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Biomedical subjects

M M Weiser

Publications and source records attributed to M M Weiser.

At least 55 records · Page 3Linked to original sources
PubMed1984

Intestinal epithelial cell differentiation-related changes in glycosyltransferase activities in rats.

Intestinal epithelial cells differentiate as they migrate from the crypt-to-villus tip. A ten-fraction crypt-to-villus gradient of epithelial cells from rat small intestine was prepared and homogenates assayed for three glycosyltransferases involved in elongation of asparagine-linked oligosaccharides. The N-acetylglucosaminyltransferases I and II (enzymes which attach N-acetylglucosamine to either the 3' or 6' core mannose, respectively) were assayed with structurally-defined glycopeptides as specific acceptors and galactosyltransferase was assayed with asialo, agalactosylfetuin (galactose is attached to exposed N-acetylglucosamine termini). Inhibitors of glycosidases and pyrophosphatases were included in the assays to minimize effects of breakdown of substrate or product. The results indicate the N-acetylglucosaminyltransferase I shows a gradient of activity increasing from a low at the villus tip to a peak in the lower crypt region. In contrast, N-acetylglucosaminyltransferase II showed two peaks of activity, one in the villus zone and another in the upper crypt region. Galactosyltransferase activity also defined a gradient quite similar to that observed for N-acetylglucosaminyltransferase I, its specific activity being highest in the crypt cells. The specific activity levels of the three enzymes correlated with the apparent order of their action: N-acetylglucosaminyltransferase I much less than N-acetylglucosaminyltransferase II much less than galactosyltransferase. These results suggest a developmental regulation of the glycosyltransferases involved in oligosaccharide chain elongation of glycoproteins during intestinal cell differentiation.

Animals↗
PubMed1984

Characterization of the vitamin D-dependent Ca2+-binding sites in rat intestinal Golgi-enriched membrane fractions.

Rat intestinal Golgi-enriched membrane fractions take up Ca2+ by a vitamin D-dependent process that has been shown to recover within 15 min of repletion of vitamin D-deficient animals with intravenous 1,25-dihydroxycholecalciferol. The present paper reports studies characterizing the Ca2+-binding sites of these membrane fractions. Equilibrium binding of Ca2+ at concentrations between 5 and 400 microM showed significant decreases at all concentrations in membranes derived from vitamin D-deficient animals when compared with normal control-diet-fed animals. The predominant class of binding sites had a relatively high affinity for Ca2+ (KD approx. 3 microM). Vitamin D-deficiency did not change the affinity of this class of site, but decreased the number from 347 +/- 26 to 168 +/- 50 nmol of Ca2+ bound/mg of protein (means +/- S.D.). Mg2+ inhibited binding only at low Ca2+ concentrations, and the characteristics of this binding suggested positive co-operativity between two binding sites. Equimolar concentrations of Zn2+, La3+, Pb2+ and Mn2+ inhibited Ca2+ binding by over 50%. Increased ionic strength decreased Ca2+ binding by no more than half. Binding was maximal at pH 7.5 and half-maximal at pH 6.3. The large number of binding sites with relatively high affinity for Ca2+ suggests that it is unlikely that this binding is to any specific protein or to non-specific sites present on many proteins, and that the most likely sites are lipid molecules.

Animals↗
PubMed1984

Relationship of non-esterified fatty acids to vitamin D-dependent Ca2+ binding by rat intestinal Golgi-enriched membrane fractions.

Ca2+ binding and concentrations of non-esterified fatty acids and phospholipids were compared in membrane fractions of rat small intestine. These fractions differed in density and were enriched for galactosyltransferase activity, a Golgi-membrane marker. Ca2+ binding was highest in the Golgi subfraction with the least density, as were the concentrations of both non-esterified fatty acids and phospholipids; galactosyltransferase activity was distributed differently. The large amount of non-esterified fatty acids was sufficient to account for a 2:1 complex of fatty acid-Ca2+. In vitamin D-deficient animals, the yield of protein in the lightest subfractions was decreased, but Ca2+ binding per mg of protein was further decreased to about 60%. In Golgi fractions from vitamin D-deficient animals, Ca2+ binding and the concentration of non-esterified fatty acids were decreased in parallel, but phospholipids were not significantly changed. There was a close correlation between Golgi Ca2+ binding and non-esterified fatty acid concentrations (r = 0.89; P less than 0.001). Non-esterified fatty acids, which are unusually prevalent in these membrane fractions, are likely to be the binding sites that account for this vitamin D-dependent Ca2+ uptake.

