Dexamethasone regulates AP-1 to repress TNF-α induced MCP-1 production in human glomerular endothelial cells

Background. Glomerular endothelial cells play a role in the pathogenesis of glomerulonephritis by producing chemotactic factors. We investigated the role of NF-kappaB and AP-1 in tumour necrosis factor alpha (TNF-alpha) induced monocyte chemoattractant protein 1 (MCP-1) production in cultured human glomerular endothelial cells (HGEC). We also examined whether or not these processes could be modified by glucocorticoid. Methods. MCP-1 protein and mRNA levels were measured by ELISA and northern blot. NF-kappaB and AP-1 binding activity were assessed by electrophoretic mobility shift assay. Cytosolic IkappaBalpha and nuclear p65 protein were evaluated by western blot. For specific inhibition of NF-kappaB or AP-1, we used a decoy oligodeoxynucleotide. Results. TNF-alpha (10 ng/ml) increased MCP-1 mRNA expression in HGEC and also the release of MCP-1 protein into culture media. These effects could be partially inhibited by dexamethasone (10 nM). TNF-alpha induced MCP-1 production appeared to be NF-kappaB and AP-1 interdependent, based on the following results. (i) TNF-alpha increased NF-kappaB and AP-1 binding activity. (ii) Both NF-kappaB decoy oligodeoxynucleotide and AP-1 decoy oligodeoxynucleotide partially suppressed TNF-alpha induced MCP-1 mRNA expression. On the other hand, dexamethasone decreased TNF-alpha induced DNA-binding activity of AP-1 without an effect on the DNA-binding activity of NF-kappaB, cytosolic IkappaBalpha degradation or p65 nuclear translocation. Conclusions. These data demonstrate that while TNF-alpha induced MCP-1 production is mediated by the cooperative action of NF-kappaB and AP-1 in HGEC, dexamethasone represses TNF-alpha induced MCP-1 production via suppression of AP-1 binding activity.