Sialyltransferase Research Articles

Repression of the Lewis fucosyl transferase by retinoic acid increases apical sialosyl Lewis(a) secretion in colorectal carcinoma cultures.

The rate of polarised secretion of sialosyl Lewis(a)(19-9) molecular species (SiaLeams) by SW1116 colorectal carcinoma cells is stimulated at least ninefold by the presence of 3 microM retinoic acid (RA). In order to investigate the intracellular origins of this augmentation, carcinoma cell membranes, membrane subfractions, and media were studied to determine alterations in sialosyl Lewis(a) levels, oligosaccharide composition, and core structures accompanying the capacity to increase export of this epitope. We observed a nine- to twentyfold increase in sialosyl Lewis(a) epitope levels in a light membrane subfraction from RA-treated cells. Antigenic molecules of < 200,000 M(r) on acrylamide gradient gels were concentrated in two doublets in the apparent M(r) range 106,000-152,000 on Western blots. Carbohydrate analyses of oligosaccharides from SiaLeams of membrane subfractions and apical media indicated much higher fucose/mannose, fucose/sialic, fucose/sialosyl Lewis(a), fucose/total CHO, and (3H) fucose incorporation in control samples than RA samples. Western blots of samples from membrane subfractions and media indicated that, in contrast to the effect of RA on the sialosyl Lewis(a) epitope, RA treatment did not augment cysteine-rich, PDTRP, blood group H-2, blood group A, and EGF receptor-like region epitopes in the media. In addition, Northern blots using the Lewis fucosyl transferase (FTIII) cDNA showed a dramatic diminution of mRNA encoding FTIII but apparently unaltered levels of sialyl transferase (ST4) mRNA. Since subterminal fucosylation of lactosyl termini blocks terminal sialylation, we conclude that one mechanism of sialosyl Lewis(a) induction in this culture system is the lower expression of the Lewis fucosyl transferase mRNA. Therefore less subterminal fucosylation of GlcNAc permits the prior sialylation of terminal Gal beta 1-3 moieties at oligosaccharide termini destined for export from the Golgi.

The Effect of the Protein Matrix Proximity on Glycan Reactivity in a Glycoprotein Model

A series of biotinylated glycan-Asn derivatives has been synthesized containing either no extension arm between biotin and Asn (glycan-biotinyl Asn) or containing HN(CH2)nCO extension arms of differing lengths, where n denotes the number of methylene groups in the arm (glycan-biotinyl[HN(CH2)nCO]Asn, n = 1-5). The glycan structures used were Man6GlcNAc2-, Man5GlcNAc2-, GlcNAcMan5GlcNAc2- and Gal2GlcNAc2Man3GlcNAc2-, the substrates for mannosidase I, GlcNAc transferase I, mannosidase II and sialyltransferase, respectively. Each family of substrates was subjected to the action of its respective enzyme in the absence and in the presence of streptavidin, and the relative rate of processing (in the presence of UDP-GlcNAc and the mannosidase II inhibitor, swainsonine for GlcNAc transferase I and CMP-sialic acid for sialyl transferase) was measured to evaluate the effect of the proximity of the protein matrix on the glycan substrate quality. Mannosidase I was found to be strongly inhibited by the protein matrix in the proximal as well as in the distal positions relative to the glycan substrate. In contrast, GlcNAc transferase I and mannosidase II, which were both strongly inhibited by the proximal substrate complexes (no extension arm) showed complete release of the inhibition even with the shortest (n = 1) extension arm. Sialyl transferase showed inhibition of both reaction steps in the proximal complex, and complete release of the inhibition of the first step, but not the second step, in the distal complexes. The results show that the availability of different glycan substrates in a given protein environment reflects, to a great extent, the nature of each individual enzyme. The mechanisms by which the protein matrix affects glycan processing are proposed to involve simple steric effects, as well as more subtle effects of the protein in permitting or preventing certain active glycan conformations to form.

