Interactions between cancer cells and the endothelium in metastasis

3D-extravasation model -- selection of highly motile and metastatic cancer cells

Extravasation has been described as a rate-limiting step in the process of hematogeneous metastasis formation. Thereby, transendothelial migration of tumor cells consists of a complex series of events involving multiple cell-cell and cell-matrix interactions. 3D-extravasation assays are valuable tools for the identification of genes, which are the key players at switchboards of the intracellular signaling pathways. In consequence, the combination of 3D-modeling and whole genome expression analysis lead to unravel molecular parameters which descripe distinct clinical phenotypes of cancer and therefore, work as prognosticators, predictors of therapy and new therapy targets.

Combined effects of zoledronic acid and doxorubicin on breast cancer cell invasion in vitro

The bisphosphonate zoledronic acid and the cytotoxic drug doxorubicin induce synergistic levels of apoptosis in breast cancer cells. As zoledronic acid and doxorubicin have been shown to reduce cell invasion and migration, we have investigated if these drugs also act synergistically on breast cancer invasion in vitro. MCF7 cells were treated with 0.05 microM doxorubicin/4 h followed by 1 or 10 microM zoledronic acid/24 h (or the reverse sequence). To study invasion, MCF7 cells were either grown on Transwell membranes coated with Matrigel or in a 24-well plate. Cells were treated sequentially using the above drug combinations, prior to starting the invasion assays for 48 h. Cell growth and death were also assessed under the same conditions. We found that invasion of MCF7 cells treated with zoledronic acid and doxorubicin was significantly reduced when compared with control, but the effect was dependent on drug sequence. At 1 microM, zoledronic acid significantly reduced invasion only if cells were pre-treated with doxorubicin, but cell growth was unaffected. For 10 microM zoledronic acid, invasion was reduced when administered before or after the doxorubicin, but this dose of zoledronic acid caused a significant reduction in MCF7 growth. Apoptosis was not induced by any of the drug doses and combinations. We conclude that pre-treatment with 0.05 microM doxorubicin followed by 1 microM zoledronic acid reduces invasion when cells were grown on Matrigel. For 10 microM zoledronic acid, pre- or post-doxorubicin also reduces invasion, but for this combination inhibition of cell growth may contribute to the reduction in invasion observed.

Association of alphavbeta3 integrin expression with the metastatic potential and migratory and chemotactic ability of human osteosarcoma cells

INTRODUCTION

Expression of adhesion molecules such as alphavbeta3 integrin has been associated with the metastatic potential of tumor cells. The purpose of this study was to determine whether alphavbeta3 expression correlated with the metastatic potential of human osteosarcoma cells.

MATERIALS AND METHODS

We developed a series of sublines (LM2-LM7) from human osteosarcoma SAOS parental cells, with progressively increasing potential to form lung metastases in nude mice after intravenous injection. SAOS parental and LM2 cells were poorly metastatic, but LM7 cells resulted in visible metastatic lung nodules by 6-8 weeks. We quantified alphavbeta3 integrin expression using flow cytometry.

RESULTS

alphavbeta3 expression correlated with the metastatic potential of the cells, with LM7 cells showing the highest expression. LM7 cell adhesion to vitronectin decreased after treatment with echistatin, a RGD-containing peptide antagonist of alphavbeta3. LM7 cells demonstrated higher chemotactic activity than SAOS cells to a homogenate made from lung tissue. This chemotactic activity was also inhibited by echistatin. These data indicated that alphavbeta3 was critical for the migration of LM7 cells to the lung homogenate. Chemotaxis to a liver homogenate was the same for LM7 and SAOS cells. Migration of LM7 cells through lung endothelial cells was higher than that through liver endothelial cells, and echistatin again inhibited this migration.

CONCLUSIONS

alphavbeta3 integrin expression may play a role in the metastatic potential of osteosarcoma cells by enhancing the ability of the cells to migrate specifically to the lung. Alphavbeta3 integrin may therefore be a potential new target for osteosarcoma.

Gas6 induces proliferation in prostate carcinoma cell lines expressing the Axl receptor

Axl is a tyrosine kinase receptor and although it is expressed in malignancy such as leukemia, colon cancer, melanoma, endometrial, prostate and thyroid cancers, its role has not been completely elucidated yet and appears to be complex. The ligand of Axl, Gas6, is a 75 KDa multimodular protein with an N-terminal gamma-carboxy-glutamic acid that is essential for binding. Gas6 has a mitogenic effect on several normal cell lines. The receptor Axl is expressed in primary prostate carcinoma and in prostate cancer cell lines as such as PC-3 and DU 145. We demonstrated a mitogenic activity determined by Gas6/Axl interaction in these undifferentiated metastatic human prostatic cancer cell lines. This effect is proportional to Axl expression, not due to inhibition of apoptosis, and induces AKT and MAPK phosphorylation. However, only MEK phosphorylation seems to be essential for growth signaling. Our results suggest that Axl overexpression and activation by Gas6 could be involved in progression of prostate neoplastic disease.

Transendothelial migration of melanoma cells involves N-cadherin-mediated adhesion and activation of the beta-catenin signaling pathway

Cancer metastasis is a multistep process involving many types of cell-cell interactions, but little is known about the adhesive interactions and signaling events during extravasation of cancer cells. Transendothelial migration of cancer cells was investigated using an in vitro assay, in which melanoma cells were seeded on top of a monolayer of endothelial cells. Attachment of melanoma cells on the endothelium induced a twofold increase in N-cadherin expression in melanoma cells and the redistribution of N-cadherin to the heterotypic contacts. Transendothelial migration was inhibited when N-cadherin expression was repressed by antisense RNA, indicating a key role played by N-cadherin. Whereas N-cadherin and beta-catenin colocalized in the contact regions between melanoma cells and endothelial cells during the initial stages of attachment, beta-catenin disappeared from the heterotypic contacts during transmigration of melanoma cells. Immunolocalization and immunoprecipitation studies indicate that N-cadherin became tyrosine-phosphorylated, resulting in the dissociation of beta-catenin from these contact regions. Concomitantly, an increase in the nuclear level of beta-catenin occurred in melanoma cells, together with a sixfold increase in beta-catenin-dependent transcription. Transendothelial migration was compromised in cells expressing a dominant-negative form of beta-catenin, thus supporting a regulatory role of beta-catenin signaling in this process.

Bi-directional interactions of prostate cancer cells and bone marrow endothelial cells in three-dimensional culture

BACKGROUND

Prostate cancer preferentially metastasizes to bone, yet little is known about the cellular and molecular factors that support this growth. Endothelial cells are likely the initial contact for circulating prostate cells entering the bone microenvironment.

METHODS

Using co-culture and conditioned media experiments, we studied cellular and molecular interactions of prostate cancer cells of varying aggressiveness (PC-3 and LNCaP) with bone marrow endothelial (HBME-1) cells in collagen gels.

RESULTS

In co-culture, HBME-1 cells stimulated proliferation ( approximately 90% increase) and migration of the more aggressive PC-3 cell line, while having little effect on LNCaP cell proliferation or migration. Concomitantly, HBME-1 cell growth was inhibited by both PC-3 and LNCaP cells and their conditioned media. Additionally, HBME-1 cells underwent significant morphological changes in co-culture, forming large, branching, cord-like structures, which mimic angiogenesis. Prostate cancer cell conditioned media induced a similar effect on HBME-1 cells. In comparison, conditioned media from PC-3 cells also inhibited growth of non-bone marrow-derived endothelial cells, but did not affect their morphology.

CONCLUSIONS

Significant bi-directional interactions, including secreted factors and direct cellular interactions, exist between bone marrow endothelial cells and highly metastatic prostate cancer cells, and may underlie the propensity for prostate cancer to metastasize to the bone.

Purity for clarity: the need for purification of tumor cells in DNA microarray studies

It is now well established that gene expression profiling using DNA microarrays can provide novel information about various types of hematological malignancies, which may lead to identification of novel diagnostic markers. However, to successfully use microarrays for this purpose, the quality and reproducibility of the procedure need to be guaranteed. The quality of microarray analyses may be severely reduced, if variable frequencies of nontarget cells are present in the starting material. To systematically investigate the influence of different types of impurity, we determined gene expression profiles of leukemic samples containing different percentages of nonleukemic leukocytes. Furthermore, we used computer simulations to study the effect of different kinds of impurity as an alternative to conducting hundreds of microarray experiments on samples with various levels of purity. As expected, the percentage of erroneously identified genes rose with the increase of contaminating nontarget cells in the samples. The simulations demonstrated that a tumor load of less than 75% can lead to up to 25% erroneously identified genes. A tumor load of at least 90% leads to identification of at most 5% false-positive genes. We therefore propose that in order to draw well-founded conclusions, the percentage of target cells in microarray experiment samples should be at least 90%.

