[13C]Methionine NMR and metal-binding studies of recombinant human transferrin N-lobe and five methionine mutants: conformational changes and increased sensitivity to chloride

The N-lobe of human serum transferrin (hTF/2N) and single point mutants in which each of the five methionine residues was individually mutated have been produced in a mammalian tissue-culture expression system. Since the five methionine residues are well distributed in the transferrin N-lobe, (13)C NMR of the [epsilon-(13)C]methionine-labelled proteins has been used to monitor conformational changes of the protein during metal binding. All five methionine residues have been assigned [Beatty, Cox, Frenkiel, Tam, Mason, MacGillivray, Sadler and Woodworth (1996) Biochemistry 35, 7635-7642]. The tentative two-dimensional NMR assignment for two of the five methionine residues, namely Met(26) and Met(109), has been corrected. A series of NMR spectra for the complexes of (13)C-Met-labelled hTF/2N with six different metal ions, Fe(III), Cu(II), Cr(III), Co(III), Ga(III) and In(III), demonstrate that the conformational change of the protein upon metal binding can be observed by means of the changes in the NMR chemical shifts associated with certain methionine residues, regardless of whether diamagnetic or paramagnetic metals are used. Changing any of the methionine residues should have minimal effects on transferrin function, since structural analysis shows that none of these residues contacts functional amino acids or has any obvious role in iron uptake or release. In fact, UV-visible spectra show little perturbation of the electronic spectra of any of the mutants. Nevertheless, the M109L mutant (Met(109)-->Leu) releases iron at half the rate of the wild-type N-lobe, and chloride shows a significantly greater retarding effect on the rate of iron release from all five mutants. All the methionine mutants (especially in the apo form) show a poor solubility in Hepes buffer lacking anions such as bicarbonate. These findings imply a more general effect of anion binding to surface residues than previously realized.

The structure of the nucleosome core particle of chromatin in chicken erythrocytes visualized by using atomic force microscopy

The structure of the nucleosome core particle of chromatin in chicken erythrocytes has been examined by using AFM. The 146 bp of DNA wrapped twice around the core histone octamer are clearly visualized. Both the ends of entry/exit of linker DNA are also demonstrated. The dimension of the nucleosome core particles is approximately 1-4 nm in height and approximately 13-22 nm in width. In addition, superbeads (width of approximately 48-57 nm, height of approximately 2-3 nm) are occasionally revealed, two turns of DNA around the core particles are also detected.

Identification of platination sites on human serum transferrin using (13)C and (15)N NMR spectroscopy

Reactions between various apo and metal-bound forms of human serum transferrin (80 kDa) and the recombinant N-lobe (40 kDa) with [Pt(en)Cl(2)] or cis-[PtCl(2)(NH(3))(2)] have been investigated in solution via observation of [(1)H,(15)N] NMR resonances of the Pt complexes, [(1)H,(13)C] resonances of the eCH(3) groups of the protein methionine residues, and by chromatographic analysis of single-site methionine mutants. For the whole protein, the preferred Pt binding site appears to be Met256. Additional binding occurs at the other surface-exposed methionine (Met499), which is platinated at a slower rate than Met256. In contrast, binding of similar Pt compounds to the N-lobe of the protein occurs at Met313, rather than Met256. Met313 is buried in the interlobe contact region of intact transferrin. After loss of one chloride ligand from Pt and binding to methionine sulfur of the N-lobe, chelate-ring closure appears to occur with binding to a deprotonated backbone amide nitrogen, and the loss of the other chloride ligand. Such chelate-ring closure was not observed during reactions of the whole protein, even after several days.

