Molecular Switching from Morule to Squamous Metaplasia via p40 and the EBP50/S100A4/Myosin 9 Axis in Endometrial...

Morule and squamous metaplasia are distinctive features of endometrial carcinoma (Em Ca). This study investigated the underlying molecular characteristics of these lesions, focusing on the deltaNp63 (p40) and ezrin-radixin-moesin-binding phosphoprotein 50 (EBP50)/S100A4/myosin heavy chain 9 (MYH9) axis. p40 expression was found at the transitions from morular to squamous metaplasia cells and in the basal/parabasal layers of squamous metaplastic epithelia. Cells stably overexpressing (OE) p40 increased expression of several cancer stem cell (CSC) markers (eg, CD44) and enhanced migration capability, suggesting that p40 induces a CSC phenotype. Expression of EBP50, S100A4, and MYH9 was significantly higher in squamous metaplastic cells compared with morular and surrounding carcinoma cells, along with enhanced interactions between MYH9 and either EBP50 or S100A4. EBP50 OE cells inhibited multinuclear/senescent features, even when MYH9 activity was inhibited; S100A4 OE cells displayed the opposite results. Inhibition of MYH9 in three-dimensional cultures led to elongated and apoptotic cells, likely due to disruption of the EBP50-MYH9 interaction. Finally, hypoxia-inducible factor-1α expression was significantly higher in squamous metaplasia, correlating positively with p40 and cytokeratin 5/6. Collectively, p40 is an initial signal for squamous metaplasia development from morular and surrounding carcinoma cells, by modulating CSC properties. This leads to terminal squamous differentiation through the MYH9 monomer-polymer equilibrium, regulated by EBP50 and S100A4 under hypoxic conditions.