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M S Liu

Publications and source records attributed to M S Liu.

At least 73 records · Page 4Linked to original sources
PubMed1992

Molecular and developmental studies of a sperm acrosome antigen recognized by HS-63 monoclonal antibody.

A conserved mouse sperm antigen (MSA-63) recognized by a monoclonal antibody (HS-63) was isolated from mouse testes by single-step immunoaffinity chromatography. Isolated MSA-63 preparation was shown to be a group of proteins ranging from 24-84 kDa and with isoelectric points (pIs) ranging from 4.0-6.0 when analyzed by two-dimensional (2-D) gel electrophoresis. Microsequencing techniques were employed to determine the relationships of various protein spots on 2-D gels. Partial amino acid sequences of some protein spots in isolated MSA-63 preparation were shown to be homologous to mouse actins, while others revealed homology only to the SP-10 protein. Rabbit antisera raised against isolated MSA-63 antigen preparation were used to immunoscreen a mouse testis cDNA library. Isolated cDNA clones carrying a 1.2-kb insert were used to obtain nucleotide sequences containing open-reading frames and to deduce the corresponding amino acid sequence of MSA-63. A high degree of homology was observed between MSA-63 and a known human sperm antigen, SP-10, at DNA/protein levels. Amino acid sequences of tryptic peptides derived from protein spots of 24-47 kDa and pIs of 4.2-4.4 were found to be identical to those deduced from isolated cDNA clones. The gene expression of MSA-63 during spermatogenesis in mice was studied using a specific cDNA probe as well as HS-63. It was observed that MSA-63 was not expressed until the postmeiotic stages of spermatogenesis.

Acrosome↗
PubMed1992

Calcium transport by rat liver plasma membranes during sepsis.

The effects of sepsis on the ATP-dependent Ca2+ transport in rat liver plasma membranes were investigated. Sepsis was induced by cecal ligation and puncture (CLP). Control rats were sham-operated. The results show that the ATP-dependent Ca2+ transport by liver plasma membranes was not affected during early sepsis (9 hr after CLP) but was decreased by 30-50% (P < 0.05) during late sepsis (18 hr after CLP). Kinetic analysis of the data indicates that during late sepsis, the Vmax values for ATP and for Ca2+ were decreased by 38.5% (P < 0.05) and 41.8% (P < 0.05), respectively, while the Km values for ATP and Ca2+ remained unchanged. Mg2+ stimulated ATP-dependent Ca2+ transport. The Mg(2+)-stimulated activity was unaffected during early sepsis but was decreased by 34-63% (P < 0.05) during late sepsis. These data demonstrate that ATP-dependent Ca2+ transport in rat liver plasma membranes was impaired during late sepsis and that the impairment is associated with a mechanism not affecting the affinity of the Ca2+ transporter for ATP and Ca2+. Since plasma membrane ATP-dependent Ca2+ transport plays an important role in the regulation of intracellular Ca2+ homeostasis in hepatocytes, an impairment in the ATP-dependent Ca2+ transport by liver plasma membranes during late sepsis may have a pathophysiological significance in contributing to the development of altered hepatic metabolism during septic shock.

Adenosine Triphosphate↗
PubMed1992

[Kinetic studies of protein kinase A in rat liver during late sepsis].

