Comparison of five commercial extraction kits for subsequent membrane protein profiling

Dietary (poly)phenols as modulators of the biophysical properties in endothelial cell membranes: its impact on nitric oxide bioavailability in hypertension

Hypertension is a major contributor to premature death, owing to the associated increased risk of damage to the heart, brain and kidneys. Although hypertension is manageable by medication and lifestyle changes, the risk increases with age. In an increasingly aged society, the incidence of hypertension is escalating, and is expected to increase the prevalence of (cerebro)vascular events and their associated mortality. Adherence to plant-based diets improves blood pressure and vascular markers in individuals with hypertension. Food flavonoids have an inhibitory effect towards angiotensin-converting enzyme (ACE1) and although this effect is greatly diminished upon metabolization, their microbial metabolites have been found to improve endothelial nitric oxide synthase (eNOS) activity. Considering the transmembrane location of ACE1 and eNOS, the ability of (poly)phenols to interact with membrane lipids modulate the cell membrane's biophysical properties and impact on nitric oxide (· NO) synthesis and bioavailability, remain poorly studied. Herein, we provide an overview of the current knowledge on the lipid remodeling of endothelial membranes with age, its impact on the cell membrane's biophysical properties and · NO permeability across the endothelial barrier. We also discuss the potential of (poly)phenols and other plant-based compounds as key players in hypertension management, and address the caveats and challenges in adopted methodologies.

Identification of transient receptor potential melastatin 3 proteotypic peptides employing an efficient membrane protein extraction method for natural killer cells

Introduction: Mutations and misfolding of membrane proteins are associated with various disorders, hence they make suitable targets in proteomic studies. However, extraction of membrane proteins is challenging due to their low abundance, stability, and susceptibility to protease degradation. Given the limitations in existing protocols for membrane protein extraction, the aim of this investigation was to develop a protocol for a high yield of membrane proteins for isolated Natural Killer (NK) cells. This will facilitate genetic analysis of membrane proteins known as transient receptor potential melastatin 3 (TRPM3) ion channels in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) research.

Methods: Two protocols, internally identified as Protocol 1 and 2, were adapted and optimized for high yield protein extraction. Protocol 1 utilized ultrasonic and salt precipitation, while Protocol 2 implemented a detergent and chloroform/methanol approach. Protein concentrations were determined by the Pierce Bicinchoninic Acid (BCA) and the Bio-Rad DC (detergent compatible) protein assays according to manufacturer’s recommendation. Using Protocol 2, protein samples were extracted from NK cells of n = 6 healthy controls (HC) and n = 4 ME/CFS patients. In silico tryptic digest and enhanced signature peptide (ESP) predictor were used to predict high-responding TRPM3 tryptic peptides. Trypsin in-gel digestion was performed on protein samples loaded on SDS-PAGE gels (excised at 150–200 kDa). A liquid chromatography-multiple reaction monitoring (LC-MRM) method was optimized and used to evaluate the detectability of TRPM3 n = 5 proteotypic peptides in extracted protein samples.

Results: The detergent-based protocol protein yield was significantly higher (p < 0.05) compared with the ultrasonic-based protocol. The Pierce BCA protein assay showed more reproducibility and compatibility compared to the Bio-Rad DC protein assay. Two high-responding tryptic peptides (GANASAPDQLSLALAWNR and QAILFPNEEPSWK) for TRPM3 were detectable in n = 10 extracted protein samples from NK cells isolated from HC and ME/CFS patients.

Conclusion: A method was optimized for high yield protein extraction from human NK cells and for the first time TRPM3 proteotypic peptides were detected using LC-MRM. This new method provides for future research to assess membrane protein structural and functional relationships, particularly to facilitate proteomic investigation of TRPM3 ion channel isoforms in NK cells in both health and disease states, such as ME/CFS.

