Butanol-extractable and detergent-solubilized cell surface components from murine large cell lymphoma cells associated with adhesion to organ microvessel endothelial cells

Cell surface sphingomyelin: key role in cancer initiation, progression, and immune evasion

Cell surface biochemical changes, notably excessive increase in outer leaflet sphingomyelin (SM) content, are important in cancer initiation, growth, and immune evasion. Innumerable reports describe methods to initiate, promote, or enhance immunotherapy of clinically detected cancer, notwithstanding the challenges, if not impossibility, of identification of tumor-specific, or associated antigens, the lack of tumor cell surface membrane expression of major histocompatibility complex (MHC) class I alpha and β2 microglobulin chains, and lack of expression or accessibility of Fas and other natural killer cell immune checkpoint molecules. Conversely, SM synthesis and hydrolysis are increasingly implicated in initiation of carcinogenesis and promotion of metastasis. Surface membrane SM readily forms inter- and intra- molecular hydrogen bond network, which excessive tightness would impair cell-cell contact inhibition, inter- and intra-cellular signals, metabolic pathways, and susceptibility to host immune cells and mediators. The present review aims at clarifying the tumor immune escape mechanisms, which face common immunotherapeutic approaches, and attracting attention to an entirely different, neglected, key aspect of tumorigenesis associated with biochemical changes in the cell surface that lead to failure of contact inhibition, an instrumental tumorigenesis mechanism. Additionally, the review aims to provide evidence for surface membrane SM levels and roles in cells resistance to death, failure to respond to growth suppressor signals, and immune escape, and to suggest possible novel approaches to cancer control and cure.

New insights into the tPA-annexin A2 interaction. Is annexin A2 CYS8 the sole requirement for this association?

Annexin A2 has been described as an important receptor for tissue-type plasminogen activator in endothelium and other cell types. Interaction between tissue-type plasminogen activator and its cellular receptor is critical for many of the functions of this protease. The annexin A2 motif that mediates tissue plasminogen activator interaction has been assigned to the hexapeptide LCKLSL in the amino-terminal domain of the protein, and it has been proposed that Cys(8) of this sequence is essential for tPA binding. In an attempt to identify other amino acids critical for tPA-annexin A2 interaction, we have analyzed a set of peptides containing several modifications of the original hexapeptide, including glycine scans, alanine scans, d-amino acid scans, conservative mutations, cysteine blocking, and enantiomer and retroenantiomer sequences. Using a non-radioactive competitive binding assay, we have found that all cysteine-containing peptides, independently of their sequence, compete the interaction between tPA and annexin A2. Cysteine-containing peptides also inhibit tPA binding to the surface of cultured human umbilical vein endothelial cells (HUVEC). Mass spectrometry demonstrates that the peptides bind through a disulfide bond to a cysteine residue of annexin A2, the same mechanism that has been suggested for the inhibition mediated by homocysteine. These data call for a revision of the role of the LCKLSL sequence as the sole annexin A2 structural region required to bind tPA and indicate that further studies are necessary to better define the annexin A2-tPA interaction.

Annexin II: a mediator of the plasmin/plasminogen activator system

The annexins constitute a family of calcium-dependent membrane binding proteins. Recently, annexin II has been shown to accelerate the activation of the clot-dissolving protease plasmin by complexing with the plasmin precursor plasminogen and with tissue plasminogen activator. Binding of plasminogen to annexin II is inhibited by the atherogenic lipoprotein, lipoprotein(a), while binding of tissue plasminogen activator to annexin II is blocked by the thiol amino acid homocysteine. Formation of the plasminogen/tissue plasminogen activator/annexin II complex may represent a key regulatory mechanism in fibrinolytic surveillance.

