Activation of Sp1 and its functional co-operation with serum amyloid a-activating sequence binding factor in synoviocyte cells trigger synergistic action of interleukin-1 and interleukin-6 in serum amyloid A gene expression

The serum amyloid A (SAA) protein has been implicated in the progression an d pathogenesis of rheumatoid arthritis through induction of collagenase act ivity in synovial fibroblast cells that line the joint tissues. We demonstr ate that SAA is synergistically induced in synovial cells by interleukin (I L)-1 and IES that are present at significantly high level in the synovial f luid of arthritis patients. These cytokines induced phenotypic changes in s ynovial cells, promoting protrusion and increased cellular contact. Inducti on of SAA under this condition is mediated by promoter elements located bet ween -254 and -226, which contains binding sites for transcription factors Sp1 and SAA activating sequence binding factor (SAF). Mutation of these seq uences abolishes SAA promoter response to IL-1 and IL-6. The role of Spl in SAA induction was demonstrated by increased DNA binding activity, phosphor ylation, and increased protein content of Spl during cytokine treatment. Sp l interacts with the SAA promoter in association with SAF as an SAF Spl het eromeric complex. Furthermore, using a phosphatase inhibitor, we demonstrat ed increased transactivation potential of both Spl and SAF as a consequence of a phosphorylation event. These results provide first evidence for cytok ine-mediated activation of Spl in synovial fibroblast cells and its partici pation in regulating SAA expression by acting in conjunction with SAF.