The role of actin polymerization in cell motility

Probing the Molecular Interactions of A22 with Prokaryotic Actin MreB and Eukaryotic Actin: A Computational and Experimental Study

Actin is a major cytoskeletal system that mediates the intricate organization of macromolecules within cells. The bacterial cytoskeletal protein MreB is a prokaryotic actin-like protein governing the cell shape and intracellular organization in many rod-shaped bacteria, including pathogens. MreB stands as a target for antibiotic development, and compounds like A22 and its analogue, MP265, are identified as potent inhibitors of MreB. The bacterial actin MreB shares structural homology with eukaryotic actin despite lacking sequence similarity. It is currently not clear whether small molecules that inhibit MreB can act on eukaryotic actin due to their structural similarity. In this study, we investigate the molecular interactions between A22 and its analogue MP265 with MreB and eukaryotic actin through a molecular dynamics approach. Employing MD simulations and free energy calculations with an all-atom model, we unveil the robust interaction of A22 and MP265 with MreB, and substantial binding affinity is observed for A22 and MP265 with eukaryotic actin. Experimental assays reveal A22's toxicity to eukaryotic cells, including yeast and human glioblastoma cells. Microscopy analysis demonstrates the profound effects of A22 on actin organization in human glioblastoma cells. This integrative computational and experimental study provides new insights into A22's mode of action, highlighting its potential as a versatile tool for probing the dynamics of both prokaryotic and eukaryotic actins.

Comparative profiling of cellular gait on adhesive micropatterns defines statistical patterns of activity that underlie native and cancerous cell dynamics

Cell dynamics are powered by patterns of activity, but it is not straightforward to quantify these patterns or compare them across different environmental conditions or cell-types. Here we digitize the long-term shape fluctuations of metazoan cells grown on micropatterned fibronectin islands to define and extract statistical features of cell dynamics without the need for genetic modification or fluorescence imaging. These shape fluctuations generate single-cell morphological signals that can be decomposed into two major components: a continuous, slow-timescale meandering of morphology about an average steady-state shape; and short-lived "events" of rapid morphology change that sporadically occur throughout the timecourse. By developing statistical metrics for each of these components, we used thousands of hours of single-cell data to quantitatively define how each axis of cell dynamics was impacted by environmental conditions or cell-type. We found the size and spatial complexity of the micropattern island modulated the statistics of morphological events-lifetime, frequency, and orientation-but not its baseline shape fluctuations. Extending this approach to profile a panel of triple negative breast cancer cell-lines, we found that different cell-types could be distinguished from one another along specific and unique statistical axes of their behavior. Our results suggest that micropatterned substrates provide a generalizable method to build statistical profiles of cell dynamics to classify and compare emergent cell behaviors.

Crowding alters F-actin secondary structure and hydration

Actin, an important component of eukaryotic cell cytoskeleton, regulates cell shape and transport. The morphology and biochemical properties of actin filaments are determined by their structure and protein-protein contacts. Crowded environments can organize filaments into bundles, but less is known about how they affect F-actin structure. This study used 2D IR spectroscopy and spectral calculations to examine how crowding and bundling impact the secondary structure and local environments in filaments and weakly or strongly bundled networks. The results reveal that bundling induces changes in actin's secondary structure, leading to a decrease in β-sheet and an increase in loop conformations. Strongly bundled networks exhibit a decrease in backbone solvent exposure, with less perturbed α-helices and nearly "locked" β-sheets. Similarly, the loops become less hydrated but maintain a dynamic environment. These findings highlight the role of loop structure in actin network morphology and stability under morphology control by PEG.

Emergence and maintenance of variable-length actin filaments in a limiting pool of building blocks

Actin is one of the key structural components of the eukaryotic cytoskeleton that regulates cellular architecture and mechanical properties. Dynamic regulation of actin filament length and organization is essential for the control of many physiological processes including cell adhesion, motility and division. While previous studies have mostly focused on the mechanisms controlling the mean length of individual actin filaments, it remains poorly understood how distinct actin filament populations in cells maintain different lengths using the same set of molecular building blocks. Here we develop a theoretical model for the length regulation of multiple actin filaments by nucleation and growth rate modulation by actin binding proteins in a limiting pool of monomers. We first show that spontaneous nucleation of actin filaments naturally leads to heterogeneities in filament length distribution. We then investigate the effects of filament growth inhibition by capping proteins and growth promotion by formin proteins on filament length distribution. We find that filament length heterogeneity can be increased by growth inhibition, whereas growth promoters do not significantly affect length heterogeneity. Interestingly, a competition between filament growth inhibitors and growth promoters can give rise to bimodal filament length distribution as well as a highly heterogeneous length distribution with large statistical dispersion. We quantitatively predict how heterogeneity in actin filament length can be modulated by tuning F-actin nucleation and growth rates in order to create distinct filament subpopulations with different lengths. SIGNIFICANCE: Actin filaments organize into different functional network architectures within eukaryotic cells. To maintain distinct actin network architectures, it is essential to regulate the lengths of actin filaments. While the mechanisms controlling the lengths of individual actin filaments have been extensively studied, the regulation of length heterogeneity in actin filament populations is not well understood. Here we show that the modulation of actin filament growth and nucleation rates by actin binding proteins can regulate actin length distribution and create distinct sub-populations with different lengths. In particular, by tuning concentrations of formin, profilin and capping proteins, various aspects of actin filament length distribution can be controlled. Insights gained from our results may have significant implications for the regulation of actin filament length heterogeneity and architecture within a cell.

