Isolation of putative progenitor endothelial cells for angiogenesis

Putative endothelial cell (EC) progenitors or angioblasts were isolated from human peripheral blood by magnetic bead selection on the basis of cell surface antigen expression. In vitro, these cells differentiated into ECs. In animal models of ischemia, heterologous, homologous, and autologous EC progenitors incorporated into sites of active angiogenesis. These findings suggest that EC progenitors may be useful for augmenting collateral vessel growth to ischemic tissues (therapeutic angiogenesis) and for delivering anti- or pro-angiogenic agents, respectively, to sites of pathologic or utilitarian angiogenesis.

Transplantation of ex vivo expanded endothelial progenitor cells for therapeutic neovascularization

Animal studies and preliminary results in humans suggest that lower extremity and myocardial ischemia can be attenuated by treatment with angiogenic cytokines. The resident population of endothelial cells that is competent to respond to an available level of angiogenic growth factors, however, may potentially limit the extent to which cytokine supplementation enhances tissue neovascularization. Accordingly, we transplanted human endothelial progenitor cells (hEPCs) to athymic nude mice with hindlimb ischemia. Blood flow recovery and capillary density in the ischemic hindlimb were markedly improved, and the rate of limb loss was significantly reduced. Ex vivo expanded hEPCs may thus have utility as a "supply-side" strategy for therapeutic neovascularization.

Cyclin D1 provides a link between development and oncogenesis in the retina and breast

Mice lacking cyclin D1 have been generated by gene targeting in embryonic stem cells. Cyclin D1-deficient animals develop to term but show reduced body size, reduced viability, and symptoms of neurological impairment. Their retinas display a striking reduction in cell number due to proliferative failure during embryonic development. In situ hybridization studies of normal mouse embryos revealed an extremely high level of cyclin D1 in the retina, suggesting a special dependence of this tissue on cyclin D1. In adult mutant females, the breast epithelial compartment fails to undergo the massive proliferative changes associated with pregnancy despite normal levels of ovarian steroid hormones. Thus, steroid-induced proliferation of mammary epithelium during pregnancy may be driven through cyclin D1.

Laser beams and resonators

This paper is a review of the theory-of laser beams and resonators. It is meant to be tutorial in nature and useful in scope. No attempt is made to be exhaustive in the treatment. Rather, emphasis is placed on formulations and derivations which lead to basic understanding and on results which bear practical significance.

Mechanism of NO-induced oxidation of myoglobin and hemoglobin

Nitric oxide (NO) has been implicated as mediator in a variety of physiological functions, including neurotransmission, platelet aggregation, macrophage function, and vasodilation. The consumption of NO by extracellular hemoglobin and subsequent vasoconstriction have been suggested to be the cause of the mild hypertensive events reported during in vivo trials of hemoglobin-based O2 carriers. The depletion of NO from endothelial cells is most likely due to the oxidative reaction of NO with oxyhemoglobin in arterioles and surrounding tissue. In order to determine the mechanism of this key reaction, we have measured the kinetics of NO-induced oxidation of a variety of different recombinant sperm whale myoglobins (Mb) and human hemoglobins (Hb). The observed rates depend linearly on [NO] but show no dependence on [O2]. The bimolecular rate constants for NO-induced oxidation of MbO2 and HbO2 are large (k.ox,NO = 30-50 microM-1 s-1 for the wild-type proteins) and similar to those for simple nitric oxide binding to deoxygenated Mb and Hb. Both reversible NO binding and NO-induced oxidation occur in two steps: (1) bimolecular entry of nitric oxide into the distal portion of the heme pocket and (2) rapid reaction of noncovalently bound nitric oxide with the iron atom to produce Fe(2+)-N=O or with Fe(2+)-O-O delta- to produce Fe(3+)-OH2 and nitrate. Both the oxidation and binding rate constants for sperm whale Mb were increased when His(E7) was replaced by aliphatic residues. These mutants lack polar interactions in the distal pocket which normally hinder NO entry into the protein. Decreasing the volume of the distal pocket by replacing Leu(B10) and Val(E11) with aromatic amino acids markedly inhibits NO-induced oxidation of MbO2. The latter results provide a protein engineering strategy for reducing hypertensive events caused by extracellular hemoglobin-based O2 carriers. This approach has been explored by examining the effects of Phe(B10) and Phe(E11) substitutions on the rates of NO-induced oxidation of the alpha and beta subunits in recombinant human hemoglobin.

