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PubMed1974

Regulation of hexose phosphate metabolism in Acetobacter xylinum.

The metabolism of glucose and fructose was studied in resting succinate-grown cells of Acetobacter xylinum. From fructose only cellulose and CO(2) were formed by the cells, whereas from glucose, gluconate was formed much more rapidly than these two products. The molar ratio of sugar converted into cellulose to sugar converted into CO(2) was significantly greater than unity for both hexoses. The pattern of label retention in the cellulose formed by the cells from specifically (14)C-labelled glucose, fructose or gluconate corresponded to that of hexose phosphate in a pentose cycle. On the other hand, the isotopic configuration of cellulose arising from variously singly (14)C-labelled pyruvate did not agree with the operation of a pentose cycle on gluconeogenic hexose phosphate. Readily oxidizable tricarboxylic acid-cycle intermediates such as acetate, pyruvate or succinate promoted cellulose synthesis from fructose and gluconate although retarding their oxidation to CO(2). The incorporation into cellulose of C-1 of fructose was greatly increased in the presence of these non-sugar substrates, although its oxidation to CO(2) was greatly diminished. It is suggested that the flow of hexose phosphate carbon towards cellulose or through the pentose cycle in A. xylinum is regulated by an energy-linked control mechanism.

Acetates↗
PubMed1976

Paradoxical effects of cycloheximide and cytochalasin B on hamster cell hexose uptake.

Cellular regulation of hexose uptake was studied in cultures of NIL hamster cells. Enhancements of galactose uptake were elicited most strikingly by maintaining confluent NIL cultures in culture media devoid of glucose. These glucose-starved cultures showed up to 8- or 9-fold enhancements in the galactose uptake test. When these cultures were treated for extended periods with cycloheximide, the enhanced uptake was left unimpaired, whereas the uptake by glucose-fed cells, similarly treated with cycloheximide, was inhibited greater than 90%. Addition of glucose to these starved cultures resulted in a gradual decline of uptake rates to the unenhanced level (t1/2 approximately 3 hr). In surprising contrast, when both glucose and cycloheximide were added simultaneously, the decline was arrested for at least 12 hr. If cytochalasin B (the specific inhibitor of hexose transport) was present, the uptake of galactose by both starved and fed cells was close to completely inhibited. By several criteria, cells maintained for 24 hr in medium containing both glucose and cytochalasin B were glucose-fed. Yet, when the cytochalasin B was removed, the cells were found to have enhanced rates of galactose uptake. The regulation of the hexose uptake system may therefore not be guided by the levels of glucose catabolites. Alternative mechanisms that may control hexose uptake are considered.

Biological Transport↗
PubMed1995

Human beta-cell glucokinase. Dual role of Ser-151 in catalysis and hexose affinity.

Glucokinase is distinguished from yeast hexokinase and low Km mammalian hexokinases by its low affinity for glucose and its cooperative behavior, even though glucose binding residues and catalytic residues are highly conserved in all of these forms of hexokinase. The roles of Ser-151 and Asn-166 as determinants of hexose affinity and cooperative behavior of human glucokinase have been evaluated by site-directed mutagenesis, expression and purification of the wild-type and mutant enzymes, and steady-state kinetic analysis. Mutation of Asn-166 to arginine increased apparent affinity for both glucose and ATP by a factor of 3. Mutation of Ser-151 to cysteine, alanine, or glycine lowered the Km for glucose by factors of 2-, 26-, and 40-fold, respectively, decreased Vmax, abolished cooperativity for glucose, and also decreased Km for mannose and fructose. The Ser-151 mutants had hexose Km values similar to those of yeast hexokinase, hexokinase I, and the recombinantly expressed COOH-terminal half of hexokinase I. However, the Ki values for the competitive inhibitors, N-acetylglucosamine and glucose-6-P, were unchanged, suggesting that Ser-151 is not important for inhibitor binding. Mutation of Ser-151 also increased the Km for ATP about 5-fold and abolished the enzyme's low ATPase activity, which indicates it is essential for ATP hydrolysis. The substrate-induced change in intrinsic fluorescence of S151A occurred at a much lower glucose concentration than that for wild-type enzyme. The results implicate a dual role for Ser-151 as a determinant of hexose affinity and catalysis, exclusive of the glucose-induced conformational change, and suggest that the low hexose affinity of glucokinase is dependent on interaction of Ser-151 with other regions of the protein.

