Biomedical subjects

S L Davies

Publications and source records attributed to S L Davies.

At least 19 recordsLinked to original sources

PubMed1998

Physiological regulation of eukaryotic topoisomerase II.

Topoisomerase II is an essential enzyme in all organisms with several independent roles in DNA metabolism. In this article we review our knowledge on the regulation of the expression and catalytic activity of topoisomerase II in both lower and higher eukaryotes. Current data indicate that the regulation of topoisomerase II gene expression is complex, with positive and negative controls in evidence at the level of both promoter activity and mRNA stability. Similarly, the activity of the mature enzyme can be regulated by the action of several different protein kinases. Of particular interest is the cell cycle-dependent phosphorylation of topoisomerase II, including multiple, mitosis-specific modifications, which are proposed to regulate the essential chromosome decatenation activity of the enzyme.

Animals↗

PubMed1998

Targeted gene disruption reveals a role for natural secretory IgM in the maturation of the primary immune response.

Accelerated development of the secondary immune response may be attributable in part to the rapid delivery of antigen to lymphoid follicles by circulating antibody elicited on primary immunization. Here we provide evidence indicating that the nonspecific IgM present in naive mice (natural antibody) plays a role in the acceleration of the primary response. Targeted deletion of the Ig microseconds polyadenylation site by use of Cre recombinase allowed the creation of mice that, although harboring a normal number of B cells expressing surface IgM, completely lacked serum IgM while retaining the other Ig isotypes. These mice retained a broadly normal B lymphocyte distribution (although containing a somewhat expanded peritoneal B1a subset) but exhibited substantial delays in mounting affinity-matured IgG responses to T cell-dependent antigens. The T cell-independent response, however, was augmented. The data indicate that the IgM present before antigen challenge (as well, possibly, as that elicited immediately after immunization) accelerates maturation of the primary response, presumably by complexing with the antigen and facilitating lymphocyte activation and/or antigen trapping.

Animals↗

PubMed1998

Casein kinase II stabilizes the activity of human topoisomerase IIalpha in a phosphorylation-independent manner.

Previous reports have indicated that topoisomerase II (topo II) co-purifies with and is a substrate for casein kinase II. We have carried out a detailed study of the effect that purified casein kinase II has on the activity of purified recombinant human topo IIalpha. Co-incubation of topo IIalpha and casein kinase II led to an apparent activation of the topo IIalpha; however, in experiments in which topo IIalpha was preincubated at 37 degrees C with or without native casein kinase II prior to assaying for decatenation activity, it emerged that the kinase was exerting its "activating" function via a decrease in the rate of topo IIalpha enzyme inactivation during the incubation period. This stabilization of topo IIalpha by casein kinase II was ATP-independent and was observed in both mutated and truncated derivatives of topo IIalpha lacking the major casein kinase II phospho-acceptor sites, indicating the lack of a requirement for phosphorylation. Consistent with a nonenzymatic role for casein kinase II, stoichiometric quantities of kinase were required for topo IIalpha stabilization. These data indicate that casein kinase II plays a significant role in regulating human topo IIalpha protein action via stabilization against thermal inactivation.

Antigens, Neoplasm↗

PubMed1998

Multiple sequences from downstream of the J kappa cluster can combine to recruit somatic hypermutation to a heterologous, upstream mutation domain.

Recruitment of somatic hypermutation to the Ig kappa locus has previously been shown to depend on the enhancer elements, Ei/MAR and E3'. Here we show that these elements are not sufficient to confer mutability. However, hypermutation is effectively targeted to a chimeric beta-globin/Ig kappa transgene whose 5' end is composed of the human beta-globin gene (promoter and first two exons) and whose 3' end consists of selected sequences derived from downstream of the J kappa cluster (Ei/MAR, C kappa + flank and E3'). Thus, multiple downstream Ig kappa sequences (all derived from 3' of the J kappa cluster) can combine to recruit mutation to a heterologous mutation domain. The location of this hypermutation domain is defined by the position of the transcription start site and this applies even if the Ig kappa Ei/MAR is positioned upstream of the promoter. Hotspots within the mutation domain are, however, defined by local DNA sequence as evidenced by a new hotspot being created within the beta-globin domain by a mutation within the transgene. We propose that multiple, moveable Ig kappa sequences (that are normally located downstream of the transcription start site) cooperate to bring a hypermutation priming factor to the transcription initiation complex; a mutation domain is thereby created downstream of the promoter but the local sequence defines the detailed pattern of mutation within that domain.

