Abstract
Small-cell lung cancer (SCLC) is associated with a high mortality rate and limited treatment efficacy. We created a microRNA (miRNA) expression signature by RNA sequencing using specimens from patients with SCLC who had failed treatment. Forty-nine miRNAs were downregulated in SCLC tissues and were candidate tumor-suppressive miRNAs. In this signature, both guide and passenger strands were downregulated for five miRNAs (miR-30a, miR-34b, miR-34c, miR-223, and miR-4529). Recent studies have revealed that passenger strands of miRNAs are involved in the molecular pathogenesis of human cancer. Although miR-30a-5p (the guide strand) has been shown to be a tumor-suppressive miRNA in various types of cancers, miR-30a-3p (the passenger strand) function is not well characterized in SCLC cells. We investigated the functional significance of miR-30a-3p and oncogenic genes regulated by miR-30a-3p in SCLC cells. Ectopic expression assays showed that miR-30a-3p expression inhibited cell proliferation and induced cell cycle arrest and apoptosis in two SCLC cell lines. Furthermore, in silico database searches and gene expression assays identified 25 genes as putative targets of miR-30a-3p in SCLC cells. Luciferase reporter assays revealed that downstream neighbor of SON (DONSON) was directly regulated by miR-30a-3p in SCLC cells. Knockdown of DONSON induced cell cycle arrest in SCLC cells and DONSON overexpression were detected in SCLC clinical samples. Analyzing the regulatory networks of tumor-suppressive miRNAs may lead to the identification of therapeutic targets in SCLC.