MUC1-C Induces the LIN28B→LET-7→HMGA2 Axis to Regulate Self-Renewal in NSCLC

The LIN28B -> let-7 pathway contributes to regulation of the epithelial-mesenchymal transition (EMT) and stem cell self-renewal. The oncogenic MUC1-C transmembrane protein is aberrantly overexpressed in lung and other carcinomas; however, there is no known association between MUC1-C and the LIN28B -> let-7 pathway. Here in non-small cell lung cancer (NSCLC), silencing MUC1-C downregulates the RNA-binding protein LIN28B and coordinately increases the miRNA let-7. Targeting MUC1-C function with a dominant-negative mutant or a peptide inhibitor provided confirming evidence that MUC1-C induces LIN28B -> let-7 signaling. Mechanistically, MUC1-C promotes NF-kappa B p65 chromatin occupancy of the LIN28B first intron and activates LIN28B transcription, which is associated with suppression of let-7. Consistent with let-7-mediated inhibition of HMGA2 transcripts, targeting of MUC1-C also decreases HMGA2 expression. HMGA2 has been linked to stemness, and functions as a competing endogenous RNA (ceRNA) of let-7-mediated regulation of the TGF beta coreceptor TGFBR3. Accordingly, targeting MUC1-C suppresses HMGA2 mRNA and protein, which is associated with decreases in TGFBR3, reversal of the EMT phenotype, and inhibition of self-renewal capacity. These findings support a model in which MUC1-C activates the double up arrow LIN28B ->double down arrow let-7 ->double up arrow HMGA2 axis in NSCLC and thereby promotes EMT traits and stemness. Implications: A novel pathway is defined in which MUC1-C drives LIN28B -> let-7 -> HMGA2 signaling, EMT, and self-renewal in NSCLC. (C) 2014 AACR.