HNF4α and CDX2 Regulate Intestinal Promoter Activity.

The Hippo pathway is important for tissue homeostasis, regulation of organ size andgrowth in most tissues. The co-transcription factor yes-associated protein 1 (YAP1) serves as a maindownstream effector of the Hippo pathway and its dysregulation increases cancer development andblocks colonic tissue repair. Nevertheless, little is known about the transcriptional regulation ofYAP1 in intestinal cells. The aim of this study to identify gene control regions in the gene andtranscription factors important for intestinal expression. Bioinformatic analysis of caudal typehomeobox 2 (CDX2) and hepatocyte nuclear factor 4 alpha (HNF4α) chromatin immunoprecipitatedDNA from differentiated Caco-2 cells revealed potential intragenic enhancers in the gene.Transfection of luciferase-expressing YAP1 promoter-reporter constructs containing the potentialenhancer regions validated one potent enhancer of the YAP1 promoter activity in Caco-2 and T84cells. Two potential CDX2 and one HNF4α binding sites were identified in the enhancer by in silicotranscription factor binding site analysis and protein-DNA binding was confirmed in vitro usingelectrophoretic mobility shift assay. It was found by chromatin immunoprecipitation experimentsthat CDX2 and HNF4α bind to the enhancer in Caco-2 cells. These results reveal a previouslyunknown enhancer of the YAP1 promoter activity in the YAP1 gene, with importance for highexpression levels in intestinal epithelial cells. Additionally, CDX2 and HNF4α binding areimportant for the enhancer activity in intestinal epithelial cells.