The function of intermediate filaments in cell shape and cytoskeletal integrity

Leukamenin E, an ent-kaurane diterpenoid, is a novel and potential keratin intermediate filament inhibitor

Many ent-kaurane diterpenoids exhibit notable antitumor activity in vitro and in vivo, and some have been used as cancer therapeutic agents in China. In this study, we identified a novel molecular target of leukamenin E, an ent-kaurane diterpenoid, using an available whole-cell model in combination with immunofluorescence imaging and mass spectrometry (MS). The cytoskeleton-disrupting drugs cytochalasin B and colchicine caused the depolymerization of microfilaments and the collapse of microtubules and vimentin filaments, respectively, but had little effects on HepG2 and NCI-H1299 cells spreading as well as keratin filament (KF) reassembly, indicating that KFs are involved in cell spreading. Leukamenin E blocked HepG2 and NCI-H1299 cells adhesion/spreading and KF reassembly at subtoxic concentrations, indicating that leukamenin E may target KFs. Moreover, leukamenin E, at 3 μM for 24 h or 10 μM for 3 h, induced massive KF depolymerization in well-spread HepG2 and NCI-H1299 cells treated with/without cytochalasin B and colchicine. MS analysis indicated that leukamenin E could covalently modify amino acid residue(s) in a synthetic peptide based on keratin 1 and keratin 10 sequences, suggesting that covalent modification of the synthetic peptide by leukamenin E caused assembly inhibition or disrupted KF polymerization in HepG2 and NCI-H1299 cells. In addition, acridine orange/ethidium bromide staining and western blotting confirmed that there was no correlation between the KF-disrupting effects and apoptosis or keratin expression. Thus, we propose that leukamenin E is a novel inhibitor of KF assembly, and as such, can serve as a chemical probe of KF functions and a potential molecular target for ent-kaurane diterpenoid-based therapeutics.

Probe Sensitivity to Cortical versus Intracellular Cytoskeletal Network Stiffness

In development, wound healing, and pathology, cell biomechanical properties are increasingly recognized as being of central importance. To measure these properties, experimental probes of various types have been developed, but how each probe reflects the properties of heterogeneous cell regions has remained obscure. To better understand differences attributable to the probe technology, as well as to define the relative sensitivity of each probe to different cellular structures, here we took a comprehensive approach. We studied two cell types-Schlemm's canal endothelial cells and mouse embryonic fibroblasts (MEFs)-using four different probe technologies: 1) atomic force microscopy (AFM) with sharp tip, 2) AFM with round tip, 3) optical magnetic twisting cytometry (OMTC), and 4) traction microscopy (TM). Perturbation of Schlemm's canal cells with dexamethasone treatment, α-actinin overexpression, or RhoA overexpression caused increases in traction reported by TM and stiffness reported by sharp-tip AFM as compared to corresponding controls. By contrast, under these same experimental conditions, stiffness reported by round-tip AFM and by OMTC indicated little change. Knockout (KO) of vimentin in MEFs caused a diminution of traction reported by TM, as well as stiffness reported by sharp-tip and round-tip AFM. However, stiffness reported by OMTC in vimentin-KO MEFs was greater than in wild type. Finite-element analysis demonstrated that this paradoxical OMTC result in vimentin-KO MEFs could be attributed to reduced cell thickness. Our results also suggest that vimentin contributes not only to intracellular network stiffness but also cortex stiffness. Taken together, this evidence suggests that AFM sharp tip and TM emphasize properties of the actin-rich shell of the cell, whereas round-tip AFM and OMTC emphasize those of the noncortical intracellular network.

Vincristine Impairs Microtubules and Causes Neurotoxicity in Cerebral Organoids

The advance of nanotechnology in drug delivery systems has allowed central nervous system (CNS) accumulation of several anti-tumor agents with poor brain penetration but also lead to concerns about central neurotoxicity. Vincristine is commonly administered as an effective anti-brain tumor drug. It is known to act by interfering with microtubule dynamics, but models for detailed elucidation of its mechanism of neurotoxicity are limited. Here we generated cerebral organoids using human-induced pluripotent stem cells (iPSCs) for evaluation of neurotoxic mechanisms. Cerebral organoids were treated with different concentrations of vincristine for 48 h and their expansion was measured. We also assayed various cell markers, microtubule associated proteins, and matrix metalloproteinases (MMP) in cerebral organoids. After treatment for 48 h, we observed dose-dependent neurotoxicity, including reduced neuron and astrocyte numbers at high concentration. Vincristine treatment also impaired the microtubule-associated protein tubulin, and fibronectin, and downregulated MMP10 activity. Further analysis using the STRING database found that, both MMP10 and fibronectin bind with MMP9 experimentally, and text-mining indicated an interaction between MMP10 and fibronectin. Our organoid model system allowed quantitative investigation of the effects of vincristine treatment. Our findings indicated vincristine exhibited dose-dependent neurotoxicity, inhibited fibronectin, tubulin, and MMP10 expression in cerebral organoids.

A shear assay study of single normal/breast cancer cell deformation and detachment from poly-di-methyl-siloxane (PDMS) surfaces

This paper presents the results of a combined experimental and analytical/computational study of viscoelastic cell deformation and detachment from poly-di-methyl-siloxane (PDMS) surfaces. Fluid mechanics and fracture mechanics concepts are used to model the detachment of biological cells observed under shear assay conditions. The analytical and computational models are used to compute crack driving forces, which are then related to crack extension during the detachment of normal breast cells and breast cancer cells from PDMS surfaces that are relevant to biomedical implants. The interactions between cells and the extracellular matrix, or the extracellular matrix and the PDMS substrate, are then characterized using force microscopy measurements of the pull-off forces that are used to determine the adhesion energies. Finally, fluorescence microscopy staining of the cytosketelal structures (actin, micro-tubulin and cyto-keratin), transmembrane proteins (vimentin) and the ECM structures (Arginin Glycine Aspartate - RGD) is used to show that the detachment of cells during the shear assay experiments occurs via interfacial cracking between (between the ECM and the cell membranes) with a high incidence of crack bridging by transmembrane vinculin structures that undergo pull-out until they detach from the actin cytoskeletal structure. The implications of the results are discussed for the design of interfaces that are relevant to implantable biomedical devices and normal/cancer tissue.

Mouse Keratinocytes Without Keratin Intermediate Filaments Demonstrate Substrate Stiffness Dependent Behaviors

INTRODUCTION

Traditionally thought to serve active vs. passive mechanical functions, respectively, a growing body of evidence suggests that actin microfilament and keratin intermediate filament (IF) networks, together with their associated cell-cell and cell-matrix anchoring junctions, may have a large degree of functional interdependence. Therefore, we hypothesized that the loss of keratin IFs in a knockout mouse keratinocyte model would affect the kinematics of colony formation, i.e., the spatiotemporal process by which individual cells join to form colonies and eventually a nascent epithelial sheet.

METHODS

Time-lapse imaging and deformation tracking microscopy was used to observe colony formation for both wild type (WT) and keratin-deficient knockout (KO) mouse keratinocytes over 24 h. Cells were cultured under high calcium conditions on collagen-coated substrates with nominal stiffnesses of ~ 1.2 kPa (soft) and 24 kPa (stiff). Immunofluorescent staining of actin and selected adhesion proteins was also performed.

RESULTS

The absence of keratin IFs markedly affected cell morphology, spread area, and cytoskeleton and adhesion protein organization on both soft and stiff substrates. Strikingly, an absence of keratin IFs also significantly reduced the ability of mouse keratinocytes to mechanically deform the soft substrate. Furthermore, KO cells formed colonies more efficiently on stiff vs. soft substrates, a behavior opposite to that observed for WT keratinocytes.

CONCLUSIONS

Collectively, these data are strongly supportive of the idea that an interdependence between actin microfilaments and keratin IFs does exist, while further suggesting that keratin IFs may represent an important and under-recognized component of keratinocyte mechanosensation and the force generation apparatus.

