Tri-ortho-cresyl phosphate (TOCP) decreases the levels of cytoskeletal proteins in hen sciatic nerve

Tri-ortho-cresyl phosphate (TOCP) is an organophosphorus ester. It is capable of producing organophosphorus ester induced delayed neurotoxicity (OPIDN) in human being and sensitive animals, which is characterized by ataxia that progresses to paralysis after 1-3 weeks following exposure to some organophosphorus ester. In present study, 18 adult hens were divided randomly into three groups, i.e. two experimental groups and control group (n = 6 each group). All hens were 10 months old and weighted 1.5-2.0 kg. The hens in two experimental groups were treated with TOCP by gavage at single dosages of 375 and 750 mg/kg respectively. TOCP was dissolved in corn oil and administered at 0.65 ml/kg. Six control hens received an equivalent volume of corn oil by gavage. All hens were sacrificed after 21 days of treatment and the sciatic nerves were dissected, homogenized and used for the determination of cytoskeletal proteins by western blotting. The levels of neurofilament (NF) subunits were decreased both in supernatant and pellet of sciatic nerves, and the most noticeable decrease in levels of NF subunits protein was observed in neurofilament medium (NF-M). Compared to the control hens, neurofilament heavy (NF-H) level decreased by 36 and 38% (P < 0.01) in the pellet and by 27 and 26% (P < 0.05) in the supernatant of sciatic nerves of hens treated with 375 and 750 mg/kg TOCP respectively. The reduction of NF-M were 36 and 68% (P < 0.01) in pellet, 50 and 67% (P < 0.01) in supernatant at 375 and 750 mg/kg dosage respectively. The neurofilament light (NF-L) lessened slightly, but the relative percentage of integrated optical density (IOD) was no significant alteration when compared to the control hens. There were significant decreases in levels of alpha-tubulin, beta-tubulin in pellet and alpha-tubulin, beta-tubulin, beta-actin in supernatant of sciatic nerves in TOCP-treated hens. Thus, the decreases of cytoskeletal proteins suggested the possible involvement of them in delayed neurotoxicity.

Regional rheological differences in locomoting neutrophils

Intracellular rheology is a useful probe of the mechanisms underlying spontaneous or chemotactic locomotion and transcellular migration of leukocytes. We characterized regional rheological differences between the leading, body, and trailing regions of isolated, adherent, and spontaneously locomoting human neutrophils. We optically trapped intracellular granules and measured their displacement for 500 ms after a 100-nm step change in the trap position. Results were analyzed in terms of simple viscoelasticity and with the use of structural damping (stress relaxation follows a power law in time). Structural damping fit the data better than did viscoelasticity. Regional viscoelastic stiffness and viscosity or structural damping storage and loss moduli were all significantly lower in leading regions than in pooled body and/or trailing regions (the latter were not significantly different). Structural damping showed similar levels of elastic and dissipative stresses in body and/or trailing regions; leading regions were significantly more fluidlike (increased power law exponent). Cytoskeletal disruption with cytochalasin D or nocodazole made body and/or trailing regions approximately 50% less elastic and less viscous. Cytochalasin D completely suppressed pseudopodial formation and locomotion; nocodazole had no effect on leading regions. Neither drug changed the dissipation-storage energy ratio. These results differ from those of studies of neutrophils and other cell types probed at the cell membrane via beta(2)-integrin receptors, which suggests a distinct role for the cell cortex or focal adhesion complexes. We conclude that 1) structural damping well describes intracellular rheology, and 2) while not conclusive, the significantly more fluidlike behavior of the leading edge supports the idea that intracellular pressure may be the origin of motive force in neutrophil locomotion.

Growth factor-estradiol interaction on DNA labeling and cytoskeletal protein expression in cultured rat astrocytes

Growth factors are major signaling agents regulating neuron-glia dialogue. Epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), insulin growth factor-I (IGF-I) and insulin (INS) induce neuronal and astroglial cell proliferation and differentiation. This is true also for estrogens that influence astrocytes and exert neuroprotectant activity. In this study interactions between growth factors and estradiol on DNA labeling and glial fibrillary acidic protein (GFAP) and vimentin expression in cultured astrocytes were investigated. DNA labeling was significantly stimulated by bFGF pretreatment followed by 24 h estradiol and EGF or IGF-I or INS added in the last 12 h. Western blotting showed also a modulation of GFAP and vimentin expression in treated astrocytes. This suggests the occurrence of a crucial growth factor-estradiol interaction on DNA labeling and cytoskeletal protein expression during astrocyte proliferation and differentiation in culture.

