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R Lotan

Publications and source records attributed to R Lotan.

At least 199 records · Page 11Linked to original sources
PubMed1989

Inter-species variations in myocardial responsiveness to cardiac glycosides: possible relations to the thyroid status.

Mammalian species differ in their myocardial responsiveness to cardiac glycosides; whereas glycosides induce a marked positive inotropic effect in species such as dog, rabbit and guinea-pig, the rat myocardium is virtually insensitive. We investigated the physiological basis for this phenomenon by testing the hypothesis that the inter-species variations in the response of the myocardium to cardiac glycosides results, at least in part, from species-related differences in the "thyroid status". In the present study we focused on the toxic effects of the glycosides, and studied ouabain-induced delayed afterdepolarizations (DAD): (1) in guinea-pigs, rats and mice, which encompass a wide range of thyroid statuses, as indicated by their O2 consumption and thyroid hormone levels; (2) in guinea-pigs and rats in which the thyroid status was decreased by propylthiouracil treatment or increased by thyroxine administration (in the former species only). DAD were readily induced in guinea-pigs after 40 to 60 min superfusion with 10(-6) M ouabain and 5.4 mM Ca2+. In rats, DAD were induced only when the Ca2+ concentration was raised to 8.1 mM, but were absent in mice even after 2 h of superfusion with ouabain and 8.1 mM Ca2+. In guinea-pigs and rats (at cycle length = 500 ms), DAD amplitude was (means +/- S.E.): 2.8 +/- 0.7 mV and 1.1 +/- 0.4 mV, respectively. The slope of the DAD ascending limb (dV/dt) in guinea-pigs was 47.6 +/- 8.6 mV/s and in rats was 8.1 +/- 3.4 mV/s. In both species DAD characteristics were altered by the thyroid status. In eu-, hyper- and hypothyroid guinea-pigs, DAD amplitude and dV/dt (cycle length = 500 ms) were as follows: 2.8 +/- 0.7 mV and 47.6 +/- 8.6 mV/s; 1.2 +/- 0.4* mV and 12.6 +/- 3.9* mV/s; 7.5 +/- 0.6* mV and 204.0 +/- 18.4* mV/s, respectively (*, P less than 0.005, compared to euthyroid guinea-pigs). The occurrence of triggered beats was also dependent on the thyroid status. They occur more frequently in hypothyroidism and less frequently in hyperthyroidism. Hypothyroidism in rats augmented ouabain toxicity as reflected by an increase in DAD amplitude and dV/dt by 109% and 105%, respectively (P less than 0.05, as compared to euthyroid rats). In conclusion, we suggest that species-related differences in the thyroid status may contribute to the inter-species (as well as for the intra-species) variations in the myocardial responsiveness to cardiac glycosides.

Action Potentials↗
PubMed1988

Endogenous lectins as mediators of tumor cell adhesion.

Endogenous carbohydrate-binding proteins have been found in various normal tissues and cells. Although lectins with different sugar-binding specificities have been described, the most prevalent ones are those that bind beta-galactosides. The ability of some normal and malignant cells to bind exogenous carbohydrate-containing ligands suggested that lectinlike activity is associated with the cell surface and that carbohydrate-binding proteins might mediate intercellular recognition and adhesion. We found that extracts of various cultured murine and human tumor cells exhibit a galactoside-inhibitable hemagglutinating activity. This activity was associated with two proteins of molecular weights of 34,000 and 14,500 daltons, which were purified by affinity chromatography by using immobilized asialofetuin. That these lectins are present on the cell surface was indicated by the binding of monoclonal antilectin antibodies to the surface of various tumor cells and by the immunoprecipitation of 125I-labeled lectins from solubilized cell-surface iodinated cells by polyclonal antilectin antibodies. That these cell surface lectins are functional was demonstrated by the ability of the galactose-terminating asialofetuin to enhance cell aggregation and of asialofetuin glycopeptides to block this homotypic aggregation as well as to suppress cell attachment to substratum, and by the inhibition of both asialofetuin-induced cell aggregation and cell attachment to substratum by the binding of monoclonal antilectin antibodies to the cell surface. These findings implicate cell surface lectins as mediators of cell-cell and cell-substratum adhesion. Some of these cellular interactions might be important determinants of tumor cell growth and metastasis.

