Dephosphorylation of the small heat shock protein Hsp27 in vivo by protein phosphatase 2A

The phosphorylation of the Hsp27 complex is rapidly altered in MRC-5 cells when they are exposed to mitogens, cytokines, stress, or serine/threonine protein phosphatase inhibitors. Here we performed experiments to identify which cellular protein phosphatase (PP1, PP2A, or PP2B) is responsible for the in vivo phosphorylation/dephosphorylation of Hsp27. In their purified forms, PP2A dephosphorylates Hsp27 more effectively than PP2B, whereas PP1 is weakly active. Measurements of enzyme activity of lysates derived from inhibitor-treated cells indicated that Hsp27 phosphatase activity is equally sensitive to okadaic acid (PPI/PP2A inhibitor) and cyclosporin (PP2B inhibitor) and that both okadaic acid and cyclosporin treatment inhibited Hsp27 phosphatase activity additively. Together the in vitro data suggest that both PP2A and PP2B can dephosphorylate Hsp27. However, the phosphorylation of Hsp27 in vivo is only affected when cells are treated with PP1 and PP2A inhibitors (okadaic acid, calyculin A) or cantharidin (PP2A inhibitor), but not the PP2B inhibitor, cyclosporin A, suggesting PP2A to be the main enzyme dephosphorylating Hsp27 in the cells. Purification and immunoblotting of Hsp27 phosphatase from MRC-5 cells also suggest it to be PP2A and not PP1 or PP2B. The ability of PP2A to dephosphorylate Hsp27 is shown to be regulated by the phosphorylation state of PP2A itself.

Extrapolation methods for setting ecological standards for water quality: statistical and ecological concerns

: Extrapolation methods form the basis for most recent techniques used to set 'safe' levels of toxicants for ecosystems. Most methods use information from several single species toxicity tests to predict safety factors for protecting all species in all communities in a nation or group of nations. There are a number of statistical and ecological concerns with this approach. These include assumptions about the shape of the distribution of tolerance to a toxicant, the ability to extrapolate information on laboratory species and condition to field species and condition and to the condition of communities and ecosystems, and assumptions about the appropriateness of laboratory measures relative to ecosystem measures. The approach has not been validated for safety and, before the approach is fully applied, needs to be validated. Other methods can be used with the extrapolation approach to reduce uncertainties.

Contracts: problems and prospects

This article focuses on the important role played by contract prices in the new NHS. The power of prices to both inform and misinform the allocation of resources is highlighted. Orthopaedic surgery is used as a case study to indicate not only the obstacles to prices leading to improvements in efficiency but also the substantial scope for the prices set to convey valuable information on relative costs. Whether the purchaser-provider split will lead to an improved use of scarce resources will depend on several factors. One of the most important of which will be the development of sophisticated contracts embodying accurate price information.

The balance of ecological destruction and repair

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Nine-year follow-up study of a plasma-derived hepatitis B vaccine in a rural African setting

One hundred and one of 255 recipients of a plasma-derived hepatitis B vaccine were evaluated in 1990, 9 years after the first vaccine dose in a study in Zambia to evaluate the efficacy of one, two, or three doses. In 1983, 2 years after the first vaccine dose, antibody to the hepatitis B surface antigen (anti-HBs) had been detectable in 90 of these 101 participants (89%). In 1990, anti-HBs was still detectable in 72 of 101 (71%), and was present at a protective level (> or = 10 mIU/mL) in 68 of 101 (67%). Although the original vaccine study elicited a protective level of antibody in a greater percentage of children and adolescents than in adults, there were no significant differences among the three groups at 9 years. (In 1990, anti-HBs was still detectable in 52 of 70 [74%] who had had no serologic markers of the hepatitis B virus in 1981, and a protective level was detected in 47 of 70 [67%].) A protective level of anti-HBs was detected in 1990 in 26 of 36 (72%) recipients of three doses and in 23 of 31 (74%) recipients of two doses; the slightly lower prevalence among recipients of one dose (19 of 34 [56%]) was not statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Sometimes sensitive, seldom specific: a review of the economics of screening

As the policy relevance of screening has increased, the application of the techniques of economic evaluation to screening has become widespread. This paper critically reviews the literature, and in so doing, highlights several ways in which future evaluations might be improved. These include: the adoption of a broader perspective regarding the questions to be addressed and the relevant margins; a reconsideration of the nature of the benefits and how they might be valued; and a greater emphasis being placed upon the role of individual behaviour and its potential impact on the outcome of economic evaluations.

