Degeneration of skeletal and cardiac muscles in c-myb transgenic mice

In order to reveal cellular processes sensitive to abnormal c-myb expression in vivo, transgenic mice were produced by introducing the c-myb nuclear proto-oncogene under the ubiquitous transcriptional regulatory unit of the cytoplasmic beta-actin gene. Expression of c-myb in thymus did not cause apparent abnormality, but the mice unexpectedly developed degenerative abnormalities in skeletal and cardiac muscles; this occurred predominantly in males. Expression of c-myb in skeletal muscle was correlated with an inflammation of muscle and was accompanied by vacuolar degeneration of muscle fibres, their regeneration, and lymphocyte infiltration. The identical pathological progression in cardiac muscle was associated with cardiomegaly.

Suppression of tumorigenicity in temperature-sensitive mutants of embryonal carcinoma cells by induction of cell differentiation at non-permissive temperature

The temperature-sensitive (ts) mutants of cell differentiation derived from the mouse teratocarcinoma cell line F9, when exposed to non-permissive temperature, undergo stem-cell differentiation concomitant with a transient retardation of cell-cycle progression. By incubating these mutant strains at non-permissive temperature, we were able to study the relationship between cell differentiation and tumorigenicity. Upon exposure to non-permissive temperature, the mutant cells undergo extensive differentiation and lose their ability to initiate tumors in vivo, but retain their in vitro proliferative potential. Our data suggest that the loss of tumorigenicity is not caused by altered proliferative potential, but rather by cell differentiation. We therefore suggest that the loss of proliferative potential and the onset of cell differentiation in teratocarcinoma F9 cells are 2 independent events which can be genetically dissected, and that there is (a) crucial step(s) in the differentiation pathway at which these ts mutant cells lose their tumorigenicity.

Changes in Hox1.6, c-jun, and Oct-3 gene expressions are associated with teratocarcinoma F9 cell differentiation in three different ways of induction

To obtain information on the mechanism of teratocarcinoma cell differentiation, the expression of genes having a specific role in gene regulation was examined using three different methods of inducing differentiation: drug treatments with retinoic acid (RA) and sodium butyrate, and a genetic approach using ts mutants. The RAR-beta and MK genes were induced specifically by RA treatment, which indicates that these two genes are solely RA responsive. By contrast, a change in c-jun, Hox1.6, and Oct-3 gene expression was observed in all three methods of F9 cell differentiation. These findings suggest that these three genes, whether down-or up-regulated, play an important and key role during teratocarcinoma cell differentiation.

13C- and 15N-NMR studies on medium-chain acyl-CoA dehydrogenase reconstituted with 13C- and 15N-enriched flavin adenine dinucleotide

The 13C- and 15N-NMR spectra of porcine kidney medium-chain acyl-CoA dehydrogenase (MCAD) reconstituted with 13C- and 15N-enriched FADs were measured. The positions of selective enrichment were C(2), C(4), C(4 alpha), C(10 alpha), N(1), N(3), and N(5) of the isoalloxazine nucleus of FAD. The NMR signals of the labeled atoms were observed as broad but distinct peaks in each NMR spectrum. The chemical shift values of the 2-, 4-, 4 alpha-, and 10 alpha-13C for the oxidized form of MCAD were 159.5, 166.8, 141.1, and 155.5 ppm, respectively, relative to the methyl resonance of 3-(trimethylsilyl)propionic acid-d4, while those of 1-, 3-, and 5-15N for the oxidized form were 183.6, 161.1, and 334.7 ppm, relative to liquid ammonia, respectively. The upfield shift of 2-13C of MCAD relative to that of FMN in the aqueous medium and its downfield shift relative to that of tetraacetylriboflavin in an apolar medium imply that a weaker hydrogen bond exists between C(2) = O and apoMCAD or a water molecule than that of free FMN with a water molecule. That the 4-13C resonance was observed downfield-shifted relative to that of free FMN in aqueous solution suggests a strong hydrogen bond between C(4) = O and apoMCAD. The chemical shift for 4 alpha-13C in oxidized MCAD is considerably downfield-shifted from that of FMN or any other flavoprotein observed thus far, indicating a unique environment around this position in MCAD. The 1-15N resonance of MCAD was most upfield-shifted among the flavoproteins observed.(ABSTRACT TRUNCATED AT 250 WORDS)

