DNA repair mechanisms are crucial for organismal health and survival. Therefore, all living organisms have evolved diverse mechanisms to repair alterations in the primary structure of DNA. Inherited defects in the mechanisms of genome maintenance is the underlying cause of cancer prone disorders such as Fanconi anemia, a disease characterized by defects in the repair of inter-strand DNA crosslinks and in the rescue of stalled replication forks. Furthermore, metabolic rewiring associated with carcinogenesis induces DNA lesions. Therefore, cancer cells rely on DNA damage responses to sustain growth in the presence of a high load of endogenous lesions and during chemotherapeutic treatments.
Our objective is to understand the biochemical mechanisms that underpin cellular responses to DNA lesions. These mechanisms are determinants for tumor growth and resistance to chemotherapies. We have analyzed systematically the protein composition of replication sites in basal conditions and in response to a variety of chemotherapeutic agents to identify proteins that ensure the progression of replication forks.
In recent years, our main focus has been on the mechanisms and functions of compartmentalization in the DNA damage response (DDR). Proteins required for the detection, the signaling and the repair of DNA lesions typically accumulate within distinct nuclear sites visualized as foci by immunofluorescence staining. We consider DDR nuclear foci as membrane-less compartments that control the spaciotemporal organization of DNA damage responses.
Our working model is that the recruitment of a key multivalent protein scaffolds at DNA lesions nucleates the assembly of DDR foci. Foci formation is triggered by posttranslational modifications that increase attractive interactions. These cooperative and reversible interactions promote the formation of micron-sized protein networks that fulfill the functions of subcellular compartments. For example, we reported recently that the multivalent protein scaffold TOPBP1 drives the assembly of nuclear foci to activate ATR/Chk1 signaling.
We use a combination of molecular biology, biochemistry, optogenetics and high-resolution microscopy to understand the mechanisms, the internal organization and the functions that arise specifically from the assembly of membrane-less compartments in the DDR.
Role of protein condensation in response to DNA damage