Decorin Antagonizes the Angiogenic Network

Decorin, a small leucine-rich proteoglycan, inhibits tumor growth by antagonizing multiple receptor tyrosine kinases including EGFR and Met. Here, we investigated decorin during normoxic angiogenic signaling. An angiogenic PCR array revealed a profound decorin-evoked transcriptional inhibition of pro-angiogenic genes, such as HIF1A. Decorin evoked a reduction of hypoxia inducible factor (HIF)-1α and vascular endothelial growth factor A (VEGFA) in MDA-231 breast carcinoma cells expressing constitutively-active HIF-1α. Suppression of Met with decorin or siRNA evoked a similar reduction of VEGFA by attenuating downstream β-catenin signaling. These data establish a noncanonical role for β-catenin in regulating VEGFA expression. We found that exogenous decorin induced expression of thrombospondin-1 and TIMP3, two powerful angiostatic agents. In contrast, decorin suppressed both the expression and enzymatic activity of matrix metalloprotease (MMP)-9 and MMP-2, two pro-angiogenic proteases. Our data establish a novel duality for decorin as a suppressor of tumor angiogenesis under normoxia by simultaneously down-regulating potent pro-angiogenic factors and inducing endogenous anti-angiogenic agents. Decorin antagonizes multiple receptor tyrosine kinases, such as Met, to suppress tumorigenesis. Decorin promotes angiostasis by blocking hypoxia inducible factor-1α and β-catenin to inhibit vascular endothelial growth factor A and matrix metalloprotease-2/9 activity concurrent with thrombospondin-1 and TIMP3 induction. Decorin abrogates the pro-angiogenic HGF/Met signaling axis, thereby repressing vascular endothelial growth factor A-mediated angiogenesis under normoxia. Soluble decorin attenuates early tumor growth by preventing normoxic angiogenic signaling through the Met receptor.