Shigella sonnei utilises colicins during inter-bacterial competition

The mammalian colon is one of the most densely populated habitats currently recognised, with 1011-1013 commensal bacteria per gram of colonic contents. Enteric pathogens must compete with the resident intestinal microbiota to cause infection. Among these enteric pathogens are Shigella species which cause approximately 125 million infections annually, of which over 90 % are caused by Shigella flexneri and Shigella sonnei. Shigella sonnei was previously reported to use a Type VI Secretion System (T6SS) to outcompete E. coli and S. flexneri in in vitro and in vivo experiments. S. sonnei strains have also been reported to harbour colicinogenic plasmids, which are an alternative anti-bacterial mechanism that could provide a competitive advantage against the intestinal microbiota. We sought to determine the contribution of both T6SS and colicins to the anti-bacterial killing activity of S. sonnei. We reveal that whilst the T6SS operon is present in S. sonnei, there is evidence of functional degradation of the system through SNPs, indels and IS within key components of the system. We created strains with synthetically inducible T6SS operons but were still unable to demonstrate anti-bacterial activity of the T6SS. We demonstrate that the anti-bacterial activity observed in our in vitro assays was due to colicin activity. We show that S. sonnei no longer displayed anti-bacterial activity against bacteria that were resistant to colicins, and removal of the colicin plasmid from S. sonnei abrogated anti-bacterial activity of S. sonnei. We propose that the anti-bacterial activity demonstrated by colicins may be sufficient for niche competition by S. sonnei within the gastrointestinal environment.

Exploring the experiences of parents of Autistic children when attending the diagnostic imaging department for an X-ray examination

INTRODUCTION

Autism is a neuro-developmental condition which affects the social-emotional skills, behaviour, language, communication skills and flexibility of thoughts of an individual and their sensory processing. This can result in Autistic service users finding it difficult to navigate current healthcare provision and cope with the unpredictable environment. This paper explores the experiences of parents of Autistic children when attending the diagnostic imaging department for an X-ray examination.

METHODS

A cross sectional, mixed methods approach was adopted and the initial phase consisting of an online survey for parents to complete is the subject of this paper. The quantitative data was analysed using descriptive statistics and cross comparison between questions was also completed. Thematic analysis was taken to analyse the data from the two open questions at the end of the survey.

RESULTS

The online survey results are presented in this paper under four key themes; waiting times and environment, forms of communication, lack of understanding of staff regarding Autism and preparation for the X-ray examination.

CONCLUSION

The overall rating of the parents' experience whilst in the X-ray/diagnostic imaging department was positive, however there are several areas which received low scores which need further attention. These were waiting areas, waiting times, staff development and patient preparation.

IMPLICATIONS FOR PRACTICE

The development of more inclusive waiting areas is needed, more effective lines of communication between staff to expedite the patient journey where possible, staff development of both radiographers and also support staff and the review of design of more accessible and inclusive patient information.

Retroperitoneal lymphadenopathy secondary to joint replacement wear and debris, a case report

We present a case of a 63-year-old female who initially presented with complaints of vulvar swelling and was subsequently found to have isolated retroperitoneal lymphadenopathy on imaging. Biopsy was performed and was indicative of weakly polarizable material that raised the consideration of joint prosthesis wear debris. Due to the patient's concern for an underlying malignancy of gynecologic origin, a laparoscopic lymphadenectomy was ultimately performed and final pathology was consistent with reactive changes due to joint wear and debris from the patient's bilateral total knee arthroplasties placed approximately 16 years prior. While this is a rare presentation, it is important to consider this in the differential of retroperitoneal lymphadenopathy as these patients are often referred to a gynecologic oncologist for further workup.

•

Lymphadenopathy due to joint wear and debris from arthroplasty is a rare finding.

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While the differential is broad, it should include this etiology.

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Gynecologic oncologists should be aware of this finding and manage accordingly.

Ipilimumab-induced hypophysitis in melanoma patients: an Australian case series

BACKGROUND

Ipilimumab (Yervoy; Bristol-Myers Squibb) is a novel fully humanised monoclonal antibody that blocks cytotoxic T-lymphocyte antigen 4, an immune checkpoint molecule, to augment anti-tumour T-cell responses. It is associated with significant immune-related side-effects including hypophysitis.