Animals↗

PubMed1998

Serum leptin concentrations and weight gain in postobese, postmenopausal women.

OBJECTIVE: This study was designed to determine if serum leptin concentrations (adjusted for fat mass) after weight loss on a low-calorie diet predict subsequent weight gain. RESEARCH METHODS AND PROCEDURES: Body composition and serum leptin concentrations were determined on 14 moderately obese, postmenopausal, nondiabetic women with a familial predisposition to obesity. Assessments were obtained under tightly controlled metabolic ward conditions of macronutrient intake and weight maintenance both before (obese state) and after a mean weight loss of 12.0 kg to normal body weight (postobese state). Four years later, without intervention, body weight and body composition were reassessed. RESULTS: Weight loss resulted in significant decreases in fat mass (29.7 +/- 5.4 vs. 20.3 +/- 4.7; kg), body mass index (27.7 +/ 1.6 vs. 23.0 +/- 1.5; kg/m2), percent body fat (40.7 +/- 4.3 vs. 33.1 +/- 5.0), and serum leptin concentrations (31.8 +/- 16.0 vs. 11.5 +/- 5.4; ng/mL). Serum leptin concentrations were positively correlated (p<0.05) with fat mass in both the obese and postobese states (r=0.67 and r=0.56, respectively). However, residual serum leptin concentrations (adjusted for fat mass) in the obese and postobese states were not related to changes in body weight (p = 0.61 and 0.52), fat mass (p = 0.72 and 0.42), body mass index (p = 0.59 and 0.33), or percent body fat (p=0.84 and 0.46) over the follow-up period. DISCUSSION: These finding do not support the hypothesis that relatively low concentrations of leptin predict weight regain after weight loss. However, because the number of subjects in this study was limited, further studies are warranted.

Aged↗

PubMed1998

Mice carrying a CD20 gene disruption.

CD20 is a hallmark antigen of B lymphocytes. Its expression is restricted to precursor and mature B cells but it is not expressed on plasma cells. The protein is a membrane-embedded phosphoprotein that appears likely to transverse the membrane four times. Its function is unknown although CD20 has been variously proposed to play a role in B-cell activation, proliferation, and calcium transport. A unique homologue of human CD20 has been described in mouse, which also shows a B-cell-specific pattern of expression. Here we describe the generating of mice carrying a CD20 gene disruption. So far, we have failed to detect any major effect of the gene disruption on the differentiation and function of B lymphocytes as judged by the expression of surface markers, antigen receptor signaling, proliferative responses, or calcium uptake. We did note, however, that the mice homozygous for the gene disruption [generated by intercrossing (129 x C57BL/6)F1 CD20+/- heterozygotes] showed a substantial depletion of the sub-population of peritoneal B cells that lack expression of the B220 (RA3-6B2) isoform of CD45. The loss of the IgM+ 6B2- peritoneal B cells is not, however, attributable to the CD20 gene disruption itself. Rather, it segregates with a polymorphic difference between the 129 and C57BL/6 strains that is linked to the CD20 locus which, intriguingly, is itself close to the CD5 gene. This demonstrates that caution must be exercised when comparing the phenotypes of F2 litter-mates generated from crosses between 129 embryonic stem-cell-derived chimeras and mice of other strains.

Animals↗

PubMed1997

Response to ICRF-159 in cell lines resistant to cleavable complex-forming topoisomerase II inhibitors.

We have studied the relationship between expression of genes implicated in mediating resistance to cleavable complex-forming topoisomerase II (topo II) inhibitors and cellular sensitivity to ICRF-159, a 'catalytic' inhibitor of topo II. Overexpression of the membrane transporters, P-glycoprotein and multidrug resistance-related protein (MRP), or down-regulation of topo IIalpha and/or -beta, did not confer ICRF-159 resistance. Indeed, marked topo IIalpha down-regulation appeared to be associated with collateral sensitivity to ICRF-159. Our results indicate that the resistance mechanisms that pertain to cleavable complex-forming topo II inhibitors and ICRF-159 are distinct. The evidence presented here suggests that topo IIalpha, not topo IIbeta, is more likely to be the major in vivo target for ICRF-159.