The covalent modification of receptor proteins via phosphorylation and dephosphorylation is one of the principal mechanisms controlling carbohydrate metabolism and is known to be regulated by various protein kinases. Recent studies indicated that many hormones may exert their effects on cellular metabolism by regulating intracellular c-AMP levels and by activating a c-AMP dependent protein kinase, i.e., protein kinase A. The metabolic disturbances during sepsis are characterized by an initial hyperglycemia followed by a progressive hypoglycemia and a depletion of hepatic glycogen content. The latter is coupled with a slowdown in glycogenesis, an accelerated glycogenolysis, and a depression in gluconeogenesis in the liver. Since the liver is the major organ that regulates the homeostatic level of blood glucose, it is conceivable that the sepsis-induced glucose dyshomeostasis might be mediated by changes in protein kinase activity and the kinetic characteristics of enzymes. The present experiment was designed to study the correlation between protein kinase A and the pathophysiology of hepatic glucose dyshomeostasis during sepsis. Sepsis was induced in rats by cecal ligation and puncture (CLP). Late sepsis occurred 18 hours after CLP. Protein kinase A was extracted from the rat livers by acid precipitation and ammonium sulfate fractionation, and then partially purified by DEAE-cellulose. The results show that in the late sepsis, type-I protein kinase A (eluted at low ionic strength) activity was significantly decreased by 34-52% (P < 0.01). The kinetic parameters such as Vmax's for ATP, histone, and c-AMP were also significantly decreased from the control values of 6.1 +/- 0.9, 5.4 +/- 0.8, and 5.1 +/- 1.9 nmoles/mg.min. to 3.6 +/- 0.5, 2.8 +/- 0.3, and 2.5 +/- 0.5 nmoles/mg.min., respectively. Analysis using Hill's equation indicates that the S0.5 and n (Hill coefficient) values of the various substrates and activators for type-I protein kinase A remained unchanged. In the case of type-II protein kinase A (eluted at high ionic strength), the Vmax, S0.5, and n values for ATP, histone, and c-AMP were unchanged during late sepsis. The results of the present study indicate that the activities and kinetic characteristics of type I protein kinase A in rat liver are modified during late sepsis. Since protein kinase A is known to regulate glucose metabolism through adrenergic receptor mediation, these findings may have a pathophysiological significance in the understanding of hepatic glucose dyshomeostasis during sepsis.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Impaired calcium uptake by cardiac sarcoplasmic reticulum and its underlying mechanism in endotoxin shock.

Effects of endotoxin administration on the ATP-dependent Ca2+ uptake by canine cardiac sarcoplasmic reticulum (SR) were investigated. Results obtained 4 h after endotoxin administration show that ATP-dependent Ca2+ uptake by cardiac SR was decreased by 27-43% (p less than 0.05). Kinetic analysis indicates that the Vmax values for Ca2+ and for ATP were significantly decreased while the S0.5 and the Hill coefficient values were not affected during endotoxin shock. Magnesium (1-5 mM) stimulated while vanadate (25-250 microM) inhibited the ATP-dependent Ca2+ uptake, but the Mg(2+)-stimulated and the vanadate-inhibited activities remained significantly lower in the endotoxin-treated animals. Phosphorylation of SR by the exogenously added catalytic subunit of the cAMP-dependent protein kinase or by the addition of calmodulin stimulated the ATP-dependent Ca2+ uptake activities both in the control and endotoxin-injected dogs. However, the phosphorylation-stimulated activities remained significantly lower in the endotoxin-injected dogs. Dephosphorylation of SR decreased the ATP-dependent Ca2+ uptake, but the half-time required for the maximal dephosphorylation was reduced by 31% (p less than 0.05) 4 h post-endotoxin. These data indicate that endotoxin administration impairs the ATP-dependent Ca2+ uptake in canine cardiac SR and the endotoxin-induced impairment in the SR calcium transport is associated with a mechanism involving a defective phosphorylation and an accelerated dephosphorylation of SR membrane protein. Since ATP-dependent Ca2+ uptake by cardiac SR plays an important role in the regulation of the homeostatic levels of the contractile calcium, our findings may provide a biochemical explanation for myocardial dysfunction that occurs during endotoxin shock.

Adenosine Triphosphate↗
PubMed1991

Reduction in the Ca2(+)-induced Ca2+ release from canine cardiac sarcoplasmic reticulum following endotoxin administration.

Effects of endotoxin administration on the Ca2(+)-induced Ca2+ release from canine cardiac sarcoplasmic reticulum (SR) were studied. Results show that the Ca2(+)-induced Ca2+ release from either passively or actively loaded SR vesicles was decreased by 28 to 46% (p less than 0.05) 4 h after endotoxin administration. Kinetic analysis reveals that the Vmax for Ca2+ was decreased significantly without changing the S0.5 and the Hill coefficient values. The binding of [3H]ryanodine to cardiac SR was reduced by 25.3% (p less than 0.01) following endotoxin administration. These data demonstrate that the Ca2(+)-induced Ca2+ release via the ryanodine-sensitive Ca2+ channel in canine cardiac SR was reduced during endotoxin shock. A reduction in the SR Ca2(+)-induced Ca2+ release may have a pathophysiological significance in contributing to the development of myocardial depression during endotoxin shock.

