Immunoproximity biotinylation reveals the axon initial segment proteome

The axon initial segment (AIS) is a specialized neuronal compartment required for action potential generation and neuronal polarity. However, understanding the mechanisms regulating AIS structure and function has been hindered by an incomplete knowledge of its molecular composition. Here, using immuno-proximity biotinylation we further define the AIS proteome and its dynamic changes during neuronal maturation. Among the many AIS proteins identified, we show that SCRIB is highly enriched in the AIS both in vitro and in vivo, and exhibits a periodic architecture like the axonal spectrin-based cytoskeleton. We find that ankyrinG interacts with and recruits SCRIB to the AIS. However, loss of SCRIB has no effect on ankyrinG. This powerful and flexible approach further defines the AIS proteome and provides a rich resource to elucidate the mechanisms regulating AIS structure and function.

Investigation of the photoluminescent properties, scintillation behaviour and toxicological profile of various magnesium tungstate nanoscale motifs

We have synthesized several morphologies and crystal structures of MgWO₄ using a one-pot hydrothermal method, producing not only monoclinic stars and large nanoparticles but also triclinic wool balls and sub-10 nm nanoparticles. Herein we describe the importance of reaction parameters in demonstrating morphology control of as-prepared MgWO₄. Moreover, we correlate structure and composition with the resulting photoluminescence and radioluminescence properties. Specifically, triclinic-phase samples yielded a photoluminescence emission of 421 nm, whereas monoclinic-phase materials gave rise to an emission maximum of 515 nm. The corresponding radioluminescence data were characterized by a broad emission peak, located at 500 nm for all samples. Annealing the wool balls and sub-10 nm particles to transform the crystal structure from a triclinic to a monoclinic phase yielded a radioluminescence (RL) emission signal that was two orders of magnitude greater than that of their unannealed counterparts. Finally, to confirm the practical utility of these materials for biomedical applications, a series of sub-10 nm particles, including as-prepared and annealed samples, were functionalized with biocompatible PEG molecules, and subsequently were found to be readily taken up by various cell lines as well as primary cultured hippocampal neurons with low levels of toxicity, thereby highlighting for the first time the potential of this particular class of metal oxides as viable and readily generated platforms for a range of biomedical applications.

Disruptive e-prevention from 2019: dummy online drug selling sites to reach new consumers

Background

The last three decades have seen the development of chemsex, the diversification of substances through New Psychoactive Substances (NPS), and new technologies allowing people to buy online and find peers to consume on applications while remaining in private spheres (Trend, Cadet-Taillou, 2020). The latter has made it more difficult to reach users, so as to document their uses and the population, and to design public health schemes aimed at users, except through targeting metapopulations known to consume more than the general population (Léobon et al., 2018; Talley et al., 2011).

Methods

The PlaySafe association designed two dummy websites, one selling GBL, the other NPS. These websites use the same graphics and syntactic codes as the main websites of the field, except for: 1) a fake drug named “love machine”; 2) an automatic redirection to a health promotion page instead of payment finalization. The information collected is: delivery region, birth year, gender, perceived usefulness of the health promotion messages, whether people would recommend to friends, the contents and quantities of the shopping cart, the time spent on each page, and data gathered via Google Analytics.

Results

On both websites 21,459 order attempts have been placed. This pathfinder research project has allowed to reach 6,203 people on the GBL website in 30 months and 7,927 people in 12 months on the NPS website, with people spending on average 1 min 35 s on the first website's prevention page and 1 min 27 s on the second. Around 85% of people consider the content useful, among whom 75% would recommend the website to friends. This communication also aims to present the characteristics of the reached population.

Conclusions

This innovative approach has allowed to precisely target a population escaping public health research and prevention schemes. It appears interesting to explore online prevention, especially since most of the respondents consider the experience helpful and recommendable.

Key messages

Directed mechanisms for apical dendrite development during neuronal polarization

The development of the dendrite and the axon during neuronal polarization underlies the directed flow of information in the brain. Seminal studies on axon development have dominated the mechanistic analysis of neuronal polarization. These studies, many originating from examinations in cultured hippocampal and cortical neurons in vitro, have established a prevalent view that axon formation precedes and is necessary for neuronal polarization. There is also in vivo evidence supporting this view. Nevertheless, the establishment of bipolar polarity and the leading edge, and apical dendrite development in pyramidal neurons in vivo occur when axon formation is prevented. Furthermore, recent mounting evidence suggest that directed mechanisms might mediate bipolar polarity/leading process and subsequent apical dendrite development. In the presence of spatially directed extracellular cues in the developing brain, these events may operate independently of axon forming events. In this perspective we summarize evidence in support of these evolving views in neuronal polarization and highlight recent findings on dedicated mechanisms acting in apical dendrite development.

