Expression and immunohistochemical localization of cathepsin L during the progression of human gliomas

Recent studies suggest that cysteine proteinase cathepsin L is involved in the process of tumor invasion and metastasis. We examined cathepsin L activity in brain tumor tissue samples by an enzymatic assay, and cathepsin L protein content by enzyme-linked immunoadsorbent assays and Western blotting to determine whether increased levels of cathepsin L correlate with the progression of human gliomas. Native and acid-activatable cathepsin L activities were highest in glioblastomas followed by anaplastic astrocytomas and were lowest in low-grade gliomas and normal brain tissues. Significantly higher amounts of an M(r) 29,000 cathepsin L were present in glioblastomas and anaplastic astrocytomas than in normal brain tissues and low-grade glioma tissue extracts. Using specific antibodies to cathepsin L, we also studied its cellular distribution by immunohistochemical procedures. Higher diffuse cathepsin L immunoreactivity was found in glioblastomas than in low-grade gliomas and normal brain tissue samples. Finally, the addition of cathepsin L antibody inhibits the invasion of glioblastoma cell lines through Matrigel invasion assay. These results suggest the expression of cathepsin L is dramatically upregulated in malignant gliomas and correlates with the malignant progression of human gliomas in vivo.

Expression and localization of 72 kDa type IV collagenase (MMP-2) in human malignant gliomas in vivo

The 72 kDa type IV collagenase (gelatinase), a matrix metalloproteinase (MMP-2), has been proposed to potentiate the invasion and metastasis of malignant tumors. To determine the potential role of the MMP-2 in human gliomas and normal brain tissue, we examined the relative amounts of protein, mRNA, and distribution. Using gelatin zymography, densitometry, and an enzyme-linked immunosorbent assay for the quantitative determination of the MMP-2, we found that the enzyme's activity was significantly elevated in malignant astrocytomas, especially in glioblastoma multiforme, compared to low-grade glioma and normal brain tissues. As determined by Northern blot analysis, the amount of MMP-2 mRNA transcript was higher in anaplastic astrocytomas and glioblastoma multiforme tumors than in normal brain tissues or low-grade gliomas, a finding that was consistent with the amounts of MMP-2 protein detected in these tissues. Immunohistochemical studies demonstrated that MMP-2 was localized in tumor cells and vasculature cells of malignant astrocytomas. Staining intensity was clearly lower in low-grade astrocytomas, and immunoreactivity was very low or undetectable in normal brain astrocytes. The results suggest that expression of the MMP-2 is dramatically upregulated in malignant gliomas, correlating with the malignant progression of human gliomas in vivo.

Expression and localization of 92 kDa type IV collagenase/gelatinase B (MMP-9) in human gliomas

Matrix metalloproteinases play an important regulatory role in tissue morphogenesis, cell differentiation and motility, and tumor cell invasiveness. We have recently demonstrated elevated activity of the 92 kDa type IV collagenase (MMP-9) in human glioblastoma and in the present study examine the relative amounts of MMP-9 protein and mRNA in human gliomas and as well as the distribution of MMP-9 in human glioma tumors in vivo. Using an enzyme-linked immunosorbent assay for the quantitative determination of MMP-9 protein, we found that levels were significantly higher in malignant astrocytomas, especially in glioblastoma multiforme, than in normal brain tissues and low-grade gliomas. In addition, the amount of MMP-9 mRNA, as determined by northern blot analysis was higher in anaplastic astrocytomas and glioblastoma multiforme than in normal brain tissue and low-grade gliomas. Immunocytochemical staining for MMP-9 showed strong cytoplasmic immunoreactivity in the tumor cells and the proliferating endothelial cells of glioblastoma multiforme and anaplastic astrocytomas. The staining intensity was lowe in low-grade astrocytomas, and was undetectable or very low in normal brain astrocytes. The results indicate that expression of MMP-9 is dramatically upregulated in highly malignant gliomas and correlates with the highly malignant progression of human gliomas in vivo, and support a role for the MMP-9 in facilitating the invasiveness seen in malignant gliomas in vivo.