AIM

We reviewed the clinical and biochemical characteristics of 10 patients with ipilimumab-induced hypophysitis (IH), and developed guidelines for the early detection and management of IH based on our experiences at three major teaching hospitals in Sydney.

METHODS

All patients were evaluated at the Crown Princess Mary Cancer Centre and Department of Endocrinology, Westmead Hospital, Department of Endocrinology, Royal Prince Alfred Hospital, the Melanoma Institute Australia and Macarthur Cancer Therapy Centre, Campbelltown Hospital from 2010 to 2014. Relevant data were extracted by review of medical records. Main outcome measures included clinical features, hormone profile and radiological findings associated with IH, and presence of pituitary recovery.

RESULTS

Ten patients were identified with IH. In four patients who underwent monitoring of plasma cortisol, there was a fall in levels in the weeks prior to presentation. The pituitary-adrenal and pituitary-thyroid axes were affected in the majority of patients, with the need for physiological hormone replacement. Imaging abnormalities were identified in five of 10 patients, and resolved without high-dose glucocorticoid therapy. To date, all patients remain on levothyroxine and hydrocortisone replacement, where appropriate.

CONCLUSIONS

There is significant morbidity associated with development of IH. We suggest guidelines to assist with early recognition and therapeutic intervention.

HCV treatment rates and sustained viral response among people who inject drugs in seven UK sites: real world results and modelling of treatment impact

Hepatitis C virus (HCV) antiviral treatment for people who inject drugs (PWID) could prevent onwards transmission and reduce chronic prevalence. We assessed current PWID treatment rates in seven UK settings and projected the potential impact of current and scaled-up treatment on HCV chronic prevalence. Data on number of PWID treated and sustained viral response rates (SVR) were collected from seven UK settings: Bristol (37-48% HCV chronic prevalence among PWID), East London (37-48%), Manchester (48-56%), Nottingham (37-44%), Plymouth (30-37%), Dundee (20-27%) and North Wales (27-33%). A model of HCV transmission among PWID projected the 10-year impact of (i) current treatment rates and SVR (ii) scale-up with interferon-free direct acting antivirals (IFN-free DAAs) with 90% SVR. Treatment rates varied from <5 to over 25 per 1000 PWID. Pooled intention-to-treat SVR for PWID were 45% genotypes 1/4 [95%CI 33-57%] and 61% genotypes 2/3 [95%CI 47-76%]. Projections of chronic HCV prevalence among PWID after 10 years of current levels of treatment overlapped substantially with current HCV prevalence estimates. Scaling-up treatment to 26/1000 PWID annually (achieved already in two sites) with IFN-free DAAs could achieve an observable absolute reduction in HCV chronic prevalence of at least 15% among PWID in all sites and greater than a halving in chronic HCV in Plymouth, Dundee and North Wales within a decade. Current treatment rates among PWID are unlikely to achieve observable reductions in HCV chronic prevalence over the next 10 years. Achievable scale-up, however, could lead to substantial reductions in HCV chronic prevalence.

Cutaneous adverse events in patients treated with BRAF inhibitor-based therapies for metastatic melanoma for longer than 52 weeks

BACKGROUND

BRAF inhibitor-based therapies have been shown to induce cutaneous toxicities, with onset generally in the first 8-26 weeks of therapy.

OBJECTIVES

To determine whether cutaneous toxicities persist in patients who have remained on BRAF inhibitor-based therapies for longer than 52 weeks, and therefore whether ongoing dermatology assessment is required.

METHODS

All patients treated with the BRAF inhibitors vemurafenib or dabrafenib or combination BRAF inhibitor and mitogen-activated protein kinase kinase (MEK) inhibitor therapy at Westmead Hospital, Sydney, Australia underwent regular dermatological assessments for the duration of therapy. All patients enrolled in a clinical trial, and 18% of patients in the compassionate access scheme underwent a baseline assessment prior to commencement of therapy and every 4-8 weeks thereafter. Patients' adverse events were recorded in a specific database.