Characterization of the heparin binding properties of annexin II tetramer

In this report, we have characterized the interaction of heparin with the Ca2+- and phospholipid-binding protein annexin II tetramer (AIIt). Analysis of the circular dichroism spectra demonstrated that the Ca2+-dependent binding of AIIt to heparin caused a large decrease in the alpha-helical content of AIIt from approximately 44 to 31%, a small decrease in the beta-sheet content from approximately 27 to 24%, and an increase in the unordered structure from 20 to 29%. The binding of heparin also decreased the Ca2+ concentration required for a half-maximal conformational change in AIIt from 360 to 84 microM. AIIt bound to heparin with an apparent Kd of 32 +/- 6 nM (mean +/- S.D., n = 3) and a stoichiometry of 11 +/- 0.9 mol of AIIt/mol of heparin (mean +/- S.D., n = 3). The binding of heparin to AIIt was specific as other sulfated polysaccharides did not elicit a conformational change in AIIt. A region of the p36 subunit of AIIt (Phe306-Ser313) was found to contain a Cardin-Weintraub consensus sequence for glycosaminoglycan recognition. A peptide to this region underwent a conformational change upon heparin binding. Other annexins contained the Cardin-Weintraub consensus sequence, but did not undergo a substantial conformational change upon heparin binding.

Annexin II tetramer: structure and function

The annexins are a family of proteins that bind acidic phospholipids in the presence of Ca2+. The interaction of these proteins with biological membranes has led to the suggestion that these proteins may play a role in membrane trafficking events such as exocytosis, endocytosis and cell-cell adhesion. One member of the annexin family, annexin II, has been shown to exist as a monomer, heterodimer or heterotetramer. The ability of annexin II tetramer to bridge secretory granules to plasma membrane has suggested that this protein may play a role in Ca(2+)-dependent exocytosis. Annexin II tetramer has also been demonstrated on the extracellular face of some metastatic cells where it mediates the binding of certain metastatic cells to normal cells. Annexin II tetramer is a major cellular substrate of protein kinase C and pp60src. Phosphorylation of annexin II tetramer is a negative modulator of protein function.

In vitro structural and functional relationships between preosteoclastic and bone endothelial cells: a juxtacrine model for migration and adhesion of osteoclast precursors

The role of vascularization in the process of bone resorption has not been clarified. The interactions between vascular endothelium and osteoclast progenitors were analyzed using clonal cell lines of bone-derived endothelial and preosteoclastic cells. Insulin-like growth factor I is a major chemotactic stimulator of preosteoclastic cell migration mediated by bone endothelial cells. Osteoclast precursors rapidly adhered to bone endothelial monolayers. This phenomenon appeared to be cell-specific and mediated through the binding of vitronectin and fibronectin receptors to fibronectin. In addition, direct contact with bone endothelial cells induced osteoclast progenitors to differentiate into more mature elements, with the tendency to cluster together to form large multinucleated cells. These findings demonstrated specific in vitro interactions between bone endothelial cells and osteoclast progenitors, offering a new model for understanding the molecular mechanisms which direct the processes of osteoclast recruitment and ontogeny.

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.

Selection for enhanced adhesion to microvessel endothelial cells or resistance to interferon-gamma modulates the metastatic potential of murine RAW117 large-cell lymphoma cells

