Elevation of carboxyl methylation activity on GTP-binding protein γ-subunit in synovial tissues from rheumatoid arthritis: how does elevation of the methylation relate to the signal transduction system of rheumatoid arthritis?

We examined guanosine triphosphate (GTP)-binding proteins (G-proteins) in synovial tissues obtained from patients with rheumatoid arthritis or osteoarthritis. The results of immunoblot analysis with anti-bovine G-protein βγ-subunit antibody in the rheumatoid synovial tissue were similar to those in the osteoarthritis synovial tissue. On the other hand, the carboxyl methylation activity on G-protein γ-subunit in the rheumatoid synovial tissue was enhanced compared with that in the osteoarthritis synovial tissues: Km and Vm values were 2.6µM and 10 pmol/mg·min, respectively, for the rheumatoid arthritis, and 4.8µM and 5.6 pmol/mg·min, respectively, for the osteoarthritis. These results suggest that G-protein-linked signal transduction, in reference to carboxyl methylation of the γ-subunit, is affected in rheumatoid tissues.