Modification of the SUMO activating enzyme subunit SAE2 directs SUMO isoform bias required for mitotic fidelity.

Mammalian cells possess three conjugatable SUMO variants: SUMO1 and the largely indistinguishable SUMO2 and SUMO3 (designated SUMO2/3). Some SUMOylated substrates are modified by both SUMO1 and SUMO2/3, while others show biased modifications towards SUMO1 or SUMO2/3. How preferential SUMO protein conjugation is coordinated is poorly understood. Here, we examine a modification of the catalytic component of the human SUMO Activation Enzyme, SAE2. We observe that lysine 164 of SAE2 is deacetylated during mitosis in an HDAC6-dependent manner. We find that an acetyl-analogue mutant, SAE2-K164Q, biases the activation and conjugation of SUMO2>SUMO1 and discriminates SUMO1 and SUMO2/3 through their C-terminal tails. Complementation of SAE2-depleted or inhibited cells with SAE2-K164Q restricts mitotic SUMO1-conjugates and increases multipolar spindle formation. We confirm the SUMO E1-dependent modification of the nuclear mitotic apparatus, NuMA, and find that the mitotic defects of both SAE2-K164Q complemented cells and HDAC6-inhibitor-treated cells are corrected by either over-expression of SUMO1 or by expression of a GFP-SUMO1-NuMA-K1766R fusion protein. Our observations suggest a model in which the SAE1:SAE2 enzyme is deacetylated on early mitosis to encourage the conjugation of SUMO1 to support mitotic fidelity. These surprising data reveal that the SUMO-activating enzyme can bias SUMO variant conjugation.