Cytoskeletal dynamics in rabbit synovial fibroblasts: I. Effects of acrylamide on intermediate filaments and microfilaments

Japanese encephalitis virus NS1 and NS1' proteins induce vimentin rearrangement via the CDK1-PLK1 axis to promote viral replication

The host cytoskeleton plays crucial roles in various stages of virus infection, including viral entry, transport, replication, and release. However, the specific mechanisms by which intermediate filaments are involved in orthoflavivirus infection have not been well understood. In this study, we demonstrate that the Japanese encephalitis virus (JEV) remodels the vimentin network, resulting in the formation of cage-like structures that support viral replication. Mechanistically, JEV NS1 and NS1' proteins induce the translocation of CDK1 from the nucleus to the cytoplasm and interact with it, leading to the phosphorylation of vimentin at Ser56. This phosphorylation event recruits PLK1, which further phosphorylates vimentin at Ser83. Consequently, these phosphorylation modifications convert the typically filamentous vimentin into non-filamentous "particles" or "squiggles." These vimentin "particles" or "squiggles" are then transported retrogradely along microtubules to the endoplasmic reticulum, where they form cage-like structures. Notably, NS1' is more effective than NS1 in triggering the CDK1-PLK1 cascade response. Overall, our study provides new insights into how JEV NS1 and NS1' proteins manipulate the vimentin network to facilitate efficient viral replication.

IMPORTANCE

Japanese encephalitis virus (JEV) is a mosquito-borne orthoflavivirus that causes severe encephalitis in humans, particularly in Asia. Despite the availability of a safe and effective vaccine, JEV infection remains a significant public health threat due to limited vaccination coverage. Understanding the interactions between JEV and host proteins is essential for developing more effective antiviral strategies. In this study, we investigated the role of vimentin, an intermediate filament protein, in JEV replication. Our findings reveal that JEV NS1 and NS1' proteins induce vimentin rearrangement, resulting in the formation of cage-like structures that envelop the viral replication factories (RFs), thus facilitating efficient viral replication. Our research highlights the importance of the interplay between the cytoskeleton and orthoflavivirus, suggesting that targeting vimentin could be a promising approach for the development of antiviral strategies to inhibit JEV propagation.

Cellular Vimentin Interacts with Foot-and-Mouth Disease Virus Nonstructural Protein 3A and Negatively Modulates Viral Replication

Nonstructural protein 3A of foot-and-mouth disease virus (FMDV) is a partially conserved protein of 153 amino acids that is in most FMDVs examined to date, and it plays important roles in virus replication, virulence, and host range. To better understand the role of 3A during FMDV infection, we used coimmunoprecipitation followed by mass spectrometry to identify host proteins that interact with 3A in FMDV-infected cells. Here, we report that cellular vimentin is a host binding partner for 3A. The 3A-vimentin interaction was further confirmed by coimmunoprecipitation, glutathione S-transferase (GST) pull down, and immunofluorescence assays. Alanine-scanning mutagenesis indicated that amino acid residues 15 to 21 at the N-terminal region of the FMDV 3A are responsible for the interaction between 3A and vimentin. Using reverse genetics, we demonstrate that mutations in 3A that disrupt the interaction between 3A and vimentin are also critical for virus growth. Overexpression of vimentin significantly suppressed the replication of FMDV, whereas knockdown of vimentin significantly enhanced FMDV replication. However, chemical disruption of the vimentin network by acrylamide resulted in a significant decrease in viral yield, suggesting that an intact vimentin network is needed for FMDV replication. These results indicate that vimentin interacts with FMDV 3A and negatively regulates FMDV replication and that the vimentin-3A interaction is essential for FMDV replication. This study provides information that should be helpful for understanding the molecular mechanism of FMDV replication.IMPORTANCE Foot-and-mouth disease virus (FMDV) nonstructural protein 3A plays important roles in virus replication, host range, and virulence. To further understand the role of 3A during FMDV infection, identification of host cell factors that interact with FMDV 3A is needed. Here, we found that vimentin is a direct binding partner of FMDV 3A, and manipulation of vimentin has a negative effect on virus replication. We also demonstrated that amino acid residues 15 to 21 at the N-terminal region of the FMDV 3A are responsible for the interaction between 3A and vimentin and that the 3A-vimentin interaction is critical for viral replication since the full-length cDNA clone harboring mutations in 3A, which were disrupt 3A-vimentin reactivity, could not produce viable virus progeny. This study provides information that not only provides us a better understanding of the mechanism of FMDV replication but also helps in the development of novel antiviral strategies in the future.

