BORIS/CTCFL-mediated chromatin accessibility alterations promote a pro-invasive transcriptional signature in melanoma cells

Abstract

Melanoma is the deadliest form of skin cancer, due to its tendency to metastasize early. Brother of Regulator of Imprinted Sites (BORIS), also known as CCCTC binding factor-Like (CTCFL), is a transcription regulator that becomes ectopically expressed in melanoma. We recently showed that BORIS contributes to melanoma phenotype switching by altering the gene expression program of proliferative melanoma cells in favor of a more invasive phenotype. However, how BORIS alters the transcriptome remains unclear. Here, ATAC-seq was used to study BORIS-mediated chromatin accessibility alterations in proliferative melanoma cells. Genes that gained promoter accessibility following ectopic BORIS expression, were enriched for melanoma-specific invasive genes as well as invasion-associated biological processes, while promoters of genes associated with proliferation show reduce accessibility. Integration of ATAC-Seq and RNA-Seq data demonstrates that increased chromatin accessibility is associated with transcriptional upregulation of genes involved in tumor progression processes, and the aberrant activation of oncogenic transcription factors, while reduced chromatin accessibility and downregulated genes, were associated with repressed activity of tumor suppressors. Together, these findings indicate that BORIS mediates transcriptional reprogramming in melanoma cells by altering chromatin accessibility and gene expression, shifting the cellular transcription landscape of proliferative melanoma cells towards a pro-invasive genetic signature. SignificanceWe recently reported that BORIS contributes to melanoma phenotype switching by altering the transcriptional landscape of melanoma cells from a proliferative to an invasive state. In this study, using ATAC-Seq, we demonstrate that ectopic BORIS expression in proliferative melanoma cells leads to increased chromatin accessibility at promoters of upregulated invasion-associated genes. Importantly, by integrating the ATAC-Seq data with RNA-Seq data, we were able to identify key cancer-associated transcription factors that become aberrantly activated or repressed following ectopic BORIS expression. Taken together, this study sheds light on the mechanisms by which BORIS mediates phenotype switching in melanoma cells.