Antineoplastic Agents↗

PubMed1996

Hyperresponsive B cells in CD22-deficient mice.

CD22 is a surface glycoprotein of B lymphocytes that is rapidly phosphorylated on cytoplasmic tyrosines after antigen receptor cross-linking. Splenic B cells from mice with a disrupted CD22 gene were found to be hyperresponsive to receptor signaling: Heightened calcium fluxes and cell proliferation were obtained at lower ligand concentrations. The mice gave an augmented immune response, had an expanded peritoneal B-1 cell population, and contained increased serum titers of autoantibody. Thus, CD22 is a negative regulator of antigen receptor signaling whose onset of expression at the mature B cell stage may serve to raise the antigen concentration threshold required for B cell triggering.

Animals↗

PubMed1996

Antibody expression from the core region of the human IgH locus reconstructed in transgenic mice using bacteriophage P1 clones.

Mice carrying transgenic human immunoglobulin gene miniloci can be used for the production of human monoclonal antibodies. The human variable region (V) gene segments in these miniloci undergo productive rearrangement in mouse lymphoid tissue to yield a population of B lymphocytes expressing a repertoire of antibodies. Many of the miniloci studied to date have included only a small number of germline gene segments in an artificially compact configuration. Here we describe the use of the bacteriophage P1 cloning system to create mice carrying the core region of the human immunoglobulin heavy chain (IgH) locus. Three P1 clones carrying overlapping regions of the human IgH locus (spanning the five JH-proximal VH segments, the entire DH and JH clusters, and the C mu and C delta constant regions) were injected into mouse eggs and appear to have reconstituted the core region of the locus (> 180 kb) following homologous recombination with each other. While this translocus yielded a titer of serum immunoglobulin similar to that obtained with a smaller plasmid-based minilocus, the P1-based locus gave rise to substantially greater diversification by somatic hypermutation. Such diversification is important for obtaining high-affinity antibodies. The results show the usefulness of the P1 system in facilitating the manipulation and recreation of large transgenes.

Amino Acid Sequence↗

PubMed1996

Response to epirubicin in patients with superficial bladder cancer and expression of the topoisomerase II alpha and beta genes.

Biopsies of superficial bladder cancer were analysed to study the relationship between response to epirubicin and the expression of the human topoisomerase II alpha and beta genes. Tissue samples were obtained prior to treatment and a marker tumour was left in the bladder. Transcript levels of both genes were generally lower in biopsies taken following treatment failure. Levels of topoisomerase II mRNA were uniformly lower in tumour tissue than in biopsies of normal tissue.

Aged↗

PubMed1996

A randomized, prospective trial of standard Hickman compared with Groshong central venous catheters in pediatric oncology patients.

BACKGROUND: Safe and reliable central venous access is critical in the management of children with cancer. A recently described valved catheter (Groshong) requires less frequent flushing to preserve catheter patency, theoretically reducing daily care costs for the catheter as well as lessening the risk of mechanical or infectious complications. This study compared standard Hickman to Groshong catheters in a group of pediatric oncology patients. STUDY DESIGN: From December 1992 to May 5, 1994, 20 consecutive pediatric oncology patients were randomized by medical record number to receive either a standard dual lumen Hickman (7F) or Groshong (9.5F) catheter. All patients were prospectively followed on a weekly basis and a log was maintained regarding complications and cost of maintenance of the catheter until it was removed. RESULTS: Ten patients received Groshong catheters and ten received Hickman catheters. Total catheter days for each group were similar (Hickman, 2,599 compared with Groshong, 2,389 days). Five Groshong catheters required removal because of mechanical complications and several required daily flushes because of blood backing up into the catheter lumen. When taking into account the cost of associated complications, no differences were noted in daily cost for maintenance between the two catheters. CONCLUSIONS: When considering the cost of complications, Groshong catheters were no less expensive to maintain compared with standard Hickman catheters. Furthermore, Groshong catheters malfunctioned more frequently and required a greater number of urokinase instillations for withdrawal occlusion. The use of the Groshong catheter in pediatric oncology patients cannot be supported by the present study.

Catheterization, Central Venous↗

PubMed1996

Self-management and other behavioral aspects of asthma.

