Adhesion molecules and their role in cancer metastasis

Targeting HECTD3-IKKα axis inhibits inflammation-related metastasis

Metastasis is the leading cause of cancer-related death. The interactions between circulating tumor cells and endothelial adhesion molecules in distant organs is a key step during extravasation in hematogenous metastasis. Surgery is a common intervention for most primary solid tumors. However, surgical trauma-related systemic inflammation facilitates distant tumor metastasis by increasing the spread and adhesion of tumor cells to vascular endothelial cells (ECs). Currently, there are no effective interventions to prevent distant metastasis. Here, we show that HECTD3 deficiency in ECs significantly reduces tumor metastasis in multiple mouse models. HECTD3 depletion downregulates expression of adhesion molecules, such as VCAM-1, ICAM-1 and E-selectin, in mouse primary ECs and HUVECs stimulated by inflammatory factors and inhibits adhesion of tumor cells to ECs both in vitro and in vivo. We demonstrate that HECTD3 promotes stabilization, nuclear localization and kinase activity of IKKα by ubiquitinating IKKα with K27- and K63-linked polyubiquitin chains at K296, increasing phosphorylation of histone H3 to promote NF-κB target gene transcription. Knockout of HECTD3 in endothelium significantly inhibits tumor cells lung colonization, while conditional knockin promotes that. IKKα kinase inhibitors prevented LPS-induced pulmonary metastasis. These findings reveal the promotional role of the HECTD3-IKKα axis in tumor hematogenous metastasis and provide a potential strategy for tumor metastasis prevention.

Pure abscopal effect of radiotherapy in a salivary gland carcinoma: Case report, literature review, and a search for new approaches

We report the case of an 84-year-old woman with poorly differentiated non-small cell carcinoma of the right parotid who presented with headache, was found to have a primary right parotid gland cancer as well as metastatic disease, and underwent palliative radiotherapy to the primary site. The patient received no chemotherapy or immunotherapy, but both the primary site and several non-irradiated foci in the lungs regressed or completely resolved. The patient remained free of disease for about one year before progression. The case is a rare instance of abscopal regression of metastatic disease in the absence of pharmacologic immunomodulation. A literature review surveys the history of the abscopal effect of radiation therapy, attempts to understand the mechanisms of its successes and failures, and points to new approaches that can inform and improve the outcomes of radioimmunotherapy.

ZINC4085554 inhibits cancer cell adhesion by interfering with the interaction of Akt1 and FAK

Perioperative or circulatory forces enhance disseminated cancer cell adhesiveness by modulating focal adhesion kinase (FAK)-Akt1 interaction. Selectively blocking FAK-Akt1 interaction by a peptide derived from the FAK-Four-point-one, ezrin, radixin, moesin (FERM) domain reduces colon cancer cell adhesion in vitro and in mice. A preliminary in silico screening identified two small molecules resembling a peptide that may inhibit pressure-stimulated SW620 cancer cell adhesion to collagen I. The present study selected ZINC4085554 for further study to validate its proposed mechanism of action, using human SW620 colon cancer cells as a model system. At 25 and 50 µM, ZINC4085554 inhibited the pressure-stimulated adhesion of SW620 colon cancer cells to collagen I. This molecule prevented pressure-stimulated FAK-Tyr-397 phosphorylation; however, it did not affect Akt1-Ser-473 phosphorylation, indicating that ZINC4085554 acts downstream of Akt1, while Akt-Thr-308 remains unchanged in the presence of pressure and or ZINC4085554. Indeed, ZINC4085554 inhibited FAK-Akt1 interaction in response to increased extracellular pressure, consistent with the proposed mechanism. ZINC4085554 did not inhibit FAK-Tyr-397 phosphorylation in response to cell adhesion to collagen I, indicating the specificity of the inhibitory effects towards force-stimulated pathways. Finally, the present study confirmed that ZINC4085554 at 50 µM prevented pressure-activation of adhesion to surgical wounds in vivo in parallel to its ablation of intracellular signaling. In summary, ZINC4085554 is a small molecule mimicking part of the structure of FAK that reduces cancer cell adhesion by impairing pressure-stimulated FAK-Akt1 interaction and its downstream consequences. ZINC4085554 does not inhibit conventional outside-in FAK signaling and may be less toxic than global FAK inhibitors, and ZINC4085554 may be an important step towards the inhibition of metastasis.

