MAPK3 and rheumatoid arthritis: The differential expression of ASK1 and ERK was confirmed at the protein level by western blot analysis, where ASK1 showed a 49% higher expression (Fig. 4B) and ERK1/2 a 27% lower expression (Fig. 4C) in CARBP2 suppressed RA FLS compared with RA FLS transfected with control siRNA.