Molecular researchers have suggested that pathways dependent on protein kinase C may regulate transcription of interleukin 16 (IL16), a proinflammatory cytokine abundant in arthritic joints.

They compared the effect of various chemical agents on steady state (IL16) mRNA transcripts in growing synovial fibroblasts from six patients with rheumatoid arthritis (RA) and three with osteoarthritis (OA). The reverse transcriptase PCR method they used enabled them to obtain results that were semiquantitative.

Early passage synovial fibroblasts from patients with RA or OA transcribed IL16 mRNA when incubated with growing medium without additives. Protein kinase inhibitor staurosporine enhanced IL16 steady state mRNA in both types of synovial fibroblasts and specific protein kinase C activator phorbol-12-myristate-13-acetate reduced transcription. Other agents—the calcium ionophore ionomycin, protein kinase A stimulator cyclic AMP, and G protein activator MAS-7—gave minor, variable responses. Phosphatase inhibitor okadaic acid and protein kinase inhibitor H-7 dihydrochloride reduced mRNA transcripts, maybe because of their killing the fibroblasts. This response pattern suggests that IL16 is regulated by protein kinase C dependent mechanisms, say the researchers.