Leading edge maintenance in migrating cells is an emergent property of branched actin network growth

Animal cell migration is predominantly driven by the coordinated, yet stochastic, polymerization of thousands of nanometer-scale actin filaments across micron-scale cell leading edges. It remains unclear how such inherently noisy processes generate robust cellular behavior. We employed high-speed imaging of migrating neutrophil-like HL-60 cells to explore the fine-scale shape fluctuations that emerge and relax throughout the process of leading edge maintenance. We then developed a minimal stochastic model of the leading edge that reproduces this stable relaxation behavior. Remarkably, we find lamellipodial stability naturally emerges from the interplay between branched actin network growth and leading edge shape – with no additional feedback required – based on a synergy between membrane-proximal branching and lateral spreading of filaments. These results thus demonstrate a novel biological noise-suppression mechanism based entirely on system geometry. Furthermore, our model suggests that the Arp2/3-mediated ~70–80° branching angle optimally smooths lamellipodial shape, addressing its long-mysterious conservation from protists to mammals.

In every human cell, there are tens of millions of proteins which work together to control everything from the cell’s shape to its behavior. One of the most abundant proteins is actin, which organizes itself into filaments that mechanically support the cell and help it to move.

These filaments are very dynamic, with individual actin molecules constantly being added or removed. This allows the cell to build large structures with distinct shapes and properties. Many motile cells, for example, have a structure called a lamellipodium which protrudes at their ‘leading edge’ and pushes them forward. The lamellipodium has a very robust shape that does not vary much between different cell types, or change significantly as cells migrate. But how the tens of thousands of actin molecules inside the lamellipodium organize themselves into this large, stable structure is not fully understood.

To investigate, Garner and Theriot used high-speed video microscopy to track the shape of human cells cultured in the laboratory. As the cells crawled along a glass surface, their leading edge undulated like strings being plucked on a guitar. A computer simulation showed that these ripples can be caused by filaments randomly adding and removing actin molecules.

While these random movements could destabilize the structure of the leading edge, the simulation suggests that another aspect of actin filament growth smooths out any fluctuations in the lamellipodium’s shape. Actin networks in the lamellipodium have a branched configuration, with new strands emerging off each other at an angle like branches in a tree. Garner and Theriot found that the specific angle in which new filaments are added smooths out the lamellipodium’s shape, which may explain why this geometry has persisted throughout evolution.

These findings suggest that the way in which actin filaments join together helps to maintain the shape of large cellular structures. In the future, scientists could use this design principle to build molecular machines that can self-organize into microstructures. These engineered constructs could be used to modulate the activity of living cells that have been damaged by disease.

Dynamics of the Actin Cytoskeleton at Adhesion Complexes

The shape of cells is altered to allow cells to adapt to their changing environments, including responding to internally generated and externally applied force. Force is sensed by cell surface adhesion proteins that are enriched in sites where cells bind to the extracellular matrix (focal adhesions) and neighboring cells (cell-cell or adherens junctions). Receptors at these adhesion sites stimulate intracellular signal transduction cascades that culminate in dramatic changes in the actin cytoskeleton. New actin filaments form, and/or new and existing filaments can be cleaved, branched, or bundled. Here, we discuss the actin cytoskeleton and its functions. We will examine the current understanding for how the actin cytoskeleton is tethered to adhesion sites. Finally, we will highlight recent studies describing how the actin cytoskeleton at these adhesion sites is remodeled in response to force.

Regulating the Supramolecular Polymerization of Fibrous Crystalline Structures in Aqueous Solution

Inspired by protein polymerizations, much progress has been made in making "polymer-like" supramolecular structures from small synthetic subunits through non-covalent bonds. A few regulation mechanisms have also been explored in synthetic platforms to create supramolecular polymers and materials with dynamic properties. Herein, a type of reactive regulator that facilitates the dimerization of the monomer precursors through dynamic bonds to trigger the supramolecular assembly from small molecules in an aqueous solution is described. The supramolecular structures are crystalline in nature and the reaction coupled assembly strategy can be extended to a supramolecular assembly of aromatic amide derivatives formed in-situ. The method may be instructive for the development of supramolecular nanocrystalline materials with desired physical properties.

Myosin and gelsolin cooperate in actin filament severing and actomyosin motor activity

Actin is a major intracellular protein with key functions in cellular motility, signaling, and structural rearrangements. Its dynamic behavior, such as polymerization and depolymerization of actin filaments in response to intracellular and extracellular cues, is regulated by an abundance of actin binding proteins. Out of these, gelsolin is one of the most potent for filament severing. However, myosin motor activity also fragments actin filaments through motor-induced forces, suggesting that these two proteins could cooperate to regulate filament dynamics and motility. To test this idea, we used an in vitro motility assay, where actin filaments are propelled by surface-adsorbed heavy meromyosin (HMM) motor fragments. This allows studies of both motility and filament dynamics using isolated proteins. Gelsolin, at both nanomolar and micromolar Ca²⁺ concentration, appreciably enhanced actin filament severing caused by HMM-induced forces at 1 mM MgATP, an effect that was increased at higher HMM motor density. This finding is consistent with cooperativity between actin filament severing by myosin-induced forces and by gelsolin. We also observed reduced sliding velocity of the HMM-propelled filaments in the presence of gelsolin, providing further support of myosin-gelsolin cooperativity. Total internal reflection fluorescence microscopy–based single molecule studies corroborated that the velocity reduction was a direct effect of gelsolin binding to the filament and revealed different filament severing pattern of stationary and HMM propelled filaments. Overall, the results corroborate cooperative effects between gelsolin-induced alterations in the actin filaments and changes due to myosin motor activity leading to enhanced F-actin severing of possible physiological relevance.