New insight into the mechanism of hip prosthesis loosening: effect of titanium debris size on osteoblast function

The incidence of rheumatoid arthritis and osteoarthritis is on the rise due to our expanding elderly population. Total joint arthroplasty is the most successful, prevalent treatment modality for these and other degenerative hip conditions. Despite the wide array of prosthetic devices commercially available, hip prostheses share a common problem with a gradual and then accelerating loss of bone tissue and bone-implant interface integrity, followed by implant instability and loosening. Implant failure is largely the result of inevitable wear of the device and generation of wear debris. To provide information for the development of improved prosthetic wear characteristics, we examined the effects of size-separated titanium particles on bone forming cell populations. We demonstrate unequivocally that particle size is a critical factor in the function, proliferation, and viability of bone-forming osteoblasts in vitro. In addition, we have elucidated the time-dependent distribution of the phagocytosed particles within the osteoblast, indicating an accumulation of particles in the perinuclear area of the affected cells. The report finds that particle size is a critical factor in changes in the bone formation-related functions of osteoblasts exposed to simulate wear debris, and that 1.5-4 microm titanium particles have the greatest effect on osteoblast proliferation and viability in vitro. The size of titanium particles generated through wear of a prosthetic device may be an important consideration in the development of superior implant technology.

The effects of clozapine on the GSK-3-mediated signaling pathway

We investigated the effect of 10 microM clozapine on the activity of glycogen synthase kinase-3beta (GSK-3beta) and its upstream and downstream molecules in SH-SY5Y human neuroblastoma cells. Clozapine activates both Akt- and Dvl-mediated phosphorylation of GSK-3beta through phosphorylation at Ser9, and increased total cellular and intranuclear levels of beta-catenin. Pretreatment with the specific inhibitor of the phosphatidylinositol 3-kinase (PI3K)-Akt pathway, LY294002 (20 microM), prevented the phosphorylation of Akt but did not affect the phosphorylation of GSK-3beta. These results suggest that clozapine regulates the phosphorylation of GSK-3beta through Wnt signal pathways involving Dvl upstream but not through the PI3K-Akt pathway in SH-SY5Y cells.

S100B protein stimulates calcineurin activity

S100B is a calcium binding protein from astrocytes that regulates protein phosphorylation by binding to substrates and protein kinases. S100B might also regulate protein phosphatases and this was investigated for protein phosphatase 2B (calcineurin). The results indicate that S100B (5-10 microM) increased the activity of both purified and cytoskeletal calcineurin in a Ca-dependent manner. This effect was blocked by a specific inhibitor of calcineurin activity, but not by TRTK-12 (an inhibitor of S100B binding to other protein targets). The present results and the known co-localization of S100B and calcineurin in the astrocyte cytoskeleton suggest that S100B may play a role in the phosphorylation state of cytoskeletal proteins.

Wnt breakers in colon cancer

Beta-catenin and Tcf4 are the downstream effectors of the Wnt signaling cascade. In colorectal cancer, mutations in Wnt cascade genes such as APC lead to the inappropriate formation of beta-catenin/Tcf4 complexes. Earlier work has predicted that disruption of the beta-catenin/Tcf4 protein-protein interaction could revert the proliferative phenotype of colorectal cancer cells. In this issue of Cancer Cell, Shivdasani and colleagues have explored high-throughput screening of compound libraries in a search for small molecule inhibitors of the Wnt cascade. Ultimately, such inhibitors could become a novel class of smart anticancer drugs.