Trophic factors and central nervous system metastasis

To metastasize to the central nervous system (CNS) malignant cells must attach to brain microvessel endothelial cells, respond to brain endothelial cell-derived motility factors, respond to CNS-derived invasion factors and invade the blood-brain barrier (BBB), and finally, respond to CNS survival and growth factors. Trophic factors such as the neurotrophins play an important role in tumor cell invasion into the CNS and in the survival of small numbers of malignant cells under stress conditions. Trophic factors promote BBB invasion by enhancing the production of basement membrane-degrading enzymes in neurotrophin-responsive cells. The expression of certain neurotrophin receptors on brain-metastasic neuroendocrine cells occurs in relation to their invasive and survival properties. For example, CNS-metastatic melanoma cells respond to particular neurotrophins (nerve growth factor, neurotrophin-2) that can be secreted by normal cells within the CNS. In addition, a paracrine form of transferrin is important in CNS metastasis, and brain-metastatic cells respond to low levels of transferrin and express high levels of transferrin receptors. CNS-metastatic tumor cells can also produce autocrine factors and inhibitors that influence their growth, invasion and survival in the brain. Synthesis of paracrine factors and cytokines may influence the production of trophic factors by normal brain cells adjacent to tumor cells. Moreover, we found increased amounts of neurotrophins in brain tissue at the invasion front of human melanoma tumors in CNS biopsies. Thus the ability to form metastatic colonies in the CNS is dependent on tumor cell responses to trophic factors as well as autocrine and paracrine growth factors and probably other underdescribed factors.

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.

Expression of 72 kDa and 92 kDa type IV collagenases from human giant-cell tumor of bone

Basement membrane forms widespread barriers to tumor invasion. It has been shown that tumor-secreted, basement membrane-degrading enzymes, namely metalloproteinases (MMPs) play an important role in tumor invasion and metastasis. In this study, we determined the enzymatic activity, content, and mRNA of both the 72 kDa (MMP-2) and 92 kDa (MMP-9) MMPs in primary cultures of human giant-cell tumor of bone (GCT) in vitro and in tissue extracts (in vivo). Gelatin zymography showed the presence of lytic bands at M(r) 121,000, 92,000, and 72,000, and these enzymatic activities were inhibited by EDTA, an inhibitor of MMPs. Western blots with antibodies specific for MMP-2 and MMP-9 confirmed the presence of MMP-2 and MMP-9 both in vitro and in vivo, but GCT cells at late passage showed only MMP-2. Northern blots using labeled cDNA probes specific for these molecules revealed the presence of 3.1 kb transcript for MMP-2 and a 2.9 kb transcript for MMP-9. Using specific antibodies to 72 kDa and 92 kDa type IV collagenases, we studied their cellular distribution by immunohistochemical means. Stronger immunoreactivity was found for 92 kDa type IV collagenase than 72 kDa type IV collagenase in the giant cells. It appears, therefore, that MMP-9 may play an important role in the malignant behavior of GCTs and suggests a potential therapeutic role for protease inhibitors in attempting to minimize the invasive behavior of GCTs.

Purification and identification of mouse lung microvessel endothelial cell-derived chemoattractant for lung-metastasizing murine RAW117 large-cell lymphoma cells: identification as mouse monocyte chemotactic protein 1