RESULTS

Patients continued to develop cutaneous adverse events after 52 weeks of continuous therapy. Patients on single-agent BRAF inhibitor therapy suffered from Grover disease (45%), plantar hyperkeratosis (45%), verrucal keratosis (18%) and even cutaneous squamous cell carcinoma (16%). The most frequent adverse event seen in patients in the combination BRAF and MEK inhibitor group was an acneiform eruption (40%).

CONCLUSIONS

Patients on BRAF inhibitor-based therapies need to continue to have regular dermatological follow-up independent of the duration of their therapy.

Fiber-optic intra-aortic balloon therapy and its role within cardiac surgery

INTRODUCTION

The patient population has changed and the cardiothoracic team are now operating on patients with more co-morbidity. One of the significant aspects of this increased co-morbidity, which affects both short- and long-term outcomes, is compromised left ventricular function. Intra-aortic balloon pump (IABP) technology offers these patients and the cardiac team an easily accessible, cost-effective, mechanical assist device. Arterial pressure monitoring for IABP therapy: Fluid-filled transducers used to measure the aortic waveform can be unreliable and inconsistent. Fiber-optic manometers located in the very tip of the IAB catheters provide accurate and fast, high quality measurements. This, in turn, presents the opportunity for the hardware and algorithm to measure key markers on the arterial waveform and optimise left ventricular support. It also provides the potential for automatic in vivo calibration, further increasing the accuracy and quality of the IAB support. The effect of fiber-optic IABP therapy on clinical management: A dual centre prospective audit comparing fluid-filled versus fiber-optic arterial pressure monitoring showed a 96% reduction in IAB-related perfusion on-site call-outs (17 vs. 1, respectively) and a 94% reduction in sub-optimal timing (55/98 vs. 2/94, respectively).

CONCLUSION

The improved timing algorithms utilise the pressure information received 50 msecs faster than with fluid-filled transducers, measuring key markers on the pressure waveform and adjusting inflation and deflation accurately on a beat per beat basis. Fiber-optic IAB technology and, specifically, these improved algorithms provide better beat per beat mechanical support. Given our evolving patient population, this technology will not only play an increased role, but will have a significant impact on cardiac surgery.

Mechanical left ventricular support using a 50 cc 8 Fr fibre-optic intra-aortic balloon technology: a case report

Introduction:

More than four decades have passed since the first clinical use of an (IABP) to improve the clinical scenario for patients with chronic left ventricular failure. The original IAB catheter size was 15 French (Fr), requiring an open surgical insertion and removal. This therapy has now become the most widely used mechanical device for failure of the left ventricle. The introduction of an 8 Fr fibre-optic IAB catheter with a 50 cc diastolic blood volume displacement has further increased the potential clinical impact of this technology. This new catheter can be used for all patients over 162 cm in height, allowing a broader spectrum of patients to benefit from increased diastolic blood volume displacement and fibre-optic pressure monitoring. The catheter has been designed on an 8 Fr shaft platform, potentially reducing the incidence of vascular complications. We present our case report on the world’s first implant of this 50cc 8 Fr IAB catheter.

Case Report:

Cardiac investigations on a 53-year-old man showed the patient to have ischaemic dilated cardiomyopathy with a left ventricular ejection fraction (LVEF) of 25%. An 8 Fr 50cc Sensation PlusTM IAB catheter was inserted pre-operatively, prior to coronary artery bypass grafting.

Results:

The world’s first insertion of this 8 Fr 50 cc IAB catheter was a complete success, with no complications. The patient’s pre-, peri- and post-operative courses were as we expected and event free, underpinned by IABP support.

Conclusion:

This new 50 cc, 8 Fr IAB expands the patient group that can benefit from greater diastolic blood volume delivery, improved distal perfusion, more accurate monitoring, subsequent better beat-per-beat support and, finally, the reduced complication rates associated with an 8 Fr shaft.

