Project Summary Barrett’s esophagus and small cell carcinoma in the esophagus are characterized by the loss of squamous cell identity while gaining other cell fates. Thus far effective treatment options for these diseases are limited in part due to an incomplete understanding of the molecular mechanisms driving the initial cell fate changes. This application will address how the transcription factor p63 directs the squamous differentiation program and safeguards esophageal basal progenitor cells from neuroendocrine cell commitment. We and others have demonstrated that loss of p63 leads to the abrogation of the stratified squamous epithelium in the developing esophagus. However, how p63 regulates cell fate determination of esophageal progenitor cells remains largely unknown. Surprisingly, we found that p63 deletion results in extensive neuroendocrine differentiation in the esophagus. Moreover, loss of p63 expression was also observed in small cell carcinoma of the esophagus. Inhibition of the key epigenetic silencing factor EZH2 re-activates p63 expression in neuroendocrine cells, which is accompanied by the acquisition of squamous cell fate. We therefore hypothesize that epigenetically regulated p63 expression suppresses neuroendocrine while promoting the squamous cell differentiation program in the esophagus. Three specific aims are formulated to test the hypothesis. Aim 1 will test whether the role played by p63 in cell fate determination is isoform-specific and conserved in human esophageal progenitor cells (EPCs). We will combine mouse genetic models and human pluripotent stem cell differentiation to address this Aim. Aim 2 will determine p63-mediated transcriptional program during the specification of EPCs. We will use multiple epigenomic assays including ChIP-seq and ATAC-seq to determine p63 downstream targets at the genome-wide level. We will also use biochemistry assays to test candidate genes implicated in cell fate transition that are potentially bound and functionally regulated by p63. Aim 3 will determine the mechanism and impact of p63 silencing on neuroendocrine commitment. In this Aim we will investigate how p63 expression is modulated by epigenetic regulatory mechanisms during aberrant cell fate commitment, thus identifying strategies to restore the squamous differentiation program. Combining our joint expertise on mouse genetics, cell biology, chromatin biology and epigenomics, this work will provide novel mechanistic insights into esophageal cell fate regulation and offer new approaches to treat neuroendocrine lesions.

Narrative Cell fate recommitment underlies the pathogenesis of multiple esophageal diseases including Barrett’s esophagus and small cell carcinoma in the esophagus. This proposal will identify the mechanism by which the transcription factor p63 safeguards esophageal basal progenitor cells from neuroendocrine cell differentiation. The knowledge gained will be used for comprehensively identifying new therapeutic targets for treating esophageal diseases involving cell fate switch.