Semaphorin3A/PlexinA3 association with the Scribble scaffold for cGMP increase is required for apical dendrite development

The development of the apical dendrite from the leading process of the bipolar pyramidal neuron might be directed by spatially organized extrinsic cues acting on localized intrinsic determinants. The extracellular cues regulating apical dendrite polarization remain elusive. We show that leading process and apical dendrite development are directed by class III Semaphorins and mediated by a localized cGMP-synthesizing complex. The scaffolding protein Scribble that associates with the cGMP-synthesizing enzyme soluble guanylate cyclase (sGC) also associates with the Semaphorin3A (Sema3A) co-receptor PlexinA3. Deletion or knockdown of PlexinA3 and Sema3A or disruption of PlexinA3-Scribble association prevents Sema3A-mediated cGMP increase and causes defects in apical dendrite development. These manipulations also impair bipolar polarity and leading process establishment. Local cGMP elevation or sGC expression rescues the effects of PlexinA3 knockdown or PlexinA3-Scribble complex disruption. During neuronal polarization, leading process and apical dendrite development are directed by a scaffold that links Semaphorin cue to cGMP increase.

Szczurkowska et al. show that spatially directed Sema3A may promote development of the leading process and the apical dendrite via the co-receptor PlexinA3 by orchestrating localized cGMP increase on the scaffold protein, Scribble, at the leading edge of developing pyramidal neurons.

A Localized Scaffold for cGMP Increase Is Required for Apical Dendrite Development

Studies in cultured neurons have established that axon specification instructs neuronal polarization and is necessary for dendrite development. However, dendrite formation in vivo occurs when axon formation is prevented. The mechanisms promoting dendrite development remain elusive. We find that apical dendrite development is directed by a localized cyclic guanosine monophosphate (cGMP)-synthesizing complex. We show that the scaffolding protein Scribble associates with cGMP-synthesizing enzymes soluble-guanylate-cyclase (sGC) and neuronal nitric oxide synthase (nNOS). The Scribble scaffold is preferentially localized to and mediates cGMP increase in dendrites. These events are regulated by kinesin KifC2. Knockdown of Scribble, sGC-β1, or KifC2 or disrupting their associations prevents cGMP increase in dendrites and causes severe defects in apical dendrite development. Local cGMP elevation or sGC expression rescues the effects of Scribble knockdown on dendrite development, indicating that Scribble is an upstream regulator of cGMP. During neuronal polarization, dendrite development is directed by the Scribble scaffold that might link extracellular cues to localized cGMP increase.

P10: LYMPH NODE YIELD IS NOT A RELIABLE PROGNOSTIC MARKER IN ANTERIOR RESECTION AND ABDOMINOPERINEAL RESECTION FOLLOWING NEOADJUVANT THERAPY FOR RECTAL CANCER

Introduction

International guidelines recommend a minimum lymph node yield (LNY) of ≥12 for oncological resection in colorectal cancer (CRC). Neoadjuvant chemoradiotherapy (NACRT) decreases LNY, which questions its ability to provide accurate prognostic information. The consensus of this significance remains undetermined. This study aimed to investigate the significance of LNY on recurrence and survival following anterior resection and abdominoperineal resection with or without NACRT for rectal cancer.

Method

Prospectively collected data on patients diagnosed with rectal cancer in a tertiary referral centre was interrogated retrospectively. Patients were divided into primary surgery and NACRT groups. Univariable analysis was performed using Fisher's exact test, t-test, and x2 test, while multivariable analysis utilised a multiple regression model. Disease recurrence and survival was analysed with logrank test for Kaplan-Meier curves.

Result

148 patients were included [56.1% (n=83) receiving NACRT]. The median LNY of the primary surgery group was 14 [interquartile range (IQR) 11-19] and for the NACRT group was 12 (IQR 8-14) (p <0.001). Disease recurrence was similar in both primary surgery and NACRT groups. There was a significant decrease in overall mortality in NACRT patients (p = 0.03), but there was no significant difference observed in recurrence or mortality amongst LNYs of <8, 8-11, and ≥12.

Conclusion

LNY less than 12 was not a negative prognostic indicator following NACRT and surgery for rectal cancer.

Take-home message

A lymph node yield of less than 12 is not a negative prognostic indicator in rectal cancer patients who receive neoadjuvant chemotherapy.

Hospital STI prevention scheme adapted to target undiagnosed LGBT migrants in Paris area since 2018

Background

In Île-de-France region, 10 000 people do not know they are living with HIV (Supervie, 2016). 70% are men, including 40% men having sex with other men (MSM) and 40% sub-Saharan African migrants. From 35% to 49% of those sub-Saharan African migrants are infected in France. The main HIV prevention issues is to target populations that are unrepresented in screening test centers.

Methods

To achieve these aims, a sexual health promotion scheme has been designed by a public health association, a Sexual Transmitted Infections (STI) center and an association supporting people asking asylum because of their “sexual orientation or gender identity”. Outreach STI screening test actions are organized monthly in places crowded by asylum seekers and associative sexual health consultation including screening, results reporting, treatments, vaccinations and Pre-Exposition Prophylaxis (PrEP), devoted to asylum seekers are taking place weekly into the hospital. Pear community members have been trained to be referent in health matters and enhance the scheme effectiveness.