Kinetics of actin networks formation measured by time resolved particle-tracking microrheology

Actin is one of the most studied cytoskeleton proteins showing a very rich span of structures and functions. For example, adenosine triphosphate (ATP)-assisted polymerization of actin is used to push protrusions forward in a mechanism that enables cells to crawl on a substrate. In this process, the chemical energy released from the hydrolysis of ATP is what enables force generation. We study a minimal model system comprised of actin monomers in an excess of ATP concentration. In such a system polymerization proceeds in three stages: nucleation of actin filaments, elongation, and network formation. While the kinetics of filament growth was characterized previously, not much is known about the kinetics of network formation and the evolution of networks towards a steady-state structure. In particular, it is not clear how the non-equilibrium nature of this ATP-assisted polymerization manifests itself in the kinetics of self-assembly. Here, we use time-resolved microrheology to follow the kinetics of the three stages of self-assembly as a function of initial actin monomer concentration. Surprisingly, we find that at high enough initial monomer concentrations the effective elastic modulus of the forming actin networks overshoots and then relaxes with a -2/5 power law. We attribute the overshoot to the non-equilibrium nature of the polymerization and the relaxation to rearrangements of the network into a steady-state structure.

Human antigen R-regulated mRNA metabolism promotes the cell motility of migrating mouse neurons

Neocortex development during embryonic stages requires the precise control of mRNA metabolism. Human antigen R (HuR) is a well-studied mRNA-binding protein that regulates mRNA metabolism, and it is highly expressed in the neocortex during developmental stages. Deletion of HuR does not impair neural progenitor cell proliferation or differentiation, but it disturbs the laminar structure of the neocortex. We report that HuR is expressed in postmitotic projection neurons during mouse brain development. Specifically, depletion of HuR in these neurons led to a mislocalization of CDP⁺ neurons in deeper layers of the cortex. Time-lapse microscopy showed that HuR was required for the promotion of cell motility in migrating neurons. PCR array identified profilin 1 (Pfn1) mRNA as a major binding partner of HuR in neurons. HuR positively mediated the stability of Pfn1 mRNA and influenced actin polymerization. Overexpression of Pfn1 successfully rescued the migration defects of HuR-deleted neurons. Our data reveal a post-transcriptional mechanism that maintains actin dynamics during neuronal migration.

Summary: Maintaining actin dynamics is crucial for cell motility. Post-transcriptional regulation plays a pivotal role in supporting actin dynamics during neuronal migration.

Stress relaxation in F-actin solutions by severing

Networks of filamentous actin (F-actin) are important for the mechanics of most animal cells. These cytoskeletal networks are highly dynamic, with a variety of actin-associated proteins that control cross-linking, polymerization and force generation in the cytoskeleton. Inspired by recent rheological experiments on reconstituted solutions of dynamic actin filaments, we report a theoretical model that describes stress relaxation behavior of these solutions in the presence of severing proteins. We show that depending on the kinetic rates of assembly, disassembly, and severing, one can observe both length-dependent and length-independent relaxation behavior.

Scattered podosomes and podosomes associated with the sealing zone architecture in cultured osteoclasts revealed by cell shearing, quick freezing, and platinum-replica electron microscopy

Osteoclasts (OCs) can adhere to a variety of substrate surfaces by highly dynamic actin-based cytoskeletal structures termed podosomes. This tight attachment is established by a sealing zone (SZ), which is made of interconnected individual podosomes. Compared with scattered podosomes in various cell types, the architecture of the SZ is still unclear. Especially, ultrastructural studies on the details of the cytoskeletal structure of an OC have been challenging, because the high density of filaments in their podosomes obscure visualization of individual filaments. Therefore, to study this organization in more exact detail, we employed shearing open combined with replica electron microscopy. The present study provides several new details of the podosome and SZ structure, which were previously unrecognized: (a) the SZ consists of recognizable podosomes with a dense actin network of interpodosomal regions characterized by multiple layers of crossing, branching and anastomosing actin filament networks; (b) the Arp2/3 complex is distributed throughout the actin network of podosomes and SZ, indicating that actin polymerization is concentrated at these regions; (c) a close spatial relationship between the podosome and the dorsal membrane; and (d) a network of membranous organelles in close proximity to the podosomes in the SZ. Taken together, the present study reveals that a more complicated interpodosomal actin network among neighboring individual podosomes, which is more complicated than previously thought, appears to form the SZ. Indeed, individual podosomes are not an isolated structural unit from other organelles; and, in turn, their dynamism might affect the surrounding interpodosomal cytoskeletons, membranous organelles, and plasma membrane.

Copper promotes the migration of bone marrow mesenchymal stem cells via Rnd3-dependent cytoskeleton remodeling

The motility of mesenchymal stem cells (MSCs) is highly related to their homing in vivo, a critical issue in regenerative medicine. Our previous study indicated copper (Cu) might promote the recruitment of endogenous MSCs in canine esophagus defect model. In this study, we investigated the effect of Cu on the motility of bone marrow mesenchymal stem cells (BMSCs) and the underlying mechanism in vitro. Cu supplementation could enhance the motility of BMSCs, and upregulate the expression of hypoxia-inducible factor 1α (Hif1α) at the protein level, and upregulate the expression of rho family GTPase 3 (Rnd3) at messenger RNA and protein level. When Hif1α was silenced by small interfering RNA (siRNA), Cu-induced Rnd3 upregulation was blocked. When Rnd3 was silenced by siRNA, the motility of BMSCs was decreased with or without Cu supplementation, and Cu-induced cytoskeleton remodeling was neutralized. Furthermore, overexpression of Rnd3 also increased the motility of BMSCs and induced cytoskeleton remodeling. Overall, our results demonstrated that Cu enhanced BMSCs migration through, at least in part, cytoskeleton remodeling via Hif1α-dependent upregulation of Rnd3. This study provided an insight into the mechanism of the effect of Cu on the motility of BMSCs, and a theoretical foundation of applying Cu to improve the recruitment of BMSCs in tissue engineering and cytotherapy.