Infection control systems in transition: the challenges for post-Soviet Bloc countries

BACKGROUND

Just two decades ago, 30 of today's countries in Europe and Asia had socialist governments under Soviet dominance or direct administration. Intensive health system reforms have altered infection control in many of these countries. However, much of the literature from these countries is difficult to access by international scientists.

AIM

To summarize existing infection control policies and practices in post-Soviet Bloc countries.

METHODS

In addition to PubMed and Google search engines, we explored local websites and grey literature. In total, 192 references published in several languages were reviewed.

FINDINGS

Infection control in these countries is in the midst of transition. Three groups of countries were identified. First, Eastern European and Baltic countries building surveillance systems for specific pathogens and antibiotic use; second, European post-Soviet Bloc countries focusing on the harmonization of recently established infection control infrastructure with European surveillance programmes; third, countries such as those formerly in the Union of Soviet Socialist Republics, Mongolia and post-conflict Eastern European countries that are in the first stages of reform. Poor commitment, resource scarcity and shortages of expertise were identified. Underreporting of official infection control statistics is widespread.

CONCLUSIONS

Guidance from international organizations has been crucial in initiating and developing contemporary infection control programmes. More support from the international community will be needed for the third group of countries, where infection control has remained a neglected issue.

Phase I/II study to assess safety, pharmacokinetics, and efficacy of the oral MEK 1/2 inhibitor GSK1120212 (GSK212) dosed in combination with the oral BRAF inhibitor GSK2118436 (GSK436)

CRA8503

Background: In preclinical models, the BRAF/MEK inhibitor (i) combination GSK436/GSK212 has demonstrated enhanced activity against BRAF-mutant cancer cells compared to either drug alone, delayed emergence of GSK436 resistance, and prevented proliferative skin lesions attributable to BRAFi exposure. Methods: Eligible patients (pts) had BRAF V600 mutation positive solid tumors. Part 1: pharmacokinetic (PK) drug-drug interaction (DDI) study. Part 2: Dose escalation of continuous daily dosing of the combination followed by expansion cohorts; Part 3: Randomized phase II trial in untreated stage IV melanoma. Results: 45 pts have received ≥ 1 dose of GSK212 + GSK436, including 43 melanoma (all BRAFi naïve), 1 NSCLC and 1 salivary duct carcinoma. PK results of 7 pts in Part 1 showed no effect of GSK212 on single dose of GSK436. There was no clinically meaningful DDI between GSK436 and GSK212 after repeat dosing of the combination (Part 2). GSK436 was dosed 75-150 mg BID in combination with GSK212 1.0, 1.5, 2.0 mg QD. The recommended dose was 2 mg QD GSK212 in combination with 150 mg BID GSK436. At 1.5 mg GSK212, there was one DLT, a recurrent grade (G) 2 neutrophilic panniculitis. The only G4 adverse event (AE) was a sepsis-like syndrome with fever/hypotension. G3 AEs included generalized rash (n=2, 4%) and neutropenia (n=2, 4%). Skin toxicity ≥ G2 occurred in 9 (20%) pts; of these, G2 rash (n=4, 8%) and G2 macular rash (n=1, 2%). No cutaneous squamous cell carcinoma (SCC) or hyperproliferative skin lesions have occurred at any dose level. Other common G2 toxicities were pyrexia (n=5, 11%), vomiting (n=2, 4%) and fatigue (n=2, 4%). Of 16 evaluable pts in Part 2, 13 pts had PR and 3 SD for an ORR of 81% (95% CI 54.4%-96.0%) and all but 2 pts remain on study. In 10 evaluable pts who received 150 mg BID GSK436 + ≥1 mg QD GSK212, 9 pts had PR and 1 SD. Conclusions: GSK212 at 2 mg QD combines safely with GSK436 150 mg BID, no SCC thus far and decreased frequency of rash compared to previous trials of single agent GSK436 and GSK212, respectively. The preliminary anti-tumor activity warrants further investigation; the randomized phase II trial (Part 3) is accruing.