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シアル酸転移酵素の「シアリルモチーフ」の機能は？

Two different glycosyltransferase defects that result in GalNAc alpha-O-peptide (Tn) expression.

This study shows for the first time that different glycosyltransferase defects in the biosynthesis of O-linked oligosaccharides give rise to the same GalNAc alpha-O-Ser/Thr determinant on Tn erythrocytes and colorectal carcinoma cells. The O-linked oligosaccharides isolated from the glycophorins of Tn erythrocytes contained predominantly alpha-N-acetylgalactosamine-O-Ser/Thr (Tn antigen) and sialyl-Tn. A marked reduction in normal sialylated oligosaccharides was also observed. Monoclonal antibody BRIC 111 raised against Tn erythrocytes reacted with both Tn erythrocytes and colorectal carcinoma tissues. Weak staining was detected in the supranuclear area and at the surface membranes in normal colorectal cells, but was absent from goblet cell vesicles. An increase in supranuclear staining over controls was found in tumour tissue and in the majority of resection margin specimens. The highest levels of staining were present in transitional mucosa, adjacent to the tumours where goblet vesicles were also positive. Glycosylation defects in the same patients were further studied by determination of the activity of glycosyltransferases in mucosal tissue from control and cancer patients. The reduction in or loss of beta 1-3 N-acetylglucosaminyl transferase activity to GalNAc-peptide in asialo-ovine submaxillary gland glycoprotein was detected by direct assay and by isolation of the oligosaccharides from the incubation products. No differences in N-acetylglucosaminyl-, galactosyl- or sialyl-transfer to Gal beta 1-3GalNAc in antifreeze glycoprotein or in sialyl transferase to asialo-ovine submaxillary gland glycoprotein were detected. Our study shows that the GalNAc alpha-O-Ser/Thr determinant on Tn erythrocytes and in colorectal carcinoma results from different glycosyltransferase defects in separate biosynthetic pathways for haematopoietic and epithelial tissues.

Sialylation of lipopolysaccharide by CMP-NANA in viable gonococci is enhanced by low M r material released from blood cell extracts but not by some UDP sugars

Serum resistance of gonococci in most patients is due to sialylation of a Galβ1-4GlcNAc group on a conserved 4.5 kDa lipopolysaccharide (LPS) component by host cytidine 5′-monophospho-N-acetyl neuraminic acid (CMP-NANA) catalysed by a gonococcal sialyl transferase. This sialylation is enhanced by a low M r factor(s) which, like CMP-NANA, is released in diffusates from high M r fractions obtained from sonicates dialysed at 4°C. Also, as shown here, this factor(s) is released when the sonicates are dialysed at 18-20°C. The enhancement of sialylation, first demonstrated using enzymes in gonococcal extracts, has been shown to occur in live gonococci and hence probably to have a role in pathogenicity. Gonococci, emerging from lag phase and incubated for 2 h with CMP- 14CNANA fixed up to 90% more radiolabel than controls when the second factor(s) was present; their LPS separated by SDS-PAGE contained more radiolabel than control samples and label was not detected in any other component. Fractions with enhancing activity absorbed maximally at about 260 nm but a mixture of UDP-galactose (UDP-Gal), UDP-N-Acetyl galactosamine (UDP-GalNAc), UDP-glucose (UDP-Glc) and UDP-N-Acetyl glucosamine (UDP-GlcNAc) showed no significant enhancing activity. The enhancing action of the low M r fractions was unaffected by incubation with β-galactosidase.

HLA class I molecules are not transported to the cell surface in cells infected with herpes simplex virus types 1 and 2.

