Medical aspects of the actin cytoskeleton

Proteins with Anti-apoptotic Action in the Hemolymph of Caterpillars of the Megalopygidae Family Acts by Maintaining the Structure of the Cellular Cytoskeleton

Brazil has a very large biological variety, which is an almost inexhaustible source of substances of pharmacological and biotechnological interest. Several studies have demonstrated the presence of bioactive peptides in insect hemolymph and their potential use as therapeutic agents. However, few data are available regarding molecules extracted from insects with anti-apoptotic action. The objective of this work was to identify the presence of proteins from the hemolymph of caterpillars of the Megalopygidae family with pharmacological and biotechnological interest. This study provides preliminary and innovative information on a new substance that inhibits cellular apoptopsis and stabilizes the tested cells, impacting the cytoskeleton, maintaining cellular structure and its functions. To this, two species of Megalopygidae family were studied, Podalia sp. and Megalopyge albicolis. Cytotoxicity tests on Vero and Sf-9 cells revealed that the hemolymph of both caterpillars was cytotoxic only at concentrations greater than 5%v/v. In the anti-apoptotic activity assays, it was verified that the supplementation of cell cultures with only 1% of hemolymph v/v is sufficient to inhibit cell death by apoptosis induced by different inducers such as terbutyl, actinomycin D, hydrogen peroxide, or even by nutrient depletion. For this study, cells were stained with trypan blue, crystal violet, and fluorescent markers to cytoskeleton (actin and tubulin), mitochondria membrane electric potential (JC-1), and apoptosis marker (acridine orange and ethidium). The protein responsible for anti-apoptotic action was isolated through gel filtration chromatography, using an AKTA purifier high-resolution liquid chromatography system. The hemolymph was fractionated into 3 pools for Podalia sp. and 6 pools for M. abicolis. In the antiapoptotic tests, semi-purified hemolymph from both caterpillars showed anti-apoptotic effect in VERO and SF-9 cells, pre-treated with only 1% v/v of hemolymph and induced to death by different and apoptotic inductors. Was observed that the molecule with anti-apoptotic effect is present in pool 3 in both hemolymphs. This protector effect blocked and attenuated the disruption of the cytoskeleton (actin filaments), being that the protective effect also was observed on the integrity of the mitochondrial membrane of SF-9 cells pre-treated with both hemolymphs and treated with the apoptosis inducer Terbutil at concentrations of 25 to 100 µM. By acting on the mitochondrial pathway of death by apoptosis, and by maintaining the structure of the cytoskeleton and cellular functions, pathway that can cause disorders and diseases neurodegenerative, the substances present in the hemolymph of these and other caterpillars could be good candidates in studies for the treatment of neurodegenerative diseases such as Parkinson's disease and Alzheimer's.

Ginsenoside Rb1 protected PC12 cells from Aβ25-35-induced cytotoxicity via PPARγ activation and cholesterol reduction

Accumulating evidences suggest that amyloid β (Aβ)-peptide plays a key role in pathogenesis of Alzheimer's disease (AD) through aggregation and deposition into plaques in neuronal cells. Membrane components such as cholesterol and gangliosides not only enhance the production of amyloidogenic Aβ fragments, but also appear to strengthen Aβ-membrane interaction. Ginsenoside Rb1 (GRb1) is a major active component of Panax, which is widely used to improve learning and memory. In the present study, whether ginsenoside Rb1 could protect pheochromocytoma cells (PC12 cells) from Aβ_25-35-induced cytotoxicity including inhibiting cell growth, inducing apoptosis, producing reactive oxygen species (ROS), destroying the cytoskeleton and bringing about membrane toxicity was investigated. Our results indicated that ginsenoside Rb1 could serve as an agonist of peroxisom proliferator-activated receptor-γ (PPARγ) and reduce the level of cholesterol in AD model cells. Reduction of the Aβ_25-35-induced cytotoxicity by lowering cholesterol was evidenced by reduction of ROS production, lipid peroxidation, and protection of cytoskeleton and membrane surface rigidity. Most importantly, the viability of PC12 cells increased from 50.42 ± 5.51% for the AD group to 102.72 ± 4.34% for the 50 μM ginsenoside Rb1 group with cholesterol reduction. Our results suggested that ginsenoside Rb1 might function as an effective candidate to promote reverse cholesterol transport and lower ROS production, therefore providing a new insight into prevention and treatment of AD.

Impaired Relaxation of Airway Smooth Muscle in Mice Lacking the Actin-Binding Protein Gelsolin

Diverse classes of ligands have recently been discovered that relax airway smooth muscle (ASM) despite a transient increase in intracellular calcium concentrations ([Ca²⁺]_i). However, the cellular mechanisms are not well understood. Gelsolin is a calcium-activated actin-severing and -capping protein found in many cell types, including ASM cells. Gelsolin also binds to phosphatidylinositol 4,5-bisphosphate, making this substrate less available for phospholipase Cβ-mediated hydrolysis to inositol triphosphate and diacylglycerol. We hypothesized that gelsolin plays a critical role in ASM relaxation and mechanistically accounts for relaxation by ligands that transiently increase [Ca²⁺]_i. Isolated tracheal rings from gelsolin knockout (KO) mice showed impaired relaxation to both a β-agonist and chloroquine, a bitter taste receptor agonist, which relaxes ASM, despite inducing transiently increased [Ca²⁺]_i. A single inhalation of methacholine increased lung resistance to a similar extent in wild-type and gelsolin KO mice, but the subsequent spontaneous relaxation was less in gelsolin KO mice. In ASM cells derived from gelsolin KO mice, serotonin-induced Gq-coupled activation increased both [Ca²⁺]_i and inositol triphosphate synthesis to a greater extent compared to cells from wild-type mice, possibly due to the absence of gelsolin binding to phosphatidylinositol 4,5-bisphosphate. Single-cell analysis showed higher filamentous:globular actin ratio at baseline and slower cytoskeletal remodeling dynamics in gelsolin KO cells. Gelsolin KO ASM cells also showed an attenuated decrease in cell stiffness to chloroquine and flufenamic acid. These findings suggest that gelsolin plays a critical role in ASM relaxation and that activation of gelsolin may contribute to relaxation induced by ligands that relax ASM despite a transient increase in [Ca²⁺]_i.

Extracellular Actin in Health and Disease

This review considers the functions of extracellular actin - cell surface bound, associated with extracellular matrix, or freely circulating. The role of this protein in different pathological processes is analyzed: its toxic effects and involvement in autoimmune diseases as an autoantigen. The extracellular actin clearance system and its role in protection against the negative effects of actin are characterized. Levels of free-circulating actin, anti-actin immunoglobulins, and components of the actin clearance system as prognostic biomarkers for different diseases are reviewed. Experimental approaches to protection against excessive amounts of free-circulating F-actin are discussed.

