Changes in soluble LDL receptor and lipoprotein fractions in response to diet in the DIETFITS weight loss study

Circulating levels of the soluble ligand-binding ectodomain of the LDL receptor (sLDLR) that is proteolytically cleaved from the cell surface have been shown to correlate with plasma triglycerides, but the lipid and lipoprotein effects of longitudinal changes in sLDLR have not been examined. We sought to assess associations between changes in sLDLR and detailed lipoprotein measurements between baseline and 6 months in participants in the DIETFITS (Diet Intervention Examining The Factors Interacting with Treatment Success) weight loss trial who were randomly assigned to the low-fat (n = 225) or low-carbohydrate (n = 236) diet arms. sLDLR was assayed using a proteomic procedure, lipids and apoprotein (apo) B and apoAI were measured by standard assays, and lipoprotein particle subfractions were quantified by ion mobility methodology. Changes in sLDLR were significantly positively associated with changes in plasma cholesterol, triglycerides, apoB, large-sized and medium-sized VLDL, and small and very small LDL, and inversely with changes in large LDL and HDL. The lipoprotein subfraction associations with sLDLR were independent of age, sex, diet, and BMI, but all except for large LDL were reduced to insignificance when adjusted for triglyceride change. Principal component analysis identified three independent clusters of changes in lipoprotein subfractions that accounted for 78% of their total variance. Change in sLDLR was most strongly correlated with change in the principal component that was loaded positively with large VLDL and small and very small LDL and negatively with large LDL and HDL. In conclusion, sLDLR is a component of a cluster of lipids and lipoproteins that are characteristic of atherogenic dyslipidemia.

Gatifloxacin derivatives: Synthesis, antimycobacterial activities, and inhibition of Mycobacterium tuberculosis DNA gyrase

Sixteen 7-substituted gatifloxacin derivatives were synthesized and evaluated for antimycobacterial activity in vitro and in vivo against Mycobacterium tuberculosis H37Rv (MTB) and multi-drug resistant M. tuberculosis (MDR-TB), and also tested for the ability to inhibit the supercoiling activity of DNA gyrase from M. tuberculosis. Among the synthesized compounds, 1-cyclopropyl-6-fluoro-8-methoxy-7-[[[N4-[1'-(5-isatinyl-beta-semicarbazo)]methyl]3-methyl]N1-piperazinyl]-4-oxo-1,4-dihydro-3-quinoline carboxylic acid (3d) was found to be the most active compound in vitro with an MIC of 0.0125 microg/mL against MTB and MTR-TB. In the in vivo animal model 3d decreased the bacterial load in lung and spleen tissues with 3.62- and 3.76-log10 protections, respectively. Compound 3d was also found to be equally active as gatifloxacin in the inhibition of the supercoiling activity of wild-type M. tuberculosis DNA gyrase with an IC50 of 3.0 microg/mL. The results demonstrate the potential and importance of developing new quinolone derivatives against mycobacterial infections.

Anisotropic origin of the bending instability of the flux-antiflux interface in type-II superconductors

The physical nature of the macroturbulence in vortex matter in YBCO superconductors is investigated by means of a magneto-optic study of the instability in a single crystal prepared especially for this purpose. The instability develops near those sample edges where the oppositely directed flow of vortices and antivortices, guided by twin boundaries, is characterized by the discontinuity of the tangential component of the hydrodynamic velocity. This fact indicates that the macroturbulence is analogous to the instability of fluid flow at a surface of a tangential velocity discontinuity in classical hydrodynamics and is related to the anisotropic flux motion in the superconductor.

Hydrodynamic instability of the flux-antiflux interface in type-II superconductors

A possible mechanism of the macroturbulence instability observed in fluxline systems during remagnetization of superconductors is proposed. It is shown that when a region with flux is invaded by antiflux the interface can become unstable if there is a relative tangential flux motion. This condition occurs at the interface owing to the anisotropy of the viscous motion of vortices. The phenomenon is similar to the instability of the tangential discontinuity in classical hydrodynamics. The obtained results are supported by magneto-optical observations of flux distribution on the surface of a YBCO single crystal with twins.

Quinolone resistance mutations in Streptococcus pneumoniae GyrA and ParC proteins: mechanistic insights into quinolone action from enzymatic analysis, intracellular levels, and phenotypes of wild-type and mutant proteins

Mutations in DNA gyrase and/or topoisomerase IV genes are frequently encountered in quinolone-resistant mutants of Streptococcus pneumoniae. To investigate the mechanism of their effects at the molecular and cellular levels, we have used an Escherichia coli system to overexpress S. pneumoniae gyrase gyrA and topoisomerase IV parC genes encoding respective Ser81Phe and Ser79Phe mutations, two changes widely associated with quinolone resistance. Nickel chelate chromatography yielded highly purified mutant His-tagged proteins that, in the presence of the corresponding GyrB and ParE subunits, reconstituted gyrase and topoisomerase IV complexes with wild-type specific activities. In enzyme inhibition or DNA cleavage assays, these mutant enzyme complexes were at least 8- to 16-fold less responsive to both sparfloxacin and ciprofloxacin. The ciprofloxacin-resistant (Cip(r)) phenotype was silent in a sparfloxacin-resistant (Spx(r)) S. pneumoniae gyrA (Ser81Phe) strain expressing a demonstrably wild-type topoisomerase IV, whereas Spx(r) was silent in a Cip(r) parC (Ser79Phe) strain. These epistatic effects provide strong support for a model in which quinolones kill S. pneumoniae by acting not as enzyme inhibitors but as cellular poisons, with sparfloxacin killing preferentially through gyrase and ciprofloxacin through topoisomerase IV. By immunoblotting using subunit-specific antisera, intracellular GyrA/GyrB levels were a modest threefold higher than those of ParC/ParE, most likely insufficient to allow selective drug action by counterbalancing the 20- to 40-fold preference for cleavable-complex formation through topoisomerase IV observed in vitro. To reconcile these results, we suggest that drug-dependent differences in the efficiency by which ternary complexes are formed, processed, or repaired in S. pneumoniae may be key factors determining the killing pathway.

Effect of adenovirus type 1 and influenza A virus on Streptococcus pneumoniae nasopharyngeal colonization and otitis media in the chinchilla

Considerable evidence has implicated respiratory tract virus potentiation of bacterial adherence, colonization, and superinfection as a significant factor contributing to the pathogenesis of otitis media (OM). Influenza A and B viruses, adenovirus, and respiratory syncytial virus are the primary respiratory tract viruses associated with this disease. Investigations have established a dramatic increase in the development of experimental OM in chinchillas co-inoculated with influenza A virus and Streptococcus pneumoniae (Spn). The mechanism underlying this phenomenon was suggested to involve, in part, viral compromise of eustachian tube mucosal integrity and function. This study was designed to assess and compare the effect of adenovirus and influenza A virus infection on adherence, the kinetics of colonization, and invasion of the middle ear by Spn in the chinchilla model of OM. Cohorts were inoculated intranasally with adenovirus type 1 or influenza A virus, and then inoculated intranasally 7 days later with Spn 6A. All cohorts were observed over a 14-day period after challenge with Spn, and the incidence and severity of OM were assessed by several methods, including culture of the nasopharynx and middle ear effusions. The data indicated that influenza A virus promotes a significant increase in nasopharyngeal colonization by Spn, an increased incidence and severity of OM, and a sustained presence of Spn in the effusions. Adenovirus infection, however, did not enhance colonization by Spn or result in an increased incidence or severity of OM.

