Hybrid E/M Phenotype(s) and Stemness: A Mechanistic Connection Embedded in Network Topology

Metastasis remains an unsolved clinical challenge. Two crucial features of metastasizing cancer cells are (a) their ability to dynamically move along the epithelial-hybrid-mesenchymal spectrum and (b) their tumor initiation potential or stemness. With increasing functional characterization of hybrid epithelial/mesenchymal (E/M) phenotypes along the spectrum, recent in vitro and in vivo studies have suggested an increasing association of hybrid E/M phenotypes with stemness. However, the mechanistic underpinnings enabling this association remain unclear. Here, we develop a mechanism-based mathematical modeling framework that interrogates the emergent nonlinear dynamics of the coupled network modules regulating E/M plasticity (miR-200/ZEB) and stemness (LIN28/let-7). Simulating the dynamics of this coupled network across a large ensemble of parameter sets, we observe that hybrid E/M phenotype(s) are more likely to acquire stemness relative to pure epithelial or mesenchymal states. We also integrate multiple phenotypic stability factors (PSFs) that have been shown to stabilize hybrid E/M phenotypes both in silico and in vitro-such as OVOL1/2, GRHL2, and NRF2-with this network, and demonstrate that the enrichment of hybrid E/M phenotype(s) with stemness is largely conserved in the presence of these PSFs. Thus, our results offer mechanistic insights into recent experimental observations of hybrid E/M phenotype(s) that are essential for tumor initiation and highlight how this feature is embedded in the underlying topology of interconnected EMT (Epithelial-Mesenchymal Transition) and stemness networks.

Automated summary

Metastasis is still a clinical challenge, with cancer cells exhibiting dynamic movement along the epithelial-hybrid-mesenchymal spectrum and stemness. A mathematical model was developed to explore the nonlinear dynamics of networks regulating E/M plasticity and stemness, revealing that hybrid E/M phenotypes are more likely to acquire stemness. The study also showed that factors stabilizing hybrid E/M phenotypes contribute to the enrichment of stemness, providing insights into tumor initiation mechanisms.