Notch ligand Delta-like 1 promotes the metastasis of melanoma by enhancing tumor adhesion

Notch signaling plays a vital role in tumorigenicity and tumor progression by regulating proliferation, invasion, and the tumor microenvironment. Previous research by our group indicated that Notch ligand Delta-like 1 (Dll1) is involved in angiogenesis in melanoma, and we noticed that it took a longer time to trypsinize Dll1-expressing B16 melanoma cells than the control cells. In this article, we extended our study to investigate the effects of Dll1 on tumor cell adhesion and metastasis. Dll1 overexpression activated Notch signaling in B16 tumor cells and significantly enhanced the adhering capacity of B16 tumor cells both in vitro and in vivo. B16-Dll1 cells also had a higher metastatic potential than their counterpart in the mouse model of lung metastasis. Along with increased Dll1 expression, N-cadherin, but not E-cadherin, was upregulated in B16-Dll1 cells. These data suggested that Notch ligand Dll1 may enhance the adhesion and metastasis of melanoma cells by upregulation of N-cadherin.

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.

Expression of E-selectin ligands on circulating tumor cells: cross-regulation with cancer stem cell regulatory pathways?

Although significant progress has been made in the fight against cancer, successful treatment strategies have yet to be developed to combat those tumors that have metastasized to distant organs. Poor characterization of the molecular mechanisms of cancer spread is a major impediment to designing predictive diagnostics and effective clinical interventions against late stage disease. In hematogenous metastasis, it is widely suspected that circulating tumor cells (CTCs) express specific adhesion molecules that actively initiate contact with the vascular endothelium lining the vessel walls of the target organ. This "tethering" is mediated by ligands expressed by CTCs that bind to E-selectin expressed by endothelial cells. However, it is currently unknown whether expression of functional E-selectin ligands on CTCs is related to cancer stem cell regulatory or maintenance pathways, particularly epithelial-to-mesenchymal transition and the reverse, mesenchymal-to-epithelial transition. In this hypothesis and theory article, we explore the potential roles of these mechanisms on the dynamic regulation of selectin ligands mediating CTC trafficking during metastasis.

Inducing apoptosis in rolling cancer cells: a combined therapy with aspirin and immobilized TRAIL and E-selectin

Though metastasis is considered an inefficient process, over 90% of cancer related deaths are attributed to the formation of secondary tumors. Thus, eliminating circulating cancer cells could lead to improved patient survival. This study was aimed at exploiting the interactions of cancer cells with selectins under flow to selectively kill captured colon cancer cells. Microtubes functionalized with E-selectin and TRAIL were perfused with colon cancer cell line Colo205 either treated with 1 mM aspirin or untreated for 1 or 2 h. Cells were collected from the microtube and analyzed by flow cytometry. Aspirin treatment alone killed only 3% cells in culture. A 95% difference in the number of cells killed between control and TRAIL + ES surfaces was seen when aspirin treated cells were perfused over the functionalized surface for 2 h. We have demonstrated a novel biomimetic method to capture and neutralize cancer cells in flow, thus reducing the chances for the formation of secondary tumors.

Different metastasis promotive potency of small G-proteins RalA and RalB in in vivo hamster tumor model

Background

Previously we have shown that oncogenic Ha-Ras stimulated in vivo metastasis through RalGEF-Ral signaling. RalA and RalB are highly homologous small G proteins belonging to Ras superfamily. They can be activated by Ras-RalGEF signaling pathway and influence cellular growth and survival, motility, vesicular transport and tumor progression in humans and in animal models. Here we first time compared the influence of RalA and RalB on tumorigenic, invasive and metastatic properties of RSV transformed hamster fibroblasts.

Methods

Retroviral vectors encoding activated forms or effector mutants of RalA or RalB proteins were introduced into the low metastatic HET-SR cell line. Tumor growth and spontaneous metastatic activity (SMA) were evaluated on immunocompetent hamsters after subcutaneous injection of cells. The biological properties of cells, including proliferation, clonogenicity, migration and invasion were determined using MTT, wound healing, colony formation and Boyden chamber assays respectively. Protein expression and phosphorylation was detected by Westen blot analysis. Extracellular proteinases activity was assessed by substrate-specific zymography.

Results

We have showed that although both Ral proteins stimulated SMA, RalB was more effective in metastasis stimulation in vivo as well as in potentiating of directed movement and invasion in vitro. Simultaneous expression of active RalA and RalB didn't give synergetic effect on metastasis formation. RalB activity decreased expression of Caveolin-1, while active RalA stimulated MMP-1 and uPA proteolytic activity, as well as CD24 expression. Both Ral proteins were capable of Cyclin D1 upregulation, JNK1 kinase activation, and stimulation of colony growth and motility. Among three main RalB effectors (RalBP1, exocyst complex and PLD1), PLD1 was essential for RalB-dependent metastasis stimulation.