Animals↗
PubMed1988

Enhancement of sialyltransferase in two melanoma cell lines that are growth-inhibited by retinoic acid results in increased sialylation of different cell-surface glycoproteins.

Previous studies have demonstrated the ability of retinoic acid (RA) to inhibit the growth of two spontaneous murine melanoma cell lines (B16-F1 and S91-C2) and to augment both sialyltransferase activity and the sialylation of an Mr 160,000 cell-surface glycoprotein. The present study examined the effects of RA on an ultraviolet irradiation-induced murine melanoma cell line K-1735P. Like the two spontaneous melanomas, the uv-induced melanoma exhibited susceptibility to the growth-inhibitory action of RA. Both the anchorage-dependent and the anchorage-independent growths of the K-1735P cells were suppressed by RA, with IC50 values of 5 X 10(-9) and 3 X 10(-12) M, respectively. Sialyltransferase activity in both S91-C2 and K-1735P cells treated with 10(-6) or 10(-5) M RA increased two- and three-fold, respectively, as compared with untreated cells. In contrast, cell-surface sialo- and galactoglycoproteins, revealed by labeling with periodate and tritiated borohydrate or with neuraminidase, galactose oxidase, and tritiated borohydrate, respectively, varied between the S91-C2 and the K-1735P cells, and each cell line's modulation by RA was also distinct. These findings suggest that although RA can increase the activity of sialyltransferase in different melanoma cells, this increased activity may, in turn, result in an increased sialylation of distinct cell-surface glycoproteins.

Animals↗
PubMed1988

Lectins in cancer cells.

Studies carried out over the last few years have demonstrated that tumor cells and malignant tissues contain lectins that are similar in sugar-binding specificity, molecular size, and antigenicity to the lectins found in normal cells and tissues. Lectins from tumor cells also share marked sequence homology with lectins from normal tissues. Lectins were purified from various tumor cells by affinity chromatography and monoclonal and polyclonal antilectin antibodies were prepared against them. These enabled us to establish the following: (1) Lectins are present on the surface of all the tumor cells that were examined, albeit at varying levels. (2) The level of cell surface lectins increases after normal cells are transformed by transfection with certain oncogenes or by retroviruses, or when cells transformed with a temperature-sensitive viral mutant are switched from growth at the nonpermissive to the permissive temperature. (3) Among tumor cells differing in metastatic propensity, those exhibiting a higher potential express higher levels of surface lectins. (4) Tumor cell surface lectins might be involved in cell-cell adhesion, cell attachment to substratum, the expression of the transformed phenotype (anchorage-independent growth), and blood-borne metastasis. (5) The levels of the lectins in tumor cells are modulated by agents that suppress the transformed phenotype (as represented by anchorage-independence) or enhance differentiation. Numerous studies by others have shown that cell surface carbohydrate-containing molecules are modified after transformation, and our findings demonstrate that the expression of cell surface carbohydrate-binding proteins is also altered by transformation. Obviously, any of these changes may result in alterations in cellular interactions. All the above findings implicate tumor cell lectins in cellular interactions (adhesion, attachment, possible binding of exogenous soluble glycoconjugates), cell growth and anchorage-independent growth, malignant transformation, tumor cell differentiation, and metastasis. It is clear that even if these lectins are involved in only a few of these fundamental processes, it is important to elucidate their functions and the mechanisms by which their expression is regulated during neoplastic transformation and tumor progression and the suppression of the transformed phenotype.

Antibodies, Monoclonal↗
PubMed1987

Differential effects of retinoic acid on the in vitro growth and cell-surface glycoconjugates of 2 human head and neck squamous-cell carcinomas.