We reported recently that medium conditioned with mouse lung microvessel endothelial cells possessed chemotactic activity for a highly lung-metastatic variant (L17) of the RAW117 murine large-cell lymphoma cell line but not for the poorly metastatic parental cells (P) or a liver-metastasizing variant (H10). The chemotactic factor was purified to homogeneity by a five-step procedure involving hydrophobic interaction, Cibacron blue F3GA affinity, metal affinity, anion exchange, and reversed phase chromatography, followed by preparative gel electrophoresis. The purified material appeared as a single broad band when analyzed by SDS-PAGE, with an average molecular weight of 26,000. The factor was cleaved by cyanogen bromide treatment, and a partial amino acid sequence of one of the cleaved polypeptides proved identical to mouse monocyte chemotactic protein 1 (mMCP-1/JE). The amino acid composition of the factor also indicated similarity to mMCP-1/JE. Separately purified mMCP-1/JE significantly stimulated the chemotactic migration of RAW117 cells (L17 >> H10, P). When recombinant human monocyte chemotactic protein 1 was compared to the purified endothelial cell chemotactic factor as a chemoattractant, similar migratory responses were observed in the RAW117 sublines. The chemotactic activity for L17 cells was significantly reduced from lung microvessel endothelial cell-conditioned medium after treatment with anti-mouse MCP-1 antibody. In contrast, the migration-stimulating activity of liver sinusoidal endothelial cell-conditioned medium to H10 cells was not affected by anti-mouse MCP-1. A major function of mMCP-1/JE is to recruit monocytes to inflammatory sites, and our results suggest that mMCP-1/JE also facilitates lymphoma lung invasion and metastasis.

Human peri-tumoral and lung fibroblasts produce paracrine motility factors for recently established human sarcoma cell strains

Paracrine motogenic cytokines secreted by normal cells can stimulate metastatic cell invasion. For example, human fibroblasts secrete hepatocyte growth factor/scatter factor (HGF/SF), which stimulates paracrine migration of epithelial and certain carcinoma cells, and migration-stimulating factor (MSF), which stimulates autocrine migration of fibroblasts from certain breast carcinomas. We found that human peri-tumoral and lung fibroblasts secrete motility-stimulating activity for several recently established human sarcoma cell strains. Motility of lung metastasis-derived SYN-I sarcoma cells was preferentially stimulated by human lung and peri-tumoral fibroblast motility-stimulating factors (FMSFs). FMSFs were non-dialyzable, susceptible to trypsin and sensitive to dithiothreitol. Cycloheximide inhibited accumulation of FMSF activity in conditioned medium; however, addition of cycloheximide to the migration assay did not significantly affect motility-stimulating activity. Purified HGF/SF, rabbit anti-hHGF and RT-PCR analysis of peri-tumoral and lung fibroblast HGF/SF mRNA expression indicated that FMSF activity was unrelated to HGF/SF. Partial purification of FMSF by gel exclusion chromatography revealed several peaks of activity, suggesting multiple FMSF molecules or complexes. Since human soft tissue sarcomas have a distinctive hematogenous metastatic pattern (predominantly lung), FMSF may play a role in this process independent of HGF/SF.

Interferon-alpha directly inhibits DNA polymerase activity in isolated chromatin nucleoprotein complexes: correlation with IFN-alpha treatment outcome in patients with chronic myelogenous leukemia

We have developed an in vitro assay to assess and predict the potential efficacy of in vivo interferon-alpha (IFN-alpha) treatment (5 x 10(6) units/m2 per day) for patients with chronic myelogenous leukemia (CML). Although determining the numbers and affinities of IFN-alpha receptors on CML cells has been developed as a method for predicting treatment response to IFN-alpha, it fails to predict response in CML. Previously, we and others observed that mitogens, toxins and lectins that bind to cell-surface receptors are endocytosed, escaping endosomes in order to act directly on cellular targets. Therefore, we tested the ability of low concentrations of IFN-alpha (5-10 units) to act directly on DNA polymerase (Pol) in purified chromatin nucleoprotein complexes (NPC). NPC were prepared by a methodology that uses direct treatment of leukocyte nuclei with MspI to generate six NPC-containing fractions (S1, M1, S2, M2, 0.1K and R). We found three general categories of in vitro DNA synthesis response for the six different NPC fractions isolated from the white blood cells of patients with CML (n = 19) before their treatment with IFN-alpha. IFN-alpha induced either stimulation, inhibition or had no apparent effect on Pol activity in the six different NPC fractions in a blind assay. In most of the NPC fractions isolated from the leukocytes of patients with progressive CML and in those from CML patients who failed to show a clinical response to IFN-alpha, this cytokine stimulated or had no effect on Pol activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of the complete sequence of the novel metastasis-associated candidate gene, mta1, differentially expressed in mammary adenocarcinoma and breast cancer cell lines