Potent antipneumococcal activity of gemifloxacin is associated with dual targeting of gyrase and topoisomerase IV, an in vivo target preference for gyrase, and enhanced stabilization of cleavable complexes in vitro

We investigated the roles of DNA gyrase and topoisomerase IV in determining the susceptibility of Streptococcus pneumoniae to gemifloxacin, a novel fluoroquinolone which is under development as an antipneumococcal drug. Gemifloxacin displayed potent activity against S. pneumoniae 7785 (MIC, 0.06 microgram/ml) compared with ciprofloxacin (MIC, 1 to 2 microgram/ml). Complementary genetic and biochemical approaches revealed the following. (i) The gemifloxacin MICs for isogenic 7785 mutants bearing either parC or gyrA quinolone resistance mutations were marginally higher than wild type at 0.12 to 0.25 microgram/ml, whereas the presence of both mutations increased the MIC to 0.5 to 1 microgram/ml. These data suggest that both gyrase and topoisomerase IV contribute significantly as gemifloxacin targets in vivo. (ii) Gemifloxacin selected first-step gyrA mutants of S. pneumoniae 7785 (gemifloxacin MICs, 0.25 microgram/ml) encoding Ser-81 to Phe or Tyr, or Glu-85 to Lys mutations. These mutants were cross resistant to sparfloxacin (which targets gyrase) but not to ciprofloxacin (which targets topoisomerase IV). Second-step mutants (gemifloxacin MICs, 1 microgram/ml) exhibited an alteration in parC resulting in changes of ParC hot spot Ser-79 to Phe or Tyr. Thus, gyrase appears to be the preferential in vivo target. (iii) Gemifloxacin was at least 10- to 20-fold more effective than ciprofloxacin in stabilizing a cleavable complex (the cytotoxic lesion) with either S. pneumoniae gyrase or topoisomerase IV enzyme in vitro. These data suggest that gemifloxacin is an enhanced affinity fluoroquinolone that acts against gyrase and topoisomerase IV in S. pneumoniae, with gyrase the preferred in vivo target. The marked potency of gemifloxacin against wild type and quinolone-resistant mutants may accrue from greater stabilization of cleavable complexes with the target enzymes.

Probing the interaction of the cytotoxic bisdioxopiperazine ICRF-193 with the closed enzyme clamp of human topoisomerase IIalpha

Topoisomerase II is an ATP-operated protein clamp that captures a DNA helix and transports it through another DNA duplex, allowing chromosome segregation at mitosis. A number of cytotoxic bisdioxopiperazines such as ICRF-193 target topoisomerase II by binding and trapping the closed enzyme clamp. To investigate this unusual mode of action, we have used yeast to select plasmid-borne human topoisomerase IIalpha alleles resistant to ICRF-193. Mutations in topoisomerase IIalpha of Leu-169 to Phe (L169F) (in the N-terminal ATPase domain) and Ala-648 to Pro (A648P) (in the core domain) were identified as conferring >50-fold and 5-fold resistance to ICRF-193 in vivo, respectively. The L169F mutation, located next to the Walker A box ATP-binding sequence, resulted in a mutant enzyme displaying ICRF-193-resistant topoisomerase and ATPase activities and whose closed clamp was refractory to ICRF-193-mediated trapping as an annulus on closed circular DNA. These data imply that the mutation interferes directly with ICRF-193 binding to the N-terminal ATPase gate. In contrast, the A648P enzyme displayed topoisomerase activities exhibiting wild-type sensitivity to ICRF-193. We suggest that the inefficient trapping of the A648P closed clamp results either from the observed increased ATP requirement, or more likely, from lowered salt stability, perhaps involving destabilization of ICRF-193 interactions with the B'-B' interface in the core domain. These results provide evidence for at least two different phenotypic classes of ICRF-193 resistance mutations and suggest that bisdioxopiperazine action involves the interplay of both the ATPase and core domains of topoisomerase IIalpha.

High-fat diet and prostate cancer: the controversial connection

High-fat diet has been associated with conditions such as heart disease and colon cancer. Is there a link between high-fat diet and prostate cancer? The summation of an abbreviated literature search strives to answer this question.

Clinical utilization of the international normalized ratio (INR)

The prothrombin time (PT) is one of the most important laboratory tests to determine the functionality of the blood coagulation system. It is used in patient care to diagnose diseases of coagulation, assess the risk of bleeding in patients undergoing operative procedures, monitor patients being treated with oral anticoagulant (coumadin) therapy, and evaluate liver function. The PT is performed by measuring the clotting time of platelet-poor plasma after the addition of calcium and thromboplastin, a combination of tissue factor and phospholipid. Intra- and interlaboratory variation in the PT was a significant problem for clinical laboratories in the past, when crude extracts of rabbit brain or human placenta were the only source of thromboplastin. The international normalized ratio (INR), developed by the World Health Organization in the early 1980s, is designed to eliminate problems in oral anticoagulant therapy caused by variability in the sensitivity of different commercial sources and different lots of thromboplastin to blood coagulation factor VII. The INR is used worldwide by most laboratories performing oral anticoagulation monitoring, and is routinely incorporated into dosage planning for patients receiving warfarin. Although the recent availability of sensitive PT reagents prepared from recombinant human tissue factor (rHTF) and synthetic phospholipids eliminated many of the earlier problems associated with the use of crude thromboplastin preparations, local instrument variability in the INR still remains a problem. Presently, the use of plasma calibrants seems the best solution to this problem. Standardizing the point-of-care instruments for INR monitoring is another dilemma faced by the industry. Ultimately, new generations of anticoagulant drugs may eliminate the need for laboratory monitoring of anticoagulant therapy.

Mutations at arg486 and glu571 in human topoisomerase IIalpha confer resistance to amsacrine: relevance for antitumor drug resistance in human cells

Human topoisomerase II, a nuclear protein involved in chromosome segregation, is the target of amsacrine and other clinically important anticancer drugs. The enzyme is expressed as alpha and beta isoforms whose mutation/down-regulation has been implicated in drug resistance. To understand the role of target mutations in cellular drug resistance, we have used yeast to select and characterize plasmid-borne human topoisomerase IIalpha mutants resistant to amsacrine. Single point changes of Glu571 to Lys (E571K) or Arg486 to Lys (R486K) in the conserved PLRGK motif, both of which reside in the GyrB homology domain of human topoisomerase IIalpha, were frequently selected and could be shown in vivo to confer >25-fold and >100-fold resistance, respectively, to amsacrine and approximately 3-fold cross-resistance to etoposide. Highly purified E571K and R486K human topoisomerase IIalpha proteins required 100-fold higher levels of amsacrine to induce DNA cleavage similar to that of wild-type protein, consistent with a resistance mechanism involving reduced cleavable complex formation. Our functional studies of the R486K mutation, previously identified in two amsacrine-resistant human cell lines and in human biopsy material, establish unequivocally that it confers resistance, and suggest mechanisms for its phenotypic expression in vivo. These results differ significantly from previous work using yeast topoisomerase II as a model system: introduction of the equivalent mutation to R486K (R476K) into the yeast enzyme did not give amsacrine resistance. We conclude that species-specific differences in topoisomerase II enzymes can affect the drug resistance phenotype of particular mutations and highlight the need to study the relevant human homolog.

Engineering the specificity of antibacterial fluoroquinolones: benzenesulfonamide modifications at C-7 of ciprofloxacin change its primary target in Streptococcus pneumoniae from topoisomerase IV to gyrase

We have examined the antipneumococcal mechanisms of a series of novel fluoroquinolones that are identical to ciprofloxacin except for the addition of a benzenesulfonylamido group to the C-7 piperazinyl ring. A number of these derivatives displayed enhanced activity against Streptococcus pneumoniae strain 7785, including compound NSFQ-105, bearing a 4-(4-aminophenylsulfonyl)-1-piperazinyl group at C-7, which exhibited an MIC of 0.06 to 0.125 microg/ml compared with a ciprofloxacin MIC of 1 microg/ml. Several complementary approaches established that unlike the case for ciprofloxacin (which targets topoisomerase IV), the increased potency of NSFQ-105 was associated with a target preference for gyrase: (i) parC mutants of strain 7785 that were resistant to ciprofloxacin remained susceptible to NSFQ-105, whereas by contrast, mutants bearing a quinolone resistance mutation in gyrA were four- to eightfold more resistant to NSFQ-105 (MIC of 0.5 microg/ml) but susceptible to ciprofloxacin; (ii) NSFQ-105 selected first-step gyrA mutants (MICs of 0.5 microg/ml) encoding Ser-81-to-Phe or -Tyr mutations, whereas ciprofloxacin selects parC mutants; and (iii) NSFQ-105 was at least eightfold more effective than ciprofloxacin at inhibiting DNA supercoiling by S. pneumoniae gyrase in vitro but was fourfold less active against topoisomerase IV. These data show unequivocally that the C-7 substituent determines not only the potency but also the target preference of fluoroquinolones. The importance of the C-7 substituent in drug-enzyme contacts demonstrated here supports one key postulate of the Shen model of quinolone action.