A Subtle Network Mediating Axon Guidance: Intrinsic Dynamic Structure of Growth Cone, Attractive and Repulsive Molecular Cues, and the Intermediate Role of Signaling Pathways

A fundamental feature of both early nervous system development and axon regeneration is the guidance of axonal projections to their targets in order to assemble neural circuits that control behavior. In the navigation process where the nerves grow toward their targets, the growth cones, which locate at the tips of axons, sense the environment surrounding them, including varies of attractive or repulsive molecular cues, then make directional decisions to adjust their navigation journey. The turning ability of a growth cone largely depends on its highly dynamic skeleton, where actin filaments and microtubules play a very important role in its motility. In this review, we summarize some possible mechanisms underlying growth cone motility, relevant molecular cues, and signaling pathways in axon guidance of previous studies and discuss some questions regarding directions for further studies.

Zerumbone, a Cyclic Sesquiterpene from Zingiber zerumbet Induces Apoptosis, Cell Cycle Arrest, and Antimigratory Effects in SW480 Colorectal Cancer Cells

Zerumbone isolated from the rhizomes of Zingiber zerumbet was investigated for the mechanisms by which it exhibits antiproliferative activity in colorectal cancer cells (SW480). The results indicated that the zerumbone suppressed cell growth and enhanced cell apoptosis. Exposure to zerumbone induced generation of reactive oxygen species, reduced the cellular antioxidant status, decreased mitochondrial membrane potential, and activated caspase 3, caspase 8, and caspase 9 (p < 0.001). It was also found that there was a decrease in the expression of Bcl 2 and elevation of Bax (p < 0.001) on exposure to zerumbone. Furthermore, treatment with 50, 75, and 100 μM zerumbone resulted in cell cycle arrest at the G2/M phase with a value of 17.2 ± 0.1, 19.63 ± 0.25, and 26.66 ± 0.25, respectively, and also distorted the microfilament network and effectively inhibited cellular migration.

Dynamics in steady state in vitro acto-myosin networks

It is well known that many biochemical processes in the cell such as gene regulation, growth signals and activation of ion channels, rely on mechanical stimuli. However, the mechanism by which mechanical signals propagate through cells is not as well understood. In this review we focus on stress propagation in a minimal model for cell elasticity, actomyosin networks, which are comprised of a sub-family of cytoskeleton proteins. After giving an overview of th actomyosin network components, structure and evolution we review stress propagation in these materials as measured through the correlated motion of tracer beads. We also discuss the possibility to extract structural features of these networks from the same experiments. We show that stress transmission through these networks has two pathways, a quickly dissipative one through the bulk, and a long ranged weakly dissipative one through the pre-stressed actin network.

Abnormal expression of leiomyoma cytoskeletal proteins involved in cell migration

Uterine leiomyomas are monoclonal tumors. Several factors are involved in the neoplastic transformation of the myometrium. In our study we focused on dysregulated cytoskeletal proteins in the leiomyoma as compared to the myometrium. Paired tissue samples of ten leiomyomas and adjacent myometria were obtained and analyzed by two‑dimensional gel electrophoresis (2-DE). Mass spectrometry was used for protein identification, and western blotting for 2-DE data validation. The values of ten cytoskeletal proteins were found to be significantly different: eight proteins were upregulated in the leiomyoma and two proteins were downregulated. Three of the upregulated proteins (myosin regulatory light polypeptide 9, four and a half LIM domains protein 1 and LIM and SH3 domain protein 1) are involved in cell migration, while downregulated protein transgelin is involved in replicative senescence. Myosin regulatory light polypeptide 9 (MYL9) was further validated by western blotting because it is considered to be a cell migration marker in several cancers and could play a key role in leiomyoma development. Our data demonstrate significant alterations in the expression of cytoskeletal proteins involved in leiomyoma growth. A better understanding of the involvement of cytoskeletal proteins in leiomyoma pathogenesis may contribute to the identification of new therapeutic targets and the development of new pharmacological approaches.

Involvement of Membrane Blebbing in Immunological Disorders and Cancer

Cellular blebbing is a unique form of dynamic protrusion emanating from the plasma membrane which can be either apoptotic or nonapoptotic in nature. Blebs have been observed in a wide variety of cell types and in response to multiple mechanical and chemical stimuli. They have been linked to various physiological and pathological processes including tumor motility and invasion, as well as to various immunological disorders. They can form and retract extremely rapidly in seconds or minutes, or slowly over hours or days. This review focuses on recent evidence regarding the role of blebbing in cell locomotion with particular emphasis on its role in tumor metastasis, indicating the role of specific causative molecules. The phenomenon of blebbing has been observed in endocrine-resistant breast cancer cells in response to brief exposure to extracellular alkaline pH, which leads to enhanced invasive capacity. Genetic or pharmacological targeting of cellular blebs could serve as a potential therapeutic option to control tumor metastasis.

Roles of contactin-1 in solid tumors

The neural cell adhesion molecule contactin-1 (CNTN1), first identified as a member of the contactin subpopulation of the immunoglobulin superfamily, is associated with many other cell surface proteins expressed on a variety of neurocytes, contributing to their functions and maturation. It has been recently found that the abnormal expression of CNTN1 has a close correlation with tumor initiation, development, invasiveness, metastasis and prognosis. The acquired metastatic ability of malignant tumors is caused by a population of cancer cells with the capacities of invasiveness, metastasis, adherence and proliferation, in which abnormal gene expression may play an important role. This review focuses on the current advances in research of CNTN1 in the nerve system, and mainly in the malignant tumors, with an aim to provide new clues to clinical prevention, diagnosis and treatment of these malignancies.

