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Biomedical subjects

C Bai

Publications and source records attributed to C Bai.

85 records · Page 5Linked to original sources
PubMed1994

Human cyclin F.

Cyclins are important regulators of cell cycle transitions through their ability to bind and activate cyclin-dependent protein kinases. In mammals several classes of cyclins exist which are thought to co-ordinate the timing of different events necessary for cell cycle progression. Here we describe the identification of a novel human cyclin, cyclin F, isolated as a suppressor of the G1/S deficiency of a Saccharomyces cerevisiae cdc4 mutant. Cyclin F is the largest cyclin, with a molecular weight of 87 kDa, and migrates as a 100-110 kDa protein. It contains an extensive PEST-rich C-terminus and a cyclin box region that is most closely related to cyclins A and B. Cyclin F mRNA is ubiquitiously expressed in human tissues. It fluctuates dramatically through the cell cycle, peaking in G2 like cyclin A and decreasing prior to decline of cyclin B mRNA. Cyclin F protein accumulates in interphase and is destroyed at mitosis at a time distinct from cyclin B. Cyclin F shows regulated subcellular localization, being localized in the nucleus in most cells, with a significant percentage of cells displaying only perinuclear staining. Overexpression of cyclin F, or a mutant lacking the PEST region, in human cells resulted in a significant increase in the G2 population, implicating cyclin F in the regulation of cell cycle transitions. The ubiquitous expression and phylogentic conservation of cyclin F suggests that it is likely to coordinate essential cell cycle events distinct from those regulated by other cyclins.

Amino Acid Sequence↗
PubMed1994

Developmental characterization of a Drosophila RNA-binding protein homologous to the human systemic lupus erythematosus-associated La/SS-B autoantigen.

Patients with humoral autoimmune diseases such as systemic lupus erythematosus and Sjögren's syndrome contain antibodies in their sera directed against certain normal cellular components such as the La/SS-B autoantigen, an RNA-binding protein believed to function as a putative processor of RNA polymerase III precursor transcripts. We have identified cDNA clones from the fruit fly Drosophila melanogaster that encode a protein displaying significant sequence homology with human La/SS-B. The fly protein (which we refer to as D-La) contains a putative ribonucleoprotein 1 (RNP1) and RNP2 RNA-binding domain. D-La also possesses a leucine zipper motif, suggesting that it may interact with itself or other proteins. Using gel retardation analysis, we show that D-La can bind RNA; in addition, we demonstrate the first reported DNA-binding activity associated with a La protein. Northern (RNA) blot analysis revealed a single 1,600-nucleotide transcript expressed throughout embryonic, larval, pupal, and adult development. Surprisingly, whole-mount in situ hybridization experiments revealed that D-La transcripts are not present in all ovarian tissues. In addition, early expression throughout the embryo is followed by a restricted pattern of mesodermal expression that is later confined to the visceral mesoderm, gonads, gut, and salivary glands. These results suggest that D-La may play a more specialized role during fly development as opposed to a rather general role inferred by its homology to La proteins from other organisms.

Amino Acid Sequence↗
PubMed1994

Glutathione transport by type II cells in perfused rat lung.

Glutathione (GSH) is an antioxidant that protects the lung against oxidative-injury. Most cells rely on synthesis of GSH to maintain intracellular supply and only a few cell types take up intact GSH. Although isolated type II cells from rat have a Na(+)-dependent uptake system that transports GSH into the cells against a concentration gradient, it is not known whether this occurs from the vasculature in the intact lung or whether other cell types in the lung also transport GSH. Based on the knowledge that gamma-glutamyl analogues of GSH are also transported by the Na(+)-GSH transporter, a method was developed and used to study the cell specificity of GSH uptake in perfused lung. A stable, fluorescent GSH S-conjugate (GSH-I14) was synthesized and separated from the original dye as analyzed by high-performance liquid chromatography. Studies with isolated alveolar type II cells showed that uptake of GSH-I14 was Na+ dependent and inhibited by GSH. In addition, uptake of GSH by the type II cells was inhibited by GSH-I14. After perfusion of the isolated rat lung with GSH-I14, the conjugate accumulated primarily in the alveolar type II cell as observed by fluorescence microscopy. This was confirmed by isolation of type II cells and measurement of GSH-I14 content. Thus these results show that specificity of GSH transport can be studied with the fluorescent derivative, GSH-I14, and that in the isolated perfused lung type II cells can transport and concentrate GSH-I14 from the perfusate. Quantitative fluorescence microscopy will be required to further determine relative transport activities by other cell types.