Cross-tissue immune cell analysis reveals tissue-specific features in humans

Despite their crucial role in health and disease, our knowledge of immune cells within human tissues remains limited. We surveyed the immune compartment of 16 tissues from 12 adult donors by single-cell RNA sequencing and VDJ sequencing generating a dataset of ~360,000 cells. To systematically resolve immune cell heterogeneity across tissues, we developed CellTypist, a machine learning tool for rapid and precise cell type annotation. Using this approach, combined with detailed curation, we determined the tissue distribution of finely phenotyped immune cell types, revealing hitherto unappreciated tissue-specific features and clonal architecture of T and B cells. Our multitissue approach lays the foundation for identifying highly resolved immune cell types by leveraging a common reference dataset, tissue-integrated expression analysis, and antigen receptor sequencing.

Retinopathy and attenuated circadian entrainment in Crx-deficient mice

Crx, an Otx-like homeobox gene, is expressed specifically in the photoreceptors of the retina and the pinealocytes of the pineal gland. Crx has been proposed to have a role in the regulation of photoreceptor-specific genes in the eye and of pineal-specific genes in the pineal gland. Mutations in human CRX are associated with the retinal diseases, cone-rod dystrophy-2 (adCRD2; refs 3, 4, 5), retinitis pigmentosa (RP) and Leber congenital amaurosis (LCA), which all lead to loss of vision. We generated mice carrying a targeted disruption of Crx. Crx-/- mice do not elaborate photoreceptor outer segments and lacked rod and cone activity as assayed by electroretinogram (ERG). Expression of several photoreceptor- and pineal-specific genes was reduced in Crx mutants. Circadian entrainment was also affected in Crx-/- mice.

Efficacy and safety of abatacept or infliximab vs placebo in ATTEST: a phase III, multi-centre, randomised, double-blind, placebo-controlled study in patients with rheumatoid arthritis and an inadequate response to methotrexate

OBJECTIVES

This double-blind trial evaluated the efficacy and safety of abatacept or infliximab vs placebo. The primary objective of this study was to evaluate the mean change from baseline in Disease Activity Score (based on erythrocyte sedimentation rates; DAS28 (ESR)) for the abatacept vs placebo groups at day 197.

METHODS

Patients with rheumatoid arthritis (RA) and an inadequate response to methotrexate (MTX) were randomised 3:3:2 to abatacept ( approximately 10 mg/kg every 4 weeks, n = 156), infliximab (3 mg/kg every 8 weeks, n = 165), or placebo (every 4 weeks, n = 110) and background MTX. Safety and efficacy were assessed throughout the study.

RESULTS

Similar patient demographics and clinical characteristics were present at baseline between groups, with mean scores of approximately 1.7 for HAQ-DI and 6.8 for DAS28 (ESR). At 6 months, mean changes in DAS28 (ESR) were significantly greater for abatacept vs placebo (-2.53 vs -1.48, p<0.001) and infliximab vs placebo (-2.25 vs -1.48, p<0.001). For abatacept vs infliximab treatment at day 365, reductions in the DAS28 (ESR) were -2.88 vs -2.25. At day 365, the following response rates were observed for abatacept and infliximab, respectively: American College of Rheumatology (ACR) 20, 72.4 and 55.8%; ACR 50, 45.5 and 36.4%; ACR 70, 26.3 and 20.6%; low disease activity score (LDAS), 35.3 and 22.4%; DAS28-defined remission, 18.7 and 12.2%; good European League Against Rheumatism (EULAR) responses, 32.0 and 18.5%; and Health Assessment Questionnaire Disability Index (HAQ-DI), 57.7 and 52.7%. Mean changes in physical component summary (PCS) were 9.5 and 7.6, and mental component summary (MCS) were 6.0 and 4.0, for abatacept and infliximab, respectively. Over 1 year, adverse events (AEs) (89.1 vs 93.3%), serious AEs (SAEs) (9.6 vs 18.2%), serious infections (1.9 vs 8.5%) and discontinuations due to AEs (3.2 vs 7.3%) and SAEs (2.6 vs 3.6%) were lower with abatacept than infliximab.

