Temperature-sensitive steps in the transport of secretory proteins through the Golgi complex in exocrine pancreatic cells

Selective delivery of imaging probes and therapeutics to the endoplasmic reticulum or Golgi apparatus: Current strategies and beyond

To maximize therapeutic effects and minimize unwanted effects, the interest in drug targeting to the endoplasmic reticulum (ER) or Golgi apparatus (GA) has been recently growing because two organelles are distributing hubs of cellular building/signaling components (e.g., proteins, lipids, Ca2+) to other organelles and the plasma membrane. Their structural or functional damages induce organelle stress (i.e., ER or GA stress), and their aggravation is strongly related to diseases (e.g., cancers, liver diseases, brain diseases). Many efforts have been developed to image (patho)physiological functions (e.g., oxidative stress, protein/lipid-related processing) and characteristics (e.g., pH, temperature, biothiols, reactive oxygen species) in the target organelles and to deliver drugs for organelle disruption using organelle-targeting moieties. Therefore, this review will overview the structure, (patho)physiological functions/characteristics, and related diseases of the organelles of interest. Future direction on ER or GA targeting will be discussed by understanding current strategies and investigations on targeting, imaging/sensing, and therapeutic systems.

Cationic liposomes overcome neutralizing antibodies and enhance reovirus efficacy in ovarian cancer

Reovirus (Reo) has shown promising potential in specifically killing tumor cells, and offering new possibilities for ovarian cancer (OC) treatment. However, neutralizing antibodies in the ascites from OC patients greatly limit the further application of Reo. In this study, we employed cationic liposomes (Lipo) to deliver Reo, significantly enhancing its ability to enter OC cells and its effectiveness in killing these cells under ascitic conditions. Pre-treatment with the MβCD inhibitor notably decreased Reo-mediated tumor cell death, indicating that Lipo primarily enables Reo's cellular uptake through caveolin-mediated endocytosis. Our results demonstrate that Lipo effectively facilitates the entry of Reo into the cytoplasm and triggers cell apoptosis. The above findings provide a new strategy to overcome the obstacle of neutralizing antibodies in the clinical application of Reo.

Temperature-dependent intracellular crystallization of firefly luciferase in mammalian cells is suppressed by D-luciferin and stabilizing inhibitors

Firefly luciferase (Fluc) from Photinus pyralis is one of the most widely used reporter proteins in biomedical research. Despite its widespread use, Fluc's protein phase transition behaviors and phase separation characteristics have not received much attention. Current research uncovers Fluc's intrinsic property to phase separate in mammalian cells upon a simple cell culture temperature change. Specifically, Fluc spontaneously produced needle-shaped crystal-like inclusion bodies upon temperature shift to the hypothermic temperatures ranging from 25 °C to 31 °C. The crystal-like inclusion bodies were not associated with or surrounded by membranous organelles and were likely built from the cytosolic pool of Fluc. Furthermore, the crystal-like inclusion formation was suppressed when cells were cultured in the presence of D-luciferin and its synthetic analog, as well as the benzothiazole family of so-called stabilizing inhibitors. These two classes of compounds inhibited intracellular Fluc crystallization by different modes of action as they had contrasting effects on steady-state luciferase protein accumulation levels. This study suggests that, under substrate insufficient conditions, the excess Fluc phase separates into a crystal-like state that can modulate intracellular soluble enzyme availability and protein turnover rate.

Quantitative live-cell imaging of lipidated peptide transport through an epithelial cell layer

Oral drug delivery increases patient compliance and is thus the preferred administration route for most drugs. However, for biologics the intestinal barrier greatly limits the absorption and reduces their bioavailability. One strategy employed to improve on this is chemical modification of the biologic through the addition of lipid side chains. While it has been established that lipidation of peptides can increase transport, a mechanistic understanding of this effect remains largely unexplored. To pursue this mechanistic understanding, end-point detection of biopharmaceuticals transported through a monolayer of fully polarized epithelial cells is typically used. However, these methods are time-consuming and tedious. Furthermore, most established methods cannot be combined easily with high-resolution live-cell fluorescence imaging that could provide a mechanistic insight into cellular uptake and transport. Here we address this challenge by developing an axial PSF deconvolution scheme to quantify the transport of peptides through a monolayer of Caco-2 cells using single-cell analysis with live-cell confocal fluorescence microscopy. We then measure the known cross-barrier transport of several compounds in our model and compare the results with results obtained in an established microfluidic model finding similar transport phenotypes. This verifies that already after two days the Caco-2 cells in our model form a tight monolayer and constitute a functional barrier model. We then apply this assay to investigate the effects of side chain lipidation of the model peptide drug salmon calcitonin (sCT) modified with 4‑carbon and 8‑carbon-long fatty acid chains. Furthermore, we compare that with experiments performed at lower temperature and using inhibitors for some endocytotic pathways to pinpoint how lipidation length modifies the main avenues for the transport. We thus show that increasing the length of the lipid chain increases the transport of the drug significantly but also makes endocytosis the primary transport mechanism in a short-term cell culture model.

Identification of Cell Culture Factors Influencing Afucosylation Levels in Monoclonal Antibodies by Partial Least-Squares Regression and Variable Importance Metrics

Retrospective analysis of historic data for cell culture processes is a powerful tool to develop further process understanding. In particular, deploying retrospective analyses can identify important cell culture process parameters for controlling critical quality attributes, e.g., afucosylation, for the production of monoclonal antibodies (mAbs). However, a challenge of analyzing large cell culture data is the high correlation between regressors (particularly media composition), which makes traditional analyses, such as analysis of variance and multivariate linear regression, inappropriate. Instead, partial least-squares regression (PLSR) models, in combination with machine learning techniques such as variable importance metrics, are an orthogonal or alternative approach to identifying important regressors and overcoming the challenge of a highly covariant data structure. A specific workflow for the retrospective analysis of cell culture data is proposed that covers data curation, PLS regression, model analysis, and further steps. In this study, the proposed workflow was applied to data from four mAb products in an industrial cell culture process to identify significant process parameters that influence the afucosylation levels. The PLSR workflow successfully identified several significant parameters, such as temperature and media composition, to enhance process understanding of the relationship between cell culture processes and afucosylation levels.

SNX5 targets a monoamine transporter to the TGN for assembly into dense core vesicles by AP-3

The time course of signaling by peptide hormones, neural peptides, and other neuromodulators depends on their storage inside dense core vesicles (DCVs). Adaptor protein 3 (AP-3) assembles the membrane proteins that confer regulated release of DCVs and is thought to promote their trafficking from endosomes directly to maturing DCVs. We now find that regulated monoamine release from DCVs requires sorting nexin 5 (SNX5). Loss of SNX5 disrupts trafficking of the vesicular monoamine transporter (VMAT) to DCVs. The mechanism involves a role for SNX5 in retrograde transport of VMAT from endosomes to the TGN. However, this role for SNX5 conflicts with the proposed function of AP-3 in trafficking from endosomes directly to DCVs. We now identify a transient role for AP-3 at the TGN, where it associates with DCV cargo. Thus, retrograde transport from endosomes by SNX5 enables DCV assembly at the TGN by AP-3, resolving the apparent antagonism. A novel role for AP-3 at the TGN has implications for other organelles that also depend on this adaptor.

ALFY localizes to early endosomes and cellular protrusions to facilitate directional cell migration

Cell migration is a complex process underlying physiological and pathological processes such as brain development and cancer metastasis. The autophagy-linked FYVE protein (ALFY; also known as WDFY3), an autophagy adaptor protein known to promote clearance of protein aggregates, has been implicated in brain development and neural migration during cerebral cortical neurogenesis in mice. However, a specific role of ALFY in cell motility and extracellular matrix adhesion during migration has not been investigated. Here, we reveal a novel role for ALFY in the endocytic pathway and in cell migration. We show that ALFY localizes to RAB5- and EEA1-positive early endosomes in a PtdIns(3)P-dependent manner and is highly enriched in cellular protrusions at the leading and lagging edge of migrating cells. We find that cells lacking ALFY have reduced attachment and altered protein levels and glycosylation of integrins, resulting in the inability to form a proper leading edge and loss of directional cell motility.