To understand the genes and gene products involved in breast cancer invasion and metastasis, we previously isolated ten differentially expressed genes by differential cDNA library screening techniques, using the 13762NF rat mammary adenocarcinoma metastatic system. In this study, we further analysed a novel candidate metastasis-associated gene, mta1, previously designated clone 10.14. Northern blotting analyses showed that the steady-state mRNA expression level of mta1 was fourfold higher in a highly metastatic line (MTLn3) than in a nonmetastatic line (MTC.4). The mta1 gene was expressed at low levels in various normal rat organs, except testis, where it was expressed in high amounts. The mRNA expression levels of the human homologue of this gene were also examined in two human breast cancer metastatic systems; the ratios of mRNA were estimated to be MCF-7 (nonmetastatic):MCF7/LCC1 (invasive):MCF7/LCC2 (metastatic) = 1:2:4 and MDA-MB-468 (nonmetastatic):MDA231 (metastatic) = 1:4. Thus, the expression of this gene directly correlated with metastatic potential in two human systems, as well as in the rat metastatic system. Clone 10.14 was used to isolate a full-length cDNA clone for mta1, yielding the clone p10.14-C4.5, which was sequenced and analysed. Clone p10.14-C4.5 was 2756-bp long and contained a single open reading frame that could encode a protein of 703 amino acid (aa) residues. The aa sequence of mta1 was found to be novel by database homology search and contained possible phosphorylation sites for tyrosine kinase, protein kinase C and casein kinase II. A Pro-rich stretch was found at the C-terminal end that completely matched the consensus sequence for the SH3-binding motif.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of trophic factors and autocrine/paracrine growth factors in brain metastasis

The brain is a unique microenvironment enclosed by the skull, lacking lymphatic drainage and maintaining a highly regulated vascular transport barrier. To metastasize to the brain malignant tumor cells must attach to microvessel endothelial cells, respond to brain-derived invasion factors, invade the blood-brain barrier and respond to survival and growth factors. Trophic factors are important in brain invasion because they can act to stimulate this process. In responsive malignant cells trophic factors such as neurotrophins can promote invasion by enhancing the production of basement membrane-degradative enzymes (such as type IV collagenase/gelatinase and heparanase) capable of locally destroying the basement membrane and the blood-brain barrier. We examined human melanoma cell lines that exhibit varying abilities to form brain metastases. These melanoma lines express low-affinity neurotrophin receptor p75NTR in relation to their brain-metastatic potentials but the variants do not express trkA, the gene encoding a high affinity nerve growth factor (NGF) tyrosine kinase receptor p140trkA. Melanoma cells metastatic to brain also respond to paracrine factors made by brain cells. We have found that a paracrine form of transferrin is important in brain metastasis, and brain-metastatic cells respond to low levels of transferrin and express high levels of transferrin receptors. Brain-metastatic tumor cells can also produce autocrine factors and inhibitors that influence their growth, invasion and survival in the brain. We found that brain-metastatic melanoma cells synthesize transcripts for the following autocrine growth factors: TGF beta, bFGF, TGF alpha and IL-1 beta. Synthesis of these factors may influence the production of neurotrophins by adjacent brain cells, such as oligodendrocytes and astrocytes. Increased amounts of NGF were found in tumor-adjacent tissues at the invasion front of human melanoma tumors in brain biopsies. Trophic factors, autocrine growth factors, paracrine growth factors and other factors may determine whether metastatic cells can successfully invade, colonize and grow in the central nervous system.