The role of vimentin in the tumor marker Nup88-dependent multinucleated phenotype

Background

Nucleoporin Nup88, a component of nuclear pore complexes, is known to be overexpressed in several types of tumor tissue. The overexpression of Nup88 has been reported to promote the early step of tumorigenesis by inducing multinuclei in both HeLa cells and a mouse model. However, the molecular basis of how Nup88 leads to a multinucleated phenotype remains unclear because of a lack of information concerning its binding partners. In this study, we characterize a novel interaction between Nup88 and vimentin. We also examine the involvement of vimentin in the Nup88-dependent multinucleated phenotype.

Methods

Cells overexpressing tagged versions of Nup88, vimentin and their truncations were used in this study. Coprecipitation and GST-pulldown assays were carried out to analyze protein-protein interactions. Vimentin knockdown by siRNA was performed to examine the functional role of the Nup88-vimentin interaction in cells. The phosphorylation status of vimentin was analyzed by immunoblotting using an antibody specific for its phosphorylation site.

Results

Vimentin was identified as a Nup88 interacting partner, although it did not bind to other nucleoporins, such as Nup50, Nup214, and Nup358, in HeLa cell lysates. The N-terminal 541 amino acid residues of Nup88 was found to be responsible for its interaction with vimentin. Recombinant GST-tagged Nup88 bound to recombinant vimentin in a GST-pulldown assay. Although overexpression of Nup88 in HeLa cells was observed mainly at the nuclear rim and in the cytoplasm, colocalization with vimentin was only partially detected at or around the nuclear rim. Disruption of the Nup88-vimentin interaction by vimentin specific siRNA transfection suppressed the Nup88-dependent multinucleated phenotype. An excess amount of Nup88 in cell lysates inhibited the dephosphorylation of a serine residue (Ser83) within the vimentin N-terminal region even in the absence and presence of an exogenous phosphatase. The N-terminal 96 amino acid residues of vimentin interacted with both full-length and the N-terminal 541 residues of Nup88.

Conclusions

Nup88 can affect the phosphorylation status of vimentin, which may contribute to the Nup88-dependent multinucleated phenotype through changing the organization of vimentin.

Redox stress in Marfan syndrome: Dissecting the role of the NADPH oxidase NOX4 in aortic aneurysm

Marfan syndrome (MFS) is characterized by the formation of ascending aortic aneurysms resulting from altered assembly of extracellular matrix fibrillin-containing microfibrils and dysfunction of TGF-β signaling. Here we identify the molecular targets of redox stress in aortic aneurysms from MFS patients, and investigate the role of NOX4, whose expression is strongly induced by TGF-β, in aneurysm formation and progression in a murine model of MFS. Working models included aortae and cultured vascular smooth muscle cells (VSMC) from MFS patients, and a NOX4-deficient Marfan mouse model (Fbn1^C1039G/+-Nox4^-/-). Increased tyrosine nitration and reactive oxygen species levels were found in the tunica media of human aortic aneurysms and in cultured VSMC. Proteomic analysis identified nitrated and carbonylated proteins, which included smooth muscle α-actin (αSMA) and annexin A2. NOX4 immunostaining increased in the tunica media of human Marfan aorta and was transcriptionally overexpressed in VSMC. Fbn1^C1039G/+-Nox4^-/- mice aortas showed a reduction of fragmented elastic fibers, which was accompanied by an amelioration in the Marfan-associated enlargement of the aortic root. Increase in the contractile phenotype marker calponin in the tunica media of MFS mice aortas was abrogated in Fbn1^C1039G/+-Nox4^-/- mice. Endothelial dysfunction evaluated by myography in the Marfan ascending aorta was prevented by the absence of Nox4 or catalase-induced H₂O₂ decomposition. We conclude that redox stress occurs in MFS, whose targets are actin-based cytoskeleton members and regulators of extracellular matrix homeostasis. Likewise, NOX4 have an impact in the progression of the aortic dilation in MFS and in the structural organization of the aortic tunica media, the VSMC phenotypic modulation, and endothelial function.

A proteomic profile of postpartum cervical repair in mice

A timely and complete uterine cervical tissue repair postpartum is of necessity to prevent obstetrical complications, such as cervicitis, ectropion, hemorrhage, repeated miscarriages or abortions and possibly preterm labor and malignancies. We recently characterized the morphological alterations, as well as changes in angiogenic expression profile in a mice uterine cervix during the immediate postpartum period. Here, we build on this previous study using a proteomic analysis to profile postpartum tissue changes in mice cervix during the same period, the first 48 h of postpartum. The current proteomics data reveal a variable expression of several intermediate filaments, cytoskeletal modulators and proteins with immune and/or wound-healing properties. We conclude that postpartum cervical repair involves a rapid and tightly regulated balance between a host of biological factors, notably between anti- and pro-inflammatory factors, executed by the M1 and M2 macrophage cells, as revealed by proteomics and verified by confocal immunofluorescence. Future studies will assess the suitability of some of the key proteins identified in this study as potential markers for determining the phase of postpartum cervical repair in obstetrical complications, such as cervical lacerations.

Simple fabrication of rough halloysite nanotubes coatings by thermal spraying for high performance tumor cells capture

Here, we reported a fast, low-cost, and effective fabrication method of large-area and rough halloysite nanotubes (HNTs) coatings by thermal spraying of HNTs ethanol dispersions. A uniform HNTs coating with high transparence is achieved with tailorable surface roughness and thickness. Compared with normal cells, the tumor cells can be captured effectively with high capture yield by the HNTs coatings (expect HeLa cells), which is attributed to the enhanced topographic interactions between HNTs coating and cancer cells. HNTs coating formed from 2.5% ethanol dispersions shows the highest tumor cells capture yeild (90%), which is related to the appropriate roughness and anti-EpCAM conjugation. The capture yield of HNTs coating towards MCF-7 cells can be further improved to 93% within 2h under dynamic shear using a peristaltic pump. The capture yield increases with the incubation time, and the flow rate with 1.25mL/min leads to the maximum capture yield. The HNTs coatings are also effective for capture of tumor cells spiked in artificial blood samples and blood samples from patients with metastatic breast cancer. More than 90% targeted MCF-7 cells and very small amounts of white blood cells are captured by the anti-EpCAM conjugated HNTs coatings from a blood sample. HNTs are further loaded anticancer drug doxorubicin (DOX) and then thermally sprayed into coatings. The MCF-7 cells captured on DOX loaded HNTs coating display significant membrane rupture characteristic and only 3% cell viability after 16h. The high capture efficiency of tumor cells by HNTs coating fabricated by the thermal spraying method makes them show promising applications in clinical circulating tumor cells capture for early diagnosis and monitoring of cancer patients. The high killing ability of the DOX loaded HNTs coating can also be designed as an implantable therapeutic device for preventing tumor metastasis.

Begomoviral Movement Protein Effects in Human and Plant Cells: Towards New Potential Interaction Partners

Geminiviral single-stranded circular DNA genomes replicate in nuclei so that the progeny DNA has to cross both the nuclear envelope and the plasmodesmata for systemic spread within plant tissues. For intra- and intercellular transport, two proteins are required: a nuclear shuttle protein (NSP) and a movement protein (MP). New characteristics of ectopically produced Abutilon mosaic virus (AbMV) MP (MPAbMV), either authentically expressed or fused to a yellow fluorescent protein or epitope tags, respectively, were determined by localization studies in mammalian cell lines in comparison to plant cells. Wild-type MPAbMV and the distinct MPAbMV: reporter protein fusions appeared as curled threads throughout mammalian cells. Co-staining with cytoskeleton markers for actin, intermediate filaments, or microtubules identified these threads as re-organized microtubules. These were, however, not stabilized by the viral MP, as demonstrated by nocodazole treatment. The MP of a related bipartite New World begomovirus, Cleome leaf crumple virus (ClLCrV), resulted in the same intensified microtubule bundling, whereas that of a nanovirus did not. The C-terminal section of MPAbMV, i.e., the protein's oligomerization domain, was dispensable for the effect. However, MP expression in plant cells did not affect the microtubules network. Since plant epidermal cells are quiescent whilst mammalian cells are proliferating, the replication-associated protein RepAbMV protein was then co-expressed with MPAbMV to induce cell progression into S-phase, thereby inducing distinct microtubule bundling without MP recruitment to the newly formed threads. Co-immunoprecipitation of MPAbMV in the presence of RepAbMV, followed by mass spectrometry identified potential novel MPAbMV-host interaction partners: the peptidyl-prolyl cis-trans isomerase NIMA-interacting 4 (Pin4) and stomatal cytokinesis defective 2 (SCD2) proteins. Possible roles of these putative interaction partners in the begomoviral life cycle and cytoskeletal association modes are discussed.