Lipid raft-mediated and upregulated coordination pathways assist transport of glycocholic acid-modified nanoparticle in a human breast cancer cell line of SK-BR-3

Bile acid transporter-targeting has been proven to be an effective strategy to improve drug delivery to hepatocytes and enterocytes. With increasing discoveries of bile acid transporter expression on tumor cells, bile acid-modified anticancer drugs are gradually attaining interests. In our previous study, we confirmed the efficacy of glycocholic acid-conjugated polystyrene nanoparticles (GCPN) on apical sodium bile acid transporter (ASBT)-expressed SK-BR-3 cells. However, the transport mechanisms remain unknown, due to the nanosized carriers are unlikely to be pumped through the narrow cavities of ASBT. To clarify their transport pathways, in this article, pharmacological inhibition and gene knocking-down studies were performed, which revealed that GCPN were primarily internalized via non-caveolar lipid raft-mediated endocytosis. Proteomics was analyzed to explore the in-depth mechanisms. In total 561 proteins were identified and statistical overrepresentation test was used to analyze the gene ontology (GO) upregulated pathways based on the highly expressed proteins. It was found that multiple pathways were upregulated and might coordinate to assist the location of the GCPN-ASBT complex and the recycling of ASBT. Among the highly expressed proteins, myelin and lymphocyte protein 2 (MAL2) was selected and confirmed to colocalize with GCPN, which further supported the lipid raft-mediated process. These findings will help set up a platform for design the bile acid-modified nanomedicines and regulate their transport to improve their anticancer efficacy.

Uptake and Intracellular Trafficking Studies of Multiple Dye-Doped Core-Shell Silica Nanoparticles in Lymphoid and Myeloid Cells

Introduction

Since most biologically active macromolecules are natural nanostructures, operating in the same scale of biomolecules gives the great advantage to enhance the interaction with cellular components. Noteworthy efforts in nanotechnology, particularly in biomedical and pharmaceutical fields, have propelled a high number of studies on the biological effects of nanomaterials. Moreover, the determination of specific physicochemical properties of nanomaterials is crucial for the evaluation and design of novel safe and efficient therapeutics and diagnostic tools. In this in vitro study, we report a physicochemical characterisation of fluorescent silica nanoparticles (NPs), interacting with biological models (U937 and PBMC cells), describing the specific triggered biologic response.

Methods

Flow Cytometric and Confocal analyses are the main method platforms. However TEM, NTA, DLS, and chemical procedures to synthesize NPs were employed.

Results

NT_B700 NPs, employed in this study, are fluorescent core-shell silica nanoparticles, synthesized through a micelle-assisted method, where the fluorescence energy transfer process, known as FRET, occurs at a high efficiency rate. Using flow cytometry and confocal microscopy, we observed that NT_B700 NP uptake seemed to be a rapid, concentration-, energy- and cell type-dependent process, which did not induce significant cytotoxic effects. We did not observe a preferred route of internalization, although their size and the possible aggregated state could influence their extrusion. At this level of analysis, our investigation focuses on lysosome and mitochondria pathways, highlighting that both are involved in NP co-localization. Despite the main mitochondria localization, NPs did not induce a significant increase of intracellular ROS, known inductors of apoptosis, during the time course of analyses. Finally, both lymphoid and myeloid cells are able to release NPs, essential to their biosafety.

Discussion

These data allow to consider NT_B700 NPs a promising platform for future development of a multifunctional system, by combining imaging and localized therapeutic applications in a unique tool.

Electroretinogram of the Cone-Dominant Thirteen-Lined Ground Squirrel during Euthermia and Hibernation in Comparison with the Rod-Dominant Brown Norway Rat

Purpose

The majority of small animal species used in research are nocturnal, with retinae that are anatomically and functionally dissimilar from humans, complicating their use as disease models. Herein we characterize the retinal structure and electrophysiological function of the diurnal, cone-dominant 13-lined ground squirrel (13-LGS) retina during euthermia and in hibernation.

Methods

Full-field electroretinography (ERG) was performed in 13-LGS and Brown Norway (BN) rat models to establish baseline values for retinal function in each species, including following intravitreal injection of pharmacologic agents to selectively block the contributions of ON- and OFF-bipolar cells. The effect of hibernation-associated retinal remodeling on electrophysiological function was assessed in 13-LGS during torpor and emergence, with correlative histology performed using transmission electron microscopy.

Results

Under light-adapted conditions, the a-, b-, and d-wave amplitude of the 13-LGS was significantly greater than that of the BN rat. Retinal function was absent in the 13-LGS during hibernation and correlated to widespread disruption of photoreceptor and RPE structure. Remarkably, both retinal function and structure recovered rapidly on emergence from hibernation, with ERG responses reaching normal amplitude within 6 hours.

Conclusions

ERG responses for both BN rats and 13-LGS reflect the relative proportions of cone photoreceptors present within the retinae, indicating that the cone-dominant 13-LGS may be a potentially useful model for studying human central retinal function and disease. That retinal remodeling and restoration of electrophysiological function occurs rapidly on emergence from hibernation implies the 13-LGS may also be a useful tool for studying aspects of retinal physiology and recovery from injury.

Design of 18 nm Doxorubicin-Loaded 3-Helix Micelles: Cellular Uptake and Cytotoxicity in Patient-Derived GBM6 Cells

The fate of nanocarrier materials at the cellular level constitutes a critical checkpoint in the development of effective nanomedicines, determining whether tissue level accumulation results in therapeutic benefit. The cytotoxicity and cell internalization of ∼18 nm 3-helix micelle (3HM) loaded with doxorubicin (DOX) were analyzed in patient-derived glioblastoma (GBM) cells in vitro. The half-maximal inhibitory concentration (IC₅₀) of 3HM-DOX increased to 6.2 μg/mL from <0.5 μg/mL for free DOX in patient-derived GBM6 cells, to 15.0 μg/mL from 6.5 μg/mL in U87MG cells, and to 21.5 μg/mL from ∼0.5 μg/mL in LN229 cells. Modeling analysis of previous 3HM biodistribution results predicts that these cytotoxic concentrations are achievable with intravenous injection in rodent GBM models. 3HM-DOX formulations were internalized intact and underwent intracellular trafficking distinct from free DOX. 3HM was quantified to have an internalization half-life of 12.6 h in GBM6 cells, significantly longer than that reported for some liposome and polymer systems. 3HM was found to traffic through active endocytic processes, with clathrin-mediated endocytosis being the most involved of the pathways studied. Inhibition studies suggest substantial involvement of receptor recognition in 3HM uptake. As the 3HM surface is PEG-ylated with no targeting functionalities, protein corona-cell surface interactions, such as the apolipoprotein-low-density lipoprotein receptor, are expected to initiate internalization. The present work gives insights into the cytotoxicity, pharmacodynamics, and cellular interactions of 3HM and 3HM-DOX relevant for ongoing preclinical studies. This work also contributes to efforts to develop predictive mathematical models tracking the accumulation and biodistribution kinetics at a systemic level.

Florigen trafficking integrates photoperiod and temperature signals in Arabidopsis

The transition to flowering is the most dramatic phase change in flowering plants and is crucial for reproductive success. A complex regulatory network in plants has evolved to perceive and integrate the endogenous and environmental signals. These signals perceived, including day length and temperature, converge to regulate FLOWERING LOCUS T (FT), which encodes a mobile stimulus required for floral induction in Arabidopsis. Despite the discovery of modulation of FT messenger RNA (mRNA) expression by ambient temperature, whether the trafficking of FT protein is controlled in response to changes in growth temperature is so far unknown. Here, we show that FT transport from companion cells to sieve elements is controlled in a temperature-dependent manner. This process is mediated by multiple C2 domain and transmembrane region proteins (MCTPs) and a soluble N-ethylmaleimide-sensitive factor protein attachment protein receptor (SNARE). Our findings suggest that ambient temperatures regulate both FT mRNA expression and FT protein trafficking to prevent precocious flowering at low temperatures and ensure plant reproductive success under favorable environmental conditions.

A novel function of FAF1, which induces dopaminergic neuronal death through cell-to-cell transmission

Background

Fas-associated factor 1 (FAF1) has been implicated in Parkinson’s disease (PD) and activates the cell death machinery in the cytosol. However, the presence of extracellular FAF1 has not been studied.

Methods

Serum-free conditioned medium (CM) from FAF1-transfected SH-SY5Y cells was concentrated and analyzed by western blotting. Exosomes were isolated from CM by ultracentrifugation and analyzed by western blotting, electron microscopy and nanoparticle tracking analysis. Soluble FAF1 from CM was immunodepleted using anti-FAF1 antibody. Transmission of secreted FAF1 was examined by transwell assay under a confocal microscope. CM-induced cell death was determined by measuring propidium iodide (PI) uptake using a flow cytometer.

