Effect of antiinflammatory agents on synthesis of MCP-1/JE transcripts by human blood monocytes

The human monocyte chemoattractant protein (MCP)-1 encoded by the JE gene belongs to a family of low molecular weight secretory cytokines with monocyte-stimulating activity. JE transcripts are constitutively synthesized by normal and leukemic monocytes, as well as mesenchymal cells, including fibroblasts, vascular endothelial cells, and smooth muscle cells. Expression of MCP-1/JE is increased severalfold upon exposure of cells to recombinant human granulocyte-macrophage colony-stimulating factor but is down-regulated when cells are treated with lipopolysaccharide (LPS). Given the proinflammatory properties of MCP-1/JE, we have examined the modulatory effects of various antiinflammatory agents, including indomethacin, dexamethasone, cyclosporin A, and interleukin-4, on levels of MCP-1/JE transcripts either constitutively or inducibly expressed by human peripheral blood monocytes. Whereas indomethacin had no detectable effect on synthesis of MCP-1/JE transcripts and interleukin-4 treatment resulted in only a modest increase in steady state JE mRNA levels, exposure of monocytes to dexamethasone (DXS) led to a significant (2.5-10-fold) down-regulation of MCP-1/JE transcript levels. Studies examining the mechanism of down-regulation of JE mRNA by DXS indicated that DXS was acting transcriptionally and posttranscriptionally, by reducing the transcriptional rate of the MCP-1/JE gene and by destabilizing JE mRNA, a process requiring de novo RNA and protein synthesis. Although cyclosporin A by itself had no effect on synthesis of JE transcripts, it apparently relieved LPS-mediated down-regulation of JE transcript levels, by interfering with the destabilizing effect of LPS on JE mRNA. These results may provide new information regarding the action of antiinflammatory agents on synthesis of endogenous proinflammatory cytokines.