Acetylglucosamine↗
PubMed2004

Crystal structure of WbpP, a genuine UDP-N-acetylglucosamine 4-epimerase from Pseudomonas aeruginosa: substrate specificity in udp-hexose 4-epimerases.

The O antigen of lipopolysaccharide in Gram-negative bacteria plays a critical role in bacterium-host interactions, and for pathogenic bacteria it is a major virulence factor. In Pseudomonas aeruginosa serotype O6 one of the initial steps in O-antigen biosynthesis is catalyzed by a saccharide epimerase, WbpP. WbpP is a member of the UDP-hexose 4-epimerase family of enzymes and exists as a homo-dimer. This enzyme preferentially catalyzes the conversion between UDP-GlcNAc and UDPGalNAc above UDP-Glc and UDP-Gal, using NAD(+) as a cofactor. The crystal structures of WbpP in complex with cofactor and either UDP-Glc or UDP-GalNAc were determined at 2.5 and 2.1 A, respectively, which represents the first structural studies of a genuine UDP-GlcNAc 4-epimerase. These structures in combination with complementary mutagenesis studies suggest that the basis for the differential substrate specificity of WbpP is a consequence of the presence of a pliable solvent network in the active site. This information allows for a comprehensive analysis of the relationship between sequence and substrate specificity for UDP-hexose 4-epimerases and enables the formulation of consensus sequences that predict substrate specificity of UDP-hexose 4-epimerases yet to be biochemically characterized. Furthermore, the examination indicates that as little as one residue can dictate substrate specificity. Nonetheless, phylogenetic analysis suggests that this substrate specificity is an evolutionary and highly conserved property within UDP-hexose 4-epimerases.

Binding Sites↗
PubMed2006

Structure-based functional annotation: yeast ymr099c codes for a D-hexose-6-phosphate mutarotase.

Despite the generation of a large amount of sequence information over the last decade, more than 40% of well characterized enzymatic functions still lack associated protein sequences. Assigning protein sequences to documented biochemical functions is an interesting challenge. We illustrate here that structural genomics may be a reasonable approach in addressing these questions. We present the crystal structure of the Saccharomyces cerevisiae YMR099cp, a protein of unknown function. YMR099cp adopts the same fold as galactose mutarotase and shares the same catalytic machinery necessary for the interconversion of the alpha and beta anomers of galactose. The structure revealed the presence in the active site of a sulfate ion attached by an arginine clamp made by the side chain from two strictly conserved arginine residues. This sulfate is ideally positioned to mimic the phosphate group of hexose 6-phosphate. We have subsequently successfully demonstrated that YMR099cp is a hexose-6-phosphate mutarotase with broad substrate specificity. We solved high resolution structures of some substrate enzyme complexes, further confirming our functional hypothesis. The metabolic role of a hexose-6-phosphate mutarotase is discussed. This work illustrates that structural information has been crucial to assign YMR099cp to the orphan EC activity: hexose-phosphate mutarotase.

Amino Acid Sequence↗
PubMed1992

In Vitro Analysis of the H-Hexose Symporter on the Plasma Membrane of Sugarbeets (Beta vulgaris L.).

