To examine the effect of thrombin on nuclear factor (NF)-kappaB activation and cell proliferation in synovial cells from patients with rheumatoid arthritis (RA).
Using cultured human synovial cells from patients with RA, electrophoretic mobility shift assay, [3H]thymidine incorporation assay, and MTT assay were performed. We tested the upregulatory effects of thrombin on NF-kappaB activation and cell proliferation. The effect of thrombin on degradation of IkappaB was analyzed by Western blot.
Thrombin transiently induced DNA-binding activity of NF-kappaB, followed by degradation of IkappaBalpha, but not IkappaBbeta1. Moreover, synovial cell proliferation was stimulated by thrombin in a dose dependent manner. The kinetics of synovial cell proliferation induced by thrombin were almost parallel to those of NF-kappaB activation. Supershift analysis revealed that thrombin induced DNA-binding complexes were made up principally of the p65 and p50 Rel family members. Further, protein kinase C inhibitor calphostin C repressed thrombin induced NF-kappaB activation and cell proliferation in synovial cells.
Thrombin stimulates synovial cell proliferation involved in NF-kappaB activation, at least in part, through a protein kinase C mediated pathway, possibly indicating that thrombin plays an important role in synovial hyperplasia in RA.