To assess the effect of herpes simplex virus (HSV) on assembly and transport of class I MHC molecules, we compared class I MHC immunoprecipitated from metabolically labeled infected and uninfected human dermal fibroblasts. The immunoprecipitates were analyzed by isoelectric focusing, allowing identification of individual class I alleles and assessment of transport through the Golgi apparatus by the sialation of carbohydrate residues. In cells infected with wild-type HSV, class I synthesis was reduced or abolished because of the host protein synthesis shutoff function of the UL41 gene product. In cells infected with mutant viruses of both HSV-2 strain G and HSV-1 strain 17 that lack the UL41 gene, class I HLA molecules failed to become sialated, suggesting that they were not transported to the Golgi apparatus. In contrast, transferrin receptor was normally sialated in both infected and uninfected cells. Drug treatments of cells to restrict viral gene expression suggested that an early gene or genes were responsible for the effect. A pulse chase showed that class I molecules were synthesized in normal amounts in infected cells, but that heavy chains were retained in a sialyl transferase negative compartment either stably associated with beta 2m or as free heavy chain in a pattern that is characteristic for each class I allele. HSV is thus the fourth example of a DNA virus that interferes with class I assembly or transport.

Human beta 1,4 galactosyltransferase and alpha 2,6 sialyltransferase expressed in Saccharomyces cerevisiae are retained as active enzymes in the endoplasmic reticulum.

Biosynthesis and intracellular transport of recombinant human full-length beta 1,4 galactosyltransferase (GT) and full-length alpha 2,6 sialyltransferase (ST) were investigated in Saccharomyces cerevisiae. Recently, enzymic activity of recombinant GT (rGT) in crude homogenates of S. cerevisiae could successfully be demonstrated [Krezdorn, C., Watzele, G., Kleene, R. B., Ivanov, S. X. & Berger, E. G. (1993) Eur. J. Biochem. 212, 113-120]. In the present work, we show that, in yeast strains transformed with plasmid pDPSIA containing the cDNA coding for human ST, rST enzymic activity using asialo-fetuin or N-acetyllactosamine as acceptor substrates could readily be detected. Analysis by 1H-NMR spectroscopy of the disaccharide product of rGT, as recently reported, and the trisaccharide product of rST demonstrated that only the expected glycosidic linkages were formed. Following mechanical disruption of yeast cells, both enzymes sedimented with a fraction enriched in membranes of the endoplasmic reticulum (ER) and were activated by Triton X-100 3-5-fold. rGT and rST could be immunoprecipitated from their [35S]Met-labelled transformed yeast extracts using polyclonal antibodies raised against fusion proteins consisting of beta-galactosidase-GT or beta-galactosidase-ST, respectively, expressed in Escherichia coli. For rGT a single glycosylated form of apparent molecular mass 48 kDa was reported, but for rST two main bands corresponding to apparent molecular masses of 48 kDa and 44 kDa, respectively, were detected. Immunoprecipitation from either tunicamycin-treated [35S]Met-labelled transformed yeast cells or labelling with radio-active sugars both indicated that the 44-kDa form of rST was non-glycosylated and that the 48-kDa form of rST was core N-glycosylated. In addition, core glycosylation of both recombinant enzymes demonstrated that they were competent for translocation across the ER membranes. However, the 44-kDa form of rST was converted to the 48-kDa glycosylated form only slowly, suggesting a mechanism of posttranslational translocation. Absence of hyperglycosylation of rST and rGT in wild type and lack of the Golgi-specific man-alpha 1,6-man epitope suggest that the recombinant enzymes did not enter the yeast Golgi apparatus. These results indicated that both rGT and rST are retained as enzymically active enzymes in the ER of yeast and suggest a ribonucleoprotein-independent import of rST into the ER.

Sialylation and malignant potential in tumour cell glycosylation mutants.