The binding of adenine nucleotides to apo-electron-transferring flavoprotein

Apoprotein of electron-transferring flavoprotein (ETF) reacts with FAD as follows: A*<-->A, A+FAD<-->holoETF. Two different forms of apoETF (A* and A) convert into each other and only one of them, A, can associate with FAD [Sato, K. et al. (1991) J. Biochem. 109, 734-740]. In the present study, the reactions between apoETF and ATP, ADP, AMP, riboflavin, or FMN were investigated. It was revealed that all three adenine nucleotides bind with apoETF with the same kinetic reaction scheme as FAD, and compete with FAD. These results suggest that the nucleotides bind to A with the same location as the ADP part of FAD in holoETF and that the ADP-binding site of apoETF is generated upon conversion from A* to A. Neither riboflavin nor FMN bound to apoETF regardless of the presence or absence of the nucleotides, indicating that the ADP part of the FAD molecule is essential to the incorporation of the isoalloxazine ring into ETF. The binding rate constant of FAD to A was 1/20 of that of ADP while the dissociation rate constant was 1/1,000. This indicates that the riboflavin part of FAD inhibits the binding of FAD by steric hindrance, while after the binding, it stabilizes the complex.

c-myc and p53 gene expression in the differentiation of temperature-sensitive mutants of teratocarcinoma F9 cells

We have previously reported the isolation of several temperature-sensitive (ts) mutants of F9 cells. Further investigations showed that some mutants were induced to differentiate at non-permissive temperature of cell growth, accompanied by changes in the expression of various genes, whereas others were not. During the differentiation induced by shifting up to the non-permissive temperature, a rapid and transient decrease in both c-myc and p53 mRNA levels and rapid induction of c-jun mRNA were observed. These changes were specific in differentiation-inducible mutants and were not observed in a non-inducible mutant. In both types of mutants, the level of c-myc mRNA decreased in association with growth retardation at the non-permissive temperature. The p53 mRNA, however, showed specific increase in the differentiation-inducible ts mutants. These observations suggest distinct roles for p53 and c-myc from proliferation to differentiation in teratocarcinoma stem cells.

Teratocarcinoma F9 cells induced to differentiate with sodium butyrate produce both tissue-type and urokinase-type plasminogen activators

Sodium butyrate (NaB) can induce teratocarcinoma cell differentiation as retinoic acid (RA). However, the function of these two agents seems to be a little different [Kosaka et al., Exp Cell Res, 192:46-51, 1991]. F9 cells treated with NaB synthesize both tissue-type (tPA) and urokinase-type (uPA) plasminogen activator, though RA induces only tPA production. Urokinase-type PA is demonstrated to exist in association with membrane and to localize its activity to the close environment of the cell surface. This may cause the specific cell morphology and characteristics of differentiated F9 cells induced with NaB.

Resonance Raman study on complexes of medium-chain acyl-CoA dehydrogenase

Resonance Raman (RR) spectra of the complex of pig kidney medium-chain acyl-CoA dehydrogenase with acetoacetyl-CoA and of the purple complex formed upon the addition of octanoyl-CoA to the dehydrogenase were obtained. RR spectra were also measured for the complexes prepared by using isotopically labeled compounds, i.e., [3-13C]-, [1,3-13C]-, and [2,4-13C2]acetoacetyl-CoA; [1-13C]octanoyl-CoA; the dehydrogenase reconstituted with [4a-13C]- and [4,10a-13C2]FAD. Both bands of oxidized flavin and acetoacetyl-CoA were resonance-enhanced in the 632.8 nm excited spectra of the acetoacetyl-CoA complex; this confirms that the broad long-wavelength absorption band is a charge-transfer absorption band between oxidized flavin and acetoacetyl-CoA. The 1,622 cm-1 band was assigned to the C(3)=O stretching mode coupling with the C(2)-H bending mode of the enolate form of acetoacetyl-CoA and the bands at 1,483 and 1,119 cm-1 were assigned to bands associated with the C(2)=C(1)-O- moiety. Both bands of fully reduced flavin and the substrate were resonance-enhanced in the 632.8 nm excited spectra of the purple complex. As the enzyme is already reduced, the substrate must be oxidized to octenoyl-CoA; the complex is a charge-transfer complex between the reduced enzyme and octenoyl-CoA. The low frequency value of the 1,577 cm-1 band, which is associated with the C(2)-C(1)=O moiety of the octenoyl-CoA, suggests that the enzyme-bound octenoyl-CoA has an appreciable contribution of C(2)=C(1)-O-.(ABSTRACT TRUNCATED AT 250 WORDS)

Significant role of an exocellular protease in utilization of heme by Vibrio vulnificus

Clinical and environmental isolates of Vibrio vulnificus could grow in a synthetic medium supplemented with heme protein as the iron source. Protease-deficient mutants of the bacterium could not utilize any of the heme proteins in the synthetic medium, but the addition of purified V. vulnificus protease restored their growth. The protease digested all heme proteins tested and elicited heme liberation from the proteins. Furthermore, the induction of protease production by the heme proteins was demonstrated. These observations suggest that protease contributes to the efficient utilization of heme by V. vulnificus.