Molecular dynamics and high throughput binding free energy calculation of anti-actin anticancer drugs-New insights for better design

Actin cytoskeleton plays an important role in cancerous cell progression. Till date many anticancer toxins are discovered that binds to different sites of actin. Mechanism of action of these toxins varies with respect to the site where they bind to actin. Latrunculin A (LAT) binds closely to nucleotide binding site and Reidispongiolide binds to the barbed end of actin. LAT is reported to reduce the displacement of domain 2 with respect to domain 1 and allosterically modulate nucleotide exchange. On the other hand Reidispongiolide binds with the higher affinity to actin and competes with the DNaseI binding loop once the inter-monomer interaction has been formed. Evolving better actin binders being the aim of this study we conducted a comparative molecular dynamics of these two actin-drug complexes and actin complexed with ATP alone, 50ns each. High throughput binding free energy calculations in conjugation with the high-throughput MD simulations was used to predict modifications in these two renowned anti-actin anticancer drugs for better design. Per residue energy profiling that contribute to free energy of binding shows that there is an unfavourable energy at the site where Asp157 interacts with 2-thiazolidinone moiety of LAT. Similarly, unfavourable energies are reported near macrocyclic region of Reidispongiolide specifically near carbons 7, 11 & 25 and tail region carbons 27 & 30. These predicted sites can be used for modifications and few of these are discussed in this work based on the interactions with the binding site residues. The study reveals specific interactions that are involved in the allosteric modulation of ATP by these two compounds. Glu207 closely interacting with LAT A initiates the allosteric effect on ATP binding site specifically affecting residues Asp184, Lys215 and Lys336. RGA bound actin shows high anti-correlated motions between sub domain 3 and 4. Unlike LAT A, Reidispongiolide induces a flat structure of actin which definitely should affect actin polymerisation and lead to disassembly of actin filaments.

Gelsolin rs1078305 and rs10818524 polymorphisms were associated with risk of oral squamous cell carcinoma in a Chinese Han population

BACKGROUND

Gelsolin (GSN) is one of the most abundant actin-binding proteins, and is involved in cancer development and progression.

PATIENTS AND METHODS

A hospital-based case-control study including 201 patients with OSCC and 199 healthy controls was conducted. Seventeen single-nucleotide polymorphisms (SNPs) of GSN were investigated by Sequenom Mass ARRAY and iPLEX-MALDI-TOF technology.

RESULTS

Through comparison of the 17 SNPs on GSN gene between the two groups, SNP rs1078305 and rs10818524 were verified to be significantly associated with an increased risk of OSCC. For GSN rs1078305, the TT genotype was associated with increased risk for OSCC (OR = 1.92, 95% CI = 1.11-3.32, p = 0.028). CT/TT variants were also associated with increased risk for OSCC compared to the CC genotype (OR = 1.83, 95% CI = 1.25-3.84, p = 0.032).

CONCLUSION

The rs1078305 and rs10818524 SNPs of GSN were associated with increased risk for OSCC development in a Chinese Han population.

Human recombinant truncated RNASET2, devoid of RNase activity; A potential cancer therapeutic agent

Human RNASET2 has been implicated in antitumorigenic and antiangiogenic activities, independent of its ribonuclease capacities. We constructed a truncated version of human RNASET2, starting at E50 (trT2-50) and devoid of ribonuclease activity. trT2-50 maintained its ability to bind actin and to inhibit angiogenesis and tumorigenesis. trT2-50 binds to cell surface actin and formed a complex with actin in vitro. The antiangiogenic effect of this protein was demonstrated in human umbilical vein endothelial cells (HUVECs) by its ability to arrest tube formation on Matrigel, induced by angiogenic factors. Immunofluorescence staining of HUVECs showed nuclear and cytosolic RNASET2 protein that was no longer detectable inside the cell following trT2-50 treatment. This effect was associated with disruption of the intracellular actin network. trT2-50 co-localized with angiogenin, suggesting that both molecules bind (or compete) for similar cellular epitopes. Moreover, trT2-50 led to a significant inhibition of tumor development. Histological analysis demonstrated abundant necrotic tissue and a substantial loss of endothelial structure in trT2-50-treated tumors. Collectively, the present results indicate that trT2-50, a molecule engineered to be deficient of its catalytic activity, still maintained its actin binding and anticancer-related biological activities. We therefore suggest that trT2-50 may serve as a potential cancer therapeutic agent.

Gelsolin regulates proliferation, apoptosis, migration and invasion in human oral carcinoma cells

Gelsolin (GSN) is one of the most abundant actin-binding proteins, and is involved in several pathological processes, including Alzheimer's disease, cardiac injury and cancer. The aim of the present study was to assess the effect of GSN on the growth and motility of oral squamous cell carcinoma Tca8113 cells. The overexpression vector pcDNA3.1-GSN was transfected into Tca8113 cells and the stable GSN overexpression cell line was identified based on G418 antibiotic selection. The effect of GSN overexpression on the proliferation, apoptosis, migration and invasion of Tca8113 cells was examined using a cell counting kit-8 assay, flow cytometry and Transwell assays. The results revealed that GSN overexpression significantly promoted the cell proliferation and apoptosis of Tca8113 cells. In addition, Transwell assays demonstrated that the migration and invasion abilities of Tca8113 cells were enhanced by GSN overexpression. Therefore, the upregulation of GSN promotes cell growth and motility, indicating that it may perform a vital function in the progression of human oral cancers.

Differential sub-cellular processing of single-wall carbon nanotubes via interfacial modifications

Real-space and fluorescence lifetime imaging reveal that non-covalently attached dispersing agents influence sub-cellular trafficking and localization of carbon nanotubes.

Identification of a subtype-specific ENC1 gene related to invasiveness in human pituitary null cell adenoma and oncocytomas

Non-functioning pituitary adenomas (NFPAs) may be locally invasive. Surgery is a treatment option, but unlike the case for functional pituitary adenomas, there are almost no drug treatments available for NFPAs. Markers of invasiveness are needed to guide therapeutic decision-making and identify potential adjuvant drugs. Owing to the highly heterogeneous nature of NFPAs, little is known regarding the subtype-specific gene expression profiles associated with invasiveness. To identify important biomarkers of invasiveness, we selected 23 null cell adenomas and 20 oncocytomas. These tumors were classified as invasive or non-invasive adenomas based on magnetic resonance imaging, pathology slides and surgical findings. Firstly, we observed that there were significant differences in expression between invasive (n = 3) and non-invasive (n = 4) adenomas by gene expression microarray. A total of 1,188 genes were differentially expressed in the invasive and non-invasive adenomas. Among these 1,188 genes, 578 were upregulated and 610 were downregulated in invasive adenomas. Secondly, the expression of ENC1, which displayed the significant alterations, was further confirmed by qRT-PCR and Western blot analysis in all 43 tumor samples and three normal pituitary glands. Low levels of ENC1 were found in tumor samples, while high levels were detected in normal pituitary glands. Interestingly, the ENC1 expression level was low in invasive null cell adenomas compared with non-invasive adenomas, but this relationship was not observed in invasive oncocytomas. Immunohistochemistry also demonstrated that the staining of ENC1 was different between invasive and non-invasive null cell adenomas. In addition, bioinformatics studies, including gene ontology and protein interaction analyses, were also performed to better understand the critical role of ENC1 in the development and progression of null cell adenomas and oncocytomas. Consequently, ENC1 may be an important biomarker for null cell adenomas and oncocytomas, and it is specific to invasive null cell adenomas.

