The SLX4 Complex Is a SUMO E3 Ligase that Impacts on Replication Stress Outcome and Genome Stability

Abstract : The SLX4 Fanconi anemia protein is a tumor suppres- sor that may act as a key regulator that engages the cell into specific genome maintenance pathways. Here, we show that the SLX4 complex is a SUMO E3 ligase that SUMOylates SLX4 itself and the XPF sub- unit of the DNA repair/recombination XPF-ERCC1 endonuclease. This SLX4-dependent activity is medi- ated by a remarkably specific interaction between SLX4 and the SUMO-charged E2 conjugating enzyme UBC9 and relies not only on newly identified SUMO- interacting motifs (SIMs) in SLX4 but also on its BTB domain. In contrast to its ubiquitin-binding UBZ4 motifs, SLX4 SIMs are dispensable for its DNA inter- strand crosslink repair functions. Instead, while detri- mental in response to global replication stress, the SUMO E3 ligase activity of the SLX4 complex is crit- ical to prevent mitotic catastrophe following common fragile site expression.