CONCLUSIONS

In this study, abatacept and infliximab (3 mg/kg every 8 weeks) demonstrated similar efficacy. Overall, abatacept had a relatively more acceptable safety and tolerability profile, with fewer SAEs, serious infections, acute infusional events and discontinuations due to AEs than the infliximab group.

TRIAL REGISTRATION NUMBER

NCT00095147.

Perturbation of CD4+ and CD8+ T-cell repertoires during progression to AIDS and regulation of the CD4+ repertoire during antiviral therapy

The T-cell antigen receptor (TCR) repertoire was studied longitudinally by analyzing the varying lengths of the beta chain CDR3 hypervariable region during the course of HIV-1 infection and following combination antiretroviral therapy. Drastic restrictions in CD8+ T-cell repertoire usage were found at all stages of natural progression and persisted during the first six months of treatment. In contrast, significant CD4+ T-cell repertoire perturbations were not found in early stages of infection but correlated with progression to AIDS. Out of ten patients presenting with pretreatment perturbations, normalization of the CD4+ repertoire was observed in eight good responders, but not in two cases of unsuccessful therapy. These results indicate that, besides CD4+ cell count rise, an efficient control of HIV replication may allow qualitative modifications of the CD4+ repertoire balance.

Synthesis of epothilones A and B in solid and solution phase

Epothilones A and B, two compounds that have been recently isolated from myxobacterium Sorangium cellulosum strain 90, have generated intense interest among chemists, biologists and clinicians owing to the structural complexity, unusual mechanism of interaction with microtubules and anticancer potential of these molecules. Like taxol, they exhibit cytotoxicity against tumour cells by inducing microtubule assembly and stabilization, even in taxol-resistant cell lines. Following the structural elucidation of these molecules by X-ray crystallography in 1996, several syntheses of epothilones A and B have been reported, indicative of the potential importance of these molecules in the cancer field. Here we report the first solid-phase synthesis of epothilone A, the total synthesis of epothilone B, and the generation of a small epothilone library. The solid-phase synthesis applied here to epothilone A could open up new possibilities in natural-product synthesis and, together with solution-phase synthesis of other epothilones, paves the way for the generation of large combinatorial libraries of these important molecules for biological screening.

Adriamycin-induced heart failure: mechanism and modulation

Adriamycin (doxorubicin) is one of the most effective chemotherapeutic agents against a variety of cancers, but its usefulness is seriously curtailed by the risk of developing heart failure. Available laboratory evidence suggests that an increase in oxidative stress, brought about by increased free radical production and decreased myocardial endogenous antioxidants, plays an important role in the pathogenesis of heart failure. Adriamycin-induced apoptosis and hyperlipidemia may also be involved in the process. Probucol, a lipid-lowering drug and an antioxidant, completely prevents the occurrence of heart failure by reducing oxidative stress as well as by the modulation of apoptosis and high lipid concentrations. Thus, combined therapy with adriamycin and probucol has a high potential for optimizing the treatment of cancer patients.

Broad-spectrum mildew resistance in Arabidopsis thaliana mediated by RPW8

Plant disease resistance (R) genes control the recognition of specific pathogens and activate subsequent defense responses. We show that the Arabidopsis thaliana locus RESISTANCE TO POWDERY MILDEW8 (RPW8) contains two naturally polymorphic, dominant R genes, RPW8.1 and RPW8.2, which individually control resistance to a broad range of powdery mildew pathogens. Although the predicted RPW8.1 and RPW8.2 proteins are different from the previously characterized R proteins, they induce localized, salicylic acid-dependent defenses similar to those induced by R genes that control specific resistance. Apparently, broad-spectrum resistance mediated by RPW8 uses the same mechanisms as specific resistance.