Activity of gemifloxacin against penicillin- and ciprofloxacin-resistant Streptococcus pneumoniae displaying topoisomerase- and efflux-mediated resistance mechanisms

Nine penicillin-resistant Streptococcus pneumoniae clinical isolates from Northern Ireland, resistant to ciprofloxacin (MICs, 2 to 64 microg/ml) through topoisomerase- and/or reserpine-sensitive efflux mechanisms, were highly susceptible to gemifloxacin (MICs, 0.03 to 0. 12 microg/ml). Two strains (requiring a ciprofloxacin MIC of 64 microg/ml) carried known quinolone resistance mutations in parC, parE, and gyrB, resulting in S79F, D435V, and E474K changes, respectively. Thus, gemifloxacin is active against clinical strains exhibiting altered topoisomerase and efflux phenotypes.

Streptococcus pneumoniae DNA gyrase and topoisomerase IV: overexpression, purification, and differential inhibition by fluoroquinolones

Streptococcus pneumoniae gyrA and gyrB genes specifying the DNA gyrase subunits have been cloned into pET plasmid vectors under the control of an inducible T7 promoter and have been separately expressed in Escherichia coli. Soluble 97-kDa GyrA and 72-kDa GyrB proteins bearing polyhistidine tags at their respective C-terminal and N-terminal ends were purified to apparent homogeneity by one-step nickel chelate column chromatography and were free of host E. coli topoisomerase activity. Equimolar amounts of the gyrase subunits reconstituted ATP-dependent DNA supercoiling with comparable activity to gyrase of E. coli and Staphylococcus aureus. In parallel, S. pneumoniae topoisomerase IV ParC and ParE subunits were similarly expressed in E. coli, purified to near homogeneity as 93- and 73-kDa proteins, and shown to generate efficient ATP-dependent DNA relaxation and DNA decatenation activities. Using the purified enzymes, we examined the inhibitory effects of three paradigm fluoroquinolones-ciprofloxacin, sparfloxacin, and clinafloxacin-which previous genetic studies with S. pneumoniae suggested act preferentially through topoisomerase IV, through gyrase, and through both enzymes, respectively. Surprisingly, all three quinolones were more active in inhibiting purified topoisomerase IV than gyrase, with clinafloxacin showing the greatest inhibitory potency. Moreover, the tested agents were at least 25-fold more effective in stabilizing a cleavable complex (the relevant cytotoxic lesion) with topoisomerase IV than with gyrase, with clinafloxacin some 10- to 32-fold more potent against either enzyme, in line with its superior activity against S. pneumoniae. The uniform target preference of the three fluoroquinolones for topoisomerase IV in vitro is in apparent contrast to the genetic data. We interpret these results in terms of a model for bacterial killing by quinolones in which cellular factors can modulate the effects of target affinity to determine the cytotoxic pathway.

Molecular cloning and characterization of the human topoisomerase IIalpha and IIbeta genes: evidence for isoform evolution through gene duplication

Human DNA topoisomerase II is essential for chromosome segregation and is the target for several clinically important anticancer agents. It is expressed as genetically distinct alpha and beta isoforms encoded by the TOP2alpha and TOP2beta genes that map to chromosomes 17q21-22 and 3p24, respectively. The genes display different patterns of cell cycle- and tissue-specific expression, with the alpha isoform markedly upregulated in proliferating cells. In addition to the fundamental role of TOP2alpha and TOP2beta genes in cell growth and development, altered expression and rearrangement of both genes are implicated in anticancer drug resistance. Here, we report the complete structure of the human topoisomerase IIalpha gene, which consists of 35 exons spanning 27.5 kb. Sequence data for the exon-intron boundaries were determined and examined in the context of topoisomerase IIalpha protein structure comprising three functional domains associated with energy transduction, DNA breakage-reunion activity and nuclear localization. The organization of the 3' half of human TOP2beta, including sequence specifying the C-terminal nuclear localization domain, was also elucidated. Of the 15 introns identified in this 20 kb region of TOP2beta, the first nine and the last intron align in identical positions and display the same phases as introns in TOP2alpha. Though their extreme 3' ends differ, the striking conservation suggests the two genes diverged recently in evolutionary terms consistent with a gene duplication event. Access to TOP2alpha and TOP2beta gene structures should aid studies of mutations and gene rearrangements associated with anticancer drug resistance.

Effect of lacto-N-neotetraose, asialoganglioside-GM1 and neuraminidase on adherence of otitis media-associated serotypes of Streptococcus pneumoniae to chinchilla tracheal epithelium

The adherence of Streptococcus pneumoniae (Spn) otitis media-associated serotypes 3, 6A and 14 to ciliated chinchilla respiratory epithelium was investigated using a whole organ perfusion technique. We demonstrated that Spn adhere to chinchilla tracheal epithelium within 30 min and exhibit saturation kinetics indicating that the effect being observed is receptor mediated. Inhibition of adherence was achieved by prior incubation of Spn with lacto-N-neotetraose (LNnT) or asialoIganglioside GM1 (aGM1), recognized by glycoconjugate analogs of known Spn receptors. NeurIaminidase treatment of the tracheae increased Spn adherence in vitro and reversed the inhibition effect of LNnT suggesting that neuraminidase treatment resulted in an increase in the number of available receptors for Spn. The chinchilla trachea organ perfusion culture system used in this study imitates eustachian tube conditions more closely than isolated cell culture systems and is a useful model for investigating the role of Spn adherence in vitro in the pathogenesis of OM.

Effect of tumor necrosis factor alpha and interleukin 1-alpha on the adherence of Streptococcus pneumoniae to chinchilla tracheal epithelium

The trachea whole organ perfusion technique was used to study the effect of tumor necrosis factor alpha (TNF alpha) and interleukin-1 alpha (IL-1 alpha) on the adherence of otitis media pathogen Streptococcus pneumoniae (Spn) type 6A. Tracheas were removed from chinchillas and divided equally. One-half trachea was activated by incubation with 1-10 ng/ml of either TNF alpha or IL-1 alpha prior to the addition of Spn 6A to the organ culture perfusion chamber. Colony forming units (cfu) of Spn/millimeter trachea were determined for activated tracheas and controls. Dose response and kinetics data were generated for each cytokine. The specificity of each reaction was determined by neutralization studies with specific anti-cytokine antibodies. The data indicate that both TNF alpha and IL-1 alpha increase the adherence of Spn to the respiratory epithelium of this tubal organ and suggest a mechanism which may facilitate enhanced adherence in vivo and thereby contribute to the pathogenesis of otitis media and other upper respiratory tract diseases.

Detection of a common mutation in factor V gene responsible for resistance to activate protein C causing predisposition to thrombosis

Hereditary predisposition to thrombosis due to activated protein C resistance (APCR) has been attributed to a missense mutation in the factor V gene at nucleotide 1691 (G to A), causing replacement of arginine at codon 506 with glutamine. Using an RFLP-PCR assay to detect this mutation, we measured a prevalence of 3.3% in healthy Caucasians and 1.25% in healthy African-Americans. In addition, we evaluated a total of 90 consecutive specimens submitted to the coagulation laboratory at the Medical College of Virginia for the presence of this mutation. We compared our results for 78 of these specimens with the values measured by a modified partial thromboplastin assay, the COATEST. Twelve of the 90 samples could not be tested using the COATEST because the patients were undergoing anticoagulant therapy. One of the latter 12 specimens was positive by the RFLP-PCR test. Using the genetic test as the definitive assay and the cutoff value established for distinguishing between normal and abnormal results by the COATEST, the COATEST had a sensitivity of 50% and specificity of 93% for the detection of factor V mutation. Analysis of the 90 samples stratified by ethnic groups revealed a frequency of mutation of 13.3% for Caucasians and 6.88% for African-Americans, although with the present sample size, the difference was not statistically significant. Although the COATEST is technically simpler to perform than the genetic test for diagnosing the presence of the factor V mutation, its use for this purpose is limited due to low sensitivity. Thus where this disorder is clinically suspected, submission of the specimen directly for genetic testing by RFLP-PCR or equivalent assay should be considered.