We review recently published literature on behavioral aspects of asthma, including program descriptions, reviews, and original research reports. Most of the literature on behavioral aspects of asthma has been in the area of self-management, including education, medication use, and peak flow monitoring. Recent studies of these factors have shown promising trends in reducing morbidity and in improving health care utilization outcomes. Medication adherence continues to be problematic, and its complexity is increased when comparing inhaled with oral medications and bronchodilators with anti-inflammatory agents. Psychobiologic factors that have been recently studied include perceptions of airway changes and the role of emotional responses in asthma self-management. Because the behavioral aspects of asthma play such a significant role in asthma treatment, further study is needed to determine how changes in patient behavior can improve patient quality of life.

Administration, Inhalation↗

PubMed1995

Relationship between expression of topoisomerase II isoforms and intrinsic sensitivity to topoisomerase II inhibitors in breast cancer cell lines.

Topoisomerase II is a key target for many anti-cancer drugs used to treat breast cancer. In human cells there are two closely related, but differentially expressed, topoisomerase II isoforms, designated topoisomerase II alpha and beta. Here, we report the production of a new polyclonal antibody raised against a fragment of the C-terminal domain of the 180 kDa form of topoisomerase II (the beta isoform), which does not cross-react with the 170 kDa form (the alpha isoform). Using this antibody, together with a polyclonal antibody specific for the 170 kDa isoform of topoisomerase II, we have examined the relationship between the sensitivity of a panel of human breast cancer cell lines to different classes of topoisomerase II inhibitors and cellular levels of the topoisomerase II alpha and beta proteins. We found that sensitivity to amsacrine showed a correlation with the level of expression of topoisomerase II alpha protein, and that sensitivity to etoposide showed a similar correlation with the level of expression of topoisomerase II beta protein. There was also a relationship between sensitivity of these cell lines to mitoxantrone and the cellular level of both isoforms of topoisomerase II. No relationship was found between the level of mRNA for topoisomerase II alpha or beta, and either sensitivity of breast cancer cell lines to topoisomerase II inhibitors or the level of topoisomerase II protein expression.

Antibody Specificity↗

PubMed1995

Topoisomerases II alpha and beta as therapy targets in breast cancer.

Topoisomerase II enzymes play an essential role in human DNA metabolism. They are also recognized as primary targets of a number of anti-cancer drugs used in the treatment of breast cancer, which remains a leading cause of cancer-related death in women. While topoisomerase inhibitors have produced significant response rates in this disease, their use has been limited both by toxicity and by the development of resistance. In this article we review the extensive work which has not only increased our understanding of the biochemistry and molecular biology of type II topoisomerases but also enabled more rational drug design. Such knowledge should translate into increased clinical efficacy in the treatment of breast cancer and other malignancies.

Antineoplastic Agents↗

PubMed1995

How to implement an asthma education program.

Given that poor asthma management leads to such devastating rates of morbidity and mortality in this country, efforts must be made to increase the knowledge, skills, and behaviors of persons with asthma. The suggestions and recommendations provided here represent a blend of academic opinion and practical advice on methods to implement an asthma education program. In developing an asthma education program, consideration must be given to what content should be included, how and by whom that content should be taught, and when education should take place. The identification of a key clinical staff member to take the lead in translating these and other asthma education guidelines will be a critical next step for clinicians committed to developing an effective asthma education program.

Asthma↗

PubMed1995

Cyclic AMP-dependent protein kinase type I is involved in hypersensitivity of human breast cells to topoisomerase II inhibitors.