As a part of an assessment of the potential use of retinoids in preventive and adjuvant treatment of HNSCC, we examined the effects of beta-all-trans retinoic acid (RA) on the growth and cell-surface glycoconjugates of 2 HNSCC cell lines. These lines, designated 1483 and 183A, were established from an untreated patient with a well-differentiated SCC of the retromolar trigone and one with a poorly differentiated SCC of the tonsil. Whereas the 1483 cells were sensitive to RA in that their anchorage-dependent growth, their colony growth on solid substratum, and their anchorage-independent growth in semi-solid agarose gel were all inhibited in a dose-dependent fashion by RA concentrations in the range between 1 nM and 10 microM, the 183A cells were not inhibited by RA. Their anchorage-dependent growth and colony formation were stimulated by RA, whereas their anchorage-dependent colony formation was not altered. Cell-surface glycoconjugates were modulated by RA in the sensitive 1483 cells but not in the 183A cells. Treatment of the 1483 cells resulted in a large increase in the cell-surface labelling of high-molecular-weight (Mr greater than 400,000) galactoglycoconjugates and sialoglycoconjugates, as well as an Mr 280,000 sialoglycoconjugate. Glycoconjugates with similar electrophoretic mobilities in polyacrylamide gels were labelled intensely on the surface of the 183A cells even before RA treatment and only minor changes were noticed in their labelling after treatment. These results demonstrate that RA can exert different effects on different HNSCC lines, and suggest that correlations might exist between responsiveness to RA and the stage of differentiation of the HNSCC, and between modulation of cell growth and enhancement of cell-surface glycoconjugate glycosylation by RA.

Carbohydrates↗
PubMed1987

New benzoic acid derivatives with retinoid activity: lack of direct correlation between biological activity and binding to cellular retinoic acid binding protein.

In this paper the biological activity of several newly synthesized benzoic acid derivatives of the Am- and Ch- series, which are structurally different from retinoic acid and arotinoids, was examined. These compounds inhibit squamous cell differentiation of rabbit tracheal epithelial cells in vitro as indicated by the inhibition of transglutaminase Type I and cholesterol 3-sulfate levels. In contrast to the inhibition of differentiation in rabbit tracheal cells, these compounds induce differentiation of mouse embryonal carcinoma F9 and human promyelocytic leukemia HL60 cells. The Am- and Ch- series of compounds also affect several parameters of cell proliferation. These agents are very potent inhibitors of growth of melanoma S91 cells and inhibit the induction of ornithine decarboxylase activity by phorbol 12-myristate 13-acetate in 3T6 fibroblasts. These results show that the Am- and Ch- derivatives elicit in several cell systems the same cellular responses as retinoic acid. We propose, therefore, that they exhibit mechanism(s) of action similar to those of retinoids. Comparison of the biological response with the binding capacity to the cellular retinoic acid-binding protein shows a lack of a direct correlation.

Animals↗
PubMed1987

Growth inhibition of murine melanoma cells by antibodies to a cell surface glycoprotein implicated in retinoic acid action.

Previous studies have shown that treatment of S91-C2 murine melanoma cells with beta-all-trans-retinoic acid (RA) results in growth inhibition, enhanced activity of sialyltransferase, and increased glycosylation of a Mr 160,000 cell surface sialoglycoprotein (gp160). None of these effects could be detected in mutant clones (e.g., S91-C154) selected from the S91-C2 cells for resistance to RA-induced growth inhibition. These findings suggest that modulation by RA of gp160 might be related causally to growth inhibition. In this study we examined the possible role of gp160 in growth regulation using specific antibodies to this glycoprotein. Metabolic labeling of S91-C2 cells with either [3H]glucosamine or [35S]methionine revealed that the cells shed into the growth medium a gp160-like glycoprotein, in addition to several other macromolecules. The gp160-like glycoprotein was isolated from concentrated conditioned medium after preparative polyacrylamide slab gel electrophoresis in the presence of sodium dodecylsulfate by excision of the corresponding protein band. Rabbits were immunized with this material and immunoblotting revealed that their sera contained antibodies that bound specifically to gp160 in extracts of untreated or RA-treated S91-C2 cells. Indirect immunofluorescence staining followed by fluorescence-activated cell sorter analysis demonstrated that the anti-gp160 antibodies bound to the surface of both untreated and RA-treated S91-C2 cells and that the treated cells bound more of the antibodies than untreated ones. In contrast, these antibodies bound to the same extent to untreated and RA-treated resistant S91-C154 cells. The growth of S91-C2 cells in the presence of anti-gp160 antibodies in semisolid medium as well as in monolayer cultures was inhibited in a dose-dependent fashion. Fifty % growth inhibition was obtained at an immunoglobulin concentration of 10 micrograms/ml. The growth of cells exposed concurrently to RA and anti-gp160 antibodies was also inhibited strongly in semisolid medium, but the antibodies caused only a small increase in the inhibitory effect of RA in monolayer cultures. No inhibition by the antibodies of either anchorage-independent growth or anchorage-dependent growth of S91-C154 cells, grown in the absence or presence of RA, was observed. These results support the suggestion that cell surface gp160 might be involved in growth regulation in the S91-C2 cells.