Animals↗
PubMed1991

Kinetic studies on the biological activity of calmodulin in canine heart and liver during endotoxin shock.

Effects of endotoxin administration on the biological activity of calmodulin isolated from canine heart and liver were studied. Calmodulin was isolated and purified to homogeneity. The biological activity of calmodulin was determined by its ability to activate Ca(2+)-dependent phosphodiesterase. Results obtained 4 h after endotoxin administration show that the Vmax and A0.5 for calmodulin, the Vmax and Km for cAMP, and the Vmax and the Hill coefficient for Ca2+ were unchanged, while the S0.5 for Ca2+ for the activation of phosphodiesterase were significantly increased in the heart. The kinetic parameters as described above were not significantly altered in the liver. These data indicate that the biological activity of calmodulin is inhibited in the heart during endotoxin shock and that the nature of inhibition is associated with a mechanism involving a decrease in the affinity (1/S0.5) towards Ca2+ binding. Since calmodulin plays an important role in the regulation of cardiac function through calmodulin-dependent calcium transport systems, our findings may have a pathophysiological significance in contributing to the understanding of myocardial dysfunction in endotoxin shock.

Animals↗
PubMed1990

Diamide reduces cadmium accumulation by human lung carcinoma A549 cells.

Human lung carcinoma A549-T27 cells were used to determine the effect of diamide on cadmium accumulation. Treatment of the cells with diamide decreased their cellular glutathione content to 51.6 +/- 7% of control and significantly decreased their cadmium accumulation both as a function of time and as a function of Cd2+ concentration. Verapamil also decreased cadmium accumulation. Its effect compares well in magnitude with that which resulted from diamide treatment. No additive effect was observed when the cells were simultaneously treated with diamide and verapamil. The results suggest that a change in the GSH/GSSG ratio affects cadmium uptake. Further, calcium channels may be involved in cadmium uptake by A549-T27 cells in a fashion that is dependent on sulfhydryl status.

Azo Compounds↗
PubMed1990

Molecular cloning of an acrosomal sperm antigen gene and the production of its recombinant protein for immunocontraceptive vaccine.

A monoclonal antibody, HS-63, which reacts specifically with a highly conserved sperm acrosome antigen, was shown to inhibit in vitro fertilization of mouse and human. The corresponding sperm antigen designated as MSA-63 was purified to homogeneity from mouse testes and used as an immunogen to generate polyclonal antisera in rabbits. The cDNA fragments of MSA-63 gene were cloned from mouse testis cDNA library by an immunoscreening method using polyclonal antisera specific for MSA-63. Using the established cDNA clone as a probe, the gene encoding for MSA-63 protein was found to be conserved among different mammalian species. Only one specific mRNA 1.5 kb in size was identified from the adult mouse testis among different mouse tissues. The recombinant fusion protein containing MSA-63 protein fragment was produced in Escherichia coli and used to immunize female mice. Similar to the original HS-63 monoclonal antibody, the antisera thus produced reacted only with the sperm acrosome and revealed significant inhibition to the in vitro fertilization of mouse oocytes. The results of this preliminary study suggest that it is feasible to mass produce sperm-specific antigens or their antigenic fragments by recombinant DNA technology for the development of sperm antigen-based immunocontraceptive vaccines.

Acrosome↗
PubMed1990

Impairment in the phosphorylation of canine cardiac sarcoplasmic reticulum following endotoxin administration.

