Exportin 1 (XPO1) inhibition leads to restoration of tumor suppressor miR-145 and consequent suppression of pancreatic cancer cell proliferation and migration

Pancreatic ductal adenocarcinoma (PDAC) is the third leading cause of cancer related deaths in the United States with a majority of these patients dying from aggressively invasive and metastatic disease. There is growing evidence that suggests an important role for microRNAs (miRNAs) in the pathobiology of aggressive PDAC. In this study, we found that the expression of miR-145 was significantly lower in PDAC cells when compared to normal pancreatic duct epithelial cells. Here we show that inhibition of the nuclear exporter protein exportin 1 (XPO1; also known as chromosome maintenance region 1 [CRM1]) by siRNA knockdown or by the Selective Inhibitor of Nuclear Export (SINE) compound (KPT-330; selinexor) increases miR-145 expression in PDAC cells resulting in the decreased cell proliferation and migration capacities. A similar result was obtained with forced expression of miR-145 in PDAC cells. To this end, SINE compound treatment mediated the down-regulation of known miR-145 targets genes including EGFR, MMP1, MT-MMP, c-Myc, Pak4 and Sox-2. In addition, selinexor induced the expression of two important tumor suppressive miRNAs miR-34c and let-7d leading to the up-regulation of p21^WAF1. These results are the first to report that targeted inhibition of the nuclear export machinery could restore tumor suppressive miRNAs in PDAC that warrants further clinical investigations.