Re-expression of SMARCA4/BRG1 in Small Cell Carcinoma of Ovary, Hypercalcemic Type (SCCOHT) promotes an epithelial-like gene signature through an AP-1-dependent mechanism [ATAC-seq]

Small cell carcinoma of the ovary, hypercalcemic type (SCCOHT) is a rare and aggressive form of ovarian cancer. SCCOHT tumors have inactivating mutations in SMARCA4 (BRG1), one of the two mutually exclusive ATPases of the SWI/SNF chromatin remodeling complex. To address the role that BRG1 loss plays in SCCOHT tumorigenesis, we performed integrative multi-omic analyses in a SCCOHT cell line +/- BRG1 re-expression. BRG1 re-expression induced a gene and protein signature similar to an epithelial cell and gained chromatin accessibility sites correlated with other epithelial originating TCGA tumors. Gained chromatin accessibility and BRG1 recruited sites were strongly enriched for transcription factor binding motifs of AP-1 family members. Furthermore, AP-1 motifs were enriched at the promoters of highly upregulated epithelial genes. Using a dominant negative AP-1 cell line, we found that both AP-1 DNA binding activity and BRG1 re-expression are necessary for the gene and protein expression of epithelial genes. Our study demonstrates that the BRG1 re-expression drives an epithelial-like gene and protein signature in SCCOHT cells that depends upon by AP-1 activity. Four biological replicates of BIN67 cells were co-transfected (FuGENE 6, Promega #E269A) with either control (pCMV-neo or pCDNA3-neo) or BRG1 (PBJ5-BRG1) plasmids at a 10:1 ratio to a plasmid containing puromycin resistance (pBABE-puro). Twenty-four hours after transfection, cells were placed on 2 µg/ml puromycin for 3 days and then harvested for analyses. Samples from each biological replicate were divided and processed for ATAC-seq and RNA-seq.