Boehly, N. | Search bioRxiv

bioRxiv2025

SMAD4 loss drives cancer chromosomal instability through transcription-replication conflict-induced replication stress

Cancer chromosomal instability (CIN) drives tumor evolution through generating structural and numerical chromosome aberrations. However, its molecular determinants remain poorly characterized. Here, we uncover a yet unrecognized role for the tumor suppressor SMAD4 as a key regulator of genome stability. Mechanistically, loss of SMAD4 induces replication stress by promoting transcription-replication conflicts (TRCs), which induces chromosomal breaks and subsequent mitotic errors, leading to the concomitant emergence of structural and numerical CIN. While the tumor suppressor function of SMAD4 has been predominantly attributed to TGF-{beta} signaling, we find that its role in genome maintenance operates via BMP signaling and its transcriptional target gene ID3. Consequently, inhibition of BMP signaling mimics the loss of SMAD4 whereas re-expression of SMAD4 or ID3 suppresses TRCs, replication stress and mitotic errors in SMAD4-deficient cancer cells. Our findings reveal a TRC- and replication stress-driven mechanism by which loss of BMP-SMAD4 signaling causes cancer chromosomal instability.

cancer biology↗

bioRxiv2021

Dormant replication origin firing links replication stress to whole chromosomal instability in human cancer

Chromosomal instability (CIN) is a hallmark of cancer and comprises structural CIN (S-CIN) and whole chromosome instability (W-CIN). Replication stress (RS), a condition of slowed or stalled DNA replication during S phase, has been linked to S-CIN, whereas defects in mitosis leading to chromosome missegregation and aneuploidy can account for W-CIN. It is well established that RS can activate additional replication origin firing that is considered as a rescue mechanism to suppress chromosomal instability in the presence of RS. In contrast, we show here that an increase in replication origin firing during S phase can contribute to W-CIN in human cancer cells. Increased origin firing can be specifically triggered by overexpression of origin firing genes including GINS1 and CDC45, whose elevated expression significantly correlates with W-CIN in human cancer specimens. Moreover, endogenous mild RS present in cancer cells characterized by W-CIN or modulation of the origin firing regulating ATR-CDK1-RIF1 axis induces dormant origin firing, which is sufficient to trigger chromosome missegregation and W-CIN. Importantly, chromosome missegregation upon increased dormant origin firing is mediated by increased microtubule growth rates leading to the generation of lagging chromosomes in mitosis, a condition prevalent in chromosomally unstable cancer cells. Thus, our study identified increased or dormant replication origin firing as a hitherto unrecognized, but cancer-relevant trigger for chromosomal instability.

cell biology↗