Inactivation of a redox-sensitive protein phosphatase during the early events of tumor necrosis factor/interleukin-1 signal transduction

Isoforms of heat shock protein (Hsp) 27 were used as intracellular markers to study tumor necrosis factor/interleukin-1 (TNF/IL-1) regulation of protein phosphatases in primary human fibroblasts. These isoforms were rapidly phosphorylated to varying degrees when fibroblasts were treated with either TNF, IL-1, okadaic acid, calyculin A, ARS, epidermal growth factor, fibroblast growth factor, H2O2, buthionine sulfoximine, N-ethylmaleimide, diethylmaleimide, or iodoacetate. However, inhibitors of protein kinases A and C, tyrosyl protein kinases, and general protein kinases had no effect on the enhanced phosphorylation of these isoforms in TNF, IL-1, okadaic acid, or calyculin A-stimulated cells, suggesting that the activation of protein kinases by itself is insufficient to produce these changes. Isoforms of 32P-labeled Hsp27 were dephosphorylated during cold-chases with excess phosphate in the absence but not in the presence of TNF/IL-1 or inhibitors of protein phosphatases suggesting that inactivation of protein phosphatase(s) plays a role in TNF/IL-1 signal transduction. Assays of phosphatase activity of cytosolic fractions from TNF or okadaic acid treated human fibroblasts showed an inactivation of protein phosphatase activity against the 32P-labeled Hsp27 protein substrates. In vitro assays of partially purified phosphatase activity from primary human fibroblasts with Hsp27 substrate also showed the protein phosphatase activity to be inhibited by ARS. Like okadaic acid, ARS mimics TNF in inducing specific patterns of cellular protein phosphorylation. Taken together these findings are consistent with the hypothesis that a SH-dependent protein phosphatase is inactivated during the early events of TNF/IL-1 signal transduction, hence inhibitors of protein phosphatases and SH modifying compounds can mimic the early effects of TNF/IL-1 on cells.

Ecotoxicological testing: small is reliable

The focus of environmental regulations has changed significantly since the introduction of the bioassay as a standard means of assessing environmental impact. Prominent in this change is an increasing emphasis on protecting the integrity of natural ecosystems, which incorporate community- and system-level properties as well as organismal and population processes. Consequently, support for the use of multispecies testing has widened to include not only ecologists in academia but environmental scientists in the regulatory and industrial sector as well. The reason for this trend is clear: the additional environmental realism gained from tests utilizing communities of organisms allows for greater insight into the potential hazard of chemicals and other forms of human activity to natural ecosystems that cannot be obtained from single species tests alone. Many of the problems cited for multispecies testing early in their evolution as a hazard assessment tool have been refuted or overcome. In particular, the use of natural microbial communities minimizes several shortcomings typically associated with multispecies toxicity testing. This article includes the utility of microcosm and mesocosm tests using aquatic microbial communities as hazard assessment tools in conjunction with accumulating information on their performance in toxicity testing protocols. An increasing body of experimental evidence supports an expansion in the use of these tests for a variety of regulatory and research purposes. A shift in research focus is needed, however, to answer remaining questions and further refine standard protocols for these valuable ecotoxicological tools.