Expression of tissue inhibitors of metalloproteinases: negative regulators of human glioblastoma invasion in vivo

Tissue inhibitors of metalloproteinases (TIMPs) are negative regulators of matrix metalloproteinases (MMPs) which degrade major components of the extracellular matrix. The aberrant expression of TIMPs is believed to represent an important modulating factor in the invasive capacity of human tumors. In the present study we analyzed the expression of TIMPs in human brain tumor tissue samples by an enzyme-linked immunosorbent assay (ELISA) and by Northern blotting analysis. Quantitation of TIMP-1 and TIMP-2 by ELISA demonstrated low levels of TIMP-1 and TIMP-2 proteins in glioblastomas, and moderate levels in anaplastic astrocytomas compared with normal brain tissues low-grade gliomas and metastatic tumors (renal and breast carcinomas and melanomas). Northern blot analysis of TIMP-1 transcripts demonstrated higher expression in meningioma, normal brain tissues and other metastatic tumors than in anaplastic astrocytoma and glioblastoma. Two distinct transcripts of 1.0 and 3.5 kb were observed for TIMP-2 mRNA in normal brain tissue and in tumor extracts. In addition, TIMP-2 mRNA expression was lower in glioblastoma and anaplastic astrocytoma than in meningioma, normal brain tissues and metastatic tumors. These findings suggest that down-regulation of both TIMP-1 and TIMP-2 contributes significantly to the invasive potential of human glioblastoma multiforme and anaplastic astrocytomas.

Overexpression and localization of cathepsin B during the progression of human gliomas

Degradation of the extracellular matrix is a prerequisite for acquisition of the invasive phenotype. Several proteinases released by invading tumor cells appear to participate in the focal degradation of extracellular matrix proteins. Using an enzyme-linked immunosorbent assay, enzymatic assays, Western and Northern blotting techniques, we determined whether increased levels of the cysteine protease cathepsin B correlated with the progression and invasion of human gliomas. The amount of cathepsin B activity and protein content were highest in glioblastomas, lower in anaplastic astrocytomas and lowest in normal brain tissue and low-grade gliomas. There were significantly higher amounts of M(r) 25,000 and 26,000 bands in glioblastoma and anaplastic astrocytoma than in normal brain and low-grade glioma tissue extracts as determined by Western blotting with anti-cathepsin antibodies. In addition, cathepsin B transcripts were overexpressed in anaplastic astrocytoma (about two- to three-fold), in glioblastoma (about eight- to 10-fold), compared with normal brain tissue and low-grade glioma. Immunohistochemical staining for cathepsin B showed intense immunoreactivity in tumor and endothelial cells of glioblastomas and anaplastic astrocytomas but only weak immunoreactivity in low-grade glioma and normal brain tissues. Therefore, we conclude that cathepsin B expression is greatest in highly malignant astrocytomas, especially in glioblastomas, and is correlated with the malignant progression of astrocytomas.

Effects of mast cell-macrophage interactions on the production of collagenolytic enzymes by metastatic tumor cells and tumor-derived and stromal fibroblasts

