Role of small ubiquitin-like modifier proteins-1 (SUMO-1) in regulating migration and invasion of fibroblast-like synoviocytes from patients with rheumatoid arthritis.

Rheumatoid arthritis (RA) is featured by erosive cartilage and bone destruction. The enhancing aggressive property of fibroblast-like synoviocytes (FLSs) plays a critical role in this process. Small ubiquitin-like modifier (SUMO) proteins, including SUMO-1, SUMO-2, SUMO-3 and SUMO-4, participate in regulating many cellular events such as survival, migration and signal transduction in some cell lines. However, their roles in the pathogenesis of RA are not well established. Therefore, we evaluated the role of SUMO proteins in RA FLSs migration and invasion. We found that expression of both SUMO-1 and SUMO-2 was elevated in FLSs and synovial tissues (STs) from patients with RA. SUMO-1 suppression by small interference RNA (siRNA) reduced migration and invasion as well as MMP-1 and MMP-3 expression in RA FLSs. We also demonstrated that SUMO-1 regulated lamellipodium formation during cell migration. To explore further into molecular mechanisms, we evaluated the effect of SUMO-1 knockdown on the activation of Rac1/PAK1, a critical signaling pathway that controls cell motility. Our results indicated that SUMO-1-mediated SUMOylation controlled Rac1 activation and modulated downstream PAK1 activity. Inhibition of Rac1 or PAK1 also decreased migration and invasion of RA FLSs. Our findings suggest that SUMO-1 suppression could be protective against joint destruction in RA by inhibiting aggressive behavior of RA FLSs.