Visualizing the dynamic coupling of claudin strands to the actin cytoskeleton through ZO-1

The organization and integrity of epithelial tight junctions depend on interactions between claudins, ZO scaffolding proteins, and the cytoskeleton. However, although binding between claudins and ZO-1/2/3 and between ZO-1/2/3 and numerous cytoskeletal proteins has been demonstrated in vitro, fluorescence recovery after photobleaching analysis suggests interactions in vivo are likely highly dynamic. Here we use superresolution live-cell imaging in a model fibroblast system to examine relationships between claudins, ZO-1, occludin, and actin. We find that GFP claudins make easily visualized dynamic strand patches between two fibroblasts; strand dynamics is constrained by ZO-1 binding. Claudin association with actin is also dependent on ZO-1, but colocalization demonstrates intermittent rather than continuous association between claudin, ZO-1, and actin. Independent of interaction with ZO-1 or actin, claudin strands break and reanneal; pulse-chase-pulse analysis using SNAP-tagged claudins showed preferential incorporation of newly synthesized claudins into break sites. Although claudin strand behavior in fibroblasts may not fully recapitulate that of epithelial tight junction strands, this is the first direct demonstration of the ability of ZO-1 to stabilize claudin strands. We speculate that intermittent tethering of claudins to actin may allow for accommodation of the paracellular seal to physiological or pathological alterations in cell shape or movement.

Download Full-text

Synthesis of putative microtubule-associated proteins by mouse blastocysts during early outgrowth in vitro

Canadian Journal of Biochemistry and Cell Biology ◽

10.1139/o84-113 ◽

1984 ◽

Vol 62 (9) ◽

pp. 885-893 ◽

Cited By ~ 5

Author(s):

William R. Bates ◽

Gerald M. Kidder

Keyword(s):

Cell Shape ◽

Polyacrylamide Gel Electrophoresis ◽

Blastocyst Stage ◽

Cytoskeletal Proteins ◽

Biochemical Basis ◽

Microtubule Associated Proteins ◽

Associated Proteins ◽

Two Stages

The outgrowth of mouse trophoblast in culture provides a simplified model system analogous in certain ways to blastocyst implantation in vivo. Day-four blastocysts cultured for 3 days in vitro undergo extensive changes in cell shape and motility which are likely to involve the complex cytoskeletal system of the trophoblast cells. To explore the biochemical basis of these changes, one set of cytoskeletal proteins, the microtubule-associated proteins (MAPs), was studied. Day 4 blastocysts were labeled with [35S]methionine and blastocyst outgrowths, after 3 days in culture from the blastocyst stage, were labeled with [3H] methionine. Labeled embryos were disrupted and the soluble supernatants were pooled, and newly synthesized proteins from the two stages were coassembled with taxol-stabilized brain microtubule polymer enriched for MAP-binding sites. Double-labeled coassembly proteins (putative MAPS) were then released from the microtubule polymer by treatment with 0.35 M NaCl and analyzed by one-dimensional polyacrylamide gel electrophoresis. 3H/35S dpm ratios were determined for individual protein bands to compare the relative synthesis rates for day 4 blastocyst and day 3 outgrowth MAPs. In spite of the extensive changes in cell shape and motility associated with blastocyst outgrowth, a common set of putative MAPs characterizes the two stages investigated, including several in the size range of tau factors. No synthesis of high molecular weight MAPs comparable with MAP 1 or MAP 2 from brain was detected. The synthesis rates of individual MAPs relative to each other remain constant over this period and are likely coordinated with total protein and tubulin synthesis.

Download Full-text

Insulin induces rapid and specific rearrangement of the cytoskeleton of rat mesangial cells in vitro.