A common gene variant in PLS3 predicts colon cancer recurrence in women

Recent evidence suggests that PLS3 (T-Plastin), an important member of the actin filamentous network, significantly influences cell invasion and metastasis. Germline polymorphisms within the PLS3 gene may impact the gene's function, resulting in inter-individual differences in tumor recurrence capacity. In the present study, we investigated the association of germline polymorphisms in PLS3 to predict time to recurrence (TTR) in patients with stage II and III colon cancer. A total of 264 patients with histologically confirmed colon cancer were included in this retrospective study. Germline DNA was genotyped for rs871773 C>T, rs757124 C>G, rs1557770 G>T, rs6643869 G>A, and rs2522188 C>T in the PLS3 gene by 5'-exonuclease (TaqMan™) technology. As the PLS3 gene is located on the X chromosome, a gender-specific statistical analysis was performed. In univariate analysis, the minor allele of PLS3 rs871773 C>T was significantly associated with decreased TTR in women (hazard ratio (HR) = 5.02; 95 % confidence interval (CI) = 1.251-20.114; p = 0.023) and remained significantly associated in multivariate analysis (HR = 6.165; 95 % CI = 1.538-24.716; p = 0.010). Female patients carrying the C/T genotype in PLS3 rs871773 showed a median TTR of 69 months. In contrast, female patients with homozygous C/C had a median TTR of 112 months. There were no significant associations between PLS3 rs871773 C>T and TTR in male and between the other polymorphisms and TTR in male or female colon cancer patients. In conclusion, we identified a common gene variant in PLS3 as an independent prognostic marker in female patients with stage II and III colon cancer. Larger prospective trials are warranted to confirm these findings.

Altered cell mechanics from the inside: dispersed single wall carbon nanotubes integrate with and restructure actin

With a range of desirable mechanical and optical properties, single wall carbon nanotubes (SWCNTs) are a promising material for nanobiotechnologies. SWCNTs also have potential as biomaterials for modulation of cellular structures. Previously, we showed that highly purified, dispersed SWCNTs grossly alter F-actin inside cells. F-actin plays critical roles in the maintenance of cell structure, force transduction, transport and cytokinesis. Thus, quantification of SWCNT-actin interactions ranging from molecular, sub-cellular and cellular levels with both structure and function is critical for developing SWCNT-based biotechnologies. Further, this interaction can be exploited, using SWCNTs as a unique actin-altering material. Here, we utilized molecular dynamics simulations to explore the interactions of SWCNTs with actin filaments. Fluorescence lifetime imaging microscopy confirmed that SWCNTs were located within ~5 nm of F-actin in cells but did not interact with G-actin. SWCNTs did not alter myosin II sub-cellular localization, and SWCNT treatment in cells led to significantly shorter actin filaments. Functionally, cells with internalized SWCNTs had greatly reduced cell traction force. Combined, these results demonstrate direct, specific SWCNT alteration of F-actin structures which can be exploited for SWCNT-based biotechnologies and utilized as a new method to probe fundamental actin-related cellular processes and biophysics.

Inhibition of interdomain motion in g-actin by the natural product latrunculin: a molecular dynamics study

As part of the cytoskeleton, actin is essential for the morphology, motility, and division of eukaryotic cells. Recent X-ray fiber diffraction studies have shown that the conformation of monomeric actin is flattened upon incorporation into the filament by a relative rotation of its two major domains. The antiproliferative activity of latrunculin, a macrolide toxin produced by sponges, seems to be related to its binding to monomeric actin and inhibition of polymerization. Yet, the mechanism of inhibition is not known in detail. Here, multiple explicit water molecular dynamics simulations show that latrunculin binding hinders the conformational transition related to actin polymerization. In particular, the presence of latrunculin at the interface of the two major domains of monomeric actin reduces the correlated displacement of Domain 2 with respect to Domain 1. Moreover, higher rotational flexibility between the two major domains is observed in the absence of ATP as compared to ATP-bound actin, offering a possible explanation as to why actin polymerizes more favorably in the absence of nucleotides.

Regulation of myofibroblast activities: calcium pulls some strings behind the scene

Myofibroblast-induced remodeling of collagenous extracellular matrix is a key component of our body's strategy to rapidly and efficiently repair damaged tissues; thus myofibroblast activity is considered crucial in assuring the mechanical integrity of vital organs and tissues after injury. Typical examples of beneficial myofibroblast activities are scarring after myocardial infarct and repair of damaged connective tissues including dermis, tendon, bone, and cartilage. However, deregulation of myofibroblast contraction causes the tissue deformities that characterize hypertrophic scars as well as organ fibrosis that ultimately leads to heart, lung, liver and kidney failure. The phenotypic features of the myofibroblast, within a spectrum going from the fibroblast to the smooth muscle cell, raise the question as to whether it regulates contraction in a fibroblast- or muscle-like fashion. In this review, we attempt to elucidate this point with a particular focus on the role of calcium signaling. We suggest that calcium plays a central role in myofibroblast biological activity not only in regulating contraction but also in mediating intracellular and extracellular mechanical signals, structurally organizing the contractile actin-myosin cytoskeleton, and establishing lines of intercellular communication.

Desmethoxymajusculamide C, a cyanobacterial depsipeptide with potent cytotoxicity in both cyclic and ring-opened forms

Cytotoxicity-guided fractionation of the organic extract from a Fijian Lyngbya majuscula led to the discovery of desmethoxymajusculamide C (DMMC) as the active metabolite. Spectroscopic analysis including 1D and 2D NMR, MS/MS, and chemical degradation and derivatization protocols were used to assign the planar structure and stereoconfiguration of this new cyclic depsipeptide. DMMC demonstrated potent and selective anti-solid tumor activity with an IC(50) = 20 nM against the HCT-116 human colon carcinoma cell line via disruption of cellular microfilament networks. A linear form of DMMC was generated by base hydrolysis, and the amino acid sequence was confirmed by mass spectrometry. Linearized DMMC was also evaluated in the biological assays and found to maintain potent actin depolymerization characteristics while displaying solid tumor selectivity equivalent to DMMC in the disk diffusion assay. A clonogenic assay assessing cytotoxicity to HCT-116 cells as a function of exposure duration showed that greater than 24 h of constant drug treatment was required to yield significant cell killing. Therapeutic studies with HCT-116 bearing SCID mice demonstrated efficacy at the highest dose used (%T/C = 60% at 0.62 mg/kg daily for 5 days).