Microfluidic platforms for extracellular vesicle isolation, analysis and therapy in cancer

Extracellular vesicles (EVs) are small lipidic particles packed with proteins, DNA, messenger RNA and microRNAs of their cell of origin that act as critical players in cell-cell communication. These vesicles have been identified as pivotal mediators in cancer progression and the formation of metastatic niches. Hence, their isolation and analysis from circulating biofluids is envisioned as the next big thing in the field of liquid biopsies for early non-invasive diagnosis and patient follow-up. Despite the promise, current benchtop isolation strategies are not compatible with point-of-care testing in a clinical setting. Microfluidic platforms are disruptive technologies capable of recovering, analyzing, and quantifying EVs within clinical samples with limited volume, in a high-throughput manner with elevated sensitivity and multiplexing capabilities. Moreover, they can also be employed for the controlled production of synthetic EVs and effective drug loading to produce EV-based therapies. In this review, we explore the use of microfluidic platforms for the isolation, characterization, and quantification of EVs in cancer, and compare these platforms with the conventional methodologies. We also highlight the state-of-the-art in microfluidic approaches for EV-based cancer therapeutics. Finally, we analyze the currently active or recently completed clinical trials involving EVs for cancer diagnosis, treatment or therapy monitoring and examine the future of EV-based point-of-care testing platforms in the clinic and EV-based therapy production by the industry.

Transport Turnover Rates for Human OCT2 and MATE1 Expressed in Chinese Hamster Ovary Cells

MATE1 (multidrug and toxin extruder 1) and OCT2 (organic cation transporter 2) play critical roles in organic cation excretion by the human kidney. The transporter turnover rate (TOR) is relevant to understanding both their transport mechanisms and interpreting the in vitro-in vivo extrapolation (IVIVE) required for physiologically-based pharmacokinetic (PBPK) modeling. Here, we use a quantitative western blot method to determine TORs for MATE1 and OCT2 proteins expressed in CHO cells. MATE1 and OCT2, each with a C-terminal V-5 epitope tag, were cell surface biotinylated and the amount of cell surface MATE1 and OCT2 protein was quantified by western analysis, using standard curves for the V5 epitope. Cell surface MATE1 and OCT2 protein represented 25% and 24%, respectively, of the total expression of these proteins in CHO cells. The number of cell surface transporters was ~55 fmol cm^-2 for MATE1 and ~510 fmol cm^-2 for OCT2. Dividing these values into the different J_max values for transport of MPP, metformin, and atenolol mediated by MATE1 and OCT2 resulted in calculated TOR values (±SE, n = 4) of 84.0 ± 22.0 s^-1 and 2.9 ± 0.6 s^-1; metformin, 461.0 ± 121.0 s^-1 and 12.6 ± 2.4 s^-1; atenolol, 118.0 ± 31.0 s^-1, respectively. These values are consistent with the TOR values determined for a variety of exchangers (NHEs), cotransporters (SGLTs, Lac permease), and uniporters (GLUTs, ENTs).

Identification of Key Amino Acids that Impact Organic Solute Transporter α/β (OSTα/β)

Organic solute transporter α/β (OSTα/β) is a bidirectional bile acid transporter localized on the basolateral membrane of hepatic, intestinal, and renal epithelial cells. OSTα/β plays a critical role in intestinal bile acid reabsorption and is upregulated in hepatic diseases characterized by elevated bile acids, whereas genetic variants in SLC51A/B have been associated with clinical cholestasis. OSTα/β also transports and is inhibited by commonly used medications. However, there is currently no high-resolution structure of OSTα/β, and structure-function data for OSTα, the proposed substrate-binding subunit, are lacking. The present study addressed this knowledge gap and identified amino acids in OSTα that are important for bile acid transport. This was accomplished using computational modeling and site-directed mutagenesis of the OSTα subunit to generate OSTα/β mutant cell lines. Out of the 10 OSTα/β mutants investigated, four (S228K, T229S, Q269E, Q269K) exhibited decreased [3H]-taurocholate (TCA) uptake (ratio of geometric means relative to OSTα/β wild type (WT) of 0.76, 0.75, 0.79, and 0.13, respectively). Three OSTα/β mutants (S228K, Q269K, E305A) had reduced [3H]-TCA efflux % (ratio of geometric means relative to OSTα/β WT of 0.86, 0.65, and 0.79, respectively). Additionally, several OSTα/β mutants demonstrated altered expression and cellular localization when compared with OSTα/β WT. In summary, we identified OSTα residues (Ser228, Thr229, Gln269, Glu305) in predicted transmembrane domains that affect expression of OSTα/β and may influence OSTα/β-mediated bile acid transport. These data advance our understanding of OSTα/β structure/function and can inform future studies designed to gain further insight into OSTα/β structure or to identify additional OSTα/β substrates and inhibitors. SIGNIFICANCE STATEMENT: OSTα/β is a clinically important transporter involved in enterohepatic bile acid recycling with currently no high-resolution protein structure and limited structure-function data. This study identified four OSTα amino acids (Ser228, Thr229, Gln269, Glu305) that affect expression of OSTα/β and may influence OSTα/β-mediated bile acid transport. These data can be utilized to inform future investigation of OSTα/β structure and refine molecular modeling approaches to facilitate the identification of substrates and/or inhibitors of OSTα/β.