The mechanism of hexose transport into plasma membrane vesicles isolated from mature sugarbeet leaves (Beta vulgaris L.) was investigated. The initial rate of glucose uptake into the vesicles was stimulated approximately fivefold by imposing a transmembrane pH gradient (DeltapH), alkaline inside, and approximately fourfold by a negative membrane potential (DeltaPsi), generated as a K(+)-diffusion potential, negative inside. The -fold stimulation was directly related to the relative DeltapH or DeltaPsi gradient imposed, which were determined by the uptake of acetate or tetraphenylphosphonium, respectively. DeltaPsi- and DeltapH-dependent glucose uptake showed saturation kinetics with a K(m) of 286 micromolar for glucose. Other hexose molecules (e.g. 2-deoxy-d-glucose, 3-O-methyl-d-glucose, and d-mannose) were also accumulated into plasma membrane vesicles in a DeltapH-dependent manner. Inhibition constants of a number of compounds for glucose uptake were determined. Effective inhibitors of glucose uptake included: 3-O-methyl-d-glucose, 5-thio-d-glucose, d-fructose, d-galactose, and d-mannose, but not 1-O-methyl-d-glucose, d- and l-xylose, l-glucose, d-ribose, and l-sorbose. Under all conditions of proton motive force magnitude and glucose and sucrose concentration tested, there was no effect of sucrose on glucose uptake. Thus, hexose transport on the sugarbeet leaf plasma membrane was by a H(+)-hexose symporter, and the carrier and possibly the energy source were not shared by the plasma membrane H(+)-sucrose symporter.

Journal Article↗
PubMed1975

Stimulation by propylthiouracil of the hexose monophosphate shunt in human polymorphonuclear leucocytes during phagocytosis.

The effect of propylthiouracil on glucose metabolism in human polymorphonuclear leucocytes was studied. At a therapeutically achievable concentration (0.1 mM), propylthiouracil stimulated hexose monophosphate shunt activity in normal leucocytes during phagocytosis but not in resting cells. However, in the presence of hydrogen peroxide it stimulated hexose monophosphate shunt activity in resting cells, and in the soluble fraction when reduced glutathione and reduced nictotinamide adenine dinucleotide phosphate (NADPH) were also present. Propylthiouracil had nor effect on glucose-1-C oxidation in either phagocytosing or resting leucocytes obtained from two male patients with chronic granulomatous disease. Stimulation of the hexose monophosphate shunt activity in normal leucocytes during phagocytosis also was demonstrated with methimazole, thiouracil and thiourea, but not with adenine, uracil or urea. There was an apparent minimal common structure requirement in thriourea. Propylthiouracil had no effect on phagocytosis, formate oxidation, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase or catalase activities. Thus, the stimulation of the hexose monophosphate shunt activity by propylthiouracil is dependent on hydrogen peroxide and is best explained by its stimulation or participation in the glutathione cycle.

Blood Glucose↗
PubMed1977

Transport of hexoses across the liver-cell membrane.

The uptake of radioactively labelled hexoses into the cellular space of isolated liver cells has been studied using silicone layer filtering centrifugation. From the hexoses tested, D-glucose is transported most rapidly followed by D-galactose and D-fructose. The rate of L-glucose transport is only 5% of that of D-glucose. This transport enables the concentration of free aldohexoses in the cellular space to reach the external concentration. For D-glucose the rate of transport into the cell largely exceeds the rate of metabolic conversion. This is different with D-fructose where the rate of transport is considerably lower but the rate of metabolism higher. Here the transport may even be a limiting step. The transport of D-glucose and D-galactose shows a saturation characteristic, whereas D-fructose appears not to be saturatable. The Km for D-glucose is found to be 30 mM. All these hexoses compete with each other for transportation. The temperature dependency of D-glucose reveals an activation energy of 22 kcal (92 kJ)/mol (4-18 degrees C) and 7 kcal (29 kJ)/mol (18-37 degrees C). The transport of D-glucose, D-galactose and D-fructose in inhibited by cytochalasin B, phloretin and phlorizin. It is not dependent on Na+ ions. Preliminary results showed no stimulation of the transport by insulin. It is concluded that D-glucose and other hexoses are transported by carrier-mediated diffusion across the plasma membrane of liver cells. This transport shows a large resemblance to the transport of D-glucose into human erythrocytes.

