miR-106b modulates cancer stem cell characteristics through TGF-β/Smad signaling pathway in CD44 positive gastric cancer cells

Abstract

Cancer stem cells have the capacity to form new tumors and are thus considered to be a cause of metastasis and tumor recurrence. However, many of the mechanisms determining cancer stem cell characteristics are still unknown. MicroRNAs (miRNAs) are studied as possible modulator of cancer stem cell generation and the retention of cancer stem cell characteristics.The aim of this study was to examine the miRNA expression profile regulating the cancer stem cell characteristics of CD44 positive gastric cancer cells. We sorted gastric cancer stem-like cells using the cell surface stem cell marker, CD44 using fluorescence-activated cell sorting (FACS). CD44(+) cells formed more and larger spheres than CD44(-) cells. Cancer stemness related markers; Oct4, Bmi, Nestin, and ABCG2 were overexpressed in CD44(+) cells at the mRNA and protein levels. CD44(+) cells showed increased tendency for increased expression of mesenchymal markers while epithelial cell markers were downregulated. In miRNA microarray, the miR-106b family; miR-106b, miR-93, and miR-25 was significantly upregulated in CD44(+) cells compare to CD44(-) cells. Smad7, which inhibits TGF-β/Smad signaling as a target of the miR-106b family, was downregulated in CD44(+) cells. Furthermore, expression of TGF-β/Smad signal molecules were activated in CD44(+) cells, in accordance with the action of miR-106b family. Inhibition of miR-106b showed suppression of TGF-β/Smad signaling pathway and decreasing of cell invasiveness. Our study suggested that CD44(+) gastric cancer cells showed cancer stem cell properties with epithelial-mesenchymal transition (EMT) characteristics. miR-106b family regulated cancer stem cell properties, particularly EMT characteristics, through the TGF-β/Smad signaling pathway. Taken together, these results indicate that targeting miR-106b might be an effective cancer therapy in gastric cancer through the modulation of cancer stem cell characteristics.