Direct evidence of lipid transport by the Drs2-Cdc50 flippase upon truncation of its terminal regions

P4-ATPases in complex with Cdc50 subunits are lipid flippases that couple ATP hydrolysis with lipid transport to the cytoplasmic leaflet of membranes to create lipid asymmetry. Such vectorial transport has been shown to contribute to vesicle formation in the late secretory pathway. Some flippases are regulated by autoinhibitory regions that can be destabilized by protein kinase-mediated phosphorylation and possibly by binding of cytosolic proteins. In addition, the binding of lipids to flippases may also induce conformational changes required for the activity of these transporters. Here, we address the role of phosphatidylinositol-4-phosphate (PI4P) and the terminal autoinhibitory tails on the lipid flipping activity of the yeast lipid flippase Drs2-Cdc50. By functionally reconstituting the full-length and truncated forms of Drs2 in a 1:1 complex with the Cdc50 subunit, we provide compelling evidence that lipid flippase activity is exclusively detected for the truncated Drs2 variant and is dependent on the presence of the phosphoinositide PI4P. These findings highlight the critical role of phosphoinositides as lipid co-factors in the regulation of lipid transport by the Drs2-Cdc50 flippase.

Activation and substrate specificity of the human P4-ATPase ATP8B1

Asymmetric distribution of phospholipids in eukaryotic membranes is essential for cell integrity, signaling pathways, and vesicular trafficking. P4-ATPases, also known as flippases, participate in creating and maintaining this asymmetry through active transport of phospholipids from the exoplasmic to the cytosolic leaflet. Here, we present a total of nine cryo-electron microscopy structures of the human flippase ATP8B1-CDC50A complex at 2.4 to 3.1 Å overall resolution, along with functional and computational studies, addressing the autophosphorylation steps from ATP, substrate recognition and occlusion, as well as a phosphoinositide binding site. We find that the P4-ATPase transport site is occupied by water upon phosphorylation from ATP. Additionally, we identify two different autoinhibited states, a closed and an outward-open conformation. Furthermore, we identify and characterize the PI(3,4,5)P3 binding site of ATP8B1 in an electropositive pocket between transmembrane segments 5, 7, 8, and 10. Our study also highlights the structural basis of a broad lipid specificity of ATP8B1 and adds phosphatidylinositol as a transport substrate for ATP8B1. We report a critical role of the sn-2 ester bond of glycerophospholipids in substrate recognition by ATP8B1 through conserved S403. These findings provide fundamental insights into ATP8B1 catalytic cycle and regulation, and substrate recognition in P4-ATPases.

Disentangling the dynamics of energy allocation to develop a proxy for robustness of fattening pigs

BACKGROUND

There is a growing need to improve robustness of fattening pigs, but this trait is difficult to phenotype. Our first objective was to develop a proxy for robustness of fattening pigs by modelling the longitudinal energy allocation coefficient to growth, with the resulting environmental variance of this allocation coefficient considered as a proxy for robustness. The second objective was to estimate its genetic parameters and correlations with traits under selection and with phenotypes that are routinely collected. In total, 5848 pigs from a Pietrain NN paternal line were tested at the AXIOM boar testing station (Azay-sur-Indre, France) from 2015 to 2022. This farm is equipped with an automatic feeding system that records individual weight and feed intake at each visit. We used a dynamic linear regression model to characterize the evolution of the allocation coefficient between the available cumulative net energy, which was estimated from feed intake, and cumulative weight gain during the fattening period. Longitudinal energy allocation coefficients were analysed using a two-step approach to estimate both the genetic variance of the coefficients and the genetic variance in their residual variance, which will be referred to as the log-transformed squared residual (LSR).

RESULTS

The LSR trait, which could be interpreted as an indicator of the response of the animal to perturbations/stress, showed a low heritability (0.05 ± 0.01), a high favourable genetic correlation with average daily growth (- 0.71 ± 0.06), and unfavourable genetic correlations with feed conversion ratio (- 0.76 ± 0.06) and residual feed intake (- 0.83 ± 0.06). Segmentation of the population in four classes using estimated breeding values for LSR showed that animals with the lowest estimated breeding values were those with the worst values for phenotypic proxies of robustness, which were assessed using records routinely collected on farm.

CONCLUSIONS

Results of this study show that selection for robustness, based on estimated breeding values for environmental variance of the allocation coefficients to growth, can be considered in breeding programs for fattening pigs.

Phosphatidylserine transport in cell life and death

Phosphatidylserine (PS) is a negatively charged glycerophospholipid found mainly in the plasma membrane (PM) and in the late secretory/endocytic compartments, where it regulates cellular activity and can mediate apoptosis. Export of PS from the endoplasmic reticulum, its site of synthesis, to other compartments, and its transbilayer asymmetry must therefore be precisely regulated. We review recent findings on nonvesicular transport of PS by lipid transfer proteins (LTPs) at membrane contact sites, on PS flip-flop between membrane leaflets by flippases and scramblases, and on PS nanoclustering at the PM. We also discuss emerging data on cooperation between scramblases and LTPs, how perturbation of PS distribution can lead to disease, and the specific role of PS in viral infection.

