Where is Waldo? or find the platelet.

Platelets evolved from nucleated thrombocytes that exhibit both coagulation and immune function. The essential role of platelets in coagulation is common knowledge. The larger and critical role of platelets in immune responses and cancer are frequently overlooked in our modern-day, large-data-set, sequencing-oriented efforts. Much like Waldo, their small size, biophysical characteristics, rapid biological responses, active cytoskeleton, migration capacity, and lack of a nucleus make them difficult to track as single platelets disappear while executing their function into the histologic "tissue scape". The adaptive evolution of platelets is linked to placentalization and stopping massive blood loss. This resulted in exclusion of any platelet nucleus and therefore sustainable gene expression due to being extruded in the billions (1011) per day from megakaryocytes under bone marrow protection. The platelets' small size and sheer number in circulation, combined with an active open canalicular exchange- and membrane-reserve system, plus an array of pathogen receptors enable them to deal with small pathogenic viral treats and to decorate larger ones for further immune identification and immune-cell recruitment. Once stimulated, platelets release most serum-based cytokines and growth factors that contribute to cell growth and wound repair, and potentially to immune suppression. From a self-taught practitioner of the illustrative arts with a ken for platelet biology, this offering is a humble attempt to provide a stimulating sketch of the critical importance of platelet biology and insights into potential new directions for finding the Waldo-esque platelet.

Magnetic Resonance Imaging and Bioluminescence Imaging for Evaluating Tumor Burden in Orthotopic Colon Cancer.

Quantifying tumor burden is important for following the natural history of orthotopic colon cancer and therapeutic efficacy. Bioluminescence imaging (BLI) is commonly used for such assessment and has both advantages and limitations. We compared BLI and magnetic resonance imaging (MRI) for quantifying orthotopic tumors in a mouse model of colon cancer. Among sequences tested, T2-based MRI imaging ranked best overall for colon cancer border delineation, contrast, and conspicuity. Longitudinal MRI detected tumor outside the colon, indistinguished by BLI. Colon tumor weights calculated from MRI in vivo correlated highly with tumor weights measured ex vivo whereas the BLI signal intensities correlated relatively poorly and this difference in correlations was highly significant. This suggests that MRI may more accurately assess tumor burden in longitudinal monitoring of orthotopic colon cancer in this model as well as in other models.

Cytokine profile and prognostic significance of high neutrophil-lymphocyte ratio in colorectal cancer.

BACKGROUND: High circulating neutrophil-lymphocyte ratio (NLR) appears to be prognostic in metastatic colorectal cancer (mCRC). We investigated the relationship of NLR with circulating cytokines and molecular alterations. METHODS: We performed retrospective analyses on multiple cohorts of CRC patients (metastatic untreated (n=166), refractory metastatic (n=161), hepatectomy (n=198), stage 2/3 (n=274), and molecularly screened (n=342)). High NLR (ratio of absolute neutrophil-to-lymphocyte counts in peripheral blood) was defined as NLR>5. Plasma cytokines were evaluated using multiplex-bead assays. Kaplan-Meier estimates, non-parametric correlation analysis, and hierarchical cluster analyses were used. RESULTS: High NLR was associated with poor prognosis in mCRC (hazard ratio (HR) 1.73; 95% confidence interval (CI):1.03-2.89; P=0.039) independent of known prognostic factors and molecular alterations (KRAS/NRAS/BRAF/PIK3CA/CIMP). High NLR correlated with increased expression of interleukin 6 (IL-6), IL-8, IL-2Rα, hepatocyte growth factor, macrophage-colony stimulating factor, and vascular epidermal growth factor in exploratory (n=39) and validation (n=166) cohorts. Fourteen additional cytokines correlated with high NLR in the validation cohort. All 20 cytokines fell into three major clusters: inflammatory cytokines, angiogenic cytokines, and epidermal growth factor ligands. In mCRC, composite stratification based on NLR-cytokine score provided enhanced prognostic information (HR 2.09; 95% CI: 1.59-2.76; P<0.001) over and above NLR. CONCLUSIONS: High NLR is an independent poor prognostic marker in CRC and correlates with a distinct cytokine profile related to key biological processes involved in carcinogenesis. A composite NLR-cytokine stratification has enhanced prognostic value in mCRC.

