Combinatorial Targeting by MicroRNAs Co-ordinates Post-transcriptional Control of EMT

MicroRNAs (miRNAs) are important post-transcriptional regulators of gene expression, functioning in part by facilitating the degradation of target mRNAs. They have an established role in controlling epithelial-mesenchymal transition (EMT), a reversible phenotypic program underlying normal and pathological processes. Many studies demonstrate the role of individual miRNAs using overexpression at levels greatly exceeding physiological abundance. This can influence transcripts with relatively poor targeting and may in part explain why over 130 different miRNAs are directly implicated as EMT regulators. Analyzing a human mammary cell model of EMT we found evidence that a set of miRNAs, including the miR-200 and miR-182/183 family members, co-operate in post-transcriptional regulation, both reinforcing and buffering transcriptional output. Investigating this, we demonstrate that combinatorial treatment altered cellular phenotype with miRNA concentrations much closer to endogenous levels and with less off-target effects. This suggests that co-operative targeting by miRNAs is important for their physiological function and future work classifying miRNAs should consider such combinatorial effects. Micro-RNAs (miRNAs) are important modulators of gene expression, providing an additional layer of post-transcriptional regulation. In epithelial-mesenchymal transition (EMT), interactions between miRNAs and key transcription factors allow for switching between phenotypes. We identify a set of miRNAs co-regulated during breast cancer EMT and demonstrate that treatment with combinations of pro-epithelial miRNAs at very low concentrations can drive highly specific phenotypic change with fewer off-target effects than individual miRNA overexpression. Our results suggest co-operative interactions should be considered when studying miRNA function.