The effects of PBRM1 loss on the ccRCC transcriptome

Subunits of SWI/SNF chromatin remodeling complexes are frequently mutated in human malignancies. The PBAF complex is composed of multiple subunits, including the tumor suppressor protein PBRM1 (BAF180), as well as ARID2 (BAF200), that are unique to this SWI/SNF complex. PBRM1 is mutated in various cancers, with a high mutation frequency in clear cell renal cell carcinoma (ccRCC). In this study, we integrate RNA-seq, histone modification ChIP-seq, and ATAC-seq data to show that loss of PBRM1 results in de novo gains in H3K4me3 peaks throughout the epigenome including activation of a retinoic acid biosynthesis and signaling gene signature. We show that one such target gene, ALDH1A1, which regulates a key step in retinoic acid biosynthesis, is consistently upregulated with PBRM1 loss in ccRCC cell lines and primary tumors, as well as non-transformed cells. We further find that ALDH1A1 increases the tumorigenic potential of ccRCC cells. Using biochemical methods, we show that ARID2 remains bound to other PBAF subunits after loss of PBRM1 and is essential for increased ALDH1A1 after loss of PBRM1, whereas other core SWI/SNF components are dispensable, including the ATPase subunit BRG1. In total, this study uses global epigenomic approaches to uncover novel mechanisms of PBRM1 tumor suppression in ccRCC. 786O cells infected with either two independent shRNAs against PBRM1 or an off-target control were grown in full RPMI media with either 10% or 1% fetal bovine serum. RNA was extracted when cells were at 70% confluency , poly-A tail captured, and subject to the Illumina TruSeq V2 library prep kit and single end sequenced on an Illumina NextSeq.