ADAMTS9 Is a Cell-Autonomously Acting, Anti-Angiogenic Metalloprotease Expressed by Microvascular Endothelial Cells

The metalloprotease ADAMTS9 participates in melanoblast development and is a tumor suppressor in esophageal and nasopharyngeal cancer. ADAMTS9 null mice die before gastrulation, but, ADAMTS9(+/-) mice were initially thought to be normal. However, when congenic with the C57B1/6 strain, 80% of ADAMTS9(+/-) mice developed spontaneous corneal neovascularization. beta-Galactosidase staining enabled by a lacZ cassette targeted to the ADAMTS9 locus showed that capillary endothelial cells (ECs) in embryonic and adult tissues and in capillaries growing into heterotopic tumors expressed ADAMTS9. Heterotopic B.16-F10 melanomas elicited greater vascular induction in ADAMTS9(+/-) mice than in wild-type littermates, suggesting a potential inhibitory role in tumor angiogenesis. Treatment of cultured human microvascular ECs with ADAMTS9 small-interfering RNA resulted in enhanced filopodial extension, decreased cell adhesion, increased cell migration, and enhanced formation of tube-like structures on Matrigel. Conversely, overexpression of catalytically active, but not inactive, ADAMTS9 in ECs led to fewer tube-like structures, demonstrating that the proteolytic activity of ADAMTS9 was essential. However, unlike the related metalloprotease ADAMTS1, which exerts anti-angiogenic effects by cleavage of thrombospondins and sequestration of vascular endothelial growth factor(165), ADAMTS9 neither cleaved thrombospondins 1 and 2, nor bound vascular endothelial growth factor(165). Taken together, these data identify ADAMTS9 as a novel, constitutive, endogenous angiogenesis inhibitor that operates cell-autono-mously in ECs via molecular mechanisms that are distinct from those used by ADAMTS1. (Am J Pathol 2010, 176:1494-1504; DOI: 10.2353/ajpath.2010.090655)