α2a adrenoceptors regulate phosphorylation of microtubule-associated protein-2 in cultured cortical neurons

Adrenoceptors have been suggested to mediate neuronal development. This study revealed the expression of alpha2A adrenoceptors in the cortical plate of fetal mouse cerebral wall. The effects of alpha2A adrenoceptor on dendrite growth were investigated in primary neuronal cultures. Application of alpha2 adrenoceptor agonists, BHT 933 or UK 14304 for 24 or 72 h resulted in a 1.5-2-fold increase in dendrite lengths. This effect was blocked by alpha2 adrenergic antagonists, RX 821002 or yohimbine, as well as a alpha2A selective antagonist, BRL 44408, but not by alpha2B/alpha2C selective antagonists ARC 239, imiloxan and rauwolscine. Guanfacine, a alpha2A selective agonists, also significantly increased the dendrite lengths in culture. These results suggest that the morphological effect is wholly attributable to alpha2A adrenoceptor activation. We further tested the hypothesis that alpha2A adrenoceptors act through altering the phosphorylation state of microtubule-associated protein 2. The results showed that the phosphorylation of microtubule-associated protein 2 was significantly reduced on both serine and threonine residues by over 40% after 2 h of application of guanfacine and was maintained at this low level for a prolonged time up to 96 h. These findings suggest that alpha2A adrenoceptors regulate the phosphorylation of microtubule-associated protein 2, which in turn mediates dendrite growth of cortical neurons.

Cholesterol oxides mediated changes in cytoskeletal organisation involves Rho GTPases☆☆

The small GTPases Rho, Rac, and Cdc42 regulate the actin cytoskeleton in all eukaryotic cells. In this study we have evaluated the effect of cholesterol oxides (7-ketocholesterol and 25-hydroxycholesterol) on cell migration, cell adhesion, and cytoskeletal organisation of lens epithelial cells (LEC). Effects of cholesterol oxides on cytoskeleton were evaluated by immunofluorescence confocal microscopy. The 7-ketocholesterol induced cell arborisation, with bundling of vimentin and tubulin in the cell processes and formation of filopodia and stress fibres. Cells treated with 25-hydroxycholesterol showed a collapse of vimentin filaments towards the nucleus and formation of lamellipodia. In addition, cells treated with 7-ketocholesterol or 25-hydroxycholesterol showed decreased migration. The effects of cholesterol oxides on cytoskeletal proteins involve the activation of the small GTPases Rho, Rac, and Cdc42. Indeed, formation of both filopodia and stress fibres induced by 7-ketocholesterol is inhibited by overexpressing dominant negatives forms of Cdc42 and RhoA, respectively. Similarly, the collapse of vimentin intermediate filament network and the formation of lamellipodia, induced by 25-hydroxycholesterol, is inhibited by overexpressing dominant negatives forms of Rac1. The effects of cholesterol oxides described in this study for LEC are also observed for at least two other cell lines (H36CE and U373), suggesting that this may represent a general mechanism whereby cholesterol oxides induces cytoskeletal disorganisation.

[Effect of adriamycin on expression and content of myocardial structural and regulatory proteins]

The biochemical and morphological study of the cytoskeleton and extracellular matrix of rat heart was carried out after single injection of adriamycin (2.2 or 0.44 mg/kg). Hearts were taken for the study after 2 hours and 3 weeks after injection. The light and electronic microscopy, immunohistochemical determination of type I, III and IV collagens and fibronectin using specific antibodies were implied for morphological study; electrophoresis and immunoblotting were implied for the determination of the content of some proteins of cardiomyocytes (KRP or telokin, desmin, tubulin and vinculin), and extracellular matrix (fibronectin) and vascular smooth muscle cells (MLCK, myosin light chain kinase). Adriamycin injection in the dose 2.2 mg/kg which is close to therapeutic and known to alter intracellular membranes approximately in the half of cardiomyocytes, did not influence the relative volume and structure of collagen network but distinctly reduced the density of fibronectin-distribution. The content of tubulin, fibronectin, MLCK and KRP was significantly decreased by 18-24%, while contents of desmin and vinculin were changed insignificantly. After 3 weeks, an increased density and extension of collagen network indicating the development of diffuse fibrosis were observed. Contents of tubulin and KRP were increased above control level by 50 and 20%, respectively. Similar hyperrestitution of tubulin, fibronectin and KRP content by 15-25% was determined after smaller dose of adriamycin (0.44 mg/kg). Only content of MLCK out of proteins studied remained at lower level in both groups by 25-34%. Isolated chick embryo cardiomyocytes subjected to adriamycin responded by increased level of KRP expression by 20% in 4 days while the level of tubulin expression remained unchanged. Results showed that damage of cardiomyocytes and extracellular matrix after single injection of adriamycin in the dose close to therapeutic was followed by increased expression of some proteins of cytoskeleton and extracellular matrix. KRP seems to play active role in this reparative response while the steadily reduced level of MLCK expression may disturb the control of coronary vessels.