Animals↗
PubMed1984

Galactosyltransferase activity and cell growth: uridine diphosphate (UDP)galactose inhibition of murine leukemic L1210 cells.

UDPgalactose inhibits the growth of mouse leukemic L1210 cells. In calf serum supplemented Dulbecco's medium (CS-DMEM), 1.2 mM UDPgalactose (UDPgal) inhibited cell growth by 50% (IC50), and 5 mM UDPgalactose inhibited cell growth by 92%. Other nucleotide sugars as well as galactose, glucose, and galactose-1-phosphate had little or no effect on cell growth. Uridine nucleotides, which inhibit galactosyltransferase activity, protected L1210 cells from the growth inhibitory effect of UDPgalactose when both were added simultaneously to culture media. Unlike mouse 3T12 cells, in which no inhibition of cell growth was observed with heat-inactivated calf serum (HICS)-DMEM, 5 mM UDPgalactose inhibited L1210 cell growth in HICS-DMEM to the same degree as that observed in CS-DMEM. In contrast to 3T12 cells, L1210 cells secrete significant galactosyltransferase activity into the media. Complete inhibition of 3T12 cell growth by UDPgal was observed if HICS-DMEM medium was first conditioned by L1210 cells for 48 hours. No difference in cell growth or [3H]thymidine uptake was detected after 6 hours of exposure to UDPgalactose, but both were significantly decreased at 24 and 48 hours. Flow cytometric analysis of UDPgalactose effects on L1210 cells revealed no differences in the distribution of cells in G1, S, or G2-M of the cell cycle after 6 hours of incubation, but after 16 hours of UDPgalactose treatment, L1210 cells were arrested in early S phase. These cells were completely viable and morphologically similar to control L1210 cells. Normal growth was resumed when UDPgal was removed. The data suggest that UDPgalactose inhibition of cell growth requires extracellular galactosyltransferase activity and that the effect is mediated via the cell membrane.

Animals↗
PubMed1982

Kinetics of subcellular distribution in rat intestine of 1,25-dihydroxycholecalciferol administered in vivo. Evidence for concentration within 5 min into purified nuclei.

To better understand the initial steps in the induction of intestinal Ca2+ transport by 1,25-dihydroxycholecalciferol [1,25(OH)2D3], we studied the early subcellular localization of 1,25(OH)2D3 in rat intestine. Vitamin D-deficient rats received 300 pmol of 1,25(OH)2[3H]D3 intravenously at 5 min to 4h before being killed. Cells homogenized in buffer of I = 90 mmol/litre were fractionated by centrifugation into a crude nuclear pellet, purified nuclei, Golgi and basal-lateral membranes, cytosol and a post-nuclear pellet. Nuclear purification was established by biochemical and morphological criteria and gave a yield of 32 +/- 2% (mean +/- S.E.M.; n = 21). Although re-establishment of Ca2+ uptake by Golgi is one of the earliest reported intestinal responses to 1,25(OH)2D3, no direct localization of 1,25(OH)2D3 to Golgi was detected. Purified nuclei had the highest specific radioactivity at all times studied, with nuclear localization detectable at 5 min and peak nuclear uptake at 1 h. Relative specific radioactivity of nuclei to cytosol increased from 5 min to 30 min, at which time equilibrium between cytosol and nucleus appeared to be attained. Nuclear uptake occurred in all cells from villus to crypt. Of total nuclear binding 10% was resistant to high ionic strength buffer (I = 365 mmol/litre); peak nuclear uptake was observed at 30 min in this buffer. This tight binding may represent the active fraction of 1,25(OH)2D3. These results indicate that localization of 1,25(OH)2D3 to rat intestinal nuclei precedes the observed Golgi-membrane effects and suggest the existence of high-affinity nuclear 1,25(OH)2D3-binding sites.

Animals↗
PubMed1982

Gastrointestinal problems in the elderly.

