TNF and rheumatoid arthritis: We investigated the expression of TAK1 in RA-FLS cells stably expressed control or TRIP (wild type) or TRIPCA (E3 ligase activity mutation) plasmid in the absence or presence of TNFα; the results showed that TAK1 expression was decreased in RA-FLS-TRIP group compared with control group without TNFα stimulated, whereas with the TNFα added into the culture medium, the expression of TAK1 significantly decreased in TRIP stable transfection RA-FLS compared with control RA-FLS (Figure 5(b)).