Expression in Saccharomyces cerevisiae and Purification of a Human Phospholipid Flippase

Membrane proteins (MPs) are challenging to study from a biochemical standpoint owing to the difficulties associated with the isolation of these proteins from the membranes they are embedded in. Even for the expression of closely-related homologues, protocols often require to be adjusted. Prominently, the solubilization step and the stabilization of recombinant proteins during the purification process are key issues, and remain a serious bottleneck. Here, we present a method for the expression and the purification of the human ATP8B1/CDC50A lipid flippase complex. Selection of the right Saccharomyces cerevisiae strain proved to be a critical step for the successful purification of this complex. Likewise, the use of cholesteryl hemisuccinate, a cholesterol analogue, contributed to significantly increase the yield of purification. We hope that the simple method described here can help researchers to succeed in the expression of other mammalian difficult-to-express lipid flippases and, by extension, help in the production of other membrane proteins whose isolation has so far proven difficult.

Robustness scores in fattening pigs based on routinely collected phenotypes: determination and genetic parameters

The objective was to determine operational proxies for robustness based on data collected routinely on farm that allow phenotyping of these traits in fattening pigs, and to estimate their genetic parameters. A total of 7,256 pigs, from two Piétrain paternal lines (Pie and Pie NN), were tested at the AXIOM boar testing station (Azay-sur-Indre, France) from 2019 to 2021. During the fattening period (from 75 to 150 d of age), individual performance indicators were recorded (growth, backfat, loin depth, feed intake, and feed conversion ratio [FCR]) together with indicators such as insufficient growth, observable defect, symptoms of diseases, and antibiotic and anti-inflammatory injections. These indicators were combined into three categorical robustness scores: R1, R2, and R3. Genetic parameters were estimated using an animal linear model. The robustness score R2 (selectable or not selectable animal) that combined information from status at testing and mortality had the highest heritability estimates of 0.08 ± 0.03 for Pie NN line and a value of 0.09 ± 0.02 for Pie line, compared with traits R1 and R3. The score R3 that combines information from the score R2 with antibiotic and anti-inflammatory injections presented slightly lower heritability estimates (0.05 ± 0.02 to 0.07 ± 0.03). Genetic correlations between R2 and R3 were high and favorable (0.93 ± 0.04 to 0.95 ± 0.03) and R2 and R3 can be considered identical with regard to the confidence interval. These two robustness scores were also highly and favorably genetically correlated with initial body weight and average daily gain, and unfavorably correlated with daily feed intake (ranging from 0.73 ± 0.06 to 0.90 ± 0.08). Estimates of genetic correlations of R2 and R3 with backfat depth and raw FCR (not standardized between starting and finishing weights) were moderate and unfavorable (0.20 ± 0.13 to 0.46 ± 0.20). A part of these genetic correlations, that are of low precision due to the number of data available, have to be confirmed on larger datasets. The results showed the interest of using routine phenotypes collected on farm to build simple robustness indicators that can be applied in breeding.

Autoinhibition and regulation by phosphoinositides of ATP8B1, a human lipid flippase associated with intrahepatic cholestatic disorders

P4-ATPases flip lipids from the exoplasmic to the cytosolic leaflet, thus maintaining lipid asymmetry in eukaryotic cell membranes. Mutations in several human P4-ATPase genes are associated with severe diseases, for example in ATP8B1 causing progressive familial intrahepatic cholestasis, a rare inherited disorder progressing toward liver failure. ATP8B1 forms a binary complex with CDC50A and displays a broad specificity to glycerophospholipids, but regulatory mechanisms are unknown. Here, we report functional studies and the cryo-EM structure of the human lipid flippase ATP8B1-CDC50A at 3.1 Å resolution. We find that ATP8B1 is autoinhibited by its N- and C-terminal tails, which form extensive interactions with the catalytic sites and flexible domain interfaces. Consistently, ATP hydrolysis is unleashed by truncation of the C-terminus, but also requires phosphoinositides, most markedly phosphatidylinositol-3,4,5-phosphate (PI(3,4,5)P₃), and removal of both N- and C-termini results in full activation. Restored inhibition of ATP8B1 truncation constructs with a synthetic peptide mimicking the C-terminal segment further suggests molecular communication between N- and C-termini in the autoinhibition and demonstrates that the regulatory mechanism can be interfered with by exogenous compounds. A recurring (G/A)(Y/F)AFS motif of the C-terminal segment suggests that this mechanism is employed widely across P4-ATPase lipid flippases in plasma membrane and endomembranes.

