Activation of Aryl Hydrocarbon Receptor Inhibits Proliferation of Human Umbilical Vein Endothelial Cells.

Abstract

The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor which mediates a variety of biological processes including reproduction and in particular normal placentation. The AhR has been extensively studied as a receptor for environmental toxicants such as dioxin. Upon binding to these toxicants, the AhR is activated and could induce adverse developmental effects on many tissues including fetal cardiovasculature. Recently, normal physiological roles of AhR have begun to be recognized, particularly after the discovery of endogenous AhR ligands such as 2-(1'H-indole-3'-carbonyl)-thiazole-4-carboxylic acid methyl ester (ITE), which has a much lower toxicity as compared with the extreme deleterious effects of dioxin. However, little is known about AhR actions in endothelial cells and their underlying signaling mechanisms. Herein, we examined if ITE activated AhR and affected proliferation of human umbilical vein (HUV) endothelial (HUVE) cells in response to fetal bovine serum. The expression of AhR in HUV and HUVE cells was evaluated by immunohistochemistry and Western blot analysis, respectively. Cell proliferation was determined in vitro using the crystal violet cell proliferation assay. AhR was immunolocalized in endothelial cells of HUV and was expressed in HUVE cells in vitro. We observed that ITE dose-dependently (0.1 nM-5 μM) and time-dependently (2-6 days) inhibits (P < 0.05) HUVE cells proliferation. ITE also reduced (P < 0.05) AhR protein levels in a time-dependent manner, with an initial decrease seen at 6 hr and completely vanished after 48 hr, indicating that ITE induced robust AhR activation. AhR plays an important role in mediating HUVE cells growth and may account for the potential deleterious effects of environmental toxicants on embryonic/fetal vasculature and thus fetal development. (HL64703 to JZ, HD38843 to RRM and JZ, HL49210 to RRM) (poster)