DNA gyrase and topoisomerase IV are dual targets of clinafloxacin action in Streptococcus pneumoniae

We examined the response of Streptococcus pneumoniae 7785 to clinafloxacin, a novel C-8-substituted fluoroquinolone which is being developed as an antipneumococcal agent. Clinafloxacin was highly active against S. pneumoniae 7785 (MIC, 0.125 microg/ml), and neither gyrA nor parC quinolone resistance mutations alone had much effect on this activity. A combination of both mutations was needed to register resistance, suggesting that both gyrase and topoisomerase IV are clinafloxacin targets in vivo. The sparfloxacin and ciprofloxacin MICs for the parC-gyrA mutants were 16 to 32 and 32 to 64 microg/ml, respectively, but the clinafloxacin MIC was 1 microg/ml, i.e., within clinafloxacin levels achievable in human serum. S. pneumoniae 7785 mutants could be selected stepwise with clinafloxacin at a low frequency, yielding first-, second-, third-, and fourth-step mutants for which clinafloxacin MICs were 0.25, 1, 6, and 32 to 64 microg/ml, respectively. Thus, high-level resistance to clinafloxacin required four steps. Characterization of the quinolone resistance-determining regions of the gyrA, parC, gyrB, and parE genes by PCR, HinfI restriction fragment length polymorphism, and DNA sequence analysis revealed an invariant resistance pathway involving sequential mutations in gyrA or gyrB, in parC, in gyrA, and finally in parC or parE. No evidence was found for other resistance mechanisms. The gyrA mutations in first- and third-step mutants altered GyrA hot spots Ser-83 to Phe or Tyr (Escherichia coli coordinates) and Glu-87 to Gln or Lys; second- and fourth-step parC mutations changed equivalent hot spots Ser-79 to Phe or Tyr and Asp-83 to Ala. gyrB and parE changes produced novel alterations of GyrB Glu-474 to Lys and of Pro-454 to Ser in the ParE PLRGK motif. Difficulty in selecting first-step gyrase mutants (isolated with 0.125 [but not 0.25] microg of clinafloxacin per ml at a frequency of 5.0 x 10(-10) to 8.5 x 10(-10)) accompanied by the small (twofold) MIC increase suggested only a modest drug preference for gyrase. Given the susceptibility of defined gyrA or parC mutants, the results suggested that clinafloxacin displays comparable if unequal targeting of gyrase and topoisomerase IV. Dual targeting and the intrinsic potency of clinafloxacin against S. pneumoniae and its first- and second-step mutants are desirable features in limiting the emergence of bacterial resistance.

Nuclear distribution of human DNA topoisomerase IIbeta: a nuclear targeting signal resides in the 116-residue C-terminal tail

We have analyzed the subcellular distribution of the beta isoform of human topoisomerase II using both isoform-specific antisera and an epitope-tagging approach. Previous immunocytochemical studies have yielded differing results with one reporting this isoform to be predominantly nucleolar. Later studies seem to refute this finding, as do our results with isoform-specific antisera reported here. Epitope tagging minimizes potential complications arising from the use of anti-topoisomerase II antisera that may recognize epitopes that are modified or masked in vivo and could lead to misleading results in immunocytochemical studies. A second strength of this approach is that it allowed a comparison with similarly tagged control proteins (derived from the nucleolar transcription factor UBF) that were known to localize unambiguously to the cytoplasmic, nucleoplasmic, or nucleolar compartments. We report that the C-terminal domain of topoisomerase IIbeta fused to a beta-galactosidase tag localizes to the nucleus (but not the nucleolar compartment) and that this is indistinguishable from the localization of native topoisomerase IIbeta detected by isoform-specific antisera. Further analysis revealed that the nuclear localization determinant lies within the 116-residue C-terminal tail of human topoisomerase IIbeta.

Human DNA topoisomerase IIalpha-dependent DNA cleavage and yeast cell killing by anthracycline analogues

Anthracyclines are among the most clinically useful topoisomerase II poisons. A complete understanding of their molecular mechanism is thus fundamental for a rational design of novel agents. We evaluated four anthracycline analogues with respect to human topoisomerase IIalpha-dependent DNA cleaving activity, efficiency in killing yeast cells, and uptake and retention in yeast and compared the yeast system to tumor cell line models. The yeast JN394top2-4 strain was used because it has a topoisomerase II ts gene mutation: enzyme activity is much less at 30 degrees C than at 25 degrees C and is completely lost at 35 degrees C. Untransformed JN394top2-4 cells were 33-fold more sensitive to idarubicin at 25 degrees C than at 30 degrees C, showing that topoisomerase II is the primary drug target. Overexpression of human topoisomerase IIalpha was toxic to yeast cells when the yeast enzyme was inactivated. Drug-dependent killing of yeast cells expressing low levels of the human alpha isoenzyme at 35 degrees C showed that the analogues spanned a 3-log range of cytotoxic potency in yeast, as they did in tumor cells. However, the compounds were much less active against the yeast strain than mammalian tumor cell lines. Drug uptake was determined and found to be altered in yeast with respect to tumor cells. Although DNA cleavage stimulated by anthracyclines roughly correlated with cytotoxicity, the cleavage level:cytotoxicity ratios were different for the studied drugs. Thus, the results suggest that other drug-dependent molecular factors contribute to drug activity in addition to the cellular content of topoisomerase IIalpha and drug uptake.

Identification of yeast DNA topoisomerase II mutants resistant to the antitumor drug doxorubicin: implications for the mechanisms of doxorubicin action and cytotoxicity

Doxorubicin is a therapeutically useful anticancer drug that exerts multiple biological effects. Its antitumor and cardiotoxic properties have been ascribed to anthracycline-mediated free radical damage to DNA and membranes. Evidence for this idea comes in part from the selection by doxorubicin from stationary phase yeast cells of mutants (petites) deficient in mitochondrial respiration and therefore defective in free radical generation. However, doxorubicin also binds to DNA topoisomerase II, converting the enzyme into a DNA damaging agent through the trapping of a covalent enzyme-DNA complex termed the 'cleavable complex.' We have used yeast to determine whether stabilization of cleavable complexes plays a role in doxorubicin action and cytotoxicity. A plasmid-borne yeast TOP2 gene was mutagenized with hydroxylamine and used to transform drug-permeable yeast strain JN394t2-4, which carries a temperature-sensitive top2-4 mutation in its chromosomal TOP2 gene. Selection in growth medium at the nonpermissive temperature of 35 degrees in the presence of doxorubicin resulted in the isolation of plasmid-borne top2 mutants specifying functional doxorubicin-resistant DNA topoisomerase II. Single-point changes of Gly748 to Glu or Ala642 to Ser in yeast topoisomerase II, which lie in and adjacent to the CAP-like DNA binding domain, respectively, were identified as responsible for resistance to doxorubicin, implicating these regions in drug action. None of the mutants selected in JN394t2-4, which has a rad52 defect in double-strand DNA break repair, was respiration-deficient. We conclude that topoisomerase II is an intracellular target for doxorubicin and that the genetic background and/or cell proliferation status can determine the relative importance of topoisomerase II- versus free radical-killing.