Transport Pathways That Contribute to the Cellular Distribution of Phosphatidylserine

Phosphatidylserine (PS) is a negatively charged phospholipid that displays a highly uneven distribution within cellular membranes, essential for establishment of cell polarity and other processes. In this review, we discuss how combined action of PS biosynthesis enzymes in the endoplasmic reticulum (ER), lipid transfer proteins (LTPs) acting within membrane contact sites (MCS) between the ER and other compartments, and lipid flippases and scramblases that mediate PS flip-flop between membrane leaflets controls the cellular distribution of PS. Enrichment of PS in specific compartments, in particular in the cytosolic leaflet of the plasma membrane (PM), requires input of energy, which can be supplied in the form of ATP or by phosphoinositides. Conversely, coupling between PS synthesis or degradation, PS flip-flop and PS transfer may enable PS transfer by passive flow. Such scenario is best documented by recent work on the formation of autophagosomes. The existence of lateral PS nanodomains, which is well-documented in the case of the PM and postulated for other compartments, can change the steepness or direction of PS gradients between compartments. Improvements in cellular imaging of lipids and membranes, lipidomic analysis of complex cellular samples, reconstitution of cellular lipid transport reactions and high-resolution structural data have greatly increased our understanding of cellular PS homeostasis. Our review also highlights how budding yeast has been instrumental for our understanding of the organization and transport of PS in cells.

ATP2, The essential P4-ATPase of malaria parasites, catalyzes lipid-stimulated ATP hydrolysis in complex with a Cdc50 β-subunit

Gene targeting approaches have demonstrated the essential role for the malaria parasite of membrane transport proteins involved in lipid transport and in the maintenance of membrane lipid asymmetry, representing emerging oportunites for therapeutical intervention. This is the case of ATP2, a Plasmodium-encoded 4 P-type ATPase (P4-ATPase or lipid flippase), whose activity is completely irreplaceable during the asexual stages of the parasite. Moreover, a recent chemogenomic study has situated ATP2 as the possible target of two antimalarial drug candidates. In eukaryotes, P4-ATPases assure the asymmetric phospholipid distribution in membranes by translocating phospholipids from the outer to the inner leaflet. In this work, we have used a recombinantly-produced P. chabaudi ATP2 (PcATP2), to gain insights into the function and structural organization of this essential transporter. Our work demonstrates that PcATP2 associates with two of the three Plasmodium-encoded Cdc50 proteins: PcCdc50B and PcCdc50A. Purified PcATP2/PcCdc50B complex displays ATPase activity in the presence of either phosphatidylserine or phosphatidylethanolamine. In addition, this activity is upregulated by phosphatidylinositol 4-phosphate. Overall, our work describes the first biochemical characterization of a Plasmodium lipid flippase, a first step towards the understanding of the essential physiological role of this transporter and towards its validation as a potential antimalarial drug target.

Genetic parameters of resistance to pasteurellosis using novel response traits in rabbits

Background

Pasteurellosis (Pasteurella infection) is one of the most common bacterial infections in rabbits on commercial farms and in laboratory facilities. Curative treatments using antibiotics are only partly efficient, with frequent relapses. Breeding rabbits for improved genetic resistance to pasteurellosis is a sustainable alternative approach. In this study, we infected 964 crossbred rabbits from six sire lines experimentally with Pasteurella multocida. After post-mortem examination and bacteriological analyses, abscess, bacteria, and resistance scores were derived for each rabbit based on the extent of lesions and bacterial dissemination in the body. This is the first study to use such an experimental design and response traits to measure resistance to pasteurellosis in a rabbit population. We investigated the genetic variation of these traits in order to identify potential selection criteria. We also estimated genetic correlations of resistance to pasteurellosis in the experimental population with traits that are under selection in the breeding populations (number of kits born alive and weaning weight).

Results

Heritability estimates for the novel response traits, abscess, bacteria, and resistance scores, ranged from 0.08 (± 0.05) to 0.16 (± 0.06). The resistance score showed very strong negative genetic correlation estimates with abscess (− 0.99 ± 0.05) and bacteria scores (− 0.98 ± 0.07). A very high positive genetic correlation of 0.99 ± 0.16 was estimated between abscess and bacteria scores. Estimates of genetic correlations of the resistance score with average daily gain traits for the first and second week after inoculation were 0.98 (± 0.06) and 0.70 (± 0.14), respectively. Estimates of genetic correlations of the disease-related traits with average daily gain pre-inoculation were favorable but with high standard errors. Estimates of genetic and phenotypic correlations of the disease-related traits with commercial selection traits were not significantly different from zero.

Conclusions

Disease response traits are heritable and are highly correlated with each other, but do not show any significant genetic correlations with commercial selection traits. Thus, the prevalence of pasteurellosis could be decreased by selecting more resistant rabbits on any one of the disease response traits with a limited impact on the selection traits, which would allow implementation of a breeding program to improve resistance to pasteurellosis in rabbits.

Correction to: In vitro prediction of stop-codon suppression by intravenous gentamicin in patients with cystic fibrosis: a pilot study

The original article [1] contains errors in Table 1 affecting some of the presented oligonucleotide sequences and readthrough values in Table 1.