Animals↗
PubMed2006

Hexose transporter mRNAs for GLUT4, GLUT5, and GLUT12 predominate in human muscle.

In the past few years, 8 additional members of the facilitative hexose transporter family have been identified, giving a total of 14 members of the SLC2A family of membrane-bound hexose transporters. To determine which of the new hexose transporters were expressed in muscle, mRNA concentrations of 11 glucose transporters (GLUTs) were quantified and compared. RNA from muscle from 10 normal volunteers was subjected to RT-PCR. Primers were designed that amplified 78- to 241-base fragments, and cDNA standards were cloned for GLUT1, GLUT2, GLUT3, GLUT4, GLUT5, GLUT6, GLUT8, GLUT9, GLUT10, GLUT11, GLUT12, and GAPDH. Seven of these eleven hexose transporters were detectable in normal human muscle. The rank order was GLUT4, GLUT5, GLUT12, GLUT8, GLUT11, GLUT3, and GLUT1, with corresponding concentrations of 404 +/- 49, 131 +/- 14, 33 +/- 4, 5.5 +/- 0.5, 4.1 +/- 0.4, 1.2 +/- .0.1, and 0.9 +/- 0.2 copies/ng RNA (means +/- SE), respectively, for the 10 subjects. Concentrations of mRNA for GLUT4, GLUT5, and GLUT12 were much higher than those for the remainder of the GLUTs and together accounted for 98% of the total GLUT isoform mRNA. Immunoblots of muscle homogenates verified that the respective proteins for GLUT4, GLUT5, and GLUT12 were present in normal human muscle. Immunofluorescent studies demonstrated that GLUT4 and GLUT12 were predominantly expressed in type I oxidative fibers; however, GLUT5 was expressed predominantly in type II (white) fibers.

Gene Expression↗
PubMed1983

Role of hexose monophosphate shunt in parathyroid hormone secretion.

The metabolism of labeled glucose by collagenase-dispersed bovine parathyroid cells was examined. When the medium calcium ion concentration was increased to 2.0 mM, the rate of 14CO2 release from [1-14C]glucose was increased 169 +/- 45% compared with the rate of 0.5 mM calcium. There was no significant change in the rate of 14CO2 release from [6-14C]glucose by this maneuver. The greatest increase in 14CO2 release and decrease in parathyroid hormone secretion occurred between medium calcium ion concentrations of 0.5-1.5 mM. This difference in the metabolism of glucose represents a true increase in hexose shunt activity because the incorporation of label from either [1-14C]- or [6-14C]glucose into parathyroid tissue lipids was equal. This suggests equilibration of label at the level of triose-phosphates. The increase in hexose shunt activity was not due to a calcium-mediated increase in glucose uptake because calcium changes did not affect 2-[3H]deoxyglucose transport by the cells. Phenazine methosulfate added to cells incubated at 0.5 mM calcium selectively increased hexose shunt activity in a dose-dependent manner (91 +/- 33% overall) and concomitantly inhibited parathyroid hormone secretion 65% overall at 0.5 mM calcium. The compound 6-aminonicotinamide inhibited hexose shunt activity but could not overcome the inhibition of hormone secretion at 2.0 mM calcium. A decrease in protein biosynthesis cannot fully explain the inhibition of hormone secretion by calcium or phenazine methosulfate because [3H]-leucine incorporation into total cell protein was not as affected as secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Stimulation of Na+/H+ exchange by insulin and phorbol ester during differentiation of 3T3-L1 cells. Relation to hexose uptake.

