title: Dioxin receptor deficiency impairs angiogenesis by a mechanism involving VEGF-A depletion in the endothelium and transforming growth factor-beta overexpression in the stroma.
abstract: Angiogenesis has key roles in development and in the progression of human diseases such as cancer. Consequently, identifying the novel markers and regulators of angiogenesis is a critical task. The dioxin receptor (AhR) contributes to vascular homeostasis and to the endothelial response to toxins, although the mechanisms involved are largely uncharacterized. Here, we show that AhR-null mice (AhR(-/-)) have impaired angiogenesis in vivo that compromises tumor xenograft growth. Aortic rings emigration experiments and RNA interference indicated that AhR(-/-) endothelial cells failed to branch and to form tube-like structures. Such a phenotype was found to be vascular endothelial growth factor (VEGF)-dependent, as AhR(-/-) aortic endothelial cells (MAECs) secreted lower amounts of active VEGF-A and their treatment with VEGF-A rescued angiogenesis in culture and in vivo. Further, the addition of anti-VEGF antibody to AhR(+/+) MAECs reduced angiogenesis. Treatment under hypoxic conditions with 2-methoxyestradiol suggested that HIF-1alpha modulates endothelial VEGF expression in an AhR-dependent manner. Importantly, AhR-null stromal myofibroblasts produced increased transforming growth factor-beta (TGFbeta) activity, which inhibited angiogenesis in human endothelial cells (HMECs) and AhR(-/-) mice, whereas the co-culture of HMECs with AhR(-/-) myofibroblasts or with their conditioned medium inhibited branching, which was restored by an anti-TGFbeta antibody. Moreover, VEGF and TGFbeta activities cooperated in modulating angiogenesis, as the addition of TGFbeta to AhR(-/-) MAECs further reduced their low basal VEGF-A activity. Thus, AhR modulates angiogenesis through a mechanism requiring VEGF activation in the endothelium and TGFbeta inactivation in the stroma. These data highlight the role of AhR in cardiovascular homeostasis and suggest that this receptor can be a novel regulator of angiogenesis during tumor development.
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Extremadura, 06071 Badajoz, Spain.
authors.forename: Angel Carlos
authors.initials: AC
authors.lastname: Roman
authors.forename: Jose M
authors.initials: JM
authors.lastname: Carvajal-Gonzalez
authors.forename: Eva M
authors.initials: EM
authors.lastname: Rico-Leo
authors.forename: Pedro M
authors.initials: PM
authors.lastname: Fernandez-Salguero
mesh_terms: D000818:Animals; D001011:Aorta / Q000473:pathology; D003035:Cobalt / Q000494:pharmacology; D053595:Embryonic Stem Cells / Q000166:cytology; D004727:Endothelium / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism; D000860:Hypoxia; D008546:Melanoma, Experimental; D051379:Mice; D009368:Neoplasm Transplantation; D009389:Neovascularization, Pathologic; D018336:Receptors, Aryl Hydrocarbon / Q000172:deficiency* / Q000502:physiology*; D011995:Recombination, Genetic; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism*
chemical_list: D018336:Receptors, Aryl Hydrocarbon; D016212:Transforming Growth Factor beta; D042461:Vascular Endothelial Growth Factor A; D003035:Cobalt; C018021:cobaltous chloride