Skeletal muscle cells and adipocytes differ in their reliance on TC10 and Rac for insulin-induced actin remodeling

Insulin causes distinct cortical actin remodeling in muscle and fat cells, and interfering with actin dynamics halts glucose transporter 4 (GLUT4) translocation to the membrane. Phosphatidylinositol 3-kinase (PI3-K) and the small G protein Rac govern myocyte actin remodeling, whereas TC10 alpha contributes to adipocyte actin dynamics downstream of Cbl-associated protein (CAP) and Cbl, independently of PI3-K. Given the importance of insulin action in both cell types, it is paramount to determine whether signaling pathways and actin manifestations are cell type specific. We found CAP expression and insulin-mediated Cbl phosphorylation in differentiated myotubes but not in myoblasts. Unlike adipocytes, Cbl is phosphorylated on Y774 and Y731 in myotubes. TC10 alpha and beta-transcripts are amplified by RT-PCR in muscle cells, but the endogenous proteins are barely detectable using two unrelated antibodies. TC10 alpha transfected into myoblasts is activated by insulin despite the lack of CAP expression and Cbl phosphorylation. Moreover, dominant-negative TC10 alpha mutants do not prevent insulin-induced actin remodeling in either myoblasts or myotubes and do not interfere with insulin-mediated recruitment of c-myc epitope-tagged GLUT4 to the cell surface. In contrast to TC10 alpha, endogenous Rac is readily detectable in both muscle cells and adipocytes and binds GTP after insulin in a PI3-K-dependent manner. These data suggest that whereas individual components of the CAP to TC10 pathway are regulated by insulin, a functional TC10-dependent signaling pathway leading to actin remodeling and GLUT4 translocation may not operate in myocytes, as it does in adipocytes.

Prenatal cocaine exposure alters glycogen synthase kinase-3beta (GSK3beta) pathway in select rabbit brain areas

Prenatal cocaine exposure in rabbits induces cerebrocortical structural abnormalities. Glycogen synthase kinase-3beta (GSK3beta) plays an important role in neuronal development and survival. This study was designed to examine the effect of prenatal cocaine on brain GSK3beta. Rabbits exposed in utero to cocaine and assessed on postnatal day 20 had increased basal levels of phospho-GSK3beta (ser-9) in frontal cortex (FCX) and striatum, but not hippocampus (HP). However, no changes in GSK3beta expression were detected in the brain regions of treated rabbits. Consistent with the change in GSK3beta activity, levels of beta-catenin, a downstream substrate of GSK3beta, increased in FCX but not in HP of cocaine offspring. Administration of a D(1) dopamine receptor agonist inhibited GSK3beta activity in FCX and HP of control rabbits but not in cocaine offspring. This loss of GSK3beta inhibition is in accord with the previously demonstrated dysfunction of this receptor in in utero cocaine-exposed animals. The results indicate that prenatal cocaine exposure alters GSK3beta pathway in select brain areas and may underlie the structural changes noted in these animals.

Nephrotoxic effects of chronic administration of microcystins -LR and -YR

Acute intoxication with MC-LR induces cytoskeletal alterations, apoptosis and necrosis of hepatocytes resulting in intrahepatic hemorrhage. Preliminary results have shown that chronic treatment of rats with intraperitoneal injections of sublethal doses of microcystins MC-LR and MC-YR could induce not only liver, but also kidney injuries. We aimed to investigate whether the induction of the cytoskeletal changes, apoptosis and necrosis could be the mechanisms involved in the injury of kidney cells in the chronic model of microcystin intoxication. Experimental rats were receiving intraperitoneal injections of MC-LR (10 microg/kg) or MC-YR (10 microg/kg) every second day for 8 months, while control rats were receiving only the vehicle. The histopathological investigation revealed collapsed glomeruli with thickened basement membranes and dilated tubuli filled with eosinophilic casts. Rhodamine-phalloidin labeling showed cytoplasmic aggregation and accumulation of fibrilar actin filaments within the epithelial tubular cells. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) showed increased number of TUNEL-positive cells in the kidney cortex and medulla. The pathological changes induced by MC-LR appeared more severe than those induced by MC-YR. The results support the view that at the cellular level, the mechanisms that underly the chronic nephrotoxicity are similar to the mechanisms of the acute hepatotoxicity of microcystins.

