Combination of the pro-inflammatory cytokines IL-1, TNF-alpha and IL-17 leads to enhanced expression and additional recruitment of AP-1 family members, Egr-1 and NF-kappaB in osteoblast-like cells.

To determine the contribution of IL-1, TNF-alpha and IL-17 on AP-1, NF-kappaB and Egr-1 activation in cytokine induced bone destruction as observed in rheumatoid arthritis, we investigated the effect of these pro-inflammatory cytokines used alone or in combination on transcription factor activation in osteoblast-like ROS 17/2.8 cells. The effects of each cytokine were measured by RT-PCR and immunocytochemistry. IL-1 and TNF-alpha induced most of these transcription factors while IL-17 had a weak effect. IL-1 and TNF-alpha induced egr-1 and all AP-1 member expression, except fosB and junD. These two cytokines used alone induced their nuclear translocation in 30 min, except for FosB and JunB. IL-17 enhanced fra-2 and egr-1 mRNA expression, while nuclear localization was observed for Fra-1, JunD and NF-kappaB. More importantly, combination of low concentrations of these cytokines, with no effect separately, showed a synergistic effect on transcription and nuclear translocation of AP-1 members, Egr-1 and NF-kappaB. Moreover, cytokine combinations were associated with an enhanced recruitment of factors not expressed when cytokines were used alone. In conclusion, AP-1, Egr-1 and NF-kappaB pathways in osteoblast cells are very sensitive to the combined effect of pro-inflammatory cytokines through synergistic mechanisms. Copyright 2004 Elsevier Ltd.