Zuzana Storchova, Kaiserslautern
Summary
Cancers are often characterized by alterations of the chromosome structure and numbers. Although both these changes usually occur simultaneously, little is known whether there is a causal mechanistic relationship between structural and numerical chromosome instability. We have established that gain of even a single chromosome leads to reduced expression of replication factors, increased DNA damage and to DNA replication stress, and subsequently to accumulation of structural rearrangements. The replication stress in aneuploid cells arises due to a reduced abundance of key proteins involved in DNA replication, which leads to reduced or aberrant formation of replication forks and abnormal replication. Evaluation of the replication dynamics by DNA combing revealed that the replication rate in aneuploid cells is often lower than in diploids. At the same time, the distance between replication origins increases, and the frequency of asymmetric replication forks, a hallmark of replication fork stalling, nearly doubles in polysomic cells compared to parental diploid cell lines. The striking changes in replication dynamics in polysomic cells are accompanied by delayed G1-S transition and preliminary data suggest that this is due to altered cyclin dependent kinase activity. Strikingly, these changes can be observed in cells with chromosome gains, but not in cells that lost chromosomes. In our planned experiments, we will further elucidate the molecular processes underlying the altered replication in cells with extra chromosomes. To this end, we will study replication dynamics as well as the phosphoregulation of the G1-S transition and replication origin firing in aneuploid cells. In addition, we will study how the polysomic cells adapt to the changes in replication dynamics and impaired proliferation. For this, we will analyze aneuploid cells whose proliferation improved after in vitro evolution and determine their genomics, transcriptomics and proteomics changes. Computational analysis will help us to identify the molecular pathways that enabled the changes and to determine whether the adaptation trajectories are similar to those identified in cancer. Finally, we will address the question of whether the aneuploidy-induced replication stress contributes to genetic and non-genetic heterogeneity and mutation load of human cells. By single cell next-generation sequencing, we will analyze the heterogeneity of evolved and non-evolved diploid and aneuploid populations and define the evolutionary trajectories in these cells. These experiments will be complemented by the analysis of genomic instability and replication stress during the course of evolution. Together, our analysis will provide information on whether and how genomic instability changes during population adaptation, and whether and how aneuploidy alters the course of adaptation in human cells.
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