Anion-induced conformational change of apo-electron-transferring flavoprotein

Apoprotein of electron-transferring flavoprotein (ETF) exists in an equilibrium between two different forms, only one of which can associate with FAD (Sato, K. et al. (1991) J. Biochem. 109, 734-740), as represented in the following kinetic scheme: A* in equilibrium with A, A+FAD in equilibrium with holoETF, where "A*" and "A" are the different forms of apoETF. In the present study, the effects of various anions on the conversion between the two forms of apoETF were investigated by kinetic analyses on binding of FAD to apoETF. All the anions tested here induced the conversion from "A*" to "A"; the order of the effectiveness was I- approximately Br- greater than Cl- greater than F-. Further, glycerol also induced the conversion from "A*" to "A". The elution pattern of apoETF on molecular sieve chromatography was changed by addition of salts or glycerol; this change was due to the conversion from "A*" to "A" by the added solutes. The "A*" form was eluted more rapidly than the "A" form, indicating that the "A*" form exists in a looser conformation than the "A" form. The far-UV CD spectral change upon addition of salts indicated that a greater part of the secondary structure is retained in the conversion from "A*" to "A," but the "A" form contains a somewhat larger amount of beta-sheet than "A*."

Expression of c-kit protooncogene is stimulated by cAMP in differentiated F9 mouse teratocarcinoma cells

Protooncogene c-kit, a transmembrane tyrosine kinase receptor, was recently shown to map to the dominant white spotting locus (W) of the mouse. W mutations affect melanogenesis, gametogenesis, and hematopoiesis during development and in adult life. In order to determine the regulation of the c-kit gene in cell differentiation, we investigated its expression during the differentiation of F9 cells. Undifferentiated F9 cells and F9 cells treated with retinoic acid (RA) alone or dbcAMP alone showed little expression of c-kit mRNA if any. The subsequent addition of dbcAMP to F9 cells treated with RA markedly increased the expression of c-kit mRNA. Furthermore, the effect of dbcAMP on c-kit expression is reversible. In differentiated cells treated with RA, c-kit gene expression is induced by agents such as forskolin or theophylline, which are known to elevate cellular cAMP level. These results indicate that the expression of the c-kit gene is regulated by the level of intracellular cAMP in differentiated F9 cells induced by RA.

A resonance Raman study on a reaction intermediate of Pseudomonas L-phenylalanine oxidase (deaminating and decarboxylating)

Resonance Raman (RR) spectra of purple intermediates of L-phenylalanine oxidase (PAO) with non-labeled and isotopically labeled phenylalanines as substrates, i.e., [1-13C], [2-13C], [ring-U-13C6], and [15N]phenylalanines, were measured with excitation at 632.8 nm within the broad absorption band around 540 nm. The spectra obtained resemble those of purple intermediates of D-amino acid oxidase (DAO). The isotope effects on the 1,665 cm-1 band with [15N] or [2-13C]phenylalanine indicate that the band is due to the C = N stretching mode of an imino acid derived from phenylalanine, i.e., alpha-imino-beta-phenylpropionate. The intense band at 1,389 cm-1 is contributed to by the CO2- symmetric stretching and C-CO2- stretching modes of alpha-imino-beta-phenylpropionate. The 1,602 cm-1 band, which does not shift upon isotopic substitution of phenylalanine, corresponds to the 1,605 cm-1 band of DAO purple intermediates and was assigned to a vibrational mode associated with the C(10a) = C(4a) - C(4) = O moiety of reduced flavin. These results confirm that PAO purple intermediates consist of the reduced enzyme and an imino acid derived from a substrate, and suggest that the plane defined by C(10a) = C(4a) - C(4) = O of reduced flavin and the plane containing H2+N = C - CO2- of an imino acid are arranged in close contact to each other, generating a charge-transfer interaction.

Isomerization of delta 1-piperideine-2-carboxylate to delta 2-piperideine-2-carboxylate on complexation with flavoprotein D-amino acid oxidase

The 1,646 cm-1 band in a resonance Raman spectrum obtained with excitation in the charge-transfer band of the complex of oxidized D-amino acid oxidase (DAO) with the oxidation product of D-lysine catalyzed by DAO shifted to 1,617 cm-1 upon 2-13C substitution of lysine. Thus, the band is assigned to a C(2) = C(3) stretching mode of the enamine, delta 2-piperideine-2-carboxylate (En). In the enzyme-free solution, the product is preferentially in the cyclic imine form, delta 1-piperideine-2-carboxylate (Im). Thus, DAO has a higher affinity for the enamine form than for the imine form. The pH effects on the affinity of DAO for the product and on the molar absorption coefficient at 630 nm in the charge-transfer band, suggest that the enzyme-bound product is En in the neutral form at the N atom. As the value of observed rate constant between DAO and the product was constant at high product concentrations, the binding mechanism can be explained as follows; E + Im in equilibrium with EIm in equilibrium with EEN: rapid bimolecular and slow unimolecular processes. The isomerization of the imine form to the enamine form proceeds in the slow process. The low affinity of Im for DAO may be due to a steric repulsion of the hydrogen atoms of Im at C(3) in the active site. The hydrogen atoms of a substrate D-amino acid at C(3), which correspond to the C(3) hydrogens of Im, may act repulsively in the active site and the repulsive energy may induce strain or distortion of the substrate and the enzyme, accelerating the catalytic reaction.

