Regulation of host cell DNA replication protein SMARCAL1 by adenovirus

Adenoviruses have evolved to inactivate host cell responses to DNA damage through interaction with host cell proteins and by targeting some of these proteins for ubiquitin-mediated proteolysis. Indeed, previous studies have suggested that early region proteins dysregulate ATR signalling pathways during infection by sequestering the MRE11-RAD50-NBS1 complex and promoting the proteasomal degradation of TopBP1. Moreover, the cellular E1B-55K-interacting protein, E1B-AP5 modulates ATR kinase activity during infection. Work presented here has established that adenovirus targets the cellular replication, and DNA damage response protein, SMARCAL1 for degradation in an E1B-55K/E4orf6 and Cullin Ring ligase-dependent manner. As such, we determined that the phosphorylation of SMARCAL1 residues, S123, S129 and S173 by ATR and CDK kinases promoted SMARCAL1 degradation during infection. We also determined that SMARCAL1 recruitment to viral replication centres during infection was partially dependent upon SMARCAL1 phosphorylation but was mainly dependent upon its ability to interact with the RPA complex. We also determined that E1B-55K interacted directly with SMARCAL1 in adenovirus E1-transformed cells and could modulate cellular DNA replication. Indeed, E1B-55K expression initially enhanced DNA replication fork speed but ultimately, promoted replication fork stalling. We propose that SMARCAL1 is targeted for degradation by adenoviruses to inhibit host cell DNA replication.