Rescue of cyclin D1 deficiency by knockin cyclin E

D-type cyclins and cyclin E represent two very distinct classes of mammalian G1 cyclins. We have generated a mouse strain in which the coding sequences of the cyclin D1 gene (Ccnd1) have been deleted and replaced by those of human cyclin E (CCNE). In the tissues and cells of these mice, the expression pattern of human cyclin E faithfully reproduces that normally associated with mouse cyclin D1. The replacement of cyclin D1 with cyclin E rescues all phenotypic manifestations of cyclin D1 deficiency and restores normal development in cyclin D1-dependent tissues. Thus, cyclin E can functionally replace cyclin D1. Our analyses suggest that cyclin E is the major downstream target of cyclin D1.

MDR1 pharmacogenetics: frequency of the C3435T mutation in exon 26 is significantly influenced by ethnicity

P-glycoprotein (PGP), the product of the multidrug resistance gene (MDR1), acts as an energy-dependent efflux pump that exports its substrates out of the cell. PGP expression is an important factor regulating absorption of a wide variety of medications. It has also been associated with intrinsic and acquired cross resistance to a number of structurally unrelated anticancer drugs. A single nucleotide polymorphism (SNP) in exon 26 of the MDR1 gene, C3435T, was recently correlated with PGP protein levels and substrate uptake. Individuals homozygous for the T allele have more than four-fold lower PGP expression compared with CC individuals. As overexpression of PGP has been associated with altered drug absorption, therapy-resistant malignancies, and lower concentrations of HIV-1 protease inhibitors, this SNP may provide a useful approach to individualize therapy. To facilitate clinical application throughout the world, 1280 subjects from 10 different ethnic groups were evaluated for this SNP using the polymerase chain reaction-restriction fragment length polymorphism assay and the genotype and allele frequency for each group were ascertained. Marked differences in genotype and allele frequency were apparent between the African populations and the Caucasian/Asian populations (P < 0.0001). The Ghanaian, Kenyan, African American and Sudanese populations studied had frequencies of 83%, 83%, 84% and 73%, respectively, for the C allele. The British Caucasian, Portuguese, South-west Asian, Chinese, Filipino and Saudi populations had lower frequencies of the C allele compared to the African group (48%, 43%, 34%, 53%, 59%, and 55%, respectively). The high frequency of the C allele in the African group implies overexpression of PGP and may have important therapeutic and prognostic implications for use of PGP dependent drugs in individuals of African origin.

The frequency and distribution of thiopurine methyltransferase alleles in Caucasian and Asian populations

Thiopurine methyltransferase metabolizes 6-mercaptopurine, thioguanine and azathioprine, thereby regulating cytotoxicity and clinical response to these thiopurine drugs. In healthy Caucasian populations, 89-94% of individuals have high thiopurine methyltransferase activity, 6-11% intermediate and 0.3% low, resulting from genetic polymorphism. Four variant thiopurine methyltransferase alleles were detected in over 80% of individuals with low or intermediate thiopurine methyltransferase activity. The wild-type allele is defined as TPMT*1 and the mutant alleles are TPMT*2 (G238C), TPMT*3A (G460A and A719G), TPMT*3B (G460A) and TPMT*3B (A719G). The frequency of these alleles in different ethnic groups is not well defined. In this study, DNA from 199 British Caucasian, 99 British South West Asian and 192 Chinese individuals was analysed for the presence of these variant alleles using polymerase chain reaction-restriction fragment length polymorphism and allele-specific polymerase chain reaction based assays. The frequency of individuals with a variant thiopurine methyltransferase genotype was: Caucasians 10.1% (20/199), South West Asians 2.0% (2/99) and Chinese 4.7% (9/192). Two TPMT*2 heterozygotes were identified in the Caucasian population, but this allele was not found in the two Asian populations. TPMT*3A was the only mutant allele found in the South West Asians (two heterozygotes). This was also the most common mutant allele in the Caucasians (16 heterozygotes and one homozygote) but was not found in the Chinese. All mutant alleles identified in the Chinese population were TPMT*3C (nine heterozygotes). This allele was found at a low frequency in the Caucasians (one heterozygote). This suggests that A719G is the oldest mutation, with G460A being acquired later to form the TPMT*3A allele in the Caucasian and South West Asian populations. TPMT*2 appears to be a more recent allele, which has only been detected in Caucasians to date. These ethnic differences may be important in the clinical use of thiopurine drugs.

