E-selectin and very late activation antigen-4 mediate adhesion of hematopoietic progenitor cells to bone marrow endothelium

Selectin-deficiency reduces the number of spontaneous metastases in a xenograft model of human breast cancer

Metastasis formation is a complex process still poorly understood. Previous work in a colon cancer xenograft model showed that E(ndothelial) and P(latelet) selectins mediate spontaneous metastasis to the lungs. To investigate the functional role of selectins in breast cancer, human DU4475 breast cancer cells were injected subcutaneously into pfp-/-rag2-/- mice and in all their selectin-deficient variants (EP-/-, E-/- and P-/-). Pfp-/-rag2-/- mice as well as all their selectin-deficient variants developed primary tumours and spontaneous metastases. Compared with the wild-type mice, disseminated tumours cells were significantly lower (74% reduction, P=0.046) in the bone marrow of selectin-deficient mice. Pfp-/-rag2-/- mice developed significantly higher numbers of lung metastases (6644.83±741.77) than the E-/- (4053.33±112.58; P=0.002) and the EP-/- pfp-/-rag2-/- mice (4665.65±754.50; P<0.001). The results indicate that E- and P-selectins play a role in spontaneous metastasis formation both into bone marrow and lungs. However, spontaneous metastasis was not completely abrogated, hence additional cell adhesion molecules must be involved in the metastatic spread.

Alpha 1,3 fucosyltransferases are master regulators of prostate cancer cell trafficking

How cancer cells bind to vascular surfaces and extravasate into target organs is an underappreciated, yet essential step in metastasis. We postulate that the metastatic process involves discrete adhesive interactions between circulating cancer cells and microvascular endothelial cells. Sialyl Lewis X (sLe(X)) on prostate cancer (PCa) cells is thought to promote metastasis by mediating PCa cell binding to microvascular endothelial (E)-selectin. Yet, regulation of sLe(X) and related E-selectin ligand expression in PCa cells is a poorly understood factor in PCa metastasis. Here, we describe a glycobiological mechanism regulating E-selectin-mediated adhesion and metastatic potential of PCa cells. We demonstrate that alpha1,3 fucosyltransferases (FT) 3, 6, and 7 are markedly elevated in bone- and liver-metastatic PCa and dictate synthesis of sLe(X) and E-selectin ligands on metastatic PCa cells. Upregulated FT3, FT6, or FT7 expression induced robust PCa PC-3 cell adhesion to bone marrow (BM) endothelium and to inflamed postcapillary venules in an E-selectin-dependent manner. Membrane proteins, CD44, carcinoembryonic antigen (CEA), podocalyxin-like protein (PCLP), and melanoma cell adhesion molecule (MCAM) were major scaffolds presenting E-selectin-binding determinants on FT-upregulated PC-3 cells. Furthermore, elevated FT7 expression promoted PC-3 cell trafficking to and retention in BM through an E-selectin dependent event. These results indicate that alpha1,3 FTs could enhance metastatic efficiency of PCa by triggering an E-selectin-dependent trafficking mechanism.

Establishment of a Stroma-Dependent Human Acute Myelomonocytic Leukemia Cell Line, NAMO-2, with FLT3 Tandem Duplication

We have established a stroma-dependent myelomonocytic cell line, NAMO-2, with FLT3 internal tandem duplication (FLT3/ITD). Leukemia cells from a patient with acute myelomonocytic leukemia were administered to form subcutaneous tumors in nude mice, which were maintained successively, although we failed to establish continuously growing cells from the original leukemia cell culture. In the cultures of cells from subcutaneous tumors, there were stroma cells that had originated from the nude mice and showed continuous growth. The leukemia cells showed continuous growth dependent on this stroma, and this cell line was named NAMO-2. Detection of FLT3/ITD by the reverse transcriptase polymerase chain reaction (PCR) and genomic PCR showed that NAMO-2 was homozygous for FLT3/ITD. Constitutive activation of FLT3 was detected by Western blotting, and the phosphorylation of Akt, MEK, and STAT5 was also observed. FLT3 kinase inhibitor AG1296 specifically inhibited cell growth. NAMO-2 provides a useful tool to analyze adherence-dependent survival signaling of leukemia with FLT3/ITD and a model for the screening of FLT3 kinase inhibitors.