Conclusions

Presented results are the first data on direct comparison of RalA and RalB impact as well as of RalA/RalB simultaneous expression influence on in vivo cell metastatic activity. We showed that RalB activation significantly more than RalA stimulates SMA. This property correlates with the ability of RalB to stimulate in vitro invasion and serum directed cell movement. We also found that RalB-PLD1 interaction is necessary for the acquisition of RalB-dependent high metastatic cell phenotype. These findings contribute to the identification of molecular mechanisms of metastasis and tumor progression.

Morphine attenuates endothelial cell adhesion molecules induced by the supernatant of LPS-stimulated colon cancer cells

A large reservoir of bacterial lipopolysaccharide (LPS) is available in the colon and this could promote colon cancer metastasis by enhancing tumor cell adhesion, intravasation, and extravasation. Furthermore, adhesion molecules like ICAM-1, VCAM-1, and E-selectin play important roles in the adhesion of tumor cells to endothelium. This study was designed to determine whether morphine can attenuate the expressions of adhesion molecules up-regulated by the supernatant of LPS-stimulated HCT 116 colon cancer cells (LPS-Sup). In this study, we divided to three groups by cell-growth medium of human umbilical vascular endothelial cells (HUVECs): the control group was incubated in growth factor-free endothelial medium, the Sup group was incubated in the supernatant of HCT 116 cells (Sup), and the LPS-Sup group was incubated in LPS-Sup. To observe effect of morphine to the adhesion molecules expressions in the LPS-Sup group, we co-treated morphine with LPS or added it to LPS-Sup. Adhesion molecule expressions on HUVECs in all three groups were measured during incubation period. Consquentially, ICAM-1, VCAM-1, and E-selectin expressions on HUVECs were significantly lower when morphine was co-treated with LPS than not co-treated. Thus, we suggest that morphine affects the expressions of adhesion molecules primarily by attenuating LPS stimuli on tumor cells.

C2-O-sLeX glycoproteins are E-selectin ligands that regulate invasion of human colon and hepatic carcinoma cells

Similar to mechanisms of recruitment of activated leukocytes to inflamed tissues, selectins mediate adhesion and extravasation of circulating cancer cells. Our objective was to determine whether sialyl Lewis X modified core 2 O-glycans (C2-O-sLe^X) present on colon and hepatic carcinoma cells promote their adhesion and invasion. We examined membrane expression of C2-O-sLe^X, selectin binding, invasion of human colon and hepatic carcinoma cell lines, and mRNA levels of alpha-2,3 fucosyltransferase (FucT-III) and core 2 beta-1,6 N-acetylglucosaminyltransferase (C2GnT1) genes, necessary for C2-O-sLe^X synthesis, by quantitative reverse-transcriptase (RT) PCR. Synthesis of core 2 branched O-glycans decorated by sLe^X is dependent on C2GnT1 function and thus we determined enzyme activity of C2GnT1. The cell lines that expressed C2GnT1 and FucT-III mRNA by quantitative RT-PCR were highly positive for C2-O-sLe^X by flow cytometry, and colon carcinoma cells possessed highly active C2GnT1 enzyme. Cells bound avidly to E-selection but not to P- and L-selectin. Gene knock-down of C2GnT1 in colon and hepatic carcinoma cells using short hairpin RNAs (shRNA) resulted in a 40–90% decrease in C2-O-sLe^X and a 30–50% decrease in E-selectin binding compared to control cells. Invasion of hepatic and colon carcinoma cells containing C2GnT1 shRNA was significantly reduced compared to control cells in Matrigel assays and C2GnT1 activity was down-regulated in the latter cells. The sLe^X epitope was predominantly distributed on core 2 O-glycans on colon and hepatic carcinoma cells. Our findings indicate that C2GnT1 gene expression and the resulting C2-O-sLe^X carbohydrates produced mediate the adhesive and invasive behaviors of human carcinomas which may influence their metastatic potential.

The high affinity selectin glycan ligand C2-O-sLex and mRNA transcripts of the core 2 beta-1,6-N-acetylglucosaminyltransferase (C2GnT1) gene are highly expressed in human colorectal adenocarcinomas

