Regulation of vascular endothelial growth factor expression in human keratinocytes by retinoids

Vascular endothelial growth factor (VEGF) is overexpressed in hyperprolifer ative diseases, such as psoriasis and cancers, which are characterized by i ncreased angiogenesis. Experimentally, VEGF overexpression can be induced b y the treatment of cell cultures and biological tissues with phorbol esters , such as 12-O-tetradecanoylphorbol-13-acetate (TPA). Using normal human ke ratinocytes in conventional cultures and skin grafted onto nude mice in viv o, we show that retinoids can inhibit TPA-mediated VEGF gene induction at t he transcriptional level. Because retinoids are biologically active either by interacting with the nuclear retinoic acid receptors or by interfering w ith the activator protein 1 (AP1) transcription factor, we studied the effe ct of the retinoic acid derivative CD 2409, which exhibits strong anti-AP1 activity but does not bind to the known retinoic acid receptors in vitro. T he results demonstrate that the inhibition of VEGF expression by retinoids only depends on their anti-AP1 activity and does not require gene transacti vation via retinoic acid response elements. Because the VEGF promoter conta ins four potential AP1 binding sites, we used different promoter constructs to identify the functional site responsible for TPA induction and retinoid inhibition. This site turned out to be localized at position -621 of the 5 ' flanking region of the VEGF gene.