Dual role of Lys206-Lys296 interaction in human transferrin N-lobe: iron-release trigger and anion-binding site

The unique structural feature of the dilysine (Lys206-Lys296) pair in the transferrin N-lobe (hTF/2N) has been postulated to serve a special function in the release of iron from the protein. These two lysines, which are located in opposite domains, hydrogen bond to each other in the iron-containing hTF/2N at neutral pH but are far apart in the apo-form of the protein. It has been proposed that charge repulsion resulting from the protonation of the dilysines at lower pH may be the trigger to open the cleft and facilitate iron release. The fact that the dilysine pair is positively charged and resides in a location close to the metal-binding center has also led to the suggestion that the dilysine pair is an anion-binding site for chelators. The present report provides comprehensive evidence to confirm that the dilysine pair plays this dual role in modulating release of iron. When either of the lysines is mutated to glutamate or glutamine or when both are mutated to glutamate, release of iron is much slower compared to the wild-type protein. This is due to the fact that the driving force for cleft opening is absent in the mutants or is converted to a lock-like interaction (in the case of the K206E and K296E mutants). Direct titration of the apo-proteins with anions as well as anion-dependent iron release studies show that the dilysine pair is part of an active anion-binding site which exists with the Lys296-Tyr188 interaction as a core. At this site, Lys296 serves as the primary anion-binding residue and Tyr188 is the main reporter for electronic spectral change, with smaller contributions from Lys206, Tyr85, and Tyr95. In iron-loaded hTF/2N, anion binding becomes invisible as monitored by UV-vis difference spectra since the spectral reporters Tyr188 and Tyr95 are bound to iron. Our data strongly support the hypothesis that the apo-hTF/2N exists in equilibrium between the open and closed conformations, because only in the closed form is Lys296 in direct contact with Tyr188. The current findings bring together observations, ideas, and experimental data from a large number of previous studies and shed further light on the detailed mechanism of iron release from the transferrin N-lobe. In iron-containing hTF/2N, Lys296 may still function as a target to introduce an anion (or a chelator) near to the iron-binding center. When the pH is lowered, the protonation of carbonate (synergistic anion for metal binding) and then the dilysine pair form the driving force to loosen the cleft, exposing iron; the nearby anion (or chelator) then binds to the iron and releases it from the protein.

[Retardation of human drug-resistant HL-60 cell in G1 phase and induction of sensitive cell to apoptosis by cyclosporine A]

To further study the relationship between resistance to apoptosis and drug resistance in harringtonine-resistant HL-60 cells (HR20), cyclosporine A (CsA) 20, 10 micrograms.ml-1 was shown to induce the sensitive HL-60 cells to apoptosis, showing a typical DNA "ladder" band. But the same concentrations of CsA retarded the HR20 cells in G1 phase and could not induce the cells to apoptosis. The cellular daunorubicin accumulation increased when HR20 cells were treated with low concentration of CsA and the reversal of drug resistance by CsA was unrelated to the retardation of cell cycle progression. High phosphorylation of about 50 kDa protein occured when HR20 cells were treated with CsA 10 micrograms.ml-1. The results domonstrate that cyclosporine A retarded the harringtonine-resistant HL-60 cells in G1 phase but induced HL-60 cells to apoptosis, and the retardation was unrelated to drug resistance.

Mutations at nonliganding residues Tyr-85 and Glu-83 in the N-lobe of human serum transferrin. Functional second shell effects

The x-ray crystal structure of the N-lobe of human serum transferrin has shown that there is a hydrogen bond network, the so-called "second shell," around the transferrin iron binding site. Tyrosine at position 85 and glutamic acid at position 83 are two nonliganding residues in this network in the human serum transferrin N-lobe (hTF/2N). Mutation of each of these two amino acids has a profound effect on the metal binding properties of hTF/2N. When Tyr-85 is mutated to phenylalanine, iron release from the resulting mutant Y85F is much more facile than from the parent protein. Elimination of the hydrogen bond between Tyr-85 and Lys-296 appears to interfere with the "di-lysine (Lys-206-Lys-296) trigger," which affects the iron binding stability of the protein. Surprisingly, mutation of Glu-83 to alanine leads to the absence of one of the normal iron binding ligands; introduction of a monovalent anion is able to restore the normal first coordination sphere. The missing ligand appears to be His-249, as revealed by comparison of the metal binding behaviors of mutants H249Q and E83A and structural analysis. Glu-83 has a strong H bond linkage with His-249 in apo-hTF/2N, which helps to hold the His-249 in the proper position for iron binding. Disabling Glu-83 by mutation to an alanine seriously disturbs the H bond network, allowing His-249 to move away. A monovalent anion can help reestablish the normal network by providing a negative charge near the position of Glu-83 to reach charge balance, so that ligand His-249 is available again for iron binding.