The threshold problem in ecotoxicology

The most commonly used threshold in environmental toxicology is the LC50 (or modifications thereof) where 50% of the organisms die or are otherwise affected at a certain concentration of a chemical for a particular time of exposure under specified environmental conditions. Most commonly, this particular threshold is derived from single species laboratory tests low in environmental realism. If the field of ecotoxicology truly examines the effects of chemicals on ecosystems (i.e., complex multivariate systems), serious consideration must be given to thresholds other than those now commonly used in the field of environmental toxicology. Attributes at the community and ecosystem level of organization are not demonstrated at lower levels of biological organization, for example, energy flow and nutrient spiralling. Key issues are whether extrapolation is possible from one threshold to another within a level of biological organization and from one level of biological organization to another for thresholds that do not exist at many levels. Thresholds may be artefacts of testing procedures and may not exist in natural systems. Nevertheless, society must make management decisions about risk with available methods, including those designed to identify some point or threshold below which no deleterious effects are observed. However, these methods and their assumptions deserve more explicit and systematic examination than they have received thus far.

Mechanisms of directed mutation

Spontaneous mutants arise among nondividing populations of Escherichia coli in apparent response to selective conditions. In this report we investigate several hypotheses to account for the role of selection in the production of these "directed" or "adaptive" mutations. We found that the Lac+ phenotypes of some mutants that arise late after lactose selection are due to suppressor mutations that are unlinked to the mutant lacZ allele; thus the production of these Lac+ mutants does not require an information flow from successful proteins back to the DNA that encodes them. Transcriptional induction of the lac operon, even in the presence of another, utilizable carbon source, did not stimulate the occurrence of Lac+ mutants in the absence of lactose, indicating that the role of the selective agent is not merely to induce transcription. The absence of two DNA repair pathways-methyl-directed mismatch repair and alkylation repair-also did not result in an accumulation of Lac+ mutants in the absence of lactose, suggesting that these repair pathways are not normally responsible for correcting transient variants that might arise in the absence of selection. However, in one case the Lac+ mutation is likely to be due to a miscoding lesion occurring on the nontranscribed DNA strand, indicating that, at least in this instance, DNA replication is required before directed mutations can arise.

Discounting and health benefits: another perspective

This paper reviews the argument advanced by Parsonage and Neuburger that the non-monetary benefits of health programmes should be discounted at a lower rate than that used for financial flows. The conceptual issues raised in that paper are discussed and others, such as the tradability of non-monetary benefits and the link between individual and social discount rates, are introduced. The collection and assessment of more evidence is needed before Parsonage and Neuburger's proposition can be supported.

Response to mitoxantrone in advanced breast cancer: correlation with expression of c-erbB-2 protein and glutathione S-transferases

Sixty-eight patients with advanced breast cancer were treated with mitoxantrone and clinical responses assessed. Expression of c-erbB-2 protein and cytosolic glutathione S-transferase (GST) isoenzymes pi, alpha and mu by the primary tumours of these patients was determined immunohistochemically, and correlated with treatment response. Tumours overexpressing c-erbB-2 (n = 16, 23%) showed a lower response rate (50% vs 58%) and shorter duration of response to treatment, compared with c-erbB-2 negative tumours. These associations were not statistically significant but survival following start of treatment was significantly shorter in the c-erbB-2 positive group. For each GST isoenzyme, the response rate and duration of response of the group showing enzyme expression did not differ significantly from those with negatively staining tumours. These data do not support a role for expression of GSTs alone in resistance to mitoxantrone monotherapy in advanced breast cancer. The poorer post treatment survival of patients with c-erbB-2 positive tumours suggests they could be selected for more intensive treatment regimens.

