Interleukin-6 (IL-6) is involved in fibroblast-like synoviocyte (FLS) activation and promotes pannus formation and bone and cartilage destruction in rheumatoid arthritis (RA). Cysteine-rich 61 (Cyr61) protein regulates cell proliferation, migration, and differentiation. The aim of this study was to investigate the role of Cyr61 in RA-FLS migration and invasion after IL-6 stimulation.
Western blotting, immunohistochemistry, reverse transcription-polymerase chain reaction, and real time-polymerase chain reaction were used to examine protein and mRNA levels of Cyr61, matrix metalloproteinases (MMPs), and other signalling proteins. Knockdown of gene expression was performed with siRNA, and RNA sequencing was performed for differential gene analysis. Migration and invasion were assessed by wound healing and Boyden chamber assays.
Cyr61 levels were elevated in FLSs from RA patients compared to those in osteoarthritis patients. Control and IL-6-treated FLSs showed differential gene expression. IL-6 stimulated protein synthesis of Cyr61, which was attenuated by the extracellular signal-related kinase 1/2 (ERK 1/2) inhibitor, PD98059, and knockdown of early growth response 3 (EGR3), but not of JUN. IL-6-induced Cyr61 protein synthesis increased expression of MMP2. Cyr61 promoted FLS migration and invasion in an autocrine manner. Knockdown of CYR61 and a neutralising antibody attenuated Cyr61 synthesis and IL-6-induced FLS migration.
By modulating the ERK/EGR3 pathway, IL-6 stimulated Cyr61 production and in turn increased invasiveness of FLS. Our data suggest that Cyr61 might be a potential target to prevent the progression of joint damage in RA.