Screening of Detergents for Stabilization of Functional Membrane Proteins

Membrane protein studies usually require use of detergents to extract and isolate proteins from membranes and manipulate them in a soluble context for their functional or structural characterization. However, solubilization with detergent may interfere with MP stability and may directly affect MP function or structure. Moreover, detergent properties can be affected such as critical micellar concentration (CMC) can be affected by the experimental conditions. Consequently, the experimenter must pay attention to both the protein and the behavior of the detergent. This article provides a convenient protocol for estimating the CMC of detergents in given experimental conditions. Then, it presents two protocols aimed at monitoring the function of a membrane protein in the presence of detergent. Such experiments may help to test various detergents for their inactivating or stabilizing effects on long incubation times, ranging from few hours to some days. © 2018 by John Wiley & Sons, Inc.

High phosphatidylinositol 4-phosphate (PI4P)-dependent ATPase activity for the Drs2p-Cdc50p flippase after removal of its N- and C-terminal extensions

P4-ATPases, also known as phospholipid flippases, are responsible for creating and maintaining transbilayer lipid asymmetry in eukaryotic cell membranes. Here, we use limited proteolysis to investigate the role of the N and C termini in ATP hydrolysis and auto-inhibition of the yeast flippase Drs2p-Cdc50p. We show that limited proteolysis of the detergent-solubilized and purified yeast flippase may result in more than 1 order of magnitude increase of its ATPase activity, which remains dependent on phosphatidylinositol 4-phosphate (PI4P), a regulator of this lipid flippase, and specific to a phosphatidylserine substrate. Using thrombin as the protease, Cdc50p remains intact and in complex with Drs2p, which is cleaved at two positions, namely after Arg¹⁰⁴ and after Arg ¹²⁹⁰, resulting in a homogeneous sample lacking 104 and 65 residues from its N and C termini, respectively. Removal of the 1291-1302-amino acid region of the C-terminal extension is critical for relieving the auto-inhibition of full-length Drs2p, whereas the 1-104 N-terminal residues have an additional but more modest significance for activity. The present results therefore reveal that trimming off appropriate regions of the terminal extensions of Drs2p can greatly increase its ATPase activity in the presence of PI4P and demonstrate that relief of such auto-inhibition remains compatible with subsequent regulation by PI4P. These experiments suggest that activation of the Drs2p-Cdc50p flippase follows a multistep mechanism, with preliminary release of a number of constraints, possibly through the binding of regulatory proteins in the trans-Golgi network, followed by full activation by PI4P.

Slow Phospholipid Exchange between a Detergent-Solubilized Membrane Protein and Lipid-Detergent Mixed Micelles: Brominated Phospholipids as Tools to Follow Its Kinetics

Membrane proteins are largely dependent for their function on the phospholipids present in their immediate environment, and when they are solubilized by detergent for further study, residual phospholipids are critical, too. Here, brominated phosphatidylcholine, a phospholipid which behaves as an unsaturated phosphatidylcholine, was used to reveal the kinetics of phospholipid exchange or transfer from detergent mixed micelles to the environment of a detergent-solubilized membrane protein, the paradigmatic P-type ATPase SERCA1a, in which Trp residues can experience fluorescence quenching by bromine atoms present on phospholipid alkyl chains in their immediate environment. Using dodecylmaltoside as the detergent, exchange of (brominated) phospholipid was found to be much slower than exchange of detergent under the same conditions, and also much slower than membrane solubilization, the latter being evidenced by light scattering changes. The kinetics of this exchange was strongly dependent on temperature. It was also dependent on the total concentration of the mixed micelles, revealing the major role for such exchange of the collision of detergent micelles with the detergent-solubilized protein. Back-transfer of the brominated phospholipid from the solubilized protein to the detergent micelle was much faster if lipid-free DDM micelles instead of mixed micelles were added for triggering dissociation of brominated phosphatidylcholine from the solubilized protein, or in the additional presence of C₁₂E₈ detergent during exchange, also emphasizing the role of the chemical nature of the micelle/protein interface. This protocol using brominated lipids appears to be valuable for revealing the possibly slow kinetics of phospholipid transfer to or from detergent-solubilized membrane proteins. Independently, continuous recording of the activity of the protein can also be used in some cases to correlate changes in activity with the exchange of a specific phospholipid, as shown here by using the Drs2p/Cdc50p complex, a lipid flippase with specific binding sites for lipids.

A robust method to screen detergents for membrane protein stabilization, revisited

This report is a follow up of our previous paper (Lund, Orlowski, de Foresta, Champeil, le Maire and Møller (1989), J Biol Chem 264:4907-4915) showing that solubilization in detergent of a membrane protein may interfere with its long-term stability, and proposing a protocol to reveal the kinetics of such irreversible inactivation. We here clarify the fact that when various detergents are tested for their effects, special attention has of course to be paid to their critical micelle concentration. We also investigate the effects of a few more detergents, some of which have been recently advertised in the literature, and emphasize the role of lipids together with detergents. Among these detergents, lauryl maltose neopentyl glycol (LMNG) exerts a remarkable ability, even higher than that of β-dodecylmaltoside (DDM), to protect our test enzyme, the paradigmatic P-type ATPase SERCA1a from sarcoplasmic reticulum. Performing such experiments for one's favourite protein probably remains useful in pre-screening assays testing various detergents.

