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  • 1
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Malignant transformation of normal cells resulting in agglutinability by the carbohydrate-binding protein Concanavalin A can be explained by three types of changes in the structural organization of sites on the surface membrane. There can be an exposure of cryptic sites, a concentration of exposed sites by a decrease in cell size, and a rearrangement of exposed sites without a decrease in cell size resulting in a clustering of sites.
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  • 2
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Amino acid and carbohydrate transport in normal and malignant transformed hamster cells was studied after binding of the protein Concanavalin A (Con. A) to the surface membrane. Experimental conditions were used so that a similar number of Con. A molecules were bound to both types of cells. The transport of amino acids was inhibited after Con. A binding in the transformed cells but not in normal cells. This was found with the metabolizable amino acidsl-leucine,l-arginine,l-glutamic acid, andl-glutamine, and with the non-metabolizable amino acids cycloleucine and α-aminoisobutyric acid. Transport ofd-glucose andd-galactose was more inhibited by Con. A in transformed than in normal cells, and in both types of cellsd-glucose was inhibited more thand-galactose. The inhibition by Con. A on transport was specific, since there was no effect on the transport ofl-fucose in either normal or transformed cells. Con. A also did not effect the entry of 3-0-methyl-d-glucose. These observations can be used to locate amino acid and carbohydrate transport sites in the surface membrane in relation to the binding sites for Con. A. The results indicate that Con. A sites are associated in normal cells with transport sites ford-glucose and to a lesser extentd-galactose, and in transformed cells with transport sites for amino acids and to a greater extent than in normal cells withd-glucose andd-galactose. Malignant transformation of normal cells therefore results in a change in the location of amino acid and carbohydrate transport sites in the surface membrane in relation to the binding sites for Con. A.
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  • 3
    ISSN: 0730-2312
    Keywords: alkaline phosphatase ; osteogenic induction ; pp60Src ; tyrosine phosphorylation ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Cyclosporin A (CsA) induces osteoporosis but not through direct activation of osteoclasts. CsA also inhibits cell-mediated mineralization in marrow stromal cell culture, whereas the tyrphostin AG-1478 increases mineralization. These antagonistic effects on mineralization were used to discern molecules that underwent phosphorylation changes in association with their opposing effects on mineralization. In parallel, quantitative changes in Src protein were followed. Multiple dexamethasone (DEX)-stimulated stromal cell cultures were grown with and without a mineralization-inhibiting dose (0.1 μM) of CsA and were harvested on different days of DEX stimulation. Immunoblots of gel-fractionated cell extracts showed that the most noticeable changes in tyrosine phosphorylated proteins (TPP) were seen on day 8 of DEX stimulation. At least 15 TPP bands, mostly smaller than 53 kDa, were more prominent in CsA-treated cultures on day 8. Under CsA, Src protein quantity decreased on day 8, but its cleavage product (52/54 kDa) was sixfold more abundant then on day 7. Day 8 was chosen to test the effect of AG-1478 on the CsA-induced TPP changes. Dimethyl sulfoxide (DMSO) alone, the solvent of AG-1478, increased mineralization in CsA-treated versus CsA-untreated cultures and slightly decreased Src and its cleavage product. AG-1478 at 5 μM, in CsA cultures increased the specific alkaline phosphatase activity threefold, with a slight change in mineralization relative to controls grown with DMSO alone. This was accompanied by decreased intensity of several TPP bands smaller than 36 kDa. In contrast, treatment with 50 μM of AG-1478 increased the intensity of TPP bands at the same molecular size range. This high AG-1478 dose decreased cell counts selecting mineralizing cells. The results indicate that increased Src protein cleavage product on day 8 by CsA is associated with mineralization inhibition, which is opposed by DMSO and 50-μM AG-1478, thus antagonizing the effect of CsA on mineralization. Direct or indirect interaction between Src and TPP, antagonistically affected by CsA and AG-1478, is likely to underlay cellular control of mineralization. Changes in p19 and p29 intensity showed association with mineralization that was reflected by a significant direct and inverse correlation, respectively, with calcium precipitation per cell. J. Cell. Biochem. 71:116-126, 1998. © 1998 Wiley-Liss, Inc.