Mutagenesis of the aspartic acid ligands in human serum transferrin: lobe-lobe interaction and conformation as revealed by antibody, receptor-binding and iron-release studies

Recombinant non-glycosylated human serum transferrin and mutants in which the liganding aspartic acid (D) in one or both lobes was changed to a serine residue (S) were produced in a mammalian cell system and purified from the tissue culture media. Significant downfield shifts of 20, 30, and 45 nm in the absorption maxima were found for the D63S-hTF, D392S-hTF and the double mutant, D63S/D392S-hTF when compared to wild-type hTF. A monoclonal antibody to a sequential epitope in the C-lobe of hTF reported affinity differences between the apo- and iron-forms of each mutant and the control. Cell-binding studies performed under the same buffer conditions used for the antibody work clearly showed that the mutated lobe(s) had an open cleft. It is not clear whether the receptor itself may play a role in promoting the open conformation or whether the iron remains in the cleft.

Inequivalence of the two tyrosine ligands in the N-lobe of human serum transferrin

Human serum transferrin N-lobe (hTF/2N) has four iron-binding ligands, including one histidine, one aspartate, and two tyrosines. The present report elucidates the inequivalence of the two tyrosine ligands (Tyr 95 and Tyr 188) on the metal-binding properties of hTF/2N by means of site-directed mutagenesis, metal release kinetics, and absorption and electron paramagnetic resonance (EPR) spectroscopies. When the liganding tyrosines were mutated individually to phenylalanine, the resulting mutant Y95F showed a weak binding affinity for iron and no affinity for copper, whereas, mutant Y188F completely lost the ability to bind iron but formed a stable complex with copper. Since other studies have demonstrated that mutations of the other two ligands, histidine and aspartate, did not completely abolish iron binding, the present findings suggest that the tyrosine ligand at position 188 is essential for binding of iron to occur. Replacement of Tyr 188 with phenylalanine created a favorable chemical environment for copper coordination but a fatal situation for iron binding. The positions of the two liganding tyrosines in the metal-binding cleft suggest a reason for the inequivalence.

Iron release from recombinant N-lobe and single point Asp63 mutants of human transferrin by EDTA

Transferrins bind ferric ion and deliver the iron to cells. The mechanism of the iron release has been studied kinetically, in vitro, with the aid of single point mutants in which the iron-binding ligand, Asp63 (aspartic acid-63, D63), has been changed to Ser, Asn, Glu and Ala. Iron release from the unmutated N-lobe of human serum transferrin (hTF/2N) by EDTA is influenced by a variety of factors. The rate-determining conformational-change mechanism may be a major pathway for iron release from hTF/2N's having a 'closed' conformation, which leads to a saturation kinetic mode with respect to ligand concentration. The effect of chloride depends on the protein conformation, showing a negative action in the case of tight binding and a positive action when the protein has an 'open' or 'loose' conformation. The negative effect of chloride could originate from the binding competition between chloride and the chelate to the active site for iron release, and the positive effect could derive from the synergistic participation of chloride in iron removal. The 'open' conformation may be induced by decreasing pH: the transitional point appears to be at about pH 6.3 for the wild-type hTF/2N; the 'loose' conformation may be facilitated by mutations at D63, which result in the loss of a key linking component in interdomain interactions of the protein. In the latter case, structural factors dominate over other potential negative effects because the weak interdomain contacts derived from the mutation of D63 cause the binding site to open easily, even at pH 7.4. Therefore chloride exhibits an accelerating action on iron release by EDTA from all the D63 mutants.