Metformin in prostate cancer: two for the price of one

BACKGROUND

Androgen deprivation therapy (ADT) for prostate cancer treatment induces a metabolic syndrome, which may contribute to non-cancer-related morbidity and mortality. Metformin may abrogate these effects. Additionally, metformin has potential antineoplastic activity in various malignancies including prostate cancer.

MATERIALS AND METHODS

A literature review using PubMed with the keywords: AMPK, androgen deprivation therapy, insulin resistance, metabolic syndrome, metformin and prostate cancer was undertaken.

RESULTS

This overview will look at the current evidence linking ADT and metabolic syndrome while discussing ongoing clinical trials under way assessing the effectiveness of metformin in abrogating these effects. The potential antineoplastic activity of metformin, mediated by multiple proposed mechanisms based on evidence from preclinical and clinical studies, will also be elucidated in this review.

CONCLUSIONS

Overall available data support the potential dual benefit of metformin on ADT-induced metabolic syndrome and in its antineoplastic activity in prostate cancer, justifying the need for ongoing clinical trials to confirm these effects as the evidence currently available for standard practice is lacking.

Sequential monitoring of hospital adverse events when control charts fail: the example of fall injuries in hospitals

OBJECTIVE

To evaluate methods for monitoring monthly aggregated hospital adverse event data that display clustering, non-linear trends and possible autocorrelation.

DESIGN

Retrospective audit.

SETTING

The Northern Hospital, Melbourne, Australia.

PARTICIPANTS

171,059 patients admitted between January 2001 and December 2006.

MEASUREMENTS

The analysis is illustrated with 72 months of patient fall injury data using a modified Shewhart U control chart, and charts derived from a quasi-Poisson generalised linear model (GLM) and a generalised additive mixed model (GAMM) that included an approximate upper control limit.

RESULTS

The data were overdispersed and displayed a downward trend and possible autocorrelation. The downward trend was followed by a predictable period after December 2003. The GLM-estimated incidence rate ratio was 0.98 (95% CI 0.98 to 0.99) per month. The GAMM-fitted count fell from 12.67 (95% CI 10.05 to 15.97) in January 2001 to 5.23 (95% CI 3.82 to 7.15) in December 2006 (p<0.001). The corresponding values for the GLM were 11.9 and 3.94. Residual plots suggested that the GLM underestimated the rate at the beginning and end of the series and overestimated it in the middle. The data suggested a more rapid rate fall before 2004 and a steady state thereafter, a pattern reflected in the GAMM chart. The approximate upper two-sigma equivalent control limit in the GLM and GAMM charts identified 2 months that showed possible special-cause variation.

CONCLUSION

Charts based on GAMM analysis are a suitable alternative to Shewhart U control charts with these data.

Organisation of hospital infection control in Mongolia

As with other areas of the public sector in Mongolia, the healthcare system has undergone significant structural and policy reforms since the early 1990s. The previous infection control system, characterised as a sanitary-epidemiological network, was dismantled with no replacement. A new infection control management system was established in 1997 with the adoption of infection control policies and guidelines, establishment of hospital infection control programmes in all major hospitals, training of health professionals and the commencement of passive surveillance of hospital-acquired infections (HAIs). Recent health statistics claim that HAIs occur in 0.01-0.02% of all hospital admissions with the highest percentage (0.05%) in tertiary hospitals in the capital city Ulaanbaatar, but this is very likely to be an underestimate. In 2002 the Government approved a national programme to establish a sentinel surveillance system for HAIs with improved laboratory-based monitoring. However, implementation has been delayed due to insufficient support from stakeholders and a shortage of resources and trained infection control professionals. Non-governmental infection control initiatives are limited by time and coverage.

