Agell, N. | bioRxiv Science

bioRxiv2024

Adaptive replication origin activation alters chromatin dynamics and stability in cancer cells

Genome duplication, critical for cell survival and identity, requires precise origin activation to ensure accurate DNA replication and chromatin structure maintenance. In colorectal cancer cells, prolonged replication stress does not hinder cell proliferation, although the mechanisms driving cancer cell adaptability remain largely unclear. Here, we demonstrate that upon recovery, cancer cells are able to activate new replication origins in distinct domains, causing persistent changes in chromatin accessibility, nuclear morphology, and replication timing, ultimately promoting chromatin instability. Chromatin accessibility, particularly in promoter regions, increased following replication stress in a subset of cells, correlating with altered gene expression and nuclear expansion. Additionally, some genes with enhanced promoter accessibility displayed sustained expression changes, further suggesting a transcriptional shift linked to stress adaptation. Our findings reveal that colorectal cancer cells recover from severe replication stress through new origin activation, a mechanism that not only maintains cell proliferation under stress but may also accelerate tumour heterogeneity. This research underscores replication origin activation as a potential therapeutic target in combating cancer cell resilience. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=176 HEIGHT=200 SRC="FIGDIR/small/626323v1_ufig1.gif" ALT="Figure 1"> View larger version (74K): org.highwire.dtl.DTLVardef@18c8779org.highwire.dtl.DTLVardef@11249f1org.highwire.dtl.DTLVardef@1b46ecaorg.highwire.dtl.DTLVardef@d5a31c_HPS_FORMAT_FIGEXP M_FIG C_FIG MAIN HIGHLIGHTSO_LIColorectal cancer cells under severe replication stress activate new replication origins upon recovery. C_LIO_LIThe firing of new origins in distinct replication domains results in long-lasting changes in chromatin accessibility, especially in promoter regions, and is associated with alterations in nuclear morphology and replication timing. C_LIO_LIIncreased chromatin accessibility in certain promoter regions correlates with prolonged gene expression changes. C_LIO_LIThe capacity of CRC cells to recover from severe replication stress fosters chromatin instability and tumour heterogeneity. C_LI

cancer biology↗

bioRxiv2022

Rad51 is a druggable target that sustains replication fork progression upon DNA replication stress

Solving the problems that replication forks encounter when synthesizing DNA is essential to prevent genomic instability. Besides their role in DNA repair in the G2 phase, several homologous recombination proteins, specifically Rad51, have prominent roles in the S phase. Using different cellular models, Rad51 has been shown not only to be present at ongoing and arrested replication forks but also to be involved in nascent DNA protection and replication fork restart. Through pharmacological inhibition, here we study the specific role of Rad51 in the S phase. Rad51 inhibition in non-transformed cell lines did not have a major effect on replication fork progression under non-perturbed conditions, but when the same cells were subjected to replication stress, Rad51 became necessary to maintain replication fork progression. Notably, the inhibition or depletion of Rad51 did not compromise fork integrity when subjected to hydroxyurea treatment. Rad51 inhibition also did not decrease the ability to restart, but rather compromised, fork progression during reinitiation. In agreement with the presence of basal replication stress in human colorectal cancer cells, Rad51 inhibition reduced replication fork speed in these cells and increased {gamma}H2Ax foci under control conditions. These alterations could have resulted from the reduced association of DNA polymerase to chromatin, as observed when inhibiting Rad51. It may be possible to exploit the differential dependence of non-transformed cells versus colorectal cancer cells on Rad51 activity under basal conditions to design new therapies that specifically target cancer cells.

cell biology↗