Acute exposure of 3T3-L1 undifferentiated fibroblasts to insulin or 4 beta-phorbol-12,13-dibutyrate (PDB) produced a moderate but significant stimulation of hexose transport (100% stimulation). In differentiated 3T3-L1 adipocytes, stimulation by insulin increased significantly (to 340%), while that by PDB remained at 130%. Total protein kinase C activity was 3-fold higher in 3T3-L1 fibroblast than adipocyte homogenates. PDB, but not insulin, induced migration of protein kinase C from the cytosol to the membrane, in both fibroblasts and adipocytes. Moreover, the hormone increased by 15% the protein kinase C activity of the cytosol. In 3T3-L1 fibroblasts, both insulin and PDB elicited a rapid (2 min lag) cytoplasmic alkalinization, measured with the fluorescent pH indicator bis-carboxyethyl carboxyfluorescein trapped in the cytoplasm. In 3T3-L1 adipocytes, PDB but not insulin elicited the cytoplasmic alkalinization. The alkalinization was prevented by amiloride or by replacing Na+ with either N-methylglucamine+ or K+. Stimulation of hexose transport by insulin or PDB was not affected by amiloride or Na+ substitution. It is concluded that: 1) Insulin and PDB have different effects on protein kinase C activity and subcellular distribution; 2) the responses of Na+/H+ exchange and hexose transport to insulin and PDB develop independently during differentiation of 3T3-L1 cells; 3) stimulation of Na+/H+ exchange and of hexose transport occur in parallel rather than in series in 3T3-L1 cells.

Animals↗
PubMed1989

Antagonism by growth hormone of insulin-sensitive hexose transport in 3T3-F442A adipocytes.

We have studied the effects of GH on basal and insulin-stimulated hexose transport by 3T3-F442A adipocytes in a hormonally defined serum-free medium. Adipocytes preincubated in defined medium exhibit a low level of hexose transport which is acutely (15 min) stimulated (greater than 5-fold) by insulin (EC50, 0.1-0.2 nM). GH has acute (15-45 min) insulin-mimetic (greater than 2-fold) and chronic (4-48 h) diabetogenic (50-80%) effects on basal and insulin-stimulated hexose transport. The insulin-mimetic effect of GH has a higher EC50 (2 nM) than its diabetogenic effect (EC50, 0.2 nM). Chronic GH exposure decreases the maximal responsiveness (50-80%) and the acute sensitivity (approximately 2-fold) of hexose transport to insulin. Insulin-stimulated transport is more (approximately 5-fold) sensitive to the diabetogenic effect of GH than is basal transport. Insulin binding and degradation were not altered by chronic exposure to GH. The diabetogenic effect of GH may occur at a postinsulin binding level.

Adipose Tissue↗
PubMed1992

Stimulation of hexose transport by metformin in L6 muscle cells in culture.

L6 muscle cells grown in culture to the stage of fused myotubes were incubated with the oral hypoglycemic drug metformin to test the effects of this drug on glucose transport. Metformin increased the initial rate of uptake of 2-deoxyglucose and 3-O-methylglucose. The effect was time dependent, with half-maximal stimulation at 5-6 h and maximal stimulation by about 16 h. The stimulation of hexose uptake was not prevented by cycloheximide. In 15 mM glucose medium, the basal rate of transport was lower than in 5 mM glucose medium. The stimulation of hexose uptake by metformin was comparable in absolute units in both media; hence, relative to basal uptake, stimulation was greater in the high glucose medium than in the low glucose medium. In 5 mM glucose medium, half-maximal stimulation was obtained with 800 microM metformin when tested for 24 h. The stimulation of hexose transport by metformin was only detectable in fused myotubes and not in perfusion myoblasts. No significant changes were observed in glucose transporter levels in total cell membranes from L6 myotubes (measured as D-glucose-protectable binding sites for cytochalasin-B) or in the total levels of the immunoreactive glucose transporter isoforms GLUT4 or GLUT1. It is concluded that metformin stimulates hexose transport into differentiated muscle cells by acting at a posttranslational level. We speculate that this might also constitute the basis for the ability of the drug to lower glycemia in diabetic individuals.

