In osteoarthritic (OA) synovial fluid, many proinflammatory cytokines coexist and stimulate chondrocytes. As interleukin 17 (IL-17) is a catabolic cytokine, we explored its effects on collagenase-3 production. In a comparative manner we identified IL-17 and IL-1beta induced transcription factors mediating upregulation of this enzyme's production.
Collagenase-3 levels were determined by ELISA. Transfection experiments of human OA chondrocytes were performed, with the plasmids -1599CAT and -133CAT consisting of 1.6 kb and the first proximal 133 bp containing polyomavirus enhancer A-3 (PEA-3), activating protein-1 (AP-1), and TATA box of the human collagenase-3 promoter, respectively. Electrophoretic mobility shift assays were done with the AP-1 and PEA-3 oligonucleotides derived from the human collagenase-3 promoter sequence. Supershift assays were carried out with the specific antibodies against the Jun and Fos proteins.
IL-17 induced collagenase-3 expression and synthesis, with an EC50 at 10 ng/ml. Transfection experiments with wild-type -1599CAT and -133CAT and their mutated AP-1 or PEA-3 derivatives revealed that the AP-1 site was essential for basal and proinflammatory cytokine induced collagenase-3 promoter activity, whereas the PEA-3 motif exerted a cooperative effect. Of note, in OA chondrocytes, IL-17 and IL-1beta induced collagenase-3 production through AP-1 occurred with differential protein complexes: IL-17 stimulation resulted in FosB activation, while IL-1beta stimulated c-Fos. Data showed a strong activation of JunB only in cells showing a higher collagenase-3 basal level and low cytokine (IL-17 and IL-1beta) inducibility, suggesting this transcription factor protein acts as a negative regulator.
We demonstrated that IL-17 and IL-1beta induced collagenase-3 production in OA chondrocytes mainly through AP-1 mediated transcriptional activity but with differential protein complexes, suggesting that some AP-1 proteins play a pivotal role in the different cytokine responses in terms of collagenase-3 production. Our data might suggest that JunB protein plays a rate-limiting step in cytokine induced collagenase-3 production in OA chondrocytes.