Patients’ experiences and reported barriers to screening colonoscopy: A systematic review

1537

Background: Colonoscopy is a component of most colorectal screening programs, as a primary test or as follow-up to an abnormal FOB test. Little is known about why some patients do not comply with colonoscopy after being referred. Methods: A search strategy using three themes of screening, colonoscopy, and patient acceptance was developed and used in MEDLINE, EMBASE and PSYCHinfo (1996–2008). Retrieved citations were assessed for eligibility by two reviewers using prespecified criteria. A qualitative synthesis was conducted. Results: From an initial 3,174 studies, 264 were identified as potentially eligible for review. After full text assessment, 64 studies met eligibility criteria and were included in the final analysis. Six studies examined the experience of a primary colonoscopy by eliciting patients’ views soon after they had the test. Fifty-six studies addressed patient-reported concerns and barriers to an anticipated primary colonoscopy. Most patients perceived the laxative bowel preparation to be the most burdensome part and the greatest barrier to colonoscopy. Other reported difficulties included anxiety and anticipation of pain. Feelings of embarrassment and vulnerability occurred, particularly in women, and also acted as barriers to adherence. Inadequate knowledge about screening was common and was identified as an obstacle to the uptake of screening colonoscopy as was fear of finding cancer. Physician endorsement, having a family history, knowing someone with cancer, and perceived accuracy of the test were incentives to having a colonoscopy. The most common reported practical barriers were inconvenience, transportation, scheduling, and cost. Only two studies focused on colonoscopy as a secondary procedure in the screening context. Similar procedural, personal, and practical concerns were reported by patients in this setting. Conclusions: Bowel preparation, lack of awareness of the importance of screening, and feelings of vulnerability in women are all significant barriers to colonoscopy in the screening context. These obstacles need to be addressed, and further research undertaken on barriers to second line colonoscopy.

No significant financial relationships to disclose.

Clinical evaluation of the Admiral 1.35m2 hollow-fibre membrane oxygenator

This prospective study was designed to evaluate the fundamental clinical performance of a new, small surface area oxygenator. Data were collected from twenty patients undergoing first-time coronary artery bypass grafting using this device. This study focuses on how the reduction of surface area and prime volume affects the essential function of the oxygenator in terms of oxygenation efficiency, heat transference, membrane pressure drops, haemolysis and safety. Oxygenation efficiency was deemed to be well within acceptable margins, even at high flows, over a temperature range of 32-36 degrees C. Heat-exchanger performance was assessed by recording the heater/chiller water temperature compared to retrospective data from a current standard oxygenator. Heater/ chiller water temperatures were on average 0.3 degrees C higher with the small surface oxygenator than the standard data. The air handling of the device was excellent and extremely safe. Haemolysis, measured as plasma free haemoglobin, did not increase during bypass (p > 0.05). This new oxygenator offers a reduced surface area and priming volume while still ensuring an acceptable safety reserve and performance.

Identifying symptoms of ovarian cancer: a qualitative and quantitative study

Introduction

Symptoms of ovarian cancer are often vague and consequently a high proportion of women with ovarian cancer are not referred to the appropriate clinic.

Objective

To identify diagnostic factors for ovarian cancer.

Design

A qualitative and quantitative study.

Setting

Four UK hospitals.

Sample

One hundred and twenty-four women referred to hospital with suspected ovarian malignancy.

Methods

Women were interviewed prior to diagnosis (n = 63), or soon after. A thematic analysis was conducted. Emergent symptoms were quantitatively analysed to identify distinguishing features of ovarian cancer.

Main outcomes

Symptoms in women with and without ovarian cancer.

Results

Diagnoses comprised 44 malignancies, 59 benign gynaecological pathologies and 21 normal findings. Of the malignancies, 25 women had stage III or more disease, with an average age of 59 years. The benign/normal cohort was significantly younger (48 years). Multivariate analysis revealed persistent abdominal distension (OR 5.2, 95% CI 1.3–20.5), postmenopausal bleeding (OR 9.2, 95% CI 1.1–76.1), appetite loss (OR 3.2, 95% CI 1.1–9.2), early satiety (OR 5.0, 95% CI 1.6–15.7) and progressive symptoms (OR 3.6, 95% CI 1.3–9.8) as independent, statistically significant variables associated with ovarian cancer. Fluctuating distension was not associated with ovarian cancer (OR 0.4, 95% CI 0–4.1). Women frequently used the term bloating, but this represented two distinct events: persistent abdominal distension and fluctuating distension/discomfort.

Conclusions

Ovarian cancer is not a silent killer. Clinicians should distinguish between persistent and fluctuating distension. Recognition of the significance of symptoms described by women could lead to earlier and more appropriate referral.

