YAP1 and neoplasm: On the contrary, cytoplasmic YAP is essential for epithelial progenitor cell differentiation in adult airways39and functions as a tumor suppressor by suppressing the WNT/β-catenin signaling pathway.40In normal human skin, YAP nuclear localization is noted in basal layer progenitor cells, while other differentiating cells feature cytoplasmic YAP.