Poorly liver metastatic large-cell lymphoma RAW117-P cells were sequentially selected in vitro for increased adhesion to murine hepatic sinusoidal endothelial cells. After three or four sequential selections, the selected sublines showed increased rates of adhesion to target hepatic microvessel endothelial cells and increased formation of experimental metastases in the liver. However, the endothelial cell adhesion-selected RAW117 sublines were generally unstable and gradually lost their enhanced adhesive and metastatic properties during passage in culture. Highly metastatic, liver-selected RAW117-H10 large-cell lymphoma cells were more resistant to the cytostatic effects of interferon-gamma (IFN-gamma) than poorly metastatic unselected parental RAW117-P cells. When tested for their sensitivity to IFN-gamma, the endothelial cell adhesion variants were significantly more resistant than the unselected RAW117-P cells, but after a 72-h treatment with IFN-gamma, the in vitro-selected cells lost their enhanced endothelial cell adhesion characteristics, their potential to colonize the liver, and their ability to grow when injected at subcutaneous or intramuscular sites. In contrast, the metastatic potential of similarly treated RAW117-P cells was unaffected by IFN-gamma during a 72-h treatment. Sequential selection of RAW117-P cells for increased resistance to IFN-gamma in vitro resulted in variant lines that were refractory to the growth-inhibiting effects of IFN-gamma, and these IFN-gamma-selected variants were also less adhesive to liver microvessel endothelial cells. The IFN-gamma-selected variants also lost their experimental metastatic potentials completely and their tumorigenicities at sites of subcutaneous or intramuscular injection. Cytofluorographic analysis indicated reduced cell surface expression of H-2Kd antigen and fibronectin receptor on the selected variant cells but no change in cell surface mu heavy chain immunoglobulin. The unselected and selected RAW117 lines had similar sensitivities to natural killer (NK) cell-mediated cytolysis, indicating that the in vivo differences were probably not due to differences in NK cell-mediated cytolysis. The results suggest that selection for adhesion to organ microvessel endothelial cells or sequential exposure to certain cytokines can affect the adhesive, growth and metastatic properties of RAW117 cells without modifying their responses to NK cells.

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

Using fixed microvessel endothelial cell monolayers the molecules involved in the adhesion of liver-preferring murine RAW117 large cell lymphoma cells to murine liver-derived microvessel endothelial cells were identified by affinity isolation. Detergent lysates obtained from poorly (P) or highly (H10) liver-metastatic cells inhibited RAW117-H10 cell adhesion to hepatic sinusoidal endothelial (HSE) cell monolayers. Allowing detergent lysates of cell surface-labeled RAW117 cells to bind to fixed HSE cell monolayers and eluting the bound components indicated that several tumor cell surface molecules (approximately 70, approximately 35, approximately 32, approximately 22, and approximately 14 kDa) might be involved in RAW117 cell-HSE cell adhesion. The approximately 35 kDa component was cation dependent in its binding to target HSE cells. Increasing detergent concentration had no effect on binding of the approximately 35 kDa component to HSE cell monolayers, whereas treatment with 0.5 M NaCl resulted in its selective elution from HSE cells. Incubation of the HSE cell monolayers with detergent lysates from cell surface-labeled RAW117-H10 cells resulted in selective depletion of the approximately 35 kDa component, suggesting that the binding is saturable. This divalent cation-dependent molecule is one of the major tumor cell surface components bound by several types of endothelial cells and murine hepatocytes, whereas there was poor binding of this component to unfixed or fixed human red blood cells. The purified, partially (approximately 40%) sequenced molecule had amino acid sequence identity with murine but not bovine annexin II, indicating that it was not bound from the bovine serum used to grow RAW117 cells. Using antibodies specific for annexin II flow cytometry indicated equivalent amounts of annexin II are expressed on RAW117 cell surfaces in the absence or presence of excess EDTA, whereas annexin I was only found in low amounts on the surfaces of RAW117 cells. Annexin II antibodies inhibited by approximately 40-50% the adhesion of RAW117 tumor cells to live or fixed endothelial cells, and purified tumor cell surface fractions containing the approximately 35 kDa component partially inhibited (approximately 35%) RAW117 cell-HSE cell adhesion. The data indicate that annexin II is expressed on the extracellular surface of RAW117 cells, and cell surface-annexin II mediates a portion of the Ca(2+)-dependent RAW117 cell adhesion to liver microvessel endothelial cells.