Coordinated Overexpression in Yeast of a P4-ATPase and Its Associated Cdc50 Subunit: The Case of the Drs2p/Cdc50p Lipid Flippase Complex

Structural and functional characterization of integral membrane proteins requires milligram amounts of purified sample. Unless the protein you are studying is abundant in native membranes, it will be critical to overexpress the protein of interest in a homologous or heterologous way, and in sufficient quantities for further purification. The situation may become even more complicated if you chose to investigate the structure and function of a complex of two or more membrane proteins. Here, we describe the overexpression of a yeast lipid flippase complex, namely the P4-ATPase Drs2p and its associated subunit Cdc50p, in a coordinated manner. Moreover, we can take advantage of the fact that P4-ATPases, like most other P-type ATPases, form an acid-stable phosphorylated intermediate, to verify that the expressed complex is functional.

On the molecular mechanism of flippase- and scramblase-mediated phospholipid transport

Phospholipid flippases are key regulators of transbilayer lipid asymmetry in eukaryotic cell membranes, critical to many trafficking and signaling pathways. P4-ATPases, in particular, are responsible for the uphill transport of phospholipids from the exoplasmic to the cytosolic leaflet of the plasma membrane, as well as membranes of the late secretory/endocytic pathways, thereby establishing transbilayer asymmetry. Recent studies combining cell biology and biochemical approaches have improved our understanding of the path taken by lipids through P4-ATPases. Additionally, identification of several protein families catalyzing phospholipid 'scrambling', i.e. disruption of phospholipid asymmetry through energy-independent bi-directional phospholipid transport, as well as the recent report of the structure of such a scramblase, opens the way to a deeper characterization of their mechanism of action. Here, we discuss the molecular nature of the mechanism by which lipids may 'flip' across membranes, with an emphasis on active lipid transport catalyzed by P4-ATPases. This article is part of a Special Issue entitled: The cellular lipid landscape edited by Tim P. Levine and Anant K. Menon.

A high-yield co-expression system for the purification of an intact Drs2p-Cdc50p lipid flippase complex, critically dependent on and stabilized by phosphatidylinositol-4-phosphate

P-type ATPases from the P4 subfamily (P4-ATPases) are energy-dependent transporters, which are thought to establish lipid asymmetry in eukaryotic cell membranes. Together with their Cdc50 accessory subunits, P4-ATPases couple ATP hydrolysis to lipid transport from the exoplasmic to the cytoplasmic leaflet of plasma membranes, late Golgi membranes, and endosomes. To gain insights into the structure and function of these important membrane pumps, robust protocols for expression and purification are required. In this report, we present a procedure for high-yield co-expression of a yeast flippase, the Drs2p-Cdc50p complex. After recovery of yeast membranes expressing both proteins, efficient purification was achieved in a single step by affinity chromatography on streptavidin beads, yielding ∼1–2 mg purified Drs2p-Cdc50p complex per liter of culture. Importantly, the procedure enabled us to recover a fraction that mainly contained a 1∶1 complex, which was assessed by size-exclusion chromatography and mass spectrometry. The functional properties of the purified complex were examined, including the dependence of its catalytic cycle on specific lipids. The dephosphorylation rate was stimulated in the simultaneous presence of the transported substrate, phosphatidylserine (PS), and the regulatory lipid phosphatidylinositol-4-phosphate (PI4P), a phosphoinositide that plays critical roles in membrane trafficking events from the trans-Golgi network (TGN). Likewise, overall ATP hydrolysis by the complex was critically dependent on the simultaneous presence of PI4P and PS. We also identified a prominent role for PI4P in stabilization of the Drs2p-Cdc50p complex towards temperature- or C₁₂E₈-induced irreversible inactivation. These results indicate that the Drs2p-Cdc50p complex remains functional after affinity purification and that PI4P as a cofactor tightly controls its stability and catalytic activity. This work offers appealing perspectives for detailed structural and functional characterization of the Drs2p-Cdc50p lipid transport mechanism.

Phosphatidylserine stimulation of Drs2p·Cdc50p lipid translocase dephosphorylation is controlled by phosphatidylinositol-4-phosphate

Here, Drs2p, a yeast lipid translocase that belongs to the family of P(4)-type ATPases, was overexpressed in the yeast Saccharomyces cerevisiae together with Cdc50p, its glycosylated partner, as a result of the design of a novel co-expression vector. The resulting high yield allowed us, using crude membranes or detergent-solubilized membranes, to measure the formation from [γ-(32)P]ATP of a (32)P-labeled transient phosphoenzyme at the catalytic site of Drs2p. Formation of this phosphoenzyme could be detected only if Cdc50p was co-expressed with Drs2p but was not dependent on full glycosylation of Cdc50p. It was inhibited by orthovanadate and fluoride compounds. In crude membranes, the phosphoenzyme formed at steady state at 4 °C displayed ADP-insensitive but temperature-sensitive decay. Solubilizing concentrations of dodecyl maltoside left this decay rate almost unaltered, whereas several other detergents accelerated it. Unexpectedly, the dephosphorylation rate for the solubilized Drs2p·Cdc50p complex was inhibited by the addition of phosphatidylserine. Phosphatidylserine exerted its anticipated accelerating effect on the dephosphorylation of Drs2p·Cdc50p complex only in the additional presence of phosphatidylinositol-4-phosphate. These results explain why phosphatidylinositol-4-phosphate tightly controls Drs2p-catalyzed lipid transport and establish the functional relevance of the Drs2p·Cdc50p complex overexpressed here.