Molecular cloning and expression of the Candida albicans TOP2 gene allows study of fungal DNA topoisomerase II inhibitors in yeast

Candida albicans topoisomerase II, encoded by the TOP2 gene, mediates chromosome segregation by a double-strand DNA break mechanism and is a potential target for anti-fungal therapy. In this paper, we report the characterization of the C. albicans TOP2 gene and its use to develop a yeast system that allows the identification and study of anti-fungal topoisomerase II inhibitors in vivo. The gene, specifying a 1461-residue polypeptide with only 40% identity with human topoisomerase IIalpha and beta isoforms, was isolated from C. albicans on a 6.3 kb EcoRI fragment that mapped to chromosome 4. It was used to construct a plasmid in which TOP2 expresses a recombinant enzyme (residues 57-1461 of C. albicans topoisomerase II fused to the first five residues of Saccharomyces cerevisiae topoisomerase II) under the control of a galactose-inducible promoter. The plasmid rescued the lethal phenotype of a temperature-sensitive S. cerevisiae DNA topoisomerase II mutant allowing growth at 35 degrees C. Yeast cells, bearing ISE2 permeability and rad52 double-strand-break-repair mutations the growth of which at 35 degrees C was dependent on C. albicans topoisomerase II, were killed by the known topoisomerase II inhibitors amsacrine and doxorubicin. Parallel experiments in yeast expressing human topoisomerase IIalpha allowed the relative sensitivities of the fungal and host topoisomerases to be examined in the same genetic background. To compare the killing in vivo with drug inhibition in vitro, the recombinant C. albicans topoisomerase II protein was expressed and purified to near-homogeneity from S. cerevisiae yielding a 160 kDa polypeptide that displayed the expected ATP-dependent DNA-relaxation and DNA-decatenation activities. The enzyme, whether examined in vitro or complementing in S. cerevisiae, was comparably sensitive to amsacrine and doxorubicin. Our results suggest that potential topoisomerase II-targeting anti-fungal inhibitors can be identified and studied in S. cerevisiae.

Targeting of DNA gyrase in Streptococcus pneumoniae by sparfloxacin: selective targeting of gyrase or topoisomerase IV by quinolones

gyrA and parC mutations have been identified inn Streptococcus pneumoniae mutants stepwise selected for resistance to sparfloxacin, an antipneumococcal fluoroquinolone. GyrA mutations (at the position equivalent to resistance hot spot Ser-83 in Escherichia coli GyrA) were found in all 17 first-step mutants examined and preceded DNA topoisomerase IV parC mutations (at Ser-79 or Glu-83), which appeared only in second-step mutants. The targeting of gyrase by sparfloxacin in S. pneumoniae but of topoisomerase IV by ciprofloxacin indicates that target preference can be altered by changes in quinolone structure.

DNA supercoiling and relaxation by ATP-dependent DNA topoisomerases

Bacterial DNA gyrase and the eukaryotic type II DNA topoisomerases are ATPases that catalyse the introduction or removal of DNA supercoils and the formation and resolution of DNA knots and catenanes. Gyrase is unique in using ATP to drive the energetically unfavourable negative supercoiling of DNA, an example of mechanochemical coupling: in contrast, eukaryotic topoisomerase II relaxes DNA in an ATP-requiring reaction. In each case, the enzyme-DNA complex acts as a ‘gate’ mediating the passage of a DNA segment through a transient enzyme-bridged double-strand DNA break. We are using a variety of genetic and enzymic approaches to probe the nature of these complexes and their mechanism of action. Recent studies will be described focusing on the role of DNA wrapping on the A 2 B 2 gyrase complex, subunit activities uncovered by using ATP analogues and the coumarin and quinolone inhibitors, and the identification and functions of discrete subunit domains. Homology between gyrase subunits and the A 2 homodimer of eukaryotic topo II suggests functional conservation between these proteins. The role of ATP hydrolysis by these topoisomerases will be discussed in regard to other energy coupling systems.

Complementation of temperature-sensitive topoisomerase II mutations in Saccharomyces cerevisiae by a human TOP2 beta construct allows the study of topoisomerase II beta inhibitors in yeast

We show herein that human DNA topoisomerase II beta is functional in yeast. It can complement a yeast temperature-sensitive mutation in topoisomerase II. The effect on human topoisomerase II beta of a number of topoisomerase II inhibitors was analysed in a yeast in vivo system and compared with that of human topoisomerase II alpha and wild-type yeast topoisomerase II. A drug permeable yeast strain (JN394 top2-4) was used to analyse the in vivo effects of known anti-topoisomerase II agents on human topoisomerase II beta transformants. A parallel analysis on human topoisomerase II alpha transformants provides the first in vivo analysis of the responses of yeast bearing the individual isoforms to these drugs. The strain was analysed at 35 degrees C, a non-permissive temperature at which only plasmid-borne topoisomerase II is active. A shuttle vector with either human topoisomerase II beta, human topoisomerase II alpha or yeast topoisomerase II under the control of a GAL1 promoter was used. The key findings were that amsacrine produced comparable levels of cell killing with both alpha and beta, whilst etoposide, doxorubicin and mitoxantrone produced higher degrees of cell killing with alpha than with beta or yeast topoisomerase II. Merbarone had the greatest effect on the yeast strain bearing plasmid-borne yeast topoisomerase II. Suramin, quercetin and genistein showed little cell killing in this system. This yeast in vivo system provides a powerful way to analyse the effects of anti-topoisomerase II agents on transformants bearing the individual human isoforms. This system also provides a means of analysing putative drug-resistance mutations in human topoisomerase II beta or to select for drug-resistance mutations in human topoisomerase II beta.

Amsacrine-promoted DNA cleavage site determinants for the two human DNA topoisomerase II isoforms alpha and beta

Site-specific DNA cleavage by topoisomerase II (EC 5.99.1.3) is induced by many antitumour drugs. Although human cells express two genetically distinct topoisomerase II isoforms, thus far the role and determinants of drug-induced DNA cleavage have been examined only for alpha. Here we report the first high-resolution study of amsacrine (mAMSA) induced DNA breakage by human topoisomerase II beta (overexpressed and purified from yeast) and a direct comparison with the recombinant alpha isoform. DNA cleavage in plasmid pBR322 and SV40 DNA was induced by alpha or beta in the absence or presence of the antitumour agent mAMSA, and sites were mapped using sequencing gel methodology. Low-resolution studies indicated that recombinant human alpha promoted DNA breakage at sites akin to those of beta, although some sites were only cleaved by one enzyme and different intensities were observed at some sites. However, statistical analysis of 70 drug-induced sites for beta and 70 sites for alpha revealed that both isoforms share the same base preferences at 13 positions relative to the enzyme cleavage site, including a very strong preference for A at +1. The result for recombinant alpha isoform is in agreement with previous studies using alpha purified from human cell lines. Thus, alpha and beta proteins apparently form similar ternary complexes with mAMSA and DNA. Previous studies have emphasized the importance of DNA topoisomerase II alpha; the results presented here demonstrate that beta is an in vitro target with similar site determinants, strongly suggesting that beta should also be considered a target of mAMSA in vivo.

Drug sensitivity and sequence specificity of human recombinant DNA topoisomerases IIalpha (p170) and IIbeta (p180)

Effective anticancer agents, such as epipodophyllotoxins and anthracyclines, exert their antitumor activity through stabilization of cleavable topoisomerase II/DNA complexes, which may result in DNA breakage on detergent addition. Two isozymes (alpha and beta) of DNA topoisomerase II are present in human cells; however, their roles as drug targets have not been completely defined. We determined the in vitro isoenzyme sensitivities to VM-26 (teniposide) and 4-demethoxy-3'-deamino-3'-hydroxy-4'-epi-doxorubicin (an anthracycline analog) and established the sequence selectivity of isoenzyme-mediated DNA cleavage. Human topoisomerases IIalpha and IIbeta were purified from yeast cells overexpressing the corresponding plasmid-borne cDNA. Enzyme sensitivities to drugs were measured by a DNA cleavage assay using 32P-labeled simian virus 40 DNA fragments, and cleavage sites were mapped using agarose and sequencing gels. Both isozymes were sensitive to the studied poisons. They stimulated similar cleavage intensity patterns in agarose and sequencing gels; however, minor differences could be detected. The results showed that local base preferences for DNA cleavage without drugs were different at positions -2 and -1. On the other hand, sequence specificities of VM-26 and 4-demethoxy-3'-deamino-3'-hydroxy-4'-epi-doxorubicin were identical for both isozymes and corresponded to those of the native murine enzyme. The identical drug sequence specificities suggested that molecular interactions of the tested drugs in the ternary complex are likely similar between the two isozymes. The current findings indicate that both topoisomerase IIalpha and IIbeta may be in vivo targets of antitumor poisons.