Withaferin-A Can Be Used to Modulate the Keratin Network of Intermediate Filaments in Human Epidermal Keratinocytes

The mechanical state of cells is a critical part of their healthy functioning and it is controlled primarily by cytoskeletal networks (actin, microtubules and intermediate filaments). Drug-based strategies targeting the assembly of a given cytoskeletal network are often used to pinpoint their role in cellular function. Unlike actin and microtubules, there has been limited interest in the role of intermediate filaments, and fewer drugs have thus been identified and characterised as modulators of its assembly. Here, we evaluate whether Withaferin-A (WFA), an established disruptor of vimentin filaments, can also be used to modulate keratin filament assembly. Our results show that in keratinocytes, which are keratin-rich but vimentin-absent, Withaferin-A disrupts keratin filaments. Importantly, the dosages required are similar to those previously reported to disrupt vimentin in other cell types. Furthermore, Withaferin-A-induced keratin disassembly is accompanied by changes in cell stiffness and migration. Therefore, we propose that WFA can be repurposed as a useful drug to disrupt the keratin cytoskeleton in epithelial cells.

Vimentin Plays a Crucial Role in Fibroblast Ageing by Regulating Biophysical Properties and Cell Migration

Ageing is the result of changes in biochemical and biophysical processes at the cellular level that lead to progressive organ decline. Here we focus on the biophysical changes that impair cellular function of human dermal fibroblasts using donors of increasing age. We find that cell motility is impaired in cells from older donors, which is associated with increased Young’s modulus, viscosity, and adhesion. Cellular morphology also displays parallel increases in spread area and cytoskeletal assembly, with a threefold increase in vimentin filaments alongside a decrease in its remodelling rate. Treatments with withaferin A or acrylamide show that cell motility can be modulated by regulating vimentin assembly. Crucially, decreasing vimentin amount in cells from older individuals to levels displayed by the neonatal donor rescues their motility. Our results suggest that increased vimentin assembly may underlay the aberrant biophysical properties progressively observed at the cellular level in the course of human ageing and propose vimentin as a potential therapeutic target for ageing-related diseases.

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

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

Vimentin enhances cell elastic behavior and protects against compressive stress

Vimentin intermediate filament expression is a hallmark of epithelial-to-mesenchymal transitions, and vimentin is involved in the maintenance of cell mechanical properties, cell motility, adhesion, and other signaling pathways. A common feature of vimentin-expressing cells is their routine exposure to mechanical stress. Intermediate filaments are unique among cytoskeletal polymers in resisting large deformations in vitro, yet vimentin's mechanical role in the cell is not clearly understood. We use atomic force microscopy to compare the viscoelastic properties of normal and vimentin-null (vim(-/-)) mouse embryo fibroblasts (mEFs) on substrates of different stiffnesses, spread to different areas, and subjected to different compression patterns. In minimally perturbed mEF, vimentin contributes little to the elastic modulus at any indentation depth in cells spread to average areas. On a hard substrate however, the elastic moduli of maximally spread mEFs are greater than those of vim(-/-)mEF. Comparison of the plastic deformation resulting from controlled compression of the cell cortex shows that vimentin's enhancement of elastic behavior increases with substrate stiffness. The elastic moduli of normal mEFs are more stable over time than those of vim(-/-)mEFs when cells are subject to ongoing oscillatory compression, particularly on a soft substrate. In contrast, increasing compressive strain over time shows a greater role for vimentin on a hard substrate. Under both conditions, vim(-/-)mEFs exhibit more variable responses, indicating a loss of regulation. Finally, normal mEFs are more contractile in three-dimensional collagen gels when seeded at low density, when cell-matrix contacts dominate, whereas contractility of vim(-/-)mEF is greater at higher densities when cell-cell contacts are abundant. Addition of fibronectin to gel constructs equalizes the contractility of the two cell types. These results show that the Young's moduli of normal and vim(-/-)mEFs are substrate stiffness dependent even when the spread area is similar, and that vimentin protects against compressive stress and preserves mechanical integrity by enhancing cell elastic behavior.