Proteomic analysis reveals the actin cytoskeleton as cellular target for the human papillomavirus type 8

Recent studies strongly support a role of human papillomavirus type 8 (HPV8) in non-melanoma skin cancer development. In this study, a quantitative two-dimensional (2D) differential gene expression (DiGE) gel approach combined with mass spectrometry has been used to identify proteins that are abundantly deregulated in primary human epidermal keratinocytes expressing HPV8 sequences. Twenty six protein spots showed significant changes in the level of expression between keratinocytes expressing E7 or the complete early region (CER) of HPV8 compared to extracts from cells lacking HPV8 gene expression. No differences between HPV8 E7 alone and HPV8 CER expressing cells were observed. The 26 protein spots that were differentially expressed corresponded to 20 different proteins, of which 14 actin-associated proteins were downregulated except for calponin-2, which was the only actin-binding protein that was overexpressed. Besides changes in actin modulating proteins, an upregulation of cytokeratins (CK) 5, 6 and 14 was also noted. This study suggests that the actin and keratin cytoskeleton modulating proteins are targets for HPV8.

Clinical significance of gelsolin-like actin-capping protein expression in oral carcinogenesis: an immunohistochemical study of premalignant and malignant lesions of the oral cavity

BACKGROUND

Gelsolin-like actin-capping protein (CapG) is a ubiquitous gelsolin-family actin-modulating protein involved in cell signalling, receptor-mediated membrane ruffling, phagocytosis, and motility. CapG has generated great interest due to its oncogenic function in the control of cell migration or invasion in a variety of cancer cells. We previously applied proteomic methods to characterize differentially expressed proteins in oral squamous-cell carcinoma (OSCC) cells and detected significantly high expression levels of CapG in OSCC-derived cell lines compared to human normal oral keratinocytes. In the current study, to further determine the potential involvement of CapG in OSCC, we evaluated the status of CapG protein and mRNA expression in human oral premalignant lesions (OPLs) and primary OSCCs and correlated the results with clinicopathologic variables.

METHODS

Matched normal and tumour tissue sections of 79 human primary OSCCs and 28 OPLs were analyzed for CapG expression by immunohistochemistry (IHC). Correlations between CapG-immunohistochemical staining scores of OSCCs and clinicopathologic features were evaluated by Fisher's exact test. Real-time quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) was used to estimate CapG expression at the mRNA level.

RESULTS

In IHC, substantial up-regulation of CapG protein was observed in primary OSCCs (52%) and OPLs (64%), whereas corresponding normal tissues showed consistently weak or absent immunoreactivity of CapG. qRT-PCR data were consistent with the protein expression status. Moreover, CapG expression was correlated with the TNM stage grading of OSCCs.

CONCLUSION

Our finding of frequent dysregulated expression of CapG in premalignant and malignant lesions together with an association with an advanced clinical disease stage suggests that CapG could contribute to cancer development and progression and that CapG may have potential as a biomarker and a therapeutic target for OSCC.

Design and evaluation of Actichip, a thematic microarray for the study of the actin cytoskeleton

Background

The actin cytoskeleton plays a crucial role in supporting and regulating numerous cellular processes. Mutations or alterations in the expression levels affecting the actin cytoskeleton system or related regulatory mechanisms are often associated with complex diseases such as cancer. Understanding how qualitative or quantitative changes in expression of the set of actin cytoskeleton genes are integrated to control actin dynamics and organisation is currently a challenge and should provide insights in identifying potential targets for drug discovery. Here we report the development of a dedicated microarray, the Actichip, containing 60-mer oligonucleotide probes for 327 genes selected for transcriptome analysis of the human actin cytoskeleton.

Results

Genomic data and sequence analysis features were retrieved from GenBank and stored in an integrative database called Actinome. From these data, probes were designed using a home-made program (CADO4MI) allowing sequence refinement and improved probe specificity by combining the complementary information recovered from the UniGene and RefSeq databases. Actichip performance was analysed by hybridisation with RNAs extracted from epithelial MCF-7 cells and human skeletal muscle. Using thoroughly standardised procedures, we obtained microarray images with excellent quality resulting in high data reproducibility. Actichip displayed a large dynamic range extending over three logs with a limit of sensitivity between one and ten copies of transcript per cell. The array allowed accurate detection of small changes in gene expression and reliable classification of samples based on the expression profiles of tissue-specific genes. When compared to two other oligonucleotide microarray platforms, Actichip showed similar sensitivity and concordant expression ratios. Moreover, Actichip was able to discriminate the highly similar actin isoforms whereas the two other platforms did not.

Conclusion

Our data demonstrate that Actichip is a powerful alternative to commercial high density microarrays for cytoskeleton gene profiling in normal or pathological samples. Actichip is available upon request.

Vascular localization and proliferation in the growing tip of the deer antler

The process of angiogenesis is of interest because of the significant clinical benefits associated with controlling vascular growth. Within the antler, chondrogenesis and antler elongation are occurring at the rate of 1-2 cm per day and thus blood vessels are growing at this same rapid pace. We demonstrate that the process of angiogenesis in the antler is controlled at various tissue locations. The findings clearly differentiate the spatial location of the stem cells that drive chondrogenesis from the proliferation process driving the angiogenesis. Vessels within the lateral dermis contained BrdU-positive cells, suggesting that these vessels were elongating. Within the precartilage region, proliferating vessels were detected in bundles of complex structure evenly distributed throughout this tissue layer. The support cells within these bundles of vessels were detected by staining with alpha-smooth muscle actin, while the endothelial cells were negative. Additionally, the alpha-smooth muscle actin staining was found in association with the cartilage cells of the antler. The marked proliferation of the vascular associated cells in the precartilage region identified this area as a major region of vascular growth in the antler. We propose that within the precartilage region, the most likely mechanisms to explain the observed vascular morphology are that of vascular extension of the existing vessels and intussusceptive angiogenesis or sprouting to generate the small bundles of vessels. Wiley-Liss, Inc.

ACTIBIND, an actin-binding fungal T2-RNase with antiangiogenic and anticarcinogenic characteristics

BACKGROUND

ACTIBIND is an Aspergillus niger extracellular ribonuclease (T2-ribonuclease [RNase]) that possesses actin-binding activity. In plants, ACTIBIND inhibits the elongation and alters the orientation of pollen tubes by interfering with the intracellular actin network. The question rose whether ACTIBIND can also affect mammalian cancer development.

METHODS

Cell colony formation was performed in human colon (HT-29, Caco-2, RSB), breast (ZR-75-1), and ovarian (2780) cancer cells in the presence or absence of 1 muM ACTIBIND. In HT-29 and ZR-75-1 cells, the effect of ACTIBIND on cell migration was studied by microscopic observations and by invasion assay through Matrigel. Tube formation was assessed in human umbilical vein endothelial cells (HUVEC) in the presence of angiogenin or basic fibroblast growth factor (bFGF) (1 microg/mL each) following overnight incubation with 1 or 10 microM ACTIBIND. In an athymic mouse xenograft model, HT-29 cells were injected subcutaneously, followed by subcutaneous (0.4-8 mg/mouse/injection) or intraperitoneal (0.001-1 mg/mouse/injection) injections of ACTIBIND. In a rat dimethylhydrazine (DMH)-colorectal carcinogenesis model, ACTIBIND was released directly into the colon via osmotic micropumps (250 microg/rat/day) or given orally via microcapsules (1.6 mg/rat/day). Aberrant crypt foci, tumors in the distal colon, and tumor blood vessels were examined.