Histological examination of the metastatic rat mammary adenocarcinoma line MTLn3 showed that macrophages and mast cells were frequently localized at the tumor periphery in the stromal tissues adjacent to the zones of tumor invasion. The interactions of these host cells with tumor cells and tumor-associated fibroblasts could be important in stimulating the production of extracellular matrix-degrading enzymes that facilitate tumor invasion and metastatic spread. Therefore, we examined the effects of isolated, activated macrophages and mast cells on the secretion of collagenolytic activities by normal fibroblasts, metastatic mammary adenocarcinoma cells and tumor-associated fibroblasts. Medium from activated macrophages or degranulated mast cells stimulated significant increases in production of collagenolytic activities by normal and tumor-associated fibroblasts and MTLn3 tumor cells. Medium from activated macrophages that had been pretreated with medium from degranulated mast cells, however, were less stimulatory to fibroblasts and tumor cell production of collagenolytic activities than medium from degranulated mast cells alone. We also examined the effects of two cytokines, interleukin-1 alpha and tumor necrosis factor-alpha on activated macrophage- and degranulated mast cell-stimulation of fibroblast and tumor cell collagenolytic activities. The two cytokines alone or in combination stimulated increased production of collagenolytic activities by fibroblasts and tumor cells. Addition of the cytokines to degranulated mast cell products resulted in secretion of higher collagenolytic enzyme activities by normal fibroblasts (but not by tumor-derived fibroblasts or tumor cells) than with degranulated mast cell product-treatment of either target cell alone. Cytokines used in combination with macrophage-conditioned medium were less effective in stimulating fibroblast and tumor cell collagenase activities than cytokines alone. Thus normal infiltrating host cells such as macrophages and mast cells can have profound effects on the production of degradative enzymes by tumor cells and tumor-associated stromal fibroblasts.

Responses to paracrine chemotactic and autocrine chemokinetic factors and lung metastatic capability of mouse RAW117 large-cell lymphoma cells

We studied the cell migration properties of poorly metastatic murine RAW117-P large-cell lymphoma cells, a highly lung metastatic subline (RAW117-L17) and a highly liver metastatic subline (RAW117-H10). L17 cells responded to the serum-free conditioned medium (CM) of mouse lung microvessel endothelial cells (MLEs) and mouse lung fibroblasts (MLFs). The migration of L17 cells was also stimulated by its own CM and, to a lesser extent, by the CM of parental (P) and H10 cells. RAW117-P and -H10 cells responded poorly to all of the CM tested. Chequerboard analyses revealed that the migration-stimulating activities of MLE CM and MLF CM were mainly chemotactic, whereas those of L17, P and H10 CM were chemokinetic. We also analysed the effect of MLE CM and MLF CM in combination with L17, P or H10 CM on cell migration of the RAW117 sublines. The migration of lung metastatic subline L17 cells to MLE or MLF CM was enhanced when L17 CM was also present. This enhancement effect was not seen when P or H10 cells were exposed to MLE or MLF CM plus the CM from P or H10 cells respectively. Thus we found that the chemotactic response of lung metastatic large-cell lymphoma cells to paracrine migration stimulation factors from lung endothelial cells and fibroblasts in concert with an autocrine chemokinetic factor may be involved in RAW117 lung-specific invasion and metastasis.

Extracellular annexin VI expression is associated with divalent cation-dependent endothelial cell adhesion of metastatic RAW117 large-cell lymphoma cells

We previously found that cell surface molecules of approximately 70, approximately 35, approximately 32, approximately 22, and approximately 14 kDa from liver-metastatic murine RAW117 large-cell lymphoma cells bound to target liver microvessel endothelial cells. Isolation and sequencing of the approximately 35-kDa component revealed it to be annexin II, a Ca(2+)-binding molecule involved in cytoskeletal and membrane interactions. Annexin II antibodies inhibited the adhesion of RAW117 tumor cells to live or fixed liver endothelial cells, and purified tumor cell surface fractions containing the approximately 35-kDa component inhibited partially RAW117 cell-endothelial cell adhesion, suggesting a role for annexins in tumor cell-endothelial cell adhesion. In the present study we identified the 70-kDa cell surface component that binds to hepatic sinusoidal endothelial cells in a Ca(2+)-dependent manner as annexin VI. Cytofluorographic analysis indicated that annexin VI was expressed on the cell surface in slightly higher amounts on highly metastatic RAW117 cells, and it was not removable by EDTA treatment. Anti-annexin VI antibodies inhibited the adhesion of RAW117 cells to fixed or unfixed murine hepatic sinusoidal endothelial cells by approximately 40%, indicating a role for annexin VI in mediating a portion of the Ca(2+)-dependent RAW117 cell adhesion to target liver microvessel endothelial cells.

