A transcriptional regulatory loop of master regulator transcription factors, PPARG, and fatty acid synthesis promotes esophageal adenocarcinoma.

Although obesity is one of the strongest risk factors for esophageal adenocarcinoma (EAC), the molecular mechanisms underlying this association remain unclear. We recently identified 4 EAC-specific master regulator transcription factors (MRTF) ELF3, KLF5, GATA6, and EHF. In the present study, Gene Set Enrichment Analysis (GSEA) of both EAC patient samples and cell line models unbiasedly underscore fatty acid synthesis as the central pathway downstream of three MRTF (ELF3, KLF5, GATA6). Further characterizations unexpectedly identified a transcriptional feedback loop between MRTF and fatty acid synthesis, which mutually activated each other through the nuclear receptor PPARG. MRTF cooperatively promoted PPARG transcription by directly regulating its promoter and a distal EAC-specific enhancer, leading to PPARG overexpression in EAC. PPARG was also elevated in Barrett's esophagus, a recognized precursor to EAC, implying that PPARG might play a role in the intestinal metaplasia of esophageal squamous epithelium. Upregulation of PPARG increased de novo synthesis of fatty acids, phospholipids, and sphingolipids as revealed by mass spectrometry-based lipidomics. Moreover, ChIP-Seq, 4C-Seq, and a high-fat diet murine model together characterized a novel, noncanonical, and cancer-specific function of PPARG in EAC. PPARG directly regulated the ELF3 super-enhancer, subsequently activating the transcription of other MRTF through an interconnected regulatory circuitry. Together, elucidation of this novel transcriptional feedback loop of MRTF/PPARG/fatty acid synthesis advances our understanding of the mechanistic foundation for epigenomic dysregulation and metabolic alterations in EAC. More importantly, this work identifies a potential avenue for prevention and early intervention of EAC by blocking this feedback loop.