Robustness and plasticity of epithelial cell state in development and malignancy

A better understanding of the molecular mechanisms that control pluripotency,
differentiation and epithelial phenotypical plasticity is crucial for the development of
the current knowledge in many general processes such as cell identity maintenance
and cell fate decision-making.
Embryonic stem cells (ESC) pluripotency maintenance and differentiation are of key
importance to the embryonic development, as well as to the progress in stem cells
technologies. The role of miR-290-295 cluster members in preserving the pluripotent
state and differentiation potential of mouse ESC is well established. Nevertheless, the
precise list of targets translating the microRNAs functionality is incomplete. In our
study we, firstly, identified and validated miR-290 targets with high confidence. We
further confirmed the expression variation of IRF2 in response to miRNAs’ depletion
in ESC. Moreover, we revisited the involvement of nuclear factor kappa-B (NF-kB)
pathway in the miRNA-dependent regulation in mESCs. Hence, our results provided
new understanding of the role and mechanistic of miR-290-295 microRNAs
involvement in ESC pluripotency and differentiation.
In a similar fashion to ESC pluripotency and differentiation mechanisms, a globalanalysis-approach that compares and combines data from different epithelial to
mesenchymal transition (EMT) models enabled us to construct a more detailed
network of regulatory entities implicated in epithelial plasticity. The maintenance and
plasticity of the epithelial cell phenotype are important events not only during normal
embryonic development, but also to cancer progression and metastasis formation.
Comparing this network between mouse and human, we identified a new transcription
factor (TF) motif TFAP2A/C that is consistently involved in EMT. When applying
the NMuMG cellular model of TGFβ-induced EMT, we found that the predicted
activity of the TFAP2A/C is inversely correlated to the Tfap2a mRNA expression
during the process. We have confirmed that TFAP2A directly binds to the promoter
of Zeb2, a TF central to EMT. Thus, it regulates the expression of this gene.
Furthermore, the TFAP2A overexpression in NMuMG cells modulates the cells’
epithelial phenotype and induces changes in cell adhesion and morphology. This
overexpression was followed by increased mRNA levels of EMT master regulator
TFs, together with an elevated expression of genes involved in cellular adhesion.
Therefore, we identified a potentially new role of TFAP2A transcription factor, which
suggests that elements of its regulatory function during neural crest development
might operate in mechanisms controlling epithelial plasticity in normal breast and
tumor tissues.
Overall, we characterized another facet of microRNAs’ function in pluripotency and
differentiation in ESC, as well as a new aspect of the implication of TFAP2A in
epithelial cell state integrity and plasticity. Therefore we contributed to expanding our
insight of how are regulated at molecular level the cell identity homeostasis and the
unfolding of cellular phenotypical plasticity.