Animals↗
PubMed1987

Differential effects of dibutyryl cyclic adenosine monophosphate and retinoic acid on the growth, differentiation, and cyclic adenosine monophosphate-binding protein of murine neuroblastoma cells.

Dibutyryl cyclic adenosine 3':5'-monophosphate (Bt2cAMP) and beta-all-trans retinoic acid (RA) have been shown separately, and in some cases in combination, to modulate the growth, differentiation, and cAMP-dependent protein kinase (PK-A) activity of various tumor cells. The effects of Bt2cAMP and RA on a cholinergic clone (S20) of C1300 mouse neuroblastoma cells were explored in the present study. Treatment of these cells with 1 mM Bt2cAMP for 3 or more days resulted in 93% inhibition of cell proliferation in monolayer cultures and in 98% inhibition of colony formation in semisolid medium (0.5% agarose). In contrast, treatment of the cells with 1 or 10 microM RA had no inhibitory effects on cell proliferation in monolayer cultures but enhanced colony formation in agarose by up to 130%. The growth of cells treated with a combination of Bt2cAMP and RA was inhibited, although less so than with Bt2cAMP alone. Cells treated with Bt2cAMP alone or Bt2cAMP and RA extended long, neurite-like, cellular processes indicative of differentiation, whereas only a few untreated or RA-treated cells produced such extensions. The amount of [3H]cAMP-binding protein increased gradually up to 2-fold during a 3-day treatment with Bt2cAMP; in contrast it decreased by nearly 2-fold during RA treatment. These changes occurred in the level of the type I regulatory subunit (RI) of PK-A as determined by photoaffinity labeling with 8-azidoadenosine cyclic 3':5'-[32P]monophosphate. The increase in RI following Bt2cAMP treatment was corroborated by DEAE-cellulose chromatography. This analysis also demonstrated that type I PK-A is the predominant kinase in the untreated S20 cells and that RI exists as a free subunit in Bt2cAMP-treated cells. The activity of PK-A decreased by about 20% following treatment with either Bt2cAMP or RA and by 45% following treatment with a combination of both agents. These results suggest that the distinct effects of Bt2cAMP and RA on the anchorage-independent growth of S20 cells may be related to their opposite effects on the level of RI.

Animals↗
PubMed1987

Transformation-related changes in the expression of endogenous cell lectins.

Endogenous lectins purified from UV-2237-IP3 murine fibrosarcoma cells by affinity chromatography consisted of two polypeptide species of Mr 14,500 (L-14.5) and Mr 34,000 (L-34). Antibodies against this material immunoprecipitated the lectins from cells radiolabelled on the cell surface as well as in the cytoplasmic compartment. Similar analyses of normal rat embryonal fibroblasts revealed the presence of only the L-14.5. In contrast, both L-14.5 and L-34 were found in oncogene-transfected, immortalized cell clones derived from the normal rat cells, as well as in untransformed BALB/c-3T3 clone A31 and its descendant subclones selected for expression of the transformed, the tumorigenic and the metastatic phenotypes. Among the cells constituting the latter system, a marked increase in the amount of cellular and cell-surface lectins was observed upon progression to the metastatic phenotype. These results suggest that the expression of endogenous tumor-cell-surface lectins is associated with transformation and metastasis.

Animals↗
PubMed1987

Endogenous galactoside-binding lectins: a new class of functional tumor cell surface molecules related to metastasis.

