miR-27a regulates the self renewal of the H446 small cell lung cancer cell line in vitro

Cancer growth is driven by cancer stem-like cells within a tumor, calledcancer stem cells (CSCs). Since miRNAs can regulate cell-fate decisions, we comparedmiRNA expression in stem-like cells and differentiated cells from small cell lungcancer (SCLC) cell lines to develop further understanding of the molecular mechanismsinvolved in the pathogenesis of SCLC. First, SCLC stem-like cells were enrichedby isolating sphere-forming cells using a dened serum-free medium. Further, microRNAmicroarrays were used to measure the expression of 1212 miRNAs in sphere-formingcells and parental cells. We found 86 miRNAs that were differentially expressed,including 48 upregulated miRNAs and 38 downregulated miRNAs between sphere-formingcells and parental cells. Among them, five downregulated miRNAs (let-7, miR-20,21, 27a and 30b) and one upregulated miRNA (miR-149*) were selected for validationin 3 sets of SCLC cell lines by qRT-RCR. The qRT-PCR analysis confirmed that allsix miRNAs were indeed differentially expressed. However, only miR-27a was consistentlydownregulated in sphere-forming cells of all 3 cell lines. Antagonizing miR-27aby inhibitor in parental cells enhanced proliferation, self renewal, and the proportionof undifferentiated cells in vitro. The candidate miRNA and some miRNAs with sameseed sequence are predicted to have several target genes related to apoptosis,cell proliferation and cell cycle. Our results suggest that downregulation ofmiR-27a enhanced the stem-like properties of SCLC cells in vitro and may be criticalto maintaining a stem cell function in SCLC.