The existence of two different forms of apo-electron-transferring flavoprotein

The association process of FAD and apo-electron-transferring flavoprotein (apoETF) from hog kidney was investigated. The reaction schemes which involve the association-dissociation of the protein species could be excluded by the light scattering data, which indicated that the molecular weights of apoETF and holoETF are identical. The binding reaction between FAD and a large excess of apoETF was monophasic and obeyed pseudo-first order kinetics. On the other hand, the reaction between apoETF and a large excess of FAD was biphasic: the fast phase obeyed a pseudo-first order reaction, and the rate of the slow phase was almost independent of FAD concentration. These results suggest the existence of two different forms of apoETF, as represented in the following reaction scheme: [formula: see text] where "F" is FAD, "H" is holoETF, and "A" and "A" are the different forms of apoETF. The kinetic parameters were determined as k-1 = 3.9 x 10(4) M-1.s-1, k-1 approximately 10(-5) s-1, k+2 = 1.0 x 10(-3) s-1, and k-2 = 3.1 x 10(-3) s-1, in 50 mM potassium phosphate buffer, pH 7.6, containing 0.3 mM EDTA, and 5% v/v glycerol, at 7 degrees C. The elution patterns of apoETF on molecular sieve chromatography were very different from that of holoETF although the true molecular weights were identical. This result suggests that the structure of apoETF differs greatly from that of holoETF.

Reversible effects of sodium butyrate on the differentiation of F9 embryonal carcinoma cells

We have studied effects of sodium butyrate on embryonal carcinoma F9 cell differentiation. In the presence of sodium butyrate, F9 cells underwent rapid and drastic morphological changes and expressed marked increases in mRNA levels of various differentiation markers. When sodium butyrate was removed from the cultures, all the examined phenotypes of F9 cell differentiation rapidly reverted to the characteristics of undifferentiated stem cells. However, under the same conditions, when cycloheximide or actinomycin D was added to the cultures, such phenotypic reversion was not observed, but high mRNA levels of the differentiation markers as well as altered cell morphology were retained. These results indicated that the effects of sodium butyrate on induction of teratocarcinoma cell differentiation were reversible and that de novo syntheses of some mRNA(s) and protein(s) were necessary for the reversion of differentiated cells to stem cells.

Proton release from flavoprotein D-amino acid oxidase on complexation with the zwitterionic ligand, trigonelline

Trigonelline, i.e., N-methylnicotinate, which has a zwitterionic structure similar to a substrate D-amino acid, is a useful active site probe for D-amino acid oxidase (DAO). The affinity of trigonelline for DAO in the deprotonated state at the enzyme bound FAD 3-imino group is higher than in the neutral state, contrary to in the case of benzoate, which is a competitive inhibitor and is in a monoanionic form. The time course of the absorbance change was monitored for the binding of DAO with trigonelline by means of a stopped-flow technique. The reaction, on monitoring at 507 nm, was found to be biphasic at pH 8.3, with fast and slow phases. The dissociation of the 3-imino proton of the enzyme bound FAD was observed in the same time course as the slow phase. These results suggest that the positive charge of trigonelline exists near the 3-imino group of the enzyme bound FAD and interacts repulsively with the proton of the 3-imino group. The absorption spectra of the DAO-trigonelline complex at various pHs also support this hypothesis. In the catalysis of DAO, a similar mechanism may be involved, that is, the positive charge of a D-amino acid may interact repulsively with the 3-imino proton of the enzyme bound FAD, and this interaction may be important for the catalysis.

Isolation of mutants showing temperature-sensitive cell growth from embryonal carcinoma cells: control of stem cell differentiation by incubation temperatures

Embryonal carcinoma(EC) cells, the undifferentiated stem cells of teratocarcinomas, have many properties in common with pluripotent embryonic cells, and thus provide an excellent system for studying the early events involved in embryonic development and stem cell differentiation. We have isolated three novel mutants with temperature-sensitive(ts) cell growth that were able to differentiate at a non-permissive temperature for cell growth. These mutations affect the progression of the cell cycle, leading to the transient accumulation of cells in a specific phase, the S phase, of the cell cycle, which is likely to be the primary cause of stem cell differentiation of EC cells at non-permissive temperature. Isolation of these mutants strongly supports the notion that there is a close association between the inhibition of DNA synthesis and EC cell differentiation.