PBRM1-deficient PBAF complexes target aberrant genomic loci to activate the NF-κB pathway in clear cell renal cell carcinoma

Abstract

Yao et al. observe and characterize genomic redistribution of the PBAF complexes upon PBRM1 loss, leading to sustained RELA occupancy by SMARCA4, activation of the NF-kB pathway and enhanced kidney tumourigenesis. PBRM1 encodes an accessory subunit of the PBAF SWI/SNF chromatin remodeller, and the inactivation of PBRM1 is a frequent event in kidney cancer. However, the impact of PBRM1 loss on chromatin remodelling is not well examined. Here we show that, in VHL-deficient renal tumours, PBRM1 deficiency results in ectopic PBAF complexes that localize to de novo genomic loci, activating the pro-tumourigenic NF-kappa B pathway. PBRM1-deficient PBAF complexes retain the association between SMARCA4 and ARID2, but have loosely tethered BRD7. The PBAF complexes redistribute from promoter proximal regions to distal enhancers containing NF-kappa B motifs, heightening NF-kappa B activity in PBRM1-deficient models and clinical samples. The ATPase function of SMARCA4 maintains chromatin occupancy of pre-existing and newly acquired RELA specific to PBRM1 loss, activating downstream target gene expression. Proteasome inhibitor bortezomib abrogates RELA occupancy, suppresses NF-kappa B activation and delays growth of PBRM1-deficient tumours. In conclusion, PBRM1 safeguards the chromatin by repressing aberrant liberation of pro-tumourigenic NF-kappa B target genes by residual PBRM1-deficient PBAF complexes.