Journal of Histochemistry & Cytochemistry ◽

10.1177/44.2.8609378 ◽

1996 ◽

Vol 44 (2) ◽

pp. 91-101 ◽

Cited By ~ 9

Author(s):

A K Berfield ◽

G J Raugi ◽

C K Abrass

Keyword(s):

Mesangial Cells ◽

Focal Adhesions ◽

Cytoskeletal Proteins ◽

Direct Effects ◽

Ligand Effects ◽

Igf I ◽

Induced Changes ◽

Secondary Ligand

Mesangial cells (MCs) grown without supplemental insulin (SI-MCs) express a quiescent phenotype and extracellular matrix (ECM) composition similar to MCs in vivo. In contrast, MCs routinely propagated in insulin (SI+MCs) are stimulated to proliferate, change their phenotype, and produce large amounts of collagens I and III. These effects of insulin may in part be mediated through cytoskeletal rearrangement. Differences in cytoskeletal arrangement were compared between SI-MCs and SI+MCs and 1 hr after addition of insulin (1 nM) or IGF-1 (100 nM) to SI-MCs. Cells were examined by light microscopy, electron microscopy, and immunostaining for specific cytoskeletal proteins and fibronectin. Insulin induced rapid rearrangement of stress fibers. Surface ruffling, actin aggregation, vimentin retraction, rearrangement of vinculin in focal adhesions, and fibronectin extraction were apparent. These direct effects of insulin on the SI-MC cytoskeleton occurred before insulin-induced changes in ECM composition. IGF-I induced cytoskeletal reorganization distinct from insulin. These observations demonstrate that insulin and IGF-I have unique effects on the MC cytoskeleton, which is turn may mediate secondary ligand effects on MCs.

Download Full-text

Regulation of GABAergic synapse formation and plasticity by GSK3β-dependent phosphorylation of gephyrin

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1011824108 ◽

2010 ◽

Vol 108 (1) ◽

pp. 379-384 ◽

Cited By ~ 116

Author(s):

Shiva K. Tyagarajan ◽

Himanish Ghosh ◽

Gonzalo E. Yévenes ◽

Irina Nikonenko ◽

Claire Ebeling ◽

...

Keyword(s):

Synaptic Plasticity ◽

Hippocampal Neurons ◽

Glycogen Synthase ◽

Phosphorylation Site ◽

Scaffolding Protein ◽

Scaffolding Proteins ◽

Gabaergic Synapse ◽

Gabaergic Synapses

Postsynaptic scaffolding proteins ensure efficient neurotransmission by anchoring receptors and signaling molecules in synapse-specific subcellular domains. In turn, posttranslational modifications of scaffolding proteins contribute to synaptic plasticity by remodeling the postsynaptic apparatus. Though these mechanisms are operant in glutamatergic synapses, little is known about regulation of GABAergic synapses, which mediate inhibitory transmission in the CNS. Here, we focused on gephyrin, the main scaffolding protein of GABAergic synapses. We identify a unique phosphorylation site in gephyrin, Ser270, targeted by glycogen synthase kinase 3β (GSK3β) to modulate GABAergic transmission. Abolishing Ser270 phosphorylation increased the density of gephyrin clusters and the frequency of miniature GABAergic postsynaptic currents in cultured hippocampal neurons. Enhanced, phosphorylation-dependent gephyrin clustering was also induced in vitro and in vivo with lithium chloride. Lithium is a GSK3β inhibitor used therapeutically as mood-stabilizing drug, which underscores the relevance of this posttranslational modification for synaptic plasticity. Conversely, we show that gephyrin availability for postsynaptic clustering is limited by Ca2+-dependent gephyrin cleavage by the cysteine protease calpain-1. Together, these findings identify gephyrin as synaptogenic molecule regulating GABAergic synaptic plasticity, likely contributing to the therapeutic action of lithium.

Download Full-text

ACTN1 Supports Tumor Growth by Inhibiting Hippo Signaling in Hepatocellular Carcinoma

10.21203/rs.3.rs-72190/v1 ◽

2020 ◽

Author(s):

Qian Chen ◽

Xiao-Wei Zhou ◽

Ai-Jun Zhang ◽

Kang He

Keyword(s):