Animals↗
PubMed1993

[Histochemical studies on the glycoconjugates of experimental alkali burned cornea in rabbit].

The model of experimental alkali burn of cornea in rabbit was obtained using 1 mol/L NaOH solution. After being burned for 1, 3, 7 and 14 days, the histochemical changes of these models were studied by using labelled concanavalin A (ConA-FITC) and wheat germ agglutinin (WGA-FITC). The results showed that after being burned, the amount of glycoconjugates interacted with these lectins decreased, and increased gradually after 7 days, then reached the level higher than that in the normal cornea. These changes were related to the recovery of alkali burned cornea.

Animals↗
PubMed1992

Individual serum bile acids as early indicators of carbon tetrachloride- and chloroform-induced liver injury.

Individual serum bile acids (SBA) are emerging as potentially useful early indicators of liver injury. This study was undertaken to compare the usefulness of individual SBA with the routinely used assays for detecting the effects of the hepatotoxicants carbon tetrachloride (CCl4) and chloroform (CHCl3). Serum samples were assayed for liver injury by determination of alanine aminotransferase (ALT), aspartate amino-transferase (AST), alkaline phosphatase (ALP), bilirubin and total bile acid (by enzymatic kit). These results were compared with levels of individual SBA measured by high performance liquid chromatography (HPLC). Liver samples from CCl4-treated rats were taken for light and electron microscopic examination. The highest dose for each chemical caused increases in serum ALT and AST but not ALP. Chloroform at the highest dose increased bilirubin. Total SBA levels as assayed by the kit were elevated in response to CCl4 and CHCl3 at doses below which serum enzymes and bilirubin were increased. Some individual SBA were increased at a still lower dose for each of these two chlorinated solvents. At the lowest dose of CCl4 tested no consistent light microscopic or ultrastructural changes were found. At all the higher doses periacinar cells displayed typical accumulation of lipid droplets and degranulation and dilation of rough endoplasmic reticulum. The extent of the ultrastructural changes were dose-dependent. Thus individual SBA assayed by HPLC may be considered as a very sensitive indicator of liver injury induced by the classical hepatotoxicants carbon tetrachloride and chloroform.

Alanine Transaminase↗
PubMed1992

Glutathione protection in alveolar type II cells from fetal and neonatal rabbits.

Previous studies have demonstrated a correlation between intracellular glutathione (GSH) pools and sensitivity to oxidative injury. In the present study, we demonstrated that de novo GSH synthesis or GSH uptake could increase intracellular GSH by 7- and 19-fold, respectively, in type II cells from neonatal rabbits. This suggested that the rate of GSH uptake was against a concentration gradient and greater than the synthetic rate. This increased intracellular GSH was associated with protection from oxidant injury by paraquat or 80% O2. A relationship between GSH uptake and protection was further supported by blockage of both processes by gamma-L-glutamyl-L-glutamate, a GSH analogue. With a greater oxidative burden, both de novo synthesis and GSH uptake were required to maintain protection. Although the transport rate was only 6% of that for neonatal cells, cells from fetal animals transported GSH and were protected from oxidative injury. From these results we conclude there was a causal relationship between GSH transport and protection from oxidative injury in type II cells from neonatal and fetal animals.

Amino Acids↗
PubMed1991

Stimulation of glutathione absorption in rat small intestine by alpha-adrenergic agonists.

