YAP1 and skin squamous cell carcinoma: Epithelial αE-catenin was shown to inhibit the β4 integrin-mediated activation of the SRC kinase, which, in turn, directly phosphorylated YAP on tyrosine sites Y341, Y357, or Y394 (Y391, Y407, and Y444 in the longer YAP1-2γ isoform) within its transcription activation domain, and phosphorylation at these sites was necessary for the SRC–YAP-mediated transformation of skin squamous cell carcinoma (SCC) [44].