Involvement of topoisomerase IV and DNA gyrase as ciprofloxacin targets in Streptococcus pneumoniae

Ciprofloxacin-resistant mutants of Streptococcus pneumoniae 7785 were generated by stepwise selection at increasing drug concentrations. Sequence analysis of PCR products from the strains was used to examine the quinolone resistance-determining regions of the GyrA and GyrB proteins of DNA gyrase and the analogous regions of the ParC and ParE subunits of DNA topoisomerase IV. First-step mutants exhibiting low-level resistance had no detectable changes in their topoisomerase quinolone resistance-determining regions, suggesting altered permeation or another novel resistance mechanism. Nine of 10 second-step mutants exhibited an alteration in ParC at Ser-79 to Tyr or Phe or at Ala-84 to Thr. Third- and fourth-step mutants displaying high-level ciprofloxacin resistance were found to have, in addition to the ParC alteration, a change in GyrA at residues equivalent to Escherichia coli GyrA resistance hot spots Ser-83 and Asp-87 or in GyrB at Asp-435 to Asn, equivalent to E. coli Asp-426, part of a highly conserved EGDSA motif in GyrB. No ParE changes were observed. Complementary analysis of two S. pneumoniae clinical isolates displaying low-level resistance to ciprofloxacin revealed a ParC change at Ser-79 to Phe or Arg-95 to Cys but no changes in GyrA, GyrB, or ParE. A highly resistant isolate, in addition to a ParC mutation, had a GyrA alteration at the residue equivalent to E. coli Asp-87. Thus, in both laboratory strains and clinical isolates, ParC mutations preceded those in GyrA, suggesting that topoisomerase IV is a primary topoisomerase target and gyrase is a secondary target for ciprofloxacin in S. pneumoniae.

Quantification of 9-carboxy-11-nor-delta 9-tetrahydrocannabinol in urine using brominated 9-carboxy-11-nor-delta 9-tetrahydrocannabinol as the internal standard and high-performance liquid chromatography with electrochemical detection

A method was developed for quantitating 9-carboxy-11-nor-delta 9-tetrahydrocannabinol in human urine as part of the process for validating an automated enzyme immunoassay for marijuana metabolites. Sample cleanup was accomplished using a mixed-mode solid-phase extraction. 9-Carboxy-11-nor-delta 9-tetrahydrocannabinol and the internal standard, brominated 9-carboxy-11-nor-delta 9-tetrahydrocannabinol, were quantified using high-performance liquid chromatography with electrochemical detection (+ 0.85 V). The linear range for this method is 0.012-0.20 microgram/mL. No interference was seen for 22 drugs and metabolites. The pooled relative standard deviation is 4.1% (n = 27) for the quality control samples. This method was compared to gas chromatography with mass spectrometry by linear regression analysis. The slope of the line is 1.00 +/- 0.05 (standard error), the intercept is approximately zero, the coefficient of determination is 0.994, and the standard error of the estimate is 0.006 microgram/mL.

Quantitative evaluation of dizziness characteristics and impact on quality of life

Patients attending an outpatient clinic with the complaint of dizziness were given a set of five items to rank the magnitude of the frequency and severity of their dizziness and the impact of dizziness on their quality of life. They were given instruments to evaluate their degree of anxiety and depression. The impact of frequency and severity on the patients' daily activities, on the quality of life, and on the fear of becoming dizzy was self-rated by the patient. The score on quality of life was compared with that provided by the physician in a blind questionnaire. The items that were developed addressed the physical, functional, and emotional impact of dizziness and can be considered promising for the evaluation of the patients' degree of overall impairment.

Cloning and characterization of the parC and parE genes of Streptococcus pneumoniae encoding DNA topoisomerase IV: role in fluoroquinolone resistance

DNA topoisomerase IV mediates chromosome segregation and is a potential target for antibacterial agents including new antipneumococcal fluoroquinolones. We have used hybridization to a Staphylococcus aureus gyrB probe in concert with chromosome walking to isolate the Streptococcus pneumoniae parE-parC locus, lying downstream of a putative new insertion sequence and encoding 647-residue ParE and 823-residue ParC subunits of DNA topoisomerase IV. These proteins exhibited greatest homology respectively to the GrlB (ParE) and GrlA (ParC) subunits of S. aureus DNA topoisomerase IV. When combined, whole-cell extracts of Escherichia coli strains expressing S. pneumoniae ParC or ParE proteins reconstituted a salt-insensitive ATP-dependent decatenase activity characteristic of DNA topoisomerase IV. A second gyrB homolog isolated from S. pneumoniae encoded a 648-residue protein which we identified as GyrB through its close homology both to counterparts in S. aureus and Bacillus subtilis and to the product of the S. pneumoniae nov-1 gene that confers novobiocin resistance. gyrB was not closely linked to gyrA. To examine the role of DNA topoisomerase IV in fluoroquinolone action and resistance in S. pneumoniae, we isolated mutant strains stepwise selected for resistance to increasing concentrations of ciprofloxacin. We analysed four low-level resistant mutants and showed that Ser-79 of ParC, equivalent to resistance hotspots Ser-80 of GrlA and Ser-84 of GyrA in S. aureus, was in each case substituted with Tyr. These results suggest that DNA topoisomerase IV is an important target for fluoroquinolones in S. pneumoniae and establish this organism as a useful gram-positive system for resistance studies.

NorA plasmid resistance to fluoroquinolones: role of copy number and norA frameshift mutations

Staphylococcus aureus NorA protein is a transmembrane multidrug efflux pump that confers low-level resistance to hydrophilic fluoroquinolones. The norA gene promoter is active in Escherichia coli HB101. We have examined the genetic basis of norA-mediated resistance in E. coli by introducing a wild-type norA gene into HB101 in plasmid pCL1921, pBR322, or pUC18 exhibiting copy numbers that spanned a 22-fold range. Increased ciprofloxacin resistance correlated with norA transcript levels seen by Northern (RNA) analysis. Thus, contrary to some reports, a wild-type norA gene confers fluoroquinolone resistance in E. coli in a copy-number-dependent fashion and does not require mutational activation. Interestingly, a multicopy pUC19norA derivative gave transformants exhibiting a range of resistance phenotypes. The norA gene of one transformant carried a single base deletion (ATACAAT to AACAAT; the deleted base is underlined) in the putative--10 Pribnow box resulting in a promoter down-regulatory mutation; a second plasmid had acquired a frameshift producing a null mutation at codon 112. These mutations override the dual resistance-growth-inhibitory phenotype of high-copy-number norA plasmids. The results have implications for using the standard E. coli HB101 system to assess NorA function and potentially for plasmid-borne transmission of norA-mediated drug resistance.

Mode of action of GR122222X, a novel inhibitor of bacterial DNA gyrase

GR122222X is a potent inhibitor of the supercoiling reaction of bacterial DNA gyrase. We show that this compound binds stoichiometrically to inactivate the ATPase activity of a 43-kDa N-terminal fragment of the B subunit and competitively inhibits the binding of a radiolabelled coumarin drug to N-terminal fragments of GyrB. These and other data suggest that GR122222X has a mode of action similar, but not identical, to that of coumarin antibiotics.