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  • 4
    ISSN: 0730-2312
    Keywords: osteoprogenitors ; mineralization ; marrow stroma ; Src ; tyrosine kinase dexamethasone ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Src protein is essential for the regulation of bone turnover primarily via bone resorption because it is required in osteoclast differentiation and function. We followed temporal changes of Src protein abundance in marrow stromal cells induced to mineralize by dexamethasone (DEX), growth in cold temperature, or both. Given the tyrosine kinase function of Src and its numerous substrates, profiles of phosphotyrosine-containing proteins were followed as well. On day 11 of stimulation, specific alkaline phosphatase (ALP) activity at 30°C decreased under DEX relative to 37°C cultures, in accord with increased cell counts. Mineralization per well under DEX increased by 25% at 37°C, whereas at 30°C it increased by more than threefold regardless of the DEX stimulation. At 30°C, on a per cell basis mineralization increased 2.5 and 3 times with and without DEX, respectively. Cultures at 37°C showed a general drop per cell of many phosphotyrosine-containing proteins on day 3 relative to days 1 and 2 in both DEX-stimulated and nonstimulated cultures; several proteins did recover (recuperate) thereafter. On days 1 and 2, the phosphotyrosine signal was higher in several proteins under DEX stimulation; this trend became inverted after day 3. The changes in abundance per cell of Src protein (pp60src) followed a similar trend, and in addition a truncated Src molecule, p54/52src, was detected as a putative cleavage product presumably representing its carboxy terminus. The pp60src was most abundant, relative to its truncated product, in day 7 nonstimulated cultures, whereas under DEX stimulation the truncated species pp54/52src showed the highest relative abundance on days 7. At 30°C, DEX stimulation accentuated the increase in Src protein on day 3, showed no change on day 7, and returned to increase Src protein on day 10. Potassium ionophorvalinomycin, considered to select against mineralizing osteoprogenitors at 30°C, showed on day 10 in the absence of DEX a relative increase in truncated Src protein compared to both DEX-stimulated and nonstimulated cultures in the absence of valinomycin. On day 7 of DEX stimulation, the presence of valinomycin resulted in low p54/52src. Among phosphotyrosine-containing proteins, a 32-34 kDa band, as yet unidentified, showed the most concordant changes with mineralization induction. P32-34 decreased by DEX on days 2 and 8 and increased by low temperature alone or combined with DEX on day 3. On day 7, p32-34 did not change under DEX, but valinomycin selected cells with less phoshpotyrosine-containing p32-34. Taken together, high Src abundance at the start of osteogenic induction followed by a decrease 1 week later is probably related to energy metabolism-dependent induction of mineralization. This is in temporal accord with the increase in Src truncation and fluctuation in mitochondrial membrane potential (which affects mineralization). The reported binding of amino-terminal Src oligopeptide to p32 ADP/ATP carrier in the mitochondrial inner membrane raises the question of its possible involvement in mitochondria-regulated mineralization. J. Cell. Biochem. 69:316-325, 1998. © 1998 Wiley-Liss, Inc.
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  • 5
    ISSN: 0730-2312
    Keywords: osteoprogenitors ; marrow-stroma ; alkaline phosphatase ; bisphosphonates ; cell proliferation ; mineralization ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Bisphosphonates (BPs) are inhibitors of bone resorption and soft tissue calcification. The biological effects of the BPs in calcium-related disorders are attributed mainly to their incorporation in bone, enabling direct interaction with osteoclasts and/or osteoblasts through a variety of biochemical pathways. Structural differences account for the considerable differences in the pharmacological activity of BPs. We compared the effects of two structurally different compounds, alendronate and 2-(3′-dimethylaminopyrazinio)ethylidene-1,1-bisphosphonic acid betaine (VS-6), in an osteoprogenitor differentiation system. The BPs were examined in a bone marrow stromal-cell culture system, which normally results in osteoprogenitor differentiation. The drugs were present in the cultures from days 2 to 11 of osteogenic stimulation, a period estimated as being comparable to the end of proliferation and the matrix-maturation stages. We found that the two different BPs have opposing effects on specific alkaline phosphatase (ALP) activity, on stromal-cell proliferation, and on cell-mediated mineralization. These BPs differentially interact with cell-associated phosphohydrolysis, particularly at a concentration of 10-2 of ALP Km, in which alendronate inhibits whereas VS-6 did not inhibit phosphatase activity. VS-6 treatment resulted in similar and significantly increased mineralization at 10 and 1 μM drug concentrations, respectively. In contrast, mineralization was similar to control, and significantly decreased at 10 and 1 μM drug concentrations, respectively, under alendronate treatment. J. Cell. Biochem. 68:186-194, 1998. © 1998 Wiley-Liss, Inc.
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