15-Lipoxygenase-2 gene regulation by its product 15-(S)-hydroxyeicosatetraenoic acid through a negative feedback mechanism that involves peroxisome proliferator-activated receptor gamma.

An inverse relationship exists between the expression of 15-lipoxygenase-2 (15-LOX-2) and peroxisome proliferator-activated receptor gamma (PPARgamma) in normal prostate epithelial cells (PrECs) compared with their expression in prostate carcinoma cells (PC-3). The reason for this difference, however, is unknown. We hypothesized that this inverse expression partly involves the 15-LOX-2 promoter and 15-S-hydroxyeicosatetraenoic acid (15-(S)-HETE), a product of 15-LOX-2 that binds to PPARgamma. We identified an active steroid nuclear receptor half-site present in the 15-LOX-2 promoter fragment F-5 (-618/+177) that can interact with PPARgamma. After forced expression of wild-type PPARgamma, 15-(S)-HETE (1 microM) decreased F-5 reporter activity in PrECs whereas forced expression of 15-LOX-2 resulted in 15-(S)-HETE production which enhanced F-5 activity in PC-3. In contrast, the expression of dominant-negative PPARgamma reversed the transcriptional activation of F-5 by enhancing it 202-fold in PrEC or suppressing it in PC-3; the effect in PC-3 was positively increased 150-fold in the presence of 15-(S)-HETE (1 microM). Peroxisome proliferator-activated receptor gamma interacted with 15-LOX-2 promoter sequences in pulldown experiments using biotinylated 15-LOX-2 (-560/-596 bp) oligonucleotides. In gelshift analyses PPARgamma and orphan receptor RORalpha were shown to interact with the F-5 fragment in PC-3 cells. These data suggest that crosstalk mechanisms exist between the 15-LOX-2 gene and PPARgamma to counterbalance expression and help explain the inverse relationship of these genes in normal versus cancer cells.

Computerized image analysis of Ki-67 in ductal breast carcinoma in situ.

OBJECTIVE: To develop and determine the staining protocols and computerized image analysis methods that are the most effective combination for performing quantitative analysis of Ki-67. STUDY DESIGN: We compared conventional bright-field light microscopy and refractive optical enhancement methods in combination with various immunodetection and filter enhancement methods, including immunogold in combination with epipolarization refractive optics and enzymatic conversion of chromogenic substrates in combination with optical filter enhancement. Initial Ki-67 tests were performed on lymph node tissues and cultured human breast cells and then applied to 200 ductal carcinoma in situ (DCIS) samples. DCIS acini were digitally acquired, and a region of interest was manually outlined in each one with a digital stylus to include only the cellular component; then the Ki-67 staining index was quantified by segmentation analysis. RESULTS: Although combining epipolarization analysis with immunohistogold staining was the most sensitive detection method, nonspecific binding was too high. The streptavidin-horseradish-peroxidase enzymatic conversion of 3,3'-diaminobenzidine (DAB) in combination with optical enhancement filters was the most effective method tested. Ki-67 stain was associated with dense fibrillar structures of the nucleoli in the less intensely staining nuclei and was most intense in paired nuclei. CONCLUSION: The method of measuring Ki-67 expression by DAB staining combined with optical enhancement filters and quantification via computer-assisted image analysis techniques produced objective and reproducible results. As such, this method can offer (1) less intraobserver and interobserver variability, (2) a digital archival record, and (3) a baseline for digital exchange of information between studies.

Differential expression of cyclooxygenase-2 and its regulation by tumor necrosis factor-alpha in normal and malignant prostate cells.