Results

549 people were screened for STI through 110 actions from March 2018 to December 2019, of which 25 were outreach and 85 inside the hospital. 74% were from sub-Saharan Africa and 86% were presumed MSM. 89% were under 40 years old. 20% of the screened people were diagnosed positive to at least one STI and 52 people have been engaged in PrEP treatment after a risky assessment. Pear referent involvement reduced the number of unreported results, 10% are still unreported. 21 people have stopped PrEP follow-up. Around 3/4 of those followed by the association on the period stand unreached.

Conclusions

The scheme allowed to targeted population according to epidemiology's indicators but we don't know if the most exposed part of the population is reached. Partnership between associations and hospital improved public health system as well as community involvement.

Key messages

Public health system needs adaptations to struggles epidemics. Community involvement must be a priority to increase prevention’s efficiency .

Hospital “Outside the walls” against HIV and other Sexually Transmitted Infections (STIs) in Russia

Background

Though sponsored by UNAIDS support program, Russia struggles to curb its soaring HIV epidemic. French authorities invited Russian leaders of the HIV strategy, medical institutions or civil society in December 2018, to discover the practices of their French peers. A bridging process designed by the Public Health association AREMEDIA and developed in partnership with Fernand-Widal Hospital’s testing center, to reach underserved populations, was shown. Merging associative and medical cultures, they created bonds with community associations to efficiently export free prevention, treatments and care for HIV and STIs, “outside the walls” of hospital facilities. In March 2019, they were mandated to detect dependable partners to transpose this method in the high-HIV burden Ural region.

Objectives

Selecting local political leaders, field associations and public health structures, jointly designing a project to adapt AREMEDIA’s model in Perm. Developing a training to implement locally outreach program in 2020.

Results

Contractual partnership with 4 entities in Perm and educational program. Presenting the interventional methodology at Perm University Conference on “World AIDS day”, 1st December 2019. Theoretical and field trainings of Russian stakeholders to outreach sexual health interventions towards key populations, by associative and medical staff from AREMEDIA and the testing center in Paris. Practical support to implement outreach actions in urban areas of Perm from March to December 2020. Valorization of scientific results in Saint Petersburg International Conference, July 2020.

Conclusions

Consensus found on a pilot training and research-action outreach program, approved by authorities. Advancing access to local key populations should foster switching the Russian strategy against HIV towards a comprehensive sexual health promotion paradigm, resulting among others in destigmatization.

Key messages

Support local stakeholders to promote equitable management of HIV and overall sexual health. Enhance socio-medical interface to reduce the hidden epidemic through reaching HIV key populations.

Combined sexual prevention targeted to LGBTI+ migrants: between ’outdoor’ and ’indoor’ hospial

Issue

It is estimated that there are about 10,000 HIV-positive and undiagnosed people in Île-de-France (French region). They are composed of 70% men, 40% of whom are MSM and 40% of sub-Saharan African migrants. A bridging process has been designed by the Public Health association AREMEDIA and developed in partnership with Fernand-Widal Hospital’s testing center, to reach underserved populations. From March 2018, a screening test session for sexually transmitted infections (STIs) is taking place weekly in the hospital walls. This action is dedicated to the population of ARDHIS association, which accompanies more than 1,000 people each year, seeking asylum because of their sexual orientation or gender identity.

Description of the problem

Despite the promotion of this ’indoor’ targeted consultation via ARDHIS volunteers and directly to asylum seekers during occasional community events, the consultation only allowed the screening of 23 people in 4 months. It has been decided to carry out screening ’outside the hospitals walls’, where the people are, in order to promote the return of results, treatment, access to PrEP, HBV vaccination at the weekly indoor hospital consultation. “Community health relays” training together with the development of phone contact procedures were developed to facilitate the access to the indoor consultation.

Results

The methodology made it possible to double the average number of consultations over the following 5 months from 5 to 10 consultations per 3-hour slot, not counting PrEP appointments and vaccines, which averaged 6 per session. By the end of 2018, 261 people were screened, 23 had a PrEP treatment and many were vaccinated. As the scheme continues to develop, the results from January to July 2019 will be reported.

Leçons

To reach the most at risk populations, specific public health approaches are needed, taking account the context and representations of the target populations. Community involvement has proven to be effective.

Key messages

To fight HIV, innovative devices are needed to reach targeted populations. This has allowed hundreds of LGBTI asylum seekers to be screened and a significant number to receive preventive treatment.

How to reach migrant transgender women in Paris? An example of collaborative sexual health action

Issue

In France, screening for HIV and sexually transmitted infections (STIs) is provided by free HIV and STIs screening centers called CeGIDD. Despite a complete combined prevention offer, the number of new HIV diagnosis has been stable for years. Transgender women have one of the highest HIV prevalence.

Description of the problem

Transgender women are a hard to reach population with multifactorial barriers in their access to healthcare including fear of stigma, leading to late HIV diagnosis and untreated STIs. The CeGIDD of a university hospital in Paris aimed to reach this public working with two associations, creating a free, complete sexual health action outside the hospital in a safe environment.