Please cite this paper as: Bankhead C, Collins C, Stokes-Lampard H, Rose P, Wilson S, Clements A, Mant D, Kehoe S, Austoker J. Identifying symptoms of ovarian cancer: a qualitative and quantitative study. BJOG 2008;115:1008–1014.

Factors associated with breast cancer-specific distress in younger women participating in a family history mammography screening programme

This multi-centre study examined factors associated with breast cancer-specific distress in 2321 women under 50 who are on a mammographic screening programme on account of their family history. Women were recruited from 21 UK centres, and completed a questionnaire one month before their screening appointment. The transactional theory of stress, appraisal, and coping provided the theoretical framework for the study. Factors measured included screening history, family history, perceived risk, cognitive appraisals, coping, optimism, and cancer worry. The findings indicate that the majority of women appraise their family history as being relevant and somewhat threatening to personal well-being, but something they can deal with emotionally. Acceptance was the most commonly used coping strategy. Hierarchical regression analysis identified that the factors most significantly associated with distress were an appraisal of high relevance and threat, increased risk perception, low dispositional optimism, and the use of both avoidant and task-orientated coping strategies. Women with children and those with relatives who have died from breast cancer were also more distressed. To conclude, most women appraised their situation positively but there is a potential profile of risk factors which may help clinicians identify those women who need extra psychological support as they progress through screening.

Structure of the Human Papillomavirus E7 Oncoprotein and Its Mechanism for Inactivation of the Retinoblastoma Tumor Suppressor

The E7 oncoprotein from human Papillomavirus (HPV) mediates cell transformation in part by binding to the human pRb tumor suppressor protein and E2F transcription factors, resulting in the dissociation of pRb from E2F transcription factors and the premature cell progression into the S-phase of the cell cycle. This activity is mediated by the LXCXE motif and the CR3 zinc binding domain of the E7 protein. In this study we report the x-ray crystal structure of the CR3 region of HPV E7 and a structure-based mutational analysis to investigate its mode of pRb and E2F binding and E2F displacement from pRb. The structure reveals a novel zinc-bound E7-CR3 obligate homodimer that contains two surface patches of sequence conservation. Mutation of residues within these patches reveals that one patch is required for pRb binding, whereas the other is required for E2F binding. We also show that both E7-mediated interactions are required to disrupt pRb.E2F complexes. Based on these studies we present a mechanistic model for how E7 displaces E2F from pRb. Because the CR3 region of HPV E7 has no detectable homology to other human proteins, the structure-function studies presented here provide an avenue for developing small molecule compounds that inhibit HPV-E7-mediated cell transformation.

Fluorescence-Based Peptide Labeling and Fractionation Strategies for Analysis of Cysteine-Containing Peptides

This study demonstrates that 1,5-I-AEDANS (5-({2-[(iodoacetyl)amino]ethyl}amino)naphthalene-1-sulfonic acid) can be used as a versatile fluorescence-based peptide quantification tool and provides readily interpretable tandem mass spectra for de novo peptide sequencing. Two AEDANS-cysteinyl-peptide fractionation strategies were evaluated. One AEDANS-cysteinyl-peptide fractionation strategy employs immobilized metal affinity chromatography (IMAC) to recover AEDANS-labeled peptides and reduce the complexity of peptide mixtures. In an alternate solid-phase approach, 1,5-I-AEDANS was coupled to an o-nitrobenzyl-based photocleavable resin to produce a resin that can label and isolate thiols and cysteine-containing peptides with a modified-AEDANS label (mAEDANS: 5-((4-amino-4-oxobutanoyl){2-[(iodoacetyl)amino]ethyl}amino)naphthalene-1-sulfonic acid). This fractionation protocol enriches cysteine-containing peptides more specifically than the IMAC strategy. Using micro-LC-ESI-MS with an on-line fluorescence detector and a Q-TOF mass spectrometer, we generated fluorescence-based elution profiles and corresponding positive ion mass spectra of AEDANS-labeled peptides. This study demonstrates that AEDANS-peptides produce positive ion ESI-MS mass spectra with detection limits comparable to those of the unlabeled peptide. Collision-induced dissociation (CID) of fluorescent AEDANS-peptides revealed readily interpretable product ion spectra with the label intact. Similar to the AEDANS-labeled peptide, an mAEDANS-labeled thiol is fluorescent and CID of a mAEDANS-labeled peptide also reveals an interpretable product ion spectrum with the label intact.

