MicroRNA-200 Cluster Regulation by Ascl2: Impact on the Epithelial-mesenchymal Transition in Colon Cancer Cells [Gene Regulation]

November 4th, 2014 by Tian, Y., Pan, Q., Shang, Y., Zhu, R., Ye, J., Liu, Y., Zhong, X., Li, S., He, Y., Chen, L., Zhao, J., Chen, W., Peng, Z., Wang, R.

Achaete scute-like 2 (Ascl2), a basic helix-loop-helix (bHLH) transcription factor, is a downstream target of Wnt signaling that controls the fate of intestinal cryptic stem cells and colon cancer progenitor cells. However, its involvement in colon cancer and downstream molecular events is largely undefined; in particular, the mechanism by which Ascl2 regulates the plasticity of epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) programs in colon cancer cells remains unknown. In this study, we systematically demonstrate that Ascl2 loss-of-function in colon cancer cells promotes MET by de-repressing the expression of miR-200s (i.e., miR-200b, miR-200a, miR-429, miR-200c and miR-141) and further activating their expression through a transcriptional mechanism that involves direct binding to the most proximal E-box (E-box2) in the miR-200b-a-429 promoter. Activation of miR-200s due to Ascl2 deficiency led to the inhibition of Zeb1/2 expression and the alteration of epithelial and mesenchymal features. Transfection of miR-200b, miR-200a and miR-429 inhibitors into Ascl2-deficient colon cancer cells promoted the epithelial-mesenchymal transition in a reversible manner. Transfection of miR-200a or miR-429 inhibitors into Ascl2-deficient colon cancer cells increased cellular proliferation and migration. Ascl2 mRNA levels and miRNA-200a, miRNA-200b, miRNA-200c, miRNA-141 or miRNA-429 levels in the colon cancerous samples were inversely correlated. These results provide the first evidence of a link between Ascl2 and miR-200s in the regulation of EMT-MET plasticity in colon cancer.