Stimulation of endothelial IL-8 (eIL-8) production and apoptosis by phenolic metabolites of benzene in HL-60 cells and human bone marrow endothelial cells

Benzene toxicity is considered to be elicited by its metabolites and phenolic metabolites of benzene are known to induce apoptosis in leukemia cells in culture and in human bone marrow progenitor cells. One potential mechanism of apoptosis induced by benzene metabolites that has not been examined is the production of pro-apoptotic cytokines such as endothelial IL-8 from endothelial cells in bone marrow stroma. In this study, we utilized HL-60 cells which are known to produce the endothelial form of IL-8 (elL-8) and human bone marrow endothelial cells (HBMEC) as model systems. Hydroquinone (HQ), Catechol (Cat) and benzenetriol (BT) all induced eIL-8 production and apoptosis in HL-60 cells. HQ induced a marked 50-70-fold stimulation of eIL-8 levels and HL-60 cells were shown to have the eIL-8 receptor, CXCR I thus enabling an autocrine pathway of apoptosis. However, treatment with recombinant elL-8 failed to induce apoptosis in HL-60 cells as previously reported and antibodies to either IL-8 or CXCRI did not significantly abrogate benzene metabolite-induced apoptosis. HQ and Cat but not BT also induced stimulation of elL-8 production in HBMEC. These data demonstrate that although metabolites of benzene induce marked stimulation of eIL-8, this is unlikely to be responsible for apoptosis induced in HL-60 cells. Our data also demonstrates that phenolic metabolites of benzene stimulate the production of eIL-8 from HBMEC suggesting that higher levels of endothelial-derived cytokines may occur in bone marrow after benzene exposure.

Stimulation of endothelial IL-8 (eIL-8) production and apoptosis by phenolic metabolites of benzene in HL-60 cells and human bone marrow endothelial cells

Benzene toxicity is considered to be elicited by its metabolites and phenolic metabolites of benzene are known to induce apoptosis in leukemia cells in culture and in human bone marrow progenitor cells. One potential mechanism of apoptosis induced by benzene metabolites that has not been examined is the production of pro-apoptotic cytokines such as endothelial IL-8 from endothelial cells in bone marrow stroma. In this study, we utilized HL-60 cells which are known to produce the endothelial form of IL-8 (eIL-8) and human bone marrow endothelial cells (HBMEC) as model systems. Hydroquinone (HQ), Catechol (Cat) and benzenetriol (BT) all induced eIL-8 production and apoptosis in HL-60 cells. HQ induced a marked 50-70 fold stimulation of eIL-8 levels and HL-60 cells were shown to have the eIL-8 receptor, CXCR1 thus enabling an autocrine pathway of apoptosis. However, treatment with recombinant eIL-8 failed to induce apoptosis in HL-60 cells as previously reported and antibodies to either IL-8 or CXCR1 did not significantly abrogate benzene metabolite-induced apoptosis. HQ and Cat but not BT also induced stimulation of eIL-8 production in HBMEC. These data demonstrate that although metabolites of benzene induce marked stimulation of eIL-8, this is unlikely to be responsible for apoptosis induced in HL-60 cells. Our data also demonstrates that phenolic metabolites of benzene stimulate the production of eIL-8 from HBMEC suggesting that higher levels of endothelial-derived cytokines may occur in bone marrow after benzene exposure.

Murine Lewis lung carcinoma-derived endothelium expresses markers of endothelial activation and requires tumor-specific extracellular matrix in vitro