Results

FAF1 was secreted from SH-SY5Y cells via exocytosis and brefeldin A (BFA)-resistant secretory pathways. Furthermore, FAF1 was secreted as a vesicle-free form and a genuine exosome cargo in the lumen of exosomes. In addition, FAF1 increased the number of exosomes, suggesting a regulatory role in exosome biogenesis. Extracellular FAF1 was transmitted via endocytosis to neighboring cells, where it induced cell death through apoptotic and necrotic pathways.

Conclusions

This study presents a novel route by which FAF1 induces neuronal death through cell-to-cell transmission.

Nanostructured lipid carriers for oral delivery of silymarin: Improving its absorption and in vivo efficacy in type 2 diabetes and metabolic syndrome model

Silymarin (SLM) is a mixture of flavonolignans extracted from the fruit of Silybum marianum L. Gaertn. which has been used for decades as a hepatoprotector. Silymarin has recently been proposed to be beneficial in type 2 diabetic patients. Constituents of SLM are poorly water-soluble and low permeable compounds, with consequently limited oral bioavailability. This study aimed to investigate the possibility of delivery of SLM via nanostructured lipid carriers (NLCs) to overcome these issues and for preparation of an oral dosage form. NLCs were prepared through an emulsion/evaporation/solidifying method. Cetyl palmitate:Lauroglycol 90 was selected as the lipid mixture and Brij S20 as surfactant. NLCs were chemically and physically characterized. Encapsulation efficiency was more than 92%. The storage stability of the NLC suspension was also investigated and the freeze-drying process was taken into consideration. After assessing the stability of the formulation in a simulated gastrointestinal environment, the release of SLM was monitored in different pH conditions. In vitro experiments with artificial membranes (PAMPA) and Caco-2 cells revealed that the NLCs enhanced the permeation of SLM. Active processes are involved in the internalization of NLCs, as evidenced by cellular uptake studies. After preliminary toxicological studies, the formulation was studied in vivo in a streptozotocin (STZ)-induced diabetic mouse model in the presence of metabolic syndrome. The formulation was also compared to an NLC containing stearic acid:Capryol 90, to evaluate the effect of the lipid matrix on the in vivo performance of nanocarriers. Finally, hepatic histopathological analyses were also conducted. Both SLM-loaded NLCs exhibited in vivo a significant down-regulation of blood glucose and triglyceride levels better than free SLM, with a liver-protective effect. Furthermore, both formulations showed a significant anti-hyperalgesic effect on STZ-induced neuropathy.

Oxidized carbon nanoparticles as an effective protein antigen delivery system targeting the cell-mediated immune response

Background: The demand for an effective vaccine delivery system that drives a suitable immune response is increasing. The oxidized carbon nanosphere (OCN), a negatively charged carbon nanoparticle, has the potential to fulfill this requirement because it can efficiently deliver macromolecules into cells and allows endosomal leakage. However, fundamental insights into how OCNs are taken up by antigen-presenting cells, and the intracellular behavior of delivered molecules is lacking. Furthermore, how immune responses are stimulated by OCN-mediated delivery has not been investigated.

Purpose: In this study, the model protein antigen ovalbumin (OVA) was used to investigate the uptake mechanism and intracellular fate of OCN-mediated delivery of protein in macrophages. Moreover, the immune response triggered by OVA delivered by OCNs was characterized.

Methods: Bone-marrow-derived macrophages (BMDMs) from mice were used to study antigen uptake and intracellular trafficking. Mice were immunized using OCN–OVA combined with known adjuvants, and the specific immune response was measured.

Results: OCNs showed no cytotoxicity against BMDMs. OCN-mediated delivery of OVA into BMDMs was partially temperature independent process. Using specific inhibitors, it was revealed that intracellular delivery of OCN–OVA does not rely on phagocytosis or the clathrin- and lipid raft/caveolae-mediated pathways. Delivered OVA was found to colocalize with compartments containing MHC class I, but not with early endosomes, lysosomes, and autophagosomes. Immunization of OVA using OCNs in combination with the known adjuvant monophosphoryl lipid A specifically enhanced interferon gamma (IFNγ)- and granzyme B-producing cytotoxic T cells (CTLs).

Conclusion: OCNs effectively delivered protein antigens into macrophages that localized with compartments containing MHC class I partially by the temperature independent, but not clathrin- and lipid raft/caveolae-mediated pathways. Increased CD8⁺ T-cell activity was induced by OCN-delivered antigens, suggesting antigen processing toward antigen presentation for CTLs. Taken together, OCNs are a potential protein antigen delivery system that stimulates the cell-mediated immune response.

Newly synthesized polycystin-1 takes different trafficking pathways to the apical and ciliary membranes

Mutations in the genes encoding polycystin-1 (PC1) and polycystin 2 (PC2) cause autosomal dominant polycystic kidney disease. These transmembrane proteins colocalize in the primary cilia of renal epithelial cells, where they may participate in sensory processes. PC1 is also found in the apical membrane when expressed in cultured epithelial cells. PC1 undergoes autocatalytic cleavage, producing an extracellular N-terminal fragment that remains noncovalently attached to the transmembrane C-terminus. Exposing cells to alkaline solutions elutes the N-terminal fragment while the C-terminal fragment is retained in the cell membrane. Utilizing this observation, we developed a "strip-recovery" synchronization protocol to study PC1 trafficking in polarized LLC-PK1 renal epithelial cells. Following alkaline strip, a new cohort of PC1 repopulates the cilia within 30 minutes, while apical delivery of PC1 was not detectable until 3 hours. Brefeldin A (BFA) blocked apical PC1 delivery, while ciliary delivery of PC1 was BFA insensitive. Incubating cells at 20°C to block trafficking out of the trans-Golgi network also inhibits apical but not ciliary delivery. These results suggest that newly synthesized PC1 takes distinct pathways to the ciliary and apical membranes. Ciliary PC1 appears to by-pass BFA sensitive Golgi compartments, while apical delivery of PC1 traverses these compartments.

Intermediate compartment (IC): from pre-Golgi vacuoles to a semi-autonomous membrane system

Despite its discovery more than three decades ago and well-established role in protein sorting and trafficking in the early secretory pathway, the intermediate compartment (IC) has remained enigmatic. The prevailing view is that the IC evolved as a specialized organelle to mediate long-distance endoplasmic reticulum (ER)–Golgi communication in metazoan cells, but is lacking in other eukaryotes, such as plants and fungi. However, this distinction is difficult to reconcile with the high conservation of the core machineries that regulate early secretory trafficking from yeast to man. Also, it has remained unclear whether the pleiomorphic IC components—vacuoles, tubules and vesicles—represent transient transport carriers or building blocks of a permanent pre-Golgi organelle. Interestingly, recent studies have revealed that the IC maintains its compositional, structural and spatial properties throughout the cell cycle, supporting a model that combines the dynamic and stable aspects of the organelle. Moreover, the IC has been assigned novel functions, such as cell signaling, Golgi-independent trafficking and autophagy. The emerging permanent nature of the IC and its connections with the centrosome and the endocytic recycling system encourage reconsideration of its relationship with the Golgi ribbon, role in Golgi biogenesis and ubiquitous presence in eukaryotic cells.

Uptake and intracellular fate of cholera toxin subunit b-modified mesoporous silica nanoparticle-supported lipid bilayers (aka protocells) in motoneurons

Cholera toxin B (CTB) modified mesoporous silica nanoparticle supported lipid bilayers (CTB-protocells) are a promising, customizable approach for targeting therapeutic cargo to motoneurons. In the present study, the endocytic mechanism and intracellular fate of CTB-protocells in motoneurons were examined to provide information for the development of therapeutic application and cargo delivery. Pharmacological inhibitors elucidated CTB-protocells endocytosis to be dependent on the integrity of lipid rafts and macropinocytosis. Using immunofluorescence techniques, live confocal and transmission electron microscopy, CTB-protocells were primarily found in the cytosol, membrane lipid domains and Golgi. There was no difference in the amount of motoneuron activity dependent uptake of CTB-protocells in neuromuscular junctions, consistent with clathrin activation at the axon terminals during low frequency activity. In conclusion, CTB-protocells uptake is mediated principally by lipid rafts and macropinocytosis. Once internalized, CTB-protocells escape lysosomal degradation, and engage biological pathways that are not readily accessible by untargeted delivery methods.

