Long noncoding RNA H19 derived miR-675 regulates cell proliferation by down-regulating E2F-1 in human pancreatic ductal adenocarcinoma

The long noncoding RNA (lncRNA) H19 has been proven to be overexpressed in human pancreatic ductal adenocarcinoma (PDAC). H19-induced PDAC cell proliferation is cell cycle-dependent by modulating E2F-1. However, the mechanism of how H19 regulates E2F-1 remains unclear. In this study, we investigated the expression of miR-675 in PDAC tumours and cells, the biological function of miR-675 in PDAC cell proliferation and the possible relationship among H19, miR-675 and E2F-1. As a transcript of the first exon of H19, the level of miR-675 was negatively correlated with H19 expression in microdissected PDAC tissues (r=-0.0646, P=0.001). The serum miR-675 expression was significantly down-regulated in patients with PDAC compared to those in healthy individuals. Moreover, an evaluation of five PDAC cases showed that there was a remarkable increase of serum miR-675 levels after resection of the primary tumours. Ectopic overexpression of miR-675 in AsPC-1 and PANC-1 cells decreased cell viability, the colony-forming ability and the percentage of cells in S phase; contrarily, miR-675 knockdown resulted in enhanced cell proliferation. Furthermore, the suppressed cell proliferation caused by H19 knockdown could be rescued by inhibiting miR-675 expression. Additionally, intratumoural injection of either miR-675 agomir or antagomir could significantly affect tumour growth in vivo. Both the bioinformatic prediction and luciferase activity assay confirmed that E2F-1 was a direct target of miR-675. And the decrease of E2F-1 protein expression caused by siH19 could be partially reversed by miR-675 knockdown. We concluded that there might be a H19/miR-675/E2F-1 regulatory loop in cell cycle modulation. Serum miR-675 might serve as a potential biomarker for not only early diagnosis but also outcome prediction in PDAC.