SUMO1 and rheumatoid arthritis: A recent study found that SUMO1 knockdown inhibits the migration and invasion of RA fibroblast-like synoviocytes (RAFLSs) and RAFLS expression of MMP1 and MMP3. Mechanistically, SUMO1 deficiency suppresses the activity of the Rac1/PAK1 pathway, which normally promotes cell motility [129].