Enhancing Inflammation Targeting Using Tunable Leukocyte-Based Biomimetic Nanoparticles

Biomimetic nanoparticles aim to effectively emulate the behavior of either cells or exosomes. Leukocyte-based biomimetic nanoparticles, for instance, incorporate cell membrane proteins to transfer the natural tropism of leukocytes to the final delivery platform. However, tuning the protein integration can affect the in vivo behavior of these nanoparticles and alter their efficacy. Here we show that, while increasing the protein:lipid ratio to a maximum of 1:20 (w/w) maintained the nanoparticle's structural properties, increasing protein content resulted in improved targeting of inflamed endothelium in two different animal models. Our combined use of a microfluidic, bottom-up approach and tuning of a key synthesis parameter enabled the synthesis of reproducible, enhanced biomimetic nanoparticles that have the potential to improve the treatment of inflammatory-based conditions through targeted nanodelivery.

Endogenous Coproporphyrin I and III are Altered in Multidrug Resistance-Associated Protein 2-Deficient (TR-) Rats

Recent studies have focused on coproporphyrin (CP)-I and CP-III (CPs) as endogenous biomarkers for organic anion transporting polypeptides (OATPs). Previous data showed that CPs are also substrates of multidrug resistance-associated protein (MRP/Mrp) 2 and 3. This study was designed to examine the impact of loss of Mrp2 function on the routes of excretion of endogenous CPs in wild-type (WT) Wistar compared to Mrp2-deficient TR^- rats. To exclude possible confounding effects of rat Oatps, the transport of CPs was investigated in Oatp-overexpressing HeLa cells. Results indicated that CPs are substrates of rodent Oatp1b2, and that CP-III is a substrate of Oatp2b1. Quantitative targeted absolute proteomic (QTAP) analysis revealed no differences in Oatps, but an expected significant increase in Mrp3 protein levels in TR^- compared to WT rat livers. CP-I and CP-III concentrations measured by LC-MS/MS were elevated in TR^- compared to WT rat liver, while CP-I and CP-III estimated biliary clearance was decreased 75- and 840-fold in TR^- compared to WT rats, respectively. CP-III concentrations were decreased 14-fold in the feces of TR^- compared to WT rats, but differences in CP-I were not significant. In summary, the disposition of CPs was markedly altered by loss of Mrp2 and increased Mrp3 function as measured in TR^- rats.

TLR7 activation in epilepsy of tuberous sclerosis complex

BACKGROUND

Neuroinflammation and toll-like receptors (TLR) of the innate immune system have been implicated in epilepsy. We previously reported high levels of microRNAs miR-142-3p and miR-223-3p in epileptogenic brain tissue resected for the treatment of intractable epilepsy in children with tuberous sclerosis complex (TSC). As miR-142-3p has recently been reported to be a ligand and activator of TLR7, a detector of exogenous and endogenous single-stranded RNA, we evaluated TLR7 expression and downstream IL23A activation in surgically resected TSC brain tissue.