Cyclooxygenase (COX)-2 expression is elevated in some malignancies; however, information is scarce regarding COX-2 contributions to the development of prostate cancer and its regulation by inflammatory cytokines. The present study compared and contrasted the expression levels and subcellular distribution patterns of COX-1 and COX-2 in normal prostate [prostate epithelial cell (PrEC), prostate smooth muscle (PrSM), and prostate stromal (PrSt)] primary cell cultures and prostatic carcinoma cell lines (PC-3, LNCaP, and DU145). The basal COX-2 mRNA and protein levels were high in normal PrEC and low in tumor cells, unlike many other normal cells and tumor cells. Because COX-2 levels were low in prostate smooth muscle cells, prostate stromal cells, and tumor cells, we also examined whether COX-1 and COX-2 gene expression was elevated in response to tumor necrosis factor-alpha (TNF-alpha), a strong inducer of COX-2 expression. Northern blot analysis and reverse transcription-PCR demonstrated different patterns and kinetics of expression for COX-1 and COX-2 among normal cells and tumor cells in response to TNF-alpha. In particular, COX-2 protein levels increased, and the subcellular distribution formed a distinct perinuclear ring in the normal cells at 4 h after TNF-alpha exposure. The COX-2 protein levels also increased in cancer cells, but the subcellular distribution was less organized; COX-2 protein appeared diffuse in some cells and accumulated as focal deposits in the cytoplasm of other cells. TNF-alpha induction of COX-2 and prostaglandin E2 correlated inversely with induction of apoptosis. We conclude that COX-2 expression may be important to PrEC cell function. Although it is low in stromal and tumor cells, COX-2 expression is induced by TNF-alpha in these cells, and this responsiveness may play an important role in prostate cancer progression.

Selenium effects on prostate cell growth.

Epidemiological and clinical data suggest that selenium may prevent prostate cancer, but the biological effects of selenium on normal or malignant prostate cells are not well known. We evaluated the effects of sodium selenite (Na2SeO3) or l-selenomethionine (SeMet) on monolayer and anchorage-independent growth in a series of normal primary prostate cultures (epithelial, stromal, and smooth muscle) and prostate cancer cell lines (LNCaP, PC-3, and DU145). We observed differential, dose-dependent growth inhibition and apoptosis within prostate cancer cells (compared with normal prostate cells) treated with 1-500 microM of Na2SeO3 or SeMet. Na2SeO3 more potently inhibited growth at any given concentration. The androgen-responsive LNCaP cells were the most sensitive to selenium growth suppression (IC50s at 72 h for Na2SeO3 and SeMet were 0.2 and 1.0 microM, respectively). Growth of the primary prostate cells virtually was not suppressed (IC50s at 72 h for Na2SeO3 and SeMet were 22-38 and >500 microM, respectively). We also observed that DNA condensation and DNA fragmentation (terminal deoxynucleotidyltransferase dUTP nick end labeling/fluorescence-activated cell sorting) were elevated in selenium-treated cells and that activated caspase-3 colocalized with terminal deoxynucleotidyltransferase dUTP nick end labeling-stained cells by immunofluorescence. Higher basal poly(ADP-ribose) polymerase (PARP) expression levels and PARP cleavage (a substrate for caspase-3) were observed during apoptosis in tumor cells, compared with normal cells. Selective tumor cell death was associated with an increase in sub-G0-G1 cells after propidium iodide staining and fluorescence-activated cell sorting analysis. SeMet caused an increase in arrest in the G2-M phase of the cell cycle selectively in cancer cells. Inhibition of cancer cell growth by SeMet was associated with phosphorylation of P-Tyr15-p34/cdc2, which caused growth arrest in the G2-M phase. Anchorage-independent growth of prostate cancer cells in soft agar was sensitive to selenium. Our results suggest that Na2SeO3 is the more potent inducer of apoptosis in normal and cancer prostate cells. Our SeMet results involving PARP and G2-M cell-cycle arrest (cited above) indicate that SeMet selectively induces apoptosis in cancer but not primary cells of the human prostate. Our overall findings are relevant to the molecular mechanisms of selenium actions on prostate carcinogenesis and help demonstrate the selective, dose-dependent effects of selenium (especially SeMet) on prostate cancer cell death and growth inhibition.

