HGF Induces Epithelial-to-Mesenchymal Transition by Modulating the Mammalian Hippo/MST2 and ISG15 Pathways

Epithelial
to mesenchymal transition (EMT) is a fundamental cell
differentiation/dedifferentiation process which is associated with
dramatic morphological changes. Formerly polarized and immobile epithelial
cells which form cell junctions and cobblestone-like cell sheets undergo
a transition into highly motile, elongated, mesenchymal cells lacking
cell-to-cell adhesions. To explore how the proteome is affected during
EMT we profiled protein expression and tracked cell biological markers
in Madin-Darby kidney epithelial cells undergoing hepatocyte growth
factor (HGF) induced EMT. We were able to identify and quantify over
4000 proteins by mass spectrometry. Enrichment analysis of this revealed
that expression of proteins associated with the ubiquitination machinery
was induced, whereas expression of proteins regulating apoptotic pathways
was suppressed. We show that both the mammalian Hippo/MST2 and the
ISG15 pathways are regulated at the protein level by ubiquitin ligases.
Inhibition of the Hippo pathway by overexpression of either ITCH or
A-Raf promotes HGF-induced EMT. Conversely, ISG15 overexpression is
sufficient to induce cell scattering and an elongated morphology without
external stimuli. Thus, we demonstrate for the first time that the
Hippo/MST2 and ISG15 pathways are regulated during growth-factor induced
EMT.