Endocytosis and intracellular traffic of cholesterol-PDMAEMA liposome complexes in human epithelial-like cells

Liposomes are generally used as delivery systems, as they are capable of encapsulating a wide variety of molecules (i.e. plasmids, recombinant proteins, therapeutic drugs). However, liposomal drug delivery have to fulfill different requirements, such as the effective internalization by the target cells and avoidance of the degradative activity of the intracellular compartments. The use of polymer lipid complexes (PLCs), by including different polymers in the liposome formulation, could improve internalization and intracellular release of drugs. The aim of the present work is to study the mechanisms of cellular uptaking and the intracellular trafficking of PLCs formed with cholesterol-poly(2-(dimethylamino)ethyl methacrylate) CHO-PDMAEMA and lecithin (LC CHO-PD). Calcein-loaded liposomes were used to determine cellular uptake and intracellular localization by flow cytometry and confocal microscopy. Incorporation of CHO-PDMAEMA to lecithin liposomes enhanced the internalization capacity of PLCs. Internalization of PLCs by human epithelial-like cells (HEK-293) diminished at 4°C, suggesting uptake by endocytosis. PLCs showed no co-localization with acidic compartments after internalization. Experiments with endocytosis inhibitors and co-localization of liposomes and albumin, suggested the caveolae endocytic pathway as the most probable route for intracellular trafficking of PLCs. In this work, we demonstrated an efficient uptake of LC CHO-PDs by human epithelial-like cells (HEK-293) through the non-degradative caveolae endocytic pathway. The mode of internalization and the intracellular fate of liposomes under study, suggest a promising use of LC CHO-PDs as drug delivery systems.

Cellular interactions of a lipid-based nanocarrier model with human keratinocytes: Unravelling transport mechanisms

Knowledge of delivery system transport through epidermal cell monolayer is vital to improve skin permeation and bioavailability. Recently, nanostructured lipid carriers (NLCs) have gained great attention for transdermal delivery due to their biocompatibility, high drug payload, occlusive properties and skin hydration effect. However, the nanocarriers transport related mechanisms in epidermal epithelial cells are not yet understood. In this research, the internalization and transport pathways of the NLCs across the epidermal epithelial cell monolayer (HaCaT cells) were investigated. The 250nm sized witepsol/miglyol NLCs, prepared by hot homogenization had reduced cytotoxicity and no effect on the integrity of cell membrane in human HaCaT keratinocytes. The internalization was time-, concentration- and energy-dependent, and the uptake of NLCs was a vesicle-mediated process by macropinocytosis and clathrin-mediated pathways. 3% of NLCs were found at the apical membrane side of the HaCaT monolayer through exocytosis mechanism. Additionally, the endoplasmic reticulum, Golgi apparatus and microtubules played crucial roles in the transport of NLCs out of HaCaT cells. NLCs were transported intact across the human keratinocytes monolayer, without disturbing the tight junction's structure. From the transcytosis data only approximately 12% of the internalized NLCs were passed from the apical to the basolateral side. The transcytosis of NLCs throughout the HaCaT cell monolayer towards the basolateral membrane side requires the involvement of the endoplasmic reticulum, Golgi apparatus and microtubules. Our findings may contribute to a systematic understanding of NLCs transport across epidermal epithelial cell monolayers and their optimization for clinical transdermal application.

STATEMENT OF SIGNIFICANCE

Transdermal drug delivery is a challenging and growing area of clinical application. Lipid nanoparticles such as nanostructured lipid carriers (NLCs) have gained wide interest for transdermal drug delivery. However these nanocarriers' interactions with epidermal epithelial barrier are yet unknown. Unveiling the mechanisms involved in NLCs transport across the epidermal epithelial monolayers will contribute with valuable information to achieve enhanced skin permeability, superior bioavailability and consequently improved therapeutic effect. With our present work we could certainly provide researchers and clinicians guidance for the design of optimized transdermal delivery systems, based on the nanomaterials and biological interactions.

Cellular uptake, genotoxicity and cytotoxicity of cobalt ferrite magnetic nanoparticles in human breast cells

Magnetic nanoparticles (MNPs) have been increasingly used for many years as MRI agents and for gene delivery and hyperthermia therapy, although there have been conflicting results on their safety. In this study, cobalt ferrite magnetic nanoparticles (CoFe-MNPs) were prepared by the co-precipitation method and their surfaces were modified with silica by the sol-gel method. The particle and hydrodynamic sizes, morphology and crystal structure of the bare and silica-coated CoFe-MNPs were evaluated by transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray diffraction spectroscopy (XRD) and Fourier transform infrared spectroscopy (FTIR). The size of the bare CoFe-MNPs was in the range 8-20 nm and they were homogeneously coated with 3-4 nm silica shells. The bare and silica-coated CoFe-MNPs were agglomerated at physiological pH. However, the sizes of the agglomerates were below 200 nm both in water and complete medium. The cytotoxic and genotoxic potentials of the bare and silica-coated CoFe-MNPs were evaluated in a metastatic breast cancer cell line, MDA-MB-231, as well as a noncancerous mammary epithelial cell line, MCF-10A, by using XTT cytotoxicity, single-cell gel electrophoresis (comet), and cytokinesis-blocked (CB) micronucleus (CBMN) assays. Characterization studies with TEM, inductively coupled plasma optical emission spectroscopy (ICP-OES) and Prussian blue staining indicated that the CoFe-MNPs were internalized into the cells by energy-dependent endocytosis. The highest amount of uptake was observed in the cancer cells and the uptake of the silica-coated CoFe-MNPs was higher than that of the bare ones in both cell lines. The bare CoFe-MNPs showed higher levels of both cytotoxicity and genotoxicity than the silica-coated CoFe-MNPs. Moreover, the cancer cells seemed to be more susceptible to the CoFe-MNPs' toxicity compared to the noncancerous cells. There was a concentration and time-dependent increase in DNA damage and the micronucleus (MN) frequency, which was statistically significant starting with the lowest concentration of bare CoFe-MNPs (p < 0.05), while no significance was observed below the concentration of 250 μg mL-1 for the silica-coated MNPs. Also, the extent of both DNA damage and MN frequency was much higher in the cancer cells compared to the noncancerous cells. According to our results, the silica coating ameliorated both the cytotoxicity and genotoxicity as well the internalization of the CoFe-MNPs.

Pseudo-Mannosylated DC-SIGN Ligands as Immunomodulants

DC-SIGN, a C-type lectin mainly expressed by DCs, mediates antigen uptake and can induce specific immune responses, depending on the ligand involved. Owing to these properties, DC-SIGN is an attracting target for approaches aimed at tailoring the immune response towards specific immunologic outcomes. A multivalent DC-SIGN ligand (Polyman26), containing at its core a fluorescent "rod-like" spacer and able to inhibit DC-SIGN mediated HIV infection in nanomolar concentration, has been recently developed by our group. We investigated the internalization pattern and the ability of Polyman26 to elicit innate immune responses. Results obtained by confocal microscopy indicate that Polyman26 is internalized by DCs via receptor- mediated endocytosis and is then routed to endolysosomal compartments, thus being presented together with MHC class II molecules, with important implications for the development of vaccines. Moreover, Polyman26 up-regulated the production of β-chemokines and pro-inflammatory cytokines (including IL-1β, IL-6, IL-12, and TNFα) as well as the expression of TLR9 and CD40L. These results indicate that glycomimetic DC-SIGN ligands should be further investigated and suggest that these compounds could be used to differentially stimulate immune responses.