METHODS

Gene expression analysis was performed on cortical tissue obtained from surgery of TSC children with pharmacoresistent epilepsy. Expression of TLRs 2, 4 and 7 was measured using NanoString nCounter assays. Real-time quantitative PCR was used to confirm TLR7 expression and compare TLR7 activation, indicated by IL-23A levels, to levels of miR-142-3p. Protein markers characteristic for TLR7 activation were assessed using data from our existing quantitative proteomics dataset of TSC tissue. Capillary electrophoresis Western blots were used to confirm TLR7 protein expression in a subset of samples.

RESULTS

TLR7 transcript expression was present in all TSC specimens. The signaling competent form of TLR7 protein was detected in the membrane fraction of each sample tested. Downstream activation of TLR7 was found in epileptogenic lesions having elevated neuroinflammation indicated by clinical neuroimaging. TLR7 activity was significantly associated with tissue levels of miR-142-3p.

CONCLUSION

TLR7 activation by microRNAs may contribute to the neuroinflammatory cascade in epilepsy in TSC. Further characterization of this mechanism may enable the combined of use of neuroimaging and TLR7 inhibitors in a personalized approach towards the treatment of intractable epilepsy.

Effect of low temperature on the regulation of cell volume after hypotonic shock in gastric cancer cells

Although peritoneal lavage with distilled water performed after surgery prevents peritoneal seeding, cancer cells may avoid rupture under mild hypotonicity through regulatory volume decrease (RVD), which is the homeostatic regulation of ion and water transport. The aim of the present study was to investigate the effect of low temperature on cell volume and cell death under hypoosmolal conditions and determine the underlying molecular mechanisms in gastric cancer (GC). Three human GC cell lines (NUGC4, KATO‑III and MKN45) were exposed to hypotonic solutions, and the effects of low temperature on cell volume and viability were examined. Low temperature‑induced changes in membrane transporters were evaluated, and knockdown and overexpression experiments were conducted to determine their effects on cell volume during hypotonic stimulation. Low temperature (24˚C) during hypotonic stimulation inhibited RVD and enhanced the cytocidal effects on GC cells. The expression of leucine‑rich repeat containing protein A (LRRC8A), a component of a Cl‑ channel, was decreased, and aquaporin 5 (AQP5) expression was increased at low temperatures. LRRC8A knockdown markedly slowed the decrease in cell volume following cell swelling by hypotonic shock. AQP5 overexpression enhanced initial cell swelling after hypotonic shock and increased the final cell volume. These results suggest that a hypotonic solution at low temperature increased initial water influx via activation of AQP5 and decreased Cl‑ efflux via inhibition of LRRC8A. Therefore, low temperature enhanced the hypotonicity‑induced cytocidal effects on GC cells, and these results may contribute to the development of a novel lavage method effective in reducing peritoneal recurrence in GC.

Stearate-Induced Apoptosis in Human Pancreatic β-Cells is Associated with Changes in Membrane Protein Expression and These Changes are Inhibited by Oleate

PURPOSE

Lipotoxicity is implicated in type 2 diabetes pathogenesis. Its molecular mechanisms are not completely understood. The aim of this study is to identify new suspect proteins involved in pancreatic β-cell death induction by saturated fatty acids and its inhibition by unsaturated fatty acids.

EXPERIMENTAL DESIGN

Employing 2DE analysis and subsequent western blot confirmation, the differences in membrane/membrane-associated protein expression in human β-cell line NES2Y are assessed during cell death induction by stearate and its inhibition by oleate.

RESULTS

Induction of apoptosis by stearate is associated with significantly increased levels of Hsp90β, peroxiredoxin-1, and 14-3-3γ in the membrane fraction of NES2Y cells and significantly decreased levels of annexin A2, annexin A4, and reticulocalbin-2. All these changes are significantly inhibited by oleate co-application. No expression changes are detected after application of stearate together with oleate. Furthermore, the expression of reticulocalbin-2 is significantly decreased after stearate application also in the whole cell lysate.