Topoisomerase II (Topo II) is an essential enzyme that catalyzes the breakage of double-strand DNA and is the target of several effective anticancer drugs, including the epipodophyllotoxins. The regulatory subunits of the cyclic AMP-dependent protein kinase are differentially expressed in normal and cancer cells. The RIalpha subunit is overexpressed in cells transformed by transforming growth factor-alpha (TGF-alpha) or Ha-ras oncogene. It has been shown that murine cells transformed by Ha-ras become hypersensitive to Topo II-targeting anticancer drugs. In this report we have tested whether any correlation exists between the expression of RIalpha protein and cellular sensitivity of Topo II-targeting drugs. Normal human breast MCF-10A cells and their derivatives overexpressing TGF-alpha, Ha-ras, or the different protein kinase subunits were treated with either Topo II inhibitors, such as etoposide, teniposide, or amsacrine, or with drugs which act independently of Topo II, such as bleomycin. Here we show that MCF-10A TGF-alpha and MCF-10A Ha-ras cells overexpress the RIalpha protein and become hypersensitive to epypodophyllotoxins and amsacrine but not to bleomycin. Direct introduction of the RIalpha gene into MCF-10A induces hypersensitivity to Topo II inhibitor drugs. In contrast, the overexpression of the other protein kinase subunits, RIIbeta or Calpha, does not modify the drug sensitivity of MCF-10A cells. No differences in the mRNA/protein content or in the activity of Topo II were found between hypersensitive cells and parental MCF-10A cells, suggesting that RIalpha may influence drug sensitivity via modulation of events downstream of the Topo II-DNA cleavable complex.

Amsacrine↗

PubMed1994

Overexpression of the RI alpha subunit of protein kinase A confers hypersensitivity to topoisomerase II inhibitors and 8-chloro-cyclic adenosine 3'5'-monophosphate in Chinese hamster ovary cells.

We have shown that a mutant derivative of Chinese hamster ovary CHO-K1 cells, ADR-5, which shows hypersensitivity to topoisomerase II (topo II)-inhibitory drugs, is cross-sensitive to the site-selective cyclic AMP analogue 8-chloro-cyclic AMP. We tested the hypothesis that overexpression of the type I alpha regulatory subunit of protein kinase A may represent a common element conferring hypersensitivity to both topo II inhibitors and 8-chloro-cyclic AMP in ADR-5 cells. We have demonstrated that ADR-5 cells overexpress RI alpha protein, compared to parental CHO-K1 cells. Moreover, retroviral vector-mediated transfer of the RI alpha gene into CHO-K1 cells was able to confer a drug-hypersensitive phenotype similar to that exhibited by ADR-5 cells. Analysis of topo II protein levels and activity revealed no differences between parental and infected cells, suggesting that protein kinase A may be involved in the downstream processing of topo II-mediated events.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed1994

Multiple mechanisms of resistance in a series of human testicular teratoma cell lines selected for increasing resistance to etoposide.

Mechanisms of resistance to VP-16 were monitored in a series of sublines of the human testicular teratoma cell line (SuSa) derived following exposure either to fractionated X-irradiation (DXR-10) or to VP-16 using pulsed 24-hr exposures (VP10) or continuous exposure conditions (VPC2, VPC3 and VPC4). Orders of resistance expressed (ranging from 3- to 33-fold based on IC50 values derived from colony forming assays) were comparable with those likely to be encountered clinically. All of these resistant sublines showed some cross-resistance to VCR, and the 3 drug-selected sublines tested also proved cross-resistant to ADR. Resistance was not associated with modified 3H-VP-16 accumulation. However, decreased VP-16-induced SSBs were detectable in all the resistant sublines and a strong positive correlation was noted between the extent of SSB formation and VP-16 resistance by linear regression analysis. Topo II alpha protein content, as judged by Western blotting, was significantly decreased only in the sublines derived by continuous exposure to VP-16, but this was not progressive with increasing levels of resistance expressed. RNase protection assays also showed no significant differences in Topo II alpha expression in the low-level resistant DXR-10 and VP10 sublines, contrasting with the 2-fold decreases identified in the VPC2, VPC3 and VPC4 sublines. Significantly, however, mRNA levels of two alternately spliced Topo II beta mRNAs were markedly decreased (2- to 9-fold) in all the drug-selected resistant sublines. No mutations in consensus ATP-binding sequences or in the DNA-binding region of Topo II alpha were detected by single strand conformational polymorphism analysis. Significant Pgp overexpression was only identified in the most highly resistant sublines VPC3 and VPC4, which both showed 4-fold cross-resistance to VCR. Decreased 3H-VCR accumulation and partial reversal of resistance by VPM (6.6 microM) addition was also identified, consistent with a functional Pgp being overexpressed in these sublines. Modifications of Topo II expression therefore appear to precede Pgp overexpression in this series of sequentially derived VP-16 resistant sublines and to represent the predominant mechanism underlying low level (< 10-fold) resistance.

ATP Binding Cassette Transporter, Subfamily B, Mem↗