Contactin 1: A potential therapeutic target and biomarker in gastric cancer

Despite advances in diagnosis and treatment, gastric cancer remains one of the most common malignant tumors worldwide, and early diagnosis remains a challenge. The lack of effective methods to detect these tumors early is a major factor contributing to the high mortality in patients with gastric cancer, who are typically diagnosed at an advanced stage. Additionally, the early detection of metastases and the curative treatment of gastric cancer are difficult to achieve, and the detailed mechanisms remain to be fully elucidated. Thus, the identification of valuable predictive biomarkers and therapeutic targets to improve the prognosis of patients with gastric cancer is becoming increasingly important. Contactin 1 (CNTN1), a cell adhesion molecule, is a glycosylphosphatidylinositol-anchored neuronal membrane protein that plays an important role in cancer progression. The expression of CNTN1 is upregulated in primary lesions, and its expression level correlates with tumor metastasis in cancer patients. The current evidence reveals that the functions of CNTN1 in the development and progression of cancer likely promote the invasion and metastasis of cancer cells via the VEGFC/FLT4 axis, the RHOA-dependent pathway, the Notch signaling pathway and the epithelial-mesenchymal transition progression. Therefore, CNTN1 may be a novel biomarker and a possible therapeutic target in cancer treatment in the near future.

Keap1-Nrf2 Interaction Suppresses Cell Motility in Lung Adenocarcinomas by Targeting the S100P Protein

PURPOSE

Kelch-like ECH-associated protein 1 (Keap1) is an E3 ligase participated in the cellular defense response against oxidative stress through nuclear factor erythroid-2-related factor 2 (Nrf2). However, the role of Keap1 in regulating cancer motility is still controversial. We investigated the contribution of the Keap1-Nrf2 axis in the progression of non-small cell lung cancer (NSCLC).

EXPERIMENTAL DESIGN

The expression of Keap1 and Nrf2 was examined via immunohistochemistry, real-time PCR, and Western blot analysis in a cohort of NSCLC tissues and cells. A series of in vivo and in vitro assays was performed to elucidate the contribution of the Keap1-Nrf2 axis in lung cancer mobility and progression.

RESULTS

Keap1 expression was decreased in specimens from NSCLC patients with lymph node metastasis compared with patients without metastasis. Higher Keap1 expression levels were correlated with the survival of NSCLC patients. Moreover, manipulation of Keap1 expression affected cell migration/invasion abilities. Depletion of Nrf2 relieved the migration promotion imposed by Keap1 suppression. Mechanistic investigations found that S100P was downregulated in both Keap1-overexpressing and Nrf2-knockdown NSCLC cells. Overexpression of Keap1 and knockdown of Nrf2 both suppressed S100P expression in NSCLC cells. Knockdown of S100P inhibited cell migration in highly invasive NSCLC cells and also relieved the migration promotion imposed by Keap1 suppression in weakly invasive NSCLC cells.

CONCLUSIONS

Our findings suggest that Keap1 functions as a suppressor of tumor metastasis by targeting the Nrf2/S100P pathway in NSCLC cells. In addition, overexpression of Keap1 may be a novel NSCLC treatment strategy and/or useful biomarker for predicting NSCLC progression.

Glycolytic inhibitors 2-deoxyglucose and 3-bromopyruvate synergize with photodynamic therapy respectively to inhibit cell migration

Most cancer cells have the specially increased glycolytic phenotype, which makes this pathway become an attractive therapeutic target. Although glycolytic inhibitor 2-deoxyglucose (2-DG) has been demonstrated to potentiate the cytotoxicity of photodynamic therapy (PDT), the impacts on cell migration after the combined treatment has never been reported yet. The present study aimed to analyze the influence of glycolytic inhibitors 2-DG and 3-bromopyruvate (3-BP) combined with Ce6-PDT on cell motility of Triple Negative Breast Cancer MDA-MB-231 cells. As determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltertrazolium-bromide-Tetraz-olium (MTT) assay, more decreased cell viability was observed in 2-DG + PDT and 3-BP + PDT groups when compared with either monotherapy. Under optimal conditions, synergistic potentiation on cell membrane destruction and the decline of cell adhesion and cells migratory ability were observed in both 2-DG + PDT and 3-BP + PDT by electron microscope observation (SEM), wound healing and trans-well assays. Besides, serious microfilament network collapses as well as impairment of matrix metalloproteinases-9 (MMP-9) were notably improved after the combined treatments by immunofluorescent staining. These results suggest that 2-DG and 3-BP can both significantly potentiated Ce6-PDT efficacy of cell migration inhibition.

Analysis of the in vivo and in vitro effects of photodynamic therapy on breast cancer by using a sensitizer, sinoporphyrin sodium

Photodynamic therapy (PDT) is an emerging theranostic modality for various cancers and diseases. Photosensitizers are critical components for PDT. Sinoporphyrin sodium, referred to as DVDMS, is a newly identified photosensitizer that was isolated from Photofrin. Here, we evaluated the effects of DVDMS-mediated PDT (DVDMS-PDT) on tumor cell proliferation and metastasis in the highly metastatic 4T1 cell line and a mouse xenograft model. DVDMS-PDT elicited a potent phototoxic effect in vitro, which was abolished using the reactive oxygen species (ROS) scavenger N-acetylcysteine. In addition, DVDMS-PDT effectively inhibited the migration of 4T1 cells in scratch wound-healing and transwell assays. Using an in vivo mouse model, DVDMS-PDT greatly prolonged the survival time of tumor-bearing mice and inhibited tumor growth and lung metastasis, consistent with in vitro findings. PDT with DVDMS had a greater anti-tumor efficacy than clinically used Photofrin. Moreover, preliminary toxicological results indicate that DVDMS is relatively safe. These results suggest that DVDMS is a promising sensitizer that warrants further development for use in cancer treatment with PDT or other sensitizing agent-based therapies.