Results

The CeGIDD identified a Parisian association, PASTT, which accompanies transgender women, mainly migrants, in accessing healthcare and social rights. Its active file is around 1500 persons a year, mostly resorting to prostitution. Another association, AREMEDIA, pioneer in outreach interventions, was involved. The partnership allowed access to the public and to gather the funds for the intervention. It included counseling, screening, Pre Exposure Prophylaxis (PrEP), and took place once a week in PASTT facilities. Any participant could be referred to other physicians if they needed it, even if they lacked health insurance coverage. From September 2017 to November 2018, 212 persons attended the consultation and 26 received PrEP.

Lessons

Working together with several associative partners presents many challenges, from the definition of the objectives to operational coordination. Overcoming these difficulties lead us to reach a new public with a high risk for STIs and HIV.

Key messages

Community based sexual health actions dedicated to transgender women are a successful way to reach this public. The safe environment provided by the association is a great opportunity to familiarize them with the medical staff and to empower them regarding healthcare.

In light of recently published clinical trials and their implication for clinical practice, does a large catchment area acute hospital require 24 hour CT neck and head angiography and/or neuro-interventional services in the setting of acute ischaemic stroke?

BACKGROUND

Recently published clinical trials have resulted in a significant change in the guidelines used to manage patients suffering an acute ischaemic stroke. New neuro-interventional techniques have revolutionised stroke outcomes. Currently, such services are only available in two specialist centres.

AIMS

We attempted to evaluate the need for the provision of routine computed tomography (CT) angiography and neuro-interventional services at a university teaching hospital in Limerick.

METHODS

A retrospective study was performed based on data collated by the stroke service, University Hospital Limerick (UHL). All patients with a suspected acute ischaemic stroke of anterior circulation and known evolution were included. Baseline clinical and imaging characteristics, thrombolysis data, stroke unit admission rates and discharge destinations were recorded.

RESULTS

All 141 patients were suitable for CT angiography and should be performed in accordance with guidelines. Additionally, 165 patients excluded from the study due to an unknown stroke evolution timeframe may have benefitted. Non-contrast CT scan confirmed just 12 anterior circulation strokes. The need for neuro-interventional services proved more difficult to assess, primarily due to the lack of provision of routine CT angiography, employed to confirm anterior circulation occlusion. Secondary results showed a thrombolysis rate of 10.8% and confirmed that time efficiencies result in higher thrombolysis eligibility rates. Stroke unit admissions and discharge destinations were also recorded.

CONCLUSION

UHL should provide routine CT angiography to all patients presenting with acute ischaemic stroke in line with current guidelines. The need for provision of neuro-interventional services on-site proved more difficult to assess and requires further analysis.

Photolithography-Based Substrate Microfabrication for Patterning Semaphorin 3A to Study Neuronal Development

Protein micropatterning techniques, including microfluidic devices and protein micro-contact printing, enable the generation of highly controllable substrates for spatial manipulation of intracellular and extracellular signaling determinants to examine the development of cultured dissociated neurons in vitro. In particular, culture substrates coated with proteins of interest in defined stripes, including cell adhesion molecules and secreted proteins, have been successfully used to study neuronal polarization, a process in which the neuron establishes axon and dendrite identities, a critical architecture for the input/output functions of the neuron. We have recently used this methodology to pattern the extracellular protein Semaphorin 3A (Sema3A), a secreted factor known to control neuronal development in the mammalian embryonic cortex. We showed that stripe-patterned Sema3A regulates axon and dendrite formation during the early phase of neuronal polarization in cultured rat hippocampal neurons. Here, we describe microfabrication and substrate stripe micropatterning of Sema3A. We note that same methodologies can be applied to pattern other extracellular proteins that regulate neuronal development in the embryonic brain, as nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and Netrin-1. We describe modifications of these methodologies for stripe micropatterning of membrane-permeable analog of the second messengers cyclic AMP (cAMP) and cyclic GMP (cGMP), intracellular regulators of neuronal polarization that might act downstream of Sema3A.

Micellar nanocomplexes for biomagnetic delivery of intracellular proteins to dictate axon formation during neuronal development

During mammalian embryonic development, neurons polarize to create distinct cellular compartments of axon and dendrite that inherently differ in form and function, providing the foundation for directional signaling in the nervous system. Polarization results from spatio-temporal segregation of specific proteins' activities to discrete regions of the neuron to dictate axonal vs. dendritic fate. We aim to manipulate axon formation by directed subcellular localization of crucial intracellular protein function. Here we report critical steps toward the development of a nanotechnology for localized subcellular introduction and retention of an intracellular kinase, LKB1, crucial regulator of axon formation. This nanotechnology will spatially manipulate LKB1-linked biomagnetic nanocomplexes (LKB1-NCs) in developing rodent neurons in culture and in vivo. We created a supramolecular assembly for LKB1 rapid neuronal uptake and prolonged cytoplasmic stability. LKB1-NCs retained kinase activity and phosphorylated downstream targets. NCs were successfully delivered to cultured embryonic hippocampal neurons, and were stable in the cytoplasm for 2 days, sufficient time for axon formation. Importantly, LKB1-NCs promoted axon formation in these neurons, representing unique proof of concept for the sufficiency of intracellular protein function in dictating a central developmental event. Lastly, we established NC delivery into cortical progenitors in live rat embryonic brain in utero. Our nanotechnology provides a viable platform for spatial manipulation of intracellular protein-activity, to dictate central events during neuronal development.