CONCLUSIONS AND CLINICAL RELEVANCE

Several membrane-associated proteins that could be related to pro- and anti-apoptotic signaling initiated by fatty acids in human pancreatic β-cells are identified. As far as we know, annexin A4, reticulocalbin-2, and 14-3-3γ represent novel molecules related to the effect of fatty acids on β-cell viability.

Analysis of Entamoeba histolytica Membrane Proteome Using Three Extraction Methods

Entamoeba histolytica membrane proteins are important players toward the pathogenesis of amoebiasis, but the roles of most of the proteins are not fully understood. Since efficient protein extraction method is crucial for a successful MS analysis, three extractions methods are evaluated for the use in studying the membrane proteome of E. histolytica: Two commercial kits (ProteoExtract from Calbiochem and ProteoPrep from Sigma), and a conventional laboratory method. The results show that ProteoExtract and the conventional method gave higher protein yields compared to ProteoPrep. LC-ESI-MS/MS identifies 456, 482, and 551 membrane fraction proteins extracted using ProteoExtract, ProteoPrep, and a conventional method, respectively. In silico analysis predicts 108 (21%), 235 (45%), and 177 (34%) membrane proteins from the extracts of ProteoExtract, ProteoPrep, and the conventional method, respectively. Furthermore, analysis of the cytosolic and membrane fractions shows the highest selectivity of the membrane proteins using the ProteoPrep extraction kit. Overall, this study reports 828 E. histolytica membrane fraction proteins that include 249 predicted membrane proteins. The data are available via ProteomeXchange with identifier PXD010171.

Graphene and graphene oxide as a solid matrix for extraction of membrane and membrane-associated proteins

The extraction of membrane proteins remain a challenge due to innate hydrophobicity, dynamic discrepancy, and restrain effect of membrane lipids. Nanomaterials with high surface area have competency of hydrophobic-hydrophobic lipid interactions. It is shown here that both graphene and graphene oxide dissolved in solubilization buffer are viable sorbents for efficient extraction of membrane proteins. LC-MS/MS analysis further revealed that graphene (50-200 nm) and graphene oxide (50-200 nm) can enrich more kinds of membrane proteins than a commercially available kit. Graphene was further applied to the enrichment of membrane proteins of normal cells as well as cancer cells, and 1079 and 872 proteins were identified, respectively, among which 56.5% and 60.5% were membrane proteins. In particular, 241 proteins were significantly regulated in cancer cells. Gene expression of 15 proteins was verified by qRT-PCR, and 4 of them were further quantified by immunoassay. These data collectively demonstrate that graphene has great potential to improve membrane protein extractions and thus can serve downstream cancer proteomics. Graphical abstract Two dimensional carbon nanomaterials, including graphene and graphene oxide, were employed as solid matrix to avoid lipid bilayer interference and enhance the extraction efficiency of membrane and membrane associated proteins. The strategy will benefit downstream membrane proteomics analysis.

Nitrogen Cavitation and Differential Centrifugation Allows for Monitoring the Distribution of Peripheral Membrane Proteins in Cultured Cells

Cultured cells are useful for studying the subcellular distribution of proteins, including peripheral membrane proteins. Genetically encoded fluorescently tagged proteins have revolutionized the study of subcellular protein distribution. However, it is difficult to quantify the distribution with fluorescent microscopy, especially when proteins are partially cytosolic. Moreover, it is often important to study endogenous proteins. Biochemical assays such as immunoblots remain the gold standard for quantification of protein distribution after subcellular fractionation. Although there are commercial kits that aim to isolate cytosolic or certain membrane fractions, most of these kits are based on extraction with detergents, which may be unsuitable for studying peripheral membrane proteins that are easily extracted from membranes. Here we present a detergent-free protocol for cellular homogenization by nitrogen cavitation and subsequent separation of cytosolic and membrane-bound proteins by ultracentrifugation. We confirm the separation of subcellular organelles in soluble and pellet fractions across different cell types, and compare protein extraction among several common non-detergent-based mechanical homogenization methods. Among several advantages of nitrogen cavitation is the superior efficiency of cellular disruption with minimal physical and chemical damage to delicate organelles. Combined with ultracentrifugation, nitrogen cavitation is an excellent method to examine the shift of peripheral membrane proteins between cytosolic and membrane fractions.