Expression in Escherichia coli and purification of human eosinophil-derived neurotoxin with ribonuclease activity

Eosinophil-derived neurotoxin (EDN) is a ribonuclease with neurotoxic and helminthotoxic properties. It is present in the crystalloid granules of human eosinophils. We report the expression and characterization of a functionally active recombinant human EDN using the pMAL-cRI expression system. A cDNA for mature EDN was obtained by PCR and inserted in pMAL-cRI downstream of the malE gene encoding maltose binding protein. Induction of the ptac promoter of the plasmid in Escherichia coli strain BL21(DE3) resulted in high level expression of soluble MAL-EDN fusion protein. Cleavage of affinity purified fusion protein with Factor Xa protease released recombinant EDN which comigrated with native EDN on SDS-polyacrylamide gels and cross-reacted with a polyclonal anti-EDN antiserum on Western blots. IN contrast to previous attempts at EDN expression, denatured and refolded EDN had ribonuclease activity and was prepared in microgram amounts. The availability of recombinant human EDN should facilitate studies of its structure and biological functions.

Expression, domain structure, and enzymatic properties of an active recombinant human DNA topoisomerase II beta

Human cells express two genetically distinct isoforms of DNA topoisomerase II, alpha and beta, which catalyze ATP-dependent DNA strand passage and are an important antitumor drug target. Here we report for the first time the successful overexpression of human topoisomerase II beta in yeast by cloning a topoisomerase II beta cDNA in a yeast shuttle vector under the control of a galactose-inducible promoter. Recombinant human topoisomerase II beta (residues 46-1621 fused to the first 5 residues of yeast topoisomerase II) was purified to homogeneity, yielding an enzymatically active polypeptide in sufficient quantity to allow analysis of its domain structure and comparison with that of recombinant human topoisomerase II alpha. Partial digestion of beta with either trypsin or protease SV8 generated fragments of approximately 130, 90, 62, and 45-50 kDa, arising from cleavage at three limited and discrete regions of the protein (A, B, and C) indicating the presence of at least four structural domains. Recombinant human topoisomerase II alpha and beta induced DNA breakage which was promoted by a variety of agents. Isoform differences in drug-induced DNA breakage were observed. These studies of human topoisomerase II beta in concert with alpha should aid the determination of their individual roles in cancer chemotherapy and should facilitate the design, targeting, and testing of cytotoxic antitumor agents.

Nucleotide sequence of the recF gene cluster from Staphylococcus aureus and complementation analysis in Bacillus subtilis recF mutants

We have determined the nucleotide sequence of a 3.5 kb segment in the recF region of the Staphylococcus aureus chromosome. The gene order at this locus, dnaA-dnaN-recF-gyrB is similar to that found in the replication origin region of many other bacteria. S. aureus RecF protein (predicted molecular mass 42.3 kDa), has 57% amino acid sequence identity with the Bacillus subtilis RecF protein (42.2 kDa), but only 26% with the Escherichia coli RecF protein (40.5 kDa). We have shown that the S. aureus recF gene partially complements the defect of a B. subtilis recF mutant, but does not complement an E. coli recF strain. The amino acid sequence alignment of seven available RecF proteins (five of them from bacteria of gram-negative origin) allowed us to identify eight highly conserved regions (alpha to theta) and to predict five new conserved regions within the gram-positive group (a to f). We suggest that the basic mechanism of homologous recombination is conserved among free-living bacteria.

Human eosinophil major basic protein, a mediator of allergic inflammation, is expressed by alternative splicing from two promoters

Human eosinophil major basic protein (MBP) is one of the principal mediators of injury to parasites and tissues in allergic inflammation. MBP is stored in eosinophil crystalloid granules and released with other granule constituents during eosinophil action. Previous studies have identified an MBP gene promoter that generates a 1.0 kb mRNA transcript encoding MBP preproprotein which undergoes processing to the mature storage form. To investigate how the MBP gene is regulated, we have examined the identity and levels of the MBP transcripts both in precursor cells and in blood eosinophils. It was found that the gene was expressed from two upstream promoters, a distal promoter P1 in addition to the previously described promoter P2. Evidence for the second promoter was initially provided by isolation from a human HL-60 leukaemic cell cDNA library of a novel 1.6 kb MBP cDNA that was distinct from the known 1.0 kb cDNA. The complete nucleotide sequence of the 1.6 kb cDNA was determined, and showed that the two cDNAs had identical coding and 3' untranslated regions but differed in their 5' sequences. By isolating and sequencing MBP genomic clones from an arrayed chromosome 11 library, it was demonstrated that the MBP gene is composed of nine upstream exons and five coding exons. The 1.6 and 1.0 kb cDNAs arise by differential splicing of alternate MBP transcripts from promoters P1 and P2 respectively, located 32 kb apart in the genomic DNA. Primer extension analysis identified two transcription start sites at P1, neither associated with a typical TATA box motif. Northern blotting and reverse-transcription PCR analysis showed that the 1.0 kb mRNA was present at higher levels than the 1.6 kb species in immature cells including HL-60 and bone-marrow cells. By contrast, low levels of 1.6 kb mRNA transcripts predominated in differentiated blood eosinophils. The results are compatible with differential use of P1 and P2 promoters as a mechanism for regulation of MBP expression during eosinophil maturation.

Aging and speed of behavior: possible consequences for psychological functioning

Over 100 years of observations have established that slowness of behavior is a characteristic of becoming old, although it is now recognized that health, use of medications, and physical activity may modify the extent of the slowing. Early research indicated that there is a limited contribution to slowing by peripheral sensory-motor factors. Substantial evidence has pointed to the central nervous system as the locus of the slowing. Recent investigators have expressed divided opinions about whether there is a pervasive general slowing of behavior by the central nervous system or whether there are specific localized mechanisms. This is not unlike early disputed views of the brain as having localized or global behavioral functions: Both principles appear to be simultaneously true. Sufficient research has been conducted to indicate that there are specific factors as well as a general process associated with the slowing of behavior with advancing age. Whether such slowing is a primary or secondary cause of age differences in cognitive processes is a significant scientific issue. A marked broadening of research on aging has been accompanied by an interest in identifying both the neurophysiological correlates of slowing as well as its role in specific cognitive processes. Yet another aspect of the changing research picture is the trend to move beyond the mere use of chronological age as the sole basis for comparing performance differences. Measurement of more independent variables is suggested as part of clusters or causal complexes that will indicate sources of the changes in speed and other aspects of behavior. These causal complexes include biological indicators such as disease, physiological capacity for work, and length of life, as well as causal complexes of social factors involving such variables as education, occupation, and ethnicity. There has been considerable discussion of markers of aging. In this approach, factors found to be closely associated with advancing age are used as measures of the effectiveness of attempts to modify the course of aging, e.g. by diet, exercise, new learning, and drugs. Along with other biomarkers of aging, speed of behavior may prove to be a criterion for assessing the impact of interventions on the rate and processes of aging. As a marker of aging, speed needs further exploration that will compare the slowness observed in different subgroups of adults with a wide range of outcomes in their productivity, capacity for adaptation to life's demands, and health. The present status of information about slowness of behavior with advancing age indicates that it is one of the most reliable features of human life.(ABSTRACT TRUNCATED AT 400 WORDS)

Use of yeast in the study of anticancer drugs targeting DNA topoisomerases: expression of a functional recombinant human DNA topoisomerase II alpha in yeast

A plasmid was constructed for the expression of human DNA topoisomerase II alpha in yeast from a galactose-inducible promoter of the yeast GAL1 gene. Expression of a recombinant human enzyme, in which the first 28 of the 1531 codons of human DNA topoisomerase II alpha were replaced by the first five codons of yeast DNA topoisomerase II, was shown to rescue the lethal phenotype of thermal sensitive yeast DNA topoisomerase II mutants at 35 degrees C. Purification of the human enzyme overexpressed in yeast yielded a single polypeptide with an apparent mass of 170 kDa, and the properties of the purified recombinant enzyme were found to be the same as those reported for human DNA topoisomerase II alpha purified from HeLa cells. Studies with the anticancer drug amsacrine indicated that the human enzyme, either inside yeast cells or in its purified form, is a target of the drug; inhibition of the purified enzyme by teniposide (VM-26) and merbarone was also demonstrated. These studies demonstrate that yeast strains expressing human DNA topoisomerase II alpha provide a convenient system for studying drugs targeting the enzyme; unlike mammalian systems, potential complications due to the presence of human DNA topoisomerase II beta can be eliminated in this system. Overexpression of human DNA topoisomerase II alpha in yeast also provides a convenient source of the enzyme for in vitro studies.