Somatic mutations and drugs that either reduce beta 1-6GlcNAc-branching of N-linked oligosaccharides or block the addition of terminal sequences containing galactose and sialic acid have been shown to inhibit tumour growth and metastasis. In an attempt to further define the oligosaccharide sequences that contribute to the malignant phenotype, we have selected spontaneous wheat germ agglutinin-resistant (WGAR) mutants from highly metastatic murine lymphoid tumour cells and characterized four mutant phenotypes. Mutants were selected from VM4, a clone of the MDAY-D2 tumour cell line which had been transfected with the bacterial beta-galactosidase gene (LacZ). VM4 cells retained the malignant phenotype of MDAY-D2 and the cells expressed LacZ, which facilitated the counting of metastases as the tumour cells stained blue when incubated with 5-bromo-4-chloro-3-indolyl beta-D-galactopyranoside (X-gal). The most frequently isolated mutant was defective in the transport of UDP-Gal into the Golgi, and as previously observed for this mutation, the cells were non-metastatic and produced very slow-growing solid tumours. Mutants expressing CMP-SA hydroxylase, and consequently glycoconjugates with N-glycolylneuraminic acid (NeuNGc), remained highly metastatic, but grew more slowly than VM4 cells as s.c. tumours in mice. A novel WGAR mutant showing a large increase in Gal beta 1-4GlcNAc:alpha 2-6 sialyltransferase (SA-T) mRNA levels (ST6N) and enzyme activity was observed to be less metastatic and also grew more slowly at the s.c. site of inoculation. Finally, a fourth phenotypic class of WGAR mutants showed a complex phenotype including expression of a beta Gal-binding cell surface lectin and reduced sialylation of glycoconjugates. These results suggest that changes in either the amount, the type or linkage of sialic acid in tumour cell glycoconjugates can affect tumour growth and metastasis.

Defective acidification of the biosynthetic pathway in cystic fibrosis.

Cystic fibrosis is associated with defective epithelial sodium chloride and fluid secretion in epithelia. In addition, there is widespread reductions in sialylation of secreted proteins and increases in the sulfation and fucosylation of mucus glycoproteins. The major morbidity in the disease is due to the colonization of respiratory epithelia by Pseudomonas. The cystic fibrosis gene (CFTR) is a cyclic AMP activated Cl channel, which when mutated is retained in the endoplasmic reticulum. We postulate that this Cl channel is responsible for effective acidification of the Golgi. In CF cells, we demonstrate the Golgi pH is higher than in normal cells and suggest that the abnormalities in glycoprotein biosynthesis is due to changes in the kinetics of sialyl transferase, a pH sensitive enzyme. Defects in sialylation also result in decreased sialylation of glycolipids and asialogangliosides are potential Pseudomonas receptors.

Effects of S-carboxymethyl-L-cysteine on pulmonary sialyl transferase activity in vitro, in healthy and in sulphur-dioxide-induced bronchitic rats.

S-carboxymethyl-L-cysteine (carbocysteine) improves the visco-elastic properties of bronchial mucus in vivo, possibly as a result of an increase in the relative proportions of sialomucins in bronchial mucus. Carbocysteine was therefore studied in vitro and ex vivo in both normal and bronchitic rats on pulmonary sialyl transferase, responsible for the addition of sialic acid to mucus glycoproteins. Bronchitis was induced in male Sprague-Dawley rats by repeated exposure to sulphur dioxide for two weeks. During this time they received either 500 mg kg-1 day-1 carbocysteine or its vehicle by the oral route. Rats not being exposed to SO2 received the same treatment. The animals were then killed, and subcellular fractions prepared by differential centrifugation of lung homogenates. Sialyl transferase was assayed using CMP-14C sialic acid as substrate and desialysed fetuin as exogenous acceptor. Enzyme activity was located in both the (Golgi-containing) 10,000 g and 100,000 g pellets with minor activity in the cytosolic supernatants. When tested in vitro between 10(-6) and 10(-3) M, carbocysteine had no effect on sialyl transferase activity in microsomes taken from healthy or bronchitis rats. Repeated administration of carbocysteine was without effect on the sialyl transferase activity in 10,000 g pellets taken from healthy rats. However, in bronchitic rats there was a small but statistically significant (P less than 0.05) increase in enzymic activity in the treated group compared to the animals receiving the vehicle. There was no difference in the activity of the microsomal enzyme compared to vehicle-treated controls in either healthy or bronchitic rats. We conclude that it is possible that an increase in sialyl transferase activity in a Golgi-containing fraction of bronchitic lungs could explain the relative increase in sialomucins in bronchitic subjects.