Association between pterostilbene and quercetin inhibits metastatic activity of B16 melanoma

Inhibition of cancer growth by resveratrol (trans-3,5,4'-trihydroxystilbene; RESV), a phytoalexin present in many plant species, is limited by its low bioavailability. Pterostilbene (3,5-dimethoxy-4'-hydroxystilbene; PTER) and quercetin (3,3',4',5,6-pentahydroxyflavone; QUER), two structurally related and naturally occurring small polyphenols, show longer half-life in vivo. In vitro growth of highly malignant B16 melanoma F10 cells (B16M-F10) is inhibited (56%) by short-time exposure (60 min/day) to PTER (40 microm) and QUER (20 microm) (approximate mean values of plasma concentrations measured within the first hour after intravenous administration of 20 mg/kg each polyphenol). Intravenous administration of PTER and QUER (20 mg/kg per day) to mice inhibits (73%) metastatic growth of B16M-F10 cell in the liver, a common site for metastasis development. The anti-metastatic mechanism involves: 1) a PTER-induced inhibition of vascular adhesion molecule 1 expression in the hepatic sinusoidal endothelium, which consequently decreases B16M-F10 cell adhesion to the endothelium through very late activation antigen 4; and 2) a QUER- and PTER-induced inhibition of Bcl-2 expression in metastatic cells, which sensitizes them to vascular endothelium-induced cytotoxicity. Our findings demonstrate that the association of PTER and QUER inhibits metastatic melanoma growth and extends host survival.

Interaction of human Thy-1 (CD 90) with the integrin αvβ3 (CD51/CD61): an important mechanism mediating melanoma cell adhesion to activated endothelium

The expression of the alphavbeta3 integrin (CD51/CD61) on human melanoma cells has been shown to be associated most closely with tumor progression and metastases formation in melanoma. Here, we demonstrated a specific interaction of the alphavbeta3 integrin on melanoma cells with the human Thy-1, an inducible cell adhesion molecule expressed on the cell surface of activated endothelial cells (EC). The interaction was shown by the binding of purified Thy-1 protein to alpha(V)beta(3) transfected cells, to alphavbeta3-expressing melanoma cells and to purified alpha(V)beta(3) integrin. Moreover, melanoma cells adhere specifically to Thy-1 transfectants via alphavbeta3 on melanoma cells showing the functional relevance of this interaction for cell adhesion. Finally, the importance of the alphavbeta3/Thy-1 interaction for the adhesion of melanoma cells to the activated endothelium was confirmed under static and flow conditions by the inhibition of melanoma cell adhesion to and transmigration across activated EC by blocking the alphavbeta3/Thy-1 interaction. In conclusion, we have identified a new pair of adhesion molecules Thy-1 and alphavbeta3 mediating the interaction of melanoma cells and activated EC. These data explain at least in part the high tumorigenicity of alphavbeta3-expressing melanoma cells and the association of alphavbeta3-positive melanoma cells with a high risk of metastasis and poor prognosis.

Lymphatic endothelium: an important interactive surface for malignant cells

Endothelial cells line the vessels which transport fluid and cells throughout the body. Although much attention has been paid to these cells in the context of the blood vascular system, endothelial cells also line lymphatic vessels. Recent progress in identifying growth factors which drive the development of lymphatic vessels and molecular markers specific for lymphatics has expanded our understanding of the role the lymphatic system plays in human pathology. Techniques for purifying populations of lymphatic endothelial cells also allow the in vitro analysis of this unique surface to explore its role in tumour metastasis, immune cell function and fluid transport. This review provides a synopsis of the recent data pertaining to the purification and culture of lymphatic endothelial cells, and the interaction of tumour cells with lymphatic endothelium.

Identification and phenotypic characterization of a subpopulation of T84 human colon cancer cells, after selection on activated endothelial cells

The extravasation of metastatic cells is regulated by molecular events involving the initial adhesion of tumor cells to the endothelium and subsequently the migration of the cells in the host connective tissue. The differences in metastatic ability could be attributed to properties intrinsic of the various primary tumor types. Thus, the clonal selection of neoplastic cells during cancer progression results in cells better equipped for survival and formation of colonies in secondary sites. A cell line (T84SF) exhibiting an altered phenotypic appearance was selected from a colon cancer cell line (T84) by repetitive plating on TNFalpha-activated human endothelial cells and subsequent selection for adherent cells. Cell growth, motility, chemoinvasive abilities, tyrosine phosphorylation signaling, and the metastasis formation in nude mice of the two cell lines was compared. T84SF cells displayed in vitro an higher proliferation rate and a more invasive behavior compared to the parental cells while formed in vivo a greater number of metastatic colonies in nude mice. As concerns the signaling underlying the phenotypes of the selected cells, we examined the general tyrosine phosphorylation levels in both cell lines. Our results indicate that T84SF have an increased basal tyrosine phosphorylation of several proteins among which src kinase was identified. Treatment of cells with a specific inhibitor of src activity caused a greater in vitro inhibition of proliferation and invasive properties of T84 parental cells with respect to T84SF cells and diminished metastasis formation in vivo. Altogether, these data provide evidences that this new cell line may be valuable for identifying molecular mechanisms involved in the metastatic progression of colon cancer.

Beta3 integrins facilitate matrix interactions during transendothelial migration of PC3 prostate tumor cells

BACKGROUND

beta3 integrins play a role in metastatic progression of prostate cancer by mediating adhesion of cancer cells to endothelium and migration through extracellular matrix (ECM). However, the role of beta3 integrins during transendothelial migration (TEM) of prostate tumor cells is poorly understood. We examined the role of beta3 integrins in TEM of PC3 human prostate cancer cells through a monolayer of human lung microvascular endothelial cells (HLMVECs).

METHODS

PC3 cells were challenged with beta3 integrin antibodies or antisense nucleotides and their efficiency to migrate through monolayers of endothelial cells (ECs) was assessed using confocal microscopy.

RESULTS

beta3 integrins in PC3 cells are not localized in focal contacts and their blockade significantly inhibited TEM by over 50% preferentially during late stages of migration. Formation of PC3 cell pseudopodia on matrigel was significantly reduced by beta3 integrin antisense oligonucleotides.

CONCLUSIONS

beta3 integrins play important roles during TEM of PC3 cells while interacting with the matrix underneath the endothelium. These interactions are independent of the ability to cluster beta3 integrins into focal adhesions.

Invasive characteristics of human prostatic epithelial cells: understanding the metastatic process

Prostate cancer has a predilection to metastasise to the bone marrow stroma (BMS) by an as yet uncharacterised mechanism. We have defined a series of coculture models of invasion, which simulate the blood/BMS boundary and allow the elucidation of the signalling and mechanics of trans-endothelial migration within the complex bone marrow environment. Confocal microscopy shows that prostate epithelial cells bind specifically to bone marrow endothelial-to-endothelial cell junctions and initiate endothelial cell retraction. Trans-endothelial migration proceeds via an epithelial cell pseudopodial process, with complete epithelial migration occurring after 232±43 min. Stromal-derived factor-1 (SDF-1)/CXCR4 signalling induced PC-3 to invade across a basement membrane although the level of invasion was 3.5-fold less than invasion towards BMS (P=0.0007) or bone marrow endothelial cells (P=0.004). Maximal SDF-1 signalling of invasion was completely inhibited by 10 μM of the SDF-1 inhibitor T140. However, 10 μM T140 only reduced invasion towards BMS and bone marrow endothelial cells by 59% (P=0.001) and 29% (P=0.011), respectively. This study highlights the need to examine the potential roles of signalling molecules and/or inhibitors, not just in single-cell models but in coculture models that mimic the complex environment of the bone marrow.