3-O-Methylglucose↗
PubMed1976

Immunoglobulin G complex interactions with rheumatoid factor and neutrophils: 51CrCl3 labelling and 14CO2 hexose monophosphate shunt studies.

The interactions of soluble and insoluble IgG complexes with macromolecular rheumatoid factor (RF) and neutrophils have been examined in an in vitro system allowing the separate assay of the biologic activities of these elements in the rheumatoid inflammatory process. Studies utilizing soluble and insoluble 51CrCl3 labelled human IgG complexes have demonstrated uptake of only the insoluble complexes by human neutrophils. A burst of hexose monophosphate shunt activity, as evidenced by increased oxidation of glucose-l-14C to 14CO2, has been shown to occur only when neutrophils are exposed to these insoluble complexes. High titer RF sera added to the insoluble complexes prior to their incubation with neutrophils did not affect either the uptake of the complexes or the magnitude of hexose monophosphate shunt activity. Native IgG and soluble IgG complexes were not taken up by the neutrophils and did not stimulate hexose monophosphate shunt activity in the presence or absence of rheumatoid sera. The addition of high titer RF sera to soluble IgG complexes produced precipitation of RF-IgG complexes which were capable of stimulating hexose monophosphate shunt activity in normal neutrophils. RF thus has been shown to change functionally inactive soluble complexes into functionally active insoluble complexes capable of stimulating normal neutrophils. Neutrophil stimulation by insoluble complexes may be important in the continuing inflammatory process occurring in the joints of patients with rheumatoid arthritis.

Arthritis, Rheumatoid↗
PubMed1976

Differential effects of sulfhydryl reagents on activation and deactivation of the fat cell hexose transport system.

A rapid filtration method was used to measure initial rates of 3-O-[3H]methylglucose uptake and thus estimate hexose transport system activity in isolated white fat cells. Insulin markedly stimulated the transport system activity and its effect was rapidly and completely reversible. In addition, such oxidants as vitamin K5 (50 muM), hydrogen peroxide (4mM), methylene blue (50 muM), and diamide (20 mM) also maximally activated 3-O-methylglucose transport and their effects were not additive to those of maximal concentrations of insulin. These oxidants had no effect on total cellular ATP levels under these conditions. Hexose transport system activity in either the presence or absence of these stimulatory agents was uniformly sensitive to inhibition by cytochalasin B. Treatment of fat cells with either 0.5 mM N-ethylmaleimide or 3 mM dithio(bis)nitrobenzoic acid abolished the ability of insulin or oxidants to activate hexose transport system activity. Control transport activity was not significantly influenced by these agents. Fat cells treated with dithio(bis)nitrobenzoic acid completely regained the ability to respond to insulin or vitamin K5 after removal of the agent by washing in low concentrations of reductant. Elevated rates of transport due to prior incubation of cells with insulin or vitamin K5 were completely resistant to inhibition by subsequent addition of N-ethylmaleimide or dithio(bis)nitrobenzoic acid. Deactivation of the hormone-stimulated transport system could be achieved by washing cells free of insulin or by destruction of insulin-receptor interaction by trypsin. N-Ethylmaleimide effectively blocked deactivation of insulin-stimulated transport system activity, while dithio(bis)nitrobenzoic acid was without effect. These results suggest that distinct cellular components mediate activation versus deactivation of the fat cell hexose transport system. N-Ethylmaleimide, which effectively penetrates fat cells, inhibits both processes while the layer, more polar dithio(bis)nitrobenzoic acid blocks activation but not deactivation of this transport system.

Adipose Tissue↗
PubMed1989

The hexose transporter of human erythrocytes in aging and Alzheimer dementia.

