BRG1 knockdown inhibits proliferation through multiple cellular pathways in prostate cancer

Abstract

Background BRG1 (encoded by SMARCA4) is a catalytic component of the SWI/SNF chromatin remodelling complex, with key roles in modulating DNA accessibility. Dysregulation of BRG1 is observed, but functionally uncharacterised, in a wide range of malignancies. We have probed the functions of BRG1 on a background of prostate cancer to investigate how BRG1 controls gene expression programmes and cancer cell behaviour. Results Our investigation of SMARCA4 revealed that BRG1 is over-expressed in the majority of the 486 tumours from The Cancer Genome Atlas prostate cohort, as well as in a complementary panel of 21 prostate cell lines. Next, we utilised a temporal model of BRG1 depletion to investigate the molecular effects on global transcription programmes. Depleting BRG1 had no impact on alternative splicing and conferred only modest effect on global expression. However, of the transcriptional changes that occurred, most manifested as down-regulated expression. Deeper examination found the common thread linking down-regulated genes was involvement in proliferation, including several known to increase prostate cancer proliferation (KLK2, PCAT1 and VAV3). Interestingly, the promoters of genes driving proliferation were bound by BRG1 as well as the transcription factors, AR and FOXA1. We also noted that BRG1 depletion repressed genes involved in cell cycle progression and DNA replication, but intriguingly, these pathways operated independently of AR and FOXA1. In agreement with transcriptional changes, depleting BRG1 conferred G1 arrest. Conclusions Our data have revealed that BRG1 promotes cell cycle progression and DNA replication, consistent with the increased cell proliferation associated with oncogenesis.

Hypoxic response is driven by the BAF form of SWI/SNF

“…We observed that depletion of the ATPase subunit, BRG1, significantly reduced cell viability both in normoxia, as well as, in hypoxia (Figure 4). Loss of BRG1 has been shown previously by others to be required for cell proliferation 47–50 , thus loss of viability is expected, as loss of a catalytic subunit will significantly affect SWI/SNF ability to alter chromatin structure needed for altered gene expression. Knockdown of ARID1A, ARID1B, PBRM1 and BRD9 under normoxic conditions showed no significant reduction in cell viability but interestingly, we observed an increase in cell proliferation when ARID1B and PBRM1 were depleted (Figure 4).…”

OTUD6A promotes prostate tumorigenesis via deubiquitinating Brg1 and AR

“…It is well established that Brg1 is an essential effector for the regulation of PCa 28 , 29 , and AR is commonly recognized as a key driver of prostate cancer, even CRPC 3 . Therefore, we hypothesized that Brg1 and AR are both essential substrates for OTUD6A to perform its oncogenic roles in PCa.…”

Multi-omic analysis of CIC’s functional networks reveals novel interaction partners and a potential role in mitotic fidelity

“…GLTSCR1 has only recently been identified as a member of the GBAF SWI/SNF complex (Alpsoy and Dykhuizen 2018), and thus GLTSCR1’s role as a SWI/SNF subunit is not fully understood. Notably, knockdown of another GBAF subunit member, SMARCA4, was shown to reduce cell proliferation and induce cell cycle arrest (Innis and Cabot 2020; Giles et al 2021), a role that may be shared by other GBAF members. Within the 88 co-essential genes, we found a significant enrichment for genes with functions related to regulation of attachment of spindle microtubules to kinetochores (BECNI and SIRT2’ , BH-adjusted p-value = 0.0015) and regulation of exit from mitosis (TGFB1 and SIRT2- , BH-adjusted p-value = 0.0031; Figure 4b; Supplemental Table S5; Methods).…”