Expression of protein mediators of type I interferon signaling in human squamous cell carcinoma of the skin.

IFN-based therapy has been shown to be active in the treatment of squamous cell carcinoma (SCC) of the skin and has promise for chemoprevention and treatment of several other cancers. In an effort to better understand the molecular mechanism of this activity, we have determined the expression pattern of several of the protein mediators of type I IFN signaling by immunohistochemistry in cutaneous SCC, SCC metastases, and adjacent nonmalignant epithelium from patient biopsies. All of the proteins, signal transducer and activator of transcription (STAT) 1alpha/beta, STAT2, p48, STAT3a, and STAT3beta, are expressed at varying levels in the adjacent epidermis, as well as in other epidermal and dermal cell types. For the majority of samples tested, the expression of one or more of these proteins was reduced in SCC primary tumors compared with the adjacent nonmalignant epithelial cells, as determined by manual scoring. Quantitative densitometry of several samples revealed differences that are statistically significant. Our study provides the first direct evidence for the expression of the IFN-stimulated gene factor 3 (STAT1alpha/beta, STAT2, and p48) and STAT3alpha and STAT3beta mediators of IFN-alpha/beta signaling in human skin and skin-derived SCCs. These data have led to the hypothesis that the loss of IFN sensitivity may contribute to the development and progression of skin SCC.

Activation of stat3 and stat1 DNA binding and transcriptional activity in human brain tumour cell lines by gp130 cytokines.

In this study we examine the activation of the latent Stat family of transcription factors by the gp130 family of cytokines in cell lines derived from human brain tumours. Of the cytokines tested, oncostatin M resulted in the most dramatic induction of Stat1 and Stat3 in all cell lines analysed, as assessed by the formation of protein/DNA complexes. Interleukin-6, leukemia inhibitory factor, and ciliary neurotrophic factor also induced Stat complexes more selectively and to a lesser magnitude than oncostatin M. The kinetics of Stat1 and Stat3 activation was rapid and transient; the nuclear accumulation of DNA binding-proficient Stat protein was detected in the nucleus within minutes of cytokine induction. The transcriptional potential of the oncostatin M-activated Stat molecules was demonstrated in two glioma cell lines (U87-MG, SNB-19) by transient transfection experiments using a Stat-responsive reporter plasmid. Oncostatin M-dependent transcription from this reporter plasmid was reduced to uninduced levels by the inclusion of a dominant-negative Stat3 molecule, demonstrating that Stat molecules were responsible for the induction. These studies demonstrate that oncostatin M is the most potent activator of Stat molecules in a variety of brain tumour-derived cell lines, an observation that could have implications affecting the balance between proliferation/apoptosis of these cells.

Retinoid receptor-dependent and -independent effects of N-(4-hydroxyphenyl)retinamide in F9 embryonal carcinoma cells.

Fenretinide (N-[4-hydroxyphenyl]retinamide (4HPR)) is a retinoid analogue with antitumor and chemopreventive activities. The mechanism of action of 4HPR is not fully understood, but it is hypothesized that this compound acts independently of the nuclear retinoid receptor pathway. To test this hypothesis directly, we have analyzed the activity of 4HPR on a panel of F9 embryonal carcinoma cell lines, which includes wild-type and mutant lines that lack expression of retinoic acid receptor gamma, retinoid X receptor alpha, or both. 4HPR (10 microM) treatment resulted in a rapid induction of cell death in F9 cells, which was responsible for their near elimination by 48 h. This effect occurred in the receptor-null cell lines as well. Treatment of the wild-type cells for 4 days with 1 microM 4HPR also resulted in a primitive endodermal differentiated phenotype that is normally seen upon all-trans-retinoic acid treatment and is characterized by the up-regulation of laminin B1 and type IV collagen. This differentiation response did not occur in the receptor-null cells. Therefore, two distinct effects of 4HPR were identified in this system: a rapid induction of cell death and a slower induction of differentiation, which are likely to be receptor independent and dependent, respectively.