Relationship between c-erbB-2 protein product expression and response to endocrine therapy in advanced breast cancer

Of 221 patients with breast cancer of known epidermal growth factor receptor (EGFR) and oestrogen receptor (ER) status, 99 had developed recurrences during the period of follow-up (range 3-60 months, median 24 months). Of these, 72 received endocrine therapy as first-line treatment for relapse. Immunohistochemical assessment of c-erbB-2 protein product expression was made using paraffin-embedded tumour tissue from 65 of these 72 patients. Including patients whose disease remained stable for more than 6 months with those showing an objective response (CR or PR for more than 3 months), only one (7%) of 14 c-erbB-2 positive tumours responded to endocrine manipulation compared with 19 (37%) of 51 c-erbB-2 negative tumours (P less than 0.05). Coexpression of c-erbB-2 reduced the response rate of ER positive patients from 48% to 20% and of ER negative cases from 27% to 0% (P less than 0.01). EGFR and c-erbB-2 protein appeared to have additive effects in reducing the likelihood of response, and none of eight patients with EGFR positive, c-erbB-2 positive tumours derived benefit from endocrine therapy. The results of this study suggest that c-erbB-2 protein overexpression, a marker of poor prognosis in breast cancer, is associated with a lack of response to endocrine therapy on relapse, and particularly in combination with EGFR may be useful in directing therapeutic choices.

Immunohistochemical demonstration of glutathioneS-transferases in primary human breast carcinomas

The expression of cytosolic glutathione S-transferase (GST) isoenzymes has been assessed in a series of 74 primary human breast carcinomas using an immunohistochemical method. GST pi was detected in sections from all 74 tumours; it was expressed by non-epithelial (stromal and inflammatory) cells in 62 tumours (84 per cent), but by tumour epithelium in only 35 (47 per cent). Non-neoplastic mammary epithelium was uniformly positive for GST pi. Expression of GST alpha and mu was observed in 19 and 42 per cent of the tumours, respectively, and was largely confined to the neoplastic component. Lack of staining of tumour epithelium for GST pi was significantly associated with poorer tumour differentiation (higher grade). There was no association between expression of any of the three isoenzymes and either menopausal status or expression of c-erbB-2 oncogene protein product. Immunohistochemistry is a useful method for the investigation of expression and cellular localization of GSTs within tumours; such data are needed to improve our understanding of the role of these enzymes in neoplasia and in resistance to cytotoxic drug therapy.

How should results from completed studies influence ongoing clinical trials? The CAFA Study experience

Seven randomized studies during the past 5 years have evaluated or are evaluating the efficacy of warfarin or aspirin or both in decreasing the risk of embolic events in patients with nonrheumatic atrial fibrillation. By March 1990, two of the studies had been published, both of which showed a statistically significant decrease in embolic events in patients treated with warfarin and a low rate of major bleeding events. The investigators associated with the other ongoing studies were forced to consider how these results should affect the decision to recruit and continue follow-up of patients in their own studies. The Steering Committee of the Canadian Atrial Fibrillation Anticoagulation (CAFA) study thought the newly published results from other studies were valid, clinically important, and generalizable. The committee considered the following options for the CAFA study: continue patient recruitment as planned, provide the data available in CAFA to its External Safety and Efficacy Monitoring Committee for analysis to determine whether the CAFA data already showed a benefit of warfarin, stop patient recruitment but continue to follow patients in the group to which they were assigned, stop the trial immediately and perform a final analysis, and attempt to perform a meta-analysis of all data available from all trials. The Steering Committee of CAFA decided that the evidence of benefit with warfarin, from the two published studies, was sufficiently compelling as to stop recruitment into CAFA without any preliminary examination of the CAFA data.

Issues in the early termination of the aspirin component of the Physicians' Health Study. Data Monitoring Board of the Physicians' Health Study

The Physicians' Health Study is a randomized, double-blind, placebo-controlled prevention trial of 22,071 US physicians, using a factorial design to evaluate the role of aspirin in the prevention of cardiovascular mortality and beta carotene in the reduction of cancer incidence. After approximately 5 years of follow-up, the aspirin component was terminated, 3 years ahead of schedule. Several factors were considered in the decision to terminate, including a cardiovascular mortality rate markedly lower than expected in both aspirin and placebo subjects, precluding the evaluation of the primary aspirin hypothesis, and a highly significant (P < .00001) and impressive (44%) reduction in the risk of first myocardial infarction in the aspirin group. Issues in the decision to terminate are described in this report.