Immunohistochemical Validation of Spontaneously Arising Canine Osteosarcoma as a Model for Human Osteosarcoma

Osteosarcoma (OS) originates from bone-forming mesenchymal cells and represents one of the primary bone tumours. It is the most common primary bone tumour in dogs and man. The characterization of an appropriate natural disease animal model to study human OS is essential to elucidate the pathogenesis of the disease. This study aimed to validate canine OS as a model for the human disease by evaluating immunohistochemically the expression of markers known to be important in human OS. The immunohistochemical panel included vimentin, alkaline phosphatase (ALP), desmin, S100, neuron-specific enolase (NSE), runt-related transcription factor 2 (Runx2) and bone morphogenetic protein 4 (BMP4). Immunohistochemistry was conducted on formalin-fixed, paraffin wax-embedded tissue sections from 59 dogs with confirmed primary OS. Vimentin, ALP, Runx2 and BMP4 were highly expressed by all tumours, while desmin, S100 and NSE were expressed variably. The findings were similar to those described previously for human OS and suggest that canine OS may represent a useful model for the study of the human disease.

Intermediate Filaments at the Junction of Mechanotransduction, Migration, and Development

Mechanically induced signal transduction has an essential role in development. Cells actively transduce and respond to mechanical signals and their internal architecture must manage the associated forces while also being dynamically responsive. With unique assembly-disassembly dynamics and physical properties, cytoplasmic intermediate filaments play an important role in regulating cell shape and mechanical integrity. While this function has been recognized and appreciated for more than 30 years, continually emerging data also demonstrate important roles of intermediate filaments in cell signal transduction. In this review, with a particular focus on keratins and vimentin, the relationship between the physical state of intermediate filaments and their role in mechanotransduction signaling is illustrated through a survey of current literature. Association with adhesion receptors such as cadherins and integrins provides a critical interface through which intermediate filaments are exposed to forces from a cell's environment. As a consequence, these cytoskeletal networks are posttranslationally modified, remodeled and reorganized with direct impacts on local signal transduction events and cell migratory behaviors important to development. We propose that intermediate filaments provide an opportune platform for cells to both cope with mechanical forces and modulate signal transduction.

Vimentin Modulates Infectious Internalization of Human Papillomavirus 16 Pseudovirions

Human papillomavirus (HPV) infection is the most common viral infection of the reproductive tract, with virtually all cases of cervical cancer being attributable to infection by oncogenic HPVs. However, the exact mechanism and receptors used by HPV to infect epithelial cells are controversial. The current entry model suggests that HPV initially attaches to heparan sulfate proteoglycans (HSPGs) at the cell surface, followed by conformational changes, cleavage by furin convertase, and subsequent transfer of the virus to an as-yet-unidentified high-affinity receptor. In line with this model, we established an in vitro infection system using the HSPG-deficient cell line pgsD677 together with HPV16 pseudovirions (HPV16-PsVs). While pgsD677 cells were nonpermissive for untreated HPV16-PsVs, furin cleavage of the particles led to a substantial increase in infection. Biochemical pulldown assays followed by mass spectrometry analysis showed that furin-precleaved HPV16-PsVs specifically interacted with surface-expressed vimentin on pgsD677 cells. We further demonstrated that both furin-precleaved and uncleaved HPV16-PsVs colocalized with surface-expressed vimentin on pgsD677, HeLa, HaCaT, and NIKS cells, while binding of incoming viral particles to soluble vimentin protein before infection led to a substantial decrease in viral uptake. Interestingly, decreasing cell surface vimentin by small interfering RNA (siRNA) knockdown in HeLa and NIKS cells significantly increased HPV16-PsV infectious internalization, while overexpression of vimentin had the opposite effect. The identification of vimentin as an HPV restriction factor enhances our understanding of the initial steps of HPV-host interaction and may lay the basis for the design of novel antiviral drugs preventing HPV internalization into epithelial cells.IMPORTANCE Despite HPV being a highly prevalent sexually transmitted virus causing significant disease burden worldwide, particularly cancer of the cervix, cell surface events preceding oncogenic HPV internalization are poorly understood. We herein describe the identification of surface-expressed vimentin as a novel molecule not previously implicated in the infectious internalization of HPV16. Contrary to our expectations, vimentin was found to act not as a receptor but rather as a restriction factor dampening the initial steps of HPV16 infection. These results importantly contribute to our current understanding of the molecular events during the infectious internalization of HPV16 and open a new direction in the development of alternative drugs to prevent HPV infection.

Changes in the biomechanical properties of a single cell induced by nonthermal atmospheric pressure micro-dielectric barrier discharge plasma

Mechanical properties of a single cell are closely related to the fate and functions of the cell. Changes in mechanical properties may cause diseases or cell apoptosis. Selective cytotoxic effects of nonthermal atmospheric pressure micro-dielectric barrier discharge (DBD) plasma have been demonstrated on cancer cells. In this work, changes in the mechanical properties of a single cell induced by nonthermal atmospheric pressure micro-DBD plasma were investigated using atomic force microscopy (AFM). Two cervical cancer cell lines (HeLa and SiHa) and normal human fibroblast cells (HFBs) were exposed to micro-DBD plasma for various exposure times. The elasticity of a single cell was determined by force-distance curve measurement using AFM. Young's modulus was decreased by plasma treatment for all cells. The Young's modulus of plasma-treated HeLa cells was decreased by 75% compared to nontreated HeLa cells. In SiHa cells and HFBs, elasticity was decreased slightly. Chemical changes induced by the plasma treatment, which were observed by Raman spectroscopy, were also significant in HeLa cells compared to SiHa cells and HFBs. These results suggested that the molecular changes induced by micro-DBD plasma were related to cell mechanical changes.

Vimentin fibers orient traction stress

The intermediate filament vimentin is required for cells to transition from the epithelial state to the mesenchymal state and migrate as single cells; however, little is known about the specific role of vimentin in the regulation of mesenchymal migration. Vimentin is known to have a significantly greater ability to resist stress without breaking in vitro compared with actin or microtubules, and also to increase cell elasticity in vivo. Therefore, we hypothesized that the presence of vimentin could support the anisotropic mechanical strain of single-cell migration. To study this, we fluorescently labeled vimentin with an mEmerald tag using TALEN genome editing. We observed vimentin architecture in migrating human foreskin fibroblasts and found that network organization varied from long, linear bundles, or "fibers," to shorter fragments with a mesh-like organization. We developed image analysis tools employing steerable filtering and iterative graph matching to characterize the fibers embedded in the surrounding mesh. Vimentin fibers were aligned with fibroblast branching and migration direction. The presence of the vimentin network was correlated with 10-fold slower local actin retrograde flow rates, as well as spatial homogenization of actin-based forces transmitted to the substrate. Vimentin fibers coaligned with and were required for the anisotropic orientation of traction stresses. These results indicate that the vimentin network acts as a load-bearing superstructure capable of integrating and reorienting actin-based forces. We propose that vimentin's role in cell motility is to govern the alignment of traction stresses that permit single-cell migration.

Epithelial-mesenchymal transition, and collective and individual cell migration regulate epithelial changes in the amikacin-damaged organ of Corti

Characterizing the microenvironment of a damaged organ of Corti and identifying the basic mechanisms involved in subsequent epithelial reorganization are critical for improving the outcome of clinical therapies. In this context, we studied the expression of a variety of cell markers related to cell shape, cell adhesion and cell plasticity in the rat organ of Corti poisoned with amikacin. Our results indicate that, after severe outer hair cell losses, the cytoarchitectural reorganization of the organ of Corti implicates epithelial-mesenchymal transition mechanisms and involves both collective and individual cell migratory processes. The results also suggest that both root cells and infiltrated fibroblasts participate in the homeostasis of the damaged epithelium, and that the flat epithelium that may emerge offers biological opportunities for late regenerative therapies.