Dissecting the contribution of actin and vimentin intermediate filaments to mechanical phenotype of suspended cells using high-throughput deformability measurements and computational modeling

Mechanical cell properties play an important role in many basic biological functions, including motility, adhesion, proliferation and differentiation. There is a growing body of evidence that the mechanical cell phenotype can be used for detection and, possibly, treatment of various diseases, including cancer. Understanding of pathological mechanisms requires investigation of the relationship between constitutive properties and major structural components of cells, i.e., the nucleus and cytoskeleton. While the contribution of actin und microtubules to cellular rheology has been extensively studied in the past, the role of intermediate filaments has been scarcely investigated up to now. Here, for the first time we compare the effects of drug-induced disruption of actin and vimentin intermediate filaments on mechanical properties of suspended NK cells using high-throughput deformability measurements and computational modeling. Although, molecular mechanisms of actin and vimentin disruption by the applied cytoskeletal drugs, Cytochalasin-D and Withaferin-A, are different, cell softening in both cases can be attributed to reduction of the effective density and stiffness of filament networks. Our experimental data suggest that actin and vimentin deficient cells exhibit, in average, 41% and 20% higher deformability in comparison to untreated control. 3D Finite Element simulation is performed to quantify the contribution of cortical actin and perinuclear vimentin to mechanical phenotype of the whole cell. Our simulation provides quantitative estimates for decreased filament stiffness in drug-treated cells and predicts more than two-fold increase of the strain magnitude in the perinuclear vimentin layer of actin deficient cells relatively to untreated control. Thus, the mechanical function of vimentin becomes particularly essential in motile and proliferating cells that have to dynamically remodel the cortical actin network. These insights add functional cues to frequently observed overexpression of vimentin in diverse types of cancer and underline the role of vimentin targeting drugs, such as Withaferin-A, as a potent cancerostatic supplement.

The intermediate filament network protein, vimentin, is required for parvoviral infection

Intermediate filaments (IFs) have recently been shown to serve novel roles during infection by many viruses. Here we have begun to study the role of IFs during the early steps of infection by the parvovirus minute virus of mice (MVM). We found that during early infection with MVM, after endosomal escape, the vimentin IF network was considerably altered, yielding collapsed immunofluorescence staining near the nuclear periphery. Furthermore, we found that vimentin plays an important role in the life cycle of MVM. The number of cells, which successfully replicated MVM, was reduced in infected cells in which the vimentin network was genetically or pharmacologically modified; viral endocytosis, however, remained unaltered. Perinuclear accumulation of MVM-containing vesicles was reduced in cells lacking vimentin. Our data suggests that vimentin is required for the MVM life cycle, presenting possibly a dual role: (1) following MVM escape from endosomes and (2) during endosomal trafficking of MVM.

Herpesviruses and intermediate filaments: close encounters with the third type

Intermediate filaments (IF) are essential to maintain cellular and nuclear integrity and shape, to manage organelle distribution and motility, to control the trafficking and pH of intracellular vesicles, to prevent stress-induced cell death, and to support the correct distribution of specific proteins. Because of this, IF are likely to be targeted by a variety of pathogens, and may act in favor or against infection progress. As many IF functions remain to be identified, however, little is currently known about these interactions. Herpesviruses can infect a wide variety of cell types, and are thus bound to encounter the different types of IF expressed in each tissue. The analysis of these interrelationships can yield precious insights into how IF proteins work, and into how viruses have evolved to exploit these functions. These interactions, either known or potential, will be the focus of this review.

Onset of human cytomegalovirus replication in fibroblasts requires the presence of an intact vimentin cytoskeleton

Like all viruses, herpesviruses extensively interact with the host cytoskeleton during entry. While microtubules and microfilaments appear to facilitate viral capsid transport toward the nucleus, evidence for a role of intermediate filaments in herpesvirus entry is lacking. Here, we examined the function of vimentin intermediate filaments in fibroblasts during the initial phase of infection of two genotypically distinct strains of human cytomegalovirus (CMV), one with narrow (AD169) and one with broad (TB40/E) cell tropism. Chemical disruption of the vimentin network with acrylamide, intermediate filament bundling in cells from a patient with giant axonal neuropathy, and absence of vimentin in fibroblasts from vimentin(-/-) mice severely reduced entry of either strain. In vimentin null cells, viral particles remained in the cytoplasm longer than in vimentin(+/+) cells. TB40/E infection was consistently slower than that of AD169 and was more negatively affected by the disruption or absence of vimentin. These findings demonstrate that an intact vimentin network is required for CMV infection onset, that intermediate filaments may function during viral entry to facilitate capsid trafficking and/or docking to the nuclear envelope, and that maintenance of a broader cell tropism is associated with a higher degree of dependence on the vimentin cytoskeleton.