Integrin alpha4beta1/VCAM-1 pathway mediates primary adhesion of RAW117 lymphoma cells to hepatic sinusoidal endothelial cells under flow.

Adhesion and stabilization of circulating tumor cells to endothelial cells in target blood vessels play an important role in the complex process of metastasis. We examined the cell surface receptors involved in the liver-metastatic adhesive interactions of murine RAW117 large-cell lymphoma cells to unstimulated hepatic sinusoidal endothelial cells (HSE) under physiological flow conditions. Flow cytometric analysis indicated that VCAM-1, ICAM-1 and PECAM-1 are constitutively expressed on the surfaces of both HSE and RAW117 cells. However, monoclonal antibody (mAb) blockade studies showed that ICAM-1 and PECAM-1 affected neither the attachment nor the stabilization step of the adhesion of RAW117 cells to HSE cell monolayers under flow. In contrast, RAW117 cells required a significantly lower shear stress to establish adhesion to HSE cells when VCAM-1 receptors on HSE cells were blocked with mAb. Furthermore, the presence of the anti-VCAM-1 mAb significantly decreased the extent of adhesion compared to that of the control, without affecting adherent cell stabilization times. Blocking the alpha4 integrin subunits present mainly on RAW117 cells produced similar results to those previously observed with anti-VCAM-1 mAb. Although constitutively present mainly on the surfaces of RAW117 cells, MAdCAM-1 and beta7 integrin subunit do not appear to play a role in either the arrest or stabilization of RAW117 cells on HSE cell monolayers. However, blocking the beta1 integrin subunit on the RAW117-H10 cells reduced adhesion to the same extent as anti-alpha4 and anti-VCAM-1 treatments. These observations suggest that an interaction of integrin alpha4/beta1 on RAW117 cells with liver endothelial VCAM-1 occurs during the early stages of the adhesion process and may be important in liver metastasis.

Regulation of lipid signaling pathways for cell survival and apoptosis by bcl-2 in prostate carcinoma cells.

Compelling evidence indicates that activation of the JNK/SAPK signaling pathway is obligatory for apoptosis induction by multiple cell stresses that activate the sphingomyelin cycle. Moreover, ectopic expression of bcl-2 can impair apoptosis signaling by most of the cell stresses that activate the ceramide/JNK pathway. Here we show that enforced expression of bcl-2 protects prostate carcinoma cells against the induction of apoptosis by exogenous C2-ceramide. Moreover, enforced bcl-2 expression blocked the capacity of C2-ceramide to activate JNK1, indicating bcl-2 functions at the level of JNK1 or upstream of JNK1 in the ceramide/JNK pathway. The contribution of bcl2 to the regulation of the arachidonate pathway for prostate carcinoma cell survival was also investigated using highly selective inhibitors of arachidonate metabolism. Our results indicate bcl-2 can protect cells against diminished availability of arachidonic acid, 12-HETE, and 15-HETE. Finally, arachidonic acid substantially suppresses the induction of apoptosis by C2-ceramide, providing evidence for the opposing influences of these lipid signaling pathways in the mediation of prostate carcinoma cell survival. These results provide evidence for opposing influences of the ceramide and arachidonate signaling pathways in the mediation of cell death and cell survival, respectively, in prostate carcinoma cells and suggest a dual role for bcl-2 in this context.

Differential adhesion of metastatic RAW117 large-cell lymphoma cells under static or hydrodynamic conditions: role of integrin alpha(v) beta3.