Gastrointestinal problems in the elderly, such as swallowing difficulties, chest pain, bleeding, constipation, and colonic diseases, which may present problems in diagnosis or management, are discussed. A screening procedure for colorectal cancer in asymptomatic geriatric patients is proposed.

Aged↗
PubMed1981

Serum levels of glycosyltransferases and related glycoproteins as indicators of cancer: biological and clinical implications.

Many studies have suggested that malignant transformation is associated with fundamental changes in the cell surface; similar changes have been described for normal stem cells and cells of embryonic or fetal origin. There is now evidence that the tumor cell secretes or sheds glycoproteins and glycosyltransferases into the surrounding medium and into serum. There are claims that some of these serum glycoproteins and glycosyltransferases are associated with, or specifically related to, the extent of tumor growth and may serve as a cancer marker. A cancer-associated galactosyltransferase isoenzyme (GT-II) has been described and purified. Different isoelectric forms of fucosyltransferase have also been described as indicative of malignancy. The articles to be published in CRC Critical Reviews in Clinical Laboratory Sciences will analyze the evidence for the association of these membrane factors with tumor growth. In order to better understand the possible significance of altered glycoproteins and of increased or different forms of glycosyltransferases during tumor growth, recent data on glycoprotein synthesis will be discussed including the new concepts on the control of glycoprotein synthesis through lipid intermediates. The possible mechanisms whereby malignant transformation could alter glycoprotein synthesis will be discussed with particular emphasis on the significance of these alterations to the biology of the malignant cell. Changes in surface membrane glycoproteins have long been implicated in the ability of a cell to metastasize. Secretion and/or shedding of the cell surface may also be important in the process of metastasis and in altering the host immune response. Detection and the study of these "shed" materials in patients appear to be indicating a new approach to cancer biology detection and therapy.

Animals↗
PubMed1981

Release of glycosyltransferase and glycosidase activities from normal and transformed cell lines.

The release of galactosyltransferase, sialyltransferase, and several glycosidase activities into the growth media from several normal and transformed cell lines was examined. Six of the seven cell lines released galactosyltransferase into their culture media. Only the human leukemia CCRF-CEM cells failed to release demonstrable galactosyltransferase activity. Release of galactosyltransferase activity into the media closely paralleled the growth curves for all but the BHKpy cells. These cells continued to release peak levels of galactosyltransferase activity into the culture media after their growth had plateaued. Media galactosyltransferase activity was unaffected by Triton X-100 treatment had remained in the supernatant fraction of a 100,000 X g, 12-hr centrifugation, suggesting that the cells release galactosyltransferase in a soluble form. In contrast to galactosyltransferase activity, only one of the cell lines (L1210) released sialyltransferase activity in appreciable amounts. Even this level of activity was 20-fold less than that observed for galactosyltransferase in the media from L1210 cells. Of the nine glycosidase activities assayed, only N-acetylglucosaminidase was observed in significant amounts in the media from all but the CCRF-CEM cells. However, N-acetylglucosaminidase release did not correlate closely with cell growth. These findings suggest a relatively specific release of galactosyltransferase and N-acetylglucosaminidase activities by cells in tissue culture. Moreover, the release of galactosyltransferase closely parallels cell growth. The significance of these released enzymes, especially to cell growth, has yet to be determined.

Acetylglucosaminidase↗
PubMed1981

Systemic lupus erythematosus and intestinal venulitis.

A 22-yr-old woman with a 7-yr history of systemic lupus erythematosus presented with anasarca and a serum albumin of 0.8 g/dl. Renal and hepatic function were near normal; the major route of protein loss appeared to be the intestine. A full-thickness section of jejunum obtained at laparotomy demonstrated a severe, diffuse vasculitis involving the venules of the submucosa and muscularis externa with infiltration of polymorphonuclear leukocytes and macrophages, and deposits of C3. There was a similar focal damage of the walls of the small vessels in the lamina propria, and deposits of C3 and fibrinogen in a thickened basement membrane of the intestinal villi. This report documents that in systemic lupus erythematosus the intestine can be affected with a vasculitis similar to that seen in the skin and can cause thickening of the basement membrane of intestinal villi. These lesions may be responsible for protein-losing enteropathy.

Adolescent↗