Background:Expression of ABCG2 is normally absent or low in the pancreas, but high in human pancreatic cancer cells. The mechanism by which ABCG2 is altered in human cancers remains unknown.Methods:We investigated ABCG2 expression in four pancreatic cancer cell lines, and used three microRNA (miRNA) target prediction programmes, and information from the existing literature to predict and identify hsa-miR-520h as an miRNA that targets ABCG2. The function of this miRNA was investigated by transient transfection of the pancreatic cancer cell line PANC-1 with oligonucleotides that mimic hsa-miR-520h.Results:Results showed that both mRNA and protein levels of ABCG2 were reduced, indicating that it was a target of hsa-miR-520h. Introduction of hsa-miR-520h mimics into PANC-1 cells also resulted in inhibition of cell migration and invasion, and reduction of side population cells. Cell proliferation, cell cycle progression and apoptosis were not affected.Conclusions:We propose that the effects of hsa-miR-520h may be, at least in part, caused by its regulation of ABCG2. Thus, our findings provide a new insight into the function of miRNA in the regulation of ABCG2 expression in pancreatic cancer. Gene therapy using miRNA mimics may therefore be useful as a pancreatic cancer therapy.

Pancreatic ductal adenocarcinoma (PDAC) is a highly invasive cancer with a poor prognosis. Although microRNA (miRNA) transcripts have a crucial role in carcinogenesis and development, little information is known regarding the aberrant DNA methylation of miRNAs in PDAC. Using methylated DNA immunoprecipitation-chip analysis, we found that miR-615-5p was hypermethylated in its putative promoter region, which silenced its expression in PDAC cell lines. In addition, the overexpression of miR-615-5p in pancreatic cancer cells suppressed cell proliferation, migration and invasion. Insulin-like growth factor 2 (IGF2) is an imprinted gene, and its abnormal expression contributes to tumor growth. Here, we identified IGF2 as a target of miR-615-5p using a luciferase reporter assay. IGF2 upregulation in PDAC tissues was not correlated with a loss of imprinting but was inversely correlated with miR-615-5p downregulation. In addition, miR-615-5p suppressed pancreatic cancer cell proliferation, migration and invasion by directly targeting IGF2, and this effect could be reversed by co-transfection with IGF2. Furthermore, the stable overexpression of miR-615-5p inhibited tumor growth in vivo and was correlated with IGF2 expression. Using RNA sequencing, we further identified miR-615-5p as potentially targeting other genes, such as the proto-oncogene JUNB, and interfering with the insulin signaling pathway. Taken together, our results demonstrate that miR-615-5p was abnormally downregulated in PDAC cells due to promoter hypermethylation, which limited its inhibition of IGF2 and other target genes, thereby contributing to tumor growth, invasion and migration. These data demonstrate a novel and important role of miR-615-5p as a tumor suppressor in PDAC.

Pancreatic cancer is one of the most deadly cancers with a poor prognosis. Though studies have implicated the roles of microRNAs in pancreatic cancer progression, little is known about the role of miR-613 in pancreatic cancer. In the present study, the expression of miR-613 was down-regulated in pancreatic cancer tissues and cancer cell lines. Down-regulation of miR-613 was positively correlated with tumor differentiation, advanced TNM stage, nodal metastasis and shorter overall survival in patients with pancreatic cancer. Overexpression of miR-613 suppressed cell proliferation, invasion and migration, and induced cell apoptosis and cell cycle arrest at G0/G1 phase in pancreatic cancer cells. Bioinformatics analysis, luciferase reporter assay and rescue experiments showed that notch3 was a direct target of miR-613. MiR-613 was inversely correlated with notch3 expression in pancreatic cancer tissues. The long non-coding RNA, HOX transcript antisense RNA (HOTAIR) was up-regulated in both pancreatic cancer tissues and cancer cell lines, and HOTAIR suppressed the expression of miR-613 via functioning as a competing endogenous RNA. In vivo studies showed that stable overexpression of miR-613 or knock-down of HOTAIR suppressed tumor growth and also reduced the expression of notch3. In conclusion, these results suggest that HOTAIR functions as a competing endogenous RNA to regulate notch3 expression via sponging miR-613 in pancreatic cancer.

No abstract