Effects of hydrostatic pressure on cytoskeleton and BMP-2, TGF-beta, SOX-9 production in rat temporomandibular synovial fibroblasts

OBJECTIVE

Recent experimental evidence has suggested that pressure may play an important role in the pathogenesis of arthritic diseases such as temporomandibular disorders (TMDs), rheumatic diseases and osteoarthritis. This study examines the effects of hydrostatic pressure (HP) on cytoskeleton and protein production of bone morphogenetic protein-2 (BMP-2), transforming growth factor-beta (TGF-beta) and the SRY HMG box related gene 9 (SOX-9) in synovial fibroblasts (SFs) of rat temporomandibular joint (TMJ).

METHODS

SFs derived from rat TMJ were grown to confluence in Dulbecco's modified Eagle medium supplemented with 15% fetal calf serum. The monolayer of SFs was subjected to different HPs (0, 30, 60, and 90kPa) by an in-house designed pressure chamber for 12h. Changes of cell morphology were observed by fluorescent microscope. Production of TGF-beta, BMP-2 and SOX-9 was examined by immunocytochemical assay and western blot.

RESULTS

Compared with the untreated control, the cellular actin configuration of SFs became elongated and more intense F-actin stress fiber staining was observed after HP loading. Exposure of SFs to HP for 12h resulted in significant up-regulation of BMP-2 by 46, 54, and 66% at 30, 60, and 90kPa, respectively, whilst TGF-beta increased by 11, 19, and 28% at 30, 60, and 90kPa, respectively. HP also induced the increase of SOX-9 by 72% at 30kPa and 83% at 60kPa, but only 54% at 90kPa.

CONCLUSIONS

The obtained data suggest that HP induced the alteration of cytoskeleton and bone-morphogenetic-related proteins' production of SFs, which may influence the pathological condition of TMDs.

Disruption of FAK signaling: a side mechanism in cytotoxicity

Focal adhesion kinase (FAK) is a non-receptor protein tyrosine kinase (PTK) which acts as an early modulator in the integrin signaling cascade. FAK phosphorylation and its consequent activation regulate several basic biological cellular functions. On the contrary, dysregulation of FAK signaling is implicated in the malignant transformation of cells, as well as in nonmalignant pathological conditions. With respect to cytotoxicity, accumulating data indicate that FAK participates in the mechanism of action of the known cytotoxic reactive oxygen species (ROS). Additionally, evidence was presented that different cytotoxic substances, such as arsenic (As), lead (Pb), acrylamide, methylisothiazolinone (MIT), dichlorovinylcysteine (DCVC) and halothane, acted, at least in part, by downregulating FAK tyrosine phosphorylation, while the bacterial toxins Pasteurella multocida toxin and Escherichia coli cytotoxic necrotizing factor, have been shown to exert cytotoxic effects by inducing FAK tyrosine phosphorylation. The observation that upregulation as well as downregulation of FAK activity both result in cytotoxic effects seems contradictory. Even though a common mode of action, with respect to the dysregulation of FAK signaling, for these cytotoxic substances has not yet been discovered, a cumulative approach could be established by focusing on FAK activation and signaling cascade. According to these data, interfering with FAK signaling might be of a potential use in blocking these cytotoxic effects. Further studies are needed on the possible implication of FAK in substance-induced cytotoxicity, as well as the possibility that such effects might be hindered or even blocked by restoring FAK signaling.

Disassembly of the vimentin cytoskeleton disrupts articular cartilage chondrocyte homeostasis

Articular cartilage functions in dissipating forces applied across joints. It comprises an extracellular matrix containing primarily collagens, proteoglycans and water to maintain its functional properties, and is interspersed with chondrocytes. The chondrocyte cytoskeleton comprises actin microfilaments, tubulin microtubules and vimentin intermediate filaments. Previous studies have determined the contribution of actin and tubulin in regulating the synthesis of the extracellular matrix components aggrecan and type II collagen. The contribution of vimentin to extracellular matrix biosynthesis in any cell type has not previously been addressed. Therefore the aim of this study was to assess the role of vimentin in cartilage chondrocyte metabolism. Vimentin intermediate filaments were disrupted in high-density monolayer articular chondrocyte cultures using acrylamide for 7 days. De novo protein and collagen synthesis were measured by adding [3H]-proline, and sulphated glycosaminoglycan (sGAG) synthesis measured by adding [35S]-sulphate to cultures. Vimentin disruption resulted in decreased collagen synthesis, whilst sGAG synthesis was unaffected. In addition, there was a significant reduction in type II collagen and aggrecan gene transcription suggesting that the effects observed occur at both the transcriptional and translational levels. A 3-day cold chase demonstrated a significant inhibition of collagen and sGAG degradation; the reduction in collagen degradation was corroborated by the observed reduction in both pro-MMP 2 expression and activation. We have demonstrated that an intact vimentin intermediate filament network contributes to the maintenance of the chondrocyte phenotype and thus an imbalance favouring filament disassembly can disturb the integrity of the articular cartilage, and may ultimately lead to the development of pathologies such as osteoarthritis.

