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PubMed1995

Interference of the sulphonylurea antidiabeticum gliquidone with mitochondrial bioenergetics in the rat under in vitro conditions.

The hypoglycaemic sulphonylurea gliquidone and glibenclamide exerted a partial uncoupling effect on mitochondrial respiration of liver under in vitro conditions using various citrate cycle intermediates as substrates. Besides the uncoupling effect, gliquidone and glibenclamide caused a direct inhibition of ATP-as well as DNP-stimulated oxygen consumption. Both phenomena proved to be dose dependent. Respiratory control ratio decreased progressively with increasing concentrations of sulphonylureas mainly through the inhibition of ADP-stimulated respiration. Basal and DNP-stimulated ATP-ase activity of isolated mitochondria changed similarly to the respiratory parameters. Changes in membrane permeability of mitochondria and the inhibition of substrate uptake further support the assumption of structural and functional alteration of mitochondria by the hypoglycaemic compounds tested.

Animals↗
PubMed2003

Targets of the cyclin-dependent kinase Cdk1.

The events of cell reproduction are governed by oscillations in the activities of cyclin-dependent kinases (Cdks). Cdks control the cell cycle by catalysing the transfer of phosphate from ATP to specific protein substrates. Despite their importance in cell-cycle control, few Cdk substrates have been identified. Here, we screened a budding yeast proteomic library for proteins that are directly phosphorylated by Cdk1 in whole-cell extracts. We identified about 200 Cdk1 substrates, several of which are phosphorylated in vivo in a Cdk1-dependent manner. The identities of these substrates reveal that Cdk1 employs a global regulatory strategy involving phosphorylation of other regulatory molecules as well as phosphorylation of the molecular machines that drive cell-cycle events. Detailed analysis of these substrates is likely to yield important insights into cell-cycle regulation.

Adenosine Triphosphate↗
PubMed1987

Detection of tyrosine protein kinase substrates in fresh leukemia cells and normal blood cells using an immunoblotting technique.

Kinases which phosphorylate proteins on tyrosine residues are of importance in the control of both normal and malignant cell proliferation. The receptors for a number of growth factors have intracellular domains with tyrosine protein kinase activity and several viral oncogenes code for tyrosine protein kinases. An abnormal tyrosine protein kinase has been implicated in the pathogenesis of chronic granulocytic leukemia. Using an immunoblot method and an antiphosphotyrosine antibody, we have detected substrates of tyrosine protein kinases in fresh human leukemia cells and normal blood and bone marrow cells. These substrates were present in all types of cells examined. Cells from patients with acute lymphoblastic leukemia, acute myeloid leukemia, and chronic lymphocytic leukemia contain prominent phosphotyrosine-containing protein bands with molecular weights in excess of 95 kDa. By contrast, chronic granulocytic leukemia cells, as well as normal bone marrow cells, lymphocytes, and monocytes, contain predominantly low molecular weight (less than 95 kDa) tyrosine kinase substrates. When lymphocytes were stimulated to enter cell cycle, however, high molecular weight substrates of similar molecular weights to those detected in acute lymphoblastic leukemia, acute myeloid leukemia, and chronic lymphocytic leukemia became prominent. The implications of these findings in the control of normal and malignant cell proliferation and differentiation are discussed.

Cell Separation↗
PubMed1996

CD45 monoclonal antibodies inhibit TCR-mediated calcium signals, calmodulin-kinase IV/Gr activation, and oncoprotein 18 phosphorylation.

The effects of a pan-CD45 mAb (CD45.2) on TCR-mediated signaling pathways were investigated in Jurkat T cells. The simultaneous addition of CD45 mAb with an activating OKT3 mAb had little effect on TCR-stimulated signals. However, when Jurkat cells were exposed to the CD45 mAb for 10 to 20 min before the addition of OKT3, a partial uncoupling of the TCR from intracellular signals was observed. The maximal increase in intracellular calcium was inhibited 47 +/- 10% (n = 11, range 33-67%), whereas no inhibition of inositol trisphosphate production was detected. The transient TCR-mediated activation of the Ca2+/calmodulin-activated kinase IV/Gr was also inhibited by the CD45 mAb, and this was reflected in a 50 to 60% inhibition in the TCR-stimulated generation of the p21 and p23 phosphoisomers of oncoprotein 18, a Ca2+/calmodulin-activated kinase IV/Gr substrate recently implicated in cell cycle regulatory events. Oncoprotein 18 is also a substrate for mitogen- activated protein kinase, but no inhibition by the CD45 mAb of TCR-triggered mitogen-activated protein kinase activation was observed. The CD45 mAb was therefore selective in causing the uncoupling of the TCR from calcium signals and calcium-regulated events without promoting a general inhibition of all TCR-mediated signals. Confocal microscopy revealed that binding of the CD45 mAb caused patching of CD45 molecules at the cell surface and, unexpectedly, a marked redistribution of intracellular CD45. However, no change was observed in the total level of CD45 expressed at the cell surface. Aggregation of CD45 at the cell surface may result in its sequestration from its tyrosine kinase substrates, with a consequent selective uncoupling of the TCR from intracellular signaling pathways.