Inhibition of harringtonine-induced apoptosis by tetradecanoylphorbol acetate in human leukemia HL-60 cells

AIM

To study the changes of the apoptosis induced by camptothecin (Cam) or harringtonine (Har) in human leukemia HL-60 cells after the cells were preincubated with tetradecanoylphorbol acetate (TA).

METHODS

Chromatin condensation observation, flow cytometry, DNA agarose gel electrophoresis, and Dot blot hybridization.

RESULTS

After the HL-60 cells were preincubated with TA 200 nmol.L-1 for 6 h, the apoptosis induced by Har 0.1 mg.L-1 for 3 h was drastically inhibited, and the apoptosis by Cam 0.2 mg.L-1 for 3 h was partly inhibited. On the other hand, the expression level of c-myc gene in HL-60 cells decreased apparently after the preincubation of TA.

CONCLUSION

TA preincubation inhibited the apoptosis induced by Har obviously or by Cam partly in human leukemia HL-60 cells, and the expression of c-myc gene decreased drastically in the preincubated cells, which might result in the inhibition of apoptosis.

[Effects of differentiation status on apoptosis of human leukemia HL60 cells]

The effects of differentiation of human leukemia HL60 cells on harringtonine(Har) and camptothecin(Cam) induced apoptosis(in these cells) were studied. When treated with phorbol 12-myriate, 13-acetate 16 nmol.L-1 for 24 h, the HL60 cells differentiated into monocyte/macrophage cells and were arrested at G1 phase. The differentiated cells were shown to be resistant to the Har and Cam induced apoptosis, but showed no change of expression of c-myc gene. HL60 cells incubated in 1.4% dimethyl sulfoxide for 48 h differentiated into granulocyte cells and were also gene arrested at G1 phase. The differentiated cells became resistant to the apoptosis induced by Cam, but not that by Har, and expression of c-myc decreased drastically in the differentiated cells. The results indicate that the differentiated status of human leukemia HL60 cells apparently affected the apoptosis induced by harringtonine and camptothecin, but it was irrelevant to the change of the expression of c-myc gene.

Effects of mutations of aspartic acid 63 on the metal-binding properties of the recombinant N-lobe of human serum transferrin

Mutations of the aspartic acid residue at position 63 of the N-lobe of human serum transferrin substantially alter the metal ion- and anion-binding properties of the protein. Substitution of serine, asparagine, glutamic acid, or alanine results in the loss of a key component of the interface in the interdomain cleft and the metal-binding ligand, aspartic acid, leading in all cases to an increased preference for NTA rather than carbonate as the "synergistic" anion relative to the wild-type protein. Excess bicarbonate is required to eliminate the NTA and obtain the "correct" visible spectrum. Carbonate replaces NTA via an intermediate. Blue shifts for the characteristic absorption band of each mutant show a range of effects on the Fe-O (Tyr) interaction. Titration with Co(III) yielded the molecular absorption coefficient for each mutant except D63A, where Co(III) appeared to oxidize the tyrosine residues and damage the ability of the mutant to bind metal. The chelator, Tiron, removes iron from hTF/2N with a simple saturation kinetic mode with respect to the ligand concentration. Chloride inhibits the release in an interesting manner: the effect is initially sharp and then levels off with a minimum k(obs) at [KCl] = 0.5 M. However, the reaction of the D63 mutants with Tiron results in the formation of the ternary complexes Fe-hTF/2N-Tiron. Significant red shifts for the characteristic absorption bands of these complexes suggest a different ligation of Tiron in the mutants from that in wild-type hTF/2N.