Strategies of Drug Transporter Quantitation by LC-MS: Importance of Peptide Selection and Digestion Efficiency

Huge variation of drug transporter abundance was seen in the literature, making PBPK prediction difficult when transporters play a major role. Among multiple factors such as membrane fraction, digestion, and peptide selection that contributed to such variation, peptide selection is the least discussed. Herein, a strategy was established by using a small amount of purified protein standard to select a peptide with near 100% digestion efficiency for quantitation of a transporter protein MDR1. The impact of native membrane protein's tertiary structure on the digestion efficiency of surrogate peptides of MDR1 was investigated. Peptides in more solvent accessible regions are found to be digested much more efficiently than those in large stretches of helical structures. The concentration of peptide EALDESIPPVSFWR(EAL) in the most solvent accessible linker region of MDR1 was found closest to the true protein concentration. When using EAL for MDR1 quantitation, the abundance is over 10 times higher than previously reported, indicating the importance of peptide selection for transporter quantitation. In addition, this study also proposes a screening strategy to select peptides appropriate for relative quantitation for in vitro-in vivo extrapolation in the absence of any protein standard.

Effects of alloantibodies to human leukocyte antigen on endothelial expression and serum levels of thrombomodulin

Essentials The effect of alloantibodies on the endothelial expression of thrombomodulin is unknown. Thrombomodulin was quantified in stimulated endothelial cells and measured in serum samples. Anti-human leukocyte antigen (HLA) I vs. II antibodies have different effects on thrombomodulin. Anti-HLA II antibodies may promote a prothrombotic state and contribute to microangiopathy.

SUMMARY

Rationale Thrombomodulin (TBM) is an anticoagulant and anti-inflammatory transmembrane protein expressed on endothelial cells. Donor-specific alloantibodies, particularly those against human leukocyte antigen (HLA) class II, are associated with microvascular endothelial damage in solid allografts. Objective Our aim was to characterize the effects of anti-HLA antibodies on endothelial expression of TBM, and in particular, the differential effects of anti-HLA class I compared with those of anti-HLA class II. Methods We used human glomerular microvascular endothelial cells to examine TBM expression on anti-HLA-treated cells, and we tested sera from transplant recipients for soluble TBM. Results We found that whereas membrane TBM expression increased in a dose-dependent manner in the presence of anti-HLA class I antibodies, treatment with anti-HLA class II led to minimal TBM expression on the endothelial surface but to a cytosolic accumulation. Platelet adhesion studies confirmed the functional impact of anti-HLA class II. Quantitative densitometry of the membrane lysates further suggested that anti-HLA class II impairs TBM glycosylation. Furthermore, we found a significant association between the presence of circulating anti-HLA class II antibodies in transplant recipients and low serum levels of TBM. Conclusion These results indicate that ligation of anti-HLA class I and II antibodies produces different effects on the endothelial expression of TBM and on serum levels of TBM in transplant recipients. Anti-HLA class II antibodies may be associated with a prothrombotic state, which could explain the higher occurrence of microangiopathic lesions in the allograft and the poor outcomes observed in patients with these alloantibodies.

Rapid Preparation of a Plasma Membrane Fraction: Western Blot Detection of Translocated Glucose Transporter 4 from Plasma Membrane of Muscle and Adipose Cells and Tissues

Membrane proteins account for 70% to 80% of all pharmaceutical targets, indicating their clinical relevance and underscoring the importance of identifying differentially expressed membrane proteins that reflect distinct disease properties. The translocation of proteins from the bulk of the cytosol to the plasma membrane is a critical step in the transfer of information from membrane-embedded receptors or transporters to the cell interior. To understand how membrane proteins work, it is important to separate the membrane fraction of cells. This unit provides a protocol for rapidly obtaining plasma membrane fractions for western blot analysis. © 2016 by John Wiley & Sons, Inc.