Control of Myofibroblast Differentiation and Function by Cytoskeletal Signaling

The cytoskeleton consists of three distinct types of protein polymer structures - microfilaments, intermediate filaments, and microtubules; each serves distinct roles in controlling cell shape, division, contraction, migration, and other processes. In addition to mechanical functions, the cytoskeleton accepts signals from outside the cell and triggers additional signals to extracellular matrix, thus playing a key role in signal transduction from extracellular stimuli through dynamic recruitment of diverse intermediates of the intracellular signaling machinery. This review summarizes current knowledge about the role of cytoskeleton in the signaling mechanism of fibroblast-to-myofibroblast differentiation - a process characterized by accumulation of contractile proteins and secretion of extracellular matrix proteins, and being critical for normal wound healing in response to tissue injury as well as for aberrant tissue remodeling in fibrotic disorders. Specifically, we discuss control of serum response factor and Hippo signaling pathways by actin and microtubule dynamics as well as regulation of collagen synthesis by intermediate filaments.

Large-area assembly of halloysite nanotubes for enhancing the capture of tumor cells

Here, polystyrene sulfonate sodium (PSS) modified Halloysite nanotubes (HNTs) were self-assembled into a patterned coating on a glass substrate with ordered nanotube arrays in a slit-like confined space. The microstructure of the formed patterned HNTs coating was investigated. The formed strips are more regular and almost parallel to each other with an increase in HNTs concentration. The HNTs coating formed from the 2% PSS-HNTs dispersion has the maximum nanotube alignment degree. The patterned HNTs coating was employed to capture tumor cells. The tumor cells can be captured by the HNTs coating effectively compared with a smooth glass surface due to the enhanced topographic interactions between the HNTs coating and cancer cells. The HNTs coating prepared from the 2% PSS-HNTs dispersion has the highest capture yield which is due to the ordered nanotube arrangement and the appropriate surface roughness. The HNTs coating was further conjugated with anti-EpCAM, which leads to the capture yield of MCF-7 cells reaching 92% within 3 h. The HNTs coating can capture 8 MCF-7 cells from 1 mL artificial blood samples spiked with 10 MCF-7 cells, showing the promising applications of HNTs in clinical circulating tumor cell capture for early diagnosis and monitoring of cancer patients.

Crystallographic Studies of Intermediate Filament Proteins

Intermediate filaments (IFs), together with microtubules and actin microfilaments, are the three main cytoskeletal components in metazoan cells. IFs are formed by a distinct protein family, which is made up of 70 members in humans. Most IF proteins are tissue- or organelle-specific, which includes lamins, the IF proteins of the nucleus. The building block of IFs is an elongated dimer, which consists of a central α-helical 'rod' domain flanked by flexible N- and C-terminal domains. The conserved rod domain is the 'signature feature' of the IF family. Bioinformatics analysis reveals that the rod domain of all IF proteins contains three α-helical segments of largely conserved length, interconnected by linkers. Moreover, there is a conserved pattern of hydrophobic repeats within each segment, which includes heptads and hendecads. This defines the presence of both left-handed and almost parallel coiled-coil regions along the rod length. Using X-ray crystallography on multiple overlapping fragments of IF proteins, the atomic structure of the nearly complete rod domain has been determined. Here, we discuss some specific challenges of this procedure, such as crystallization and diffraction data phasing by molecular replacement. Further insights into the structure of the coiled coil and the terminal domains have been obtained using electron paramagnetic resonance measurements on the full-length protein, with spin labels attached at specific positions. This atomic resolution information, as well as further interesting findings, such as the variation of the coiled-coil stability along the rod length, provide clues towards interpreting the data on IF assembly, collected by a range of methods. However, a full description of this process at the molecular level is not yet at hand.

Fuerstia marisgermanicae gen. nov., sp. nov., an Unusual Member of the Phylum Planctomycetes from the German Wadden Sea

Members of the phylum Planctomycetes are ubiquitous bacteria that dwell in aquatic and terrestrial habitats. While planctomycetal species are important players in the global carbon and nitrogen cycle, this phylum is still undersampled and only few genome sequences are available. Here we describe strain NH11^T, a novel planctomycete obtained from a crustacean shell (Wadden Sea, Germany). The phylogenetically closest related cultivated species is Gimesia maris, sharing only 87% 16S rRNA sequence identity. Previous isolation attempts have mostly yielded members of the genus Rhodopirellula from water of the German North Sea. On the other hand, only one axenic culture of the genus Pirellula was obtained from a crustacean thus far. However, the 16S rRNA gene sequence of strain NH11^T shares only 80% sequence identity with the closest relative of both genera, Rhodopirellula and Pirellula. Thus, strain NH11^T is unique in terms of origin and phylogeny. While the pear to ovoid shaped cells of strain NH11^T are typical planctomycetal, light-, and electron microscopic observations point toward an unusual variation of cell division through budding: during the division process daughter- and mother cells are connected by an unseen thin tubular-like structure. Furthermore, the periplasmic space of strain NH11^T was unusually enlarged and differed from previously known planctomycetes. The complete genome of strain NH11^T, with almost 9 Mb in size, is among the largest planctomycetal genomes sequenced thus far, but harbors only 6645 protein-coding genes. The acquisition of genomic components by horizontal gene transfer is indicated by the presence of numerous putative genomic islands. Strikingly, 45 “giant genes” were found within the genome of NH11^T. Subsequent analysis of all available planctomycetal genomes revealed that Planctomycetes as such are especially rich in “giant genes”. Furthermore, Multilocus Sequence Analysis (MLSA) tree reconstruction support the phylogenetic distance of strain NH11^T from other cultivated Planctomycetes of the same phylogenetic cluster. Thus, based on our findings, we propose to classify strain NH11^T as Fuerstia marisgermanicae gen. nov., sp. nov., with the type strain NH11^T, within the phylum Planctomycetes.

Structural Rearrangements in CHO Cells After Disruption of Individual Cytoskeletal Elements and Plasma Membrane

Cellular structural integrity is provided primarily by the cytoskeleton, which comprises microtubules, actin filaments, and intermediate filaments. The plasma membrane has been also recognized as a mediator of physical forces, yet its contribution to the structural integrity of the cell as a whole is less clear. In order to investigate the relationship between the plasma membrane and the cytoskeleton, we selectively disrupted the plasma membrane and each of the cytoskeletal elements in Chinese hamster ovary cells and assessed subsequent changes in cellular structural integrity. Confocal microscopy was used to visualize cytoskeletal rearrangements, and optical tweezers were utilized to quantify membrane tether extraction. We found that cholesterol depletion from the plasma membrane resulted in rearrangements of all cytoskeletal elements. Conversely, the state of the plasma membrane, as assessed by tether extraction, was affected by disruption of any of the cytoskeletal elements, including microtubules and intermediate filaments, which are located mainly in the cell interior. The results demonstrate that, besides the cytoskeleton, the plasma membrane is an important contributor to cellular integrity, possibly by acting as an essential framework for cytoskeletal anchoring. In agreement with the tensegrity model of cell mechanics, our results support the notion of the cell as a prestressed structure.

