Tumor necrosis factor-alpha (TNF-alpha)-induced and interleukin-1 beta (IL-1 beta)-induced shedding of TNF receptors from gingival fibroblasts

Tumor necrosis factor-alpha (TNF-alpha) exerts its functions by binding two different receptors (TNFR55 and TNFR75). Both TNFR55 and TNFR75 exist in cell-associated and soluble forms. Soluble TNF receptors (sTNFR), sTNFR55 and sTNFR75, are proteolytically shed upon inflammatory stimuli and then modulate various TNF-alpha bioactivities. As human gingival fibroblasts (HGF) can be potential targets for TNF-alpha in inflamed gingiva, we hypothesized that HGF partially modulate the cellular responses to TNF-alpha by regulating their own TNFR. In this study, the kinetics of expression of cell-associated and soluble forms of both receptors from cultured HGF in response to proinflammatory cytokines TNF-alpha and interleukin-1 beta (IL-1 beta) were investigated in vitro. Both TNF-alpha and IL-1 beta upregulated the gene expression of TNFR75 and did not affect that of TNFR55. TNF-alpha and IL-1 beta decreased binding of [(125)I]TNF-alpha to HGF. Moreover, TNF-alpha and IL-1 beta upregulated the release of sTNFR75 from HGF but not that of sTNFR55. These results suggest that HGF under inflammatory conditions may contribute to the inactivation of circulating TNF-alpha through the preferential induction and shedding of TNFR75.