ADARp150 prohibits whole genome duplication

Impaired control of the G1/S checkpoint allows initiation of DNA replication under non-permissive conditions. Unscheduled S-phase entry is associated with DNA replication stress, demanding for other checkpoints or cellular pathways to maintain proliferation. Here, we uncovered a requirement for ADARp150 to sustain proliferation of G1/S-checkpoint-defective cells under growth-restricting conditions. Besides its well-established mRNA editing function in inversely oriented short interspersed nuclear elements (SINEs), we found ADARp150 to exert a critical function in mitosis. ADARp150 depletion resulted in tetraploidization, impeding cell proliferation in mitogen-deprived conditions. Mechanistically we show that ADAR1 depletion induced aberrant expression of Cyclin B3, which was causative for mitotic failure and whole-genome duplication. Finally, we find that also in vivo ADAR1-depletion-provoked tetraploidization hampers tumor outgrowth. Overall design: RNA sequencing data used to generate to Figure 6A, Supplemental Figure 2J and 4. Each sample is cultured and sequenced in triplicate. TBP ARPE transduced with a non-targeting (NT) shRNA is used as a reference in both unperturbed (+FCS) and serum starved (-FCS) conditions. We analyzed the log-fold changes of transcripts upon ADAR1 depletion and ADARp150 reconstitution to identify genes/pathways that could explain the tetraploidization that we observed upon ADAR1 depletion.