The formation of secondary tumors by circulating cancer cells (blood-borne metastasis) correlates with an increased tendency of the cells to form emboli by aggregation with other tumor cells or with host cells. Although it is evident that cell-cell recognition and adhesion are mediated by cell surface components, the identity of these molecules is only now being unraveled. Over the last decade an increasing number of studies have demonstrated the presence of endogenous carbohydrate-binding proteins on the surface of various normal cells, and it has been proposed that such lectin-like molecules might be involved in intercellular adhesion. We have shown that various tumor cell lines contain endogenous galactose-specific lectins. Lectin activity was detected at the cell surface by the binding of asialofetuin. This glycoprotein also enhanced the aggregation of the tumor cells. After purification by affinity chromatography on immobilized asialofetuin the lectin activity was associated with two proteins of Mr 14,500 and 34,000. By using polyclonal and monoclonal antilectin antibodies in conjunction with various immunologic techniques we have demonstrated that the endogenous lectins are present on the surface of different tumor cells. Quantitation of cell surface lectins by flow cytometric analyses of antilectin antibody binding revealed that among related tumor cells those exhibiting a higher metastatic potential expressed more lectin on their surface. The binding of monoclonal antilectin antibodies to metastatic cells decreased asialofetuin-induced homotypic aggregation in vitro and suppressed the ability of the cells to form lung metastases after intravenous injection in the tail vein of syngeneic mice. These results strongly implicate the tumor cell surface lectins in cell adhesion and metastasis. We propose that such lectins can increase the ability of tumor cells that enter the blood stream to form aggregates with other tumor cells, or to adhere to host cells or the extracellular matrix and thereby increase their metastatic potential. Other contributing components to tumor cell-host cell interactions are cell surface carbohydrate-binding proteins that have been detected on lymphocytes, platelets, macrophages, hepatocytes, and endothelial cells. These lectin-like molecules might recognize and bind carbohydrates expressed on the surface of tumor cells and enhance emboli formation and organ colonization.

Animals↗
PubMed1987

Modulation of polycation-induced redistribution of melanoma cell surface anionic macromolecules by retinoic acid.

The ability of cationized ferritin (CF) to redistribute negatively charged cell surface molecules has been shown to increase after malignant transformation. Pretreatment of murine melanoma S91-C2 and B16-F1 cells with retinoic acid (RA), which suppresses their transformed phenotype, decreased the ability of CF to cluster surface anionic sites. In contrast, a similar pretreatment of RA-resistant mutant clone S91-C154 and subline B16-F10 caused only a minor reduction in CF-induced patching of anionic sites. These results indicate that the effect of RA on the redistribution of negatively charged cell surface molecules is related to the growth-inhibitory action of this vitamin A metabolite.

Animals↗
PubMed1987

Enhanced glycosylation of a melanoma cell surface glycoprotein by retinoic acid: carbohydrate chain analysis by lectin binding.

Retinoic acid (RA) inhibits the growth of mouse S91-C2 melanoma cells and enhances the glycosylation of a cell surface sialoglycoprotein (gp160). The present study analyzed the binding of 125I-labeled lectins to gp160 within polyacrylamide slab gels after electrophoretic separation of cellular macromolecules. Wheat germ agglutinin (WGA) and concanavalin A (Con A) bound to gp160 of RA-treated cells (RA-gp160) more extensively than to gp160 of control cells (C-gp160). Lens culinaris hemagglutinin (LCH), pokeweed mitogen (PWM), Ricinus communis agglutinin I (RCAI), and peanut agglutinin (PNA) failed to bind to either C-gp160 or to RA-gp160. The binding of WGA was greatly diminished after sialic acid removal. In contrast, desialylation made possible the binding of RCAI to RA-gp160. LCH, PWM and PNA did not bind to gp160 even after desialylation. Smith degradation exposed WGA-binding sites on RA-gp 160. These results suggest that gp 160 contains one or more highly branched, sialylated, N-linked complex-type side chains and lacks O-linked oligosaccharides and poly N-acetyllactosamine side chains.

Animals↗
PubMed1986

Distribution and modulation of surface charges of cells from human leukemia-lymphoma lines at various stages of differentiation.

