Aromatic Hydrocarbon Receptor Suppresses Prostate Cancer Bone Metastasis Cells-Induced Vasculogenesis of Endothelial Progenitor Cells under Hypoxia

Background/Aims: Hypoxia leads to the development of neovascularization in solid tumor by regulating VEGF expression. Aromatic hydrocarbon receptor (AHR), a receptor for dioxin like compounds, functions as a transcription factor through dimerization with hypoxia inducible factors 1 beta (HIF-1 beta) and inhibits the secretion of vascular endothelial growth factor (VEGF). The purpose of this study was to explore whether AHR can suppress hypoxia induced VEGF production in prostate bone metastasis cells and repress neovascularization in endothelial progenitor cells (EPCs), and, if so, through what mechanisms. Methods: PC-3 or LNCaP cells induced angiogenesis was detected by Matrigel-based tube formation assay, mRNA expression levels was measured by qRT-PCR, VEGF secretion level was determined by ELISA assay, respectively. Results: AHR activation inhibits hypoxia-induced adhesiveness and vasculogenesis of EPCs induced by PC-3 or LNCaP cells under hypoxia. Moreover, AHR activation suppressed hypoxia-induced VEGF production in PC-3 and LNCaP cells (48 +/- 14% in PC-3, p = 0.000; 41 +/- 14% in LNCaP, p = 0.000) by attenuating HIF-1 alpha and HIF-1 beta level that in turn diminished the angiogenic ability of EPCs in vitro. Furthermore, we found the mRNA level of hypoxia-inducible factors 1 alpha (HIF-1 alpha) (1.54 +/- 0.13 fold in PC-3, p = 0.002, 1.62 +/- 0.12 fold in LNCaP, p = 0.001) and HIF-1 beta (1.67 +/- 0.23 fold in PC-3, p = 0.007; 1.75 +/- 0.26 fold in LNCaP, p=0.008) were upregulated in prostate cancer bone metastasis PC-3 and LNCaP cell lines in response to hypoxia, and revealed that the regulation of VEGF by HIF-1 alpha and HIF-1 beta was possibly mediated by the activation of phosphatidylinositol 3-kinase pathway. Conclusion: By providing a mechanistic insight into the modulation of neovascularization by AHR ligand, we suggest that AHR ligand has a strong potential of being a new therapeutic agent with applications in the field of bone metastatic prostate cancer. (C) 2016 The Author(s) Published by S. Karger AG, Basel