No abstract

Rheumatoid arthritis (RA), one of the most common articular diseases, is characterized by chronic inflammation, hyperproliferation of synovial cells, and bone destruction. CD81, which belongs to a family of cell-surface proteins (tetraspanin), is known to be up-regulated in RA synoviocytes. Recently, we showed the therapeutic effect of using small interfering RNA in targeting CD81 (CD81 siRNA) for RA. Here we show how tumor necrosis factor-alpha (TNF-α) can induce the expression of synoviolin, which is decreased by the addition of CD81 siRNA in SW982 cells. In addition, CD81 siRNA decreases the expression of TNF-α in SW982 cells, suggesting that TNF-α stimulates the expression of synoviolin via CD81. Furthermore, knock down of CD81 by the addition of CD81 siRNA decreases the expression of TNF-α, and TNF-α-induces expression of synoviolin in direct and indirect ways. These results in SW982 cells might explain the therapeutic effect of CD81 siRNA in animal models.

CD81 belongs to a family of cell-surface proteins (tetraspanins) known to be up-regulated in rheumatoid arthritis (RA) synoviocytes. Recently, we showed that small interfering RNA targeting CD81 (CD81 siRNA) has a therapeutic effect on RA. We also showed that CD81 siRNA decreased the expression of TNF-in SW982 cells, suggesting that TNF-stimulates the expression of synoviolin via CD81. Here, we show that a monoclonal antibody (MAb) against CD81, which was raised by immunization with recombinant CD81, decreased the proliferation of rat C6 glioma cells, showing that this antibody is functionally active and probably inhibits cell proliferation through the inhibition of CD81 function on the cell surface.

CD81 belongs to a family of cell-surface proteins (tetraspanins) that have four transmembrane domains and two outer-membrane loops. CD81 has been shown to be up-regulated in rheumatoid arthritis (RA) synoviocytes and is involved in the progression of RA through the promotion of synoviolin expression. Recently, we showed that small interfering RNA targeting CD81 (CD81 siRNA) ameliorates paw swelling in collageninduced arthritic (CIA) rats. CD81 siRNA also decreases the expression of TNF-in SW982 cells. Previously, we established hybridoma cell lines producing monoclonal antibodies (MAbs) against CD81, which decrease the proliferation of rat C6 glioma cells. Here, we established a sandwich enzyme-linked immunosorbent assay (ELISA) system for the quantitation of CD81 using these MAbs.

Tetraspanin CD81, which is up-regulated in rheumatoid arthritis (RA) synoviocytes, is a molecule containing four transmembrane domains. We recently showed that small interfering RNA targeting CD81 (CD81 siRNA) ameliorated arthritis in rats. In that study, the expression of synoviolin was decreased in RA joints by CD81 siRNA. We also showed that CD81 siRNA decreased the expression of synoviolin and TNF- in SW982 synovial sarcoma cells, suggesting that overexpression of CD81 in synovial cells induces the expression of both synoviolin and TNF- in the same cells. Here we raised monoclonal antibodies (MAbs) against CD81 by immunization of the outer membrane region of CD81 (LEL) that was overexpressed as a recombinant protein.One of these MAbs stimulated CD81 on the membrane of SW982 and up-regulated the expression of synoviolin. We also defined the region of the synoviolin gene promoter that is essential for induction of synoviolin gene expression by using reporter gene system. This system might be useful for the screening of anti-RA medicine.