Novel HeLa topoisomerase II is the II beta isoform: complete coding sequence and homology with other type II topoisomerases

DNA topoisomerase (topo) II mediates DNA strand passage in an ATP-dependent reaction. Human cell lines express at least two genetically distinct forms of the enzyme, topo II alpha (p170) and II beta (p180). Previously, we isolated a novel HeLa cDNA clone (CAA5) that partially encodes a protein homologous to topo II alpha (Austin, C.A. and Fisher, L.M. (1990) FEBS Lett. 266, 115-117). In this paper we show that CAA5 encodes a C-terminal segment of human topo II beta. We report here for the first time cDNA clones spanning the entire coding sequence. Overlapping clones specifying the 3' end of the cDNA have been isolated, mapped and sequenced. The missing 5' coding sequence was obtained by an inverse PCR protocol and from a specifically primed cDNA library. Human topo II beta is a 1621 amino acid protein which is closely homologous to topo II alpha in the N-terminal three quarters of its sequence. In contrast, the C-terminal segments of the alpha and beta sequences show considerable divergence suggesting these regions may mediate different cellular functions of the two isoforms. Southern blot analysis of yeast and Drosophila DNA using human alpha and beta specific probes detected a single topo II homologue in these lower eukaryotes. Comparison of the protein sequence for human topo II beta with other type II topoisomerases revealed several conserved motifs and has allowed identification of the likely ATPase- and DNA breakage-reunion domains.

Item and relational processing in young and older adults

The item and relational information framework of memory provided a methodology for an analytical approach to age differences in encoding and retrieval processes. Subjects were given related or unrelated words to sort or rate for pleasantness. Young adults performed better than older adults in free recall, but older adults were able to use both item and relational information as well as young adults. In a second experiment, subjects also sorted or rated a list composed of different numbers of category items. The pattern of free recall and cued recall scores indicated that item and relational information affected the memory performance of both age groups in a similar fashion. By examining memory in terms of item and relational information, it appears that older adults do not have difficulty combining two types of target information during encoding and that the information assists in recall of target items.

Novel selection and genetic characterisation of an etoposide-resistant human leukaemic CCRF-CEM cell line

We have studied the genetic alterations acquired during selection of a cloned human leukaemic cell line (CEM/VP-1) that is 15-fold more resistant to the anticancer topoisomerase II-inhibitor etoposide than parental CCRF-CEM cells. CEM/VP-1 cells exhibit an 'atypical MDR' phenotype: cross resistance to other topo II inhibitors (but not Vinca alkaloids) and expression of a drug-resistant topo II activity. Cytogenetic and molecular studies revealed that the cell line carried multiple genetic changes affecting TOP2 genes encoding both topo II alpha and beta isoforms. CEM/VP-1 was diploid, 47,XX,+20, and appears to have been preferentially selected from a 1% diploid subpopulation present in the tetraploid parental cells. The same chromosomal abnormalities were present in resistant and sensitive cells except for an acquired 3p- change most likely deleting one TOP2 beta allele. PCR/DNA sequence analysis and allele-specific hybridisation showed that one of two TOP2 alpha alleles expressed in CEM/VP-1 cells had acquired a Lys-797-->Asn codon change. This mutation lies close to the catalytic Tyr-804 residue of the protein and may interfere with drug-induced trapping of the cleavable complex. Alternatively, it could exert a loss of function phenotype. CEM/VP-1 cells did not exhibit codon 449 or 486 TOP2 alpha mutations in the ATP binding domain reported in two other resistant cell lines. Diploid selection and multiple changes observed in CEM/VP-1 cells appear to be consequences of the recessive phenotype of at-MDR. These results may be useful in approaching the mechanisms of clinical resistance.

Escherichia coli DNA gyrase: genetic analysis of gyrA and gyrB mutations responsible for thermosensitive enzyme activity

Escherichia coli gyrA43 and gyrB203 alleles conferring temperature-sensitive (ts) growth encoded Gly751-->Asp and Pro171-->Ser substitutions in the DNA gyrase A and B subunits, respectively. A plasmid-borne gyrA43 allele was genetically dominant over a chromosomal quinolone-resistant gyrA gene at 30 degrees C but not at 42 degrees C. These results and others confirm the ts phenotype of the mutation, the first to be identified in the C-terminal DNA binding/complex stabilizing domain of gyrase A protein. By contrast, the Pro171-->Ser mutation is located near the ATP-binding site of gyrase B protein and could interfere with energy coupling during DNA supercoiling. These data are discussed in regard to recently described gyrA(ts) mutations that affect the control of chromosome segregation.

An Escherichia coli DNA topoisomerase I mutant has a compensatory mutation that alters two residues between functional domains of the DNA gyrase A protein

Nucleotide sequence analysis revealed that the compensatory gyrA mutation in Escherichia coli DM750 affects DNA supercoiling by interchanging the identities of Ala-569 and Thr-586 in the DNA gyrase A subunit. These residues flank Arg-571, a site for trypsin cleavage that splits gyrase A protein between DNA breakage-reunion and DNA-binding domains. The putative interdomain locations of the DM750 mutation and that of E. coli DM800 (in gyrase B protein) suggests that these compensatory mutations may reduce DNA supercoiling activity by altering allosteric interactions in the gyrase complex.

Site-specific DNA cleavage by mammalian DNA topoisomerase II induced by novel flavone and catechin derivatives

Four naturally occurring flavones (baicalein, quercetin, quercetagetin and myricetin) and two novel catechins [(-)-epicatechin gallate and (-)-epigallocatechin gallate, from the tea plant Camellia sinensis], which are known inhibitors of reverse transcriptase, were shown to induce mammalian topoisomerase II-dependent DNA-cleavage in vitro. The flavones differed from the catechins in causing unwinding of duplex DNA, but both classes of compound induced enzymic DNA breakage at the same sites on DNA. Moreover, the cleavage specificity was the same as that for the known intercalator 4'-(acridin-9-ylamino)methanesulphon-m-anisidide, suggesting that these agents trap the same cleavable complex. Analysis of some 30 flavonoid compounds allowed elucidation of the structure-function relationships for topoisomerase II-mediated DNA cleavage. For flavonoid inhibitors an unsaturated double bond between positions 2 and 3 of the pyrone ring and hydroxy groups at the 5, 7, 3' and 4' positions favoured efficient cleavage. Hydroxy substitutions could be tolerated at the 3, 6 and 5' positions. Indeed, the absence of substituents at the 3', 4' and 5' positions could be compensated by a hydroxy group at position 6 (baicalein). Similar requirements have been reported for flavonoid inhibitors of protein kinase C that act competitively with ATP, suggesting interaction with a conserved protein feature. Formation of the cleavable complex is a cytotoxic lesion that may contribute to the growth-inhibitory properties of flavones observed for three human tumour cell lines. These results are discussed in regard to the selectivity of antiviral agents.

Nucleotide sequence of the Staphylococcus aureus gyrB-gyrA locus encoding the DNA gyrase A and B proteins

We have determined the nucleotide sequence of a 5.3-kb segment of the Staphylococcus aureus chromosome that includes the gyrA and gyrB genes coding for both subunits of DNA gyrase, the enzyme that catalyzes ATP-dependent DNA supercoiling. The gene order at this locus, dnaA-dnaN-recF-gyrB-gyrA, is similar to that found in the Bacillus subtilis replication origin region. S. aureus recF, gyrB, and gyrA genes are closely spaced, occupy the same reading frame, and may be coordinately expressed. The S. aureus gyrB and gyrA genes encode 640- and 889-residue proteins, respectively, that share strong homology with other bacterial gyrase subunits, notably those from B. subtilis. These results are discussed in regard to the mechanism of DNA gyrase and its role as a target for the 4-quinolones and other antistaphylococcal agents.