The role of carboxy-terminal glycosaminoglycan-binding domain of vitronectin in cytoskeletal organization and migration of endothelial cells

The high and low molecular weight forms of hyaluronan have distinct effects on CD44 clustering

CD44 is a major cell surface receptor for the glycosaminoglycan hyaluronan (HA). Native high molecular weight hyaluronan (nHA) and oligosaccharides of hyaluronan (oHA) provoke distinct biological effects upon binding to CD44. Despite the importance of such interactions, however, the feature of binding with CD44 at the cell surface and the molecular basis for functional distinction between different sizes of HA is still unclear. In this study we investigated the effects of high and low molecular weight hyaluronan on CD44 clustering. For the first time, we provided direct evidence for a strong relationship between HA size and CD44 clustering in vivo. In CD44-transfected COS-7 cells, we showed that exogenous nHA stimulated CD44 clustering, which was disrupted by oHA. Moreover, naturally expressed CD44 was distributed into clusters due to abundantly expressed nHA in HK-2 cells (human renal proximal tubule cells) and BT549 cells (human breast cancer cell line) without exogenous stimulation. Our results suggest that native HA binding to CD44 selectively induces CD44 clustering, which could be inhibited by oHA. Finally, we demonstrated that HA regulates cell adhesion in a manner specifically dependent on its size. oHA promoted cell adhesion while nHA showed no effects. Our results might elucidate a molecular- and/or cellular-based mechanism for the diverse biological activities of nHA and oHA.

The lipoxygenase inhibitor, baicalein, modulates cell adhesion and migration by up-regulation of integrins and vinculin in rat heart endothelial cells

BACKGROUND AND PURPOSE

Endothelial cell proliferation, migration and adhesion are necessary for the formation of new blood vessels. We reported previously that baicalein strongly inhibited proliferation of rat heart endothelial cells and here we assess effects on migration and adhesion of these cells.

EXPERIMENTAL APPROACH

Effects of baicalein on endothelial migration and adhesion were determined by in vitro wound assays and in modified Boyden chambers. Protein expression and subcellular distribution in rat heart endothelial cells were analysed by immunoblots and immunofluorescence staining.

RESULTS

Pretreatment with baicalein for 48 h resulted in a concentration-dependent inhibition of endothelial migration, with an IC(50) of approximately 20 microM. Adhesion assays revealed that baicalein stimulated endothelial cell adhesion to fibronectin and vitronectin, effects blocked by the synthetic peptide Arg-Gly-Asp (RGD). Moreover, treatment with a blocking antibody against integrin alpha5beta1 drastically attenuated baicalein-mediated endothelial adhesion to fibronectin, but not to vitronectin. Furthermore, baicalein-mediated anti-migration effect and adhesion promotion could be partially reversed by the addition of 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE). Western blot analysis indicated that baicalein increased expression levels of integrin-alpha5beta1, -alphavbeta3 and vinculin proteins. Immunofluorescence staining showed that baicalein induced a marked reorganization of actin stress fibres and the recruitment of vinculin and integrins to focal adhesion plaques, with consequently increased formation of focal adhesion contacts.

CONCLUSIONS AND IMPLICATIONS

Baicalein markedly inhibited the migration and enhanced the adhesion of rat heart endothelial cells, possibly by up-regulation of the integrins (alpha5beta1 and alphavbeta3) and vinculin and by promotion of actin reorganization and focal adhesion contact formation.

Involvement of tumor cell integrin alpha v beta 3 in hematogenous metastasis of human melanoma cells

Early metastasis is the primary cause of death in melanoma patients. The adhesion receptor integrin alpha v beta 3 contributes to tumor cell functions that are potentially involved in melanoma growth and metastasis. We tested whether integrin alpha v beta 3 supports metastasis of human melanoma cells when injected into the bloodstream of immune deficient mice. Comparing variants of the same melanoma cell type that expressed either alpha v beta 3, alpha IIb beta 3 or no beta 3 integrin, we found that only alpha v beta 3 strongly supported metastasis. Inhibition of tumor cell alpha v beta 3 function reduced melanoma metastasis significantly and prolonged animal survival. To understand mechanisms that allow alpha v beta 3, but not alpha IIb beta 3 to support melanoma metastasis, we analyzed proteolytic and migratory activities of the melanoma cell variants. Melanoma cells expressing alpha v beta 3, but not those expressing alpha IIb beta 3 or no beta 3 integrin, produced the active form of metalloproteinase MMP-2 and expressed elevated mRNA levels of MT1-MMP and TIMP-2. This indicates an association between alpha v beta 3 expression and protease processing. Furthermore, alpha v beta 3 expression was required for efficient melanoma cell migration toward the matrix proteins fibronectin and vitronectin. The results suggest that expression of integrin alpha v beta 3 promotes the metastatic phenotype in human melanoma by supporting specific adhesive, invasive and migratory properties of the tumor cells and that the related integrin alpha IIb beta 3 cannot substitute for alpha v beta 3 in this respect.

Decorin inhibits endothelial migration and tube-like structure formation: role of thrombospondin-1

Interactions between endothelial cell receptors and the extracellular matrix (ECM) play a critical, yet poorly understood role in angiogenesis. Based on the anti-adhesive role of decorin, we hypothesized that decorin binding to ECM molecules such as thrombospondin-1 (TSP-1) plays a regulatory role in endothelial tube-like structure (TLS) formation. To test this hypothesis, endothelial cells were plated on TSP-1, decorin, or mixed substrates of TSP-1 plus decorin. TLS formation was induced by applying type I collagen on the confluent endothelial monolayer. Cartilage decorin inhibited the formation of TLSs in a concentration-dependent manner. On substrates of high decorin concentrations (2.5 and 5.0 microg/cm(2)) the reduction in TLSs was due either to a reduction in the number of adhering cells or to decreased cell migration. At low decorin concentrations (0.05 and 0.25 microg/cm(2)) the reduction in TLSs was independent of the number of attached cells. Time-lapse video microscopy revealed that decorin substrates facilitated homotypic aggregation and isolated cord formation at the expense of endothelial migration and TLS formation. Consistent with the reduced migration, endothelial cells formed fewer vinculin-positive focal adhesions and actin-stress fibers on decorin substrates. Endothelial migration and TLS formation were also significantly inhibited by skin decorin and the protein core of cartilage decorin. The inhibition of TLS formation by the protein core of cartilage decorin was potentiated by TSP-1. These findings suggest that decorin alone or in combination with TSP-1 interferes with the activation of endothelial cell receptors by ECM molecules, thus blocking intracellular signals that induce cytoskeletal reorganization, migration, and TLS formation.