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. 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.