Chemoenzymatic synthesis of a glycosphingolipid

The novel glycosphingolipid 7 is synthesised by two successive enzymatic glycosylation steps from 5 using a β(1–4)-galactosyl transferase and an α(2–6)-sialyl transferase, both of which are commercially available.

Changes in the ganglioside composition of human neuroblastoma cells under different growth conditions

The ganglioside composition of human neuroblastoma cells (LA-N-1 and LA-N-5) was studied in samples obtained from (1) original cells in tissue cultures, (2) tumors grown in nude mice inoculated with original cells and (3) cells in tissue cultures re-established from the mouse tumors. The amounts of "a" pathway gangliosides (GM2, GM1 and GD1a) and those of the "b" pathway (GD3, GD2, GD1b and GT1b) differed according to the culture conditions. The "b" pathway gangliosides were markedly increased in the tumors grown in nude mice. In contrast, the "a" pathway gangliosides were abundant in cultures of both original and re-established cells. We also measured the enzymatic activities of UDP-N-acetylgalactosamine: GM3, N-acetylgalactosaminyl transferase (EC 2.4.1.92) and of CMP-N-acetylneuraminic acid: GM3 sialyl transferase (EC 2.4.99.8) in neuroblastoma cells cultured under these conditions. These enzymes are thought to be the key enzymes involved in the synthesis of the "a" and "b" pathway gangliosides. Though there was no significant difference in the activity of N-acetylgalactosaminyl transferase between original cells and tumors in nude mice, re-established cells showed a definitely higher activity (3.5 times higher than in the original cells). On the other hand, tumors grown in nude mice had a markedly higher activity of sialyl transferase than that of original cells or re-established cells. These findings suggest that the culture conditions and/or the type of cell growth play some role in the synthesis and expression of gangliosides in neuroblastoma cells.

EVIDENCE FOR REGION-SPECIFIC REGULATION AND CORTISONE INDUCTION OF SIALYLTRANSFERASE mRNA EXPRESSION IN THE DEVELOPING INTESTINE

The immature intestinal epithelium is characterized by increased sialyltransferase (ST) activity that controls the sialylation of glycoproteins and glycolipids. Cell-surface sialic acid with specific glycosidic linkages may serve as a receptor determinant for certain viruses, bacteria and their toxins, and thereby may increase the host susceptibility in neonates. Further study of the rat small intestine reveals that developmental changes in ST activity occurred primarily in the distal (ileal), but not in the proximal (jejunal) region. Furthermore, the Galβl, 4GlcNAc α2, 6-ST activity, but not the Galβl, 4GlcNAc α2, 3-ST activity, was the major ST activity under developmental regulation. Northern blots of total RNA prepared from the proximal and distal small intestine of neonatal and adult rats were probed with a cDNA clone encoding the rat liver α2, 5-ST (a gift of Dr. James C. Paulson, UCLA). The data show that α2, 6-ST mRNA expression was age-dependent and regionally specific, with the highest level of mRNA expressed in the immature distal gut. Cortisone, a known transciption modulator, when injected into suckling rats, induced expression of ST mRNA only In the distal intestine. A parallel induction of distal ST activity by cortisone was also noted. This study indicates that the levels of ST activity are well correlated with the levels of ST mRNA and suggests that developmental variation in the intestinal ST activity is mainly caused by the control of the steady state levels of ST mRNA.

Protein matrix effects on glycan processing by mannosidase II and sialyl transferase from rat liver.