Acrylamide inhibits gravitropism and affects microtubules in rice coleoptiles

To find components which participate in gravitropic signal transmission, we screened different cell biological inhibitors for their effect on gravitropic bending of rice coleoptiles. Acrylamide, which is known to affect intermediate filaments in mammalian cells, strongly inhibited gravitropic bending at concentrations that did not inhibit growth of coleoptile segments. This inhibition was reversible. Investigating the acrylamide effect further, we found that it interferes with an event that occurs around 15 min after the onset of stimulation. We also observed that acrylamide inhibits polar indolyl-3-acetic acid transport. Furthermore, acrylamide efficiently eliminated microtubules, whereas actin filaments remained intact. To our knowledge this is the first report of effects of monoacrylamide in plant cells.

JAM-C is a component of desmosomes and a ligand for CD11b/CD18-mediated neutrophil transepithelial migration

Neutrophil (PMN) transepithelial migration is dependent on the leukocyte beta(2) integrin CD11b/CD18, yet the identity of epithelial counterreceptors remain elusive. Recently, a JAM protein family member termed JAM-C was implicated in leukocyte adhesive interactions; however, its expression in epithelia and role in PMN-epithelial interactions are unknown. Here, we demonstrate that JAM-C is abundantly expressed basolaterally in intestinal epithelia and localizes to desmosomes but not tight junctions. Desmosomal localization of JAM-C was further confirmed by experiments aimed at selective disruption of tight junctions and desmosomes. In assays of PMN transepithelial migration, both JAM-C mAbs and JAM-C/Fc chimeras significantly inhibited the rate of PMN transmigration. Additional experiments revealed specific binding of JAM-C to CD11b/CD18 and provided evidence of other epithelial ligands for CD11b/CD18. These findings represent the first demonstration of direct adhesive interactions between PMN and epithelial intercellular junctions (desmosomes) that regulate PMN transepithelial migration and also suggest that JAM-C may play a role in desmosomal structure/function.

Fluid shear stress induction of COX-2 protein and prostaglandin release in cultured MC3T3-E1 osteoblasts does not require intact microfilaments or microtubules

Cultured osteoblasts express three major types of cytoskeleton: actin microfilaments, microtubules, and intermediate filaments. The cytoskeletal network is thought to play an important role in the transmission and conversion of a mechanical stimulus into a biochemical response. To examine a role for the three different cytoskeletal networks in fluid shear stress-induced signaling in osteoblasts, we individually disrupted actin microfilaments, micro-tubules, and intermediate filaments in MC3T3-E1 osteoblasts with multiple pharmacological agents. We subjected these cells to 90 min of laminar fluid shear stress (10 dyn/cm(2)) and compared the PGE(2) and PGI(2) release and induction of cyclooxygenase-2 protein to control cells with intact cytoskeletons. Disruption of actin microfilaments, microtubules, or intermediate filaments in MC3T3-E1 cells did not prevent a significant fluid shear stress-induced release of PGE(2) or PGI(2). Furthermore, disruption of actin microfilaments or microtubules did not prevent a significant fluid shear stress-induced increase in cyclooxygenase-2 protein levels. Disruption of intermediate filaments with acrylamide did prevent the fluid shear stress-induced increase in cyclooxygenase-2 but also prevented a PGE(2)-induced increase in cyclooxygenase-2. Thus none of the three major cytoskeletal networks are required for fluid shear stress-induced prostaglandin release. Furthermore, although neither actin microfilaments nor microtubules are required for fluid shear stress-induced increase in cyclooxygenase-2 levels, the role of intermediate filaments in regulation of cyclooxygenase-2 expression is less clear.