The purpose of the study was to identify characteristics specific to tumor-derived endothelium that may be important in tumor biology, or for the development of targeted therapeutics or imaging agents. Normal C57Bl/6 murine heart or lung endothelium, or C57Bl/6 murine Lewis lung carcinoma tumor-derived endothelium was isolated from excised tissues using specific antibodies. The endothelium was cultured using either native fibronectin, or the oncofetal form of fibronectin. Cell surface adhesion molecule expression was analyzed by flow cytometry, and the cellular distribution of specific molecules was examined using indirect immunofluorescence staining. Oncofetal fibronectin was critical for maintaining the phenotype of tumor-derived endothelium, which demonstrated an elongated morphology in vitro, with few cell-cell contacts. They expressed high levels of CD31, CD102, and vascular endothelial cadherin, and constitutively expressed CD62E, CD54, and CD106, indicating an "activated" phenotype. Moreover, they expressed significantly greater levels of Sca-1 and Flk-1 than normal murine endothelium. Cellular distribution of CD31, beta-catenin, and CD106 in tumor-derived endothelium was not continuous at cell borders, as observed in cultures of murine heart endothelium. In conclusion, Lewis lung carcinoma-derived tumor endothelium exhibits a specific phenotype in vitro, distinct from normal endothelium, and could be used as an in vitro tool for developing targeted agents.

Effect of recombinant human deoxyribonuclease on the expression of cell adhesion molecules of thawed and processed cord blood hematopoietic progenitors

BACKGROUND AND OBJECTIVES

The integrity of granulocytic cells and platelets is compromised within cryopreserved stem cell transplants, and consequent DNA release during the thawing procedure can therefore lead to clotting phenomena or microaggregate formation and that in turn may cause loss of progenitor cells. To circumvent this problem a new processing protocol was introduced using recombinant human deoxyribonuclease (rhDNase) to prevent cell aggregate formation. In addition, the impact of this new processing protocol on CD34+ umbilical cord blood (UCB) cells was assessed.

MATERIALS AND METHODS

Fifty samples derived from 7 buffy coat (BC) volume reduced UCB units were cryopreserved, thawed, and processed with washing solutions that were supplemented with rhDNase in various concentrations. Thereafter, clotting and microaggregate formation was scored microscopically. In addition, expression of the adhesion molecules leukocyte function-associated antigen 1 (LFA-1, n = 6), intercellular adhesion molecule-1 (ICAM-1, n = 11), and L-selectin (n = 11) on CD34+ UCB cells was analyzed by flow cytometry after incubating the samples with either dimethyl sulfoxide (DMSO) 5.5%, rhDNase 10 or 50 U/mL, or a combination of DMSO 5.5% and rhDNase 50 U/mL.

RESULTS

At a minimal concentration of 10 U rhDNase/mL, clotting or microaggregate formation could be prevented for all tested samples, whereas cell clots could be observed for concentrations up to 8 U/mL. The expression of adhesion molecules on untreated CD34+ UCB cells (L-selectin: 64.6 +/- 18.8%; LFA-1: 62.6 +/- 7.5%; ICAM-1: 14.8 +/- 4.1%) did not show any significant difference compared with cells that were incubated with up to 50 U/mL rhDNase (L-selectin: 62.2 +/- 19.3%; LFA-1: 63.1 +/- 5.9%; ICAM-1: 17.5 +/- 6.7%). However, after a combined treatment with DMSO 5.5% and rhDNase 50 U/mL, a slight but significant decrease in L-selectin expression could be observed (P < 0.03).

CONCLUSION

The supplementation of rhDNase to a final concentration of 10 U/mL cell suspension proved to be effective in preventing clot formation under the conditions examined and did not lead to decreased expression levels of adhesion molecules. We therefore recommend the use of rhDNase for the prevention of clot formation and cell loss during the processing of thawed UCB transplants.

CD34+ cells in peripheral blood of healthy human beings and allergic subjects: clue to acute and minimal persistent inflammation

BACKGROUND

There is compelling evidence that hemopoietic precursor cells (HPC) play a crucial role in establishing cellular inflammation in allergic diseases. Increased levels of circulating CD34+ HPC committed to the myeloid lineage have been extensively reported in allergic rhinitis, asthma and eczema, whereas CD34+ cells have been identified within the cellular infiltrates of tissues, at peripheral sites of inflammation.

