ADAMTS (a disintegrin and metalloproteinase domain with thrombospondin motifs) constitute a family of endopeptidases related to matrix metalloproteinases. These proteases have been largely implicated in tissue remodeling and angiogenesis associated with physiological and pathological processes. To elucidate the in vivo functions of ADAMTS-12, we have generated a knockout mouse strain (Adamts12) in which Adamts12 gene was deleted. The mutant mice had normal gestations and no apparent defects in growth, life span and fertility. By applying three different in vivo models of angiogenesis (malignant keratinocyte transplantation, Matrigel plug and aortic ring assays) to Adamts12 À/À mice, we provide evidence for a protective effect of this host enzyme toward angiogenesis and cancer progression. In the absence of Adamts-12, both the angiogenic response and tumor invasion into host tissue were increased. Complementing results were obtained by using medium conditioned by cells overexpressing human ADAMTS-12, which inhibited vessel outgrowth in the aortic ring assay. This angioinhibitory effect of ADAMTS-12 was independent of its enzymatic activity as a mutated inactive form of the enzyme was similarly efficient in inhibiting endothelial cell sprouting in the aortic ring assay than the wild-type form. Altogether, our results show that ADAMTS-12 displays antiangiogenic properties and protect the host toward tumor progression.

As invading breast carcinoma cells breach their underlying basement membrane, they become confronted with a dense three-dimensional reactive stroma dominated by type I collagen. To develop metastatic capabilities, invading tumor cells must acquire the capacity to negotiate this novel microenvironment. Collagen influences the fate of epithelial cells by inducing apoptosis. However, the mechanisms used by invading tumor cells to evade collagen-induced apoptosis remain to be defined. We demonstrate that membrane type-1 matrix metalloproteinase (MT1-MMP/MMP-14) confers breast cancer cells with the ability to escape apoptosis when embedded in a collagen gel and after orthotopic implantation in vivo. In the absence of MMP-14-dependent proteolysis, type I collagen triggers apoptosis by inducing the expression of the pro-apoptotic Bcl-2-interacting killer in luminallike breast cancer cells. These findings reveal a new mechanism whereby MMP-14 activity promotes tumor progression by circumventing apoptosis.

Embryo implantation requires extensive angiogenesis at the maternal-fetal interface. Hyperglycosylated human chorionic gonadotropin (hCG-H), a trophoblast invasive signal produced by extravillous cytotrophoblasts and by choriocarcinoma, was evaluated for its angiogenic role. hCG-H was purified by HPLC from choriocarcinoma supernatant, and the glycosylation pattern was determined by 2D gel analysis. Angiogenesis models used were aortic ring assay with wild-type and LHCGR-knockout mice, endothelial and mural cell proliferation, and migration assays. The TGF-β signaling pathway was studied by coimmunoprecipitation, competitive binding, TGF-β reporter gene assays, and Smad immunoblotting. hCG-H displayed a potent angiogenic effect [3.2-fold increase of number of vessel intersections in wild-type aortic rings (11.406 to 36.964)]. hCG-H-induced angiostimulation was independent of the classic hCG signaling pathway since it persisted in LHCGR-knockout mice [4.73-fold increase of number of vessel intersections (10.826 to 51.288)]. Using TGF-β signaling inhibitors, Tβ-RII was identified as the hCG-H receptor responsible for its angiogenic switch. hCG-H exposure enhanced phosphorylation of Smad 2 in endothelial and mural cells and genomic activation of Smad-responsive elements. Interaction between hCG-H and Tβ-RII was demonstrated by coimmunoprecipitation and binding competition with (125)I-TGF-β. This new paracrine interaction between trophoblast and endothelial cells through the hCG-H and the TGF-β receptor complex plays a key role in angiogenesis associated with placental development and tumorigenesis.

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