The researchers found that the Slug protein is preferentially SUMOylated compared to the Snail protein. They used HEK293T cells to show that when Flag-tagged Snail or Slug and GFP-tagged SUMO-1 were co-transfected, only Slug was SUMOylated. This means that Slug undergoes a specific modification called SUMOylation, while Snail does not. This finding suggests that SUMOylation of Slug may play a role in enhancing lung cancer metastasis.