The efficacy and safety of abatacept in patients with non-life-threatening manifestations of systemic lupus erythematosus: results of a twelve-month, multicenter, exploratory, phase IIb, randomized, double-blind, placebo-controlled trial

OBJECTIVE

To evaluate abatacept therapy in patients with non-life-threatening systemic lupus erythematosus (SLE) and polyarthritis, discoid lesions, or pleuritis and/or pericarditis.

METHODS

In a 12-month, multicenter, exploratory, phase IIb randomized, double-blind, placebo-controlled trial, SLE patients with polyarthritis, discoid lesions, or pleuritis and/or pericarditis were randomized at a ratio of 2:1 to receive abatacept (∼10 mg/kg of body weight) or placebo. Prednisone (30 mg/day or equivalent) was given for 1 month, and then the dosage was tapered. The primary end point was the proportion of patients with new flare (adjudicated) according to a score of A/B on the British Isles Lupus Assessment Group (BILAG) index after the start of the steroid taper.

RESULTS

A total of 118 patients were randomized to receive abatacept and 57 to receive placebo. The baseline characteristics were similar in the 2 groups. The proportion of new BILAG A/B flares over 12 months was 79.7% (95% confidence interval [95% CI] 72.4, 86.9) in the abatacept group and 82.5% (95% CI 72.6, 92.3) in the placebo group (treatment difference -3.5 [95% CI -15.3, 8.3]). Other prespecified flare end points were not met. In post hoc analyses, the proportions of abatacept-treated and placebo-treated patients with a BILAG A flare were 40.7% (95% CI 31.8, 49.5) versus 54.4% (95% CI 41.5, 67.3), and the proportions with physician-assessed flare were 63.6% (95% CI 54.9, 72.2) and 82.5% (95% CI 72.6, 92.3), respectively; treatment differences were greatest in the polyarthritis group. Prespecified exploratory patient-reported outcomes (Short Form 36 health survey, sleep problems, fatigue) demonstrated a treatment effect with abatacept. The frequency of adverse events (AEs) was comparable in the abatacept and placebo groups (90.9% versus 91.5%), but serious AEs (SAEs) were higher in the abatacept group (19.8 versus 6.8%). Most SAEs were single, disease-related events occurring during the first 6 months of the study (including the steroid taper period).

CONCLUSION

Although the primary/secondary end points were not met in this study, improvements in certain exploratory measures suggest some abatacept efficacy in patients with non-life-threatening manifestations of SLE. The increased rate of SAEs requires further assessment.

Scattering and Interference in Epitaxial Graphene

A single sheet of carbon, graphene, exhibits unexpected electronic properties that arise from quantum state symmetries, which restrict the scattering of its charge carriers. Understanding the role of defects in the transport properties of graphene is central to realizing future electronics based on carbon. Scanning tunneling spectroscopy was used to measure quasiparticle interference patterns in epitaxial graphene grown on SiC(0001). Energy-resolved maps of the local density of states reveal modulations on two different length scales, reflecting both intravalley and intervalley scattering. Although such scattering in graphene can be suppressed because of the symmetries of the Dirac quasiparticles, we show that, when its source is atomic-scale lattice defects, wave functions of different symmetries can mix.