Antibodies, Monoclonal↗
PubMed1984

pp60c-src is a substrate for phosphorylation when cells are stimulated to enter cycle.

The endogenous cellular oncogene products, pp60c-src, exhibits a protein kinase activity, but is itself a phosphoprotein. Based on the assumption that pp60c-src might play a role in the control of cell proliferation, we have studied its behaviour as a substrate for phosphorylation known to occur when quiescent, serum-deprived cells are stimulated to enter cell cycle following addition of either serum, platelet-derived growth factor or the phorbol ester derivative, 12-O-tetradecanoyl-phorbol-13-acetate. For this purpose a partial purification of pp60c-src on DEAE ion-exchange chromatography was combined with immune precipitation. A 2-4-fold increase in serine phosphorylation of pp60c-src was consistently observed after stimulation of quiescent cells to growth.

Animals↗
PubMed2002

Heat-shock protein 90, a chaperone for folding and regulation.

Heat-shock protein 90 (Hsp90) is an abundant and highly conserved molecular chaperone that is essential for viability in eukaryotes. Hsp90 fulfills a housekeeping function in contributing to the folding, maintenance of structural integrity and proper regulation of a subset of cytosolic proteins. A remarkable proportion of its substrates are proteins involved in cell cycle control and signal transduction. Hsp90 acts with a cohort of Hsp90 co-chaperones that modulate its substrate recognition, ATPase cycle and chaperone function. The large conformational flexibility of Hsp90 and a multitude of dynamic co-chaperone complexes contribute to generating functional diversity, and allow Hsp90 to assist a wide range of substrates.

Amino Acid Sequence↗
PubMed2005

Cryoreduction EPR and 13C, 19F ENDOR study of substrate-bound substates and solvent kinetic isotope effects in the catalytic cycle of cytochrome P450cam and its T252A mutant.

We recently used cryoreduction EPR/ENDOR techniques to show that a substrate can modulate the properties of both the monooxygenase active-oxygen intermediates and of the proton-delivery network which encompasses them. In the present report we use Q-band pulsed 19F ENDOR (Mims 3-pulse sequence) to examine the substrate binding geometries of camphor, through use of the 5,5'--difluorocamphor, and 13C ENDOR to examine the binding of 5-methylenyl camphor labeled with 13C at C11. These probes are examined in multiple states of the catalytic cycle of P450cam and its T252A mutant. As part of this investigation we further report a new cryoreduction reaction, the reduction of a ferroheme to the EPR-visible Fe(I) state, and use it to probe the substrate binding to the EPR-silent ferroheme state. Finally we report the solvent kinetic isotope effect on the decay of the camphor complex of the hydroperoxo-ferric intermediate, the first such measurement on an individual step within the P450cam reaction cycle. Following reduction of oxyferrous-P450cam, this step is the rate-limiting step in camphor hydroxylation, and its solv-KIE of 1.8 at 190 K establishes that it involves activation of the hydroperoxo moiety by transfer of the 'second' proton of catalysis. We suggest that the finding that the heme pocket can exist in multiple substates, including multiple substrate binding locations, even in P450cam, along with the established possibility that the hydroperoxo-ferriheme intermediate can react with substrate, may explain the formation of multiple products by P450s.

Alanine↗
PubMed1983

Effects of menstrual cycle on metabolic responses to exercise.