Requirement for intracellular calcium modulation in zebrafish dorsal-ventral patterning

The phosphoinositide (PI) cycle is an important signal transduction pathway that, upon activation, generates intracellular second messengers and leads to calcium release. To determine whether PI cycle-mediated intracellular calcium release is required for body plan formation, we systematically dissect PI cycle function in the zebrafish (Danio rerio). We inhibit PI cycle function at three different steps and deplete internal calcium stores, demonstrating an impact on endogenous calcium release and Wnt/beta-catenin signaling. Inhibition of endogenous calcium modulation induces hyperdorsalized phenotypes in a dose-dependent manner. Ectopic dorsal-signaling centers are generated in PI cycle-inhibited embryos as demonstrated by altered beta-catenin subcellular localization and ectopic expression of beta-catenin target genes. These results provide evidence that modulation of calcium release is critical for early embryonic patterning and acts by influencing the stabilization of beta-catenin protein.

[Signaling pathways that control the growth and survival of prostate tumor cells in the absence of androgens]

Androgen-dependent human prostate adenocarcinoma cell line LNCaP was used to study the effect of androgen deprivation on the cell response to TNF-related cytokines. Several signaling pathways were implicated in cell survival in the absence of androgens. In androgen-deprived LNCaP cells, TNF-alpha and TRAIL stimulated the cell growth and activated the mitogenic and antiapoptotic signaling pathways involving NF-kappa B, STAT3, PI3K, and beta-catenin. The results suggested a role of cytokines in the survival of prostate adenocarcinoma cells deprived of androgens in vitro.

Retinoic acid inhibits chondrogenesis of mesenchymal cells by sustaining expression of N-cadherin and its associated proteins

Retinoic acid (RA) is a well-known regulator of chondrocyte phenotype. RA inhibits chondrogenic differentiation of mesenchymal cells and also causes loss of differentiated chondrocyte phenotype. The present study investigated the mechanisms underlying RA regulation of chondrogenesis. RA treatment in chondrifying mesenchymal cells did not affect precartilage condensation, but blocked progression from precartilage condensation to cartilage nodule formation. This inhibitory effect of RA was independent of protein kinase C and extracellular signal-regulated protein kinase, which are positive and negative regulators of cartilage nodule formation, respectively. The progression from precartilage condensation to cartilage nodule requires downregulation of N-cadherin expression. However, RA treatment caused sustained expression of N-cadherin and its associated proteins including alpha- and beta-catenin suggesting that modulation of expression of these molecules is associated with RA-induced inhibition of chondrogenesis. This hypothesis was supported by the observation that disruption of the actin cytoskeleton by cytochalasin D (CD) blocks RA-induced sustained expression of cell adhesion molecules and overcomes RA-induced inhibition of chondrogenesis. Taken together, our results suggest RA inhibits chondrogenesis by stabilizing cell-to-cell interactions at the post-precartilage condensation stage.

Regulation of cell morphology and adhesion by the tuberous sclerosis complex (TSC1/2) gene products in human kidney epithelial cells through increased E-cadherin/beta-catenin activity

We investigated the effects of overexpression of the tuberous sclerosis-1 and -2 (TSC1/2) gene products (hamartin and tuberin, respectively) in the human kidney epithelial cell line 293 with an inducible expression system. As we had observed previously in fibroblasts, 293 cells overexpressing hamartin and/or tuberin grew more slowly in vitro. However, here we also observed that the 293 overexpressing cells underwent a dramatic morphological change in which groups of cells formed compact clusters. The overexpressing cells also displayed decreased dissociation and increased reaggregation in vitro. These changes were found to be associated with an increased level of E-cadherin, which is known to regulate cell-cell interactions in epithelial cells, and of its binding partner beta-catenin. Consistent with the role of E-cadherin in these effects, we found that the observed changes in 293 cell morphology, dissociation, and adhesion were calcium-dependent, and were reproduced by overexpression of E-cadherin. In contrast, overexpression of TSC1 in rat embryo fibroblasts, which lack E-cadherin, failed to elicit the same changes as in 293 cells. We conclude that the hamartin/tuberin complex exerted a direct effect on the morphology and adhesive properties of 293 cells through regulation of the level and/or activity of cellular E-cadherin/beta-catenin.