Background

The metastasis of cancer cells and leukocyte extravasation into inflamed tissues share common features. Specialized carbohydrates modified with sialyl Lewis x (sLe^x) antigens on leukocyte membranes are ligands for selectin adhesion molecules on activated vascular endothelial cells at inflammatory sites. The activity of the enzyme core 2 β1,6 N-acetylglucosaminyltransferase (C2GnT1) in leukocytes greatly increases their ability to bind to endothelial selectins. C2GnT1 is essential for the synthesis of core 2-branched O-linked carbohydrates terminated with sLe^x (C2-O-sLe^x). Our goal was to determine the expression profiles of C2-O-sLe^x in the malignant progression and metastasis of colorectal adenocarcinomas. The well characterized CHO-131 monoclonal antibody (mAb) specifically recognizes C2-O-sLe^x present in human leukocytes and carcinoma cells. Using CHO-131 mAb, we investigated whether C2-O-sLe^x was present in 113 human primary colorectal adenocarcinomas, 10 colorectal adenomas, 46 metastatic liver tumors, 28 normal colorectal tissues, and 5 normal liver tissues by immunohistochemistry. We also examined mRNA levels of the enzyme core 2 β1,6-N-acetylglucosaminyltransferase (C2GnT1) in 20 well, 15 moderately, and 2 poorly differentiated colorectal adenocarcinomas, and in 5 normal colorectal tissues by using quantitative real-time polymerase chain reactions (RT-PCR).

Results

We observed high reactivity with CHO-131 mAb in approximately 70% of colorectal carcinomas and 87% of metastatic liver tumors but a lack of reactivity in colorectal adenomas and normal colonic and liver tissues. Positive reactivity with CHO-131 mAb was very prominent in neoplastic colorectal glands of well to moderately differentiated adenocarcinomas. The most intense staining with CHO-131 mAb was observed at the advancing edge of tumors with the deepest invasive components.

Finally, we analyzed C2GnT1 mRNA levels in 37 colorectal adenocarcinomas and 5 normal colorectal tissues by RT-PCR. Significantly, we observed a greater than 15-fold increase in C2GnT1 mRNA levels in colorectal adenocarcinomas compared to normal colorectal tissues.

Conclusion

C2-O-sLe^x, detected by the CHO-131 mAb, is a tumor associated antigen whose expression is highly upregulated in colorectal adenocarcinomas and metastatic liver tumors compared to normal tissues. C2-O-sLe^x is a potentially useful early predictor of metastasis.

Chemo-enzymatic synthesis of tripeptide RGD diamide in organic solvents

The tripeptide BzArgGlyAsp(NH(2))(2) was synthesized by a combination of chemical and enzymatic methods in this study. First of all, GlyAsp(NH(2))(2) was synthesized by a novel chemical method in three steps including chloroacetylation of L-aspartic acid, esterification of chloroacetyl L-aspartic acid and ammonolysis of chloroacetyl L-aspartic acid diethyl ester. Secondly, kinetically controlled synthesis of BzArgGlyAsp(NH(2))(2) catalyzed by trypsin in organic solvent was conducted. The optimum conditions are pH 8.0, 30 degrees C in ethanol/Tris-HCl buffer system (85:15, v/v) for 80 min in the maximum yield of 74.4%.

Adhesion molecules CD171 (L1CAM) and CD24 are expressed by primary neuroendocrine carcinomas of the skin (Merkel cell carcinomas)

BACKGROUND

The neuroendocrine carcinoma of the skin is a rare malignant neuroendocrine tumor, which frequently metastasizes in regional lymph nodes or visceral organs. As adhesive interactions with endothelia, leukocytes, or thrombocytes enable malignant cells to penetrate the endothelium and to circulate in blood or lymphatic vessels, we here addressed the adhesion molecules CD171 (L1CAM) and CD24, which are known to be expressed by neurons, neuroblastomas, and other malignant tumors.

METHODS

Thirty-one neuroendocrine carcinomas of the skin (22 primary tumors, four recurrent tumors, and five metastases) were included in the study. Immunohistochemical staining of CD171 and CD24 was performed by the streptavidin-biotin-peroxidase-complex technique and a nickel-enhanced diaminobenzidine (DAB) reaction using the monoclonal antibodies UJ 127.11 and ML-5, respectively.

RESULTS

CD171 expression was detected in most neuroendocrine carcinomas of the skin, and staining was less frequent in metastases and recurrences in comparison with primary tumors which was statistically significant. The majority of neuroendocrine carcinomas of the skin was also positive for the mucin-like adhesion protein CD24. In contrast to tumor cells, cytokeratin 20-positive Merkel cells in 12 trichoblastomas and one fibroepithelioma of Pinkus were all negative for CD171 and CD24 staining.

CONCLUSIONS

Expression of CD171 and CD24 is found in most neuroendocrine carcinomas of the skin, which may be used diagnostically. Further studies will assess whether this feature may contribute to metastasis of neuroendocrine carcinomas of the skin by facilitating transendothelial migration or tumor cell dissemination as has been suggested for other malignancies.