Out-of-Hospital screening for HIV, HBV, HCV and Syphilis in a vulnerable population, a public health challenge

We explored rates of Hepatitis B virus (HBV), Human Immunodeficiency Virus, Hepatitis C virus and Syphilis in a vulnerable population (mostly intravenous drug users, sex workers and homeless people) and focused on factors associated with failure to return for results (FTR) and with having a false perception (FP) of Immunization against HBV. We performed a prospective multicenter observational study in nine mobile (Out-of-Hospital) areas of screening located in Paris from 1 January 2014 through 31 December 2014. A total of 341 patients were recruited. The proportion of FTR for results was 38.75%. In multivariate analysis, unemployment was significantly associated with FTR (OR = 4.29; IC = [1.12; 16.39]), as well as having been screened in the past (OR = 4.32, IC = [1.70; 10.97]); 18.03% of patients had a FP of an Immunization against HBV. In multivariate analysis, having one's own place of residence protected against FP (OR = 0.33, [0.12; 0.95]), while being screened in the past enhanced the risk of FP (OR = 3.28, IC = [1.06; 10.11]). The rate of FTR is a problem and use of currently available technologies, such as phone texting, might be a partial solution in conjunction with rapid tests for diagnosis. In addition, more information and comprehension of the results should be provided together with specific anti-HBV vaccination campaigns targeting these specific populations.

Non-hyperpolarizing GABAB receptor activation regulates neuronal migration and neurite growth and specification by cAMP/LKB1

γ-Aminobutyric acid is the principal inhibitory neurotransmitter in adults, acting through ionotropic chloride-permeable GABAA receptors (GABAARs), and metabotropic GABABRs coupled to calcium or potassium channels, and cyclic AMP signalling. During early development, γ-aminobutyric acid is the main neurotransmitter and is not hyperpolarizing, as GABAAR activation is depolarizing while GABABRs lack coupling to potassium channels. Despite extensive knowledge on GABAARs as key factors in neuronal development, the role of GABABRs remains unclear. Here we address GABABR function during rat cortical development by in utero knockdown (short interfering RNA) of GABABR in pyramidal-neuron progenitors. GABABR short interfering RNA impairs neuronal migration and axon/dendrite morphological maturation by disrupting cyclic AMP signalling. Furthermore, GABABR activation reduces cyclic AMP-dependent phosphorylation of LKB1, a kinase involved in neuronal polarization, and rescues LKB1 overexpression-induced defects in cortical development. Thus, non-hyperpolarizing activation of GABABRs during development promotes neuronal migration and morphological maturation by cyclic AMP/LKB1 signalling.

Semaphorin3A regulates neuronal polarization by suppressing axon formation and promoting dendrite growth

Semaphorin 3A (Sema3A) is a secreted factor known to guide axon/dendrite growth and neuronal migration. We found that it also acts as a polarizing factor for axon/dendrite development in cultured hippocampal neurons. Exposure of the undifferentiated neurite to localized Sema3A suppressed its differentiation into axon and promoted dendrite formation, resulting in axon formation away from the Sema3A source, and bath application of Sema3A to polarized neurons promoted dendrite growth but suppressed axon growth. Fluorescence resonance energy transfer (FRET) imaging showed that Sema3A elevated the cGMP but reduced cAMP and protein kinase A (PKA) activity, and its axon suppression is attributed to the downregulation of PKA-dependent phosphorylation of axon determinants LKB1 and GSK-3β. Downregulating Sema3A signaling in rat embryonic cortical progenitors via in utero electroporation of siRNAs against the Sema3A receptor neuropilin-1 also resulted in polarization defects in vivo. Thus, Sema3A regulates the earliest step of neuronal morphogenesis by polarizing axon/dendrite formation.

Role of LKB1-SAD/MARK pathway in neuronal polarization

The formation of axon/dendrite polarity is critical for the neuron to perform its signaling function in the brain. Recent advance in our understanding of cellular and molecular mechanisms underlying the development and maintenance of neuronal polarity has been greatly facilitated by the use of the culture system of dissociated hippocampal neurons. Among many polarization-related proteins, we here focus on the mammalian LKB1, the counterpart of the C. elegans Par-4, which is an upstream regulator among six Par (partitioning-defective) genes that act as master regulators of cell polarity in different cell types across evolutionary distant species. Recent studies have identified LKB1 and its downstream targets SAD/MARK kinases (mammalian homologs of Par-1) as key regulators of neuronal polarization and axon development in cultured neurons and in developing cortical neurons in vivo. We will review the properties of and interactions among proteins in this LKB1-SAD/MARK pathway, drawing upon information obtained from both neuronal and non-neuronal systems. Due to central role of the protein kinase A-dependent phosphorylation of LKB1 in the activation of this pathway, we will review recent findings on how cAMP and cGMP signaling may serve as antagonistic second messengers for axon/dendrite development, and how these cyclic nucleotides may mediate the action of extracellular polarizing factors by modulating the activity of the LKB1-SAD/MARK pathway.