Streamlined Membrane Proteome Preparation for Shotgun Proteomics Analysis with Triton X-100 Cloud Point Extraction and Nanodiamond Solid Phase Extraction

While mass spectrometry (MS) plays a key role in proteomics research, characterization of membrane proteins (MP) by MS has been a challenging task because of the presence of a host of interfering chemicals in the hydrophobic protein extraction process, and the low protease digestion efficiency. We report a sample preparation protocol, two-phase separation with Triton X-100, induced by NaCl, with coomassie blue added for visualizing the detergent-rich phase, which streamlines MP preparation for SDS-PAGE analysis of intact MP and shot-gun proteomic analyses. MP solubilized in the detergent-rich milieu were then sequentially extracted and fractionated by surface-oxidized nanodiamond (ND) at three pHs. The high MP affinity of ND enabled extensive washes for removal of salts, detergents, lipids, and other impurities to ensure uncompromised ensuing purposes, notably enhanced proteolytic digestion and down-stream mass spectrometric (MS) analyses. Starting with a typical membranous cellular lysate fraction harvested with centrifugation/ultracentrifugation, MP purities of 70%, based on number (not weight) of proteins identified by MS, was achieved; the weight-based purity can be expected to be much higher.

Anoctamin Calcium-Activated Chloride Channels May Modulate Inhibitory Transmission in the Cerebellar Cortex

Calcium-activated chloride channels of the anoctamin (alias TMEM16) protein family fulfill critical functions in epithelial fluid transport, smooth muscle contraction and sensory signal processing. Little is known, however, about their contribution to information processing in the central nervous system. Here we examined the recent finding that a calcium-dependent chloride conductance impacts on GABAergic synaptic inhibition in Purkinje cells of the cerebellum. We asked whether anoctamin channels may underlie this chloride conductance. We identified two anoctamin channel proteins, ANO1 and ANO2, in the cerebellar cortex. ANO1 was expressed in inhibitory interneurons of the molecular layer and the granule cell layer. Both channels were expressed in Purkinje cells but, while ANO1 appeared to be retained in the cell body, ANO2 was targeted to the dendritic tree. Functional studies confirmed that ANO2 was involved in a calcium-dependent mode of ionic plasticity that reduces the efficacy of GABAergic synapses. ANO2 channels attenuated GABAergic transmission by increasing the postsynaptic chloride concentration, hence reducing the driving force for chloride influx. Our data suggest that ANO2 channels are involved in a Ca2+-dependent regulation of synaptic weight in GABAergic inhibition. Thus, in balance with the chloride extrusion mechanism via the co-transporter KCC2, ANO2 appears to regulate ionic plasticity in the cerebellum.

Coronin-1C and RCC2 guide mesenchymal migration by trafficking Rac1 and controlling GEF exposure

Sustained forward migration through a fibrillar extracellular matrix requires localization of protrusive signals. Contact with fibronectin at the tip of a cell protrusion activates Rac1, and for linear migration it is necessary to dampen Rac1 activity in off-axial positions and redistribute Rac1 from non-protrusive membrane to the leading edge. Here, we identify interactions between coronin-1C (Coro1C), RCC2 and Rac1 that focus active Rac1 to a single protrusion. Coro1C mediates release of inactive Rac1 from non-protrusive membrane and is necessary for Rac1 redistribution to a protrusive tip and fibronectin-dependent Rac1 activation. The second component, RCC2, attenuates Rac1 activation outside the protrusive tip by binding to the Rac1 switch regions and competitively inhibiting GEF action, thus preventing off-axial protrusion. Depletion of Coro1C or RCC2 by RNA interference causes loss of cell polarity that results in shunting migration in 1D or 3D culture systems. Furthermore, morpholinos against Coro1C or RCC2, or mutation of any of the binding sites in the Rac1-RCC2-Coro1C complex delays the arrival of neural crest derivatives at the correct location in developing zebrafish, demonstrating the crucial role in migration guidance in vivo.