The actin cytoskeleton as a sensor and mediator of apoptosis

Apoptosis is an important biological process required for the removal of unwanted or damaged cells. Mounting evidence implicates the actin cytoskeleton as both a sensor and mediator of apoptosis. Studies also suggest that actin binding proteins (ABPs) significantly contribute to apoptosis and that actin dynamics play a key role in regulating apoptosis signaling. Changes in the organization of the actin cytoskeleton has been attributed to the process of malignant transformation and it is hypothesized that remodeling of the actin cytoskeleton may enable tumor cells to evade normal apoptotic signaling. This review aims to illuminate the role of the actin cytoskeleton in apoptosis by systematically analyzing how actin and ABPs regulate different apoptosis pathways and to also highlight the potential for developing novel compounds that target tumor-specific actin filaments.

Anti-cancer effect and the underlying mechanisms of gypenosides on human colorectal cancer SW-480 cells

BACKGROUND

Gypenosides (Gyp), the main components from Gynostemma pentaphyllum Makino, are widely used in traditional Chinese medicine. The present study aimed to investigate the anti-cancer effect and the underlying mechanisms of Gyp on human colorectal cancer cells SW-480.

MATERIALS AND METHODS

The inhibitory effect of Gyp on SW-480 cells was evaluated by MTT assay. Apoptotic cell death was detected by nuclear Hoechst 33342 staining and DNA fragmentation analysis. Apoptosis was analyzed using Annexin V-PE/7-amino-actinomycin D staining. Cell membrane integrity was evaluated with flow cytometry following PI staining. Changes of mitochondrial membrane potential (Δψm) were detected through flow cytometry analysis of rhodamine 123 (Rh123). The role of reactive oxygen species (ROS) in Gyp induced cell death was investigated by intracellular ROS generation and general ROS scavenger. Wound-healing assay was carried out to investigate Gyp-inhibited migration of SW-480 cells in vitro. Additionally, the alterations in F-actin microfilaments were analyzed by FITC-labeled phalloidin toxin staining and the morphological changes were evaluated under scanning electron microscope (SEM).

RESULTS

After the Gyp treatment, the plasma membrane permeability of SW-480 cell was increased, Δψm was decreased significantly, the level of intracellular ROS level was increased, DNA fragmentation and apoptotic morphology were observed. Cells treated with Gyp exert serious microfilament network collapse as well as the significant decrease in the number of microvilli. Gyp induced the changes of cell viability, cell migration, intracellular ROS generation and nuclear morphology were alleviated obviously by NAC.

CONCLUSION

The results in this study implied that ROS play an important role in Gyp induced cell toxicity and apoptosis, and the mitochondria damage may be upstream of ROS generation post Gyp treatment. The findings of the present study provide new evidences for anti-tumor mechanisms by which Gyp induces apoptosis in vitro.

Mechanism of calponin stabilization of cross-linked actin networks

The actin-binding protein calponin has been previously implicated in actin cytoskeletal regulation and is thought to act as an actin stabilizer, but the mechanism of its function is poorly understood. To investigate this underlying physical mechanism, we studied an in vitro model system of cross-linked actin using bulk rheology. Networks with basic calponin exhibited a delayed onset of strain stiffening (10.0% without calponin, 14.9% with calponin) and were able to withstand a higher maximal strain before failing (35% without calponin, 56% with calponin). Using fluorescence microscopy to study the mechanics of single actin filaments, we found that calponin increased the flexibility of actin filaments, evident as a decrease in persistence length from 17.6 μm without to 7.7 μm with calponin. Our data are consistent with current models of affine strain behavior in semiflexible polymer networks, and suggest that calponin stabilization of actin networks can be explained purely by changes in single-filament mechanics. We propose a model in which calponin stabilizes actin networks against shear through a reduction of persistence length of individual filaments.

Structural basis for profilin-mediated actin nucleotide exchange

Actin is a ubiquitous eukaryotic protein that is responsible for cellular scaffolding, motility, and division. The ability of actin to form a helical filament is the driving force behind these cellular activities. Formation of a filament depends on the successful exchange of actin's ADP for ATP. Mammalian profilin is a small actin binding protein that catalyzes the exchange of nucleotide and facilitates the addition of an actin monomer to a growing filament. Here, crystal structures of profilin-actin have been determined to show an actively exchanging ATP. Structural analysis shows how the binding of profilin to the barbed end of actin causes a rotation of the small domain relative to the large domain. This conformational change is propagated to the ATP site and causes a shift in nucleotide loops, which in turn causes a repositioning of Ca(2+) to its canonical position as the cleft closes around ATP. Reversal of the solvent exposure of Trp356 is also involved in cleft closure. In addition, secondary calcium binding sites were identified.

Hyper-activated motility in sperm capacitation is mediated by phospholipase D-dependent actin polymerization

In order to fertilize the oocyte, sperm must undergo a series of biochemical changes in the female reproductive tract, known as capacitation. Once capacitated, spermatozoon can bind to the zona pellucida of the egg and undergo the acrosome reaction (AR), a process that enables its penetration and fertilization of the oocyte. Important processes that characterize sperm capacitation are actin polymerization and the development of hyper-activated motility (HAM). Previously, we showed that Phospholipase D (PLD)-dependent actin polymerization occurs during sperm capacitation, however the role of this process in sperm capacitation is not yet known. In the present study, we showed for the first time the involvement of PLD-dependent actin polymerization in sperm motility during mouse and human capacitation. Sperm incubated under capacitation conditions revealed a time dependent increase in actin polymerization and HAM. Inhibition of Phosphatidic Acid (PA) formation by PLD using butan-1-ol, inhibited actin polymerization and motility, as well as in vitro fertilization (IVF) and the ability of the sperm to undergo the AR. The inhibition of sperm HAM by low concentration of butan-1-ol is completely restored by adding PA, further indicating the involvement of PLD in these processes. Furthermore, exogenous PA enhanced rapid actin polymerization that was followed by a rise in the HAM, as well as an increased in IVF rate. In conclusion, our results demonstrate that PLD-dependent actin polymerization is a critical step needed for the development of HAM during mouse and human sperm capacitation.

