Finance. Do tariffs stack up?
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Biomedical subjects
Andrew Street
Publications and source records attributed to Andrew Street.
The Hepatitis C virus NS5A protein activates a phosphoinositide 3-kinase-dependent survival signaling cascade.
Hepatitis C virus (HCV) establishes a persistent infection, with up to 80% of infected individuals proceeding to chronic hepatitis, which in many cases may result in liver cirrhosis and hepatocellular carcinoma (HCC); indeed HCV infection is increasingly associated with the development of HCC. The long time period (up to 30 years) between primary infection and the onset of HCC implies that HCV is not directly oncogenic but in some way predisposes patients to develop tumors, though the mechanism for this is unclear as yet. We report here that NS5A binds directly to the Src homology 3 domain of the p85 regulatory subunit of phosphoinositide 3-kinase (PI3K), and this interaction is mediated by a novel (non-proline-rich) motif within NS5A. Coimmunoprecipitation analysis revealed that NS5A bound native heterodimeric PI3K and enhanced the phosphotransferase activity of the catalytic (p110) subunit both in vitro and in human cell lines harboring a subgenomic HCV replicon or expressing NS5A alone. NS5A-mediated activation of PI3K resulted in increased phosphorylation and activity of Akt/protein kinase B and concomitantly provided protection against the induction of apoptosis in both replicon-harboring cells and cells stably expressing NS5A alone. These data suggest that stimulation of PI3K by NS5A may represent an indirect mechanism for development of HCC in HCV-infected patients and further suggests potential therapeutic strategies to counteract the occurrence of HCV-related HCC.
Amino Acid Motifs↗
The hepatitis C virus NS5A protein binds to members of the Src family of tyrosine kinases and regulates kinase activity.
The hepatitis C virus (HCV) non-structural NS5A protein has been shown to associate with a variety of cellular signalling proteins. Of particular interest is the observation that a highly conserved C-terminal polyproline motif in NS5A was able to interact with the Src-homology 3 (SH3) domains of the adaptor protein Grb2. As it has previously been shown that specific polyproline motifs can interact with a range of SH3 domains, we investigated whether NS5A was capable of interacting with other SH3 domain-containing proteins. We show here that NS5A interacts with the SH3 domains of members of the Src family of tyrosine kinases: a combination of in vitro binding assays and co-immunoprecipitation experiments revealed an interaction between NS5A and Hck, Lck, Lyn and Fyn, but interestingly not Src itself. Mutational analysis confirmed that the polyproline motif responsible for binding to Grb2 also bound to the SH3 domains of Hck, Lck, Lyn and Fyn. Furthermore, a previously unidentified polyproline motif, adjacent to the first motif, was also able to mediate binding to the SH3 domain of Lyn. Using transient transfections and Huh-7 cells harbouring a persistently replicating subgenomic HCV replicon we demonstrate that NS5A bound to native Src-family kinases in vivo and differentially modulated kinase activity, inhibiting Hck, Lck and Lyn but activating Fyn. Lastly, we show that signalling pathways controlled by Src-family kinases are modulated in replicon cells. We conclude that the interactions between NS5A and Src-family kinases are physiologically relevant and may play a role in either virus replication or pathogenesis.
Animals↗
The hepatitis C virus non-structural NS5A protein inhibits activating protein-1 function by perturbing ras-ERK pathway signaling.
The hepatitis C virus nonstructural 5A (NS5A) protein is a pleiotropic phosphoprotein that has been shown to associate with a wide variety of cellular signaling proteins. Of particular interest is the observation that a highly conserved C-terminal Class II polyproline motif within NS5A mediated association with the Src homology 3 domains of members of the Src family of tyrosine kinases and the mitogenic adaptor protein Grb2 (A. Macdonald, K. Crowder, A. Street, C. McCormick, and M. Harris, submitted for publication). In this study, we analyzed the consequences of NS5A expression on mitogenic signaling pathways within a variety of cell lines. Utilizing a transient luciferase reporter system, we observed that NS5A inhibited the activity of the mitogenic and stress-activated transcription factor activating protein-1 (AP1). This inhibition was dependent upon a Class II polyproline motif within NS5A. Using a combination of dominant active and negative mutants of components of the MAPK signaling pathways, selective inhibitors, together with immunoblotting with phospho-specific and phosphorylation-independent antibodies, we determined the signaling pathways targeted by NS5A to inhibit AP1. These studies demonstrated that in both stable NS5A-expressing cells and Huh-7-derived cells harboring subgenomic hepatitis C virus (HCV) replicons, this inhibition was mediated through the ERK signaling pathway. Importantly, a comparable inhibition of AP1 reporter activity was observed in hepatocyte-derived cell lines transduced with a baculovirus vector driving expression of full-length HCV polyprotein. In conclusion, these data strongly suggest a role for the NS5A protein in the perturbation of mitogenic signaling pathways in HCV-infected hepatocytes.