Inhibition of aldose reductase attenuates TNF-alpha-induced expression of adhesion molecules in endothelial cells

Increased expression of adhesion molecules by the activated endothelium is a critical feature of vascular inflammation associated with several disease states such as atherosclerosis. However, mechanisms regulating the endothelial induction of adhesion molecules are not entirely clear. Herein we report that inhibition of the polyol pathway enzyme aldose reductase (AR) prevents the increase in ICAM-1 and VCAM-1 in human umbilical vein endothelial cells (HUVECs) and decreases monocyte adhesion to these cells. In TNF-alpha-stimulated HUVECs, treatment with AR inhibitors sorbinil and tolrestat diminished NF-kappaB activity, phosphorylation and degradation of Ikappa-Balpha, and the nuclear translocation of NF-kappaB. Inhibition of AR abrogated TNF-alpha-induced activation and membrane translocation of PKC, and antisense ablation of AR prevented both TNF-alpha-induced PKC and NF-kappaB activation. However, inhibition of AR did not prevent phorbol ester-induced activation of PKC or NF-kappaB, indicating that inhibition of AR does prevents events upstream of PKC activation. These results identify a novel regulator of endothelial activation and suggest that AR is an obligatory mediator of TNF-alpha signaling leading to an increase in the expression of adhesion molecules and increased binding of monocytes to the endothelium.

Coagulation facilitates tumor cell spreading in the pulmonary vasculature during early metastatic colony formation

Coagulation has long been known to facilitate metastasis. To pinpoint the steps where coagulation might play a role in the metastasis, we used three-dimensional visualization of direct infusion of fluorescence labeled antibody to observe the interaction of tumor cells with platelets and fibrinogen in isolated lung preparations. Tumor cells arrested in the pulmonary vasculature were associated with a clot composed of both platelets and fibrin(ogen). Initially, the cells attached to the pulmonary vessels were rounded. Over the next 2 to 6 hours, they spread on the vessel surface. The associated clot was lysed coincident with tumor cell spreading. To assess the importance of clot formation, we inhibited coagulation with hirudin, a potent inhibitor of thrombin. The number of tumor cells initially arrested in the lung of hirudin-treated mice was essentially the same as in control mice. However, tumor cell spreading and subsequent retention of the tumor cells in the lung was markedly inhibited in the anticoagulated mice. These associations of the tumor cells with platelets were independent of tumor cell expression of P-selectin ligands. This work identifies tumor cell spreading onto the vascular surface as an important component of the metastatic cascade and implicates coagulation in this process.

Discovery of Inhibitors of MCF-7 Tumor Cell Adhesion to Endothelial Cells and Investigation on their Mode of Action

Metastasis, the main reason for high mortality of cancer, is a multistep process. One important step in this process is the adhesion of tumor cells to vascular endothelium at sites distant from primary tumors during hematogenous dissemination. In order to investigate and quantify the adhesion of tumor cells to endothelial cells we developed an in vitro model using MCF-7 breast cancer cells and monolayers of human umbilical vein endothelial cells (HUVEC). The tumor cells were specifically labeled with a fluorescent dye for quantification; for increasing the amount of adherent cells, HUVEC monolayers were stimulated with phorbol ester before the addition of the tumor cells. Due to previous reports that products of several P450 enzymes contribute to the progression of certain kinds of cancer, inhibitors of CYP5 (thromboxane A(2) synthase), CYP17 (17alpha-hydroxylase-C17, 20-lyase), and CYP19 (aromatase) were tested in this in vitro model for their potency to reduce cancer cell adhesion. Within each series of P450 inhibitors, compounds with high inhibitory activity on tumor cell adhesion were identified. At an initial concentration of 100 microM, BW26, a potent inhibitor of CYP5, reduced tumor cell adhesion of MCF-7 to HUVECs to 15%, BW40 (CYP17) to 29%, and SU5a (CYP19) to 11% of the corresponding controls (no inhibitor). Reduction of tumor cell adhesion was shown to occur in a concentration-dependent manner. In addition to these inhibitors of CYP5, CYP17, and CYP19, liarozole, known to be a potent inhibitor of CYP26 (retinoic acid-4-hydroxylase) and ATRA (all-trans-retinoic acid) metabolism, was able to reduce tumor cell adhesion to 51% of the initial rate. Experiments elucidating the mode of action of these compounds revealed that inhibition of the mentioned CYP enzymes is not responsible for their ability to reduce tumor cell adhesion.

Spontaneous regression of lung metastasis in the absence of tumor necrosis factor receptor p55

In order to clarify the roles of tumor necrosis factor (TNF)-alpha in lung metastasis, we injected Renca cells intravenously into TNF receptor p55-deficient (TNF-Rp55 KO) and wild-type (WT) mice. Microscopic and macroscopic metastasis foci appeared in lungs at 7 and 14 days after the tumor injection, respectively. Moreover, metastasis foci expanded at similar rates in both WT and TNF-Rp55 KO mice until 21 days, and lungs were occupied with metastasis foci. However, later than 21 days after the injection, metastasis foci spontaneously regressed in TNF-Rp55 KO mice, whereas WT mice exhibited a progressive growth of metastasis foci. Moreover, metastasis foci remained reduced sizes in TNF-Rp55 KO mice even at 26 days, when all WT mice died with lungs filled with metastasis foci. Later than 21 days after the tumor injection, the number of apoptotic tumor cells was increased in TNF-Rp55 KO mice. In contrast, neovascularization was less evident in TNF-Rp55 KO than WT mice, with depressed hepatocyte growth factor (HGF) gene in TNF-Rp55 KO mice at 21 days after the tumor injection. Thus, TNF-Rp55-mediated signals can maintain tumor neovascularization at least partly by inducing HGF expression, and eventually support lung metastasis process.

Adhesion of gastric carcinoma cells to peritoneum mediated by alpha3beta1 integrin (VLA-3)

The interaction between gastric carcinoma cells and the peritoneal lining is a key step in peritoneal dissemination. In this study, we examined the roles of the beta1 family of integrin receptors in the adhesion of such cells to the peritoneum. The adhesion of several gastric carcinoma cell lines to peritonea excised from mice was inhibited most by an anti-alpha3 integrin antibody and to a lesser extent by an anti-alpha2 integrin antibody. In the peritoneal implantation of NUGC-4 human gastric carcinoma cells in athymic mice, treatment of the cells with anti-alpha2 or anti-alpha3 integrin antibody reduced the number of disseminated nodules; suppression by the anti-alpha3 integrin antibody was stronger than that by the anti-alpha2 integrin antibody. The cDNAs to human alpha2 and alpha3 integrins were introduced into K562 leukemic cells, which were positive for the integrin beta1 subunit but negative for the alpha2 or alpha3 subunit. The alpha3 integrin-transfected cells adhered to excised peritoneum and to a monolayer of peritoneal mesothelial cells more firmly than did the alpha2 integrin-transfected cells or the mock transfectant. Reverse transcription-PCR was used to analyze the expression of laminin-5 and laminin-10/11, which have been reported to serve as high-affinity ligands for alpha3beta1 integrin. mRNA for these laminin isoforms was found in mesothelial cells from the diaphragm and parietal peritoneum. These results strongly suggest that alpha3beta1 integrin plays an essential role in mediating the initial attachment of cancer cells to the peritoneum, leading to the formation of peritoneal metastasis.

CX3CR1-fractalkine expression regulates cellular mechanisms involved in adhesion, migration, and survival of human prostate cancer cells

Chemokines and their receptors might be involved in the selection of specific organs by metastatic cancer cells. For instance, the CXCR4-SDF-1alpha pair regulates adhesion and migration of breast as well as prostate cancer cells to metastatic sites. In this study, we present the first evidence for the expression of CX3CR1--the specific receptor for the chemokine fractalkine--by human prostate cancer cells, whereas human bone marrow endothelial cells and differentiated osteoblasts express fractalkine. The adhesion of prostate cancer cells to human bone marrow endothelial cells in flow conditions is significantly reduced by a neutralizing antibody against fractalkine, and they migrate toward a medium conditioned by osteoblasts, which secrete the soluble form of the chemokine. Finally, fractalkine activates the PI3K/Akt survival pathway in human prostate cancer cells.

A semianalytic model of leukocyte rolling

Rolling allows leukocytes to maintain adhesion to vascular endothelium and to molecularly coated surfaces in flow chambers. Using insights from adhesive dynamics, a computational method for simulating leukocyte rolling and firm adhesion, we have developed a semianalytic model for the steady-state rolling of a leukocyte. After formation in a force-free region of the contact zone, receptor-ligand bonds are transported into the trailing edge of the contact zone. Rolling velocity results from a balance of the convective flux of bonds and the rate of dissociation at the back edge of the contact zone. We compare the model's results to that of adhesive dynamics and to experimental data on the rolling of leukocytes, with good agreement. We calculate the dependence of rolling velocity on shear rate, intrinsic forward and reverse reaction rates, bond stiffness, and reactive compliance, and use the model to calculate a state diagram relating molecular parameters and the dynamic state of adhesion. A dimensionless form of the analytic model permits exploration of the parameters that control rolling. The chemical affinity of a receptor-ligand pair does not uniquely determine rolling velocity. We elucidate a fundamental relationship between off-rate, ligand density, and reactive compliance at the transition between firm and rolling adhesion. The model provides a rapid method for screening system parameters for the potential to mediate rolling.

