Complex and variable regulation of Np63 and TAp63 by TGF has implications for the dynamics of squamous cell epithelial to mesenchymal transition

TGF beta has roles in inflammation, wound healing, epithelial to mesenchymal transition (EMT), and cancer stem cell states, and acts as a tumor suppressor gene for squamous cell carcinoma (SCC). SCCs are also characterized by high levels of Delta Np63, which induces epithelial cell phenotypes and maintains squamous stem cells. Previous studies indicate a complex interplay between Delta Np63 and TGF beta signaling, with contradictory effects reported. We investigated the effects of TGF beta on p63 isoform proteins and mRNAs in non-malignant squamous and SCC cells, and the role of either canonical or non-canonical TGF beta signaling pathways. TGF beta selectively increased Delta Np63 protein levels in non-malignant keratinocytes in association with SMAD3 activation and was prevented by TGF beta receptor inhibition, indicating activation of canonical TGF beta pathway signaling. TP63 isoform mRNAs showed discordance from protein levels, with an initial increase in both TAP63 and Delta NP63 mRNAs followed by a decrease at later times. These data demonstrate complex and heterogeneous effects of TGF beta in squamous cells that depend on the extent of canonical TGF beta pathway aberrations. The interplay between TGF beta and p63 is likely to influence the magnitude of EMT states in SCC, with clinical implications for tumor progression and response to therapy.