Role of the cytoskeleton in adhesion stabilization of human colorectal carcinoma cells to extracellular matrix components under dynamic conditions of laminar flow

Adhesion stabilization of malignant cells in the microcirculation is necessary for successful metastasis formation. The adhesion of colon carcinoma cells to microcirculation extracellular matrix (ECM) components is mediated, in part, by integrins that can be intracellularly linked to cytoskeletal proteins. Thus the functional status of at least certain integrins can be regulated by complex interactions with cytosolic, cytoskeletal and membrane-bound proteins. Wall shear stress caused by fluid flow also influences cellular functions, such as cell morphology, cytoskeletal arrangements and cell signaling. Using a parallel plate laminar flow chamber dynamic adhesion of human HT-29 colon carcinoma cells to collagen was investigated and compared with cell adhesion under static conditions. Cells were pretreated with cytochalasin D, nocodazole, colchicine or acrylamide to disrupt actin filaments, microtubules or intermediate filaments. Disruption of actin filaments completely inhibited all types of adhesive interactions. In contrast, impairment of tubulin polymerization or disruption of intermediate filaments resulted in different effects on static and dynamic adhesion. Treatment with acrylamide did not interfere with dynamic cell adhesion, whereas under static conditions it partially reduced adhesion rates. Under dynamic conditions increased initial adhesive interactions between HT-29 cells and collagen were found after disruption of microtubules, and the adherent cells demonstrated extensive crawling on collagen surfaces. In contrast, under static adhesion disrupting microtubules did not affect cell adhesion rates. Cytochalasin D and acrylamide were found to inhibit Tyr-phosphorylation of FAK and paxillin, whereas microtubule disrupting agents at low but not high concentrations increased phosphorylation of these focal adhesion proteins. Our results revealed that cytoskeletal components appear to be involved in adhesion stabilization of HT-29 cells to ECM components, and hydrodynamic shear forces modulate this involvement. Tyr-phosphorylation of focal adhesion proteins, such as paxillin and FAK, appears to be a part of this cytoskeleton-mediated process.

Apoptosis overview emphasizing the role of oxidative stress, DNA damage and signal-transduction pathways

Apoptosis (programmed cell death) is a central protective response to excess oxidative damage (especially DNA damage), and is also essential to embryogenesis, morphogenesis and normal immune function. An understanding of the cellular events leading to apoptosis is important for the design of new chemotherapeutic agents directed against the types of leukemias and lymphomas that are resistant to currently used chemotherapeutic protocols. We present here a review of the characteristic features of apoptosis, the cell types and situations in which it occurs, the types of oxidative stress that induce apoptosis, the signal-transduction pathways that either induce or prevent apoptosis, the biologic significance of apoptosis, the role of apoptosis in cancer, and an evaluation of the methodologies used to identify apoptotic cells. Two accompanying articles, demonstrating classic apoptosis and non-classic apoptosis in the same Epstein-Barr virus-transformed lymphoid cell line, are used to illustrate the value of employing multiple criteria to determine the type of cell death occurring in a given experimental system. Aspects of apoptosis and programmed cell death that are not covered in this review include histochemistry, details of cell deletion processes in the sculpting of tissues and organs in embryogenesis and morphogenesis, and the specific pathways leading to apoptosis in specific cell types. The readers should refer to the excellent books and reviews on the morphology, biochemistry and molecular biology of apoptosis already published on these topics. Emphasis is placed, in this review, on a proposed common pathway of apoptosis that may be relevant to all cell types.

Alteration in cell morphology triggers transforming growth factor-beta 1, collagenase, and tissue inhibitor of metalloproteinases-I expression in normal and hypertrophic scar fibroblasts

Using immunocytochemistry and Northern blot analysis, we investigated the role of cell morphology and reorganization of the cytoskeleton in the expression of transforming growth factor-beta 1 (TGF-beta 1) in human dermal fibroblasts. Disruption of the cytoskeleton was induced by three different agents--trypsin, ethyl-eneglycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA), or cytochalasin--and was confirmed by staining with rhodamine-labeled phalloidin. Immunocytochemical staining with antibodies specific for TGF-beta 1 revealed a cell-shape-related induction of TGF-beta 1. Northern blot analysis of total RNA showed a significant increase in the expression of TGF-beta 1 mRNA as early as 4 h and peaking at 12 h after disruption of the cytoskeleton. Quantitative analysis of TGF-beta 1 mRNA expression at 4 h after treatment with trypsin, EGTA, or cytochalasin C showed increases of 2.6-, 3.3-, and 2.6-fold, respectively. Disruption of the cytoskeleton by trypsin, EGTA, or cytochalasin C increased mRNA for collagenase by 3.8-fold, 2.3-fold, or 2.5-fold, respectively. The expression of mRNA for tissue inhibitor of metalloproteinases I (TIMP-I) also showed a 3.2-fold increase by trypsin, a 3.6-fold increase by EGTA, and a 2.5-fold increase by cytochalasin C. Cell-shape-related induction of TGF-beta 1, collagenase, and TIMP-I genes appears to be selective, as the levels of mRNA for fibronectin and type I procollagen were not significantly altered. These data suggest that gene expression of TGF-beta 1, collagenase, and TIMP-I is governed by the status of the cytoskeleton microfilament organization, which may be a mechanism of gene regulation during cell division, migration, and differentiation, events fundamental to wound healing.