Trp128Tyr mutation in the N-lobe of recombinant human serum transferrin: 1H- and 15N-NMR and metal binding studies

The conserved Trp residue within helix 5 of the N-lobe of human serum transferrin (hTF/2N, 40 kDa) has been mutated to Tyr. NMR and CD spectra and energy calculations show that the mutation causes little perturbation of the overall structure of hTF/2N although the chelating agent Tiron removed Fe3+ from the mutant protein about three times faster than from wild-type hTF/2N. 1H-NMR resonances of residues in the Leu122-Trp128-Ile132 hydrophobic patch are assigned both by ring current calculations and with the aid of the mutation. [1H, 15N]-NMR resonances for 11 of the 14 Tyr residues were observed in the spectra of 15N-Tyr-hTF/2N and a resonance for Tyr128 was assignable in spectra of the mutant. The 15N resonance of Y128 was sensitive to oxalate and Ga3+ binding, and Ga3+ binding perturbed 15N resonances for most of the Tyr residues. Since these are well distributed over the N-lobe, it can be concluded that metal-induced structural changes are not merely local to the binding site.

Resistance to apoptosis of harringtonine-resistant HL60 cells induced by tetrandrine

AIM

To study the mechanism of resistance to apoptosis in the harringtonine (Har)-resistant HL60 cells with tetrandrine (Tet).

METHODS

Growth inhibition, flow cytometry, DNA agarose gel electrophoresis, protein phosphorylation, and RNA dot hybridization.

RESULTS

The resistant cells had no cross resistance to Tet. Tet induced the sensitive but not the Har-resistant HL60 cells to apoptosis. The high phosphorylation of protein < 30 kDa occurred when the resistant cells were treated with Tet. Tet and Har increased the expression of c-myc mRNA in the sensitive HL60 cells. The expression of c-myc mRNA in the resistant cells was obviously decreased and almost not changed in treatment with Tet and Har.

CONCLUSION

Tet induced the sensitive but not the Har-resistant HL60 cells to apoptosis, and the resistance to apoptosis induced by Tet was associated with the high protein phosphorylation and reduction of the expression of c-myc mRNA.

Characteristics of harringtonine-resistant human leukemia HL60 cell

AIM

To study the mechanisms of the resistance to harringtonine (Har) in the HL60 cells.

METHODS

Growth inhibition, karyotype analysis, flow cytometry, Western blotting and polymerase chain reaction.

RESULTS

The Har-resistant HL60 cell line, named HR20, showed cross resistance to homoharringtonine, doxorubicin, daunorubicin, vincristine, and colchicine. The growth doubling time and the cell numbers in G1 phase were increased. The accumulation of cellular daunorubicin in the resistant cells was obviously reduced, but distinctly increased by tetrandrine and verapamil. The numbers of telocentromeric chromosome increased and the chromosomal aberration more occured in the resistant cells. The resistant cells overexpressed multidrug resistant mdr-1 gene and P-glycoprotein 150 kDa.

CONCLUSION

The Har-resistant HL60 cell strain belonged to a multidrug resistance strain, overexpressing mdr-1 gene and P-glycoprotein.

Spectrophotometric titration with cobalt(III) for the determination of accurate absorption coefficients of transferrins

A rapid and sensitive technique, involving difference spectral titration with cobalt(III), to measure the epsilon values of chicken ovotransferrin, human serum transferrin, the N-lobe of human transferrin and several single point mutants is reported. The resulting epsilon values were compared with the values calculated from the equation proposed by Pace, Vajdos, Fee, Grimsley and Gray [(1995) Protein Sci. 4, 2411-2423]. The titrations with cobalt feature sharp break-points and do not destroy the protein samples. The choice of buffer was found to be important, depending on the metal-binding avidity of the proteins. Cobalt titration should prove useful for studying the comparative metal-binding properties of transferrin and mutants of transferrin being generated by recombinant technology.

Reduction of doxorubicin resistance by tetrandrine and dauricine in harringtonine-resistant human leukemia (HL60) cells

AIM

To study whether tetrandrine (Tet) and dauricine (Dau) can reduce doxorubicin (Dox) resistance in the harringtonine (Har)-resistant human leukemia cells.