Phosphorylation of E3 ligase Smurf1 switches its substrate preference in support of axon development

Ubiquitin E3 ligases serve for ubiquitination of specific substrates, and its ligase efficacy is regulated by interacting proteins or substrate modifications. Whether and how the ligases themselves are modified by cellular signaling is unclear. Here we report that protein kinase A (PKA)-dependent phosphorylation of Smad Ubiquitin Regulatory Factor 1 (Smurf1) can switch its substrate preference between two proteins of opposing actions on axon development. Extracellular factors that promote axon formation elevated Smurf1 phosphorylation at a PKA site Thr³⁰⁶, and preventing this phosphorylation reduced axon formation in cultured hippocampal neurons and impaired polarization of cortical neurons in vivo. Thr³⁰⁶-phosphorylation changed the relative affinities of Smurf1 for its substrates, leading to reduced degradation of polarity protein Par6 and increased degradation of growth-inhibiting RhoA. Thus, PKA-dependent phosphorylation of the E3 ligase could switch its substrate preference, contributing to selective protein degradation required for localized cellular function.

Local and long-range reciprocal regulation of cAMP and cGMP in axon/dendrite formation

Cytosolic cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) often mediate antagonistic cellular actions of extracellular factors, from the regulation of ion channels to cell volume control and axon guidance. We found that localized cAMP and cGMP activities in undifferentiated neurites of cultured hippocampal neurons promote and suppress axon formation, respectively, and exert opposite effects on dendrite formation. Fluorescence resonance energy transfer imaging showed that alterations of the amount of cAMP resulted in opposite changes in the amount of cGMP, and vice versa, through the activation of specific phosphodiesterases and protein kinases. Local elevation of cAMP in one neurite resulted in cAMP reduction in all other neurites of the same neuron. Thus, local and long-range reciprocal regulation of cAMP and cGMP together ensures coordinated development of one axon and multiple dendrites.

LKB1/STRAD promotes axon initiation during neuronal polarization

Axon/dendrite differentiation is a critical step in neuronal development. In cultured hippocampal neurons, the accumulation of LKB1 and STRAD, two interacting proteins critical for establishing epithelial polarity, in an undifferentiated neurite correlates with its subsequent axon differentiation. Downregulation of either LKB1 or STRAD by siRNAs prevented axon differentiation, and overexpression of these proteins led to multiple axon formation. Furthermore, interaction of STRAD with LKB1 promoted LKB1 phosphorylation at a PKA site S431 and elevated the LKB1 level, and overexpressing LKB1 with a serine-to-alanine mutation at S431 (LKB1(S431A)) prevented axon differentiation. In developing cortical neurons in vivo, downregulation of LKB1 or overexpression of LKB1(S431A) also abolished axon formation. Finally, local exposure of the undifferentiated neurite to brain-derived neurotrophic factor or dibutyryl-cAMP promoted axon differentiation in a manner that depended on PKA-dependent LKB1 phosphorylation. Thus local LKB1/STRAD accumulation and PKA-dependent LKB1 phosphorylation represents an early signal for axon initiation.

Polar expression of ErbB-2/HER2 in epithelia. Bimodal regulation by Lin-7

ErbB-2/HER2 drives epithelial malignancies by forming heterodimers with growth factor receptors. The primordial invertebrate receptor is sorted to the basolateral epithelial surface by binding of the PDZ domain of Lin-7 to the receptor's tail. We show that all four human ErbBs are basolaterally expressed, even when the tail motif is absent. Mutagenesis of hLin-7 unveiled a second domain, KID, that binds to the kinase region of ErbBs. The PDZ interaction mediates stabilization of ErbB-2 at the basolateral surface. On the other hand, binding of KID is involved in initial delivery to the basolateral surface, and in its absence, unprocessed ErbB-2 molecules are diverted to the apical surface. Hence, distinct domains of Lin-7 regulate receptor delivery to and maintenance at the basolateral surface of epithelia.

The effect of chronic feeding of diacetoxyscirpenol and T-2 toxin on performance, health, small intestinal physiology and antibody production in turkey poults

1. The effects of feeding T-2 toxin or diacetoxyscirpenol (DAS) at levels up to 1 ppm for 32 d on performance, health, small intestinal physiology and immune response to enteral and parenteral immunisation were examined in young poults. 2. Slight improvement in growth was observed in some groups of poults fed T-2 or DAS mycotoxins for 32 d, with no change in feed efficiency. Feeding both T-2 and DAS resulted in oral lesions which had maximal severity after 7-15 d. 3. Mild intestinal changes were observed at 32 d but no pathological or histopathological lesions were found. Both mycotoxins altered small intestinal morphology, especially in the jejunum where villi were shorter and thinner. In addition, both DAS and T-2 mycotoxins enhanced the proportion of proliferating cells both in the crypts and along the villi. Migration rates were reduced in the jejunum of poults fed T-2 toxin but did not change in the duodenum or in poults fed DAS. 4. No significant effects of T-2 or DAS were observed on antibody production to antigens administered by enteral or parenteral routes. 5. This study indicates that tricothecene toxins at concentrations of up to 1 ppm for more than 30 d influenced small intestinal morphology but did not affect growth or antibody production.

