Abstract 1494: PBRM1-deficient PBAF complexes target de novo genomic loci to activate NF-κB pathway in clear cell renal cell carcinoma

Abstract PBRM1 is an accessory subunit of the PBAF subclass of the SWI/SNF chromatin remodeler and the inactivation of PBRM1 is the second most frequent mutational event in kidney tumorigenesis. However, the impact of PBRM1 loss on chromatin remodeling, especially pertaining to kidney tumorigenesis, has not been examined previously. Here we show that in VHL-deficient ccRCC tumors, PBRM1 deficiency results in altered PBAF complexes that retain the association between SMARCA4 and ARID2 but disengage BRD7 from SMARCA4. The PBRM1-deficient PBAF complexes redistribute from promoter proximal regions to distal enhancer regions containing motifs of pro-tumorigenic factors including NF-κB. Subsequently, PBRM1-deficient cells display heightened NF-κB activity across multiple cell models. The ATPase function of SMARCA4 maintains chromatin occupancy of both pre-existing and newly acquired RELA specific to PBRM1 loss, and activates downstream target gene expression. Proteasome inhibitor bortezomib reverses NF-κB activation by reducing RELA occupancy and delays growth of PBRM1-deficient tumors. In conclusion, PBRM1 safeguards the chromatin by repressing aberrant liberation of pro-tumorigenic NF-κB target genes by residual PBRM1-deficient PBAF complexes. Citation Format: Xiaosai Yao, Jing Han Hong, Amrita Nargund, Michelle Shu Wen Ng, Hong Lee Heng, Zhimei Li, Peiyong Guan, Masahiro Sugiura, Pek Lim Chu, Loo Chien Wang, Xiaofen Ye, Robert Yauch, Kenneth Tou-En Chang, Radoslaw M. Sobota, Patrick Tan, Bin Tean Teh. PBRM1-deficient PBAF complexes target de novo genomic loci to activate NF-κB pathway in clear cell renal cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1494.