METHOD

We conducted a pilot study to evaluate CD34+ traffic in the peripheral blood of 22 consecutive patients (13 men and nine women; mean age 28.9 years), independently of treatment. The patients presented rhinitis, asthma, eczema, urticaria and adverse food reactions of suspected allergic origin. Allergic reactions were extrinsic in 18 patients and intrinsic in four. In 12 patients who underwent sublingual specific immunotherapy, CD34+ cells were quantified at enrollment (T0), one year later (T1) and two years later (T2). The severity of symptoms was graded on a five-point scale (0 = absence of symptoms and 4 = severe symptoms). Twenty healthy human subjects (10 men and 10 women; mean age 24.5 years) were evaluated as controls. To obtain information about the total amount of circulating HPC, independently of the lineage commitment (Lin+/-) and the degree of differentiation (CD34bright/dim), we used a modification of the Milan protocol of peripheral blood CD34+ cell estimation. The cells were analyzed using a BD FACScan or FACSCalibur and the results were expressed as the percentage of positive cells.

RESULTS

CD34+ cell traffic in the control group was very low since all values were < 0.10 (median value: 0.03 %). Values in the patient group were increased in both extrinsic and intrinsic forms with a median value of 0.25 % (interquartile range: 0.13- 0.33 %). The relationship between CD34+ traffic and the severity score was highly significant (Spearman's rho = 0.954; test of Ho: CD34; independent score: Pr > t = 0.000).

CONCLUSIONS

The data reported herein suggest that the method employed is effective in assessing acute allergic inflammation, as well as minimal persistent inflammation underlying an asymptomatic clinical condition. Evaluation of CD34bright/dim peripheral traffic, if confirmed by the outcomes of a multicenter study currently being planned together with traditional study of circulating IgE, could be a reliable non-invasive laboratory tool for monitoring allergic inflammation.

Migration of human hematopoietic progenitor cells across bone marrow endothelium is regulated by vascular endothelial cadherin

The success of stem cell transplantation depends on the ability of i.v. infused stem cells to engraft the bone marrow, a process referred to as homing. Efficient homing requires migration of CD34(+) cells across the bone marrow endothelium, most likely through the intercellular junctions. In this study, we show that loss of vascular endothelial (VE)-cadherin-mediated endothelial cell-cell adhesion increases the permeability of monolayers of human bone marrow endothelial cells (HBMECs) and stimulates the transendothelial migration of CD34(+) cells in response to stromal cell-derived factor-1alpha. Stromal cell-derived factor-1alpha-induced migration was dependent on VCAM-1 and ICAM-1, even in the absence of VE-cadherin function. Cross-linking of ICAM-1 to mimic the leukocyte-endothelium interaction induced actin stress fiber formation but did not induce loss of endothelial integrity, whereas cross-linking of VCAM-1 increased the HBMEC permeability and induced gaps in the monolayer. In addition, VCAM-1-mediated gap formation in HBMEC was accompanied by and dependent on the production of reactive oxygen species. These data suggest that modulation of VE-cadherin function directly affects the efficiency of transendothelial migration of CD34(+) cells and that activation of ICAM-1 and, in particular, VCAM-1 plays an important role in this process through reorganization of the endothelial actin cytoskeleton and by modulating the integrity of the bone marrow endothelium through the production of reactive oxygen species.

Homing of human hematopoietic stem and progenitor cells: new insights, new challenges?

In healthy adults, hematopoiesis takes place in the bone marrow, where the majority of hematopoietic progenitor cells (HPC) reside. In patients undergoing chemo- and/or radiotherapy, hematopoiesis is seriously disturbed. Reconstitution of bone-marrow function can be achieved by bone marrow transplantation or peripheral blood stem cell transplantation. The success of stem cell transplantation depends on the ability of intravenously infused stem cells to lodge in the bone marrow, a process referred to as homing. However, the molecular mechanisms that govern this process are poorly understood. It is hypothesized that homing is a multistep process, consisting of adhesion of the HPC to endothelial cells of the marrow sinusoids, followed by transendothelial migration directed by chemoattractants, and finally anchoring within the extravascular bone marrow spaces where proliferation and differentiation will occur. In this review, we discuss the factors that determine the engraftment potential of stem cells, and focus on various aspects of migration and homing of HPC, i.e., the role of the chemokine stromal cell-derived factor-1 (SDF-1) and its receptor CXCR-4, the involvement of adhesion molecules, and the induction of actin polymerization in the HPC. Defining the role of chemokines and adhesion molecules in human stem cell migration and engraftment will help us uncover the underlying mechanisms that regulate stem cell homing and will eventually advance clinical stem cell transplantation.

