The transcription factor Sox18 plays a role in angiogenesis, including lymphangiogenesis, where it is upregulated by growth factors and directs the expression of genes encoding, e.g., guidance molecules and a matrix metalloproteinase. Conversely, we found that in human umbilical vein endothelial cells (HUVEC) Sox18 is repressed by the pro-inflammatory mediator TNF alpha (as well as IL-1 and LPS). Since a common feature of these mediators is the activation of the NF-kappa B signaling pathway, we investigated whether Sox18 downregulation is dependent on this transcription factor. Transduction of HUVEC with an adenoviral vector directing the expression of the NF-kappa B inhibitor I kappa B alpha prevented the downregulation of Sox18. Transient transfections of Sox18 promoter reporter genes revealed that the downregulation takes place on the level of transcription, and that the p65/RelA subunit of NF-kappa 8 was operative. Furthermore, the responsible promoter region of Sox18 is located within -1.0 kb from the transcriptional start site. The repression of Sox18 and its target genes may lead to altered formation of vessels in inflamed settings. (C) 2013 Elsevier Inc. All rights reserved.