Abstract

Pancreatic ductal adenocarcinoma (PDAC) isa highly invasive cancer with a poor prognosis. Although microRNA (miRNA)transcripts have a crucial role in carcinogenesis and development, littleinformation is known regarding the aberrant DNA methylation of miRNAs in PDAC.Using methylated DNA immunoprecipitation-chip analysis, we found thatmiR-615-5p was hypermethylated in its putative promoter region, which silencedits expression in PDAC cell lines. In addition, the overexpression ofmiR-615-5p in pancreatic cancer cells suppressed cell proliferation, migrationand invasion. Insulin-like growth factor 2 (IGF2) is an imprinted gene, and itsabnormal expression contributes to tumor growth. Here, we identified IGF2 as atarget of miR-615-5p using a luciferase reporter assay. IGF2 upregulation inPDAC tissues was not correlated with a loss of imprinting but was inverselycorrelated with miR-615-5p downregulation. In addition, miR-615-5p suppressedpancreatic cancer cell proliferation, migration and invasion by directlytargeting IGF2, and this effect could be reversed by co-transfection with IGF2.Furthermore, the stable overexpression of miR-615-5p inhibited tumor growth invivo and was correlated with IGF2 expression. Using RNA sequencing, we furtheridentified miR-615-5p as potentially targeting other genes, such as theproto-oncogene JUNB, and interfering with the insulin signaling pathway. Takentogether, our results demonstrate that miR-615-5p was abnormally downregulatedin PDAC cells due to promoter hypermethylation, which limited its inhibition ofIGF2 and other target genes, thereby contributing to tumor growth, invasion andmigration. These data demonstrate a novel and important role of miR-615-5p as atumor suppressor in PDAC.