RAC1 and rheumatoid arthritis: Additionally, Ras-related C3 botulinum toxin substrate 1 (Rac1), a member of the Rho family of Ras-like small GTPases, interacts with a series of effectors and thus mediates various biological functions (122). Ca2+/Rac1 signaling has been reported to regulate the migration and invasion of RA-FLSs (123, 124).