PARP1 ufmylation modulates replication stress response

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High-fidelity DNA replication ensures the accurate transmitting of parental genetic information to daughter cells. Studying the molecular mechanisms of the cellular response to replication stress has important implications on aging, tissue homeostasis, and pathogenesis, including cancer and neurodegeneration. UFM1 is the most recently identified ubiquitin-like protein and conjugates to target protein(s), a process known as ufmylation, via an E1-like enzyme (UBA5), an E2-like enzyme (UFC1), and an E3 ligase (UFL1). However, the biological function of ufmylation remains largely unknown. We found that defects in UFM1 compromise the DNA replication stress response by delaying the activation of the S-phase checkpoint kinase CHK1. Moreover, PARP1 is found ufmylated, which enhances its enzymatic activity. Furthermore, a defective ufmylation compromises the recruitment of the MRN complex to DNA damage sites. We showed previously that the PARP1 product PAR binds to CHK1 to facilitate its activation in the S-phase checkpoint. Thus, we hypothesize that a PARP1 ufmylation promotes CHK1-mediated replication stress and coordinates a MRN-mediated repair of the stalled forks. This project aims to study (1) whether ufmylation plays an important role in the S-phase checkpoint; (2) its underlying molecular mechanism, and (3) its biological function in vivo. To achieve these goals, my lab at the Fritz Lipmann Institute (FLI), Germany and Prof. Dr. Xingzhi Xu from the Shenzhen University, China decided to combine our effort to carry out biochemical and cellular experiments, as well as genetic studies. Specifically, we will investigate whether the ATR-CHK1 pathway is directly modulated by ufmylation and how PARP1 ufmylation coordinates the response to replication stress with the repair of stalled replication forks. To this end, we will employ human cell lines and mouse models, in which ufmylation is genetically modified. We will perform a biochemical study to map the ufmylation site in PARP1 and test its impact on the CHK1 activation and fork stability. Finally, we will examine a possible interplay of PARylation and ufmylation by generating and using hypoPARylated or enzymatic dead PARP1 cells and mice. Our research will reveal a novel function of UFM1 signaling in handling DNA replication stress and the maintenance of genome stability. Exploring the specific function of ufmylation in the network of the ATR-CHK1 and PARP1/CHK1 pathways may provide scientific knowledge to modulate this novel post-translational modification process as new therapeutic strategies for the treatment of human malignancy and aging-related diseases.