Dermal-epidermal membrane systems by using human keratinocytes and mesenchymal stem cells isolated from dermis

Dermal-epidermal membrane systems were developed by co-culturing human keratinocytes with Skin derived Stem Cells (SSCs), which are Mesenchymal Stem Cells (MSCs) isolated from dermis, on biodegradable membranes of chitosan (CHT), polycaprolactone (PCL) and a polymeric blend of CHT and PCL. The membranes display physico-chemical, morphological, mechanical and biodegradation properties that could satisfy and fulfil specific requirements in skin tissue engineering. CHT membrane exhibits an optimal biodegradation rate for acute wounds; CHT-PCL for the chronic ones. On the other hand, PCL membrane in spite of its very slow biodegradation rate exhibits mechanical properties similar to in vivo dermis, a lower hydrophilic character, and a surface roughness, all properties that make it able to sustain cell adhesion and proliferation for in vitro skin models. Both CHT-PCL and PCL membranes guided epidermal and dermal differentiation of SSCs as pointed out by the expression of cytokeratins and the deposition of the ECM protein fibronectin, respectively. In the dermal-epidermal membrane systems, a more suitable microenvironment for the SSCs differentiation was promoted by the interactions and the mutual interplay with keratinocytes. Being skin tissue-biased stem cells committed to their specific final dermal and/or epidermal cell differentiation, SSCs are more suitable for skin tissue engineering than other adult MSCs with different origin. For this reason, they represent a useful autologous cell source for engineering skin substitutes for both in vivo and in vitro applications.

Medical applications of the intrinsic mechanical properties of single cells

The mechanical properties of single cells have been recently identified as the basis of an emerging approach in medical applications because they are closely related to the biological processes of cells and, ultimately, human health conditions. In this article, we provide a brief review of the intrinsic mechanical properties of single cells related to cancer and aging. The mechanical properties can be used as biomarkers for early cancer diagnosis because cancer cells have a lower Young's modulus, indicating higher elasticity or softness than their counterpart normal cells. The metastatic potential of cancer cells is inversely correlated with their elastic properties. Aging induces stiffness through an increased amount of cytoskeletal fiber. Changes in the mechanical properties also show potential for drug screening. Although there are several challenges to be met before clinical applications can be made, such mechanical properties of single cells may provide new approaches to human diseases.

Vimentin Intermediate Filaments Template Microtubule Networks to Enhance Persistence in Cell Polarity and Directed Migration

Increased expression of vimentin intermediate filaments (VIFs) enhances directed cell migration, but the mechanism behind VIFs' effect on motility is not understood. VIFs interact with microtubules, whose organization contributes to polarity maintenance in migrating cells. Here, we characterize the dynamic coordination of VIF and microtubule networks in wounded monolayers of retinal pigment epithelial cells. By genome editing, we fluorescently labeled endogenous vimentin and α-tubulin, and we developed computational image analysis to delineate architecture and interactions of the two networks. Our results show that VIFs assemble an ultrastructural copy of the previously polarized microtubule network. Because the VIF network is long-lived compared to the microtubule network, VIFs template future microtubule growth along previous microtubule tracks, thus providing a feedback mechanism that maintains cell polarity. VIF knockdown prevents cells from polarizing and migrating properly during wound healing. We suggest that VIFs' templating function establishes a memory in microtubule organization that enhances persistence in cell polarization in general and migration in particular.

Deficiency of the intermediate filament synemin reduces bone mass in vivo

While the type IV intermediate filament protein, synemin, has been shown to play a role in striated muscle and neuronal tissue, its presence and function have not been described in skeletal tissue. Here, we report that genetic ablation of synemin in 14-wk-old male mice results in osteopenia that includes a more than 2-fold reduction in the trabecular bone fraction in the distal femur and a reduction in the cross-sectional area at the femoral middiaphysis due to an attendant reduction in both the periosteal and endosteal perimeter. Analysis of serum markers of bone formation and static histomorphometry revealed a statistically significant defect in osteoblast activity and osteoblast number in vivo. Interestingly, primary osteoblasts isolated from synemin-null mice demonstrate markedly enhanced osteogenic capacity with a concomitant reduction in cyclin D1 mRNA expression, which may explain the loss of osteoblast number observed in vivo. In total, these data suggest an important, previously unknown role for synemin in bone physiology.

Depletion of STYK1 inhibits intrahepatic cholangiocarcinoma development both in vitro and in vivo

Intrahepatic cholangiocarcinoma (ICC) has been reported to be the second most common primary hepatic carcinoma worldwide, and very limited therapies are currently available. Serine threonine tyrosine kinase (STYK1), a member of the receptor tyrosine kinase family, exhibits tumorigenicity in many types of cancers and is a potential therapeutic target for ICC. In this study, STYK1 was knocked down in the ICC cell lines HCCC-9810 and RBE via a lentivirus-mediated system using short hairpin RNA (shRNA). Next, cell proliferation, colony formation, cell cycle progression, tumor formation in nude mice, migration and invasion, and the expression levels of cell cycle proteins in Lv-sh STYK1- or Lv-sh Con-infected cells were analyzed by CCK-8 assay, colony formation evaluation, flow cytometry, tumor formation evaluation, wound scratch assay, transwell assay, and western blotting. The results indicated that depletion of STYK1 inhibits ICC development both in vitro and in vivo.

Seasonal Changes in the Immunolocalization of Cytoskeletal Proteins and Laminin in the Testis of the Black-Backed Jackal (Canis mesomelas)

Manipulation of the reproductive activity of jackals is dependent on a thorough understanding of the reproductive biology of this species. This study describes seasonal morphological changes in the adult testis of the black-backed jackal in relation to the immunoexpression of the basement membrane marker, laminin and the cytoskeletal proteins, cytokeratin, smooth muscle actin and vimentin. Laminin was immunolocalized in basement membranes surrounding seminiferous tubules, as well as in basement membranes associated with Leydig, peritubular myoid and vascular smooth muscle cells. Scalloped basement membranes enclosed seminiferous tubules in regressing testes. The seminiferous epithelium and interstitial tissue in all animals studied were cytokeratin immunonegative. Smooth muscle actin was demonstrated in vascular smooth muscle cells, as well as in peritubular myoid cells encircling seminiferous tubules. Vimentin immunoreactivity was exhibited in the cytoplasm of Sertoli cells, Leydig cells, vascular endothelial cells, vascular smooth muscle cells and fibrocytes. Vimentin immunostaining in Sertoli, Leydig and peritubular myoid cells varied depending on the functional state of the testis. The results of the study have shown that dramatic seasonal histological changes occur in the testes of the jackal. In addition, the use of immunohistochemistry accentuates these morphological changes.

Dephosphorylation of MAP2D enhances its binding to vimentin in preovulatory ovarian granulosa cells

Preovulatory granulosa cells express the low-molecular-mass MAP2D variant of microtubule-associated protein 2 (MAP2). Activation of the luteinizing hormone choriogonadotropin receptor by human choriogonadotropin (hCG) promotes dephosphorylation of MAP2D on Thr256 and Thr259. We sought to evaluate the association of MAP2D with the cytoskeleton, and the effect of hCG on this association. MAP2D partially colocalized, as assessed by confocal immunofluorescence microscopy, with the vimentin intermediate filament and microtubule cytoskeletons in naive cells. In vitro binding studies showed that MAP2D bound directly to vimentin and β-tubulin. Phosphorylation of recombinant MAP2D on Thr256 and Thr259, which mimics the phosphorylation status of MAP2D in naive cells, reduces binding of MAP2D to vimentin and tubulin by two- and three-fold, respectively. PKA-dependent phosphorylation of vimentin (Ser32 and Ser38) promoted binding of vimentin to MAP2D and increased contraction of granulosa cells with reorganization of vimentin filaments and MAP2D from the periphery into a thickened layer surrounding the nucleus and into prominent cellular extensions. Chemical disruption of vimentin filament organization increased progesterone production. Taken together, these results suggest that hCG-stimulated dephosphorylation of MAP2D at Thr256 and Thr259, phosphorylation of vimentin at Ser38 and Ser72, and the resulting enhanced binding of MAP2D to vimentin might contribute to the progesterone synthetic response required for ovulation.