METHODS

The drug cytotoxities were determined by counting cell numbers and colony formation. Cell cycle phases were assayed by flow cytometry, Dox contents were quantified by Dox fluorescence.

RESULTS

The non-cytotoxic concentrations of Tet and Dau potentiated the growth-inhibitory actions of Dox in the Har-resistant HL60 cells. The colony formation effiencies were reduced from 60% by Dox to 0.2% by Tet + Dox and 9.2% by Dau + Dox. Retardation of the G2M phase cells was increased. But Tet and Dau did not potentiate Dox cytotoxities in the sensitive HL60 cells. Dox accumulation in the Har-resistant HL60 cells treated by Tet was increased.

CONCLUSION

Dox resistance in the Har-resistant HL60 cells treated by Tet or Dau was reduced, due to the increase of Dox accumulation in the cells. One of the mechanisms of multidrug resistance in tumor cells is overexpression of cell membrane glycoproteins, termed P-glycoprotein (PGP). PGP pumps antitumor drugs out of tumor cells, causing drug resistance. Calcium antagonists and some calmodulin inhibitors such as verapamil, nifedepine, trifluorapine have effect on reversion of drug resistance, binding directly to PGP, but side effect of them is intolerable in clinical use. So searching for other potentiators to overcome drug resistance may be another avenue. Tetrandrine (Tet) effectively circumvented the resistance of Chinese hamster ovary cells to doxorubicin (Dox). Dauricine (Dau) is a bisbenzylisoquinoline alkaloid from Stephaia tetrandra. In this paper we studied whether Tet and Dau could reduce Dox resistance in the harringtonine (Har)-resistant human leukemia 60 (HL60) cells.

[The sero-epidemiological investigation of leptospirosis in Hainan Province]

This paper reported that 529 serum samples were collected from healthy people in ten townships of nine cities or counties of Hainan Province in 1993 and anti-leptospira antibody was examined. Results showed that 274 cases were positive (51.8%), indicating the natural infection rates were from 25.9% to 72.2% in different areas. The infection was irrelevant to sex, but was interrelated to age and occupations. There were 15 serogroups of anti-leptospira antibody identified in this study. Bataviae, Grippotyphosa and Icterohaemorrhagiae serogroups were the dominant serogroups, different from that the Grippotyphosa and Autumnalis serogroups as the superior serogroups in the 1970s. Data shows that the main epidemic serogroups are likely to change, which suggests that the surveillance of leptospirosis needs to be strengthened.

Selective recognition of the m5CpG dinucleotide sequence in DNA by mitomycin C for alkylation and cross-linking

The clinically used natural antitumor agent mitomycin C (MC) is known to alkylate DNA monofunctionally and bifunctionally, resulting in the cross-linking of DNA. These reactions occur selectively with guanines at the CpG sequence. We show, confirming a previous report (Millard, J. T.; Beachy, T. M. Biochemistry 1993, 32, 12850) that cross-linking in oligonucleotides is further enhanced when the cytosines in CpG.CpG are 5-methylated to m5CpG.m5CpG. It is shown, furthermore, that guanines in m5CpG are monoalkylated two- to three-times faster than in CpG indicating that the m5C-induced rate enhancement occurs at the first, monoalkylation step of the two-step cross-linking process. The same MC-DNA adducts are formed in methylated as in non-methylated DNA. The basepaired but not the 5'-flanking, m5C residue is responsible for the enhanced alkylation of guanine. Enzymatically activated or Na2S2O4-activated MC shows identical rate-enhancement of alkylation at m5CpG. pBR322 DNA methylated by CpG-methylase was cross-linked two- to three-times more efficiently by MC than non-methylated DNA, indicating that the m5C effect is not an artifact of oligonucleotides. An electronic effect of the 5-methyl group of cytosine transmitted via G.C H-bonding to N2 of guanine is suggested as responsible for increased reactivity with MC. CpG is severely depleted in mammalian DNA and it is speculated that this factor attenuates MC cytotoxicity in human cells.