RGD-containing substrates were used to study static and hydrodynamic adhesion of murine RAW117 large-cell lymphoma sublines with differential liver-metastatic potentials. Highly liver-metastatic RAW117-H10 cells had higher rates of static adhesion to vitronectin, fibronectin and (GRGDS)4 than poorly metastatic RAW117-P and moderately liver-metastatic RAW117-L17 cells. Under hydrodynamic conditions, adhesion stabilization was more rapid for H10 cells compared to P or L17 cells. Among the RGD peptides, only the polymeric RGD peptide (GRGDS)4 mediated strong static adhesion of H10 cells. Interestingly, all the RGD peptides mediated adhesion stabilization for H10 cells but still not for L17 or P cells under hydrodynamic conditions. Integrin alpha(v) beta3 was involved in stabilizing hydrodynamic adhesion to (GRGDS)4, monomeric RGD peptide R1, but was less important in static adhesion to monomeric RGD peptides. Differential adhesion to liver sinusoidal endothelial cell-derived extracellular matrix (H10 >> L17 > P) was observed under hydrodynamic but not static conditions. Integrin alpha(v) beta3 was also important in hydrodynamic adhesion to liver sinusoidal endothelial cell-derived extracellular matrix. We believe that strong static and hydrodynamic adhesion of H10 cells and their capability of altering adhesive behavior in response to fluid shear may contribute to liver metastasis.

Regulation of melanoma cell adhesion stabilization to fibronectin.

Tumour cell arrest and the formation of stable adhesive interactions between tumour cells and endothelial cells or underlying matrix in the microvasculature are crucial steps in the metastatic process. We have developed a sensitive hydrodynamic adhesion assay to investigate the regulation of melanoma cell adhesion stabilization to the extracellular matrix protein fibronectin. Modulators of human MeWo melanoma Ca2+ concentration and stores, including ionomycin, thapsigargin, dantrolene and caffeine, inhibited cell adhesion stabilization to fibronectin; however, removal of Ca2+ from the extracellular medium did not affect stabilization. The calmodulin inhibitor W-7 and the protein kinase C inhibitor chelerythrine also blocked MeWo adhesion stabilization to fibronectin, as did the tyrosine kinase inhibitor genistein and the cytoskeletal inhibitor cytochalasin D. Manipulation of MeWo cell intracellular CAMP levels had no effect of adhesion stabilization to fibronectin, nor did treatment of cells with phorbol ester, pertussis toxin or cholera toxin. Drug treatments that inhibited adhesion stabilization also had significant effects on the actin cytoskeleton organization of the melanoma cells. This study suggests a role for calcium, calmodulin, protein kinase C and tyrosine kinases in the intracellular regulation of MeWo adhesive stabilization.

Involvement of integrin alphavbeta3 in cell adhesion, motility, and liver metastasis of murine RAW117 large cell lymphoma.

The molecules that mediate metastatic cell homing to specific organ sites remain largely unidentified. As a target organ for metastasis, the liver is a unique environment characterized by fenestrated sinusoidal endothelium, lack of a complete basement membrane, and production of serum components, including fibronectin and vitronectin. We examined a series of marine RAW117 large cell lymphoma variants selected in vivo for liver-colonizing properties (H10 >> L17 > P). Compared with L17 or P cells, the highly liver-colonizing H1O cells expressed much higher levels of surface integrin alphavbeta3, as shown by affinity chromatography, immunoprecipitation, and flow cytometry. H10 cells adhered at higher rates to vitronectin and fibronectin than to fibrinogen, fibrin, laminin, and type I collagen. Among the RGD peptides, H10 cells adhered at significantly higher rates to the polymeric RGD peptide (glycyl-arginyl-glycyl-aspartyl-serine)4 than to monomeric RGD peptides. H10 cells were able to spread on immobilized vitronectin with highly polarized morphology but not on fibronectin. In contrast, the poorly liver-metastatic P and L17 cells did not adhere or spread well on vitronectin or fibronectin. H10 cells also migrated toward vitronectin concentration gradients. Blocking cell surface alphavbeta3 molecules with specific anti-beta3 monoclonal antibodies resulted in significant decreases in the adhesion of H10 cells to vitronectin and (glycyl-arginyl-glycyl-aspartyl-serine)4 and significant inhibition of the formation of experimental liver metastases. These data suggest an important role of integrin alphavbeta3 in the metastasis of RAW117 cells to the liver.