Effect of pro-inflammatory stimuli on tumor cell-mediated induction of endothelial cell adhesion molecules in vitro

The object of our study was the question about the relevance of the tumor surrounding inflammatory cells with respect to the metastatic potential of the tumor cells. To imitate the role of inflammatory cells, three colon carcinoma (HT-29, HRT-18, and SW-620), one breast carcinoma (MCF-7), and one melanoma (ST-ML-12) cell lines were treated with pro-inflammatory stimuli, LPS, TNF-alpha, or IL-1beta. HUVEC monolayers were then stimulated by the collected supernatants (SN) of the tumor cells, following washing out of the applied stimuli. Analysis of CAM expression on HUVEC was performed using cell enzyme immunoassay. E-selectin, VCAM-1, and, in part, ICAM-1 were significantly up-regulated on HUVEC by exposure to SN of all LPS-stimulated tumor cells. This was especially the case for the colon carcinoma cell lines. A minimal increase of expression of VCAM-1 was observed after exposure to SN from TNF-alpha-stimulated HT-29 and MCF-7 cells. IL-1beta stimulation had no effect on endothelial CAM expression. These observations indicate that LPS could play a crucial role in tumor metastasis by inducing the release of soluble factors from different tumor cell lines capable of up-regulating CAM expression. This might be of special significance in colon carcinomas, where a large source of bacterial LPS is available in the intestinal lumen.

Nuclear localization of beta-catenin and plakoglobin in primary and metastatic human colonic carcinomas, colonic adenomas, and normal colon

Beta-catenin is a cytoskeleton-associated signaling molecule shown to be elevated in various carcinomas but mostly in colon cancer owing to its impaired degradation. In contrast, its close homologue plakoglobin was shown to suppress the tumorigenicity of certain tumor cells. In the present study, we have used a semiquantitative immunohistochemical approach to evaluate the extent of nuclear localization of beta-catenin in human colonic adenocarcinomas and adenomas and compared it to the distribution of plakoglobin in the same tissues. We show that beta-catenin accumulates in the nuclei of the epithelium of primary and metastatic colonic adenocarcinoma as well as in colonic adenomas. In contrast, nuclear plakoglobin levels in these tissues were low, even compared to those found in epithelial cells of normal colon. These results support the view that the increase in beta-catenin levels in colon cancer cells occurs early in the tumorigenic process, leading to its nuclear localization, not only in invasive adenocarcinoma, but also in colonic adenoma with mild dysplasia.

Endothelial cell activation following moderate traumatic brain injury

Traumatic brain injury (TBI) initiates a cascade of acute and chronic injury responses which include disturbances in the cerebrovasculature that may result in the activation of the microvascular endothelial development of a dysfunction endothelium. The present study examines endothelial cell (EC) activation in a percussion model of moderate TBI. The criteria for endothelial activation used in these studies was surface expression of a number of markers collectively termed endothelial activation antigens. Temporal induction of the major histocompatibility (MHC) class II molecules, E-selectin (CD62E), vascular cell adhesion molecule (VACM-1) (CD106) as well as altered expression of constitutively expressed intercellular adhesion molecule-1 (ICAM-1) (CD54), the glucose transporter protein (glut-1), the transferrin receptor (tfR) (CD71), and MHC class I molecules was examined at various times following impact. Induction of E-selectin and increased expression of ICAM-1 was seen by 2 h post-impact (PI) and was sustained through 24 h PI. Decreased expression of immunologically reactive glut-1 and tfR was observed by 2-4 h PI and remained low up to 24 h PI. No induction of VCAM-1, MHC class II molecules or altered constitutive expression or MHC class I molecules was seen. Changes in EC activation were observed predominantly at the site of impact and were diminished temporarily. These results indicate that mild concussive injury to the brain results in activation of the endothelium.

A microcantilever device to assess the effect of force on the lifetime of selectin-carbohydrate bonds

A microcantilever technique was used to apply force to receptor-ligand molecules involved in leukocyte rolling on blood vessel walls. E-selectin was adsorbed onto 3-microm-diameter, 4-mm-long glass fibers, and the selectin ligand, sialyl Lewis(x), was coupled to latex microspheres. After binding, the microsphere and bound fiber were retracted using a computerized loading protocol that combines hydrodynamic and Hookean forces on the fiber to produce a range of force loading rates (force/time), r(f). From the distribution of forces at failure, the average force was determined and plotted as a function of ln r(f). The slope and intercept of the plot yield the unstressed reverse reaction rate, k(r)(o), and a parameter that describes the force dependence of reverse reaction rates, r(o). The ligand was titrated so adhesion occurred in approximately 30% of tests, implying that >80% of adhesive events involve single bonds. Monte Carlo simulations show that this level of multiple bonding has little effect on parameter estimation. The estimates are r(o) = 0.048 and 0.016 nm and k(r)(o) = 0.72 and 2.2 s(-1) for loading rates in the ranges 200-1000 and 1000-5000 pN s(-1), respectively. Levenberg-Marquardt fitting across all values of r(f) gives r(o) = 0.034 nm and k(r)(o) = 0.82 s(-1). The values of these parameters are in the range required for rolling, as suggested by adhesive dynamics simulations.