Binding of 2,7-diaminomitosene to DNA: model for the precovalent recognition of DNA by activated mitomycin C

Mitomycin C (MC), mitomycin A, porfiromycin, BMY-25067, and BMY-25287, antitumor antibiotics collectively termed "mitosanes", were found to have no appreciable binding affinity to various natural and synthetic DNAs, as tested by UV spectrophotometry and equilibrium dialysis. Further tests of DNA binding applied to MC including thermal melting measurements, displacement of ethidium fluorescence, and unwinding of closed circular DNA were similarly negative. In contrast, 2,7-diaminomitosene (2,7-DAM), a major end product of the reductive activation of MC, binds to the same series of DNAs by all of these criteria. In the presence of DNA its UV absorbance at the 313 nm maximum decreased and underwent a slight red shift. This effect was used for determining DNA binding constants (Kb) by the spectrophotometric titration method. At pH 6.0 the Kbs of three natural DNAs with varying GC content, as well as poly(dA-dT).poly(dA-dT), and poly(dG-dC).poly(dG-dC), were all in the range of (1.2-5.3) x 10(4) (M nucleotide)-1, with no apparent specificity of binding. Poly(dG-m5dC).poly(dG-m5dC) displayed a slightly higher Kb ((7.5-8.4) x 10(4)). Binding of other, closely related mitosenes was tested to calf thymus DNA by equilibrium dialysis. Neither the presence of a 1-OH substituent, removal of the 10-carbamoyl group, nor methylation of the 2-amino group modifies the binding affinity of the mitosenes significantly. The 1-phosphate substituent abolishes binding. The binding of 2,7-DAM to DNA increased with decreasing pH and decreasing ionic strength. It was determined that 2,7-DAM is protonated at the 2-amino group with a pKa = 7.55, and this correlated well with the observed pH dependence of the binding, indicating that the binding affinity has a strong electrostatic component. This was confirmed by the finding that the extrapolated Kb to 1 M Na+ concentration diminishes to only 10% of the value of Kb at 0.01 M Na+ concentration. Viscosity tests showed conclusively that 2,7-DAM intercalates in DNA, in a nonspecific manner. DNA binding by 2,7-DAM is shown to be a close model of the binding of the reduced activated form of MC, previously characterized indirectly [Teng, S. P., Woodson, S. A., and Crothers, D. M. (1989) Biochemistry 28, 3901-3907]. The nonspecific precovalent binding of the active form may serve in the cell to concentrate the drug at its critical target, DNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of glutathione on alkylation and cross-linking of DNA by mitomycin C. Isolation of a ternary glutathione-mitomycin-DNA adduct

Mitomycin C (MC), a clinically used antitumor antibiotic, is known to alkylate DNA monofunctionally, and to generate DNA interstrand cross-links by bifunctional alkylation. Both processes are dependent on the reductive activation of MC. Glutathione (GSH) was shown here to cause three types of changes in the pattern of alkylation of DNA by MC: (i) GSH caused a decrease of both the overall covalent binding ratio of MC to Micrococcus luteus DNA and the extent of interstrand cross-linking of 32P-pBR322 DNA, as the concentration of GSH was increased in the reaction media. Approximately 50% inhibition of cross-linking was observed at 20 mM GSH. It is likely that the inhibition is caused by the formation of MC-GSH conjugates competing with DNA alkylation, since both processes are triggered by reductive activation of MC [Sharma, M., and Tomasz, M. (1994) Chem. Res. Toxicol. (preceding paper in this issue)]. (ii) GSH causes a switch from monofunctional to bifunctional activation of MC by the prototype "monofunctional" MC-activating agents H2/PtO2 and NADPH:cytochrome c reductase/NADPH. This was seen by the predominance of bisadducts (i.e., cross-linked adducts) instead of the usual monoadducts in the enzymatic digests of MC-DNA complexes formed in the presence of GSH, as analyzed by HPLC. This finding suggests that GSH participates in the bifunctional activation of MC in vivo. (iii) A ternary MC-GSH-DNA adduct (6) was formed in the presence of GSH both with M. luteus DNA and with a synthetic duplex oligonucleotide; in this adduct the mitosene C1 is linked to N2 of guanine and the mitosene C10 is linked to GSH via sulfur.(ABSTRACT TRUNCATED AT 250 WORDS)