Trafficking Dynamics of PCSK9-Induced LDLR Degradation: Focus on Human PCSK9 Mutations and C-Terminal Domain

PCSK9 is a secreted ligand and negative post-translational regulator of low-density lipoprotein receptor (LDLR) in hepatocytes. Gain-of-function (GOF) or loss-of-function (LOF) mutations in PCSK9 are directly correlated with high or low plasma LDL-cholesterol levels, respectively. Therefore, PCSK9 is a prevailing lipid-lowering target to prevent coronary heart diseases and stroke. Herein, we fused monomeric fluorescent proteins to PCSK9 and LDLR to visualize their intra- and extracellular trafficking dynamics by live confocal microscopy. Fluorescence recovery after photobleaching (FRAP) showed that PCSK9 LOF R46L mutant and GOF mutations S127R and D129G, but not the LDLR high-affinity mutant D374Y, significantly accelerate PCSK9 exit from the endoplasmic reticulum (ER). Quantitative analysis of inverse FRAP revealed that only R46L presented a much slower trafficking from the trans-Golgi network (TGN) to the plasma membrane and a lower mobile fraction likely suggesting accumulation or delayed exit at the TGN as an underlying mechanism. While not primarily involved in LDLR binding, PCSK9 C-terminal domain (CTD) was found to be essential to induce LDLR degradation both upon its overexpression in cells or via the extracellular pathway. Our data revealed that PCSK9 CTD is required for the localization of PCSK9 at the TGN and increases its LDLR-mediated endocytosis. Interestingly, intracellular lysosomal targeting of PCSK9-ΔCTD was able to rescue its capacity to induce LDLR degradation emphasizing a role of the CTD in the sorting of PCSK9-LDLR complex towards late endocytic compartments. Finally, we validated our dual fluorescence system as a cell based-assay by preventing PCSK9 internalization using a PCSK9-LDLR blocking antibody, which may be expended to identify protein, peptide or small molecule inhibitors of PCSK9.

Control of protein trafficking by reversible masking of transport signals

A system for controlled trafficking of proteins is based on modifying the streptavidin-binding peptide with trafficking signals and appending it to reporter proteins. Coexpression with streptavidin results in signal masking, which is reversed upon biotin addition.

Systems that allow the control of protein traffic between subcellular compartments have been valuable in elucidating trafficking mechanisms. Most current approaches rely on ligand or light-controlled dimerization, which results in either retardation or enhancement of the transport of a reporter. We developed an alternative approach for trafficking regulation that we term “controlled unmasking of targeting elements” (CUTE). Regulated trafficking is achieved by reversible masking of the signal that directs the reporter to its target organelle, relying on the streptavidin–biotin system. The targeting signal is generated within or immediately after a 38–amino acid streptavidin-binding peptide (SBP) that is appended to the reporter. The binding of coexpressed streptavidin to SBP causes signal masking, whereas addition of biotin causes complex dissociation and triggers protein transport to the target organelle. We demonstrate the application of this approach to the control of nuclear and peroxisomal protein import and the generation of biotin-dependent trafficking through the endocytic and COPI systems. By simultaneous masking of COPI and endocytic signals, we were able to generate a synthetic pathway for efficient transport of a reporter from the plasma membrane to the endoplasmic reticulum.

Lactose-modified DNA tile nanostructures as drug carriers

BACKGROUND

DNA hybridization allows the preparation of nanoscale DNA structures with desired shape and size. DNA structures using simple base pairing can be used for the delivery of drug molecules into the cells. Since DNA carries multiple negative charges, their cellular uptake efficiency is low. Thus, the modification of the DNA structures with molecules that may enhance the cellular internalization may be an option.

OBJECTIVE

The objective of this study is to construct DNA-based nanocarrier system and to investigate the cellular uptake of DNA tile with/without lactose modification.

METHODS

Doxorubicin was intercalated to DNA tile and cellular uptake of drug-loaded DNA-based carrier with/without lactose modification was investigated in vitro. HeLa, BT-474, and MDA-MB-231 cancer cells were used for cellular uptake studies and cytotoxicity assays. Using fluorescence spectroscopy, flow cytometry, and confocal microscopy, cellular uptake behavior of DNA tile was investigated. The cytotoxicity of DNA tile structures was determined with WST-1 assay.

RESULTS

The results show that modification with lactose effectively increases the intracellular uptake of doxorubicin loaded DNA tile structure by cancer cells compared with the unmodified DNA tile.

CONCLUSION

The findings of this study suggest that DNA-based nanostructures modified with carbohydrates can be used as suitable multifunctional nanocarriers with simple chemical modifications.

Prion protein "gamma-cleavage": characterizing a novel endoproteolytic processing event

The cellular prion protein (PrP(C)) is a ubiquitously expressed protein of currently unresolved but potentially diverse function. Of putative relevance to normal biological activity, PrP(C) is recognized to undergo both α- and β-endoproteolysis, producing the cleavage fragment pairs N1/C1 and N2/C2, respectively. Experimental evidence suggests the likelihood that these processing events serve differing cellular needs. Through the engineering of a C-terminal c-myc tag onto murine PrP(C), as well as the selective use of a far-C-terminal anti-PrP antibody, we have identified a new PrP(C) fragment, nominally 'C3', and elaborating existing nomenclature, 'γ-cleavage' as the responsible proteolysis. Our studies indicate that this novel γ-cleavage event can occur during transit through the secretory pathway after exiting the endoplasmic reticulum, and after PrP(C) has reached the cell surface, by a matrix metalloprotease. We found that C3 is GPI-anchored like other C-terminal and full length PrP(C) species, though it does not localize primarily at the cell surface, and is preferentially cleaved from an unglycosylated substrate. Importantly, we observed that C3 exists in diverse cell types as well as mouse and human brain tissue, and of possible pathogenic significance, γ-cleavage may increase in human prion diseases. Given the likely relevance of PrP(C) processing to both its normal function, and susceptibility to prion disease, the potential importance of this previously underappreciated and overlooked cleavage event warrants further consideration.

Dual pulse-chase microscopy reveals early divergence in the biosynthetic trafficking of the Na,K-ATPase and E-cadherin

The trafficking of newly synthesized Na,K-ATPase and E-cadherin is observed in polarized epithelial cells. E-cadherin’s exit from the Golgi complex is not susceptible to 19°C temperature block. Furthermore, these proteins exit the Golgi and are delivered to the basolateral cell surface in separate vascular carriers.

Recent evidence indicates that newly synthesized membrane proteins that share the same distributions in the plasma membranes of polarized epithelial cells can pursue a variety of distinct trafficking routes as they travel from the Golgi complex to their common destination at the cell surface. In most polarized epithelial cells, both the Na,K-ATPase and E-cadherin are localized to the basolateral domains of the plasma membrane. To examine the itineraries pursued by newly synthesized Na,K-ATPase and E-cadherin in polarized MDCK epithelial cells, we used the SNAP and CLIP labeling systems to fluorescently tag temporally defined cohorts of these proteins and observe their behaviors simultaneously as they traverse the secretory pathway. These experiments reveal that E-cadherin is delivered to the cell surface substantially faster than is the Na,K-ATPase. Furthermore, the surface delivery of newly synthesized E-cadherin to the plasma membrane was not prevented by the 19°C temperature block that inhibits the trafficking of most proteins, including the Na,K-ATPase, out of the trans-Golgi network. Consistent with these distinct behaviors, populations of newly synthesized E-cadherin and Na,K-ATPase become separated from one another within the trans-Golgi network, suggesting that they are sorted into different carrier vesicles that mediate their post-Golgi trafficking.

Hypothermic Preconditioning of Human Cortical Neurons Requires Proteostatic Priming

Hypothermia is potently neuroprotective but poor mechanistic understanding has restricted its clinical use. Rodent studies indicate that hypothermia can elicit preconditioning, wherein a subtoxic cellular stress confers resistance to an otherwise lethal injury. The molecular basis of this preconditioning remains obscure. Here we explore molecular effects of cooling using functional cortical neurons differentiated from human pluripotent stem cells (hCNs). Mild-to-moderate hypothermia (28–32 °C) induces cold-shock protein expression and mild endoplasmic reticulum (ER) stress in hCNs, with full activation of the unfolded protein response (UPR). Chemical block of a principal UPR pathway mitigates the protective effect of cooling against oxidative stress, whilst pre-cooling neurons abrogates the toxic injury produced by the ER stressor tunicamycin. Cold-stress thus preconditions neurons by upregulating adaptive chaperone-driven pathways of the UPR in a manner that precipitates ER-hormesis. Our findings establish a novel arm of neurocryobiology that could reveal multiple therapeutic targets for acute and chronic neuronal injury.

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Clinically-relevant cooling induces archetypal cold-shock and mild endoplasmic reticulum (ER) stress in human neurons.

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Hypothermic neuronal ER-stress elicits an adaptive unfolded protein response (UPR) with ER-hormesis.

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Hypothermic preconditioning of the ER provides cross-tolerance to oxidative neuronal injury and requires an intact UPR.