IL-1ra administration does not improve cardiac function in patients with severe sepsis

PURPOSE

The purpose of this study was to investigate the effects of interleukin-1 receptor antagonist (IL-1ra) on myocardial function in septic patients.

MATERIALS AND METHODS

A subgroup of patients from a prospective, randomized, double-blind, placebo-controlled, multicenter trial was studied from 63 academic medical centers in the United States, Canada, and Europe. A subgroup of 71 patients with severe sepsis in whom vasoactive support was little altered during the study was included. The patients were randomized to receive either placebo (n = 29) or IL-1ra at a dose of 1 mg/kg/h (n = 20) or 2 mg/kg/h (n = 22).

RESULTS

Hemodynamic measurements were taken at baseline, and 1, 2, 3, 4, 8, and 12 hours after placebo or IL-1ra administration. No significant differences in hemodynamic parameters were observed between the groups or over time during the study period.

CONCLUSIONS

IL-1ra administration has no effect on cardiac function in septic patients.

Neuregulin-4: a novel growth factor that acts through the ErbB-4 receptor tyrosine kinase

The ErbB/HER family of receptor tyrosine kinases consists of four receptors that bind a large number of growth factor ligands sharing an epidermal growth factor- (EGF)-like motif. Whereas ErbB-1 binds seven different ligands whose prototype is EGF, the three families of neuregulins (NRGs) activate ErbB-3 and/or ErbB-4. Here we characterize a fourth neuregulin, NRG-4, that acts through ErbB-4. The predicted pro-NRG-4 is a transmembrane protein carrying a unique EGF-like motif and a short cytoplasmic domain. A synthetic peptide encompassing the full-length EGF-like domain can induce growth of interleukin-dependent cells ectopically expressing ErbB-4, but not cells expressing the other three ErbB proteins or their combinations. Consistent with specificity to ErbB-4, NRG-4 can displace an ErbB-4-bound NRG-1 and can activate signaling downstream of this receptor. Expression of NRG-4 mRNA was detected in the adult pancreas and weakly in muscle; other tissues displayed no detectable NRG-4 mRNA. The primary structure and the pattern of expression of NRG-4, together with the strict specificity of this growth factor to ErbB-4, suggest a physiological role distinct from that of the known ErbB ligands.

Pathogenic poxviruses reveal viral strategies to exploit the ErbB signaling network

Virulence of poxviruses, the causative agents of smallpox, depends on virus-encoded growth factors related to the mammalian epidermal growth factor (EGF). Here we report that the growth factors of Shope fibroma virus, Myxoma virus and vaccinia virus (SFGF, MGF and VGF) display unique patterns of specificity to ErbB receptor tyrosine kinases; whereas SFGF is a broad-specificity ligand, VGF binds primarily to ErbB-1 homodimers, and the exclusive receptor for MGF is a heterodimer comprised of ErbB-2 and ErbB-3. In spite of 10- to 1000-fold lower binding affinity to their respective receptors, the viral ligands are mitogenically equivalent or even more potent than their mammalian counterparts. This remarkable enhancement of cell growth is due to attenuation of receptor degradation and ubiquitination, which leads to sustained signal transduction. Our results imply that signal potentiation and precise targeting to specific receptor combinations contribute to cell transformation at sites of poxvirus infection, and they underscore the importance of the often ignored low-affinity ligand-receptor interactions.

ErbB tyrosine kinases and the two neuregulin families constitute a ligand-receptor network

The recently isolated second family of neuregulins, NRG2, shares its primary receptors, ErbB-3 and ErbB-4, and induction of mammary cell differentiation with NRG1 isoforms, suggesting functional redundancy of the two growth factor families. To address this possibility, we analyzed receptor specificity of NRGs by using an engineered cellular system. The activity of isoform-specific but partly overlapping patterns of specificities that collectively activate all eight ligand-stimulatable ErbB dimers was revealed. Specifically, NRG2-alpha [corrected], like NRG1-beta [corrected], emerges as a narrow-specificity ligand, whereas NRG2-beta [corrected] is a pan-ErbB ligand that binds with different affinities to all receptor combinations, including those containing ErbB-1, but excluding homodimers of ErbB-2. The latter protein, however, displayed cooperativity with the direct NRG receptors. Apparently, signaling by all NRGs is funneled through the mitogen-activated protein kinase (MAPK). However, the duration and potency of MAPK activation depend on the identity of the stimulatory ligand-receptor ternary complex. We conclude that the NRG-ErbB network represents a complex and nonredundant machinery developed for fine-tuning of signal transduction.