Hepatocellular Carcinoma ◽

Cell Proliferation ◽

Tumor Growth ◽

Expression Pattern ◽

Cytoskeletal Proteins ◽

Gene Set Enrichment Analysis ◽

Hippo Signaling ◽

Hcc Cells

Abstract Background: Alpha actinins (ACTNs) are major cytoskeletal proteins and exhibit many non-muscle functions. Emerging evidence have uncovered the regulatory role of ACTNs in tumorigenesis, however, the expression pattern, biological functions, and underlying mechanism of ACTN1 in hepatocellular carcinoma (HCC) remain largely unexplored.Methods: Immunohistochemical analysis of a HCC tissue microarray (n = 157) was performed to determine the expression pattern and prognostic value of ACTN1 in HCC. In vitro loss-of-function study in HCC cells were carried out to investigate ACTN1 knockdown on cell proliferation. In vivo subcutaneous xenograft model and intrahepatic transplantation model were generated to decipher the contribution of ACTN1 in the tumor growth of HCC. Gene set enrichment analysis, quantitative real-time PCR, Co-immunoprecipitation, immunofluorescence and western blotting were performed to identify the underlying molecular mechanism.Results: It was found that ACTN1 was significantly upregulated in HCC tissues and closely related to llpha-fetoprotein level, tumor thrombus, tumor size, TNM stage and patient prognoses. Knockdown of ACTN1 suppressed in vitro cell proliferation and in vivo tumor growth of HCC cells. Mechanistically, knockdown of ACTN1 increased Hippo signaling pathway activity and decrease Rho GTPases activities. Mechanistically, ACTN1 could competitively interact with MOB1 and decrease the phosphorylation of LATS1 and YAP. The growth-promoting effect induced by ACTN1 was significantly abrogated by pharmacological inhibition of YAP with verteporfin or super-TDU.Conclusions: ACTN1 is highly expressed in HCC tissues and acts as a tumor promoter by suppressing Hippo signaling via physical interaction with MOB1. ACTN1 may serve as a potential prognostic marker and therapeutic target for HCC.

Download Full-text

Role of estrogen receptor coregulators in endocrine resistant breast cancer

Exploration of Targeted Anti-tumor Therapy ◽

10.37349/etat.2021.00052 ◽

2021 ◽

pp. 385-400

Author(s):

Kristin A. Altwegg ◽

Ratna K. Vadlamudi

Keyword(s):

Breast Cancer ◽

Estrogen Receptor ◽

Therapy Resistance ◽

Vital Role ◽

In Vivo Studies ◽

Scaffolding Proteins ◽

Current State ◽

Er Alpha

Breast cancer (BC) is the most ubiquitous cancer in women. Approximately 70-80% of BC diagnoses are positive for estrogen receptor (ER) alpha (ERα). The steroid hormone estrogen [17β-estradiol (E2)] plays a vital role both in the initiation and progression of BC. The E2-ERα mediated actions involve genomic signaling and non-genomic signaling. The specificity and magnitude of ERα signaling are mediated by interactions between ERα and several coregulator proteins called coactivators or corepressors. Alterations in the levels of coregulators are common during BC progression and they enhance ligand-dependent and ligand-independent ERα signaling which drives BC growth, progression, and endocrine therapy resistance. Many ERα coregulator proteins function as scaffolding proteins and some have intrinsic or associated enzymatic activities, thus the targeting of coregulators for blocking BC progression is a challenging task. Emerging data from in vitro and in vivo studies suggest that targeting coregulators to inhibit BC progression to therapy resistance is feasible. This review explores the current state of ERα coregulator signaling and the utility of targeting the ERα coregulator axis in treating advanced BC.

Download Full-text

FtsZ-Dependent Elongation of a Coccoid Bacterium

mBio ◽

10.1128/mbio.00908-16 ◽

2016 ◽

Vol 7 (5) ◽

Cited By ~ 13

Author(s):

Ana R. Pereira ◽

Jen Hsin ◽

Ewa Król ◽

Andreia C. Tavares ◽

Pierre Flores ◽

...