Nasal polyposis and cystic fibrosis(CF): review of the literature

The aim of this study was to address whether NP might be a predictive factor for severity of CF. The authors collected data from the literature on NP as a unique or associated sign in CF and reviewed the clinical and molecular aspects of CF associated with NP. CF genotypes and clinical severity in NP(+) vs. NP(-) patients were reviewed, taking into account pulmonary function, frequency of P. aeruginosa lung infection, frequency of allergy, nutritional status, and exocrine pancreatic function. The CFTR gene was also analyzed in a patient with isolated severe NP as the unique feature of CF. This review of the literature showed a `milder` phenotype in `NP+` vs. `NP-` CF patients, contrasting with a marked association between NP and `severe` CF mutations. In addition, a complex genotype was identified, associating four heterozygous variants, namely p.Q493X (a severe mutation) on the paternal allele, and p.V562I, p.A1006E, and (TG)11(T)5 (IVS8-5T) on the maternal allele, in a case of CF presenting as isolated NP. The authors speculate that genetic/environmental factors associated with NP might attenuate the functional impact of `severe` CF mutations. The overrepresentation of CF carriers among patients with isolated NP also advocates the need for CFTR molecular screening in such populations for genetic counselling purposes.

CDC50 proteins are critical components of the human class-1 P4-ATPase transport machinery

Members of the P(4) subfamily of P-type ATPases catalyze phospholipid transport and create membrane lipid asymmetry in late secretory and endocytic compartments. P-type ATPases usually pump small cations and the transport mechanism involved appears conserved throughout the family. How this mechanism is adapted to flip phospholipids remains to be established. P(4)-ATPases form heteromeric complexes with CDC50 proteins. Dissociation of the yeast P(4)-ATPase Drs2p from its binding partner Cdc50p disrupts catalytic activity (Lenoir, G., Williamson, P., Puts, C. F., and Holthuis, J. C. (2009) J. Biol. Chem. 284, 17956-17967), suggesting that CDC50 subunits play an intimate role in the mechanism of transport by P(4)-ATPases. The human genome encodes 14 P(4)-ATPases while only three human CDC50 homologues have been identified. This implies that each human CDC50 protein interacts with multiple P(4)-ATPases or, alternatively, that some human P(4)-ATPases function without a CDC50 binding partner. Here we show that human CDC50 proteins each bind multiple class-1 P(4)-ATPases, and that in all cases examined, association with a CDC50 subunit is required for P(4)-ATPase export from the ER. Moreover, we find that phosphorylation of the catalytically important Asp residue in human P(4)-ATPases ATP8B1 and ATP8B2 is critically dependent on their CDC50 subunit. These results indicate that CDC50 proteins are integral part of the P(4)-ATPase flippase machinery.

[Cancer genetic predisposition: current events and perspectives in 2010]

Studies performed during these last 30 years have had a major impact on the understanding of carcinogenesis. They have opened a new field: cancer genetic predisposition. At the present time, most of the cancer predispositions linked to the alteration of one gene, associated with a high risk of cancer and with a specific phenotype have been identified. About 70 genes have been identified and have led to genetic testing. The indication of genetic testing, the management of at risk patients require the establishment of guidelines. The next challenge is the identification of cancer susceptibility genes associated with low risk or modifying the effect of treatment.

Cdc50p plays a vital role in the ATPase reaction cycle of the putative aminophospholipid transporter Drs2p

Members of the P(4) subfamily of P-type ATPases are believed to catalyze transport of phospholipids across cellular bilayers. However, most P-type ATPases pump small cations or metal ions, and atomic structures revealed a transport mechanism that is conserved throughout the family. Hence, a challenging problem is to understand how this mechanism is adapted in P(4)-ATPases to flip phospholipids. P(4)-ATPases form heteromeric complexes with Cdc50 proteins. The primary role of these additional polypeptides is unknown. Here, we show that the affinity of yeast P(4)-ATPase Drs2p for its Cdc50-binding partner fluctuates during the transport cycle, with the strongest interaction occurring at a point where the enzyme is loaded with phospholipid ligand. We also find that specific interactions with Cdc50p are required to render the ATPase competent for phosphorylation at the catalytically important aspartate residue. Our data indicate that Cdc50 proteins are integral components of the P(4)-ATPase transport machinery. Thus, acquisition of these subunits may have been a crucial step in the evolution of flippases from a family of cation pumps.

