Analyses of the genome stabilising function of the tumor suppressor BRCA1 in mitosis.
Final Report Abstract
BRCA1 is an important tumor suppressor gene frequently lost in breast, ovarian and other cancer types. It is well established that BRCA1 is required for the maintenance of genomic stability by having a key role for homologues recombination (HR) repair. However, our own studies have shown that loss of BRCA1 also causes mitotic defects, in particular leading to abnormally increased microtubule polymerization within mitotic spindles causing chromosome missegregation and aneuploidy. In our DFG-funded project we aimed to gain new insights into the role of BRCA1 as a regulator suppressing chromosomal instability in mitosis. In accordance with previous reports, we found that BRCA1 contributes to different cellular functions required for genome stability including a role in homologous recombination repair, in suppression of replication stress and in ensuring normal execution of mitosis. Our work revealed that loss of HR repair factors like BRCA1 or RAD51 also causes mitotic defects, but the functional HR repair process seems not to be a prerequisite for the suppression of mitotic errors. In contrast, we found strong evidence for a role of replication stress which is induced upon loss of BRCA1 or RAD51, in the induction of abnormally increased microtubule polymerization and chromosome missegregation in mitosis. Moreover, our results indicate that not a slow-down of replication forks during replication stress, but rather an increase in dormant origin firing is a key factor for the subsequent induction of mitotic errors. In addition, we found that replication stress can be associated with increased levels of transcription-replication conflicts and the formation of R-loops and both, inhibition of transcription and experimental resolution of R-loops results in efficient suppression of mitotic errors upon replication stress. Based on this, we propose a model, in which loss of BRCA1 is a key driver for replication stress and dormant origin firing that causes increased levels of transcription-replication conflicts and R-loop formation as a source for a deregulation of mitotic microtubule dynamics triggering mitotic chromosomal instability. Ongoing and future work will be directed towards an understanding of how replication stress and its downstream consequences are linked to the deregulation of microtubule dynamics in mitosis.
Publications
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Mild replication stress causes aneuploidy by deregulating microtubule dynamics in mitosis. Cell Cycle, 18(20), 2770-2783.
Böhly, Nicolas; Kistner, Magdalena & Bastians, Holger
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Increased replication origin firing links replication stress to whole chromosomal instability in human cancer. Cell Reports, 41(11), 111836.
Böhly, Nicolas; Schmidt, Ann-Kathrin; Zhang, Xiaoxiao; Slusarenko, Benjamin O.; Hennecke, Magdalena; Kschischo, Maik & Bastians, Holger