Identification of Vimentin as a Potential Therapeutic Target against HIV Infection

A combination of antiviral drugs known as antiretroviral therapy (ART) has shown effectiveness against the human immunodeficiency virus (HIV). ART has markedly decreased mortality and morbidity among HIV-infected patients, having even reduced HIV transmission. However, an important current disadvantage, resistance development, remains to be solved. Hope is focused on developing drugs against cellular targets. This strategy is expected to prevent the emergence of viral resistance. In this study, using a comparative proteomic approach in MT4 cells treated with an anti-HIV leukocyte extract, we identified vimentin, a molecule forming intermediate filaments in the cell, as a possible target against HIV infection. We demonstrated a strong reduction of an HIV-1 based lentivirus expressing the enhanced green fluorescent protein (eGFP) in vimentin knockdown cells, and a noteworthy decrease of HIV-1 capsid protein antigen (CAp24) in those cells using a multiround infectivity assay. Electron micrographs showed changes in the structure of intermediate filaments when MT4 cells were treated with an anti-HIV leukocyte extract. Changes in the structure of intermediate filaments were also observed in vimentin knockdown MT4 cells. A synthetic peptide derived from a cytoskeleton protein showed potent inhibitory activity on HIV-1 infection, and low cytotoxicity. Our data suggest that vimentin can be a suitable target to inhibit HIV-1.

Significance of 1B and 2B domains in modulating elastic properties of lamin A

Nuclear lamins are type V intermediate filament proteins which form an elastic meshwork underlying the inner nuclear membrane. Lamins directly contribute to maintain the nuclear shape and elasticity. More than 400 mutations have been reported in lamin A that are involved in diseases known as laminopathies. These mutations are scattered mainly in the lamin rod domain along with some in its C-terminal domain. The contribution of the rod domain towards the elasticity of lamin A molecule was hitherto unknown. Here, we have elucidated the significance of the 1B and 2B domains of the rod in modulating the elastic behavior of lamin A by single-molecule force spectroscopy. In addition, we have also studied the network forming capacity of these domains and their corresponding viscoelastic behavior. We have shown that the 1B domain has the ability to form a lamin-like network and resists larger deformation. However at the single-molecular level, both the domains have comparable mechanical properties. The self-assembly of the 1B domain contributes to the elasticity of the lamin A network.

Vimentin filaments regulate integrin-ligand interactions by binding to the cytoplasmic tail of integrin β3

Vimentin, an intermediate filament protein induced during epithelial-to-mesenchymal transition, is known to regulate cell migration and invasion. However, it is still unclear how vimentin controls such behaviors. In this study, we aimed to find a new integrin regulator by investigating the H-Ras-mediated integrin suppression mechanism. Through a proteomic screen using the integrin β3 cytoplasmic tail protein, we found that vimentin might work as an effector of H-Ras signaling. H-Ras converted filamentous vimentin into aggregates near the nucleus, where no integrin binding can occur. In addition, an increase in the amount of vimentin filaments accessible to the integrin β3 tail enhanced talin-induced integrin binding to its ligands by inducing integrin clustering. In contrast, the vimentin head domain, which was found to bind directly to the integrin β3 tail and compete with endogenous vimentin filaments for integrin binding, induced nuclear accumulation of vimentin filaments and reduced the amount of integrin-ligand binding. Finally, we found that expression of the vimentin head domain can reduce cell migration and metastasis. From these data, we suggest that filamentous vimentin underneath the plasma membrane is involved in increasing integrin adhesiveness, and thus regulation of the vimentin-integrin interaction might control cell adhesion.

Müller glia reactivity follows retinal injury despite the absence of the glial fibrillary acidic protein gene in Xenopus

Intermediate filament proteins are structural components of the cellular cytoskeleton with cell-type specific expression and function. Glial fibrillary acidic protein (GFAP) is a type III intermediate filament protein and is up-regulated in glia of the nervous system in response to injury and during neurodegenerative diseases. In the retina, GFAP levels are dramatically increased in Müller glia and are thought to play a role in the extensive structural changes resulting in Müller cell hypertrophy and glial scar formation. In spite of similar changes to the morphology of Xenopus Müller cells following injury, we found that Xenopus lack a gfap gene. Other type III intermediate filament proteins were, however, significantly induced following rod photoreceptor ablation and retinal ganglion cell axotomy. The recently available X. tropicalis and X. laevis genomes indicate a small deletion most likely resulted in the loss of the gfap gene during anuran evolution. Lastly, a survey of representative species from all three extant amphibian orders including the Anura (frogs, toads), Caudata (salamanders, newts), and Gymnophiona (caecilians) suggests that deletion of the gfap locus occurred in the ancestor of all Anura after its divergence from the Caudata ancestor around 290 million years ago. Our results demonstrate that extensive changes in Müller cell morphology following retinal injury do not require GFAP in Xenopus, and other type III intermediate filament proteins may be involved in the gliotic response.

Methods for Determining the Cellular Functions of Vimentin Intermediate Filaments

The type III intermediate filament protein vimentin was once thought to function mainly as a static structural protein in the cytoskeleton of cells of mesenchymal origin. Now, however, vimentin is known to form a dynamic, flexible network that plays an important role in a number of signaling pathways. Here, we describe various methods that have been developed to investigate the cellular functions of the vimentin protein and intermediate filament network, including chemical disruption, photoactivation and photoconversion, biolayer interferometry, soluble bead binding assay, three-dimensional substrate experiments, collagen gel contraction, optical-tweezer active microrheology, and force spectrum microscopy. Using these techniques, the contributions of vimentin to essential cellular processes can be probed in ever further detail.

Cytoskeletal signaling in TGFβ-induced epithelial-mesenchymal transition

Epithelial-mesenchymal transition (EMT) is a physiological process that plays an important role in embryonic development and wound healing and is appropriated during pathological conditions including fibrosis and cancer metastasis. EMT can be initiated by a variety of factors, including transforming growth factor (TGF)-β, and is characterized by loss of epithelial features including cell-cell contacts and apicobasal polarity and acquisition of a motile, mesenchymal phenotype. A key feature of EMT is reorganization of the cytoskeleton and recent studies have elucidated regulation mechanisms governing this process. This review describes changes in gene expression patterns of cytoskeletal associated proteins during TGFβ-induced EMT. It further reports TGFβ-induced intracellular signaling cascades that regulate cytoskeletal reorganization during EMT. Finally, it highlights how changes in cytoskeletal architecture during EMT can regulate gene expression, thus further promoting EMT progression.

Altered Traffic of Cardiolipin during Apoptosis: Exposure on the Cell Surface as a Trigger for "Antiphospholipid Antibodies"

Apoptosis has been reported to induce changes in the remodelling of membrane lipids; after death receptor engagement, specific changes of lipid composition occur not only at the plasma membrane, but also in intracellular membranes. This paper focuses on one important aspect of apoptotic changes in cellular lipids, namely, the redistribution of the mitochondria-specific phospholipid, cardiolipin (CL). CL predominantly resides in the inner mitochondrial membrane, even if the rapid remodelling of its acyl chains and the subsequent degradation occur in other membrane organelles. After death receptor stimulation, CL appears to concentrate into mitochondrial “raft-like” microdomains at contact sites between inner and outer mitochondrial membranes, leading to local oligomerization of proapoptotic proteins, including Bid. Clustering of Bid in CL-enriched contacts sites is interconnected with pathways of CL remodelling that intersect membrane traffic routes dependent upon actin. In addition, CL association with cytoskeleton protein vimentin was observed. Such novel association also indicated that CL molecules may be expressed at the cell surface following apoptotic stimuli. This observation adds a novel implication of biomedical relevance. The association of CL with vimentin at the cell surface may represent a “new” target antigen in the context of the apoptotic origin of anti-vimentin/CL autoantibodies in Antiphospholipid Syndrome.

