miR-196a-5p modulates gastric cancer stem cell characteristics by targeting Smad4

Cancer stem cells (CSCs) are undifferentiated cancer cells with a high tumorigenic activity, the ability to undergo self-renewal, and a multilineage differentiation potential. Clinical evidence suggests that CSCs in a tumor mass are the cellular determinants to promote cancer invasion and metastasis. MicroRNAs (miRNAs) have emerged as important modulators of cancer stem cell characteristics. Unveiling the candidate miRNAs that regulate CSCs may provide novel therapeutic targets against cancer. We analyzed the miRNA expression profiles regulating the cancer stem-like cell characteristics in gastric cancer. Gastric cancer stem cells (GCSCs) were sorted using the stem cell marker CD44 by fluorescence-activated cell sorting. Functional studies revealed that CD44(+) cells formed more sphere colonies and showed higher invasiveness than CD44(-) cells. miRNA microarray analysis revealed that miR-196a-5p was significantly upregulated in CD44(+) cells than CD44(-) cells. Suppression of miR-196a-5p led to decreased colony formation and invasion of GCSCs. miR-196a-5p decreased the expression of Smad4 by targeting 3'-UTR of the mRNA. The expression of Smad4 in gastric cancer tissues was correlated with differentiation state of tumors, TNM stage and depth of invasion. The stimulation of epithelial-mesenchymal transition (EMT) by miR-196a-5p in cancer stem-like cells was abolished by overexpression of Smad4. Collectively, these data demonstrate that miR-196a-5p has a key role in EMT and invasion by targeting Smad4 in GCSCs. miR-196a-5p may serve as a potential target for gastric cancer therapy.