Effects of endotoxin administration on the phosphorylation and dephosphorylation of phospholamban in canine cardiac sarcoplasmic reticulum (SR) were studied. Results obtained 4 h after endotoxin administration show that the Ca2(+)-calmodulin dependent phosphorylation of phospholamban was reduced by 17-25% (P less than 0.05). Kinetic analysis reveals that the Vmax values for Ca2+, for calmodulin, and for ATP for the Ca2(+)-calmodulin dependent phosphorylation were significantly decreased, while the S0.5 values (for Ca2+ and calmodulin) and the Km (for ATP) and Hill coefficients (for Ca2+ and calmodulin) remained unaffected during endotoxic shock. The cAMP-dependent phosphorylation of phospholamban measured in the presence of the exogenously added catalytic subunit of the cAMP-dependent protein kinase remained unaffected. The basal/endogenous (cAMP- and Ca2(+)-independent) phosphorylation of phospholamban was significantly decreased after endotoxin administration. The half-time for the dephosphorylation of phospholamban prephosphorylated in the presence of Ca2+ and calmodulin was shortened by 58% (P less than 0.01) in endotoxin shock. These data indicate that the phosphorylation of phospholamban was inhibited while the dephosphorylation was stimulated in canine cardiac SR during endotoxin shock. Since the phosphorylation and dephosphorylation of phospholamban in cardiac SR plays an important role in the control of myocardial contractility, these findings may have a pathophysiological significance in contributing to the understanding of myocardial dysfunction in endotoxin shock.

Animals↗
PubMed1990

Mechanisms of myocardial membrane alterations in endotoxin shock: roles of phospholipase and phosphorylation.

Current progress in the studies of myocardial membrane alterations during endotoxin shock indicates that endotoxin administration impairs (Na(+) + K(+)-ATPase enzyme system by disrupting the coordination of the ouabain receptor subunit and the catalytic subunit of the enzyme system, and that the disruption is due to an alteration in the lipid microenvironment and a decrease in the phosphorylated intermediate of the enzyme cycle. Studies of the membrane lipid profile provide evidence that endotoxin administration modifies the molecular structure of cardiac membrane lipids in association with the activation of phospholipases A1 and A2 and with the inhibition of phospholipid methylating enzymes. Using liposomes as a membrane model for investigation, endotoxin was found to be capable of modifying the physical property of membrane phospholipids by altering the molecular packing and the phase transition temperature of lipid bilayers. Further studies with Na(+)-Ca2+ exchange system in cardiac sarcolemma have established the roles of phospholipase A2 and protein phosphorylation on the endotoxin-induced derangement in myocardial Na(+)-Ca2+ exchange. Based on these studies, it is concluded that endotoxin administration exerts multiple injuries in different membrane-associated enzyme/receptor systems and that the mechanisms responsible for the endotoxin-induced membrane damage can be categorized into two conceptual frameworks: namely, changes in membrane lipid microenvironment in response to phospholipase A activation and alterations in the phosphorylation of the enzyme/receptor proteins.

Animals↗
PubMed1989

Purification of an acrosomal antigen recognized by a monoclonal antibody and antifertility effects of isoimmune serum.

A highly conserved acrosomal antigen reactive to a monoclonal antibody (HS-63), generated against human sperm, was purified to homogeneity with a combination of conventional procedures and immunoaffinity chromatography using a soluble extract of mouse and rabbit testes. The molecular weight of the purified antigen was 42-50 kD when analysed by sodium dodecylsulphate polyacrylamide gel electrophoresis. The high specificity of the purified antigen to monoclonal antibody HS-63 was shown by indirect immunofluorescent inhibition assay, enzyme-linked immunosorbent assay, Western blot analysis and radioimmunosorbent assay. The purified antigen was used for isoimmunization of mice and rabbits. Following successive immunizations, antisera of high titres were raised and reacted specifically with antigen on the sperm acrosome and in testes of several mammalian species, but not with somatic tissues. These isoimmune sera exhibited strong inhibition on mouse in-vitro fertilization and human sperm penetration of zona-free hamster eggs. The results of this study suggest that the sperm-specific acrosomal antigen reacting with HS-63 could be a good candidate for the development of immunocontraceptive vaccines in humans and in other animals.

Acrosome↗
PubMed1988

Activation of phospholipases A1 and A2 in heart, liver, and blood during endotoxin shock.