Altered cytoskeletal organization characterized lethal but not surviving Brtl+/- mice: insight on phenotypic variability in osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a heritable bone disease with dominant and recessive transmission. It is characterized by a wide spectrum of clinical outcomes ranging from very mild to lethal in the perinatal period. The intra- and inter-familiar OI phenotypic variability in the presence of an identical molecular defect is still puzzling to the research field. We used the OI murine model Brtl(+/-) to investigate the molecular basis of OI phenotypic variability. Brtl(+/-) resembles classical dominant OI and shows either a moderately severe or a lethal outcome associated with the same Gly349Cys substitution in the α1 chain of type I collagen. A systems biology approach was used. We took advantage of proteomic pathway analysis to functionally link proteins differentially expressed in bone and skin of Brtl(+/-) mice with different outcomes to define possible phenotype modulators. The skin/bone and bone/skin hybrid networks highlighted three focal proteins: vimentin, stathmin and cofilin-1, belonging to or involved in cytoskeletal organization. Abnormal cytoskeleton was indeed demonstrated by immunohistochemistry to occur only in tissues from Brtl(+/-) lethal mice. The aberrant cytoskeleton affected osteoblast proliferation, collagen deposition, integrin and TGF-β signaling with impairment of bone structural properties. Finally, aberrant cytoskeletal assembly was detected in fibroblasts obtained from lethal, but not from non-lethal, OI patients carrying an identical glycine substitution. Our data demonstrated that compromised cytoskeletal assembly impaired both cell signaling and cellular trafficking in mutant lethal mice, altering bone properties. These results point to the cytoskeleton as a phenotypic modulator and potential novel target for OI treatment.

Edaravone leads to proteome changes indicative of neuronal cell protection in response to oxidative stress

Neuronal cell death, in neurodegenerative disorders, is mediated through a spectrum of biological processes. Excessive amounts of free radicals, such as reactive oxygen species (ROS), has detrimental effects on neurons leading to cell damage via peroxidation of unsaturated fatty acids in the cell membrane. Edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) has been used for neurological recovery in several countries, including Japan and China, and it has been suggested that Edaravone may have cytoprotective effects in neurodegeneration. Edaravone protects nerve cells in the brain by reducing ROS and inhibiting apoptosis. To gain further insight into the cytoprotective effects of Edaravone against oxidative stress condition we have performed comparative two-dimensional gel electrophoresis (2DE)-based proteomic analyses on SH-SY5Y neuroblastoma cells exposed to oxidative stress and in combination with Edaravone. We showed that Edaravone can reverse the cytotoxic effects of H2O2 through its specific mechanism. We observed that oxidative stress changes metabolic pathways and cytoskeletal integrity. Edaravone seems to reverse the H2O2-mediated effects at both the cellular and protein level via induction of Peroxiredoxin-2.

Classic Ras Proteins Promote Proliferation and Survival via Distinct Phosphoproteome Alterations in Neurofibromin-Null Malignant Peripheral Nerve Sheath Tumor Cells

Neurofibromin, the tumor suppressor encoded by the neurofibromatosis type 1 (NF1) gene, potentially suppresses the activation of H-Ras, N-Ras, and K-Ras. However, it is not known whether these classic Ras proteins are hyperactivated in NF1-null nerve sheath tumors, how they contribute to tumorigenesis, and what signaling pathways mediate their effects. Here we show that H-Ras, N-Ras, and K-Ras are coexpressed with their activators (guanine nucleotide exchange factors) in neurofibromin-null malignant peripheral nerve sheath tumor (MPNST) cells, and that all 3 Ras proteins are activated. Dominant negative (DN) H-Ras, a pan-inhibitor of the classic Ras family, inhibited MPNST proliferation and survival, but not migration. However, NF1-null MPNST cells were variably dependent on individual Ras proteins. In some lines, ablation of H-Ras, N-Ras, and/or K-Ras inhibited mitogenesis. In others, ablation of a single Ras protein had no effect on proliferation; in these lines, ablation of a single Ras protein resulted in compensatory increases in the activation and/or expression of other Ras proteins. Using mass spectrometry-based phosphoproteomics, we identified 7 signaling networks affecting morphology, proliferation, and survival that are regulated by DN H-Ras. Thus, neurofibromin loss activates multiple classic Ras proteins that promote proliferation and survival by regulating several distinct signaling cascades.

Absence of keratins 8 and 18 in rodent epithelial cell lines associates with keratin gene mutation and DNA methylation: Cell line selective effects on cell invasion

Epithelial-mesenchymal transition (EMT) in carcinoma is associated with dramatic up-regulation of vimentin and down-regulation of the simple-type keratins 8 and 18 (K8/K18), but the mechanisms of these changes are poorly understood. We demonstrate that two commonly-studied murine (CT26) and rat (IEC-6) intestinal cell lines have negligible K8/K18 but high vimentin protein expression. Proteasome inhibition led to a limited increase in K18 but not K8 stabilization, thereby indicating that K8/K18 absence is not due, in large part, to increased protein turnover. CT26 and IEC-6 cells had <10% of normal K8/K18 mRNA and exhibited decreased mRNA stability, with K8 mRNA levels being higher in IEC-6 versus CT26 and K18 being higher in CT26 versus IEC-6 cells. Keratin gene sequencing showed that KRT8 in CT26 cells had a 21-nucleotide deletion while K18 in IEC-6 cells had a 9-amino acid in-frame insertion. Furthermore, the KRT8 promoter in CT26 and the KRT18 promoter in IEC-6 are hypermethylated. Inhibition of DNA methylation using 5-azacytidine increased K8 or K18 in some but all the tested rodent epithelial cell lines. Restoring K8 and K18 by lentiviral transduction reduced CT26 but not IEC-6 cell matrigel invasion. K8/K18 re-introduction also decreased E-cadherin expression in IEC-6 but not CT26 cells, suggesting that the effect of keratin expression on epithelial to mesenchymal transition is cell-line dependent. Therefore, some commonly utilized rodent epithelial cell lines, unexpectedly, manifest barely detectable keratin expression but have high levels of vimentin. In the CT26 and IEC-6 intestinal cell lines, keratin expression correlates with keratin gene insertion or deletion and with promoter methylation, which likely suppress keratin transcription and mRNA or protein stability.

PRRS virus receptors and their role for pathogenesis

Porcine reproductive and respiratory syndrome virus (PRRSV) is endemic in most pig producing countries worldwide and causes enormous economic losses to the swine industry. Specifically differentiated porcine alveolar macrophages are the primary target for PRRSV infection in pigs. At least six cellular molecules have been described so far as putative receptors for PRRSV, and they include heparan sulfate, vimentin, CD151, sialoadhesin (CD169; siglec-1), dendritic cell-specific intercellular adhesion melecule-3-grabbing non-integrin (DC-SIGN; CD209), and CD163 (SRCR, cysteine-rich scavenger receptor). Progress has been made to shed light on the interactions between cells and PRRSV, and this review describes the advances and current understanding of the entry of PRRSV to cells with a particular focus on the role of CD163 and sialoadhesin for infection and PRRSV pathogenesis. CD163 is most likely the primary and core receptor for PRRSV and determines the susceptibility of cells to the virus. Sialoadhesin is either unnecessary for infection or may function as an accessory protein. Sialoadhesin has been mostly studied for genotype I PRRSV whereas the utilization of CD163 has been mostly studied using genotype II PRRSV, and whether each genotype indeed utilizes a different receptor is unclear.

Restoration of chondrocytic phenotype on a two-dimensional micropatterned surface

Chondrocytes within mature cartilage reside in a 3D matrix and adopt a distinctive round morphology. A vast 2D-culture surface is well-known to induce chondrocyte dedifferentiation characterized by the loss of spherical morphology and ceased expression of chondrogenic markers. Methods to restore chondrogenesis so far only occur on a certain level producing varied cell subpopulations and inferior cartilage matrix; the critical parameters, especially for the pericellular microenvironment, are still to be precisely determined. In this study, arrays of 2D circular micropatterns were designed to hold single subcultured chondrocytes with stable adhesion. The chondrocytes rounded up forming a 3D architecture; they remodeled their cytoskeleton to resemble in-situ chondrocytes and expressed collagen II instead of collagen I or fibronectin. This technique suggested that pure physical constraints can induce chondrocytic phenotype restoration on a 2D surface; it also provides a new design pathway to precisely control the microenvironment surrounding every chondrocyte therefore to unify the redifferentiation level of individual cell.