Upregulation of long noncoding RNA ZEB1-AS1 promotes tumor metastasis and predicts poor prognosis in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related mortality worldwide. Despite progress in diagnostics and treatment of HCC, its prognosis remains poor. Emerging studies showed that long noncoding RNAs (lncRNAs) have crucial regulatory roles in cancer biology. In the current study, differentially expressed lncRNAs between HCC and paired non-tumor tissues were identified using microarrays. The effects of a specific differentially expressed lncRNA (termed ZEB1-AS1) on tumor progression were investigated in vitro and in vivo. We found that ZEB1-AS1 is frequently upregulated in HCC samples, especially in metastatic tumor tissues. DNA methylation analysis shows a tumor-specific ZEB1-AS1 promoter hypomethylation. Aberrant methylation is tightly correlated with overexpression of ZEB1-AS1 in HCC. Patients with ZEB1-AS1 hypomethylation or with high ZEB1-AS1 expression have poor recurrence-free survival. Functionally, ZEB1-AS1 promotes tumor growth and metastasis, acts as an oncogene in HCC. The ZEB1-AS1 gene is located in physical contiguity with ZEB1 and positively regulates the ZEB1 expression. ZEB1 inhibition partially abrogates ZEB1-AS1-induced epithelial to mesenchymal transition (EMT) and cancer metastasis. Our results provide novel insights into the function of lncRNA-driven hepatocarcinogenesis, highlight the important role of ZEB1-AS1 and ZEB1 in HCC progression, and indicate that ZEB1-AS1 may be served as a valuable prognostic biomarker for HCC.

Structural determinants of the stretching frequency of CO bound to myoglobin

In order to assess the relative importance of polar versus steric interactions, infrared spectra and overall CO binding properties were measured at room temperature for 41 different recombinant myoglobins containing mutations at His64(E7), Val68(E11), Phe43(CD1), Arg45(CD3), Phe46(CD4), and Leu29(B10). The results were compared to the crystal structures of wild-type, Phe29, Val46, Ala68, Phe68, Gln64, Leu64, and Gly64 sperm whale CO-myoglobin and that of Thr68 pig CO-myoglobin. As observed in several previous studies, replacement of the distal histidine (His64) with aliphatic amino acids results in the appearance of a single IR band in the 1960-1970-cm-1 region and in large increases in CO affinity (KCO). More complex behavior is observed for Gly, Ala, Gln, Met, and Trp substitutions at position 64, but in each case there is a net increase in the intensity of this high-frequency component. Replacement of Val68 with Ala, Leu, Ile, and Phe produces little effect on the IR spectrum, whereas these mutations cause 20-fold changes in KCO, presumably due to steric effects. Replacement of Val68 with Thr decreases KCO 4-5-fold, whereas the position of the major IR band increases from 1945 to 1961 cm-1. Replacement of Val68 with Asn also causes a large decrease in KCO, but in this case, the peak position of the major IR band decreases from 1945 to 1916 cm-1. Nine replacements were made in the CD corner at positions 43, 45, and 46. All of the resultant mutants show increased stretching frequencies that can be correlated with movement of the imidazole side chain of His64 away from the bound ligand. All five substitutions at position 29 cause changes in the IR spectra. The Leu29-->Phe mutation had the largest effect, producing a single band centered at 1932 cm-1. Together these data demonstrate that there is little direct correlation between affinity, vCO, and Fe-C-O geometry. The major factor governing vCO appears to be the electrostatic potential surrounding the bound ligand and not steric hindrance. The presence of positive charges from proton donors, such as N epsilon of His64 and N delta of Asn68, cause a decrease in the bond order and stretching frequency of bound CO. In contrast, the negative portion of the Thr68 dipole points directly toward the bound ligand and increases the C-O bond order and stretching frequency. Movement of His64 away from the bound ligand or replacement of this residue with aliphatic amino acids prevents hydrogen-bonding interactions, causing vCO to increase.(ABSTRACT TRUNCATED AT 250 WORDS)