Physiological and Pathological Roles of α3β1 Integrin

Alpha3beta1 integrin has been considered to be a mysterious adhesion molecule due to the pleiotropy in its ligand-binding specificity. However, recent studies have identified laminin isoforms as high-affinity ligands for this integrin, and demonstrated that alpha3beta1 integrin plays a number of essential roles in development and differentiation, mainly by mediating the establishment and maintenance of epithelial tissues. Furthermore, alpha3beta1 integrin is also implicated in many other biological phenomena, including cell growth and apoptosis, angiogenesis and neural functions. This integrin receptor forms complexes with various other membrane proteins, such as the transmembrane-4 superfamily proteins (tetraspanins), cytoskeletal proteins and signaling molecules. Recently, lines of evidence have been reported showing that complex formation regulates integrin functions in cell adhesion and migration, signal transduction across cell membranes, and cytoskeletal organization. In addition to these roles in physiological processes, alpha3beta1 integrin performs crucial functions in various pathological processes, especially in wound healing, tumor invasion and metastasis, and infection by pathogenic microorganisms.

VEGF regulates PCB 104-mediated stimulation of permeability and transmigration of breast cancer cells in human microvascular endothelial cells

Polychlorinated biphenyl (PCB) congeners, a group of worldwide, persistent environmental contaminants, are known to cause carcinogenesis and tumor promotion, and may also affect the development of cancer metastasis. Because vascular endothelial cells create a selective barrier to the passage of cancer cells, we hypothesize that specific PCB congeners can disrupt endothelial integrity and increase the transendothelial migration of tumor cells. To examine this hypothesis, we elucidated the effects of 2,2',4,6,6'-pentachlorobiphenyl (PCB 104), a representative of highly ortho-substituted non-coplanar PCB congeners, on the endothelial permeability and transendothelial migration of MDA-MB-231 breast cancer cells. Exposure of human microvascular endothelial cell 1 (HMEC-1) to PCB 104 induced endothelial hyperpermeability and markedly increased transendothelial migration of MDA-MB-231 cells. These effects were associated with overexpression of vascular endothelial growth factor (VEGF). PCB 104-mediated elevation of VEGF expression was induced by phosphatidylinositol 3-kinase (PI3K) but not affected by co-treatments with antioxidants or the NF-kappaB inhibitor SN50. In addition, the PI3K-dependent pathway was involved in PCB 104-induced activation of AP-1, a transcription factor implicated in the regulation of VEGF gene expression. The VEGF receptor (KDR/Flk-1) antagonist SU1498 and the PI3K inhibitor LY294002 inhibited PCB 104-induced hyperpermeability. These results indicate that PCB 104 may contribute to tumor metastasis by inducing VEGF overexpression that stimulates endothelial hyperpermeability and transendothelial migration of cancer cells.

Direct visualization of nitric oxide release by liver cells after the arrest of metastatic tumor cells in the hepatic microvasculature1

BACKGROUND

Our previous studies have shown that the injection of B16F1 melanoma cells into the mesenteric vein can induce the rapid local release of nitric oxide (NO) in the liver, causing apoptosis of the melanoma cells in the liver sinusoids and inhibiting the subsequent formation of hepatic metastases. In this study, we have investigated the distribution and cellular source of NO in this model.

MATERIALS AND METHODS

In situ liver perfusion was established in both wild-type (wt) and endothelial nitric oxide synthase knockout (eNOS KO) C57BL/6 mice. A specific fluorescent NO probe, 4,5-diaminofluorescein diacetate (DAF-2 DA) (5 micromol/L), was perfused into the portal venous system to label the liver tissue. Then, a MitoTracker Orange labeled B16F1 melanoma cell suspension (2 x 10(6) cells/ml) was injected through a portal vein catheter by a peristaltic pump. Images of the liver tissue were taken by confocal microscopy from a selected area to determine the cellular source of NO. For quantification, the fluorescence intensity of this area was measured over time by Fluoview software.

RESULTS

Diaminotriazolofluorescein (DAF-2T) fluorescence (indicating NO generation) was detected in hepatic parenchymal cells located in the periportal region in both wt C57BL/6 and eNOS KO C57BL/6 mice and was intensified by increased flow rate in the portal venous system. The B16F1 cells arrested in the periportal sinusoids, corresponding to zone 1 of the hepatic acinus. DAF-2T fluorescence was expressed by both sinusoidal lining cells and hepatocytes at the site of tumor cell arrest. The fluorescence intensity of these cells increased approximately 2-fold over a time of 500 s. In contrast, there was no increase in the fluorescence intensity of the sinusoidal lining cells and hepatocytes in mice perfused with buffer or in eNOS KO mice perfused with B16F1 cells.

CONCLUSION

This study demonstrates that NO is produced by hepatic parenchymal cells mainly located in the periportal zones and that the arrest of the B16F1 melanoma cells causes an eNOS-dependent local burst of NO by the sinusoidal lining cells and hepatocytes in the periportal areas.

Inhibition of cytokine-induced microvascular arrest of tumor cells by recombinant endostatin prevents experimental hepatic melanoma metastasis

We investigated effects of endostatin (ES) in the prometastatic microenvironment of inflammation occurring during the microvascular phase of cancer cell infiltration in the liver. We used a model of intrasplenic injection of B16 melanoma (B16M) cells leading to hepatic metastasis through vascular cell adhesion molecule-(VCAM-1)-mediated capillary arrest of cancer cells via interleukin-18 (IL-18)-dependent mechanism. We show that administration of 50 mg/kg recombinant human (rh) ES 30 min before B16M, plus repetition of same dose for 3 additional days decreased metastasis number by 60%. A single dose of rhES before B16M injection reduced hepatic microvascular retention of luciferase-transfected B16M by 40% and inhibited hepatic production of tumor necrosis factor alpha (TNF-alpha) and IL-18 and VCAM-1 expression by hepatic sinusoidal endothelia (HSE). Consistent with these data, rhES inhibited VCAM-1-dependent B16M cell adhesion to primary cultured HSE receiving B16M conditioned medium, and it abolished the HSE cell production of TNF-alpha and IL-18 induced by tumor-derived vascular endothelial cell growth factor (VEGF). rhES abrogated recombinant murine VEGF-induced tyrosine phosphorylation of KDR/flk-1 receptor in HSE cells, preventing the proinflammatory action of tumor-derived VEGF on HSE. rhES also abolished hepatic production of TNF-alpha, microvascular retention of luciferase-transfected B16M, and adhesion of B16M cells to isolated HSE cells, all of them induced in mice given 5 micro g/kg recombinant murine VEGF for 18 h. This capillary inflammation-deactivating capability constitutes a nonantiangiogenic antitumoral action of endostatin that decreases cancer cell arrest within liver microvasculature and prevents metastases promoted by proinflammatory cytokines induced by VEGF.

Prostate Cancer Cell Adhesion to Bone Marrow Endothelium

Bone metastasis is the most frequent complication of prostate cancer (PC). Elucidation of the biological basis of this specificity is required for the development of approaches for metastatic inhibition. We investigated the possibility that the preferential attachment of PC cells to bone marrow endothelium (as opposed to endothelium from other organs) affects this specificity. We selected, from peptide phage-displayed libraries, peptide ligands to surfaces of PC cells (C4-2B) attenuated (30-40%) binding of C4-2B cells to bone marrow endothelial cells (BMECs). We then determined the molecules on the surface of C4-2B cells interacted with the selected peptides using column affinity chromatography and a cDNA expression phage-displayed library generated from C4-2B cells in T7 phage. We identified a phage from the cDNA library that specifically bound to one of the selected peptides-L11. This phage displayed the amino acid sequence homologous for the COOH-terminal portion of prostate-specific antigen (PSA). To examine the possible direct involvement of PSA in the interactions between PC and BMECs, we performed a cell-cell adhesion assay. Antibodies to PSA attenuated PC cells adhesion to BMECs. In addition, exogenous proteolytically active PSA modulated this adhesion. Finally, inactivation of mRNA coding PSA by a small interfering RNA (siRNA) diminished C4-2B cell adhesion to BMECs. These results indicate that PSA expressed as secreted and surface-associated molecules in C4-2B cells is involved in cell-cell interactions and/or digests components of bone marrow endothelium for preferential adhesion and penetration of PC cells. The suggested experimental approach is a promising strategy for identification of cell surface molecules involved in intercellular interactions.