Untreated and retinoic acid (RA) treated human leukemia-lymphoma cell lines reflecting hematopoietic cells at various stages of differentiation, were examined electron microscopically for their surface negative charge distribution using cationized ferritin (CF), an electron dense label of anionic sites. The results indicate that there is a correlation between the CF labeling density/distribution and the stage of lymphoid cell differentiation. Viable unfixed null cell lines show a low CF labeling density with few and small CF patches. A gradual increase in CF labeling density and increase in size and number of CF patches correlates with the stage of differentiation on cell lines of both T or B origin. Treatment of viable unfixed cells with 10(-5) MRA for 10 days seems to prevent the CF-induced formation of CF patches, resulting in a continuous and even distribution of the CF label, similar to that observed on the surface of cells fixed before CF labeling. Some correlation between the distribution of surface anionic sites and the malignant potential of the human leukemic lines could be detected.

Anions↗
PubMed1986

Implications of endogenous tumor cell surface lectins as mediators of cellular interactions and lung colonization.

A monoclonal antibody (mAb) designated 5D7 that is directed against endogenous, galactoside-specific lectin and binds to the surface of various tumor cells was used to examine the involvement of cell surface lectin molecules in cellular interactions in vitro and in vivo. The mAb 5D7 was found to inhibit asialofetuin-induced homotypic aggregation of B16 melanoma and UV-2237 fibrosarcoma cell variants by up to 80%. The rate at which these cells, as well as the virally transformed fibroblasts (SVPy-3T3), adhere to tissue culture dishes was reduced in the presence of mAb 5D7 to less than 50% of the control. The anti-lectin mAb had no effect on the adhesion rate of untransformed 3T3 fibroblasts. Treatment of B16 and UV-2237 cells with mAb 5D7 in vitro before their injection into the tail vein of syngeneic mice resulted in a decrease of up to 90% in the appearance of tumor lung colonies. These findings imply that tumor cell surface lectins might play a role in mediation of cell-to-cell and cell-to-substratum adhesion in vitro as well as in similar interactions in vivo that are relevant for metastasis.

Animals↗
PubMed1986

Differential expression of endogenous lectins on the surface of nontumorigenic, tumorigenic, and metastatic cells.

A monoclonal antibody that was found to recognize endogenous galactoside-specific lectins of various tumor cells by immunoblot analysis was used for quantitative analyses of cell surface lectin on nontumorigenic, tumorigenic, and metastatic cells of diverse histological types and origin. Indirect immunofluorescent staining of viable cells followed by analysis with a fluorescence-activated cell sorter revealed marked differences in the amount of surface lectins between untransformed and malignant cells. While lectin was either absent or present in a very low density on the surface of normal cells, neoplastic cells were invariably stained by the antilectin antibodies. Furthermore, among related tumor cell variants of the K-1735 melanoma and UV-2237 fibrosarcoma tumor systems, cells exhibiting a higher lung-colonizing potential also expressed higher levels of cell surface lectin. These results suggest that the presence of a lectin on the cell surface may be related to neoplastic transformation and progression toward metastasis.

Animals↗
PubMed1985

Inhibition of tumor cell colony formation in culture by a monoclonal antibody to endogenous lectins.

The presence of endogenous, galactoside-specific lectin molecules on the surface of various neoplastic cells has been demonstrated recently using monoclonal antibody (mAb) 5D7 [Raz et al., EMBO (Eur. Mol. Biol. Organ.) J., 3: 2979, 1984]. The effect of this mAb on the growth of several transformed and tumor cell lines of murine and human origin was investigated using in vitro techniques. A dose-dependent reduction (30 to 100%) in colony formation on a solid substrate or in a semisolid medium was observed when the cells were cultured in the presence of 15 to 100 micrograms of mAb 5D7 per ml of medium. Inhibition of anchorage-independent growth was more pronounced (2- to 3-fold) than inhibition of anchorage-dependent growth for most of the cells. The growth-inhibitory effects of mAb 5D7 were not the result of a cytolytic activity, for neither DNA nor protein synthesis was suppressed in semiconfluent cell cultures after 3 days of exposure to the antibody. Other mAbs that recognize cell surface components, such as chondroitin sulfate or fibronectin, failed to inhibit colony formation. These results suggest that endogenous tumor cell-surface lectin molecules may be involved in intercellular interactions or interactions between the cells and exogenous ligands; these interactions are important for growth regulation.

Animals↗