Selected substrate and hormonal responses to exercise were compared in two phases of the menstrual cycle. Exercise-induced changes in substrate [glucose, lactate, free fatty acids (FFA), glycerol] and hormonal patterns [luteinizing hormone (LH), follicle-stimulating hormone (FSH), insulin, progesterone (P), growth hormone (GH), cortisol] were compared in the follicular and luteal phases of the menstrual cycle in 24-h-fasted (n = 5), glucose-loaded (n = 6; 1.50 g/kg, 20% solution), and control subjects (n = 8). A treadmill walk was maintained for 60 min (30 min, 40% VO2 max; 30 min, 80% VO2 max). Blood samples were obtained 5 min before, 15, 30, 45, and 60 min during, and 30 min after exercise. In the glucose group a blood sample was also taken 20 min before exercise, and glucose was ingested 15 min before exercise. Within each nutritional group the metabolic and endocrine responses to exercise were similar in the two phases for glucose, lactate, glycerol, LH, FSH, and cortisol (P greater than 0.05). In the glucose group the FFA response was lower in the luteal phase (P less than 0.05). In the fasted subjects insulin and GH responses were elevated in the luteal phase (P less than 0.05). P responses in the control and glucose groups were markedly greater in the luteal phase (P less than 0.05). In the fasted subjects no alteration in P occurred in either phase (P less than 0.05), and the LH concentration was lower in these subjects relative to the control groups (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2005

Hsp70 chaperones: cellular functions and molecular mechanism.

Hsp70 proteins are central components of the cellular network of molecular chaperones and folding catalysts. They assist a large variety of protein folding processes in the cell by transient association of their substrate binding domain with short hydrophobic peptide segments within their substrate proteins. The substrate binding and release cycle is driven by the switching of Hsp70 between the low-affinity ATP bound state and the high-affinity ADP bound state. Thus, ATP binding and hydrolysis are essential in vitro and in vivo for the chaperone activity of Hsp70 proteins. This ATPase cycle is controlled by co-chaperones of the family of J-domain proteins, which target Hsp70s to their substrates, and by nucleotide exchange factors, which determine the lifetime of the Hsp70-substrate complex. Additional co-chaperones fine-tune this chaperone cycle. For specific tasks the Hsp70 cycle is coupled to the action of other chaperones, such as Hsp90 and Hsp100.

Adenosine Triphosphatases↗
PubMed1975

Glycosphingolipid glycosyl hydrolases and glycosidases of synchronized human KB cells.

KB cells were synchronized by a double thymidine block procedure. An investigation was made of the activities of alpha-L-fucosidase (EC 3.2.1.51), alpha-D-galactosidase (EC 3.2.1.22), beta-D-galactosidase (ec 3.2.1.23), alpha-D-glucosidase (EC 3.2.1.20), beta-D-glucosidase (EC 3.2.1.21), alpha-D-mannosidase (EC 3.2.1.24), beta-D-N-acetylgalactosaminidase (EC 3.2.1.53), and beta-D-N-acetylglucosaminidase (EC 3.2.1.52) from synchronized cultures, using appropriate artificial substrates. Ceramide glucosidase (EC 3.2.1.45) and ceramide trihexosidase levels (EC 3.2.1.47) were also investigated at various stages in the cell cycle, using appropriate glycosphingolipid substrates. Whereas each of these enzymes exhibited some activity throughout the cell cycle, peak activity (2- to 6-fold increase) occurred late in the S phase. Two molecular forms of ceramide glucosidase (optimal activity at pH 4.0 and pH 6.0) and two forms of ceramide trihexosidase (pH 4.0 and pH 7.5) were identified. Peak levels of the forms that preferred the relatively acid pH occurred earlier in the S phase of the cell cycle than those of the forms that were more active at the higher pH. The possibility that the forms with optimal activity at pH 4 are precursors of those with optimal activity at pH 6 to 7.5 is discussed. Precipitation of beta-galactosidase of synchronized KB cells with specific antibody revealed that changes in the activity of this enzyme during the cell cycle were the result of fluctuations in the amount of the enzyme.

Acetylgalactosamine↗
PubMed1997

Induction of p27Kip1 degradation and anchorage independence by Ras through the MAP kinase signaling pathway.

While most untransformed cells require substrate attachment for growth (anchorage dependence), the oncogenic transformed cells lack this requirement (anchorage independence) and are often tumorigenic. However, the mechanism of loss of anchorage dependence is not fully understood. When rat normal fibroblasts were cultured in suspension without substrate attachment, the cell cycle arrested in G1 phase and the cyclin-dependent kinase inhibitor p27Kip1 protein and its mRNA accumulated. Conditional expression of oncogenic Ras induced the G1-S transition of the cell cycle and significantly shortened the half-life of p27Kip1 protein without altering its mRNA level. Inhibition of the activation of mitogen-activated protein (MAP) kinase by cyclic AMP-elevating agents and a MEK inhibitor prevented the oncogenic Ras-induced degradation of p27Kip1. These results suggest that the loss of substrate attachment induces the cell cycle arrest through the up-regulation of p27Kip1 mRNA, but the oncogenic Ras confers anchorage independence by accelerating p27Kip1 degradation through the activation of the MAP kinase signaling pathway. Furthermore, we have found that p27Kip1 is phosphorylated by MAP kinase in vitro and the phosphorylated p27Kip1 cannot bind to and inhibit cdk2.

