Signaling events involved in macrophage chemokine expression in response to monosodium urate crystals

Chemokine production has been associated with leukocyte infiltration into the joint during gouty arthritis, and monosodium urate (MSU) crystals, the causative agent of this arthropathy, have been shown to modulate their expression. In the present study, we investigated the transductional mechanisms underlying this cellular regulation in the murine macrophage cell line B10R. We report that MSU crystals rapidly and transiently increase mRNA levels of various chemokines in a concentration-dependent manner. Examination of second messenger activation revealed that macrophage exposure to MSU crystals led to MEK1/2, ERK1/2, and inhibitory protein kappaBalpha phosphorylation as well as to NF-kappaB and AP-1 nuclear translocation. Of interest, specific blockage of the ERK1/2 pathway drastically reduced up-modulation of MSU crystal-mediated chemokine production and activation of nuclear factors. Similarly, selective inhibition of NF-kappaB suppressed NF-kappaB DNA binding activity and the induction of all chemokine transcripts. These findings indicate that ERK1/2-dependent signals seem to be required for AP-1 and NF-kappaB activation and subsequent mRNA expression of the various macrophage chemokines. In addition, transcription and stability assays performed in presence of actinomycin D showed that MSU crystal-mediated MIP-1beta mRNA up-regulation resulted solely from transcriptional control, whereas that of MIP-1alpha, MIP-2, and MCP-1 was due to both gene transcription activation and mRNA posttranscriptional stabilization. Overall, the results of this study help to define the molecular events that govern macrophage chemokine regulation in response to MSU crystals, which is of paramount importance to better understand, and eventually to tame, the inflammatory response during acute gout.