A transcription-based mechanism for oncogenic β-catenin-induced lethality in BRCA1/2-deficient cells

Abstract

BRCA1 or BRCA2 germline mutations predispose to breast, ovarian and other cancers. High-throughput sequencing of tumour genomes revealed that oncogene amplification and BRCA1/2 mutations are mutually exclusive in cancer, however the molecular mechanism underlying this incompatibility remains unknown. Here, we report that activation of β-catenin, an oncogene of the WNT signalling pathway, inhibits proliferation of BRCA1/2-deficient cells. RNA-seq analyses revealed β-catenin-induced discrete transcriptome alterations in BRCA2-deficient cells, including suppression of CDKN1A gene encoding the CDK inhibitor p21. This accelerates G1/S transition, triggering illegitimate origin firing and DNA damage. In addition, β-catenin activation accelerates replication fork progression in BRCA2-deficient cells, which is critically dependent on p21 downregulation. Importantly, we find that upregulated p21 expression is essential for the survival of BRCA2-deficient cells and tumours. Thus, our work demonstrates that β-catenin toxicity in cancer cells with compromised BRCA1/2 function is driven by transcriptional alterations that cause aberrant replication and inflict DNA damage.

Identification of MAD2L1 as a Potential Biomarker in Hepatocellular Carcinoma via Comprehensive Bioinformatics Analysis

“…Herein, GSEA results showed that MAD2L1 was associated with DNA repair, G2M checkpoint, p53 signaling pathway, PI3K/AKT/mTOR signaling pathway, and Wnt/ β -catenin signaling pathway in cancer. It is widely acknowledged that DNA replication ensures that cellular genetic information is accurately copied and correctly transmitted to offspring cells [ 32 , 40 , 41 ]. However, DNA replication is prone to interference and damage under various pressures in the body, leading to stagnant DNA replication, affecting genome stability, and even inducing apoptosis [ 42 ], necrosis [ 43 ], and carcinogenesis [ 44 ].…”

Mitotic DNA synthesis is caused by transcription-replication conflicts in BRCA2-deficient cells

“…These cells were released from G1/S arrest in media containing RO-3306 and low-concentration aphidicolin (0.2 μM) and subsequently processed, as described above, for mitotic cell isolation ( Figure S1 D). We refer to the protocols used here to identify MiDAS sites as MiDAS-seq, to differentiate them from the EdU-seq protocols used for mapping sites of replication origin firing ( Dagg et al., 2021 ; Macheret and Halazonetis, 2018 ).…”

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Figure 2 MiDAS sites induced by BRCA2 inactivation map to genes within early-replicating genomic regions (A) Distribution of MiDAS sites (n = 150) identified in BRCA2-deficient (−BRCA2) H1299 cells within genomic regions replicating in early, mid, and late S-phase. (B) MiDAS sites identified using MiDAS-seq (pink) and replication initiation sites identified using EdU-seq ( Dagg et al., 2021 ; gray) at representative genomic regions in BRCA2-deficient (−BRCA2) H1299 cells. RT, replication timing; Ge, genes; IGe, intergenic regions.

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“… (B) MiDAS sites identified using MiDAS-seq (pink) and replication initiation sites identified using EdU-seq ( Dagg et al., 2021 ; gray) at representative genomic regions in BRCA2-deficient (−BRCA2) H1299 cells. RT, replication timing; Ge, genes; IGe, intergenic regions.…”

“…A common feature of CFSs and aphidicolin-induced MiDAS sites is the scarcity of replication origins in their genomic environment ( Le Tallec et al., 2011 ; Letessier et al., 2011 ; Macheret et al., 2020 ). To test whether this was also the case for MiDAS events triggered by BRCA2 inactivation, we calculated the distance between each MiDAS peak and the nearest replication origin, previously mapped by EdU-seq ( Dagg et al., 2021 ). We found that the MiDAS sites in BRCA2-deficient cells were positioned closer to replication origins than the aphidicolin-induced MiDAS sites ( Figure 2 H).…”