Differential roles of prostaglandin E-type receptors in activation of hypoxia-inducible factor 1 by prostaglandin E(1) in vascular-derived cells under non-hypoxic conditions

Prostaglandin E(1) (PGE(1)), known pharmaceutically as alprostadil, has vasodilatory properties and is used widely in various clinical settings. In addition to acute vasodilatory properties, PGE(1) may exert beneficial effects by altering protein expression of vascular cells. PGE(1) is reported to be a potent stimulator of angiogenesis via upregulation of VEGF expression, which is under the control of the transcription factor hypoxia-inducible factor 1 (HIF-1). However, the molecular mechanisms behind the phenomenon are largely unknown. In the present study, we investigated the mechanism by which PGE(1) induces HIF-1 activation and VEGF gene expression in human aortic smooth muscle cells (HASMCs) and human umbilical vein endothelial cells (HUVECs), both vascular-derived cells. HUVECs and HASMCs were treated with PGE(1) at clinically relevant concentrations under 20% O(2) conditions and HIF-1 protein expression was investigated. Expression of HIF- 1α protein and the HIF-1-downstream genes were low under 20% O(2) conditions and increased in response to PGE(1) treatment in both HUVECs and HASMCs in a dose- and time-dependent manner under 20% O(2) conditions as comparable to exposure to 1% O(2) conditions. Studies using EP-receptor-specific agonists and antagonists revealed that EP1 and EP3 are critical to PGE(1)-induced HIF-1 activation. In vitro vascular permeability assays using HUVECs indicated that PGE(1) increased vascular permeability in HUVECs. Thus, we demonstrate that PGE(1) induces HIF- 1α protein expression and HIF-1 activation under non-hypoxic conditions and also provide evidence that the activity of multiple signal transduction pathways downstream of EP1 and EP3 receptors is required for HIF-1 activation.