Intron 1-Mediated Regulation of EGFR Expression In EGFR-Dependent Malignancies
The epidermal growth factor receptor is known to be overexpressed in numerous solid tumor types and has been the subject of extensive therapeutic development efforts. Much of the research on EGFR is focused on protein dynamics and downstream signaling, however few studies have explored how the gene is regulated transcriptionally. Here, we identified two novel enhancers (CE1 and CE2) present within the first intron of the EGFR gene in models of glioblastoma (GBM) and head and neck squamous cell carcinoma (HNSCC). CE1 and CE2 contain open chromatin and H3K27Ac histone marks, functionally enhance transcription in reporter assays, and interact with the EGFR promoter. Genetic deletion of CE1 and CE2 by CRISPR/Cas9 editing significantly reduces EGFR transcript levels, with double deletion exercising an additive effect. Similarly, targeted repression of CE1 and CE2 by dCas9-KRAB targeting demonstrates repression of transcription similar to that of genomic deletion. We identify AP-1 transcription factor family members in concert with BET bromodomain proteins as candidate modulators of CE1 and CE2 activity in HNSCC and GBM through de novo motif identification and validate their presence in these enhancers. Genetic inhibition of AP-1 or pharmacologic disruption of BET/AP-1 binding results in downregulated EGFR protein and transcript levels, further confirming a role for these factors in CE1 and CE2. Our results identify and characterize these novel enhancers, shedding light on the role that epigenetic mechanisms play in regulating EGFR transcription in EGFR-dependent cancer types.