Mutations of the noggin (NOG) and of the activin A type I receptor (ACVR1) genes in a series of twenty-seven French fibrodysplasia ossificans progressiva (FOP) patients

Fibrodysplasia ossificans progressiva (FOP) is a rare but very severe disease, characterised by congenital malformations of the toes and by progressive heterotopic ossification of muscles and joints. Two genes, the noggin (NOG) gene and the activin A type I receptor (ACVRI) gene, are involved in FOP. In this study we have searched for the NOG and the 617G>A (ACVR1) mutations in a well characterized series of twenty-seven French FOP patients. Five NOG mutations (delta 42, 274G>C, 275G>A, 276G>A, and 283G>A) have been found in seven (26%) of our FOP patients. The 617G>A mutation in the ACVR1 gene is found in fourteen (52%) of the patients. With one exception (patient number 22), 617G>A and NOG mutations are mutually exclusive in patients. Mutations 274G>C, 283G>A and 617G>A segregate with the trait in five different FOP families, some members of them being partially affected by the disease.

[HHV-6 infection and acute lymphoblastic leukemia in a child]

We report the case of a child who was infected by HHV-6 and who started an acute lymphoblastic leukemia two months later. This case reminds that an etiologic role have been suggested for many viral infections in some leukemias in childhood, particularly the human herpesvirus 6 (HHV-6).

Inhibitors bound to Ca(2+)-free sarcoplasmic reticulum Ca(2+)-ATPase lock its transmembrane region but not necessarily its cytosolic region, revealing the flexibility of the loops connecting transmembrane and cytosolic domains

Ca2+-free crystals of sarcoplasmic reticulum Ca2+-ATPase have, up until now, been obtained in the presence of inhibitors such as thapsigargin (TG), bound to the transmembrane region of this protein. Here, we examined the consequences of such binding for the protein. We found that, after TG binding, an active site ligand such as beryllium fluoride can still bind to the ATPase and change the conformation or dynamics of the cytosolic domains (as revealed by the protection afforded against proteolysis), but it becomes unable to induce any change in the transmembrane domain (as revealed by the intrinsic fluorescence of the membranous tryptophan residues). TG also obliterates the Trp fluorescence changes normally induced by binding of MgATP or metal-free ATP, as well as those induced by binding of Mg2+ alone. In the nucleotide binding domain, the environment of Lys515 (as revealed by fluorescein isothiocyanate fluorescence after specific labeling of this residue) is significantly different in the ATPase complex with aluminum fluoride and in the ATPase complex with beryllium fluoride, and in the latter case it is modified by TG. All these facts document the flexibility of the loops connecting the transmembrane and cytosolic domains in the ATPase. In the absence of active site ligands, TG protects the ATPase from cleavage by proteinase K at Thr242-Glu243, suggesting TG-induced reduction in the mobility of these loops. 2,5-Di-tert-butyl-1,4-dihydroxybenzene or cyclopiazonic acid, inhibitors which also bind in or near the transmembrane region, also produce similar overall effects on Ca2+-free ATPase.

Tuméfaction cervicale chez une jeune fille atteinte de mucoviscidose

Lobular emphysema and soft-tissue emphysema can exceptionally complicate malnutrition. We report the case of a teenager presenting malnutrition with cystic fibrosis and anorexia nervosa with soft-tissue emphysema.

[Evaluation of patients' knowledge regarding counsels provided in case of chest pain after an acute myocardial infarction]

INTRODUCTION

an early call to the department of urgent medical assistance--Center 15 (SAMU-centre 15) is associated to shortest delays of reperfusion in case of myocardial infarction. However, patients are not always aware of this.

OBJECTIVE

to assess the assimilated counsels by patients after an acute myocardial infarction.

METHODS

from January 1998 to June 2004, patients managed by SAMU 93 and having benefited from thrombolytic therapy prior to hospitalization and/or primary angioplasty for a ST+ acute coronary syndrome with a confirmation of acute myocardial infarction during their hospital stay were prospectively enrolled into this study. A questionnaire was administered by phone from december 2003 to july 2005, assessing the knowledge about the necessity to alert SAMU-center 15 in case of chest pain and availability of medical files data.

RESULTS

among the 976 patients: 111 (11%) were lost during follow-up, 162 (19%) were deceased when phone contact and 119 (12%) could not be interrogated. Among the 584 (60%) remaining subjects interrogated with a median follow-up period of 985 days (413-1596), 290 (50%) patients answered they received counseling, including 156 (27%) for taking nitrates, 19 (29%) stated they know that they should call SAMU-center 15. Patients with a high level of education and those treated by thrombolytic therapy prior to hospitalization were better informed; 464 (79%) patients declared having a prescription, 392 (67%) a hospital report, 406 (69%) an electrocardiogram, 227 (39%) a CD with their coronary angiography, and 79(14%) their medical file.