Protein surface recognition by calixarenes

The present review summarizes recently developed calixarene derivatives for protein surface recognition which are able to identify, inhibit, and separate specific proteins.

TLR4 Signaling augments monocyte chemotaxis by regulating G protein-coupled receptor kinase 2 translocation

Monocytes are critical effector cells of the innate immune system that protect the host by migrating to inflammatory sites, differentiating to macrophages and dendritic cells, eliciting immune responses, and killing pathogenic microbes. MCP-1, also known as CCL2, plays an important role in monocyte activation and migration. The chemotactic function of MCP-1 is mediated by binding to the CCR2 receptor, a member of the G protein-coupled receptor (GPCR) family. Desensitization of GPCR chemokine receptors is an important regulator of the intensity and duration of chemokine stimulation. GPCR kinases (GRKs) induce GPCR phosphorylation, and this leads to GPCR desensitization. Regulation of subcellular localization of GRKs is considered an important early regulatory mechanism of GRK function and subsequent GPCR desensitization. Chemokines and LPS are both present during Gram-negative bacterial infection, and LPS often synergistically exaggerates leukocyte migration in response to chemokines. In this study, we investigated the role and mechanism of LPS-TLR4 signaling on the regulation of monocyte chemotaxis. We demonstrate that LPS augments MCP-1-induced monocyte migration. We also show that LPS, through p38 MAPK signaling, induces phosphorylation of GRK2 at serine 670, which, in turn, suppresses GRK2 translocation to the membrane, thereby preventing GRK2-initiated internalization and desensitization of CCR2 in response to MCP-1. This results in enhanced monocyte migration. These findings reveal a novel function for TLR4 signaling in promoting innate immune cell migration.

Reproducible method to enrich membrane proteins with high purity and high yield for an LC-MS/MS approach in quantitative membrane proteomics

The proportionately low abundance of membrane proteins hampers their proteomic analysis, especially for a quantitative LC-MS/MS approach. To overcome this limitation, a method was developed that consists of one cell disruption step in a hypotonic reagent using liquid nitrogen, one isolation step using a low speed centrifugation, and three wash steps using high speed centrifugation. Pellets contained plasma, nuclear, and mitochondrial membranes, including their integral, peripheral, and anchored membrane proteins. The reproducibility of this method was verified by protein assay of four separate experiments with a CV of 7.7%, and by comparative LC-MS/MS label-free quantification of individual proteins between two experiments with 99% of the quantified proteins having a CV ≤30%. Western blot and LC-MS/MS results of markers for cytoplasm, nucleus, mitochondria, and their membranes indicated that the enriched membrane fraction was highly pure by the absence of, or presence of trace amounts of, nonmembrane marker proteins. The average yield of membrane proteins was 237 μg/10 million HT29-MTX cells. LC-MS/MS analysis of the membrane-enriched sample resulted in the identification of 2597 protein groups. In summary, the developed method is reproducible, produces a highly pure membrane fraction, and generates a high yield of membrane proteins.

Scanning fluorescence correlation spectroscopy in model membrane systems

Fluorescence correlation spectroscopy (FCS) is an emerging technique employed in biophysical studies that exploits the temporal autocorrelation of fluorescence intensity fluctuations measured in a tiny volume (in the order of fL). The autocorrelation curve derived from the fluctuations can then be fitted with diffusion models to obtain parameters such as diffusion time and number of particles in the diffusion volume/area. Application of FCS to membranes allows studying membrane component dynamics, which includes mobility and interactions between the components. However, FCS encounters several difficulties like accurate positioning and stability of the setup when applied to membranes. Here, we describe the theoretical basis of point FCS as well as the scanning FCS (SFCS) approach, which is a practical way to address the challenges of FCS with membranes. We also list materials necessary for FCS experiments on two model membrane systems: (1) supported lipid bilayers and (2) giant unilamellar vesicles. Finally, we present simple protocols for the preparation of these model membrane systems, calibration of the microscope setup for FCS, and acquisition and analysis of point FCS and SFCS data so that diffusion coefficients and concentrations of fluorescent probes within lipid membranes can be calculated.