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.

Arachidonic acid activates mitogen-activated protein (MAP) kinase-activated protein kinase 2 and mediates adhesion of a human breast carcinoma cell line to collagen type IV through a p38 MAP kinase-dependent pathway

Adhesion of metastatic human mammary carcinoma MDA-MB-435 cells to the basement membrane protein collagen type IV can be activated by treatment with arachidonic acid. We initially observed that this arachidonic acid-mediated adhesion was inhibited by the tyrosine kinase inhibitor genistein. Therefore, we examined the role of the mitogen-activated protein (MAP) kinase family tyrosine phosphorylation-regulated pathways in arachidonic acid-stimulated cell adhesion. Arachidonic acid stimulated the phosphorylation of p38, the activation of MAP kinase-activated protein kinase 2 (MAPKAPK2, a downstream substrate of p38), and the phosphorylation of heat shock protein 27 (a downstream substrate of MAP kinase-activated protein kinase 2). Treatment with the p38 inhibitor PD169316 completely and specifically inhibited arachidonic acid-mediated cell adhesion to collagen type IV. p38 activity was specifically associated with arachidonic acid-stimulated adhesion; this was demonstrated by the observation that 12-O-tetradecanoylphorbol 13-acetate-activated cell adhesion was not blocked by inhibiting p38 activity. Extracellular signal-regulated protein kinases (ERKs) 1 and 2 were also activated by arachidonic acid; however, cell adhesion to collagen type IV was not highly sensitive to PD98059, an inhibitor of MAP kinase kinase/ERK kinase 1 (MEK1) that blocks activation of the ERKs. c-Jun NH(2)-terminal kinase was not activated by arachidonic acid treatment of these cells. Together, these data suggest a novel role for p38 MAP kinase in regulating adhesion of breast cancer cells to collagen type IV.

Tumor necrosis factor-alpha stimulates attachment of small cell lung carcinoma to endothelial cells

Tumor cell attachment to endothelial cells (ECs) is an important step in the metastasis of small cell lung carcinoma (SCLC). Tumor necrosis factor-alpha (TNF-alpha) stimulation of ECs increases the attachment of some malignant cell types to ECs by affecting the expression of cell adhesion molecules (CAMs). Similarly, the inhibition of EC protein kinase C (PKC) and tyrosine kinase (TK) pathways modulates TNF-alpha-mediated effects on CAM expression. We hypothesized that TNF-alpha would increase SCLC attachment to ECs by affecting CAM expression through activation of PKC and TK pathways. To test this hypothesis, human umbilical vein endothelial cells (HUVECs) were stimulated with TNF-alpha (0 to 500 U/mL) for variable time periods (1 to 24 hours), and the attachment of H82 cells (an SCLC cell line) to the HUVECs was quantified. TNF-alpha stimulation of the HUVECs increased H82 attachment from 28.1% +/- 1.6% to 48.8% +/- 1.7% (P < .05). Preincubation of HUVECs with the PKC inhibitors bis-indolylmaleimide (BIN) or calphostin C or the TK inhibitors genistein or herbimycin A (HMA) blocked the TNF-alpha-induced increase in H82 cell attachment. The addition of antibodies to vitronectin (Vn) or beta1-integrin to TNF-alpha-activated HUVECs before the addition of the H82 cells also significantly decreased H82 attachment, whereas the addition of antibodies to E-selectin, P-selectin, vascular cell adhesion molecule (VCAM), intercellular adhesion molecule (ICAM), neural cell adhesion molecule (NCAM), sialyl-Lewis(x), fibronectin (Fn), alpha(v)-integrin, alpha3-integrin, alpha4-integrin, or alpha5-integrin had no effect on SCLC attachment. In summary, the TNF-alpha-mediated increase in SCLC attachment to ECs appears to be mediated by the activation of EC PKC and TK pathways as well as through effects on the function or expression of EC Vn and beta1 integrin.