CONCLUSION

the level of knowledge regarding the recommended attitude in case of chest pain is poor. The availability of medical data was better. Arch Mal Cceur

[Anti Pseudomonas aeruginosa antibiotic therapy in cystic fibrosis (exclusion of macrolides)]

Antibiotherapy is one of the main treatment in cystic fibrosis. Pseudomonas aeruginosa infection is one of the main causes of pulmonary degradation. The chronic sputum colonisation is characterized by the emergence of the mucoid phenotype, the formation of biofilm and the induction of excessive inflammatory response and consecutive tissue lesion. The choice of antibiotics depends on quantitative and qualitative analysis of sputum, bacteria resistance phenotypes and severity of infection. Treatment of P. aeruginosa is different in case of first colonization or chronic infection. In the first case, parenteral antibiotherapy (beta-lactams-aminoglycosids) followed by inhaled antibiotherapy may eradicate the germ. In the other case, superinfections can be treated with parenteral biantibiothérapy (beta-lactams or quinolons and aminoglycosides) during 15 to 21 days. This is associated with a better nutritional and respiratory status and a prolonged survival. Inhaled antibiotics between the courses have decreased the number of superinfections. This prolonged antibiotherapy must be monitored because of possible induction of bacterial resistance, nephrotoxicity and ototoxicity of aminosids and allergy to beta-lactams.

Prognosis of early-onset breast cancer based on BRCA1/2 mutation status in a French population-based cohort

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Background: The debate concerning poorer survival for patients with breast cancer (BC) carrying a BRCA1 germline mutation is unresolved, and requires additional data from population-based studies. Methods: We followed 232 women with invasive BC under age 46, ascertained prospectively through a French population-based BC registry, and tested for BRCA1/2 mutations (median follow-up: 82 months). We compared tumour characteristics and survival rates between 21 BRCA1/2 deleterious mutation carriers and 211 non-carriers. Results: As compared to sporadic tumours, BRCA1/2 tumours showed higher grade (p = 0.02), fewer ductal carcinoma in situ (p = 0.02), more frequent medullary histology (p = 0.02), more frequent negative oestrogen and progesterone receptors (p = 0.001 each). At five years, BC-specific survival, metastasis-free survival, ipsilateral recurrence-free survival and contralateral BC-free survival rates for BRCA1/2 mutation carriers were 95.0%, 94.7%, 100% and 90.0% respectively, compared with 89.6%, 78.2%, 88.8% and 94.4% respectively, for non-carriers (not significant). Rates for women carrying only a BRCA1 mutation were 93.3%, 93.3%, 100%, 86.7%, respectively. 76% of BRCA1/2 carriers received chemotherapy. Conclusions: Despite unfavourable tumour features, we found no evidence for poorer short-term survival in BRCA1 mutation carriers compared to non-carriers in this prospective population-based cohort. The high rate of BRCA1 carriers who received chemotherapy for their BC should question the positive impact of this treatment, as suggested by preclinical studies showing increased chemosensitivity of BRCA1-associated tumours.

No significant financial relationships to disclose.

Conformational changes in sarcoplasmic reticulum Ca(2+)-ATPase mutants: effect of mutations either at Ca(2+)-binding site II or at tryptophan 552 in the cytosolic domain

By analyzing, after expression in yeast and purification, the intrinsic fluorescence properties of point mutants of rabbit Ca(2+)-ATPase (SERCA1a) with alterations to amino acid residues in Ca(2+)-binding site I (E(771)), site II (E(309)), in both sites (D(800)), or in the nucleotide-binding domain (W(552)), we were able to follow the conformational changes associated with various steps in the ATPase catalytic cycle. Whereas Ca(2+) binding to purified wild-type (WT) ATPase in the absence of ATP leads to the rise in Trp fluorescence expected for the so-called E2 --> E1Ca(2) transition, the Ca(2+)-induced fluorescence rise is dramatically reduced for the E(309)Q mutant. As this purified E(309)Q mutant retains the ability to bind Ca(2+) at site I (but not at site II), we tentatively conclude that the protein reorganization induced by Ca(2+) binding at site II makes the major contribution to the overall Trp fluorescence changes observed upon Ca(2+) binding to both sites. Judging from the fluorescence response of W(552)F, similar to that of WT, these changes appear to be primarily due to membranous tryptophans, not to W(552). The same holds for the fluorescence rise observed upon phosphorylation from P(i) (the so-called E2 --> E2P transition). As for WT ATPase, Mg(2+) binding in the absence of Ca(2+) affects the fluorescence of the E(309)Q mutant, suggesting that this Mg(2+)-dependent fluorescence rise does not reflect binding of Mg(2+) to Ca(2+) sites; instead, Mg(2+) probably binds close to the catalytic site, or perhaps near transmembrane span M3, at a location recently revealed by Fe(2+)-catalyzed oxidative cleavage. Mutation of W(552) hardly affects ATP-induced fluorescence changes in the absence of Ca(2+), which are therefore mostly due to membranous Trp residues, demonstrating long-range communication between the nucleotide-binding domain and the membranous domain.