Combinatorial cooperativity can facilitate epithelial-mesenchymal transition in a miR200-Zeb feedback network

Carcinoma cells often utilize epithelial-mesenchymal transition (EMT) programs for cancer progression and metastasis. Numerous studies point to the SNAIL-induced miR200/Zeb feedback circuit as crucial in regulating EMT by shifting cancer cells to at least three (epithelial (E), hybrid (h E/M), mesenchymal (M)) phenotypic states arrayed along the epithelial-mesenchymal phenotypic spectrum. However, a coherent molecular-level understanding of how such a tiny circuit controls carcinoma cell entrance into and residence in various states is lacking. Here, we use molecular binding data and mathematical modeling to report that miR200/Zeb circuit can essentially utilize combinatorial cooperativity to control E-M phenotypic plasticity. We identify minimal combinatorial cooperativities that give rise to E, hybrid-E/M, and M phenotypes. We show that disrupting a specific number of miR200 binding sites on Zeb as well as Zeb binding sites on miR200 can have phenotypic consequences - the circuit can dynamically switch between two (E, M) and three (E, hybrid-E/M, M) phenotypes. Further, we report that in both SNAIL-induced and SNAIL knock-out miR200/Zeb circuits, cooperative transcriptional feedback on Zeb as well as Zeb translational inhibition due to miR200 are essential for the occurrence of intermediate hybrid-E/M phenotype. Finally, we demonstrate that SNAIL can be dispensable for EMT, and in the absence of SNAIL, the transcriptional feedback can control cell state transition from E to hybrid-E/M, to M state. Our results thus highlight molecular-level regulation of EMT in miR200/Zeb circuit and we expect these findings to be crucial to future efforts aiming to prevent EMT-facilitated dissemination of carcinomas.