RESULTS

ACTIBIND had an anticlonogenic effect unrelated to its ribonuclease activity. It also inhibited angiogenin-induced HUVEC tube formation in a dose-responsive manner. ACTIBIND was found to bind actin in vitro. It also bound to cancer cell surfaces, leading to disruption of the internal actin network and inhibiting cell motility and invasiveness through Matrigel-coated filters. In mice, ACTIBIND inhibited HT-29 xenograft tumor development, given either as a subcutaneous or intraperitoneal treatment. In rats, ACTIBIND exerted preventive and therapeutic effects on developing colonic tumors induced by DMH. It also reduced the degree of tumor observation.

CONCLUSIONS

This study indicated that ACTIBIND is an effective antiangiogenic and anticarcinogenic factor.

A recombinant human RNASET2 glycoprotein with antitumorigenic and antiangiogenic characteristics

BACKGROUND

Human RNASET2 is a T2-RNase glycoprotein encoded by the RNASET2 gene, which is located on chromosome 6 (6q27). Deletion in 6q27 is associated with several human malignancies.

METHODS

A synthetic RNASET2 gene that was optimized for expression in the yeast Pichia pastoris was designed according to the cDNA sequence and was cloned under the control of the methanol-induced promoter fused to the alpha-mating secretion peptide. The recombinant protein was purified from the culture supernatant of transformed P. pastoris through an affinity Sepharose-concanavalin A column. Actin-binding activity was examined by membrane blotting using monoclonal mouse antiactin immunoglobulin M and by cross-linking in solution to G-actin using 1-[3-(dimethylamino)propyl]-3-ethyl-carboimide methiodide. The antiangiogenic activity of RNASET2 (from 0.5 microM to 10 microM) was assessed by a human umbilical vein endothelial (HUVE) cell assay in the presence of 1 microg/mL angiogenin, basic fibroblast growth factor (bFGF), or recombinant human vascular endothelial growth factor (VEGF). Cell colony formation was examined in human colon HT29 cancer cells to assess the antitumorigenic activity of RNASET2 or the enzymatic-inactivated RNASET2 (EI-RNASET2) (1 microM each). In an athymic mouse xenograft model, LS174T human cancer cells were injected subcutaneously. When tumors were palpable, the mice were treated for 3 weeks with RNASET2 (1 mg/kg), paclitaxel (10 mg/kg or 15 mg/kg), or a combination of the 2 drugs.

RESULTS

The recombinant RNASET2 was identified as a 27-kilodalton glycoprotein that possessed the ability to bind actin in vitro. RNASET2 significantly inhibited clonogenicity in HT29 cells. EI-RNASET2 produced a similar effect, suggesting that its antitumorigenic activity is unrelated to its RNase activity. In HUVE cells, RNASET2 inhibited angiogenin-, bFGF-, and VEGF-induced tube formation in a dose-dependent manner. In athymic mice, RNASET2 inhibited the development of an LS174T-derived xenograft by 40%. A synergistic effect was obtained with combined RNASET2 and paclitaxel treatments.

CONCLUSIONS

The current results suggested that RNASET2 represents a new class of antitumorigenic and antiangiogenic drugs, and the findings of this study emphasize the advantage of using agents like RNASET2 in combined therapy.

A solid-phase approach to the phallotoxins: total synthesis of [Ala7]-phalloidin

Herein we report a solid-phase synthetic approach to [Ala7]-phalloidin (1). Prior syntheses of phallotoxins were carried out using solution-phase routes that required large scale and preclude library production. The route presented here consists of solution-phase preparation of key orthogonally protected amino acid building blocks, followed by a solid-phase peptide synthesis sequence, featuring two resin-bound macro-cyclization reactions. The final product mixture was composed of two atropisomeric compounds, one designated "natural" (1) and the other designated "non-natural" (1'). The structures of these species were modeled using restrained energy minimization with NMR-derived restraints.

Comparison of the effects of surface tension and osmotic pressure on the interfacial hydration of a fluid phospholipid bilayer

The effects of three so-called kosmotropic solutes, namely, betaine, sucrose, and choline chloride on 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine large unilamellar vesicles, were studied by measuring the generalized polarization (GP) for the fluorescence emission of the membrane partitioning probe Laurdan. The latter has been shown to be sensitive to the depth of water penetration into phospholipid bilayers. At equal osmotic pressures the three solutes produced different increments in GP, with a qualitative positive correlation. However, the increments in GP correlated also quantitatively with the increase of air-water surface tension caused by the three kosmotropes. Our findings suggest surface tension to determine the impact of these solutes on the lateral packing of the lipid bilayer. Based on the changes in area/lipid at different surface tensions, the equilibrium lateral pressure for a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine bilayer at 25 degrees C was estimated to be approximately 34 mN/m.

N Terminus Is Essential for Tropomyosin Functions

Down-regulation of several key actin-binding proteins, such as alpha-actinin, vinculin, gelsolin, and tropomyosins (TMs), is considered to contribute to the disorganized cytoskeleton present in many neoplastic cells. TMs stabilize actin filaments against the gel severing actions of proteins such as cofilin. Among multiple TMs expressed in non-muscle cells, tropomyosin-1 (TM1) isoform induces stress fibers and functions as a suppressor of malignant transformation. However, the molecular mechanisms of TM1-mediated cytoskeletal effects and tumor suppression remain poorly understood. We have hypothesized that the ability of TM1 to stabilize microfilaments is crucial for tumor suppression. In this study, by employing a variant TM1, which contains an N-terminal hemagglutinin epitope tag, we demonstrate that the N terminus is a key determinant of tropomyosin-1 function. Unlike the wild type TM1, the modified protein fails to restore stress fibers and inhibit anchorage-independent growth in transformed cells. Furthermore, the N-terminal modification of TM1 disorganizes the cytoskeleton and delays cytokinesis in normal cells, abolishes binding to F-actin, and disrupts the dimeric associations in vivo. The functionally defective TM1 allows the association of cofilin to stress fibers and disorganizes the microfilaments, whereas wild type TM1 appears to restrict the binding of cofilin to stress fibers. TM1-induced cytoskeletal reorganization appears to be mediated through preventing cofilin interaction with microfilaments. Our studies provide in vivo functional evidence that the N terminus is a critical determinant of TM1 functions, which in turn determines the organization of stress fibers.