Null RPGRIP1 alleles in patients with Leber congenital amaurosis

We isolated and characterized the entire coding sequence of a human gene encoding a protein that interacts with RPGR, a protein that is absent or mutant in many cases of X-linked retinitis pigmentosa. The newly identified gene, called "RPGRIP1" for RPGR-interacting protein (MIM 605446), is located within 14q11, and it encodes a protein predicted to contain 1,259 amino acids. Previously published work showed that both proteins, RPGR and RPGRIP1, are present in the ciliary structure that connects the inner and outer segments of rod and cone photoreceptors. We surveyed 57 unrelated patients who had Leber congenital amaurosis for mutations in RPGRIP1 and found recessive mutations involving both RPGRIP1 alleles in 3 (6%) patients. The mutations all create premature termination codons and are likely to be null alleles. Patients with RPGRIP1 mutations have a degeneration of both rod and cone photoreceptors, and, early in life, they experience a severe loss of central acuity, which leads to nystagmus.

Adriamycin cardiomyopathy: pathophysiology and prevention

Current knowledge about adriamycin cardiomyopathy indicates that the major cause of this condition is increased oxidative stress although the drug's antitumor action in patients may involve other mechanisms. Controversies about the different antioxidants in preventing cardiomyopathy likely stem from the fact that antioxidants must be effective in both the lipid and water phases, and the dose must be optimal, in order to be protective. Probucol, an antioxidant and promoter of endogenous antioxidants, is one such agent. Conducting clinical trials with an optimal dose of probucol is the next step and should make this great anticancer drug safer and more efficient in the fight against the cancer.

Role in cell permeability of an essential two-component system in Staphylococcus aureus

A temperature-sensitive lethal mutant of Staphylococcus aureus was found to harbor a mutation in the uncharacterized two-component histidine kinase (HK)-response regulator (RR) pair encoded by yycFG; orthologues of yycFG could be identified in the genomes of Bacillus subtilis and other gram-positive bacteria. Sequence analysis of the mutant revealed a point mutation resulting in a nonconservative change (Glu to Lys) in the regulator domain of the RR at position 63. To confirm that this signal transduction system was essential, a disrupted copy of either the RR (yycF) or the HK (yycG) was constructed with a set of suicide vectors and used to generate tandem duplications in the chromosome. Resolution of the duplications, leaving an insertion in either the yycF or the yycG coding region, was achieved only in the presence of an additional wild-type copy of the two open reading frames. Phenotypic characterization of the conditional lethal mutant showed that at permissive growth conditions, the mutant was hypersusceptible to macrolide and lincosamide antibiotics, even in the presence of the ermB resistance determinant. Other mutant phenotypes, including hypersensitivity to unsaturated long-chain fatty acids and suppression of the conditional lethal phenotype by high sucrose and NaCl concentrations, suggest that the role of the two-component system includes the proper regulation of bacterial cell wall or membrane composition. The effects of this point mutation are strongly bactericidal at the nonpermissive temperature, indicating that this pathway provides an excellent target for the identification of novel antibiotics.

Resistance studies with daptomycin

We studied the in vitro emergence of resistance to daptomycin using three methods: spontaneous resistance incidence, serial passage in the presence of increasing drug concentrations, and chemical mutagenesis. No spontaneously resistant mutants were obtained for any organism tested (<10(-10) for Staphylococcus aureus, <10(-9) for Staphylococcus epidermidis, <10(-9) for Enterococcus faecalis, <10(-9) for Enterococcus faecium, <10(-8) for Streptococcus pneumoniae). Population analysis demonstrated that bacterial susceptibility to daptomycin is heterogeneous. Assay results were sensitive to calcium concentration and culture density, both of which can affect apparent resistance rates. Stable S. aureus mutants were isolated by both serial passage in liquid media and chemical mutagenesis. The daptomycin MICs for these isolates were 8- to 32-fold higher than for the parental strain. Many mutants with high MICs (>12.5 microg/ml) had significant growth defects but did not display phenotypes typical of S. aureus small colony variants. The voltage component (Delta psi) of the bacterial membrane potential was increased in three independent resistant isolates. In vivo data showed that some daptomycin-resistant mutants had lost significant virulence. For other mutants, the degree of in vitro resistance was greater than the change in in vivo susceptibility. These results suggest that infection with some daptomycin-resistant organisms may still be easily treatable.