Abstract
Interferons (IFNs) have proven antitumor activity against a variety of human malignancies, which may result, at least in part, from inhibition of angiogenesis. The objective of this study was to identify IFN-stimulated genes (ISGs) that played a role in mediation of angiogenic inhibition. IFN-beta was a more potent antiangiogenic agent compared to IFN-alpha2b (80% versus 20%, respectively) and suggests that IFNs inhibited angiogenesis by preventing endothelial cell differentiation, and not by direct antiproliferative effects. To identify ISGs that were key inhibitors of angiogenesis, we utilized an in vitro fibrin gel angiogenic assay which closely recapitulated the in vivo processes of angiogenesis. DNA microarray analysis of IFN-beta-treated endothelial cells in the fibrin gel assay identified 11 ISGs that were induced >10-fold during angiogenesis inhibition. Recombinant IP-10 inhibited angiogenesis in a dose-dependent fashion, but was a less effective inhibitor compared to IFN-beta, suggesting that additional ISGs are involved in inhibiting angiogenesis. ISG20 was upregulated by microarray analysis, but did not inhibit angiogenesis when overexpressed in human umbilical vein endothelial cells (HUVECs). However, a dominant negative mutant of ISG20 inhibited angiogenesis by 43%. Results suggest that IFN-induced angiogenic inhibition was likely mediated by multiple ISGs; our novel finding is that decreased exonuclease activity in HUVECs associated with expression of the ISG20 ExoII mutant inhibited angiogenesis.