Aging and the endothelium

One link between aging and endothelial function is the inflammatory response. On one hand, the latter shortens the biological engaged by activated leukocytes against invaders or stressing agents. On the other hand, the surveyed tissues become targets of the toxicity of reactive oxygen species, ROS. The ensuing regeneration is source of transcriptional infidelity, leading to the alteration of the repaired tissue. Hence, the toll of inflammatory stress consists in premature senescence of cell and tissues. This hypothesis is discussed in the present review, which focuses on the molecular targets relevant for cancer and degenerative diseases, both tributary to an inflammatory environment and taking advantage from the consequences of cell and tissue dysfunctions characteristic of aging. Eventually, adaptation to stress, whatever its origin -inflammatory and/or psychosocial-is discussed. Basal nitric oxide (NO) release, such as provided through moderate exercise, seems to be the most potent guardian against immune, nervous and cardiovascular over-stimulation. Tissue regeneration is also obtained by circulating endothelial progenitors able to recognize the damaged tissue. To avoid post-inflammatory alterations resulting in detrimental changes of tissues and organs, the pharmacological protection of endothelium by agents able to modulate its activation seems crucial to us.

Role of the aging vasculature andErb B-2 signaling in epidermal growth factor-dependent intravasion of breast carcinoma cells

BACKGROUND

The risks for developing breast carcinoma and dying from the disease increase with age. Mortality from breast carcinoma usually is due to metastatic disease. Metastatic cells are able to invade into the vascular tissue in a growth factor-dependent manner. Because breast carcinoma mortality increases with age, examination of breast carcinoma interactions with young and aged endothelial cells is essential.

METHODS

We studied a series of breast epithelial cells (HMT-3522 cells) that exhibited either noninvasive characteristics (S-1 cells) or epidermal growth factor (EGF)-dependent invasive characteristics (T4-2 cells).

RESULTS

Increased invasion of HMT-3522 cells was observed across an aged rat brain microvascular endothelial cell (BMEC) monolayer that was isolated from aged rats (24 months) compared with young rats (age 1 month). This increased invasion was inhibited by the specific EGF receptor inhibitor, AG1478, and by the Erb B-2-specific inhibitor, AG825. To analyze further the contribution of Erb B-2 to the EGF-dependent invasion of HMT-3522 cells, T4-2 cells were treated with the Erb B-2-specific therapeutic antibody trastuzumab and with the specific inhibitor AG825 and were then assayed for invasion. Both inhibitors led to a significant decrease in EGF-dependent invasion. Erb B-2 expression was found to be elevated in T4-2 cells ( approximately 5-fold higher) compared with S-1 cells. However, treatment of T4-2 cells with the specific Erb B-2 inhibitor, AG825, failed to inhibit EGF-mediated signaling to phosphatidylinositol 3-kinase or extracellular-regulated kinases 1 and 2.

CONCLUSIONS

The current study findings indicate that aging of endothelium may contribute to the invasive phenotype of breast carcinoma cells and that "cross-talk" between Erb B-2 and EGF receptor is required for the intravasion of these cells into the surrounding vasculature.

Enhanced green fluorescent protein-transfection of murine colon carcinoma cells: key for early tumor detection and quantification

Many animal models for metastatic colorectal cancer represent clinical manifestations just inaccurately. We introduce a novel mouse model for metastastatic colorectal cancer. In order to remain close to the clinical disease a syngenic murine colon carcinoma cell line (colon 26 cells) was transfected with enhanced green fluorescent protein (EGFP). The transfected cells maintain the highly malignant attributes of the wild-type cells. Following injection into the portal circulation of Balb/c-mice, liver metastases occur in the same time span. Using the fluorescent attributes of the transfected cells, an approximation of the tumor load in liver tissue can be achieved by fluorescence activated cell sorting (FACS) and fluoroscan analysis. Tumor cell load in liver tissue can be accurately measured by Northern blot and Western blot analysis of liver tissue containing EGFP-transfected colon cancer metastases (1250 cells/mg liver tissue and 1000 cells/mg liver tissue) respectively. Confocal microscopy and intravital microscopy confirmed the growth of tumor metastases, originating from the intravascular compartments. The presented animal model using EGFP-transfected colon 26 cells allows the detecting of tumor growth in vivo and post mortem, as well as an accurate quantification of the tumor load in the liver tissue.

Continuous real time ex vivo epifluorescent video microscopy for the study of metastatic cancer cell interactions with microvascular endothelium

Recent studies suggest that only endothelium-attached malignant cells are capable of giving rise to hematogenous cancer metastases. Moreover, tumor cell adhesion to microvascular endothelium could be crucial in metastasis predilection to specific organs or tissues. However, the existing in vitro and in vivo techniques do not provide for sufficient delineation of distinct stages of a dynamic multi-step intravascular adhesion process. Here we report the development of an experimental system allowing for prolonged continuous ex vivo real-time observation of malignant cell adhesive interactions with perfused microvessels of a target organ in the context of its original tissue. Specifically, the vasculature of excised dura mater perfused with prostate cancer cells is described. An advantage of this technique is that selected fluorescently labeled tumor cells can be followed along identified vascular trees across the entire tissue specimen. The techniques provide for superior microvessel visualization and allow for uninterrupted monitoring and video recording of subsequent adhesion events such as rolling, docking (initial reversible adhesion), locking (irreversible adhesion), and flattening of metastatic cancer cells within perfused microvasculature on a single cell level. The results of our experiments demonstrate that intravascular adhesion of cancer cells differs dramatically from such of the leukocytes. Within dura microvessels perfused at physiological rate, non-interacting, floating, tumor cells move at velocities averaging 7.2 x 10(3) microm/s. Some tumor cells, similarly to leukocytes, exhibit rolling-like motion patterns prior to engaging into more stable adhesive interactions. In contrast, other neoplastic cells became stably adhered without rolling showing a rapid reduction in velocity from 2 x 10(3) to 0 microm/s within fractions of a second. The experimental system described herein, while developed originally for studying prostate cancer cell interactions with porcine dura mater microvasculature, offers great flexibility in adhesion experiments design and is easily adapted for use with a variety of other tissues including human.

Influence of TNFA on the formation of liver metastases in a syngenic mouse model

The level of TNFalpha expression is increased after partial hepatectomy, and experimental evidence exists that TNFalpha plays a key role in liver regeneration. Contradictory results are reported about the influence of TNFalpha on tumor growth: on the one hand, stimulation of tumor growth in various animal models and, on the other hand, intraperitoneally administered TNFalpha leads to reduced metastasis formation. TNFalpha may be one responsible factor for increased metastasis formation after surgical trauma. The objective of our study was to clarify the influence of TNFalpha on the formation of liver metastases in a syngenic mouse model in vivo. We used a novel marker system, EGFP transfected C26 tumor cells for in vivo observation of metastasis formation by intravital microscopy. We analyzed the effect of intraperitoneal TNFalpha-injection on tumor cell adhesion, extravasation and tumor development. The expression of ICAM-1, VCAM-1 and E-Selectin was measured by Western blot and immunohistochemical staining. Tumor load was assessed by determining EGFP in Western blots. GdCl(3) was employed 24 and 48 hr before tumor cell injection to selectively deplete the liver of functioning Kupffer cells. We observed significantly more extravasated tumor cells in the TNFalpha-pre-treated animals at early time points with increased expression of adhesion molecules. Measurement of the EGFP levels showed fewer liver metastases in the TNFalpha-pretreated animals at day 8. After GdCl(3) pretreatment even lower levels of EGFP, i.e., fewer metastases and also lower expression levels of ICAM-1, VCAM-1 and E-Selectin could be observed. TNFalpha, acts in a bidirectional manner: whereas TNFalpha facilitates tumor cell adhesion and extravasation of C26 tumor cells by inducing the expression of adhesion molecules, at later time points, TNFalpha seems to hinder the formation of liver metastases.