Adhesion of colorectal carcinoma cells to the endothelium is mediated by cytokines from CEA stimulated Kupffer cells

We hypothesize that a major factor regulating hepatic metastasis is the ability of CEA (carcinoembryonic antigen) producing colorectal carcinomas to activate Kupffer cells. CEA and NCA (nonspecific cross-reacting antigen) bind to an 80 kDa Kupffer cell receptor by the peptide sequence PELPK and stimulate cytokine production. Cytokines induce sinusoidal endothelial cells to express intercellular adhesion molecules and increase adhesion of the tumor cells and retention in the liver. In this study human Kupffer cells were activated in vitro with CEA, NCA, and the peptide PELPK. This resulted in release of IL-1beta, TNF-alpha and IL-6. CEA non-producing MIP-101 colon carcinoma cells labeled with 51Cr were incubated on monolayers of ECV-304 human umbilical vein endothelial cells treated with these Kupffer cell derived cytokines or with comparable recombinant human (rH) cytokines. Specific antibodies to the adhesion molecules ICAM-1, VCAM-1, E-selectin and beta2integrin were used to block their functions. A significant enhancement in the adhesion of colorectal carcinoma cells occurred when endothelial cells were stimulated with a very low concentration of Kupffer-cell derived cytokines. Activated endothelium demonstrated significant up-regulation primarily of ICAM-1. The adhesion was blocked by an antibody to ICAM-1. A combination of Kupffer-cell derived cytokines was more effective than IL-1beta or TNF-alpha alone. IL-6 alone did not influence adhesion under our conditions. Our results suggest a mechanism for CEA in the modulation of colorectal carcinoma adhesion to the hepatic endothelium and its enhancement of metastatic potential.

Lung endothelial dipeptidyl peptidase IV promotes adhesion and metastasis of rat breast cancer cells via tumor cell surface-associated fibronectin

Endothelial cell adhesion molecules are partly responsible for the distinct organ distribution of cancer metastases. Dipeptidyl peptidase IV (DPP IV) expressed on rat lung capillary endothelia is shown here to be an adhesion receptor for rat breast cancer cells and to mediate lung colonization by these tumor cells. Fibronectin (FN) assembled on breast cancer cell surfaces into multiple, randomly dispersed globules from cellular and plasma FN is identified as the principal ligand for DPP IV. Ligand expression correlates quantitatively with the tumor cells' capabilities to bind to DPP IV and to metastasize to the lungs. DPP IV/FN-mediated adhesion and metastasis are blocked when tumor cells are incubated with soluble DPP IV prior to conducting adhesion and lung colony assays. Adhesion is also blocked by anti-DPP IV monoclonal antibody 6A3 and anti-FN antiserum. However, adhesion to immobilized FN is unaffected by soluble plasma FN and, thus, can happen during hematogenous spread of cancer cells at high plasma FN concentrations. The ability of many cancer cells to capture FN molecules on their surface and to augment such deposits by FN self-association during passage in the blood suggests that DPP IV/FN binding may be a relatively common mechanism for lung metastasis.

CD24 mediates rolling of breast carcinoma cells on P-selectin

P-selectin mediates rolling of neutrophils and other leukocytes on activated endothelial cells and platelets through binding to P-selectin glycoprotein ligand-1 (PSGL-1). Certain PSGL-1 negative tumor cell lines can bind P-selectin under static conditions through the GPI-linked surface mucin, CD24, but the physiological significance of this interaction and whether it can occur under flow conditions is not known. Here, we show that CD24+ PSGL-1- KS breast carcinoma cells attach to and roll on recombinant P-selectin under a continuous wall shear stress, although at a lower density and higher velocity than CD24+ PSGL-1+ cells, such as HL-60. Adding excess soluble CD24 or removing CD24 from the cell surface with phosphatidylinositol-phospholipase C (PI-PLC) significantly reduced KS cell rolling on P-selectin. The ability of KS cells to roll on P-selectin was positively correlated with the CD24 expression level. Comparison with three other CD24+ cell lines established that expression of sialyl-Lewis(x) antigen was also necessary for CD24-mediated rolling on P-selectin. CD24 purified from KS cells supported rolling of P-selectin transfectants, but not L-selectin transfectants. Finally, KS cells rolled on vascular endothelium in vivo in a P-selectin-dependent manner. Together our data show that CD24 serves as a ligand for P-selectin under physiological flow conditions. Interaction of tumor cells with P-selectin via CD24 may be an important adhesion pathway in cancer metastasis.

Cloning and characterization of a transforming growth factor beta 1-induced anti-apoptotic adhesion protein TIF2

Transforming growth factor-beta (TGF-beta) antagonizes the cytotoxic function of tumor necrosis factor (TNF). By differential display and library screening, we isolated a murine TIF2 (TGF-beta-induced factor 2) cDNA, encoding a putative 15-kDa membrane adhesion protein, which possesses an RGD sequence at the extracellular region. When TNF-sensitive murine L929 fibroblasts were stably transfected with TIF2 cDNA, these cells significantly resisted TNF killing. In contrast, L929 cells, which stably expressed the TIF2 antisense mRNA, acquired enhanced TNF susceptibility. Calculated EC50 values, i.e., the amount of TNF needed for killing 50% cells, are 10, 55, and 1.5 ng/ml, respectively, for vector control, sense transfectant, and antisense transfectant. TGF-beta 1 rapidly induces TIF2 gene expression (approximately 1 hr), which correlates with time-related acquisition of TNF-resistance in TGF-beta 1-treated L929 cells. Notably, TIF2 gene expression is markedly increased in human breast cancer and lymphoid leukemia cells, compared to normal human cells, suggesting its potential role in cancer development. Together, the anti-apoptotic function of TIF2 is responsible in part for TGF-beta-mediated protection of L929 cells against TNF cytotoxicity.