Structure and autoregulation of the yeast Hst2 homolog of Sir2

Yeast Hst2 (yHst2) is a member of the silencing information regulator 2 (Sir2) family of NAD(+)-dependent protein deacetylases that are implicated in transcriptional silencing, DNA repair, genome stability and longevity. The X-ray crystal structure of the full-length yHst2 protein reveals a central catalytic core domain fold that is characteristic of the other Sir2 homologs, and C- and N-terminal extensions that interact with the NAD(+) and acetyl-lysine substrate-binding sites, respectively, suggesting an autoregulatory function for these domains. Moreover, the N-terminal extension mediates formation of a homotrimer within the crystal lattice. Enzymatic and sedimentation equilibrium studies using deletion constructs of yHst2 support the involvement of the N- and C-terminal yHst2 regions and trimer formation in catalysis by yHst2. Together, these studies indicate that the sequence-divergent N- and C-terminal regions of the eukaryotic Sir2 proteins may have a particularly important role in their distinct substrate-binding properties, biological activities or both.

Structural Basis for Histone and Phosphohistone Binding by the GCN5 Histone Acetyltransferase

Distinct posttranslational modifications on histones occur in specific patterns to mediate certain chromosomal events. For example, on histone H3, phosphorylation at Ser10 can enhance GCN5-mediated Lys14 acetylation to promote transcription. To gain insight into the mechanism underlying this synergism, we determined the structure of Tetrahymena GCN5 (tGCN5) and coenzyme A (CoA) bound to unmodified and Ser10-phosphorylated 19 residue histone H3 peptides (H3p19 and H3p19Pi, respectively). The tGCN5/CoA/H3p19 structure reveals that a 12 amino acid core sequence mediates extensive contacts with the protein, providing the structural basis for substrate specificity by the GCN5/PCAF family of histone acetyltransferases. Comparison with the tGCN5/CoA/H3p19Pi structure reveals that phospho-Ser10 and Thr11 mediate significant histone-protein interactions, and nucleate additional interactions distal to the phosphorylation site. Functional studies show that histone H3 Thr11 is necessary for optimal transcription at yGcn5-dependent promoters requiring Ser10 phosphorylation. Together, these studies reveal how one histone modification can modulate another to affect distinct transcriptional signals.

Crystal structure of the retinoblastoma tumor suppressor protein bound to E2F and the molecular basis of its regulation

The retinoblastoma tumor suppressor protein (pRb) regulates the cell cycle, facilitates differentiation, and restrains apoptosis. Furthermore, dysfunctional pRb is thought to be involved in the development of most human malignancies. Many of the functions of pRb are mediated by its regulation of the E2F transcription factors. To understand the structural basis for this regulation, we have determined the crystal structure of a fragment of E2F in complex with the pocket domain of the tumor suppressor protein. The pRb pocket, comprising the A and B cyclin-like domains, is the major focus of tumourigenic mutations in the protein. The fragment of E2F used in our structural studies, residues 409-426 of E2F-1, represents the core of the pRb-binding region of the transcription factor. The structure shows that E2F binds at the interface of the A and B domains of the pocket making extensive interactions with conserved residues from both. We show by solution studies that a second site, probably contained within the "marked box" region of E2F, is responsible for additional interactions with the pRb pocket but is insufficient for complex formation on its own. In addition, we show that the interaction of the core binding fragment of E2F with pRb is inhibited by phosphorylation of the tumor suppressor protein by CDK2cyclin DE. Finally, our data reveal that the tight binding of the human papillomavirus E7 oncoprotein to pRb prevents subsequent interactions with the marked box region of E2F but not with its core binding region.