is critical for promoting cell proliferation in esophageal squamous cell carcinoma by targeting EGFR-AKT signaling [12]. MicroRNAs (miRNAs) are small non-coding regulatory RNAs that are involved in temporal and tissue-specific eukaryotic gene regulation These miRNAs pair with either full or partial complementary sequences in the 3' untranslated fu et al: miR-20b reduces 5-FU resistance in colon cancer regions (3'UTRs) of target mRNAs, leading to sequencespecific mRNA cleavage and/or translational repression [17]. Our results provide evidence that miR-20b can directly modulate chemoresistance in these cells by regulating its downstream target, the ADAM9/EGFR signaling pathway.
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