5-Lipoxygenase (5-LO) expression is strongly induced by transforming growth factor-beta (TGF beta) and 1 alpha,25-dihydroxyvitamin D-3 in Mono Mac 6 cells. Since Smads have been described as downstream effectors of TGF beta, we have investigated the role of the TGF beta/Smad signalling system in the regulation of 5-LO gene expression. The rapid induction of 5-LO mRNA, determined with real-time quantitative RT-PCR, suggests that 5-LO is a primary TGF beta target gene. In reporter gene assays with plasmids containing the 5-LO promoter plus different parts of the gene, Smads3/4 mediate a prominent upregulation of reporter activity that strongly depends on the coding sequence and to a lesser extent on the 3'-UTR and introns J-M. Deletion studies revealed the most profound decrease of inducibility by Smads3/4 when exons 10-14 are deleted. Sequence analysis and deletion studies indicate the existence of up to four Smad binding elements and at least one TGFP responsive element far downstream of the transcriptional start site. (c) 2006 Elsevier Inc. All rights reserved.