Cell uptake mechanisms of glycosylated cationic pDNA–cyclodextrin nanoparticles

β-Cyclodextrin-based glycoCDplexes are internalized through several redundant pathways whose relative prevalence depends on the coating sugar and on the cell line.

Starvation and inhibition of lysosomal function increased tau secretion by primary cortical neurons

Recent studies have demonstrated that human tau can be secreted by neurons and non-neuronal cells, an event linked to the propagation of tau pathology in the brain. In the present study, we confirmed that under physiological conditions, one tau-positive band was detected in the culture medium with an anti-tau antibody recognizing total tau and the Tau-1 antibody directed against unphosphorylated tau. We then examined whether tau secretion was modified upon insults. Tau secretion was increased by starvation [Earle's Balanced Salt Solution (EBSS)], inhibition of lysosomal function (leupeptin) and when both of these conditions were superimposed, this combined treatment having the most important effects on tau secretion. Interestingly, the pattern of tau secretion was distinct from that of control neurons when neurons were treated either with EBSS alone or EBSS + leupeptin. In these conditions, three tau-positive bands were detected in the culture medium. Two of these three bands were immunoreactive to Tau-1 antibody revealing that at least two tau species were released upon these treatments. Collectively, our results indicate that insults such as nutrient deprivation and lysosomal dysfunction observed in neurodegenerative diseases could result in an increase of tau secretion and propagation of tau pathology in the brain.

Enhanced cellular uptake of short polyarginine peptides through fatty acylation and cyclization

Many of the reported arginine-rich cell-penetrating peptides (CPPs) for the enhanced delivery of drugs are linear peptides composed of more than seven arginine residues to retain the cell penetration properties. Herein, we synthesized a class of nine polyarginine peptides containing 5 and 6 arginines, namely, R₅ and R₆. We further explored the effect of acylation with long chain fatty acids (i.e., octanoic acid, dodecanoic acid, and hexadecanoic acid) and cyclization on the cell penetrating properties of the peptides. The fluorescence-labeled acylated cyclic peptide dodecanoyl-[R₅] and linear peptide dodecanoyl-(R₅) showed approximately 13.7- and 10.2-fold higher cellular uptake than that of control 5,6-carboxyfluorescein, respectively. The mechanism of the peptide internalization into cells was found to be energy-dependent endocytosis. Dodecanoyl-[R₅] and dodecanoyl-[R₆] enhanced the intracellular uptake of a fluorescence-labeled cell-impermeable negatively charged phosphopeptide (F′-GpYEEI) in human ovarian cancer cells (SK-OV-3) by 3.4-fold and 5.5-fold, respectively, as shown by flow cytometry. The cellular uptake of F′-GpYEEI in the presence of hexadecanoyl-[R₅] was 9.3- and 6.0-fold higher than that in the presence of octanoyl-[R₅] and dodecanoyl-[R₅], respectively. Dodecanoyl-[R₅] enhanced the cellular uptake of the phosphopeptide by 1.4–2.5-fold higher than the corresponding linear peptide dodecanoyl-(R₅) and those of representative CPPs, such as hepta-arginine (CR₇) and TAT peptide. These results showed that a combination of acylation by long chain fatty acids and cyclization on short arginine-containing peptides can improve their cell-penetrating property, possibly through efficient interaction of rigid positively charged R and hydrophobic dodecanoyl moiety with the corresponding residues in the cell membrane phospholipids.

Structure and dynamics of thylakoids in land plants

Thylakoids of land plants have a bipartite structure, consisting of cylindrical grana stacks, made of membranous discs piled one on top of the other, and stroma lamellae which are helically wound around the cylinders. Protein complexes predominantly located in the stroma lamellae and grana end membranes are either bulky [photosystem I (PSI) and the chloroplast ATP synthase (cpATPase)] or are involved in cyclic electron flow [the NAD(P)H dehydrogenase (NDH) and PGRL1-PGR5 heterodimers], whereas photosystem II (PSII) and its light-harvesting complex (LHCII) are found in the appressed membranes of the granum. Stacking of grana is thought to be due to adhesion between Lhcb proteins (LHCII or CP26) located in opposed thylakoid membranes. The grana margins contain oligomers of CURT1 proteins, which appear to control the size and number of grana discs in a dosage- and phosphorylation-dependent manner. Depending on light conditions, thylakoid membranes undergo dynamic structural changes that involve alterations in granum diameter and height, vertical unstacking of grana, and swelling of the thylakoid lumen. This plasticity is realized predominantly by reorganization of the supramolecular structure of protein complexes within grana stacks and by changes in multiprotein complex composition between appressed and non-appressed membrane domains. Reversible phosphorylation of LHC proteins (LHCPs) and PSII components appears to initiate most of the underlying regulatory mechanisms. An update on the roles of lipids, proteins, and protein complexes, as well as possible trafficking mechanisms, during thylakoid biogenesis and the de-etiolation process complements this review.

Influence of surface chemistry on cytotoxicity and cellular uptake of nanocapsules in breast cancer and phagocytic cells

The present work tests the hypothesis that stabilizers have a critical role on nanocarrier stealthiness and anticancer drug efficacy. Two different types of docetaxel (Doc)-loaded nanocapsules (NCs) stabilized with polysorbate 80 (NC(T80)) and polyvinyl alcohol (NC(PVA)) were synthesized using the emulsion solvent diffusion method. These NCs were characterized for particle mean diameter (PMD), drug content, morphology, surface composition, and degree of crystallinity. Furthermore, the cytotoxicity and cellular uptake of the NCs were investigated in MDA-MB 231 cells, THP-1 monocytes, and THP-1-derived macrophages. The optimized spherical NC(T80) had 123.02 ± 14.6 nm, 0.27 ± 0.1, and 101 ± 37.0% for PMD, polydispersity index, and drug encapsulation efficiency, respectively. Doc release kinetics from NC(T80) and NC(PVA) mostly provided better fit to zero-order and Higuchi models, respectively. Powder X-ray diffraction (PXRD) and X-ray photoelectron spectroscopy (XPS) results revealed the presence of amorphous stabilizers on the surface of the NCs. At high drug concentration, the cytotoxicity of NC(T80) was substantially improved (1.3-1.6-fold) compared with that of NC(PVA) in MDA-MB 231 cells. The uptake of both NCs was inhibited by latrunculin A and dynasore, indicating an actin- and dynamin-dependent endocytosis in MDA-MB 231 cells. This occurred via a multifaceted mechanism involving clathrin, caveolin, cytoskeleton, and macropinocytosis. Interestingly, the uptake of NC(PVA) was 2.7-fold greater than that of NC(T80) and occurred through phagocytosis in monocytes and macrophages. This study demonstrates the potential impact of the surface chemistry on the cytotoxicity and phagocytic clearance of nanocarriers for a subsequent improvement of the efficacy of Doc intended for breast cancer chemotherapy.

Arf4 is required for Mammalian development but dispensable for ciliary assembly

The primary cilium is a sensory organelle, defects in which cause a wide range of human diseases including retinal degeneration, polycystic kidney disease and birth defects. The sensory functions of cilia require specific receptors to be targeted to the ciliary subdomain of the plasma membrane. Arf4 has been proposed to sort cargo destined for the cilium at the Golgi complex and deemed a key regulator of ciliary protein trafficking. In this work, we show that Arf4 binds to the ciliary targeting sequence (CTS) of fibrocystin. Knockdown of Arf4 indicates that it is not absolutely required for trafficking of the fibrocystin CTS to cilia as steady-state CTS levels are unaffected. However, we did observe a delay in delivery of newly synthesized CTS from the Golgi complex to the cilium when Arf4 was reduced. Arf4 mutant mice are embryonic lethal and die at mid-gestation shortly after node formation. Nodal cilia appeared normal and functioned properly to break left-right symmetry in Arf4 mutant embryos. At this stage of development Arf4 expression is highest in the visceral endoderm but we did not detect cilia on these cells. In the visceral endoderm, the lack of Arf4 caused defects in cell structure and apical protein localization. This work suggests that while Arf4 is not required for ciliary assembly, it is important for the efficient transport of fibrocystin to cilia, and also plays critical roles in non-ciliary processes.