Beta-adrenergic receptor-mediated DNA synthesis in neonatal rat cardiac fibroblasts proceeds via a phosphatidylinositol 3-kinase dependent pathway refractory to the antiproliferative action of cyclic AMP

The following study was undertaken to elucidate the cytoskeletal phenotype of neonatal rat cardiac fibroblasts (NNCF) and the signaling pathways coupled to beta-adrenergic receptor stimulated DNA synthesis. The cytoskeletal proteins vimentin, and smooth muscle alpha-actin were detected in NNCF, suggestive of a myofibroblast phenotype. Isoproterenol (ISO) treatment stimulated (3)H-thymidine uptake, and concomitantly increased intracellular cyclic AMP levels. However, cyclic AMP-elevating agents markedly decreased DNA synthesis. Coincident with growth, ISO-stimulated phosphatidylinositol 3-kinase (PI3-K) activity, and the PI3-K inhibitor LY294002 abrogated enzyme activity, and DNA synthesis. Unexpectedly, the serine/threonine kinase protein kinase Balpha (PKBalpha), a putative downstream target of PI3-K, was dephosphorylated following ISO treatment. Despite PKBalpha inactivation, the phosphorylation of its putative downstream target, the pro-apoptotic enzyme glycogen synthase kinase-3alpha was significantly increased in response to ISO. These latter effects of ISO were mimicked by the cyclic AMP-elevating agent forskolin. Lastly, ISO treatment increased p70 ribosomal S6 kinase (p70S6K) phosphorylation, as reflected by an upward electrophoretic mobility shift. The pretreatment with rapamycin abrogated the ISO-mediated mobility shift of p70S6K, and DNA synthesis. Collectively, these data demonstrate that NNCF express a myofibroblast phenotype, and beta-adrenergic agonists promote DNA synthesis via a PI3-K-dependent pathway involving p70S6K. Although unable to suppress ISO-stimulated DNA synthesis, cyclic AMP can influence specific downstream targets of PI3-K highlighting a novel crosstalk between these signaling pathways.

In vitro regulation of budding yeast Bfa1/Bub2 GAP activity by Cdc5

The Cdc5 protein of budding yeast is a polo-like kinase that has multiple roles in mitosis including control of the mitotic exit network (MEN). MEN activity brings about loss of mitotic kinase activity so that the mitotic spindle is disassembled and cytokinesis can proceed. Activity of the MEN is regulated by a small GTPase, Tem1, which in turn is controlled by a two-component GTPase-activating protein (GAP) formed by Bfa1 and Bub2. Bfa1 has been identified as a regulatory target of Cdc5 but there are conflicting deductions from indirect in vivo assays as to whether phosphorylation inhibits or stimulates Bfa1 activity. To resolve this question, we have used direct in vitro assays to observe the effects of phosphorylation on Bfa1 activity. We show that when Bfa1 is phosphorylated by Cdc5, its GAP activity with Bub2 is inhibited although its ability to interact with Tem1 is unaffected. Thus, in vivo inactivation of Bfa1-Bub2 by Cdc5 would have a positive regulatory effect by increasing levels of Tem1-GTP so stimulating exit from mitosis.

Effects of etodolac, a selective cyclooxygenase-2 inhibitor, on the expression of E-cadherin-catenin complexes in gastrointestinal cell lines

BACKGROUND

Recent studies have shown that cyclooxygenase-2 (COX-2) inhibitors may participate in the proliferation of cancer cells. Because the cadherin-catenin complex is not only a key component of the adherens junction but also has been suggested to regulate cell proliferation, modulation of these molecules may be a mechanism by which COX-2 activity affects cell proliferation. In this study, we evaluated the effect of a COX-2 inhibitor on the proliferation and expression of E-cadherin-complexes in gastrointestinal cancer cell lines.

