YAP is a candidate oncogene for esophageal squamous cell carcinoma

Yes-associated protein (YAP), the nuclear effector of the Hippo pathway, is a key regulator of organ size and a candidate human oncogene located at chromosome 11q22. Since we previously reported amplification of 11q22 region in esophageal squamous cell carcinoma (ESCC), in this study we focused on the clinical significance and biological functions of YAP in this tumor. Frequent overexpression of YAP protein was observed in ESCC cells including those with a robust amplicon at position 11q22. Overexpression of the YAP protein was frequently detected in primary tumors of ESCC as well. Patients with YAP-overexpressing tumors had a worse overall rate of survival than those with non-expressing tumors, and YAP positivity was independently associated with a worse outcome in the multivariate analysis. Further analyses in cells in which YAP was either overexpressed or depleted confirmed that cell proliferation was promoted in a YAP isoform-independent but YAP expression level-dependent manner. YAP depletion inhibited cell proliferation mainly in the G₀-G₁ phase and induced an increase in CDKN1A/p21 transcription but a decrease in BIRC5/survivin transcription. Our results indicate that YAP is a putative oncogene in ESCC and it represents a potential diagnostic and therapeutic target.