Primary cilia are ubiquitous sensory organelles that play vital roles in an ever-growing class of human diseases termed ciliopathies including obesity, retinal degeneration and polycystic kidney disease. The proper function of the primary cilium relies on a cell's ability to target and concentrate specific receptors to the ciliary membrane – a unique subdomain of the plasma membrane yet little is known about how receptors are trafficked to the primary cilium. Mutations affecting the ciliary localized receptor fibrocystin (PKHD1) cause autosomal recessive polycystic kidney disease, which affects approximately 1∶20,000 individuals. Previously we identified a motif located in the cytoplasmic domain of fibrocystin that is required for its ciliary localization. In this work we demonstrate that the ciliary targeting sequence (CTS) of fibrocystin interacts with the small G protein Arf4 and this interaction is important for the efficient delivery of the CTS to cilia in cultured cells. Disruption of Arf4 in mice results in defects in the non-ciliated visceral endoderm and death at mid-gestation indicating Arf4 has vital functions in addition to ciliary protein trafficking.

Spreading of tau pathology in Alzheimer's disease by cell-to-cell transmission

It is well documented that neurofibrillary tangles composed of aggregated tau protein propagate in a predictable pattern in Alzheimer's disease (AD). The mechanisms underlying the propagation of tau pathology are still poorly understood. Recent studies have provided solid data demonstrating that in several neurodegenerative diseases including AD, the spreading of misfolded protein aggregates in the brain would result from prion-like cell-to-cell transmission. Consistent with this new concept, recent studies have reported that human tau can be released in the extracellular space by an active process of secretion, and can be endocytosed both in vitro and in vivo. Most importantly, it was reported that the spreading of tau pathology was observed along synaptically connected circuits in a transgenic mouse model where human tau overexpression was restricted in the entorhinal cortex. This indicates that secretion of tau by presynaptic neurons and its uptake by postsynaptic neurons could be the sequential events leading to the propagation of tau pathology in the brain.

A role for cargo in Arf-dependent adaptor recruitment

Membrane traffic requires the specific concentration of protein cargos and exclusion of other proteins into nascent carriers. Critical components of this selectivity are the protein adaptors that bind to short, linear motifs in the cytoplasmic tails of transmembrane protein cargos and sequester them into nascent carriers. The recruitment of the adaptors is mediated by activated Arf GTPases, and the Arf-adaptor complexes mark sites of carrier formation. However, the nature of the signal(s) that initiates carrier biogenesis remains unknown. We examined the specificity and initial sites of recruitment of Arf-dependent adaptors (AP-1 and GGAs) in response to the Golgi or endosomal localization of specific cargo proteins (furin, mannose-6-phosphate receptor (M6PR), and M6PR lacking a C-terminal domain M6PRΔC). We find that cargo promotes the recruitment of specific adaptors, suggesting that it is part of an upstream signaling event. Cargos do not promote adaptor recruitment to all compartments in which they reside, and thus additional factors regulate the cargo's ability to promote Arf activation and adaptor recruitment. We document that within a given compartment different cargos recruit different adaptors, suggesting that there is little or no free, activated Arf at the membrane and that Arf activation is spatially and temporally coupled to the cargo and the adaptor. Using temperature block, brefeldin A, and recovery from each, we found that the cytoplasmic tail of M6PR causes the recruitment of AP-1 and GGAs to recycling endosomes and not at the Golgi, as predicted by steady state staining profiles. These results are discussed with respect to the generation of novel models for cargo-dependent regulation of membrane traffic.

Analysis of ciliary membrane protein dynamics using SNAP technology

The sensory functions of the primary cilium rely on receptors and other membrane proteins that are specifically sorted to the ciliary compartment, which is a subdomain of the plasma membrane. Defects in this process underlie a large number of human diseases, yet it is poorly understood. Thus, it is of great interest to understand the mechanisms by which the cell sorts and traffics proteins to the ciliary membrane. Here, we provide an overview of our method to study the sorting and trafficking of ciliary membrane proteins using SNAP technology. This technology enables pulse-chase analysis of the movement of proteins through the endomembrane system and onto the cilium.

Translation suppression promotes stress granule formation and cell survival in response to cold shock

Cells respond to stress by inhibition of protein synthesis and subsequent assembly of stress granules (SGs). Cold shock is identified as a novel trigger of SG assembly in yeast and mammals. Cells actively suppress protein synthesis by parallel pathways to induce SG formation and ensure cellular survival at low temperatures.

Cells respond to different types of stress by inhibition of protein synthesis and subsequent assembly of stress granules (SGs), cytoplasmic aggregates that contain stalled translation preinitiation complexes. Global translation is regulated through the translation initiation factor eukaryotic initiation factor 2α (eIF2α) and the mTOR pathway. Here we identify cold shock as a novel trigger of SG assembly in yeast and mammals. Whereas cold shock–induced SGs take hours to form, they dissolve within minutes when cells are returned to optimal growth temperatures. Cold shock causes eIF2α phosphorylation through the kinase PERK in mammalian cells, yet this pathway is not alone responsible for translation arrest and SG formation. In addition, cold shock leads to reduced mitochondrial function, energy depletion, concomitant activation of AMP-activated protein kinase (AMPK), and inhibition of mTOR signaling. Compound C, a pharmacological inhibitor of AMPK, prevents the formation of SGs and strongly reduces cellular survival in a translation-dependent manner. Our results demonstrate that cells actively suppress protein synthesis by parallel pathways, which induce SG formation and ensure cellular survival during hypothermia.

Mon1a protein acts in trafficking through the secretory apparatus

Mon1a was originally identified as a modifier gene of vesicular traffic, as a mutant Mon1a allele resulted in increased localization of cell surface proteins, whereas reduced levels of Mon1a showed decreased secretory activity. Here we show that Mon1a affects different steps in the secretory pathway including endoplasmic reticulum-to-Golgi traffic. siRNA-dependent reduction of Mon1a levels resulted in a delay in the reformation of the Golgi apparatus after Brefeldin A treatment. Endoglycosidase H treatment of ts045VSVG-GFP confirmed that knockdown of Mon1a delayed endoplasmic reticulum-to-Golgi trafficking. Reductions in Mon1a also resulted in delayed trafficking from Golgi to the plasma membrane. Immunoprecipitation and mass spectrometry analysis showed that Mon1a associates with dynein intermediate chain. Reductions in Mon1a or dynein altered steady state Golgi morphology. Reductions in Mon1a delayed formation of ERGIC-53-positive vesicles, whereas reductions in dynein did not affect vesicle formation. These data provide strong evidence for a role for Mon1a in anterograde trafficking through the secretory apparatus.

Hyperphosphorylation and cleavage at D421 enhance tau secretion

It is well established that tau pathology propagates in a predictable manner in Alzheimer’s disease (AD). Moreover, tau accumulates in the cerebrospinal fluid (CSF) of AD’s patients. The mechanisms underlying the propagation of tau pathology and its accumulation in the CSF remain to be elucidated. Recent studies have reported that human tau was secreted by neurons and non-neuronal cells when it was overexpressed indicating that tau secretion could contribute to the spreading of tau pathology in the brain and could lead to its accumulation in the CSF. In the present study, we showed that the overexpression of human tau resulted in its secretion by Hela cells. The main form of tau secreted by these cells was cleaved at the C-terminal. Surprisingly, secreted tau was dephosphorylated at several sites in comparison to intracellular tau which presented a strong immunoreactivity to all phospho-dependent antibodies tested. Our data also revealed that phosphorylation and cleavage of tau favored its secretion by Hela cells. Indeed, the mimicking of phosphorylation at 12 sites known to be phosphorylated in AD enhanced tau secretion. A mutant form of tau truncated at D421, the preferential cleavage site of caspase-3, was also significantly more secreted than wild-type tau. Taken together, our results indicate that hyperphosphorylation and cleavage of tau by favoring its secretion could contribute to the propagation of tau pathology in the brain and its accumulation in the CSF.