The effect of the protein environment on the reaction sequence and the relative rates of two two-step reactions involved in the biosynthesis of complex glycans in glycoproteins has been explored by comparing the processing of biotinylated substrates either free or bound to avidin. By use of biotinyl and biotinamidohexanoyl derivatives, the display of the glycan in a proximal and distal association with the avidin surface could also be assessed. Mannosidase II removes two Man residues from the substrate GlcNAcMan5GlcNAc2-R to yield GlcNAcMAn3GlcNAc2-R. The NMR spectra of the substrate, intermediate, and product showed that the first Man is removed from the 6-arm of the substrate. The rate constants for the first and second step (estimated by direct analysis of the reactants by anion-exchange chromatography with a pulsed amperometric detector) were determined to be about 0.05 and 0.08 min-1, respectively, for the free substrates. In the proximal complex k1 was reduced 80-fold, and the k2 step could not be observed under the same conditions. In the distal complex both k1 and k2 were reduced about 8-fold. Sialyl transferases transfer Sia from CMP-Sia to the biantennary substrate Gal2GlcNAc2-Man3GlcNA2-R to yield the product Sia2Gal2-GlcNAc2Man3GlcNAc2-R with the Sia linked either 2-3 or 2-6 to the Gal residues. The NMR spectra showed that the first step involved the Gal on the 3-arm of the substrate and that both Sia residues were added 2-6.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of 12‐O‐Tetradecanoyl Phorbol‐13‐Acetate (TPA) on Rat Thymocytes

The short-term incubation of rat thymocytes with 12-O-tetradecanoylphorbol-13-acetate (TPA) resulted in a significant increase in sialyltransferase (S-T) activity and a decrease in terminal deoxyribonucleotidyl transferase (TdT) activity. The ratio of peanut agglutinin (PNA)-positive cells and of TdT-positive cells in TPA-treated cells also decreased. However, TPA had no significant effects on the viability, morphology, DNA synthesis, and DNA polymerase alpha activity of the cells. More marked changes were observed by incubating a non-T, non-B human lymphoid leukaemia cell line with TPA. Similar findings were also noted in TPA-treated mouse thymocytes. These changes may represent an aspect of TPA-induced differentiation of murine thymocytes.

Biosynthesis of sialosyllactotetraosylceramide in human colorectal carcinoma cells

A monosialoganglioside, IV 3-NeuNAcLcOse 4Cer, has recently been detected in colorectal carcinoma cells, small cell lung carcinoma cells, embryonal carcinoma cells and in human brain extracts. We report here the presence of a CMP-sialic: LcOse 4Cer sialyl transferase activity in subcellular membrane fractions of the human colorectal carcinoma, SW1116, which recognizes the non-reducing terminal galactosyl moiety of lactotetraosylceramide. A convenient method for structural analysis of picomolar quantities of the radioactive enzymatic product(s) using bacterial endoglycoceramidase, sialidase and a viral sialidase is presented.

Sialyl transferase in human semen.

The activity of the enzyme sialyl transferase, which is responsible for the transfer of sialic acid, has been examined in the following human seminal plasma: (1) originating from semen with sperm counts above 30 X 10(6)/ml and exhibiting normal values of other andrological parameters; (2) from semen with sperm counts below 25 X 10(6)/ml and with other andrological parameters of poor quality; (3) from semen devoid of sperm. Additionally, enzyme activity was examined in fractionated (split) semen. The activity in plasma based on measurement of radioactivity incorporated into asialofetuin, following incubation in the presence of 14C sialic acid, was expressed as cpm both per volume and per mg protein. There was a tendency for decreased activity with the decrease in sperm density of semen. The difference, however, lacked statistical significance. Enzyme activity in split semen was significantly lower in the first than in the second fraction.

