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SMARCB1 maintains lineage fidelity in renal cancer - RNA-seq

ABSTRACT: Transcriptional lineage factors are a prominent class of essential genes in cancer, but the mechanisms that maintain lineage fidelity in advanced cancer clones, and whether lineage factor pathways could be broadly exploited for cancer therapy remain poorly understood. Here, we have used clear cell renal cell carcinoma (ccRCC) as a model to characterise the mechanisms that underlie lineage factor dependence in cancer. Through CRISPR/Cas9 loss-of-function screening and functional validation we find that loss of SMARCB1, a member of the SWI/SNF chromatin remodelling complex, can confer an advantage to ccRCC cells upon inhibition of the essential renal lineage factor PAX8. PAX8 inhibition resistant cells formed tumours with a dramatically altered histology showing neuroendocrine differentiation. Based on ATAC-seq and RNA-seq analysis, SMARCB1 inactivation leads to large-scale loss of kidney-specific epigenetic programmes, acquisition of a cellular state resembling that of rhabdoid tumours, and eventual activation of proliferative pathways. We show that these pathways are supported by the adoption of new transcriptional dependencies on IRF2, BHLHE40, and ZNFX1, factors that represent rare essential genes across different lineage-specific and oncogenic pathways, a principle validated in a large-scale CRISPR/Cas9 screening data set comprising hundreds of cancer cell lines. Thus, lineage factor requirements in cancer can switch upon challenge. The rules governing such lineage switching should be considered when designing novel lineage factor-targeted cancer therapies.

ORGANISM(S): Homo sapiens

PROVIDER: GSE183352 | GEO | 2023/07/19

REPOSITORIES: GEO

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Project description:PBRM1 is the 2nd-most frequently inactivated gene in clear cell renal cell cancer (RCC) but the oncogenic mechanisms, and hence methods for correction, are unclear. PBRM1 is a subunit of the PBAF coactivator complex that transcription factors use to reposition nucleosomes (‘open chromatin’) for gene activation. We therefore looked for transcription factors that recruit endogenous PBRM1 in kidney lineage/RCC cells, as a waypoint to identifying pathways impacted by PBRM1 loss. Unbiased immunoprecipitation/mass-spectrometry analyses of the endogenous PBRM1 interactome in kidney lineage cells revealed PAX8, a master transcription factor essential for proximal tubule epithelial fates, as the major transcription factor recruiting PBRM1/PBAF. The reverse analyses of the PAX8 interactome confirmed recruitment specifically of PBRM1/PBAF, and not the functionally similar BAF coactivator complex. More conspicuous in the PAX8 hub in RCC cells, however, were several corepressors, e.g. DNMT1, which oppose coactivators to repress instead of activate genes. Accordingly, key PAX8 target genes, e.g., GATA3, LHX1, WT1, and ~1000 other downstream kidney epithelial genes, but not PAX8 or PAX2, demonstrated loss of the histone lysine 27 acetylation (H3K27ac) activation mark, increase in CpG methylation repression marks, and lower expression in RCC vs normal kidney cortex, with the greatest repression in cases with bi-allelic PBRM1 inactivation. PBRM1 re-introduction into RCC cells, or depletion of the corepressor DNMT1 using siRNA or a clinical drug decitabine, rebalanced composition and function of the PAX8 transcription factor hub to coactivators, to thereby activate terminal epithelial-fates in vitro and in vivo. In sum, PBRM1 loss in RCC cells skews coregulator composition of the PAX8 master transcription factor hub toward corepressors and repression instead of activation of the downstream terminal epithelial-program; this oncogenic action could be reversed by pharmacologic corepressor depletion/inhibition.

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SMARCB1 maintains lineage fidelity in renal cancer - RNA-seq

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