ADP-ribosylation factor 1 protein regulates trypsinogen activation via organellar trafficking of procathepsin B protein and autophagic maturation in acute pancreatitis

Several studies have suggested that autophagy might play a deleterious role in acute pancreatitis via intra-acinar activation of digestive enzymes. The prototype for this phenomenon is cathepsin B-mediated trypsin generation. To determine the organellar basis of this process, we investigated the subcellular distribution of the cathepsin B precursor, procathepsin B. We found that procathepsin B is enriched in Golgi-containing microsomes, suggesting a role for the ADP-ribosylation (ARF)-dependent trafficking of cathepsin B. Indeed, caerulein treatment increased processing of procathepsin B, whereas a known ARF inhibitor brefeldin A (BFA) prevented this. Similar treatment did not affect processing of procathepsin L. BFA-mediated ARF1 inhibition resulted in reduced cathepsin B activity and consequently reduced trypsinogen activation. However, formation of light chain 3 (LC3-II) was not affected, suggesting that BFA did not prevent autophagy induction. Instead, sucrose density gradient centrifugation and electron microscopy showed that BFA arrested caerulein-induced autophagosomal maturation. Therefore, ARF1-dependent trafficking of procathepsin B and the maturation of autophagosomes results in cathepsin B-mediated trypsinogen activation induced by caerulein.

Electron tomography reveals Rab6 is essential to the trafficking of trans-Golgi clathrin and COPI-coated vesicles and the maintenance of Golgi cisternal number

We have shown previously that Rab6, a small, trans-Golgi-localized GTPase, acts upstream of the conserved oligomeric Golgi complex (COG) and ZW10/RINT1 retrograde tether complexes to maintain Golgi homeostasis. In this article, we present evidence from the unbiased and high-resolution approach of electron microscopy and electron tomography that Rab6 is essential to the trans-Golgi trafficking of two morphological classes of coated vesicles; the larger corresponds to clathrin-coated vesicles and the smaller to coat protein I (COPI)-coated vesicles. On the basis of the site of coated vesicle accumulation, cisternal dilation and the normal kinetics of cargo transport from the endoplasmic reticulum (ER) to Golgi followed by delayed Golgi to cell surface transport, we suggest that Golgi function in cargo transport is preferentially inhibited at the trans-Golgi/trans-Golgi network (TGN). The >50% increase in Golgi cisternae number in Rab6-depleted HeLa cells that we observed may well be coupled to the trans-Golgi accumulation of COPI-coated vesicles; depletion of the individual Rab6 effector, myosin IIA, produced an accumulation of uncoated vesicles with if anything a decrease in cisternal number. These results are the first evidence for a Rab6-dependent protein machine affecting Golgi-proximal, coated vesicle accumulation and probably transport at the trans-Golgi and the first example of concomitant cisternal proliferation and increased Golgi stack organization under inhibited transport conditions.

Class II ADP-ribosylation factors are required for efficient secretion of dengue viruses

Identification and characterization of virus-host interactions are very important steps toward a better understanding of the molecular mechanisms responsible for disease progression and pathogenesis. To date, very few cellular factors involved in the life cycle of flaviviruses, which are important human pathogens, have been described. In this study, we demonstrate a crucial role for class II Arf proteins (Arf4 and Arf5) in the dengue flavivirus life cycle. We show that simultaneous depletion of Arf4 and Arf5 blocks recombinant subviral particle secretion for all four dengue serotypes. Immunostaining analysis suggests that class II Arf proteins are required at an early pre-Golgi step for dengue virus secretion. Using a horseradish peroxidase protein fused to a signal peptide, we show that class II Arfs act specifically on dengue virus secretion without altering the secretion of proteins through the constitutive secretory pathway. Co-immunoprecipitation data demonstrate that the dengue prM glycoprotein interacts with class II Arf proteins but not through its C-terminal VXPX motif. Finally, experiments performed with replication-competent dengue and yellow fever viruses demonstrate that the depletion of class II Arfs inhibits virus secretion, thus confirming their implication in the virus life cycle, although data obtained with West Nile virus pointed out the differences in virus-host interactions among flaviviruses. Our findings shed new light on a molecular mechanism used by dengue viruses during the late stages of the life cycle and demonstrate a novel function for class II Arf proteins.

Effects of transport inhibitors on the cellular uptake of carboxylated polystyrene nanoparticles in different cell lines

Nanotechnology is expected to play a vital role in the rapidly developing field of nanomedicine, creating innovative solutions and therapies for currently untreatable diseases, and providing new tools for various biomedical applications, such as drug delivery and gene therapy. In order to optimize the efficacy of nanoparticle (NP) delivery to cells, it is necessary to understand the mechanisms by which NPs are internalized by cells, as this will likely determine their ultimate sub-cellular fate and localisation. Here we have used pharmacological inhibitors of some of the major endocytic pathways to investigate nanoparticle uptake mechanisms in a range of representative human cell lines, including HeLa (cervical cancer), A549 (lung carcinoma) and 1321N1 (brain astrocytoma). Chlorpromazine and genistein were used to inhibit clathrin and caveolin mediated endocytosis, respectively. Cytochalasin A and nocodazole were used to inhibit, respectively, the polymerisation of actin and microtubule cytoskeleton. Uptake experiments were performed systematically across the different cell lines, using carboxylated polystyrene NPs of 40 nm and 200 nm diameters, as model NPs of sizes comparable to typical endocytic cargoes. The results clearly indicated that, in all cases and cell types, NPs entered cells via active energy dependent processes. NP uptake in HeLa and 1321N1 cells was strongly affected by actin depolymerisation, while A549 cells showed a stronger inhibition of NP uptake (in comparison to the other cell types) after microtubule disruption and treatment with genistein. A strong reduction of NP uptake was observed after chlorpromazine treatment only in the case of 1321N1 cells. These outcomes suggested that the same NP might exploit different uptake mechanisms to enter different cell types.

The ceramide-enriched trans-Golgi compartments reorganize together with other parts of the Golgi apparatus in response to ATP-depletion

In this study, the ceramide-enriched trans-Golgi compartments representing sites of synthesis of sphingomyelin and higher organized lipids were visualized in control and ATP-depleted hepatoma and endothelial cells using internalization of BODIPY-ceramide and the diaminobenzidine photooxidation method for combined light-electron microscopical exploration. Metabolic stress induced by lowering the cellular ATP-levels leads to reorganizations of the Golgi apparatus and the appearance of tubulo-glomerular bodies and networks. The results obtained with three different protocols, in which BODIPY-ceramide either was applied prior to, concomitantly with, or after ATP-depletion, revealed that the ceramide-enriched compartments reorganize together with other parts of the Golgi apparatus under these conditions. They were found closely associated with and integrated in the tubulo-glomerular bodies formed in response to ATP-depletion. This is in line with the changes of the staining patterns obtained with the Helix pomatia lectin and the GM130 and TGN46 immuno-reactions occurring in response to ATP-depletion and is confirmed by 3D electron tomography. The 3D reconstructions underlined the glomerular character of the reorganized Golgi apparatus and demonstrated continuities of ceramide positive and negative parts. Most interestingly, BODIPY-ceramide becomes concentrated in compartments of the tubulo-glomerular Golgi bodies, even though the reorganization took place before BODIPY-ceramide administration. This indicates maintained functionalities although the regular Golgi stack organization is abolished; the results provide novel insights into Golgi structure-function relationships, which might be relevant for cells affected by metabolic stress.

Inner/Outer nuclear membrane fusion in nuclear pore assembly: biochemical demonstration and molecular analysis

Nuclear pore complexes (NPCs) are large proteinaceous channels embedded in double nuclear membranes, which carry out nucleocytoplasmic exchange. The mechanism of nuclear pore assembly involves a unique challenge, as it requires creation of a long-lived membrane-lined channel connecting the inner and outer nuclear membranes. This stabilized membrane channel has little evolutionary precedent. Here we mapped inner/outer nuclear membrane fusion in NPC assembly biochemically by using novel assembly intermediates and membrane fusion inhibitors. Incubation of a Xenopus in vitro nuclear assembly system at 14°C revealed an early pore intermediate where nucleoporin subunits POM121 and the Nup107-160 complex were organized in a punctate pattern on the inner nuclear membrane. With time, this intermediate progressed to diffusion channel formation and finally to complete nuclear pore assembly. Correct channel formation was blocked by the hemifusion inhibitor lysophosphatidylcholine (LPC), but not if a complementary-shaped lipid, oleic acid (OA), was simultaneously added, as determined with a novel fluorescent dextran-quenching assay. Importantly, recruitment of the bulk of FG nucleoporins, characteristic of mature nuclear pores, was not observed before diffusion channel formation and was prevented by LPC or OA, but not by LPC+OA. These results map the crucial inner/outer nuclear membrane fusion event of NPC assembly downstream of POM121/Nup107-160 complex interaction and upstream or at the time of FG nucleoporin recruitment.