Even under physiological conditions, DNA replication is continuously challenged. For instance, some genomic regions are intrinsically difficult to replicate due to repetitive sequences (e.g. common fragile sites or contain alternative DNA structures (e.g. DNA/RNA hybrids and G-quadruplex DNA). Conversely, DNA can be chemically modified by cellular metabolites. In cancer cells, however, many additional processes lead to perturbed DNA replication, with a central role for oncogene activation.
We study how cancer cells deal with DNA lesions that arise upon oncogene overexpression. Amplification of the CCNE1 or MYC proto-oncogenes, for instance, leads to uncoordinated firing of replication origins, causing collisions between the translation and replication machinery and depletion of the nucleotide pool.
When replication is persistently perturbed, replication forks can stall and collapse, leading to DNA double-strand breaks (DSBs). For the repair of these highly toxic DNA lesions, cells depend on homologous recombination (HR), which is only active in S/G2 phase of the cell-cycle, and uses the newly formed sister chromatids as the repair template. Repair of these DNA lesions is achieved in coordination with cell-cycle checkpoints. These checkpoints integrate kinase-driven and transcriptional signaling, allowing for both rapid and sustained checkpoint activation to prevent entry into mitosis. These combined mechanisms prevent the initiation of mitosis in the presence of unrepaired DNA damage or incompletely replicated DNA.
We study how replication-born DNA lesions are processed in the cell cycle. Remarkably, we observed that DNA damage in Cyclin E1-overexpression cells frequently is transmitted into mitosis. Using isogenic models and analysis of patient samples, we aim to understand how oncogene-overexpressing cells deal with DNA damage, and if these mechanisms can be therapeutically targeted.