Prolongation of the active lifetime of a biomolecular motor for in vitro motility assay by using an inert atmosphere

Over the last few decades, the in vitro motility assay has been performed to probe the biophysical and chemo-mechanical properties as well as the self-organization process of biomolecular motor systems such as actin-myosin and microtubule-kinesin. However, aggression of the reactive oxygen species (ROS) and concomitant termination of the activity of biomolecular motors during investigation remains a drawback of this assay. Despite enzymatic protection that makes use of a combination of glucose, glucose oxidase, and catalase, the active lifetime of biomolecular motors is found to be only a few hours and this short lifetime restricts further study on those systems. We have solved this problem by using a newly developed system of the in vitro motility assay that is conducted in an inert nitrogen gas atmosphere free of ROS. Using microtubule-kinesin as a model system we have shown that our system has prolonged the active lifetime of the biomolecular motor until several days and even a week by protecting it from oxidative damage.

Evolutionary selection of new breast cancer cell-targeting peptides and phages with the cell-targeting peptides fully displayed on the major coat and their effects on actin dynamics during cell internalization

Filamentous phage as a bacteria-specific virus can be conjugated with an anticancer drug and has been proposed to serve as a carrier to deliver drugs to cancer cells for targeted therapy. However, how cell-targeting filamentous phage alone affects cancer cell biology is unclear. Phage libraries provide an inexhaustible reservoir of new ligands against tumor cells and tissues that have potential therapeutic and diagnostic applications in cancer treatment. Some of these identified ligands might stimulate various cell responses. Here we identified new cell internalizing peptides (and the phages with such peptides fused to each of ~3900 copies of their major coat protein) using landscape phage libraries and for the first time investigated the actin dynamics when selected phages are internalized into the SKBR-3 breast cancer cells. Our results show that phages harboring VSSTQDFP and DGSIPWST peptides could selectively internalize into the SKBR-3 breast cancer cells with high affinity, and also show rapid involvement of membrane ruffling and rearrangements of actin cytoskeleton during the phage entry. The actin dynamics was studied by using live cell and fluorescence imaging. The cell-targeting phages were found to enter breast cancer cells through energy dependent mechanism and phage entry interferes with actin dynamics, resulting in reorganization of actin filaments and increased membrane rufflings in SKBR-3 cells. These results suggest that, when phage enters epithelial cells, it triggers transient changes in the host cell actin cytoskeleton. This study also shows that using multivalent phage libraries considerably increases the repertoire of available cell-internalizing ligands with potential applications in targeted drug delivery, imaging, molecular monitoring and profiling of breast cancer cells.

HSPB1, actin filament dynamics, and aging cells

Investigations into the possible roles of human HSPB1 in aging have focused on its role as a molecular chaperone protecting partially folded or unfolded proteins, particularly during oxidative stress. A thorough analysis of potential roles of HSPB1 in aging cells has been hampered by a limited knowledge of its functions in living cells. Most studies have employed cell-free extracts and purified proteins. For example, HSPB1 is known to bind actin in vitro, and this observation led to the hypothesis that HSPB1 regulates actin filament dynamics. In the study summarized herein, the role of HSPB1 in regulating actin filament dynamics was further investigated by using cultured human cells. These results show that HSPB1 and actin form a complex in vivo and that HSPB1 is important for cell motility. A model for HSPB1 as a regulator of actin filament dynamics is presented, and evidence from the literature on cytoskeletal alterations in aging cells is discussed.

Microfilament orientation constrains vesicle flow and spatial distribution in growing pollen tubes

The dynamics of cellular organelles reveals important information about their functioning. The spatio-temporal movement patterns of vesicles in growing pollen tubes are controlled by the actin cytoskeleton. Vesicle flow is crucial for morphogenesis in these cells as it ensures targeted delivery of cell wall polysaccharides. Remarkably, the target region does not contain much filamentous actin. We model the vesicular trafficking in this area using as boundary conditions the expanding cell wall and the actin array forming the apical actin fringe. The shape of the fringe was obtained by imposing a steady state and constant polymerization rate of the actin filaments. Letting vesicle flux into and out of the apical region be determined by the orientation of the actin microfilaments and by exocytosis was sufficient to generate a flux that corresponds in magnitude and orientation to that observed experimentally. This model explains how the cytoplasmic streaming pattern in the apical region of the pollen tube can be generated without the presence of actin microfilaments.

Mechanism on polarity sorting of actin bundles formed with polycations

In this paper we explored factors that determine the polarity of an Actin bundle formed with polycation through electrostatic interaction. We found that the polarity decreases with an increase in the polycation concentration while it hardly depends on the KCl salt concentration. Additionally, the polarity of the Actin bundle increases with an increase in the degree of polymerization of the polycation at a constant polymer concentration. From these results we proposed that the kinetics of nuclei formation determines the polarity of the Actin bundle.

Toxins affecting actin filaments and microtubules

Actin and tubulin are the two major proteins of the cytoskeleton in eukaryotic cells and both display a common property to reversibly assemble into long and flexible polymers, actin filaments and microtubules, respectively. These proteins play important roles in a variety of cellular functions and are also involved in numbers of diseases. An emerging number of marine-derived cytotoxins have been found to bind either actin or tublin, resulting in either inhibition or enhancement of polymerization. Thus, these toxins are valuable molecular probes for solving complex mechanisms of biological processes. This chapter describes actin- and tubulin-targeting marine natural products and their modes of action, with reference to their use as research tools and their clinical applications.