Amino Acid Sequence↗
PubMedDate not supplied

[Adrenergic and cholinergic regulation of respiratory efficiency of secretory cells].

The influence of sympathetic and parasympathetic systems on the secretory cell respiration is mediated at the subcellular level by adreno- and cholinoreceptors of plasmatic membranes and is related to selective oxidation of two different substrates of the Krebs cycle: succinate and alpha-ketoglutarate, both being involved into two reciprocal mediator-hormonal-substrate-nucleotide systems: catecholamines-succinate-cAMP-ATP and acetylcholint-alpha-ketoglutarate-cGMP-GTP. The reciprocation of these systems is necessary for regulation of cell oxygen demand and effective oxygen utilization for ATP-synthesis and synthesis of other macroergical compounds depending on the functional state of a cell.

Adenosine Triphosphate↗
PubMed2000

Testing the versatility of the sarcoplasmic reticulum Ca(2+)-ATPase reaction cycle when p-nitrophenyl phosphate is the substrate.

A detailed characterization of p-nitrophenyl phosphate as energy-donor substrate for the sarcoplasmic reticulum Ca(2+)-ATPase was undertaken in this study. The fact that p-nitrophenyl phosphate can be hydrolyzed in the presence or absence of Ca(2+) by the purified enzyme is consistent with the observed phenomenon of intramolecular uncoupling. Under the most favorable conditions, which include neutral pH, intact microsomal vesicles, and low free Ca(2+) in the lumen, the Ca(2+)/P(i) coupling ratio was 0.6. A rise or decrease in pH, high free Ca(2+) in the lumenal space, or the addition of dimethyl sulfoxide increase the intramolecular uncoupling. Alkaline pH and/or high free Ca(2+) in the lumen potentiate the accumulation of enzyme conformations with high Ca(2+) affinity. Acidic pH and/or dimethyl sulfoxide favor the accumulation of enzyme conformations with low Ca(2+) affinity. Under standard assay conditions, two uncoupled routes, together with a coupled route, are operative during the hydrolysis of p-nitrophenyl phosphate in the presence of Ca(2+). The prevalence of any one of the uncoupled catalytic cycles is dependent on the working conditions. The proposed reaction scheme constitutes a general model for understanding the mechanism of intramolecular energy uncoupling.

Calcium↗
PubMed2004

Indole-3-acetic acid increases glutamine utilization by high peroxidase activity-presenting leukocytes.

Indole-3-acetic acid (IAA) is toxic for human tumor cells and in association with horseradish peroxidase (HRP) can be used as a new prodrug/enzyme combination for targeted cancer therapy. The toxic effect of IAA on neutrophils, macrophages and lymphocytes is associated with cell peroxidase activity, which is high in neutrophils and low in lymphocytes. The effect of IAA on glucose and glutamine metabolism in leukocytes presenting different peroxidase activities: neutrophils, thioglycollate-elicited macrophages and lymphocytes was investigated. A time-course effect (from 6 to 48 h in culture) of IAA on glucose and glutamine metabolism of neutrophils, thioglycollate-elicited macrophages, and lymphocytes was then carried out. Addition of IAA (0.25 mM) did not have a marked effect on glucose utilization and lactate formation by the three cell types but it raised glutamine consumption and glutamate production by neutrophils and macrophages. IAA had no effect on glutamine consumption and glutamate production by lymphocytes. A strong relationship was found between glutamine utilization (0.999) and glutamate production (0.999) and peroxidase activity. IAA did not change the activities of hexokinase, glucose-6-phosphate dehydrogenase, citrate synthase, lactate dehydrogenase, and phosphate-dependent glutaminase of 24 h cultured neutrophils and lymphocytes. The effect of IAA (1 mM) on glucose and glutamine metabolism was also investigated by 1 h incubated leukocytes in PBS. IAA did not affect glucose and glutamine metabolism of lymphocytes but enhanced glucose and glutamine metabolism by 1 h incubated neutrophils and thioglycollate-elicited macrophages. IAA caused a marked increase on oxygen consumption by neutrophils, which was more pronounced in the presence of the glutamine as compared to glucose. The stimulation of oxygen consumption leads to a reduction in NADH/NAD+ ratio that activates the flux of substrates through the Krebs cycle. Since glutamine is mainly metabolized through the left hand side of the Krebs cycle, a reduction in the redox state of the cells may accelerate the flux of substrates through glutaminolysis. The toxic results presented here show that the affect of IAA in association with peroxidase involves activation of glutamine metabolism.