The effects of endotoxin shock on the activities of phospholipases A1 and A2 were studied in canine heart sarcolemma, liver plasma membrane, and blood serum. Results obtained from control dogs indicate that phospholipases A1 and A2 were equally active in cardiac sarcolemma. In liver plasma membrane the activity of phospholipase A1 was twice that of phospholipase A2, while in blood serum phospholipase A1 activity was only half that of phospholipase A2. Results obtained 4 hr after endotoxin administration (0.5 mg/kg, iv) demonstrate that phospholipase A1 activities were activated by 117% in cardiac sarcolemma, 188% in liver plasma membrane, and 150% in blood serum, while phospholipases A2 activities were stimulated by 71% in cardiac sarcolemma, 175% in liver plasma membrane, and 31% in blood serum. The in vitro incubation of all three enzyme preparations from control dogs with endotoxin (5-15 micrograms/0.5 ml) stimulated both phospholipase A1 and A2 activities and the stimulation was concentration dependent. These data suggest that endotoxin may have a direct stimulatory effect on phospholipases A1 and A2 activities in the cell membranes of heart and liver, and also in blood serum. Since phospholipases A play an important role in the regulation of membrane structure and function, the observed activation of phospholipases A1 and A2 may have a physiological significance in the pathogenesis of cellular dysfunction in endotoxin shock.

Animals↗
PubMed1987

Presence of episomal and integrated human papillomavirus DNA sequences in cervical carcinoma.

Thirty surgical samples of squamous cell carcinoma of the cervix obtained from Chinese women were analysed for the presence of human papillomavirus (HPV) types 16 and 18 using Southern blot hybridization procedure. HPV16 was detected in 53% while HPV18 was found in only 6% of the samples analyzed. When compared with other reports, variation in the geographic distribution of these two HPV types in association with cervical carcinoma is noted. Thirty-seven and a half percent of the HPV16-positive samples contained this HPV type in episomal form and an equal number in cellular DNA-integrated form. The simultaneous presence of both episomal and integrated forms was found in the remaining 25% of the positive samples. The two HPV18-positive cases harbored only episomal viral genome and were not superinfected by HPV16. Analysis of the HPV16 integration samples showed that single integration events had probably occurred and some of the viral sequences had been lost on or subsequent to integration.

Carcinoma, Squamous Cell↗
PubMed1987

Liver glycogen metabolism in endotoxin shock. I. Endotoxin administration decreases glycogen synthase activities in dog livers.

The effects of E. coli endotoxin administration on hepatic glycogen content and glycogen synthase activities in dogs were studied. Liver glycogen content was decreased by 80% 2 hr after endotoxin injection. When enzyme preparations were preincubated at 25 degrees C for 3 hr prior to their assays, 75% of total glycogen synthase was in I form in control dogs. Under such conditions, endotoxin administration decreased the percentage I activity from 75 to 37%; decreased the Vmax and Km for UDP-glucose for total glycogen synthase by 62.2 and 35.3%, respectively; decreased the Vmax and Km for UDP-glucose for glycogen synthase I by 75.6 and 15.6%, respectively; increased the A0.5 for glucose-6-P for the activation of glycogen synthase D by 126% at high (10 mM) and by 18-fold at low (1 mM) UDP-glucose concentration; increased the percentage D activity from 24 to 72%; decreased the I50 for ATP for the inhibition of total glycogen synthase by 49.7%; decreased the I50 for ATP for the inhibition of glycogen synthase I by 26.4%; and decreased the percentage I activity from 78 to 33% at ATP concentrations below 6 mM. When enzyme preparations were not preincubated prior to their assays, 90% of total glycogen synthase was in D form in control dogs. Under such conditions, endotoxin administration decreased the Vmax and Km for UDP-glucose for total glycogen synthase by 47.1 and 33.3%, respectively, and increased the A0.5 for glucose-6-P for the activation of glycogen synthase D by 24.2% at high (10 mM) and by 106% at low (1 mM) UDP-glucose concentration. From these results, it is clear that endotoxin administration greatly impaired hepatic glycogenesis by decreasing the activity of glycogen synthase; this impairment is at least in part responsible for the depletion of liver glycogen content in endotoxin shock. Kinetic analyses revealed that the decrease in the activity of glycogen synthase in endotoxic shock is a result of a decrease in the interconversion of this enzyme from inactive to active form and an increase in the interconversion from active to inactive form.