METHODS

The gastrointestinal cancer cell lines Caco2, HT29, and MKN45 were grown for 24 h in the presence and absence of a selective COX-2 inhibitor, etodolac (10(-5), 10(-4), and 10(-3) M). Cell proliferation was assessed by (3)H-thymidine incorporation, and the expression of E-cadherin and catenins was assessed by Western blotting, Northern blotting, and immunofluorescence.

RESULTS

Etodolac induced a significant reduction in cell proliferation in Caco2 and MKN45 cells. E-cadherin expression was upregulated after stimulation with etodolac in Caco2 cells, whereas the expression of alpha-, beta-, gamma- and p120-catenins was not modified. The expression of E-cadherin mRNA was also upregulated in Caco2 cells, and was upregulated also in MKN45 cells, which did not express normal E-cadherin protein by the use of a mouse monoclonal antibody against human E-cadherin, HECD-1 antibody. Immunofluorescence revealed that the increased E-cadherin was localized at the cytoplasmic membrane.

CONCLUSIONS

The inhibition of cell growth by etodolac in Caco-2 cells was associated with a dose-dependent upregulation and intense cytoplasmic localization of E-cadherin. No quantitative change in catenin expression was found in this phenomenon. These findings suggest that the COX-2 inhibitor affects the transcription of E-cadherin, or that there may be some homeostatic link between the cell cycle and E-cadherin transcription.

Glutamate-induced delta-catenin redistribution and dissociation from postsynaptic receptor complexes

Delta-catenin (or neural plakophilin-related arm-repeat protein/neurojungin) is primarily a brain specific member of the p120(ctn) subfamily of armadillo/beta-catenin proteins that play important roles in neuronal development. Our previous studies have shown that the ectopic expression of delta-catenin induces the formation of dendrite-like extensions and that the overexpression of delta-catenin promotes dendritic branching and increases spine density. Here we demonstrate that delta-catenin displays a dendritic distribution pattern in the adult mouse brain and is co-enriched with postsynaptic density-95 (PSD-95) in the detergent insoluble postsynaptic scaffolds. Delta-catenin forms stable complexes with excitatory neurotransmitter receptors including ionotropic N-methyl-D-aspartic acid receptor 2A (NR2A), metabotropic glutamate receptor 1alpha (mGluR1alpha), as well as PSD-95 in vivo. In cultured primary embryonic neurons, delta-catenin clusters co-distribute with filamentous actin and resist detergent extraction. In dissociated hippocampal neurons overexpressing delta-catenin, glutamate stimulation leads to a rapid redistribution of delta-catenin that can be attenuated by 6-cyano-7-nitroquinoxaline-2,3-dione and dizocilpine, selective inhibitors of ionotropic glutamate receptors. Upon glutamate receptor activation, delta-catenin becomes down-regulated and its association with NR2A and mGluR1alpha in cultured neurons is diminished. These findings support a possible functional connection between delta-catenin and the glutamatergic excitatory synaptic signaling pathway during neuronal development.

Constitutive activation of Rho proteins by CNF-1 influences tight junction structure and epithelial barrier function

The apical-most epithelial intercellular junction, referred to as the tight junction (TJ), regulates paracellular solute flux in diverse physiological and pathological states. TJ affiliations with the apical filamentous actin (F-actin) cytoskeleton are crucial in regulating TJ function. F-actin organization is influenced by the Rho GTPase family, which also controls TJ function. To explore the role of Rho GTPases in regulating TJ structure and function, we utilized Escherichia coli cytotoxic necrotizing factor-1 (CNF-1) as a tool to activate constitutively Rho, Rac and Cdc42 signaling in T84 polarized intestinal epithelial monolayers. The biological effects of the toxin were polarized to the basolateral membrane, and included profound reductions in TJ gate function, accompanied by displacement of the TJ proteins occludin and zonula occludens-1 (ZO-1), and reorganization of junction adhesion molecule-1 (JAM-1) away from the TJ membrane. Immunogold electron microscopy revealed occludin and caveolin-1 internalization in endosomal/caveolar-like structures in CNF-treated cells. Immunofluorescence/confocal microscopy suggested that a pool of internalized occludin went to caveolae, early endosomes and recycling endosomes, but not to late endosomes. This provides a novel mechanism potentially allowing occludin to evade a degradative pathway, perhaps allowing efficient recycling back to the TJ membrane. In contrast to the TJ, the characteristic ring structure of proteins in adherens junctions (AJs) was largely preserved despite CNF-1 treatment. CNF-1 also induced displacement of a TJ-associated pool of phosphorylated myosin light chain (p-MLC), which is normally also linked to the F-actin contractile machinery in epithelial cells. The apical perjunctional F-actin ring itself was maintained even after toxin exposure, but there was a striking effacement of microvillous F-actin and its binding protein, villin, from the same plane. However, basal F-actin stress fibers became prominent and cabled following basolateral CNF-1 treatment, and the focal adhesion protein paxillin was tyrosine phosphorylated. This indicates differences in Rho GTPase-mediated control of distinct F-actin pools in polarized cells. Functionally, CNF-1 profoundly impaired TJ/AJ assembly in calcium switch assays. Re-localization of occludin but not E-cadherin along the lateral membrane during junctional reassembly was severely impaired by the toxin. A balance between activity and quiescence of Rho GTPases appears crucial for both the generation and maintenance of optimal epithelial barrier function. Overactivation of Rho, Rac and Cdc42 with CNF-1 seems to mirror key barrier-function disruptions previously reported for inactivation of RhoA.