Integrin receptors and ECM proteins involved in preferential adhesion of colon carcinoma cells to lung cells

To assess the putative role of extracellular matrix (ECM) proteins on lung cells interacting with integrin receptors on colon carcinoma cells, an in vitro adhesion assay was used to investigate these factors. Tumor necrosis factor (TNF)-alpha treatment of fetal lung cell line MRC 9, upregulated expression of ECM proteins and also supported enhanced adhesion of PTC colon carcinoma cells. Antibodies to ECM proteins significantly blocked this enhanced adhesion of PTC cells. Similarly, antibody blocking of beta1 and beta2 integrin receptors on PTC cells revealed the integrin receptors involved in this enhanced adhesion. beta1 integrin receptors like alpha2beta1, alpha4beta1 and alpha5beta1 on PTC cells were found interacting with their ECM ligands like fibronectin and laminin on TNF-alpha stimulated MRC 9 cells. Interestingly, PTC cells were found to constitutively express alphaLbeta2, which is normally expressed by leukocytes. The data from the present study indicates that expression of multiple beta1 and beta2 integrins by colon carcinoma cells putatively allows these cells to successfully adhere to secondary sites like lungs.

Interleukin-8 secreted by endothelial cells induces chemotaxis of melanoma cells through the chemokine receptor CXCR1

There is increasing evidence that both cell adhesion molecules and soluble factors are involved in tumor metastasis. We have found that endothelial cells secrete chemoattractants that can induce melanoma cell chemotaxis. Protein separation on an ion-exchange column shows the association of IL-8 with fractions that contain the chemoattractant activity. This activity is completely lost from the conditioned medium after immunoprecipitation with anti-IL-8 antibodies, indicating that IL-8 is the major melanoma chemoattractant secreted by endothelial cells. IL-877, the predominant endothelial IL-8 isoform that contains 77 amino acids, is found to be twice as potent as the more common 72-amino acid isoform IL-872. Antibody inhibition studies indicate that the chemotactic response of melanoma cells is mediated by the CXC-chemokine receptor CXCR1 and not by the more promiscuous CXCR2. When stimulated by tumor necrosis factor alpha, the nonresponsive WM35 melanoma cells synthesize a higher level of CXCR1 and become chemotactic toward interleukin (IL)-8. Pretreatment of cells with pertussis toxin nullifies their chemotactic response, suggesting the involvement of G proteins. Antibodies against either IL-8 or CXCR1 inhibit melanoma transendothelial migration in a coculture assay by 30%. These results are consistent with a role for IL-8-induced chemotaxis in the transendothelial migration of melanoma cells.

Endothelial signaling during development

Blood vessels perfuse all tissues in the body and mediate vital metabolic exchange between tissues and blood. Increasing evidence, however, points to a direct role for paracrine signaling between blood vessel cells and surrounding target organ cells, during embryonic development and cell differentiation. Understanding the nature of this signaling and its heterogeneity, both in the embryo and in adult tissues, may not only provide insights into mechanisms for normal developmental cell fate decisions, but could also lead to novel targeted therapeutic approaches for a variety of diseases such as heart disease, diabetes or cancer.

Tumor cytotoxicity by endothelial cells. Impairment of the mitochondrial system for glutathione uptake in mouse B16 melanoma cells that survive after in vitro interaction with the hepatic sinusoidal endothelium

High GSH content associates with high metastatic activity in B16-F10 melanoma cells cultured to low density (LD B16M). GSH homeostasis was investigated in LD B16M cells that survive after adhesion to the hepatic sinusoidal endothelium (HSE). Invasive B16M (iB16M) cells were isolated using anti-Met-72 monoclonal antibodies and flow cytometry-coupled cell sorting. HSE-derived NO and H(2)O(2) caused GSH depletion and a decrease in gamma-glutamylcysteine synthetase activity in iB16M cells. Overexpression of gamma-glutamylcysteine synthetase heavy and light subunits led to a rapid recovery of cytosolic GSH, whereas mitochondrial GSH (mtGSH) further decreased during the first 18 h of culture. NO and H(2)O(2) damaged the mitochondrial system for GSH uptake (rates in iB16M were approximately 75% lower than in LD B16M cells). iB16M cells also showed a decreased activity of mitochondrial complexes II, III, and IV, less O(2) consumption, lower ATP levels, higher O(2) and H(2)O(2) production, and lower mitochondrial membrane potential. In vitro growing iB16M cells maintained high viability (>98%) and repaired HSE-induced mitochondrial damages within 48 h. However, iB16M cells with low mtGSH levels were highly susceptible to TNF-alpha-induced oxidative stress and death. Therefore depletion of mtGSH levels may represent a critical target to challenge survival of invasive cancer cells.

NF-kappaB dependent activation of human endothelial cells treated with soluble products derived from human lymphomas

Nuclear factor of the Immunoglobulin Kappa chain of B cells (NF-kappaB) activation is an early event during cytokine-mediated endothelial activation related to increased adhesion of leucocytes. We report that soluble products secreted by two human lymphomas activate NF-kappaB, and increase the ability of endothelial cells to adhere U937 cells in vitro. Analysis of the tumor-derived products revealed the absence of tumor necrosis factor-alpha and interleukin-1beta. Interference of NF-kappaB activation prevented the increase in U937 cell adhesion, suggesting a potential role for endothelial NF-kappaB activation in the establishment of physical interactions between the vascular endothelium and tumor cells.

Vascular endothelial growth factor modulates the transendothelial migration of MDA-MB-231 breast cancer cells through regulation of brain microvascular endothelial cell permeability

Vascular endothelial growth factor (VEGF), also known as vascular permeability factor (VPF), has been shown to increase potently the permeability of endothelium and is highly expressed in breast cancer cells. In this study, we investigated the role of VEGF/VPF in breast cancer metastasis to the brain. Very little is known about the role of endothelial integrity in the extravasation of breast cancer cells to the brain. We hypothesized that VEGF/VPF, having potent vascular permeability activity, may support tumor cell penetration across blood vessels by inducing vascular leakage. To examine this role of VEGF/VPF, we used a Transwell culture system of the human brain microvascular endothelial cell (HBMEC) monolayer as an in vitro model for the blood vessels. We observed that VEGF/VPF significantly increased the penetration of the highly metastatic MDA-MB-231 breast cancer cells across the HBMEC monolayer. We found that the increased transendothelial migration (TM) of MDA-MB-231 cells resulted from the increased adhesion of tumor cells onto the HBMEC monolayer. These effects (TM and adhesion of tumor cells) were inhibited by the pre-treatment of the HBMEC monolayer with the VEGF/VPF receptor (KDR/Flk-1) inhibitor, SU-1498, and the calcium chelator 1,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (acetoxymethyl)ester. These treatments of the HBMEC monolayer also inhibited VEGF/VPF-induced permeability and the cytoskeletal rearrangement of the monolayer. These data suggest that VEGF/VPF can modulate the TM of tumor cells by regulating the integrity of the HBMEC monolayer. Taken together, these findings indicate that VEGF/VPF might contribute to breast cancer metastasis by enhancing the TM of tumor cells through the down-regulation of endothelial integrity.

Lipid peroxidation and antioxidant capacity in selected tissues of healthy black C57BL/6J mice and B16 melanoma-bearing mice

During the process of melanogenesis free radicals are generated. The aim of this study was to investigate the effects of melanogenesis in B16 melanoma on lipid peroxidation and antioxidant capacity in selected tissues of black C57BL/6J mice. The study was conducted on 24 mice: 12 healthy controls and 12 with a transplanted B16 melanoma. Two weeks after the melanoma transplant, when the average weight of the tumours was approximately 2.0 g, blood samples were taken from the orbital venous plexus. The mice were killed by dislocation of the spinal cord, and the brain, liver and lungs were removed for analysis. The level of thiobarbituric acid-reactive substances (TBARS) and of 1,1-diphenyl-2-picrylhydrazyl (DPPH) reactive substances were determined in full liver, lung and brain homogenates and in serum. The activity of superoxide dismutase (SOD) was determined only in homogenized tissue. The concentration of TBARS and the SOD activity were statistically significantly higher in all the studied tissues from mice with B16 melanoma than in tissues from healthy mice. The antioxidant capacity, however, was lower in the tissues of melanoma-bearing mice. The results obtained demonstrate an increase in oxidative stress in the tissues of mice bearing a transplanted B16 melanoma.

