NFATC2IP is a mediator of SUMO-dependent genome integrity

The post-translational modification of proteins by SUMO is crucial for cellular viability andmammalian development in part due to the contribution of SUMOylation to genome duplicationand repair. To investigate the mechanisms underpinning the essential function of SUMO, weundertook a genome-scale CRISPR/Cas9 screen probing the response to SUMOylationinhibition. This effort identified 130 genes whose disruption reduce or enhance the toxicity ofTAK-981, a clinical-stage inhibitor of the SUMO E1 activating enzyme. Among the strongesthits, we validated and characterized NFATC2IP, an evolutionarily conserved protein related tothe fungal Esc2 and Rad60 proteins, which harbors tandem SUMO-like domains. Cells lackingNFATC2IP are viable but are hypersensitive to SUMO E1 inhibition, likely due to theaccumulation of mitotic chromosome bridges and micronuclei. NFATC2IP primarily acts ininterphase and associates with nascent DNA, suggesting a role in the post-replicative resolutionof replication or recombination intermediates. Mechanistically, NFATC2IP interacts with theSMC5/6 complex and UBC9, the SUMO E2, via its first and second SUMO-like domains,respectively. AlphaFold-multimer modeling suggests that NFATC2IP positions and activates theUBC9-NSMCE2 complex, the SUMO E3 ligase associated with SMC5/SMC6. We conclude thatNFATC2IP is a key mediator of SUMO-dependent genomic integrity that collaborates with theSMC5/6 complex.