Mutant α-actinin-4 promotes tumorigenicity and regulates cell motility of a human lung carcinoma

The precise role of alpha-actinin-4 encoding gene (ACTN4) is not very well understood. It has been reported to elicit tumor suppressor activity and to regulate cellular motility. To further assess the function of human ACTN4, we studied a lung carcinoma cell line expressing a mutated alpha-actinin-4, which is recognized as a tumor antigen by autologous CD8(+) cytotoxic T lymphocytes (CTL). Confocal immunofluorescence microscopy indicated that, while wild-type (WT) alpha-actinin-4 stains into actin cytoskeleton and cell surface ruffles, the mutated protein is only dispersed in the cytoplasm of the lung carcinoma cells. This loss of association with the cell surface did not appear to correlate with a decrease in in vitro alpha-actinin-4 crosslinking to filamentous (F)-actin. Interestingly, experiments using cell lines stably expressing ACTN4 demonstrated that as opposed to WT gene, mutant ACTN4 was unable to inhibit tumor cell growth in vitro and in vivo. Moreover, the expression of mutant alpha-actinin-4 resulted in the loss of tumor cell capacity to migrate. The identification of an inactivating mutation in ACTN4 emphasizes its role as a tumor suppressor gene and underlines the involvement of cytoskeleton alteration in tumor development and metastasis.

Differences in morphology, cytoskeletal architecture and protease production between zone II tendon and synovial fibroblasts in vitro

Fibroblast migration is an integral component of the processes resulting in the formation of restrictive adhesions in the injured tendon, especially in Zone II. Pre-requisites for cell migration are an intact cytoskeleton and an ability to biochemically degrade the extra-cellular matrix. The relative characteristics of fibroblasts from the fibro-osseus sheath (SC), the tissue surrounding the tendon in Zone II, and the endotenon (TC) with respect to morphology, cytoskeletal structure and ability to produce matrix metalloproteinases (MMPs) 2 and 9 were compared in vitro. It was found that SCs were larger in size and demonstrated greater amounts of intra-cellular alpha-smooth muscle actin (alpha-SMA) and intra-membranous vinculin. Filamentous actin (F-actin) fibres in SCs were more densely packed and concentrated, resulting in stress fibres. The SCs also produce greater amounts of MMP-2 and MMP-9 compared to TCs. These observations imply that SCs play an active role in adhesion formation and should be specifically targeted to inhibit or treat tendon adhesions.

Interactions between surface-bound actin and complement, platelets, and neutrophils

Actin exists as globular (G) monomers or polymeric filaments (F) in the cytoplasm of eukaryotic cells, mediating cell morphologic changes and motility. Large amounts of this protein may be released out to the extracellular compartment during tissue injury, but little is known about its role in biomaterial-related inflammation. We immobilized actin to methylated glass, methylated and aminated silicon, and gold model surfaces and studied the subsequent blood serum deposition and complement activation, generation of reactive oxygen species (ROS), and adhesion and aggregation of neutrophils and platelets. Null ellipsometry showed that approximately one monolayer of G-actin can be immobilized onto the model surfaces and that actin in buffer polymerized on top of this by the addition of K(+) and Mg(2+) ions to form a thicker layer of firmly bound F-actin. After serum incubation, F-actin bound low amounts of anti-complement factor 1q (anti-C1q). Cell responses upon contact with actin-coated surfaces were analyzed by luminol-amplified chemiluminescence, lumi-aggregometry, and fluorescence microscopy. It was shown that surface-triggered aggregation, spreading, and generation of ROS are down-regulated and comparable to the response by adsorbed albumin. However, F-actin on gold surfaces recruited platelets in a C1q-dependent manner. We conclude that in vitro adsorbed actin is a weak complement, platelet, and neutrophil activator, but that F-actin associates with both C1q and platelets.

Actin-binding marine macrolides: total synthesis and biological importance

Marine organisms produce a fascinating range of structurally diverse secondary metabolites, which often possess unusual and sometimes unexpected biological activities. This structural diversity makes these marine natural products excellent molecular probes for the investigation of biochemical pathways. Recently, a number of novel and stereochemically complex macrolides, having a large macrolactone (22- to 44-membered) ring, that interact with the actin cycloskeleton have been isolated from different marine sources. Actin, like tubulin, is a major component of the cytoskeleton and has important cellular functions. Although the details of these interactions are still under investigation, these marine macrolides are becoming increasingly important as novel molecular probes to help elucidate the cellular functions of actin. Owing to their potent antitumor activities, these compounds, for example the aplyronines, also have potential for preclinical development in cancer chemotherapy. Their appealing molecular structures, with an abundance of stereochemistry, and biological significance, coupled with the extremely limited availability from the marine sources, have stimulated enormous interest in the synthesis of these compounds. This review summarizes the biological properties of these unusual marine natural products and features the recently completed total syntheses of swinholide A, scytophycin C, aplyronine A, mycalolide A--all of these being potent cytotoxic agents that target actin--and a diastereoisomer of ulapualide A. Rather than detailing each individual step of these multistep total syntheses, the different synthetic strategies, key reactions, and methods adopted for controlling the stereochemistry are compared.

Antitumor cytotoxic T-lymphocyte response in human lung carcinoma: identification of a tumor-associated antigen

We have isolated several cytotoxic T lymphocyte (CTL) clones from lymphocytes infiltrating a lung carcinoma of a patient with long survival. These clones showed a CD3+, CD8+, CD4-, CD28- phenotype and expressed a T-cell receptor (TCR) encoded either by Vbeta8-Jbeta1.5 or Vbeta22-Jbeta1.4 rearrangements. Functional studies indicated that these clones mediated a high human leukocyte antigen (HLA)-A2.1-restricted cytotoxic activity against the autologous tumor cell line. Interestingly, TCRbeta chain gene usage indicated that CTL clones identified in vitro were selectively expanded in vivo at the tumor site as compared to autologous peripheral blood lymphocytes (PBL). These findings provide evidence that an immune response may take place in non-small cell lung carcinoma and that effector T cells may contribute to tumor regression. Further study indicated that the CTL clones recognized the same decamer peptide encoded by a mutated alpha-actinin-4 gene. Using tetramers of soluble HLA-A2 molecules loaded with the mutated antigenic peptide, we have derived several anti-alpha-actinin-4 T-cell clones from patient PBL. These CTL, recognizing a truly tumor-specific antigen, may play a role in the clinical evolution of this lung cancer patient. Adoptive transfer of CTL clones in a SCID/NOD mice model transplanted with autologous tumor supported their antitumor effect in vivo.