The hexose transporter protein of human erythrocyte membranes was investigated in aging and in demented patients with Alzheimer disease (AD) and Parkinson disease (PD) by assessing the D-glucose-displaceable binding of the ligand cytochalasin-B. We found no alteration in the hexose transporter of erythrocyte membranes in aging or in dementia of AD and PD. These findings indicate that the marked decrease in the density of hexose transporter that we previously reported in the cerebral cortex and brain microvessels in AD do not occur in erythrocyte membranes that have the highest density of the hexose transporter protein.

Adult↗
PubMed1985

Limiting role of 6-phosphogluconolactonase in erythrocyte hexose monophosphate pathway metabolism.

The natural product of the glucose-6-phosphate dehydrogenase reaction is 6-phosphoglucono-delta-lactone, which must be hydrolyzed to 6-phosphogluconic acid before it can be further metabolized by 6-phosphogluconate dehydrogenase. Because this lactone is very unstable, it has been uncertain whether the enzyme that hydrolyzes it, 6-phosphogluconolactonase, is required for functioning of the hexose monophosphate pathway. We have purified glucose-6-phosphate dehydrogenase, 6-phosphogluconolactonase, and 6-phosphogluconate dehydrogenase from human erythrocytes to the point where each enzyme is essentially free of each of the other activities. We constructed an artificial hexose monophosphate pathway from these enzymes, providing as substrate 14C-labeled glucose-6-phosphate either directly or by continual generation from 14C-glucose by yeast hexokinase and adenosine triphosphate. The oxidation of 6-phosphogluconic acid was estimated by measuring the CO2 formed. In the absence of a reduced nicotinamide-adenine dinucleotide phosphate (NADPH)-oxidizing system, such as oxidized glutathione (GSSG)-glutathione reductase or phenazine methosulfate, little CO2 was formed, and the presence of 6-phosphogluconolactonase did not affect the amount that was produced. When the hexose monophosphate pathway was stimulated by providing an NADPH-oxidizing system, CO2 was produced two and a half to five times as fast in the presence of 6-phosphogluconolactonase as in its absence. These studies suggest that 6-phosphogluconolactonase is required for the functioning of the hexose monophosphate pathway when the rate of oxidation of NADPH is accelerated.

Carbon Dioxide↗
PubMed1980

Lack of correlation between effects of tumor promoter TPA on plasminogen activator production, phosphatidyl choline synthesis, and hexose transport in mammalian cell culture systems.

We have investigated the effects of the tumor promoter 12-0-tetradecanoyl-phorbol-13-acetate (TPA) on plasminogen activator production, hexose transport and metabolism, and the incorporation of choline into the acid soluble pool and into phosphatidylcholine in suspension cultures of mouse L, mouse P388 leukemia, human HeLa, and Chinese hamster ovary cells, and in monolayer cultures of baby hamster kidney (BHK), mouse 3T3, mouse 3T6, and mouse P388D1 macrophage-like cells. BHK, 3T3, P388D1, and P388 cells produced plasminogen activator constitutively, but no significant production was observed in the other cell lines. Plasminogen activator production was induced or stimulated by TPA only in P388 cells (10- to 20-fold by 100 ng TPA/ml). On the other hand, phosphatidylcholine synthesis was stimulated by TPA only in HeLa cells, and hexose transport, as measured with 3-0-methyl-D-glucose, only in 3T3 and P388D1 cells, as well as in human lymphocytes. The stimulation of hexose transport occurred more rapidly than the induction of plasminogen activator production and seemed to be part of the mitogenic response of cells to TPA treatment. A stimulation of deoxyglucose uptake was similarly limited to 3T3 and P388D1 cells. A significant decarboxylation of carbon 1 of deoxyglucose occurred in P388 and P388D1 cells, but not in Novikoff cells, and any decarboxylation that occurred was not stimulated by TPA. The results indicate that the various investigated responses of cells to TPA are unrelated and occur independent of each other. The time courses of the biochemical responses also differ significantly.

Animals↗