Direct sialic acid transfer from a protein donor to glycolipids of trypomastigote forms of Trypanosoma cruzi

Labeled sialoglycolipids were purified from tissue culture-derived trypomastigotes incubated with [ 3H]fetuin. Thin layer chromatography of [ 3H]sialoglycolipids showed three components with the same migration as gangliosides extracted from parasites incubated with [ 3H]palmitic acid. Neuraminidase treatment or mild acid hydrolysis confirmed the presence of [ 3H]sialyl residues in sialoglycolipids synthesized after [ 3H]fetuin incubation. Labeling was not observed when parasites were incubated with free [ 3H]sialic acid (C 7 derivative), suggesting that sialyl residues are directly transferred in vivo to gangliosides, by an enzymatic reaction possibly catalysed by a sialyl transferase (transglycosylase). Sonicated extracts of trypomastigotes incubated with [ 3H]fetuin catalysed the labeling of endogenous glycoconjugates as well as of bovine brain gangliosides. The transglycosylase activity was found associated with the particulate fraction and could be solubilized with Triton X-100. The specific activity of the sialic acid transglycosylase in epimastigotes is 17% of that found in trypomastigotes. Addition of an excess free sialic acid did not inhibit the reaction, suggesting that transfer does not occur via a pool of free sialic acid.

IN UTERO CORTISONE ALTERS THE INTESTINAL SIALYL-AND FUCOSYLTRANSFERASE ACTIVIES IN NEWBORN RATS

Changes in intestinal surface carbohydrates, such as sialic acid and fucose, may influence the binding of membrane receptors to bacteria/toxins or antigens. We have recently reported (Biochim. Biophys. Acta 883, 496, 1986) that the activities of intestinal sialyltransferase (ST) and fucosyltransferase (FT) are reciprocally related and modulated by cortisone during postnatal development. These glycosyl-transferase changes may provide an enzyme basis for the shift from sialylatipn to fucosylation of the intestinal surface during maturation. To further study whether prenatal treatment of cortisone may affect the activities of these two enzymes, cortisone (20 mg/100 g body weight) was injected i.p. in pregnant rats daily beginning at 17 days of gestation. The newborn rats (<24 hr old) were sacrificed and ST and FT were assayed in the membranous (105,000 × g pellet) fraction of small intestine, using asialofetuin as an exogenous acceptor. The results show that the activity of ST was decreased by 50% in the newborn rat exposured to cortisone in utero, while the activity of FT in the cortisone-treated group was induced 2-3 fold compared to the control. This study indicates that cortisone seems able to act as a signal in utero to modulate the expression of intestinal ST and FT and suggests that the cortisone-induced changes in intestinal glycosyltransferases may play a role in the maturation of the mucosal barrier in neonates. (Support by NIH grant DK37521).

Mitogen-induced changes in sialyltransferase activity in human normal and leukemic lymphocytes.

Phytohemagglutinin-P (PHA-P) and concanavalin A (Con A) induced an increase in sialyltransferase (S-T) activity of the blood lymphocytes within 24 hours. PHA-P induced the maximal increase in S-T activity in the lymphocytes at 10 micrograms/ml and with Con A at 5 micrograms/ml. PHA-P induced a greater response than that by Con A. An additional effect of these mitogens was not observed. The exposure of cell extracts to these mitogens did not induce the increase in S-T activity. PHA-P or Con A had no effect on the induction of terminal deoxynucleotidyl transferase (TdT) activity, TdT-positive cells or peanut agglutinin (PNA)-positive cells from blood lymphocytes. Therefore, the change of the lymphocytes induced by these mitogens does not indicate a reversion to more immature state of lymphocyte differentiation, but represents a process of the functional differentiation to more activated lymphocytes. These mitogens had only a slight effect on S-T activity of human T-lymphoid leukemia cell lines. The decreased effects of the mitogens on S-T activity of leukemic cells may reflect the change of the membranes due to malignant transformation or the incomplete membrane structure in undifferentiated leukemic cells.