Adenosine Triphosphate↗
PubMed1987

Liver glycogen metabolism in endotoxin shock. II. Endotoxin administration increases glycogen phosphorylase activities in dog livers.

The effects of E. coli endotoxin administration on hepatic glycogen phosphorylase activities in dogs were investigated. Hepatic glycogen phosphorylase activities in both control and endotoxic dogs were inactivated spontaneously by preincubation of enzyme preparations at 25 degrees C. Total glycogen phosphorylase activity was not significantly altered during preincubation. The activity of glycogen phosphorylase a was increased by 83 and 80% at 1 and 2 hr postendotoxin, respectively, without preincubation; and by 203 and 133% at 1 and 2 hr postendotoxin, respectively, after 30 min preincubation. Without preincubation, the glycogen phosphorylase percentage a activity was increased from the control value of 37 to 58% at 1 hr postendotoxin and to 53% at 2 hr postendotoxin. After 30 min preincubation, the glycogen phosphorylase percentage a activity was increased from the control value of 10 to 28% at 1 hr postendotoxin and to 20% at 2 hr postendotoxin. The time required for half maximum inactivation of percentage a activity was 16.5, 33, and 24 min for control, 1 and 2 hr postendotoxin, respectively. Although the Vmax and Km for glucose-1-P for total glycogen phosphorylase were not affected by endotoxin administration, the Vmax for glucose-1-P for glycogen phosphorylase a was increased by 57.3 and 42.7% at 1 and 2 hr postendotoxin, respectively, with no change in the Km values. Glucose inhibited glycogen phosphorylase a activity both in control and endotoxin-injected dogs, but the I50 value was increased by 35% in endotoxin-injected (2 hr) dogs. AMP activated glycogen phosphorylase b activity both in control and endotoxin-injected dogs with no change in A0.5 values between the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Monophosphate↗
PubMed1987

Phospholipid methylation in canine myocardium: kinetic characteristics and the effect of endotoxin administration.

The kinetic characteristics and the effect of endotoxin administration on the enzymatic methylation of phospholipids in dog heart microsomes were studied using S-adenosyl-L-[methyl-3H]methionine as a methyl donor. Kinetic studies in control dogs reveal that the stepwise methylation of phosphatidylethanolamine to phosphatidylcholine was catalyzed by three different enzymes. Methyltransferase I catalyzed the methylation of phosphatidylethanolamine to phosphatidyl-N-monomethylethanolamine, had a very low Km (approximately 1.5 microM) for S-adenosylmethionine, and a pH optimum of 6.5, and it was stimulated by Mg2+ and Ca2+. Methyltransferase II catalyzed the methylation of phosphatidyl-N-monomethylethanolamine to phosphatidyl-N,N-dimethylethanolamine, had a low Km (8-12 microM) for S-adenosylmethionine, and a pH optimum of 8.5, and it was stimulated by low concentrations (less than 1 mM) of Ca2+ but was unaffected by Mg2+. Methyltransferase III catalyzed the formation of phosphatidylcholine from phosphatidyl-N,N-dimethylethanolamine, had a high Km (approximately 33 microM) for S-adenosylmethionine, and a pH optimum of 9.5, and it was unaffected by Mg2+ or Ca2+. Experiments with trypsin digestion indicate that methyltransferases I and III were partially embedded while methyltransferase II was completely exposed to the surface of the membrane. Endotoxin administration (2 and 4 hr) decreased the Km and Vmax by 30 to 36% and 24 to 37.7%, respectively, for S-adenosylmethionine. Since the enzymatic methylation of phospholipids has been implicated to play an important role in the regulation of membrane structure and function, the endotoxin-induced decreases in the Km and Vmax of phospholipid-methylating enzymes in dog heart microsomes may contribute to the development of myocardial dysfunction in endotoxin shock.

Animals↗