Roles and potential clinical applications of intermediate filament proteins in brain tumors

Intermediate filament (IF) proteins are cytoplasmic and nuclear cytoskeletal proteins. Of the ~70 IF proteins, nearly 12 are found in the nervous system, where their expression is largely cell-type specific. Astrocytes express glial fibrillary acidic protein (GFAP), whereas different neuron types contain neurofilament proteins, α-internexin, or peripherin. These proteins are often downregulated in brain cancer. In addition, brain cancer cells may also contain vimentin, nestin, and synemin, which are the IF proteins found in neural progenitor cells. In different brain tumor types, the expression of nestin, vimentin, and α-internexin appears to correlate with the clinical outcome. Experimental investigations have also demonstrated that IF proteins have distinct roles in specific brain tumor cell behaviors: nestin, for instance, is important for the proliferation of glioma cells, whereas synemin also affect their mobility. The mechanisms responsible for these effects involve the interaction of IF proteins with specific signaling pathways. Synemin, for instance, positively regulates glioma cell proliferation by antagonizing protein phosphatase 2A. Further evidence for the potential of IF proteins as therapeutic targets derives from animal models showing the influence of IF proteins on tumor growth. Nestin downregulation, for instance, dramatically reduced intracerebral glioma growth. Selective targeted therapies of IFs to date primarily include gene therapy approaches using nestin or GFAP gene promoters to drive transgene expression into glioma cells. Although attempts to identify small molecules specifically antagonizing IF proteins have been unsuccessful to date, it is anticipated that the identification of such compounds will be instrumental in expanding therapeutic approaches for brain tumors.

Scaffold composition affects cytoskeleton organization, cell-matrix interaction and the cellular fate of human mesenchymal stem cells upon chondrogenic differentiation

The stem cell niche, or microenvironment, consists of soluble, matrix, cell and mechanical factors that together determine the cellular fates and/or differentiation patterns of stem cells. Collagen and glycosaminoglycans (GAGs) are important scaffolding materials that can mimic the natural matrix niche. Here, we hypothesize that imposing changes in the scaffold composition or, more specifically, incorporating GAGs into the collagen meshwork, will affect the morphology, cytoskeletal organization and integrin expression profiles, and hence the fate of human mesenchymal stem cells (MSCs) upon the induction of differentiation. Using chondrogenesis as an example, we microencapsulated MSCs in three scaffold systems that had varying matrix compositions: collagen alone (C), aminated collagen (AC) and aminated collagen with GAGs (ACG). We then induced the MSCs to differentiate toward a chondrogenic lineage, after which, we characterized the cell viability and morphology, as well as the level of cytoskeletal organization and the integrin expression profile. We also studied the fate of the MSCs by evaluating the major chondrogenic markers at both the gene and protein level. In C, MSC chondrogenesis was successfully induced and MSCs that spread in the scaffolds had a clear actin cytoskeleton; they expressed integrin α2β1, α5 and αv; promoted sox9 nuclear localization transcription activation; and upregulated the expression of chondrogenic matrix markers. In AC, MSC chondrogenesis was completely inhibited but the scaffold still supported cell survival. The MSCs did not spread and they had no actin cytoskeleton; did not express integrin α2 or αv; they failed to differentiate into chondrogenic lineage cells even on chemical induction; and there was little colocalization or functional interaction between integrin α5 and fibronectin. In ACG, although the MSCs did not express integrin α2, they did express integrin αv and there was strong co-localization and hence functional binding between αv and fibronectin. In addition, vimentin was the dominant cytoskeletal protein in these cells, and the chondrogenic marker genes were expressed but at a much lower level than in the MSCs encapsulated in C alone. This work suggests the importance of controlling the matrix composition as a strategy to manipulate cell-matrix interactions (through changes in the integrin expression profile and cytoskeleton organization), and hence stem cell fates.

Tissue specific dysregulated protein subnetworks in type 2 diabetic bladder urothelium and detrusor muscle

Diabetes mellitus is well known to cause bladder dysfunction; however, the molecular mechanisms governing this process and the effects on individual tissue elements within the bladder are poorly understood, particularly in type 2 diabetes. A shotgun proteomics approach was applied to identify proteins differentially expressed between type 2 diabetic (TallyHo) and control (SWR/J) mice in the bladder smooth muscle and urothelium, separately. We were able to identify 1760 nonredundant proteins from the detrusor smooth muscle and 3169 nonredundant proteins from urothelium. Pathway and network analysis of significantly dysregulated proteins was conducted to investigate the molecular processes associated with diabetes. This pinpointed ERK1/2 signaling as a key regulatory node in the diabetes-induced pathophysiology for both tissue types. The detrusor muscle samples showed diabetes-induced increased tissue remodeling-type events such as Actin Cytoskeleton Signaling and Signaling by Rho Family GTPases. The diabetic urothelium samples exhibited oxidative stress responses, as seen in the suppression of protein expression for key players in the NRF2-Mediated Oxidative Stress Response pathway. These results suggest that diabetes induced elevated inflammatory responses, oxidative stress, and tissue remodeling are involved in the development of tissue specific diabetic bladder dysfunctions. Validation of signaling dysregulation as a function of diabetes was performed using Western blotting. These data illustrated changes in ERK1/2 phosphorylation as a function of diabetes, with significant decreases in diabetes-associated phosphorylation in urothelium, but the opposite effect in detrusor muscle. These data highlight the importance of understanding tissue specific effects of disease process in understanding pathophysiology in complex disease and pave the way for future studies to better understand important molecular targets in reversing bladder dysfunction.

Myopathic changes in murine skeletal muscle lacking synemin

Diseases of striated muscle linked to intermediate filament (IF) proteins are associated with defects in the organization of the contractile apparatus and its links to costameres, which connect the sarcomeres to the cell membrane. Here we study the role in skeletal muscle of synemin, a type IV IF protein, by examining mice null for synemin (synm-null). Synm-null mice have a mild skeletal muscle phenotype. Tibialis anterior (TA) muscles show a significant decrease in mean fiber diameter, a decrease in twitch and tetanic force, and an increase in susceptibility to injury caused by lengthening contractions. Organization of proteins associated with the contractile apparatus and costameres is not significantly altered in the synm-null. Elastimetry of the sarcolemma and associated contractile apparatus in extensor digitorum longus myofibers reveals a reduction in tension consistent with an increase in sarcolemmal deformability. Although fatigue after repeated isometric contractions is more marked in TA muscles of synm-null mice, the ability of the mice to run uphill on a treadmill is similar to controls. Our results suggest that synemin contributes to linkage between costameres and the contractile apparatus and that the absence of synemin results in decreased fiber size and increased sarcolemmal deformability and susceptibility to injury. Thus synemin plays a moderate but distinct role in fast twitch skeletal muscle.

Ovalbumin sensitization of guinea pig at birth prevents the ontogenetic decrease in airway smooth muscle responsiveness

Airway smooth muscle (ASM) displays a hyperresponsive phenotype at young age and becomes less responsive in adulthood. We hypothesized that allergic sensitization, which causes ASM hyperresponsiveness and typically occurs early in life, prevents the ontogenetic loss of the ASM hyperresponsive phenotype. We therefore studied whether neonatal allergic sensitization, not followed by later allergen challenges, alters the ontogenesis of ASM properties. We neonatally sensitized guinea pigs to ovalbumin and studied them at 1 week, 3 weeks, and 3 months (adult). A Schultz‐Dale response in isolated tracheal rings confirmed sensitization. The occurrence of inflammation was evaluated in the blood and in the submucosa of large airways. We assessed ASM function in tracheal strips as ability to produce force and shortening. ASM content of vimentin was also studied. A Schultz‐Dale response was observed in all 3‐week or older sensitized animals. A mild inflammatory process was characterized by eosinophilia in the blood and in the airway submucosa. Early life sensitization had no effect on ASM force generation, but prevented the ontogenetic decline of shortening velocity and the increase in resistance to shortening. Vimentin increased with age in control but not in sensitized animals. Allergic sensitization at birth without subsequent allergen exposures is sufficient to prevent normal ASM ontogenesis, inducing persistence to adulthood of an ASM hyperresponsive phenotype.

Airway smooth muscle (ASM) displays a hyperresponsive phenotype at young age and becomes less responsive in adulthood. In this study, we found that allergic sensitization at birth without subsequent allergen exposures is sufficient to prevent normal ASM ontogenesis, inducing persistence to adulthood of an ASM hyperresponsive phenotype.