YAP AND TEAD ARE TRANSCRIPTIONAL REGULATORS OF NEUROENDOCRINE DIFFERENTIATION AND GROWTH IN CARCINOID CELLS [RNA-seq]

Molecular regulators of variably aggressive carcinoid tumors are unknown. Since carcinoids have low expression of Yes-associated protein (YAP), we hypothesized that low YAP expression provides a molecular advantage to carcinoids by preventing YAP from binding its partner, TEA domain transcription factor (TEAD). To test this hypothesis, we overexpressed constitutively active YAP and a TEAD-binding defective form of YAP in lung (H727) and pancreatic (BON1) carcinoid cells. We found that active YAP overexpression inhibited neuroendocrine markers, morphology, cell proliferation and anchorage-independent cell growth, while TEAD-binding defective YAP recovered these features. Through integrated ChIP-seq and RNA-seq analyses, we found that YAP-TEAD binding downregulated neuroendocrine transcription factor genes and upregulated transforming growth factor (TGFβ) and Notch genes related to cell growth. We conclude that low YAP expression permits neuroendocrine differentiation and growth in carcinoid cells by preventing YAP-TEAD binding and subsequent dysregulation of neuroendocrine transcription factors, TGFβ and Notch gene targets. These results identify unknown molecular mechanisms in carcinoid development that may apply to the broader family of neuroendocrine cancers.