Computerized analysis of tumor cell interactions with extracellular matrix proteins, peptides, and endothelial cells under laminar flow.

Arrest and formation of stable adhesive interactions between circulating cells and the endothelium or exposed subendothelial matrix are important processes in many biological situations. We have developed a highly sensitive hydrodynamic assay that utilizes a parallel-plate flow chamber, video microscopy, and digital image processing to separate and measure the primary arrest and adhesion stabilization of flowing cells. Our data indicate that primary cell contact triggers secondary adhesion stabilization, and the secondary events are likely to be critical to metastasis formation. To study the relationship between tumor cell adhesion stabilization and organ-specific blood-borne metastasis, we investigated the adhesion stabilization of metastatic murine RAW117 large-cell lymphoma cells to the extracellular matrix proteins fibronectin and vitronectin, several Arg-Gly-Asp (RGD) containing peptides, and microvascular endothelial cells from the liver or lung. The highly liver metastatic RAW117-H10 subline showed the fastest stabilization to fibronectin, vitronectin, and RGD peptides. Poorly metastatic RAW117-P cells had stabilization times 3-10 times longer than for RAW117-H10 cells, while the lung- and liver-metastatic RAW117-L17 subline failed to stabilize at all. The adhesion stabilization of the RAW117-H10 cells to the extracellular matrix proteins and RGD peptides was inhibited by anti-beta(3) integrin monoclonal antibodies and RGD peptides. In contrast, the RAW117-L17 subline had the shortest stabilization time to unstimulated microvascular endothelial cells of the lung and hepatic sinusoids, followed by RAW117-H10 cells and RAW117-P cells. Monoclonal antibodies against the beta(3) integrin subunit and RGD peptides did not inhibit adhesion stabilization of RAW117-H10 cells to endothelial cells, suggesting that different metastatic variants of large-cell lymphoma cells use differing mechanisms to adhere to organ-specific endothelial cells.

Human melanoma integrins contribute to arrest and stabilization potential while flowing over extracellular matrix.

To form distant metastases, tumour cells must stabilize adhesive interactions that prevent detachment at secondary sites. Primary receptor-ligand interactions alone may not maintain prolonged adhesive contacts without secondary events that lead to adhesion stabilization. Computerized imaging methods enable us to examine various substrates for: (i) the wall shear adhesion threshold (WSAT), a measure of the dynamic adhesive potential of tumour cells; (ii) the number of tumour cells that adhered; and (iii) the adhesion stabilization lag time (ASLT) or length of time required for tumour cells to stabilize adhesive contacts capable of withstanding high wall shear force (up to 100 dynes/cm2). The relative WSAT ratios found were: wheat germ agglutinin (WGA) > laminin > fibronectin > vitronectin > collagen I > collagen IV > von Willebrand factor (vWF) (the greater the shear rate the higher the adhesive potential). The relative stabilization ratios found were as follows: laminin < fibronectin < vitronectin < collagen IV < collagen I < vWF < WGA (shorter times correlate with greater stabilization potential). Stabilization data using fibronectin as a substrate correlated the best with metastatic potential. Using three melanoma lines of different metastatic potential semiquantitative reverse transcriptase-polymerase chain reaction (PCR) showed a two- to four-fold increase in alpha1, alpha3, alpha4, alpha5, alpha6, and ICAM-1 in the highly metastatic 70W cells compared to the MeWo and non-metastatic 3S5 melanoma cells. There were no differences in alphav, beta1 and beta3 levels among the three melanoma lines, and PCR products for alphaIIb, alpha2, CD36, or ICAM-2 were not detected. The 70W cells also had higher levels of alphax and beta2 (CD11/CD18 and p150 leukocyte antigen) than either the MeWo or 3S5 cells. The data indicate that melanoma cells exhibit differences in the adhesion properties under fluid shear and differences in the expression of adhesion components that correlate with their metastatic potential.