Tissue inhibitors of metalloproteinases (TIMPs) suppress matrix metalloproteinase (MMP) activity critical for extracellular matrix turnover associated with both physiologic and pathologic tissue remodeling. We demonstrate here that TIMP-2 abrogates angiogenic factor-induced endothelial cell proliferation in vitro and angiogenesis in vivo independent of MMP inhibition. These effects require alpha 3 beta 1 integrin-mediated binding of TIMP-2 to endothelial cells. Further, TIMP-2 induces a decrease in total protein tyrosine phosphatase (PTP) activity associated with beta1 integrin subunits as well as dissociation of the phosphatase SHP-1 from beta1. TIMP-2 treatment also results in a concomitant increase in PTP activity associated with tyrosine kinase receptors FGFR-1 and KDR. Our findings establish an unexpected, MMP-independent mechanism for TIMP-2 inhibition of endothelial cell proliferation in vitro and reveal an important component of the antiangiogenic effect of TIMP2 in vivo.

No abstract

CD97, a membrane protein expressed at high levels on inflammatory cells and some carcinomas, is a member of the adhesion G protein-coupled receptor family, whose members have bipartite structures consisting of an extracellular peptide containing adhesion motifs noncovalently coupled to a class B 7-transmembrane domain. CD97␣, the extracellular domain of CD97, contains 3 to 5 fibrillin class 1 epidermal growth factor (EGF)-like repeats, an Arg-Gly-Asp (RGD) tripeptide, and a mucin stalk. We show here that CD97␣ promotes angiogenesis in vivo as demonstrated with purified protein in a directed in vivo angiogenesis assay (DIVAA) and by enhanced vascularization of developing tumors expressing CD97. These data suggest that CD97 can contribute to angiogenesis associated with inflammation and tumor progression. Strong integrin ␣5␤1 interactions with CD97 have been identified, but ␣v␤3 also contributes to cell attachment. Furthermore, soluble CD97 acts as a potent chemoattractant for migration and invasion of human umbilical vein endothelial cells (HUVECs), and this function is integrin dependent. CD97 EGF-like repeat 4 is known to bind chondroitin sulfate. It was found that coengagement of ␣5␤1 and chondroitotin sulfate proteoglycan by CD97 synergistically initiates endothelial cell invasion. Integrin ␣5␤1 is the first high-affinity cellular counterreceptor that has been identified for a member within this family of adhesion receptors. ( IntroductionThe adhesion G protein-coupled receptors are membrane-bound proteins with long N-termini containing multiple and distinct combinations of adhesion motifs. 1 These proteins contain domains such as epidermal growth factor (EGF)-like, cadherin, lectin, laminin, olfactomedin, immunoglobulin, or thrombospondin modules. The extracellular domains are bound to a conserved family of 7 transmembrane (TM) receptors that are distantly related to the class B, or secretin family, G protein-coupled receptors. A characteristic feature of the receptors within this family is their posttranslational proteolysis prior to expression at the cell membrane from a single peptide to 2 noncovalently associated subunits. [2][3][4] The ␣ subunit comprises the majority of the extracellular domain and contains the adhesion motifs, whereas the ␤ subunit comprises the 7 TM receptor with a short extracellular extension. A lack of knowledge concerning high-affinity ligand or counterreceptor interactions has impeded progress in defining signaling pathways and physiologic actions of this family of receptors.CD97 belongs to the EGF-TM7 subgroup of adhesion G proteincoupled receptors. 5 The proteins in this group contain varying numbers of extracellular fibrillin class 1 type EGF-like repeats and include CD97, EMR1, EMR2, EMR3, and EMR4. CD97 is found in myeloid cells, lymphoid cells, and muscle cells, whereas the other members of this family are predominantly in myeloid lineage cells. 3,[6][7][8] In addition, CD97 is often expressed in advanced-stage thyroid, colorectal, gastric, esophageal, and pancreatic carc...