The influence of vinyl-4-cyclohexene dioxide on the vimentin-containing intermediate filaments and the microtubular cytoskeleton of cultured mouse fibroblasts: Immunofluorescence investigations

The exposure of 3T3 mouse fibroblasts to vinyl-4-cyclohexene dioxide (VCD), a compound used as a chemical intermediate and as a reactive diluent for diepoxides and epoxy resins, induces changes in cellular shape and cytoplasmic organization. Toxicological effects on the cytoskeletal elements were investigated by culturing 3T3 cells in medium containing VCD for increasing times (15, 30, 60 and 180 min). The immunofluorescence investigations demonstrated that both vimentin-containing intermediate filaments and microtubules were compromised by the treatment in a time-dependent manner. Increasing the duration of exposure to VCD increased cellular damage.

Acrylamide alters neurofilament protein gene expression in rat brain

Acrylamide, a prototype neurotoxin, alters neurofilament protein (NF) gene expression in rat brain. Levels of mRNA coding for neurofilament protein subunits NF-L, NF-M, and NF-H have been determined by Northern blot analysis using 32P-labeled cDNA probes. Acrylamide given acutely (100 mg/kg, single intraperitoneal injection) causes a selective increase in NF-M mRNA (approximately 50%) compared to controls. The expression of NF-L or NF-H mRNA is not affected by acrylamide. In contrast, chronic treatment with acrylamide [0.03% (w/v) in drinking water for 4 weeks] induces a modest but significant increase (approximately 22%) in NF-L mRNA compared to controls. Levels of NF-M, and NF-H mRNA are not altered by acrylamide treatment. The expression of beta-actin mRNA, an ubiquitous protein, is not affected by either treatment regimen of acrylamide. The results of this study show that acrylamide increases the expression of mRNA for NF protein subunits in rat brain. The increase of specific mRNA for NF subunits depends on the dose, duration and route of acrylamide administration.

Direct measurement of fast axonal organelle transport in the sciatic nerve of rats treated with acrylamide

The effects of acrylamide on fast axonal transport have been measured primarily using the indirect methods of isotope or enzyme accumulation. We report the first direct evaluation of the effects of subchronic acrylamide dosing (150, 300, or 500 mg/kg total dose, i.e., 50 mg/kg, 2x/wk, for 1.5, 3, 5 wk, respectively) on the fast axonal transport motility machinery itself using video-enhanced differential interference contrast optics with digital image processing and computer analysis. Four principle observations were made: (1) Rapid anterograde transport was not affected at any dosage level within 1 wk after cessation of dosing. (2) A high cumulative dosage (500 mg/kg total) of acrylamide or bisacrylamide produced approximately 7-18% decrease in the rate of retrograde transport in both myelinated and unmyelinated axons. (3) Lower dosages of acrylamide (150 or 300 mg/kg total) produced an increase in retrograde transport rates in myelinated axons only. (4) During the "recovery" phase for the 500 mg/kg acrylamide animals (i.e., 3 or 5 wk after the last dosage of acrylamide) the rate of anterograde transport in the myelinated axons was decreased at 3 wk but not at 5 wk, and the rate of retrograde transport in the myelinated axons returned to control levels while the retrograde transport in the unmyelinated axons continued at abnormally slow speeds. The application of this new technique to evaluate the neurotoxic effects of acrylamide provides evidence of dynamic changes in the axonal transport motility machinery itself and differential effects on myelinated versus unmyelinated fibers.

