Induction of macrophage-inflammatory protein-3alpha gene expression by TNF-dependent NF-kappaB activation

Macrophage-inflammatory protein-3alpha (MIP-3alpha), also designated as liver and activation-regulated chemokine (LARC), Exodus, or CCL20, is a recently identified CC chemokine that is expected to play a crucial role in the initiation of immune responses. In this study, we describe that MIP-3alpha expression is under the direct control of NF-kappaB, a key transcription factor of immune and inflammatory responses. Overexpression of the p65/RelA subunit of NF-kappaB significantly increased the MIP-3alpha mRNA level. MIP-3alpha transcription was stimulated by TNF, and this stimulation was inhibited by an NF-kappaB inhibitor, I-kappaBalpha superrepressor. Analysis of the human MIP-3alpha promoter demonstrated a functional NF-kappaB site responsible for its expression. We also show that MIP-3alpha expression is induced in LPS-treated mouse livers that were primed with Propionibacterium acnes, which developed massive liver injury with infiltration of inflammatory cells. This induction was fully dependent on the TNF signaling cascade, because it was not observed in the livers of TNFR1-deficient mice. Furthermore, pretreatment with gliotoxin, an inhibitor of NF-kappaB activity, abrogated the P. acnes/LPS-induced MIP-3alpha expression of wild-type mice. These results clearly demonstrate that MIP-3alpha gene expression is dependent on NF-kappaB activity in vitro, and indicate that the TNFR1-mediated TNF signaling cascade that leads to NF-kappaB activation plays an essential role in MIP-3alpha expression in the murine liver injury model.