Expression of smooth muscle actin in connective tissue cells participating in fracture healing in a murine model

The role of alpha-smooth muscle actin (SMA)-expressing fibroblasts in the contraction of skin wounds has been known for three decades. Recent studies have demonstrated that osteoblasts can also express the gene for this contractile muscle actin isoform and can contract a collagen-glycosaminoglycan analog of extracellular matrix in vitro. These findings provided rationale for the hypothesis that SMA-expressing cells contribute to fracture healing by drawing the bone ends together. To begin to test this hypothesis, immunohistochemistry was employed to evaluate the distribution of connective tissue cells expressing SMA in a mouse model of successful fracture healing. The results demonstrated that the majority of the cells comprising the mesenchymal tissue interposed between the fracture ends contained SMA after 7 and 21 days, supporting the working hypothesis. Most of the osteoblasts lining the surfaces of newly forming bone and the chondrocytes comprising the cartilaginous callus also expressed this contractile actin isoform. The maximal SMA expression extended from 7 to 21 days postfracture. The finding of high levels of SMA expression in connective tissue cells participating in fracture healing suggests that SMA-enabled contraction may be playing a role in the healing process. These results warrant further study of the specific SMA-dependent cell behavior.

Expression of smooth muscle actin in osteoblasts in human bone

It is well known that certain connective tissue cells (viz., dermal fibroblasts) can express the gene for a muscle actin--alpha-smooth muscle actin--and can contract. This process contributes to skin wound closure and is responsible for Dupuytren's contracture. The objective of this study was to determine if human osteoblasts can also express the gene for alpha-smooth muscle actin. Immunohistochemistry using a monoclonal antibody for alpha-smooth muscle actin was performed on human cancellous bone samples obtained from 20 individuals at the time of total joint arthroplasty. The percentages of resting and active osteoblasts on the bone surfaces containing this muscle actin isoform were evaluated. Explants of human bone were also studied for the expression of alpha-smooth muscle actin in the tissue and in the outgrowing cells with time in culture. Western blot analysis was performed to quantify the alpha-smooth muscle actin content of the outgrowing cells relative to smooth muscle cell controls. Nine +/- 2% (mean +/- SEM; n = 20) of the cells classified as inactive osteoblasts and 69 +/- 3% (n = 19) of the cells identified as active osteoblasts on the bone surface contained alpha-smooth muscle actin. This difference was highly statistically significant (Student's t test, p < 0.0001). Similar profiles of alpha-smooth muscle actin-expressing cells were found in explants cultured for up to 12 weeks. Cells forming a layer on the surface of the explants and growing out from them in monolayer also contained alpha-smooth muscle actin by immunohistochemistry and Western blot analysis. Human osteoblasts can express the gene for alpha-smooth muscle actin. This expression should be considered a phenotypic characteristic of this cell type, conferred by its progenitor cells: bone marrow stromal-derived stem cells, and perhaps pericytes and smooth muscle cells.

Inhibition of anchorage-independent growth of transformed NIH3T3 cells by epithelial protein lost in neoplasm (EPLIN) requires localization of EPLIN to actin cytoskeleton

Epithelial protein lost in neoplasm (EPLIN) is a cytoskeleton-associated protein characterized by the presence of a single centrally located lin-11, isl-1, and mec-3 (LIM) domain. We have reported previously that EPLIN is down-regulated in transformed cells. In this study, we have investigated whether ectopic expression of EPLIN affects transformation. In untransformed NIH3T3 cells, retroviral-mediated transduction of EPLIN did not alter the cell morphology or growth. NIH3T3 cells expressing EPLIN, however, failed to form colonies when transformed by the activated Cdc42 or the chimeric nuclear oncogene EWS/Fli-1. This suppression of anchorage-independent growth was not universal because EPLIN failed to inhibit the colony formation of Ras-transformed cells. Interestingly, the localization of EPLIN to the actin cytoskeleton was maintained in the EWS/Fli-1- or Cdc42-transformed cells, but not in Ras-transformed cells where it was distributed heterogeneously in the cytoplasm. Using truncated EPLIN constructs, we demonstrated that the NH(2)-terminal region of EPLIN is necessary for both the localization of EPLIN to the actin cytoskeleton and suppression of anchorage-independent growth of EWS/Fli-1-transformed cells. The LIM domain or the COOH-terminal region of EPLIN could be deleted without affecting its cytoskeletal localization or ability to suppress anchorage-dependent growth. Our study indicates EPLIN may function in growth control by associating with and regulating the actin cytoskeleton.

Upregulation of thymosin beta-10 by Mycobacterium bovis infection of bovine macrophages is associated with apoptosis

Bovine macrophages underwent apoptosis as a result of infection with a Mycobacterium bovis field strain. Macrophages infected with a multiplicity of infection (MOI) of 25:1 developed chromatin condensation and DNA fragmentation at 4 h and 8 h, respectively, whereas changes in chromatin condensation induced by MOIs of 10:1 and 1:1 required more time and had a reduced number of apoptotic cells. Not only infected macrophages underwent apoptosis, but also uninfected bystander macrophages became apoptotic. Increased differential expression of thymosin beta-10 was identified in M. bovis-infected bovine macrophages by differential display reverse transcriptase PCR. Phagocytosis of latex beads had no effect on the expression of thymosin beta-10, whereas bacterial suspensions upregulated thymosin beta-10 expression, suggesting that M. bovis or mycobacterial products are essential in the process. Heat-inactivated M. bovis induced a slight increase in thymosin beta-10 mRNA, whereas live virulent and attenuated M. bovis organisms increased the gene expression almost twofold. A mouse macrophage cell line (RAW 264.7) overexpressing the bovine thymosin beta-10 transgene had spontaneous apoptosis at a higher rate (66.5%) than parental cells (4.7%) or RAW cells harboring the empty vector (22.8%). The apoptotic rates of the overexpressing cells were significantly higher when compared with both the empty vector transfected (P < 0.01) and parental cells (P < 0.001). Our evidence suggests that upregulation of thymosin beta-10 in M. bovis-infected macrophages is linked with increased cell death due to apoptosis.

Increased expression of T-fimbrin gene after DNA damage in CHO cells and inactivation of T-fimbrin by CpG methylation in human colorectal cancer cells

When DNA damage is induced by unprogrammed extrinsic events, activating-cell-cycle checkpoints delay cell-cycle progression in the G1 or G2 phases and allow repair of a damaged template. In this study, we evaluated changes in gene expression upon radiation-induced G2 cell-cycle arrest using Chinese hamster ovary (CHO) cells. T-fimbrin, an actin-binding protein, was overexpressed in CHO cells in which G2 arrest had been induced by X-radiation. Northern blot analysis revealed that T-fimbrin gene expression was induced not only by X-radiation but also by a topoisomerase II inhibitor, etoposide. Transfection of CHO cells with a vector encoding T-fimbrin antisense RNA demonstrated that reduced T-fimbrin expression induced alterations in cell-cycle control; radiation-induced G2 arrest was short and decreased in cells transfected with antisense T-fimbrin. Additionally, T-fimbrin gene expression was suppressed in a human colorectal cancer cell line, SW948, because of promoter-specific DNA methylation. These results suggest that downregulation of T-fimbrin may be involved in cancer development through G2/M cell-cycle control in mammalian cells.