Colon cancer cell adhesion to endothelial E-selectin inhibits detachment of endothelial cells through activation of beta(1)-integrin

Previous studies have implicated a role for E-selectin in carcinoma cell adhesion to vascular endothelium. We examined the role of colon cancer cell adhesion to vascular endothelium via E-selectin using adenoviral vector-mediated transfection in human umbilical vein endothelial cells (HUVECs). We found that the amount of HUVEC detachment from the gelatin matrix 24 h after LS-180 cell adhesion was inhibited only when the HUVECs were transduced with wild-type E-selectin, but not with a cytoplasmic domain truncated mutant E-selectin or the control Lac-Z vector. We also found that the adhesion of LS-180 cells to wild-type E-selectin transduced HUVEC-induced activation of beta(1)-integrin receptors without affecting MMP activity. These results indicate that colon cancer cell adhesion via E-selectin inhibits HUVEC detachment from the monolayer, at least in part by modulating beta(1)-integrin activity in HUVECs. In addition, they indicate the importance of the cytoplasmic domain of E-selectin with this phenomenon.

CD44 is a major E-selectin ligand on human hematopoietic progenitor cells

E-selectin plays a critical role in mediating tissue-specific homing of T cells into skin, and of primitive hematopoietic progenitor cells (HPCs) into bone marrow (BM). Though it is known that a glycoform of PSGL-1 (CLA) functions as the principal E-selectin ligand on human T lymphocytes, the E-selectin ligand(s) of human HPCs has not been identified. We used a shear-based adherence assay to analyze and define the E-selectin ligand activity of membrane proteins from human HPCs. Our data show that PSGL-1 expressed on human HPCs is an E-selectin ligand, and that HPCs also express a previously unrecognized E-selectin ligand, CD44. The E-selectin ligand activity of CD44 is conferred by the elaboration of sialylated, fucosylated binding determinants on N-glycans. This glycoform of CD44 is expressed on primitive CD34+ human HPCs, but not on more mature hematopoietic cells. Under physiologic flow conditions, this molecule mediates E-selectin-dependent rolling interactions over a wider shear range than that of PSGL-1, and promotes human HPC rolling interactions on E-selectin expressed on human BM endothelial cells. These findings offer new insights into the structural biology and physiology of CD44, and into the molecular basis of E-selectin-dependent adhesive interactions that direct homing of human HPC to BM.

Adhesion molecules involved in transendothelial migration of human hematopoietic progenitor cells

In the process of homing, CD34(+) hematopoietic progenitor cells migrate across the bone marrow endothelium in response to stromal cell-derived factor (SDF)-1. To develop more efficient stem cell transplantation procedures, it is important to define the adhesion molecules involved in the homing process. Here, we identified the adhesion molecules that control the migration of primary human CD34(+) cells across human bone marrow endothelial cells. Migration of CD34(+) cells is enhanced across interleukin 1beta prestimulated bone marrow endothelium, suggesting an important role for the endothelium in adhesion and formation of the chemotactic gradient. Under these conditions, 30-100 ng/ml SDF-1 induced a rapid and efficient migration of CD34(+) cells (+/- 46% migration in 4 h). In contrast, 600-1,000 ng/ml SDF-1 were required for optimal migration across fibronectin-coated filters. Subsequent studies revealed that transendothelial migration of CD34(+) cells is mediated by beta1- and beta2-integrins and PECAM-1 (CD31) but not by CD34 or E-selectin. Whereas these antibodies individually blocked migration for 25%-35%, migration was reduced by 68% when the antibodies were combined. Thus, these adhesion molecules play specific and independent roles in the transmigration process. Finally, O-glycosylated proteins appeared to play a role, since SDF-1-induced migration of CD34(+) cells (treated with a glycoprotease from Pasteurella haemolytica) across endothelial cells was clearly inhibited. In conclusion, we show that efficient SDF-1-induced migration of primary human CD34(+) cells across bone marrow endothelium is mediated by beta1-integrins, beta2-integrins, CD31 and O-glycosylated proteins.