Expression of galectins on microvessel endothelial cells and their involvement in tumour cell adhesion

Lactoside-binding lectins (galectins) with molecular weights of about 14.5 kDa (galectin-1) and 29-35 kDa (galectin-3) bind preferentially to polylactosaminoglycan-containing glycoconjugates and have been found on the surface of tumour cells and implicated in cell-cell and cell-extracellular matrix adhesion and metastasis. We have demonstrated by immunoblotting that both galectin-1 and galectin-3 are present in extracts of endothelial cells cultured from bovine aorta, rat lung, mouse lung and mouse brain microvessels, whereas mouse hepatic sinusoidal endothelial cells expressed primarily galectin-1. These galectins were also localized by indirect immunofluorescent labelling on the surface of the different endothelial cells in culture and by immunohistochemical staining in human tissues in vivo. Anti-galectin-1 antibodies inhibited the adhesion of liver-preferring murine RAW117-H10 large-cell lymphoma cells to hepatic sinusoidal endothelial cells or lung microvessel endothelial cells in vitro. The data indicate that galectin-1 is expressed on the extracellular surface of endothelial cells and can mediate in part the adhesion of RAW117-H10 cells to liver microvessel endothelial cells.

A novel candidate metastasis-associated gene, mta1, differentially expressed in highly metastatic mammary adenocarcinoma cell lines. cDNA cloning, expression, and protein analyses

To understand the genes involved in breast cancer invasion and metastasis, we analyzed a novel candidate metastasis-associated gene, mta1, which was isolated by differential cDNA library screening using the 13762NF rat mammary adenocarcinoma metastatic system. Northern blot analyses showed that the mRNA expression level of the mta1 gene was 4-fold higher in the highly metastatic cell line MTLn3 than in the nonmetastatic cell line MTC.4. The mta1 gene was expressed in various normal rat organs, especially in the testis, suggesting its essential normal function. The mRNA expression levels of the human homologue of this gene also correlated with the metastatic potential in two human breast cancer metastatic systems. The full-length mta1 cDNA sequence contained an open reading frame encoding a protein of 703 amino acid residues, and sequence analysis by data base homology search indicated that mta1 is a novel gene. The Mta1 protein contained several possible phosphorylation sites, and a proline-rich amino acid stretch at the carboxyl-terminal end completely matched the consensus sequence for the src homology 3 domain-binding motif. Using antibodies raised against glutathione S-transferase-Mta1 fusion protein or a synthetic oligopeptide, Western blots showed that the molecular mass of the Mta1 protein was approximately 80 kDa, and the levels of the Mta1 protein also correlated with the metastatic potential, results similar to those obtained from the Northern analyses. Thus, the novel gene mta1 may encode a molecule that is functional in normal cells as well as in breast cancer invasion and metastasis.

Expression and localization of urokinase-type plasminogen activator receptor in human gliomas

Urokinase-type plasminogen activator receptors (uPARs) play an important role in tumor invasion by localizing degradative enzymes at the invasive zone. In the present study, we examined the presence and distribution of uPARs in human gliomas in vivo. The amounts of uPARs were measured by radioreceptor assays and Northern blotting and were significantly higher in anaplastic astrocytomas and glioblastomas than they were in normal brain tissues and low-grade gliomas. In situ hybridization was performed to investigate the cellular source of uPAR mRNA in various types of astrocytomas and normal brain tissues. uPAR mRNA was localized in astrocytoma cells and endothelial cells within tumor tissue, especially near sites of vascular proliferation and at the leading edges of tumors. uPAR mRNA was also expressed in tumor cells near necrotic areas. Expression was barely detectable in low-grade astrocytomas and normal brain tissues. These results suggest that expression of uPAR in the invading astrocytoma cells may play a significant role in the invasive behaviors of glioblastomas.