[Measurement of total glutathione concentration in bronchoalveolar lavage recovered from the patients with diffuse interstitial lung disease]

In order to investigate the change of glutathione concentration in BAL from the patients with diffuse interstitial lung disease. We measured the levels of glutathione in BAL from the patients with interstitial lung disease, including idiopathic interstitial pneumonitis (IIP), hypersensitivity pneumonitis (HP), collagen disease with pneumonitis, and sarcoidosis. The result showed that the glutathione concentration in BAL of the patients with IIP, HP, collage disease with pneumonitis, were significantly lower than that of the control group, but compared with the control group, the glutathione concentration of the patients with sarcoidosis did not show significant difference. The results may provide further insight into the pathogenesis of oxidant-induced interstitial lung disease and its therapy.

[Measurement of T cell subsets in bronchoalveolar lavage fluid for diagnosis of pulmonary sarcoidosis]

Pulmonary sarcoidosis is characterized by the accumulation in the lower respiratory tract of large numbers of activated CD4 T cells and elevated ratio of CD4/CD8 in bronchoalveolar lavage fluid (BALF). To study the value of CD4/CD8 ratio in BALF in the diagnosis of pulmonary sarcoidosis, we measured T cell subsets in BALF of patients with pulmonary sarcoidosis. The CD4/CD8 ratio in the patients (7.5 +/- 4.3) was significantly higher than that of the controls (2.1 +/- 0.7). The sensitivity and specificity of CD4/CD8 ratio in BALF for the diagnosis of sarcoidosis were 86% and 100%, respectively. We found that the CD4/CD8 ratio in BALF plays an important role in the diagnosis of pulmonary sarcoidosis. The analysis of CD4 in BALF may be useful in assessing the activity of sarcoidosis. The measurement of the CD4/CD8 ratio may be used to determine prognosis of pulmonary sarcoidosis.

Reversal of doxorubicin resistance by tetrandrine in Chinese hamster ovary cell line

Tetrandrine (Tet) 0.5 microgram.ml-1 and 1 microgram.ml-1 potentiated 2.88- and 4.3-fold growth-inhibitory effects of doxorubicin (Dox) in Chinese hamster ovary cell line (CHO), respectively, while Tet 1 microgram.ml-1 and 2.5 micrograms.ml-1 potentiated 7.3- and 8.4-fold in its resistant cell line (CHO/Dox), respectively. The colony-forming efficiencies were reduced in CHO and CHO/Dox when the cells were treated with noncytotoxic doses of Tet 2.5 micrograms.ml-1 and 5 micrograms.ml-1 in combination with different concentration of Dox. Increase in accumulation of Dox in CHO/Dox cells was shown by fluorometry. The result indicated that Tet reversed the resistance to Dox in CHO/Dox cells.

[Report of 2 cases with sarcoid pericardiac effusion]

Two cases of sarcoidosis with pericardial effusion were reported. They had the typical presentation of sarcoidosis with bilateral hilar and mediastinal lymph-node enlargement, reticular pattern in chest X-ray examination and increase of SACE. Biopsy of the scalene lymph nodes confirmed the diagnosis of sarcoidosis and Kveim test was also positive in one subject. The unusual manifestation was their pericardiac effusion confirmed by x-ray and UCG examination. The amount of pericardial effusion remarkably decreased after treatment with oral steroids. In this paper we reviewed the literatures and discussed the clinical features, diagnostic procedures, pathologic changes, treatment and prognosis of sarcoidosis complicated with pericardial effusion.