Leukotactin-1 (Lkn-1)/CCL15, is a recently cloned chemotactic chemokine that appears to play important roles in the inflammatory process by recruiting immune cells to inflammatory sites. Expression of the Lkn-1/CCL15 gene is inducible in monocytes but its transcriptional regulation has not been studied. To identify Lkn-1/CCL15 regulatory sequences in monocytic cells, U937 cells were transiently transfected with the luciferase reporter gene linked to various deletions of the Lkn-1/CCL15 promoter region. The region ?269 to ?43 bp from the transcription start site proved to be important for induction by PMA. This region contained two potential NF-kB sites: one between ?191 and ?182 bp, and the other between ?60 and ?51 bp. Mutation of either element reduced PMA-induced expression and electrophoretic mobility shift assays revealed that NF-kB recognized both potential NF-kB sites. In addition, PMA-induction of Lkn-1/CCL15 in transiently transfected U937 cells was blocked by proteasome inhibitor 1. These observations demonstrate that the two NF-kB binding sites are essential for PMA-induced Lkn-1/CCL15 expression in human monocytes.