Amino Acid Motifs↗
How much confidence should we place in efficiency estimates?
Ordinary least squares (OLS) and stochastic frontier (SF) analyses are commonly used to estimate industry-level and firm-specific efficiency. Using cross-sectional data for English public hospitals, a total cost function based on a specification developed by the English Department of Health is estimated. Confidence intervals are calculated around the OLS residuals and around the inefficiency component of the SF residuals. Sensitivity analysis is conducted to assess whether conclusions about relative performance are robust to choices of error distribution, functional form and model specification. It is concluded that estimates of relative hospital efficiency are sensitive to estimation decisions and that little confidence can be placed in the point estimates for individual hospitals. The use of these techniques to set annual performance targets should be avoided.
Confidence Intervals↗
Should general practitioners purchase health care for their patients? The total purchasing experiment in Britain.
Until relatively recently, general practitioners (GPs) have been allowed to work independently, with no requirement to consider the resource implications of their referral and prescribing decisions. In order to align the interests of GPs with the overall objectives of health systems a number of countries have introduced primary care based capitation, funds pooling and budget holding either as experiments or as an overall policy. Are these experiments and policies likely to work? This paper presents evidence from the UK total purchasing experiment, which was the first major quasi-market development in the NHS to be independently evaluated from the outset. Total purchasing gave volunteer groups of practices freedom to purchase all hospital and community health services for their patients. The evidence suggests that whilst GPs have great potential as purchasers, they also have considerable limitations. The expectation that they will be able to improve the quality of patient experience of care, or to alter the use of resources, may not be generally realised. GP-based purchasing may be more appropriate where the task is to alter the balance or location of care between hospital and extramural settings. However, budgetary incentives are not 'magic potions' which have similar effects on behaviour wherever they are introduced. Holding budgets and having independent contracts, while important pre-requisites for being taken seriously in a quasi-market, were not sufficient for effective total purchasing. The paper concludes that health systems should not only value innovation and experimentation and encourage learning from evaluative research; they should also recognise the importance of supportive circumstances for any innovation to effect real and sustained change.
Budgets↗
Comparing the efficiency of national health systems: a sensitivity analysis of the WHO approach.
The World Health Organization (WHO) has used econometric methods to measure the efficiency of health care systems. We assess the robustness of WHO results to definitions of efficiency and statistical procedures. Originally analysed by the WHO, the data are for 1997 (50 countries) and 1993-1997 (141 countries). The efficiency of each country in promoting population health is estimated after taking into account health care expenditure, all other expenditure and education levels. Efficiency scores are compared under different definitions of efficiency and different estimation methods. The results show that the country rankings and efficiency scores are sensitive to the definition of efficiency and choice of model specification. We conclude that econometric methods can yield insights into complex socioeconomic phenomena. However, the lack of robust results to reasonable alternative specifications suggests that it is premature to use the methods adopted by the WHO to construct league tables of health systems.
Data Collection↗
The resurrection of hospital mortality statistics in England.
Mortality statistics for English hospitals were published by the Labour government in 1998, partly in response to the tragedy at the Bristol Royal Infirmary involving the deaths or serious injury of babies and children who had had unsuccessful heart operations. Despite being presented as an important innovation, this publication policy had a number of precedents, most notably the data produced as a result of Florence Nightingale's efforts in the 1860s and the clinical indicators developed by the Scottish Office in the early 1990s. In addition, league tables of death rates for English hospitals were available from 1992 to 1996, although there was widespread ignorance of their existence. This paper examines each of these precedents before discussing events that weakened public trust in the medical profession's ability to regulate itself and led to the Labour government's decision to resurrect the publication of hospital mortality data. It is suggested that these performance indicators may be largely symbolic of the government's broader commitment to performance assessment, but it is also recognised that, if coupled with appropriate incentives, public disclosure of mortality data may foster genuine performance improvements.
Access to Information↗