Analysis of Variance↗
PubMed2004

Importin alpha/beta-mediated nuclear protein import is regulated in a cell cycle-dependent manner.

Functional nuclear proteins are selectively imported into the nucleus by transport factors such as importins alpha and beta. The relationship between the efficiency of nuclear protein import and the cell cycle was measured using specific import substrates for the importin alpha/beta-mediated pathway. After the microinjection of SV40 T antigen nuclear localization signal (NLS)-containing substrates into the cytoplasm of synchronized culture cells at a certain phase of the cell cycle, the nuclear import of the substrates was measured kinetically. Cell cycle-dependent change in import efficiency, but not capacity, was found. That is, import efficiency was found low in the early S, G2/M, and M/G1 phases compared with other phases. In addition, we found that the extent of co-imunoprecipitation of importin alpha with importin beta from cell extracts was strongly associated with import efficiency. These results indicate that the importin alpha/beta-mediated nuclear import machinery is regulated in a cell cycle-dependent manner through the modulation of interaction modes between importins alpha and beta.

Active Transport, Cell Nucleus↗
PubMed1997

The regulation of pHi in osteoclasts is dependent on the culture substrate and on the stage of the resorption cycle.

The present study was performed to clarify the role of vacuolar H+-ATPase in the regulation of the intracellular pH (pHi) in osteoclasts. Bafilomycin A1 or amiloride were added to rat osteoclast cultures to block the H+-ATPases and Na+/H+-exchangers, respectively. Addition of 10(-8) M bafilomycin A1 to osteoclasts cultured on bone induced a rapid decrease of the pHi, while addition of amiloride had only a minor effect. The response to bafilomycin A1 appeared simultaneously with resorption activity and was abolished when resorption was inhibited by calcitonin. Osteoclasts on bone recovered from acid loading caused by propionate in the presence of amiloride, while bafilomycin A1 inhibited this recovery almost completely. The pHi of osteoclasts cultured on glass responded to the addition of amiloride, but was not effected by even high concentrations of bafilomycin A1. In contrast, as little as 10(-10) M bafilomycin A1 caused accumulation of large vesicles in the cytoplasm.

Amiloride↗
PubMed2001

Cytosolic chaperonin-containing t-complex polypeptide 1 changes the content of a particular subunit species concomitant with substrate binding and folding activities during the cell cycle.

The chaperonin-containing t-complex polypeptide 1 (CCT) is a cytosolic molecular chaperone composed of eight subunits that assists in the folding of actin, tubulin and other cytosolic proteins. We show here that the content of particular subunits of CCT within mammalian cells decreases concomitantly with the reduction of chaperone activity during cell cycle arrest at M phase. CCT recovers chaperone activity upon resumption of these subunits after release from M phase arrest or during arrest at S phase. The levels of alpha, delta and zeta-1 subunits decreased more rapidly than the other subunits during M phase arrest by colcemid treatment and recovered after release from the arrest. Gel filtration chromatography or native (nondenaturing) PAGE analysis followed by immunoblotting indicated that the alpha and delta subunit content in the 700- to 900-kDa CCT complex was appreciably lower in the M phase cells than in asynchronous cells. In vivo, the CCT complex of M-phase-arrested cells was found to bind lower amounts of tubulin than that of asynchronous cells. In vitro, the CCT complex of M phase-arrested cells was less active in binding and folding denatured actin than that of asynchronous cells. On the other hand, the CCT complex of asynchronous cells (a mixture of various phases of cell cycle) exhibited lower alpha and delta subunit content and lower chaperone activity than that of S-phase-arrested cells obtained by excess thymidine treatment. In addition, turnover (synthesis and degradation) rates of the alpha and delta subunits in vivo were more rapid than those of most other subunits. These results suggest that the content of alpha and delta subunits of CCT reduces from the complete active complex in S phase cells to incomplete inactive complex in M phase cells.

Animals↗