Keyword(s):

Staphylococcus Aureus ◽

Cell Shape ◽

Single Point ◽

Spherical Shape ◽

Single Point Mutation ◽

Wild Type ◽

Dead End ◽

Dynamics Simulations

ABSTRACT A mechanistic understanding of the determination and maintenance of the simplest bacterial cell shape, a sphere, remains elusive compared with that of more complex shapes. Cocci seem to lack a dedicated elongation machinery, and a spherical shape has been considered an evolutionary dead-end morphology, as a transition from a spherical to a rod-like shape has never been observed in bacteria. Here we show that a Staphylococcus aureus mutant (M5) expressing the ftsZ G193D allele exhibits elongated cells. Molecular dynamics simulations and in vitro studies indicate that FtsZ G193D filaments are more twisted and shorter than wild-type filaments. In vivo , M5 cell wall deposition is initiated asymmetrically, only on one side of the cell, and progresses into a helical pattern rather than into a constricting ring as in wild-type cells. This helical pattern of wall insertion leads to elongation, as in rod-shaped cells. Thus, structural flexibility of FtsZ filaments can result in an FtsZ-dependent mechanism for generating elongated cells from cocci. IMPORTANCE The mechanisms by which bacteria generate and maintain even the simplest cell shape remain an elusive but fundamental question in microbiology. In the absence of examples of coccus-to-rod transitions, the spherical shape has been suggested to be an evolutionary dead end in morphogenesis. We describe the first observation of the generation of elongated cells from truly spherical cocci, occurring in a Staphylococcus aureus mutant containing a single point mutation in its genome, in the gene encoding the bacterial tubulin homologue FtsZ. We demonstrate that FtsZ-dependent cell elongation is possible, even in the absence of dedicated elongation machinery.

Download Full-text

Localization of cytoskeletal proteins in preimplantation mouse embryos

Development ◽

10.1242/dev.55.1.211 ◽

1980 ◽

Vol 55 (1) ◽

pp. 211-225

Author(s):

E. Lehtonen ◽

R. A. Badley

Keyword(s):

Blastocyst Stage ◽

Cytoskeletal Proteins ◽

Mouse Embryos ◽

Trophectoderm Cells ◽

Apparent Concentration ◽

Preimplantation Mouse ◽

Early Mouse ◽

Filament Protein

The immunofluorescence technique was used to detect the presence and distribution of actin, alpha-actinin, tubulin and 10 nm filament protein in early mouse embryos. Actin and alpha-actinin stainings showed a distinct concentration to a peripheral layer in the cleavage-stage blastomeres and in trophectoderm cells. Dots of fluorescence appeared in this cortical staining pattern. The distribution of tubulin staining in the blastomere cytoplasm was relatively even with apparent concentration at the perinuclear region and frequently at wide intercellular contact areas. 10 nm filament protein was distributed evenly in the blastomere cytoplasm without cortical concentration of the label. At the blastocyst stage, the trophectoderm cells in blastocyst outgrowths in vitro developed well organized cytoskeletons including both microfilament, microtubule and 10 nm filament elements. Comparable structures were not observed in blastocysts in vivo, or in late hatched blastocysts cultured in suspension. The morphogenetic significance of the observations is discussed.

Download Full-text

Steroidal glycoalkaloids fromSolanum nigrumtarget cytoskeletal proteins: anin silicoanalysis

PeerJ ◽

10.7717/peerj.6012 ◽

2019 ◽

Vol 7 ◽

pp. e6012 ◽

Cited By ~ 2

Author(s):

Rumana Ahmad

Keyword(s):