Lithium inhibits a late step in agrin-induced AChR aggregation

Agrin activates an intracellular signaling pathway to induce the formation of postsynaptic specializations on muscle fibers. In myotubes in culture, this pathway has been shown to include autophosphorylation of the muscle-specific kinase MuSK, activation of Src-family kinases, tyrosine phosphorylation of the acetylcholine receptor (AChR) beta subunit, a decrease in receptor detergent extractability, and the accumulation of AChRs into high-density aggregates. Here we report that treating chick myotubes with lithium prevented any detectable agrin-induced change in AChR distribution without affecting the number of AChRs or the agrin-induced change in AChR tyrosine phosphorylation and detergent extractability. Lithium treatment also increased the rate at which AChR aggregates disappeared when agrin was removed. The effects of lithium developed slowly over the course of approximately 12 h. Thus, sensitivity to lithium identifies a late step in the agrin signaling pathway, after agrin-induced MuSK and AChR phosphorylation, that is necessary for the recruitment of AChRs into visible aggregates.

[Effects of burn serum on the viscoelasticity and the structure of rat intestinal epithelial cells]

OBJECTIVE

To investigate the effects of burn serum on the viscoelasticity and the structure of rat intestinal epithelial cells.

METHODS

The rat intestinal epithelial cell strain (IEC-6) was cultured and stimulated by burn serum. The changes of IECs before and after the stimulation were dynamically observed by cytoskeleton immunohistochemistry, ELISA and the measurement of cytomembranous viscoelasticity.

RESULTS

During the early stage of burn serum stimulation, the skeleton protein expression in IEC decreased obviously with weakened positive signals of microfilaments and microtubules and with decreased cellular elasticity.

CONCLUSION

The cytoskeleton injury could cause the increase of cellular fragility and the decrease of the viscoelasticity, which ultimately lead to the change of cellular biodynamics. These changes might directly participate the development of postburn intestinal epithelial injury.

The effect of nickel sulphate, potassium dichromate, cobalt nitrate and cadmium sulphate on the proteins of cellular contacts and actin skeleton of cultivated human keratinocytes

The authors tested the effects of known allergens, namely nickel sulphate, potassium dichromate, cobalt nitrate and cytotoxic cadmium sulphate on the proteins of cellular contacts (vinculin, talin, E-cadherin, desmoplaktin) and actin cytoskeleton (actin filaments) of cultivated human keratinocytes. The localisation of proteins of cellular contacts was detected by means of direct immunofluorescence. The authors have detected a decrease in, and destruction of cellular contact proteins and actin cytoskeleton after testing the effect of all allergens, while the most significant changes were detected in E-cadherin, vunkulin and actin filaments. Desmoplaktin and talin were less damaged. Potassium dichromate caused damage already in concentration of 1 microg/ml. A similar effect of the other two tested haptanes was brought about in concentration being 100-fold higher.

CONCLUSION

the gained results indicate that the investigation of cellular contact proteins and actin cytoskeleton of cultivated human keratinocytes can possibly become a part of the testing of allergy-triggering potential of chemical substances. (Tab. 1, Fig. 4, Ref. 18.)