Effects of acrylamide on germinal vesicle migration and dissolution in oocytes of the frog, Rana pipiens

We have demonstrated that when Rana oocytes are treated with 10 mM acrylamide, germinal vesicle migration (GVM) is promoted while meiosis reinitiation by progesterone is inhibited. A number of other specific alterations result from the acrylamide treatment: (i) A dense band of fibrillar material appears adjacent to the oolemma in acrylamide-treated oocytes. Furthermore, (ii) the fibrillar material reacts with an intermediate filament antibody using immunogold techniques applied to transmission electron microscopy. Moreover, (iii) acrylamide inhibits progestogen-induced annulate lamellae breakdown. In addition, (iv) the cortical mitochondria-rich layer appears to be thickened by acrylamide, which also (v) affects oocyte microvillar retraction and organization. Finally, (vi) electrophysiological measurement of membrane voltage indicates that acrylamide does not significantly affect cell viability during the incubation period used in this study. In summary, acrylamide exerts profound effects on the physiological event of GVM, and these are consistent with the hypothesis that changes in the cytoskeleton are a contributing factor in meiosis reinitiation.

Modulation of milk protein synthesis through alteration of the cytoskeleton in mouse mammary epithelial cells cultured on a reconstituted basement membrane

Recent studies indicate that the cytoskeleton may be involved in modulating tissue-specific gene expression in mammalian cells. We have studied the role of the cytoskeleton in regulating milk protein synthesis and secretion by primary mouse mammary epithelial cells cultured on a reconstituted basement membrane that promotes differentiation. After 8 days in culture, cells were treated with cytochalasin D (CD) (0.5-1 micrograms/ml) to alter actin filaments or acrylamide (Ac) (5 mM) to alter intermediate filaments (cytokeratins). CD inhibited synthesis of most proteins in a concentration-dependent manner, with beta-casein being the first affected. In contrast, Ac increased protein synthesis and secretion by 17-31% after a 12 hr treatment. Polyacrylamide gel electrophoresis of total secreted proteins indicates that synthetic rates of most proteins were increased equally by Ac treatment. This increase is apparently controlled at the level of translation, because control and Ac-treated cells contained the same amount of poly-A+ RNA, and neither CD nor Ac altered mRNA levels for beta-casein. There was also no indication that either CD or Ac can induce the expression of milk proteins in quiescent cells cultured on a plastic substratum. In conjunction with the biochemical studies, changes in cytoskeletal morphology caused by the drug treatments were analyzed by immunofluorescence microscopy. As has been observed in other cell types, low concentrations of CD caused cells to round up by disrupting actin filaments. Ac treatment slightly decreased the intensity of actin staining, but no changes in microfilament organization were observed. Ac-treated cells showed slight disorganization of the cytokeratin filaments, with some peripheral interfibrillar bundling, but the cytokeratin network did not collapse and no retraction of cell extensions or breakdown of cell-cell contacts was observed. These results confirm previous reports that the actin cytoskeleton may play a role in regulating tissue-specific protein synthesis. How Ac stimulates protein synthesis is unknown, but it is unlikely that this effect is directly mediated through intermediate filaments.

Cytoskeletal dynamics in rabbit synovial fibroblasts: II. Reformation of stress fibers in cells rounded by treatment with collagenase-inducing agents

Modulation of the synthesis and secretion of extracellular matrix proteins and matrix-degrading metalloproteases by rabbit synovial fibroblasts is an important model system for studying the control of tissue-specific gene expression. Induction of collagenase expression is correlated with changes in cell shape and actin filament distribution, but the role of the cellular cytoskeleton in the sustained synthesis and secretion of metalloproteases has not been closely examined. When cells were allowed to respread after rounding by trypsin or cytochalasin, two known metalloprotease inducers, reformation of stress fibers was observed within 2 h in the presence of serum. In the absence of serum, trypsin-treated cells did not respread substantially, even after 24 h in culture. In contrast, cytochalasin-treated cells recovered almost as rapidly in the absence as in the presence of serum, showing reformation of well-formed microfilament bundles within 30 min of drug removal, especially at the spreading cell edges. High resolution electron-microscopic views of detergent-extracted cytoskeletons confirmed the rapid rebundling of peripheral microfilaments. Acrylamide-treated cells fell between these two extremes, spreading slowly in the absence of serum, but almost as rapidly as cytochalasin-treated cells in its presence. Reestablishment of normal intermediate filament distribution generally lagged slightly behind actin for all treatments, and intermediate filaments always appeared to spread back into the cellular cytoplasm within the confines of the reforming peripheral microfilament bundles. No obvious interaction between these two cytoskeletal elements was observed after any treatment, and no specific role for intermediate filaments in modulating gene expression in these cells is suggested by these results. The serum dependence displayed after trypsin or acrylamide treatment may be due to the disturbances in fibronectin synthesis observed in these cells and is consistent with evidence that both induction and sustained expression of matrix-degrading metalloprotease may involve signals transduced through plasma membrane matrix receptors (integrins).