Epiregulin is a potent pan-ErbB ligand that preferentially activates heterodimeric receptor complexes

The ErbB signaling network consists of four transmembrane receptor tyrosine kinases and more than a dozen ligands sharing an epidermal growth factor (EGF) motif. The multiplicity of ErbB-specific ligands is incompletely understood in terms of signal specificity because all ErbB molecules signal through partially overlapping pathways. Here we addressed the action of epiregulin, a recently isolated ligand of ErbB-1. By employing a set of factor-dependent cell lines engineered to express individual ErbBs or their combinations, we found that epiregulin is the broadest specificity EGF-like ligand so far characterized: not only does it stimulate homodimers of both ErbB-1 and ErbB-4, it also activates all possible heterodimeric ErbB complexes. Consistent with its relaxed selectivity, epiregulin binds the various receptor combinations with an affinity that is approximately 100-fold lower than the affinity of ligands with more stringent selectivity, including EGF. Nevertheless, epiregulin's action upon most receptor combinations transmits a more potent mitogenic signal than does EGF. This remarkable discrepancy between binding affinity and bioactivity is permitted by a mechanism that prevents receptor down-regulation, and results in a weak, but prolonged, state of receptor activation.

Bivalence of EGF-like ligands drives the ErbB signaling network

Signaling by epidermal growth factor (EGF)-like ligands is mediated by an interactive network of four ErbB receptor tyrosine kinases, whose mechanism of ligand-induced dimerization is unknown. We contrasted two existing models: a conformation-driven activation of a receptor-intrinsic dimerization site and a ligand bivalence model. Analysis of a Neu differentiation factor (NDF)-induced heterodimer between ErbB-3 and ErbB-2 favors a bivalence model; the ligand simultaneously binds both ErbB-3 and ErbB-2, but, due to low-affinity of the second binding event, ligand bivalence drives dimerization only when the receptors are membrane anchored. Results obtained with a chimera and isoforms of NDF/neuregulin predict that each terminus of the ligand molecule contains a distinct binding site. The C-terminal low-affinity site has broad specificity, but it prefers interaction with ErbB-2, an oncogenic protein acting as a promiscuous low-affinity subunit of the three primary receptors. Thus, ligand bivalence enables signal diversification through selective recruitment of homo- and heterodimers of ErbB receptors, and it may explain oncogenicity of erbB-2/HER2.

Neu differentiation factor/neuregulin isoforms activate distinct receptor combinations

The multiple isoforms of Neu differentiation factor (NDF/neuregulin) induce a pleiotropic cellular response that is isoform-specific and cell type-dependent. The molecular basis of this heterogeneity was addressed by comparing the two major groups of isoforms, alpha and beta. Both groups bind to the catalytically impaired receptor tyrosine kinase ErbB-3, whose mitogenic stimulation by NDF requires transactivation by other ErbB proteins, either ErbB-1 or ErbB-2. By expressing each pair of receptors in interleukin 3-dependent myeloid cells, we found that both isoforms induced mitogenic signals in cells co-expressing the combination of ErbB-3 with ErbB-2. However, only the beta isoform stimulated cells that expressed both ErbB-3 and ErbB-1, and neither isoform was active on cells expressing ErbB-3 alone. Both isoforms bind to all ErbB-3-expressing cells, albeit with different affinities, but the co-stimulatory mitogenic effect is correlated with the ability of each auxiliary receptor to transphosphorylate ErbB-3. These results imply that NDF isoforms differ in their ability to induce receptor heterodimers; whereas both types of isoforms signal through ErbB-3/ErbB-2 heterodimers, only beta isoforms are able to stabilize ErbB-3/ErbB-1 heterodimers.

Immunization of monkeys with baculovirus-dengue type-4 recombinants containing envelope and nonstructural proteins: evidence of priming and partial protection

Groups of rhesus monkeys were immunized with baculovirus-dengue type-4 (DEN-4) recombinant-infected cell extracts. One recombinant contained all of the DEN-4 structural proteins and two nonstructural (NS) proteins (C-M-E-NS1-NS2a), while the other was a fusion protein containing a portion of the respiratory syncytial virus G glycoprotein and DEN-4 envelope glycoprotein (RSVG-E). Both preparations were immunogenic; all monkeys receiving either immunogen responded with the production of antivirion antibodies in enzyme immunoassays. All except one monkey receiving the recombinant b(C-M-E-NS1-NS2a) made antibodies to NS1. One monkey that received b(RSVG-E) showed the production of low levels of neutralizing antibodies. Following challenge with unmodified DEN-4 virus, seven of nine monkeys in the immunized group became infected and were viremic for a mean of 4.1 days. The control, sham-inoculated monkeys were also viremic; the mean number of days of viremia in this group was 4.7 days. The remaining monkeys in the immunized group (n = 7), although not protected, had evidence of priming. Hemagglutination inhibition antibody responses following challenge indicated an anamnestic response in this group of animals. Based on these results, it was concluded that future immunization schedules should be altered to optimize immune responses and that immunization with more potent and purified immunogens would probably result in higher seroconversion rates and antibody levels in monkeys.

A comparison of five heat and moisture exchangers

Five heat and moisture exchangers were investigated to compare their efficiency of humidification, their ability to filter bacterial spores and their various physical properties. The results are presented and the various mechanisms of heat and moisture exchange are reviewed. The Pall Ultipor BB50, because of its hydrophobic properties, has a slightly different action from heat and moisture exchangers already in use, The place of the Pall Ultipor BB50 in clinical practice is discussed.