The alpha-adrenergic agonist, phenylephrine (1.6 microM), caused a threefold stimulation of glutathione (GSH) transport from the lumen into the vasculature in isolated, vascularly perfused rat small intestine. Stimulation of GSH transport by phenylephrine was blocked by the alpha-adrenergic antagonists, prazosin or phentolamine. Norepinephrine and epinephrine (both alpha and beta agonists) also stimulated GSH absorption but not to the same extent as phenylephrine. Isoproterenol, a strict beta-adrenergic agonist, had no effect on the rate of GSH absorption. Under physiological luminal GSH concentrations, phenylephrine stimulated GSH efflux from the lumen, accumulation in the intestinal mucosa, and transport into the mesenteric vasculature. Phenylephrine did not stimulate the transport of polyethylene glycol, a high molecular weight molecule, and stimulated uptake of cysteine and glycine by 30%. This suggests that the effect of phenylephrine on GSH transport is not due to enhanced bulk flow through paracellular pathways. Studies with isolated small intestinal epithelial cells showed that phenylephrine also stimulated the release of GSH from the cells. Oral administration of phenylephrine with GSH caused a two- to fivefold transient increase in plasma GSH concentrations in rats. Phenylephrine alone or with the amino acid constituents of GSH caused no increase in plasma GSH concentration. Thus, absorption of dietary GSH is under hormonal regulation. The physiological importance of this regulation is not known, although such regulation may function to control utilization of dietary GSH for detoxication and may have therapeutic benefits for individuals with deficient GSH or increased risk of oxidative or chemically induced injury.

Adrenergic alpha-Agonists↗
PubMed1989

Fractionation and analysis of mitochondria with polycarbonate membrane filters.

Polycarbonate membrane filters were used to fractionate mitochondrial populations depending on their aggregation or association with other subcellular structures. Isolated rat liver mitochondria penetrated through filters which have pore sizes larger than 1 micron. In contrast, mitochondria which were induced to aggregate in vitro by incubation at low pH were retained by the filters and thus could be separated from the single or small aggregates of mitochondria. Use of this membrane filtration method to analyze release of mitochondria from isolated hepatocytes showed that treatment with digitonin at concentrations only sufficient to lyse the plasma membrane did not release mitochondria. Homogenization or sonication following digitonin treatment released 25-50% of the mitochondria, but only a small fraction was intact. A high yield of intact mitochondria was released from digitonin-treated cells by a brief treatment with a low concentration of the proteolytic enzyme nagarse. Thus, this membrane filtration method provides a simple and rapid approach to analyze the extent of mitochondrial aggregation and association with other subcellular structures.

Animals↗
PubMedDate not supplied

Modulation of monoamine oxidase activity in different brain regions and platelets following exposure of rats to methylmercury.

Monoamine oxidase (MAO; EC 1.4.3.4) is known to have an important role in the regulation of biogenic amines in the brain and peripheral tissues. It is also known that circulating platelets represent an excellent model for an easy assessment of the effect of MAO-B inhibitors in extracerebral tissue. The present study was carried out to determine the effects of methylmercury (MeHg) on the activity of MAO in synaptosomes of different brain regions of male Sprague-Dawley rats as well as in rat blood platelets both in vitro and in vivo. MeHg pretreatment inhibited the activity of MAO in the synaptosomes of the cortex, hypothalamus, hippocampus, striatum, cerebellum, and brain stem in a concentration-dependent (0-10 microM) manner. The threshold concentration of MeHg for such inhibition in different brain synaptosomes was found to be the same (i.e., 1 microM) except for in the rat striatum it was 2.5 microM, and the IC50 value for MeHg was found to be around 2.1 microM. Significant inhibition of the MAO activity was also observed in synaptosomes of the cortex, cerebellum, hypothalamus, and hippocampus as well as in platelets of rats 24 h after treatment by gavage with a total cumulative dose of 35 mg/kg (5 mg/kg/day for 7 days). The decrease of such activity was found to be at maximum in different brain synaptosomes and platelets 24 h following treatment with a cumulative total dose of 75 mg/kg (7.5 mg/kg/day for 10 days); the treated animals showed signs of ataxia under these conditions. The data have further shown that methylmercury is capable of inhibiting the MAO activity in different brain synaptosomes to different degrees but without showing any specificity towards any specific brain region. The present in vivo results suggest that the platelet MAO activity may be used as a potential biomarker of early neurotoxicity due to repeated exposure to MeHg in rats.

Animals↗