Binding Affinity ◽

Anticancer Agents ◽

Principal Component ◽

Cytoskeletal Proteins ◽

Hydroxyl Group ◽

Docking Analysis ◽

Drug Candidates ◽

Division Cell

BackgroundSolanum nigrum(black nightshade;S. nigrum), a member of family Solanaceae, has been endowed with a heterogeneous array of secondary metabolites of which the steroidal glycoalkaloids (SGAs) and steroidal saponins (SS) have vast potential to serve as anticancer agents. Since there has been much controversy regarding safety of use of glycoalkaloids as anticancer agents, this area has remained more or less unexplored. Cytoskeletal proteins like actin play an important role in maintaining cell shape, synchronizing cell division, cell motility, etc. and along with their accessory proteins may also serve as important therapeutic targets for potential anticancer candidates. In the present study, glycoalkaloids and saponins fromS. nigrumwere screened for their interaction and binding affinity to cytoskeletal proteins, using molecular docking.MethodsBioactivity score and Prediction of Activity Spectra for Substances (PASS) analysis were performed using softwares Molinspiration and Osiris Data Explorer respectively, to assess the feasibility of selected phytoconstituents as potential drug candidates. The results were compared with two standard reference drugs doxorubicin hydrochloride (anticancer) and tetracycline (antibiotic). Multivariate data obtained were analyzed using principal component analysis (PCA).ResultsDocking analysis revealed that the binding affinities of the phytoconstituents towards the target cytoskeletal proteins decreased in the order coronin>villin>ezrin>vimentin>gelsolin>thymosin>cofilin. Glycoalkaloid solasonine displayed the greatest binding affinity towards the target proteins followed by alpha-solanine whereas amongst the saponins, nigrumnin-I showed maximum binding affinity. PASS Analysis of the selected phytoconstituents revealed 1 to 3 violations of Lipinski’s parameters indicating the need for modification of their structure-activity relationship (SAR) for improvement of their bioactivity and bioavailability. Glycoalkaloids and saponins all had bioactivity scores between −5.0 and 0.0 with respect to various receptor proteins and target enzymes. Solanidine, solasodine and solamargine had positive values of druglikeness which indicated that these compounds have the potential for development into future anticancer drugs. Toxicity potential evaluation revealed that glycoalkaloids and saponins had no toxicity, tumorigenicity or irritant effect(s). SAR analysis revealed that the number, type and location of sugar or the substitution of hydroxyl group on alkaloid backbone had an effect on the activity and that the presence of α-L-rhamnopyranose sugar at C-2 was critical for a compound to exhibit anticancer activity.ConclusionThe present study revealed some cytoskeletal target(s) forS. nigrumphytoconstituents by docking analysis that have not been previously reported and thus warrant further investigations bothin vitroandin vivo.

Download Full-text

Regulation of human epithelial tight junction proteins by Lactobacillus plantarum in vivo and protective effects on the epithelial barrier

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00327.2009 ◽

2010 ◽

Vol 298 (6) ◽

pp. G851-G859 ◽

Cited By ~ 288

Author(s):

Jurgen Karczewski ◽

Freddy J. Troost ◽

Irene Konings ◽

Jan Dekker ◽

Michiel Kleerebezem ◽

...

Keyword(s):

Tight Junction ◽

Lactobacillus Plantarum ◽

Transmembrane Protein ◽

Intestinal Barrier ◽

Protective Effects ◽

Epithelial Tight Junction ◽

Vitro Model ◽

Probiotic Mechanisms

Lactobacillus plantarum , a commensal bacterium of humans, has been proposed to enhance the intestinal barrier, which is compromised in a number of intestinal disorders. To study the effect of L. plantarum strain WCFS1 on human barrier function, healthy subjects were administered L. plantarum or placebo in the duodenum for 6 h by means of a feeding catheter. The scaffold protein zonula occludens (ZO)-1 and transmembrane protein occludin were found to be significantly increased in the vicinity of the tight-junction (TJ) structures, which form the paracellular seal between cells of the epithelium. In an in vitro model of the human epithelium, L. plantarum induced translocation of ZO-1 to the TJ region; however, the effects on occludin were minor compared with those seen in vivo. L. plantarum was shown to activate Toll-like receptor 2 (TLR2) signaling, and treatment of Caco-2 monolayers with the TLR2 agonist Pam3-Cys-SK4(PCSK) significantly increased fluorescent staining of occludin in the TJ. Pretreatment of Caco-2 monolayers with L. plantarum or PCSK significantly attenuated the effects of phorbol ester-induced dislocation of ZO-1 and occludin and the associated increase in epithelial permeability. Our results identifying commensal bacterial stimulation of TLR2 in the gut epithelium as a regulator of epithelial integrity have important implications for understanding probiotic mechanisms and the control of intestinal homeostasis.

Download Full-text