Expression of the adherens junction protein vinculin in human basal and squamous cell tumors: relationship to invasiveness and metastatic potential

The acquisition of an invasive or metastatic phenotype in malignant neoplasms is often correlated with reduced cellular adhesiveness. We investigated the expression of the adhesion-associated cytoplasmic protein, vinculin, in normal and neoplastic human squamous epithelia, as well as in metastases of squamous cell carcinomas, and correlated the results with invasiveness and metastatic potential. Tissue samples from various tumors were examined, including basal cell carcinomas (BCC), keratoacanthomas, and squamous cell carcinomas (SCC). In addition, lymph node metastases from nine of the SCC were tested in this study. Our results indicate that most BCC, keratoacanthomas, and in situ SCC display strong positive staining for vinculin. The level of immunolabeling for vinculin and its pattern of distribution in the low malignant, nonmetastasizing lesions was similar to those observed in normal squamous epithelia. In contrast, in SCC, which are invasive and possess metastatic potential, as well as in their metastases, vinculin labeling was negative or poor, irrespective of their degree of differentiation. In conclusion, poor vinculin labeling in tumors of squamous epithelial origin examined here appears to be related to the metastatic potential of the tumor. Vinculin immunostaining of primary tumors originating in stratified squamous epithelia may thus be of value in helping to determine the metastatic potential of these neoplasms.

Lu-ECAM-1-mediated adhesion of melanoma cells to endothelium under conditions of flow

Lu-ECAM-1 is a lung-derived, venular endothelial cell adhesion molecule. It promotes the selective adhesion of lung-metastatic B16-F10 melanoma cells to endothelium under static conditions and mediates colonization of the lungs by the same tumor cells. To test whether Lu-ECAM-1 by itself is sufficient to cause vascular arrest of B16-F10 cells, we measured here under conditions of flow tumor cell adhesion to endothelia that express different amounts of Lu-ECAM-1 on their surfaces. At physiological shear stresses, adhesion of B16-F10 melanoma cells to endothelia correlates positively with the amount of Lu-ECAM-1 expression on the endothelial cell surface and inversely with the level of the applied shear stress. Tumor cell trajectories are biphasic; i.e., B16-F10 melanoma cells initially move along the endothelial surface with a velocity similar to the theoretical velocity, then arrest within a fraction of a second. Arrest is permanent for most B16-F10 melanoma cells at all shear stresses tested. Tumor cells never engaged in a rolling motion prior to arrest. Masking of the Lu-ECAM-1 ligand on the surface of B16-F10 melanoma cells with soluble Lu-ECAM-1 impedes arrest of tumor cells on the surface of the test endothelium. Purified Lu-ECAM-1 also mediates B16-F10 arrest, but arrest is mostly transient at shear stresses of 0.59 dynes/cm2 and higher, implying adhesion by single receptor/ligand bonds. Our data suggest that Lu-ECAM-1 plays a critical role in the recognition and initial arrest of murine melanoma cells in lung venules.

Steps in tumor metastasis: new concepts from intravital videomicroscopy

Metastases are responsible for the majority of failures in cancer treatment. Clarifying steps in metastasis and their molecular mechanisms will be important for the development of anti-metastasis therapeutic strategies. Considerable progress has been made in identifying molecules involved in metastasis. However, because of the nature of assays that have been available, conclusions about steps in metastasis and their molecular bases have been drawn primarily from inference. In order to complete the picture of how metastases form, a technique is needed to directly watch the process in vivo as it occurs over time. We have developed an intravital videomicroscopy (IVVM) procedure to make such observations possible. Results from IVVM are providing us with new conceptual understanding of the metastatic process, as well as the nature and timing of the contributions of molecules implicated in metastasis (e.g. adhesion molecules and proteinases). Our findings suggest that early steps in metastasis, including hemodynamic destruction and extravasation, may contribute less to metastatic inefficiency than previously believed. Instead, our results suggest that the control of post-extravasation growth of individual cancer cells is a significant contributor to metastatic inefficiency. Thus, this stage may be an appropriate target for design of novel strategies to prevent metastases.