Patterns of living beta-actin movement in wounded human coronary artery endothelial cells exposed to shear stress

We previously demonstrated that physiologic levels of shear stress enhance endothelial repair. Cell spreading and migration, but not proliferation, were the major mechanisms accounting for the increases in wound closure rate (Albuquerque et al., 2000, Am. J. Physiol. Heart Circ. Physiol. 279, H293-H302). However, the patterns and movements of beta-actin filaments responsible for cell motility and translocation in human coronary artery endothelial cells (HCAECs) have not been previously investigated under physiologic flow. HCAECs transfected with beta-actin-GFP were cultured on type I collagen-coated coverslips. Confluent cell monolayers were subjected to laminar shear stress of 12 dynes/cm(2) for 18 h in a parallel-plate flow chamber to attain cellular alignment and then wounded by scraping with a metal spatula and subsequently exposed to a laminar shear stress of 20 dynes/cm(2) (S-W-sH) or static (S-W-sT) conditions. Time-lapse imaging and deconvolution microscopy was performed during the first 3 h after imposition of S-W-sH or S-W-sT conditions. The spatial and temporal dynamics of beta-actin-GFP motility and translocation during wound closure in HCAEC monolayers were analyzed under both conditions. Compared with HCAEC under S-W-sT conditions, our data show that HCAEC under S-W-sH conditions demonstrated greater beta-actin-GFP motility, filament and clumping patterns, and filament arcs used during cellular attachment and detachment. These findings demonstrate intriguing patterns of beta-actin organization and movement during wound closure in HCAEC exposed to physiological flow.

Gelsolin functions as a metastasis suppressor in B16-BL6 mouse melanoma cells and requirement of the carboxyl-terminus for its effect

Gelsolin, an actin-binding protein, is implicated as a critical regulator in cell motility. In addition, we have reported that cellular levels of gelsolin are decreased in various tumor cells, and overexpression of gelsolin by gene transfer suppresses tumorigenicity. We sought to assess the effects of gelsolin overexpression on metastasis and to determine the importance of a carboxyl-terminus that confers Ca(2+) dependency on gelsolin for effects of its overexpression. Expression vectors with cDNA encoding either full-length wild-type or His321 mutant form, isolated from a flat revertant of Ras-transformed cells and a carboxyl-terminal truncate, C-del of gelsolin, were transfected into a highly metastatic murine melanoma cell line, B16-BL6. Expression of introduced cDNA in transfectants was confirmed using Western blotting, 2-dimensional gel electrophoresis and reverse transcription-polymerase chain reaction (RT-PCR). We characterized phenotypes of transfectants, such as growth rate, colony formation in soft agar, cell motility and metastasis formation in vivo. Transfectants expressing the wild-type, His321 mutant and C-del gelsolin exhibited reduced growth ability in soft agar. Although expression of integrin beta1 or alpha4 on the cell surface of transfectants was not changed, wild-type and His321 mutant gelsolin, except for C-del gelsolin, exhibited retardation of cell spreading, reduced chemotatic migration to fibronectin and suppressed lung colonization in spontaneous metastasis assay. Gelsolin may function as a metastasis suppressor as well as a tumor suppressor gene. The carboxyl-terminus of gelsolin is important for retardation of cell spreading, reduced chemotasis and metastasis suppression.

The effect of chitosan on stiffness and glycolytic activity of human bladder cells

The cell's cytoskeleton together with the cell membrane and numerous accessory proteins determines the mechanical properties of cell. Any factors influencing cell organization and structure can cause alterations in mechanical properties of cell (its ability for deformation and adhesion). The determination of the local elastic properties of cells in their culture conditions has opened the possibility for the measurement of the influence of different factors on the mechanical properties of the living cells. The effect of the chitosan on the stiffness of the non-malignant transitional epithelial cells of ureter (HCV 29) and the transitional cell cancer of urine bladder (T24) was determined using scanning force microscopy. The investigations were performed in the culture medium (RPMI 1640) containing 10% fetal calf serum in the presence of the microcrystalline chitosan of the three different deacetylation degrees. In parallel, the effect of chitosan on production of lactate and ATP level was determined. The results showed the strong correlation between the decrease of the energy production and the increase in Young's modulus values obtained for the cancer cells treated with chitosan.

Cytoskeletal organization in tropomyosin-mediated reversion of ras-transformation: Evidence for Rho kinase pathway

Tropomyosin (TM) family of cytoskeletal proteins is implicated in stabilizing actin microfilaments. Many TM isoforms, including tropomyosin-1 (TM1), are down-regulated in transformed cells. Previously we demonstrated that TM1 is a suppressor of the malignant transformation, and that TM1 reorganizes microfilaments in the transformed cells. To investigate how TM1 induces microfilament organization in transformed cells, we utilized ras-transformed NIH3T3 (DT) cells, and those transduced to express TM1, and/or TM2. Enhanced expression of TM1 alone, but not TM2, results in re-emergence of microfilaments; TM1, together with TM2 remarkably improves microfilament architecture. TM1 induced cytoskeletal reorganization involves an enhanced expression of caldesmon, but not vinculin, alpha-actinin, or gelsolin. In addition, TM1-induced cytoskeletal reorganization and the revertant phenotype appears to involve re-activation of RhoA controlled pathways in DT cells. RhoA expression, which is suppressed in DT cells, is significantly increased in TM1-expressing cells, without detectable changes in the expression of Rac or Cdc42. Furthermore, expression of a dominant negative Rho kinase, or treatment with Y-27632 disassembled microfilaments in normal NIH3T3 and in TM1 expressing cells. These data suggest that reactivation of Rho kinase directed pathways are critical for TM1-mediated microfilament assemblies.

How do fibroblasts interact with the extracellular matrix in wound contraction?

Two strong yet contradictory theories exist on how wound contraction occurs. This article, in two parts, reviews the research on both sides and discusses the limitations of non-human experiments.

Functional specificity of actin isoforms

Actin, one of the main proteins of muscle and cytoskeleton, exists as a variety of highly conserved isoforms whose distribution in vertebrates is tissue-specific. Synthesis of specific actin isoforms is accompanied by their subcellular compartmentalization, with both processes being regulated by factors of cell proliferation and differentiation. Actin isoforms cannot substitute for each other, and the high-level synthesis of exogenous actins leads to alterations in cell organization and morphology. This indicates that the highly conserved actins are functionally specialized for the tissues in which they predominate. The first goal of this review is to analyze the data on the polymerizability of actin isoforms to show that cytoskeleton isoactins form less stable polymers than skeletal muscle actin. This difference correlates with the dynamics of actin microfilaments versus the stability of myofibrillar systems. The three-dimensional actin structure as well as progress in the analysis of conformational changes in both the actin monomer and the filament allows us to view the data on the structure and polymerization of isoactins in terms of structure-function relationships within the actin molecule. Most of the amino acid substitutions that distinguish actin isoforms are located apart from actin-actin contact sites in the polymer. We suggest that these substitutions can modulate the ability of actin monomers to form more or less stable polymers by long-range (allosteric) regulation of the contact sites.