Focal adhesion kinase activated by beta(4) integrin ligation to mCLCA1 mediates early metastatic growth

Early metastatic growth occurs at sites of vascular arrest of blood-borne cancer cells and is entirely intravascular. Here we show that lung colonization by B16-F10 cells is licensed by beta(4) integrin adhesion to the mouse lung endothelial Ca(2+)-activated chloride channel protein mCLCA1. In a manner independent of Met, beta(4) integrin-mCLCA1-ligation leads to complexing with and activation of focal adhesion kinase (FAK) and downstream signaling to extracellular signal-regulated kinase (ERK). FAK/ERK signaling is Src-dependent and is interrupted by adhesion blocking antibodies and by dominant-negative (dn)-FAK mutants. Levels of ERK activation in B16-F10 cells transfected with wild-type or mutant FAK are closely associated with rates of proliferation and bromodeoxyuridine (BrdUrd) incorporation of tumor cells grown in mCLCA1-coated dishes, the ability to form tumor cell colonies on CLCA-expressing endothelial cell monolayers, and the extent of pulmonary metastatic growth. Parallel with the transfection rates, B16-F10 cells transfected with dn-FAK mutants and injected intravenously into syngeneic mice generate approximately half the number and size of lung colonies that vector-transfected B16-F10 cells produce. For the first time, beta(4) integrin ligation to its novel CLCA-adhesion partner is shown to be associated with FAK complexing, activation, and signaling to promote early, intravascular, metastatic growth.

Inhibition of cancer growth by resveratrol is related to its low bioavailability

The relationship between resveratrol (RES) bioavalability and its effect on tumor growth was investigated. Tissue levels of RES were studied after i.v. and oral administration of trans-resveratrol (t-RES) to rabbits, rats, and mice. Half-life of RES in plasma, after i.v. administration of 20 mg t-RES/kg b.wt., was very short (e.g., 14.4 min in rabbits). The highest concentration of RES in plasma, either after i.v. or oral administration (e.g., 2.6 +/- 1.0 microM in mice 2.5 min after receiving 20 mg t-RES/kg orally), was reached within the first 5 min in all animals studied. Extravascular levels (brain, lung, liver, and kidney) of RES, which paralleled those in plasma, were always < 1 nmol/g fresh tissue. RES measured in plasma or tissues was in the trans form (at least 99%). Hepatocytes metabolized t-RES in a dose-dependent fashion (e.g., 43 nmol of t-RES/g x min in the presence of 20 microM tRES), which means that the liver can remove circulating RES very rapidly. In vitro B16 melanoma (B16M) cell proliferation and generation of reactive oxygen species (ROS) was inhibited by t-RES in a concentration-dependent fashion (100% inhibition of tumor growth was found in the presence of 5 microM t-RES). Addition of 10 microM H(2)O(2) to B16M cells, cultured in the presence of 5 microM t-RES, reactivated cell growth. Oral administration of t-RES (20 mg/kg twice per day; or included in the drinking water at 23 mg/l) did not inhibit growth of B16M inoculated into the footpad of mice (solid growth). However, oral administration of t-RES (as above) decreased hepatic metastatic invasion of B16M cells inoculated intrasplenically. The antimetastatic mechanism involves a t-RES (1 microM)-induced inhibition of vascular adhesion molecule 1 (VCAM-1) expression in the hepatic sinusoidal endothelium (HSE), which consequently decreased in vitro B16M cell adhesion to the endothelium via very late activation antigen 4 (VLA-4).

Unique ability of integrin alpha(v)beta 3 to support tumor cell arrest under dynamic flow conditions

Shear-resistant arrest of circulating tumor cells is required for metastasis from the blood stream. Arrest during blood flow can be supported by tumor cell interaction with attached, activated platelets. This is mediated by tumor cell integrin alpha(v)beta3 and cross-linking plasma protein ligands. To analyze the mechanism of tumor cell ligand interactions under dynamic flow conditions, we used real-time video microscopy and tested human melanoma cell binding to fibrinogen, von Willebrand Factor, or fibronectin matrices in a buffer perfusion system. When perfused at venous flow, melanoma cells arrested abruptly and began to spread immediately. This was uniquely mediated by integrin alpha(v)beta3 on all tested ligands, and required alpha(v)beta3 activation and actin polymerization. Under static conditions, alpha(v)beta3 cooperated with alpha(v)beta1 and alpha5beta1 in supporting melanoma cell adhesion to fibronectin. But even when activated, beta1 integrins did not contribute to melanoma cell arrest during flow. Soluble ligand served as a cross-linker between attached and circulating tumor cells and enhanced melanoma cell arrest. Cohesion of activated melanoma cells was restricted to the matrix surface and did not occur in suspension. We conclude that the presence of alpha(v)beta3 in a functionally activated state provides a unique advantage for circulating tumor cells by promoting tumor cell arrest in the presence of flow-dependent shear forces.

Induction of fascin spikes in breast cancer cells by activation of the insulin-like growth factor-I receptor

Insulin-like growth factor-I receptor (IGF-IR) signaling contributes to the formation of mammary carcinomas and has chiefly been studied with regard to the proliferative and anti-apoptotic effects of IGF-IR signaling. However, IGF-IR activation also affects the actin cytoskeleton and alterations in cell migratory behavior are of known importance for the malignant conversion and metastasis of epithelial cells. The actin-binding protein fascin is found in cell projections and spikes that are involved in the locomotion of mesenchymal cells. Fascin expression is typically low in normal epithelial cells, but is markedly upregulated in several types of carcinomas. Here, we also demonstrate increased fascin expression in breast carcinoma cell lines and adopt MCF-7 human mammary carcinoma cells that over-express wild-type or kinase-inactivated forms of the IGF-IR as a model system to test the hypothesis that IGF-IR activation induces fascin projections. We show that the time-dependent dissociation of cell colonies that occurs upon receptor activation by IGF-I involves the formation of dynamic, fascin-containing lateral cell projections that co-localize with ruffling membranes in association with protrusive activity and cell migratory phenotype. The molecular mechanism of these effects is completely dependent on IGF-IR tyrosine kinase activity and is mediated by a phosphatidylinositol (PI) 3-kinase-dependent process. In demonstrating transduction of fascin spike assembly by activation of a peptide growth factor receptor, these novel data reveal a wide role for fascin spikes in cell motility and provide new insight into the complex effects of IGF-IR signaling on actin cytoskeletal organization.

Clinical overview of leukocyte adhesion and migration: where are we now?

This article discusses the potential for clinical translation of the large amount of information on the molecular basis of leukocyte-endothelial cell interactions that has been collected over the last twenty years. Areas of current interest include the identification of adhesion molecule expression in inflammation by diagnostic imaging, understanding variability in inflammatory responsiveness and disease susceptibility through identification of adhesion molecule and chemokine polymorphisms and the application to the treatment of inflammatory diseases of monoclonal antibodies and conventional drugs with specific actions on leukocyte adhesion and migration.

Selective activation of cervical microvascular endothelial cells by human papillomavirus 16-e7 oncoprotein

BACKGROUND

Human papillomavirus type 16 (HPV16) is strongly implicated in the etiology of cervical cancer, with the expression of HPV16-encoded E7 oncoprotein in infected epithelial cells contributing to their malignant transformation. Although nuclear E7 interacts with several nuclear targets, we have previously shown that extracellular E7 can cause suppression of immune cell function. Moreover, cervical microvascular endothelial (CrMVEn) cells treated with E7 increase their expression of adhesion molecules. High levels of some cytokines in serum and in cervicovaginal secretions are associated with the progression of cervical cancer. In this study, we investigated the effects of extracellular E7 on cytokine production and on cytoskeleton structure of CrMVEn cells and vascular endothelial cells from different organs.

METHODS

Immunocytochemical staining and flow cytometry techniques were used to detect E7 in endothelial cells incubated with purified E7 protein. Laser scanning confocal microscopy was used to study the E7-induced modification of the endothelial cytoskeleton. An enzyme-linked immunosorbent assay was performed to measure the production of two cytokines, interleukin 6 (IL-6) and interleukin 8 (IL-8), by E7-treated endothelial cells. All statistical tests were two-sided.

RESULTS

Extracellular E7 was taken up by CrMVEn cells and localized to the cytoplasm. CrMVEn cells showed a statistically significant (P<.02) increase in the production of IL-6 and IL-8 after treatment with E7 compared with the controls. CrMVEn cells also produced higher levels of these cytokines than did the other endothelial cells (P<.01). E7 also induced marked alterations in the endothelial cytoskeleton of CrMVEn cells as a result of actin fiber polymerization.

