expressed on the leading edge of membrane filopodia and colocalizes with a-actinin. Purified recombinant GPR56 extracellular domain protein inhibits glioma cell adhesion and causes abnormal cytoskeletal morphology and cell rounding. These results indicate that the extracellular domain may compete for unidentified ligand(s), and block the normal function of GPR56 in cell attachment. In reporter assays, overexpression of GPR56 activates the NF-jB, PAI-1 and TCF transcriptional response elements. These pathways have been implicated in cytoskeletal signaling, adhesion and tumor biology. The above results indicate that GPR56 serves as an adhesion GPCR and is involved in adhesion signaling.

Previously we showed the superior in vitro survival of human telomerase reverse transcriptase (hTERT)-transduced human endothelial cells (EC). Here we show that retroviral-mediated transduction of hTERT in human dermal microvascular EC (HDMEC) results in cell lines that form microvascular structures when subcutaneously implanted in severe combined immunodeficiency (SCID) mice. Anti-human type IV collagen basement membrane immunoreactivity and visualization of enhanced green fluorescent protein (eGFP)-labeled microvessels confirmed the human origin of these capillaries. No human vasculature was observed after implantation of HT1080 fibrosarcoma cells, 293 human embryonic kidney cells, or human skin fibroblasts. Intravascular red fluorescent microspheres injected into host circulation were found within green "telomerized" microvessels, indicating functional murine-human vessel anastamoses. Whereas primary HDMEC-derived vessel density decreased with time, telomerized HDMEC maintained durable vessels six weeks after xenografting. Modulation of implant vessel density by exposure to different angiogenic and angiostatic factors demonstrated the utility of this system for the study of human microvascular remodeling in vivo.

The ␣4 laminin subunit is a component of the basement membrane of blood vessels where it codistributes with the integrins ␣v␤3, ␣3␤1, and ␣6␤1. An antibody against the G domain (residues 919-1207; G 919 -1207 ) of the ␣4 laminin subunit inhibits angiogenesis in a mouse-human chimeric model, indicating the functional importance of this domain. Additional support for the latter derives from the ability of recombinant G 919 -1207 to support endothelial cell adhesion. In particular, endothelial cell adhesion to G 919 -1207 is half-maximal at 1.4 nM, whereas residues 919-1018 and 1016 -1207 of the G domain are poor cellular ligands. Function blocking antibodies against integrins ␣v␤3 and ␤1 and a combination of antibodies against ␣3 and ␣6 integrin subunits inhibit endothelial cell attachment to G 919 -1207 . Moreover, both ␣v␤3 and ␣3␤1 integrin bind with high affinity to G 919 -1207 . Together, our studies demonstrate that the G domain of laminin ␣4 chain is a specific, high affinity ligand for the ␣v␤3 and ␣3␤1 integrin heterodimers and that these integrins, together with ␣6␤1, function cooperatively to mediate endothelial cell-␣4 laminin interaction and hence blood vessel development. We propose a model based on these data that reconcile apparent discrepancies in the recent literature with regard to the role of the ␣v␤3 integrin in angiogenesis. matrix ͉ matrix receptor ͉ blood vessels

Invasion of glioma cells involves the attachment of invading tumor cells to extracellular matrix (ECM), disruption of ECM components, and subsequent cell penetration into adjacent brain structures. Discoidin domain receptor 1 (DDR1) tyrosine kinases constitute a novel family of receptors characterized by a unique structure in the ectodomain (discoidin-I domain). These cell surface receptors bind to several collagens and facilitate cell adhesion. Little is known about DDR1 expression and function in glioblastoma multiforme. In this study we demonstrate that DDR1 is overexpressed in glioma tissues using cDNA arrays, immunohistochemistry and Western blot analysis. Functional comparison of two splice variants of DDR1 (DDR1a and DDR1b) reveal novel differences in cell based glioma models. Overexpression of either DDR1a or DDR1b caused increased cell attachment. However, glioma cells overexpressing DDR1a display enhanced invasion and migration. We also detect increased levels of matrix metalloproteinase-2 in DDR1a overexpressing cells as measured by zymography. Inhibition of MMP activity using MMP inhibitor suppressed DDR1a stimulated cell-invasion. Similarly, an antibody against DDR1 reduced DDR1a mediated invasion as well as the enhanced adhesion of DDR1a and DDR1b overexpressing cells. These results suggest that DDR1a plays a critical role in inducing tumor cell adhesion and invasion, and this invasive phenotype is caused by activation of matrix metalloproteinase-2.