Adhesion molecules and their role in cancer metastasis

This article describes various adhesion molecules and reviews evidence to support a mechanistic role for adhesion molecules in the process of cancer metastasis. A variety of evidence supports the involvement of specific adhesion molecules in metastasis. 1. For example, some cancer cells metastasize to specific organs, irrespective of the first organ encountered by the circulating cancer cells. This ability to colonize a specific organ has been correlated with the preferential adhesion of the cancer cells to endothelial cells derived from the target organ. This suggests that cancer cell/endothelial cell adhesion is involved in cancer cell metastasis and that adhesion molecules are expressed on the endothelium in an organ-specific manner. 2. Further, inclusion of peptides that inhibit cell adhesion, such as the YIGSR- or RGD-containing peptides, is capable of inhibiting experimental metastasis. 3. Metastasis can be enhanced by acute or chronic inflammation of target vessels, or by treatment of animals with inflammatory cytokines, such as interleukin-1. In vitro, cancer cell/endothelial cell adhesion can be enhanced by pretreating the endothelial cell monolayer with cytokines, such as interleukin-1 or tumor necrosis factor-alpha. This suggests that, in addition to organ-specific adhesion molecules, a population of inducible endothelial adhesion molecules is involved and is relevant to metastasis. 4. Further support for this model is found in the comparison to leukocyte/endothelial adhesion during leukocyte trafficking. Convincing evidence exists, both in vivo and in vitro, to demonstrate an absolute requirement for leukocyte/endothelial adhesion before leukocyte extravasation can occur. The relevance of this comparison to metastasis is reinforced by the observation that some of the adhesion molecules involved in leukocyte/endothelial adhesion are also implicated in cancer cell/endothelial adhesion. The involvement of adhesion molecules suggests a potential therapy for metastasis based on interrupting adhesive interactions that would augment other treatments for primary tumors.

Modulating the metastatic potential of murine RAW117 large-cell lymphoma cells by selection for resistance to interferon-gamma

Highly metastatic, in vivo-selected cells of RAW117-H10 large-cell lymphoma have been shown to be more resistant than poorly metastatic parental RAW117-P cells to the cytolytic and cytostatic activities of activated macrophages in co-culture experiments. Activated macrophages are known to produce soluble, cytostatic respiration-inhibiting factors, and such activities can be duplicated by interferon-gamma (IFN-gamma) or by combinations of IFN-gamma and Escherichia coli lipopolysaccharide (LPS). Highly metastatic RAW117-H10 cells are more resistant to the cytostatic effects of IFN-gamma and LPS than poorly metastatic RAW117-P cells, and short-term (up to 72 hr) treatment with IFN-gamma and LPS does not change the metastatic potentials of RAW117 cells. We have studied the effects of sequential selection of RAW117-P cells for increased resistance to IFN-gamma and LPS. After 7 to 13 sequential selections, the resulting variant lines were completely refractory to the growth-inhibitory effects of IFN-gamma and LPS and cross-tolerant to macrophage-conditioned medium. The selected variants also completely lost their experimental metastatic potentials and their tumorigenicities after s.c. or i.m. injection. Cytofluorographic analysis indicated reduced cell-surface expression of H-2Kd antigen and fibronectin receptor on the variant cells but no change in surface mu heavy-chain immunoglobulin. The IFN-gamma-selected lines were less adhesive to liver microvascular endothelial cells than the unselected RAW117 cell lines, but were equally sensitive to NK cytolysis by spleen cells. Our results suggest that exposure to certain cytokines can affect the growth and metastatic potential of RAW117 cells and result in the selection of resistant variants with altered biologic properties.

Expression of annexins on the surfaces of non-metastatic and metastatic human and rodent tumor cells

Annexins are a large group of calcium-dependent cytoskeletal- and membrane-associated proteins whose properties include cytoskeleton and phospholipid binding and mitotic signal transduction. Although annexin-like molecules have been reported on the external plasma membranes of certain cells, in general they are considered to be cytoplasmic proteins. We report here the heterogenous expression of certain annexins (I-VI) on the external cell surfaces of non-metastatic and metastatic murine (RAW117 large-cell lymphoma), rat (13762NF mammary adenocarcinoma) and some human (KM12 and HT29 colorectal carcinoma) cell lines but not on some other cell lines such as human (A375 and MeWo) and mouse (B16) melanoma. The implication of annexin cell surface expression in the metastatic process is discussed with respect to tumor cell adhesion.