Abstract
Metastasis remains the cause of over 90% of cancer-related deaths. Cells undergoing metastasis use phenotypic plasticity to adapt to their changing environmental conditions and avoid therapy and immune response. Reversible transitions between epithelial and mesenchymal phenotypes – epithelial–mesenchymal transition (EMT) and its reverse mesenchymal–epithelial transition (MET) – form a key axis of phenotypic plasticity during metastasis and therapy resistance. Recent studies have shown that the cells undergoing EMT/MET can attain one or more hybrid epithelial/mesenchymal (E/M) phenotypes, the process of which is termed as partial EMT/MET. Cells in hybrid E/M phenotype(s) can be more aggressive than those in either epithelial or mesenchymal state. Thus, it is crucial to identify the factors and regulatory networks enabling such hybrid E/M phenotypes. Here, employing an integrated computational-experimental approach, we show that the transcription factor nuclear factor of activated T-cell (NFATc) can inhibit the process of complete EMT, thus stabilizing the hybrid E/M phenotype. It increases the range of parameters enabling the existence of a hybrid E/M phenotype, thus behaving as a phenotypic stability factor (PSF). However, unlike previously identified PSFs, it does not increase the mean residence time of the cells in hybrid E/M phenotypes, as shown by stochastic simulations; rather it enables the co-existence of epithelial, mesenchymal and hybrid E/M phenotypes and transitions among them. Clinical data suggests the effect of NFATc on patient survival in a tissue-specific or context-dependent manner. Together, our results indicate that NFATc behaves as a non-canonical PSF for a hybrid E/M phenotype.
Highlights
The steady state value of ZEB mRNA levels was higher in case of nuclear factor of activated T-cell (NFATc)-epithelial–mesenchymal transition (EMT) coupled network as compared to the control case; this difference can be ascribed to the activation of ZEB by NFATc (Figure 1B)
In presence of NFATc, cells undergo a delayed or stalled EMT; maintaining cells in hybrid E/M phenotypes; knockdown of NFATc in H1975 non-small cell lung cancer (NSCLC) cells drove the progression toward a complete EMT phenotype, reminiscent of observations made for other phenotypic stability factor (PSF) – GRHL2, OVOL2, NUMB, and NRF2 [18,19,20,21,22,23]
NFATc transcriptional activity was shown to be capable of maintaining E-cadherin levels even in the presence of transforming growth factor β (TGFβ) induced EMT [29], suggesting that NFATc acted as a “molecular brake” or “guardian” of epithelial traits, preventing a complete EMT [40]
Summary
Metastasis remains clinically insuperable and causes over 90% of cancer related deaths [1]. A crucial axis of phenotypic plasticity during metastasis is epithelial-mesenchymal plasticity, which allows bidirectional switching of cells among an epithelial phenotype, a mesenchymal phenotype, and one or more hybrid epithelial/mesenchymal (E/M) phenotypes [6]. These hybrid E/M cells can be more metastatic than cells in epithelial or mesenchymal states [7, 8] and can exhibit collective cell migration as clusters of circulating tumor cells (CTCs) [9,10,11] – the major drivers of metastasis [12]. Understanding the molecular mechanisms enabling one or more hybrid E/M phenotype(s) is key to decoding and eventually restricting metastasis
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