CONCLUSION

These findings suggest a novel mechanism by which E7, as an extracellular factor, can play a role in the progression and dissemination of cervical cancer via its selective effects on endothelial cells.

Regulatory role of tetraspanin CD9 in tumor-endothelial cell interaction during transendothelial invasion of melanoma cells

Heterotypic interaction among tumor cells (TCs) and endothelial cells (ECs) may play a critical role during the vascular dissemination of neoplastic cells and during pathologic angiogenesis in tumors. To identify molecules involved in these processes, the distribution of vascular junctional proteins was first studied by immunofluorescence at sites of heterologous intercellular contact using TC-EC mosaic monolayers grown on 2-dimensional collagen. Several members of the tetraspanin superfamily, including CD9, CD81, and CD151, were found to localize at the TC-EC contact area. The localization of tetraspanins to the TC-EC heterologous contact area was also observed during the active transmigration of TCs across EC monolayers grown onto 3-dimensional collagen matrices. Dynamic studies by time-lapse immunofluorescence confocal microscopy showed an active redistribution of endothelial CD9 to points of melanoma insertion. Anti-CD9 monoclonal antibodies were found to specifically inhibit the transendothelial migration of melanoma cells; the inhibitory effect was likely caused by a strengthening of CD9-mediated heterotypic interactions of TCs to the EC monolayer. These data support a novel mechanism of tetraspanin-mediated regulation of TC transcellular migration independent of TC motility and growth during metastasis and a role for these molecules in the formation of TC-EC mosaic monolayers during tumor angiogenesis.

Organ-specificity of the extravasation process: an ultrastructural study

The process of extravasation of the high metastatic Lewis lung carcinoma line was examined in different organs. Four of the five organs (liver, lungs, brain and adrenals) represent the most frequent metastatic sites in humans. In the case of each organ 150-350 tumor cells were analysed. The interaction of tumor cells with endothelial cells and the basement membrane showed significant differences between the organs. In the liver and lungs, endothelial cells were found to migrate onto the surface of the tumor cells, resulting in the removal of tumor cells from the circulation. The process was initiated by development of cytoplasmic projections on the luminal surface of the endothelial cells. In the liver only half of the tumor cells showed basement membrane degradation even after 24 h, although 6 h after injection 40% of the tumor cells were sequestered from the circulation. In the adrenals and brain, tumor cells were not covered by endothelial cells instead, limited retraction of endothelial cells was followed by penetration of the basement membrane. In the kidney both types of tumor cell-endothelial cell interactions were observed, but the process of extravasation was not completed, stopping as the tumor cells reached the basement membrane or the mesangial matrix. The time course of tumor cell extravasation also showed significant differences between the organs. The process was most rapid in case of the liver and adrenals. By 6 h 40-50% of the tumor cells were in the process of extravasation or were in an extracapillary position. These organs are preferential metastatic sites of this tumor line. The time of extravasation was much longer in the other organs (lungs 16 h, brain 48 h), for which this tumor line shows no preference.

CONCLUSIONS

(1) Type and duration of tumor cell extravasation differ between the organs. (2) The time needed to reach extraluminal position, but not the type of extravasation correlates with the organ preference. (3) Endothelial cells of the lungs and liver can play a much more active role in the process of extravasation than previously suggested. (4) Tumor cells can complete the metastatic process without reaching a complete extracapillary position; contact with the basement membrane or extracellular matrix seems to be sufficient.

Platelet-endothelial cell adhesion molecule-1 (CD31) redistributes from the endothelial junction and is not required for the transendothelial migration of melanoma cells

We have examined the role of platelet-endothelial cell adhesion molecule-1 (PECAM-1/CD31) during the transendothelial migration of melanoma cells using a novel in vitro system. Comparable studies have suggested the involvement of PECAM-1 in leukocyte transendothelial migration. Such studies have been confirmed using in vivo models of inflammation. These studies prompted us to examine the role of PECAM-1 in tumor cell transendothelial migration. Anti-PECAM-1 monoclonal antibodies, known to block leukocyte transendothelial migration, were tested in co-cultures of human melanoma cells seeded on a monolayer of human lung microvascular endothelial cells. None of these antibodies inhibited the transmigration of melanoma cells. Moreover, confocal microscopy revealed the dissolution of the PECAM-1 adhesion complexes in the endothelial junctions associated with melanoma cells and the lack of PECAM-1 in heterotypic contacts between transmigrating melanoma cells and adjacent endothelial cells. These data, therefore, indicate that PECAM-1 is not required for the transendothelial migration of melanoma cells.

Involvement of integrin alpha(v)beta(3) and cell adhesion molecule L1 in transendothelial migration of melanoma cells

Tumor metastasis involves many stage-specific adhesive interactions. The expression of several cell adhesion molecules, notably the integrin alpha(v)beta(3), has been associated with the metastatic potential of tumor cells. In this study, we used a novel in vitro assay to examine the role of alpha(v)beta(3) in the transmigration of melanoma cells through a monolayer of human lung microvascular endothelial cells. Confocal microscopy revealed the presence of the integrin alpha(v)beta(3) on melanoma membrane protrusions and pseudopods penetrating the endothelial junction. alpha(v)beta(3) was also enriched in heterotypic contacts between endothelial cells and melanoma cells. Transendothelial migration of melanoma cells was inhibited by either a cyclic Arg-Gly-Asp peptide or the anti-alpha(v)beta(3) monoclonal antibody LM609. Although both platelet endothelial cell adhesion molecule-1 and L1 are known to bind integrin alpha(v)beta(3), only L1 serves as a potential ligand for alpha(v)beta(3) during melanoma transendothelial migration. Also, polyclonal antibodies against L1 partially inhibited the transendothelial migration of melanoma cells. However, addition of both L1 and alpha(v)beta(3) antibodies did not show additive effects, suggesting that they are components of the same adhesion system. Together, the data suggest that interactions between the integrin alpha(v)beta(3) on melanoma cells and L1 on endothelial cells play an important role in the transendothelial migration of melanoma cells.

In vivo evaluation of the early events associated with liver metastasis of circulating cancer cells

The mechanism of metastasis formation remains still largely unknown. Many studies underline the importance and complexity of the initial arrest of the circulating tumour cells in the target organ, a key stage in metastasis occurrence. In our study, we evaluated by visual means the metastasis formation using an in vivo microscopy system in a murine model. Moreover, we investigated the involvement of P-selectin in these processes using immunohistochemistry and P-selectin knockout mice. The present study offers direct evidence of distinct pathways for tumour metastasis formation by a lymphoma cell - EL-4 and a solid tumour cell - C26. Off-line analysis of the images and histological data confirmed that mechanical entrapment of the solid tumour cell, which had a bigger diameter than that of the liver sinusoids, promoted metastasis without any detectable involvement of adhesion molecules. On the other hand, we observed that lymphoma cells, in spite of their smaller diameter as compared to the sinusoids, promoted liver metastasis as well, but with the essential participation in their arrest of P-selectin, indicating an adhesion molecule-mediated pathway.

The breast cancer beta 4 integrin and endothelial human CLCA2 mediate lung metastasis

Adhesion of blood-borne cancer cells to the endothelium is a critical determinant of organ-specific metastasis. Here we show that colonization of the lungs by human breast cancer cells is correlated with cell surface expression of the alpha(6)beta(4) integrin and adhesion to human CLCA2 (hCLCA2), a Ca(2+)-sensitive chloride channel protein that is expressed on the endothelial cell luminal surface of pulmonary arteries, arterioles, and venules. Tumor cell adhesion to endothelial hCLCA2 is mediated by the beta(4) integrin, establishing for the first time a cell-cell adhesion property for this integrin that involves an entirely new adhesion partner. This adhesion is augmented by an increased surface expression of the alpha(6)beta(4) integrin in breast cancer cells selected in vivo for enhanced lung colonization but abolished by the specific cleavage of the beta(4) integrin with matrilysin. beta(4) integrin/hCLCA2 adhesion-blocking antibodies directed against either of the two interacting adhesion molecules inhibit lung colonization, while overexpression of the beta(4) integrin in a model murine tumor cell line of modest lung colonization potential significantly increases the lung metastatic performance. Our data clearly show that the beta(4)/hCLCA2 adhesion is critical for lung metastasis, yet expression of the beta(4) integrin in many benign breast tumors shows that this integrin is insufficient to bestow metastatic competence on cells that lack invasiveness and other established properties of metastatic cells.