Models for actin polymerization motors

Actin polymerization drives cell membrane protrusions and the propulsion of intracellular pathogens. The molecular mechanisms driving actin polymerization are not yet fully understood. Various mathematical models have been proposed to explain how cells convert chemical energy released upon actin polymerization into a pushing force on a surface. These models have attempted to explain puzzling properties of actin-based motility, including persistent attachment of the network to the membrane during propulsion and the interesting trajectories of propelled particles. These models fall generally into two classes: those requiring filament (+)-ends to fluctuate freely from the membrane to add subunits, and those where filaments elongate with their (+)-ends persistently associated with surface through filament end-tracking proteins ("actoclampin" models). This review compares and contrasts the key predictions of these two classes of models with regard to force-velocity profiles, and evaluates them with respect to experiments with biomimetic particles, and the experimental evidence on the role of end-tracking proteins such as formins and nucleation-promoting factors in actin-based motility.

Linking Ras to myosin function: RasGEF Q, a Dictyostelium exchange factor for RasB, affects myosin II functions

Ras guanine nucleotide exchange factor (GEF) Q, a nucleotide exchange factor from Dictyostelium discoideum, is a 143-kD protein containing RasGEF domains and a DEP domain. We show that RasGEF Q can bind to F-actin, has the potential to form complexes with myosin heavy chain kinase (MHCK) A that contain active RasB, and is the predominant exchange factor for RasB. Overexpression of the RasGEF Q GEF domain activates RasB, causes enhanced recruitment of MHCK A to the cortex, and leads to cytokinesis defects in suspension, phenocopying cells expressing constitutively active RasB, and myosin-null mutants. RasGEF Q⁻ mutants have defects in cell sorting and slug migration during later stages of development, in addition to cell polarity defects. Furthermore, RasGEF Q⁻ mutants have increased levels of unphosphorylated myosin II, resulting in myosin II overassembly. Collectively, our results suggest that starvation signals through RasGEF Q to activate RasB, which then regulates processes requiring myosin II.

Abnormal cytoskeletal protein expression in cultured skin fibroblasts from type 1 diabetes mellitus patients with nephropathy: A proteomic approach

Diabetic nephropathy (DN) develops in about 40% of insulin-dependent type 1 diabetes mellitus (T1DM) patients, and is associated not only with diabetes duration and metabolic control, but also with a genetic predisposition. Constitutive alterations of cytoskeletal proteins may play a role in the development of DN. We investigated the expression of these proteins in cultured skin fibroblasts, obtained from long-term T1DM patients with and without DN but comparable metabolic control, and from matched healthy subjects, by means of 2-DE electrophoresis and MS-MALDI analyses. In T1DM with DN, compared to the other two groups, quantitative analyses revealed an altered expression of 17 spots (p<0.05-p<0.01), corresponding to 12 unique proteins. In T1DM with DN, beta-actin and three isoforms of tubulin beta-2 chain, tropomodulin-3, and LASP-1 were decreased, whereas two tubulin beta-4 chain isoforms, one alpha actinin-4 isoform, membrane-organizing extension spike protein (MOESIN), FLJ00279 (corresponding to a fragment of myosin heavy chain, non-muscle type A), vinculin, a tropomyosin isoform, and the macrophage capping protein were increased. A shift in caldesmon isoforms was also detected. These results demonstrate an association between DN and the constitutive expression of cytoskeleton proteins in cultured skin fibroblasts from T1DM with DN, which may retain pathophysiologycal implications.

Human kallikrein 8 protease confers a favorable clinical outcome in non-small cell lung cancer by suppressing tumor cell invasiveness

The human kallikrein 8 (KLK8) gene, a member of the human tissue kallikrein gene family, encodes a serine protease. The KLK8 protein (hK8) is known to be a favorable prognostic marker in ovarian cancer, but the biological basis of this is not understood. We found that overexpressing the KLK8 gene in highly invasive lung cancer cell lines suppresses their invasiveness. This role in invasiveness was further confirmed by the fact that inhibition of endogenous KLK8 expression with a specific short hairpin RNA reduced cancer cell invasiveness. In situ degradation and cell adhesion assays showed that proteins produced from KLK8 splice variants modify the extracellular microenvironment by cleaving fibronectin. DNA microarray experiments and staining of cells for actin filaments revealed that the degradation of fibronectin by hK8 suppresses integrin signaling and retards cancer cell motility by inhibiting actin polymerization. In addition, studies in a mouse model coupled with the detection of circulating tumor cells by quantitative PCR for the human Alu sequence showed that KLK8 suppresses tumor growth and invasion in vivo. Finally, studies of clinical specimens from patients with non-small cell lung cancer showed that the time to postoperative recurrence was longer for early-stage patients (stages I and II) with high KLK8 expression (mean, 49.9 months) than for patients with low KLK8 expression (mean, 22.9 months). Collectively, these findings show that KLK8 expression confers a favorable clinical outcome in non-small cell lung cancer by suppressing tumor cell invasiveness.

The expression of RAGE and EN-RAGE in leprosy

BACKGROUND

Extracellular newly identified RAGE-binding protein (EN-RAGE) is a ligand of the receptor for advanced glycation endproducts (RAGE) and has been termed S100A12. The ligation of EN-RAGE with RAGE on the endothelium, mononuclear phagocytes and lymphocytes triggers cellular activation with the generation of the key proinflammatory mediators interleukin (IL)-1beta and tumour necrosis factor (TNF)-alpha.

OBJECTIVES

The aim of this study was to investigate the presence of RAGE and EN-RAGE, their spatial localization and their coexpression in leprosy lesions.

METHODS

Immunohistochemistry and confocal laser scanning microscopy were used to evaluate the expression of RAGE and EN-RAGE in leprosy. By enzyme-linked immunosorbent assay, RAGE and EN-RAGE were detected in the serum.

RESULTS

(1) In the multibacillary (MB) and paucibacillary (PB) groups, the level of RAGE production was significantly higher than in patients with atypical mycobacterial infection or sarcoidosis (P < 0.01). In the MB group, the production of RAGE was higher than in the PB group (P < 0.01), and it was higher in patients without the lepra reaction than in patients with the lepra reaction (P < 0.05). (2) In MB, PB and atypical mycobacterial infection, the level of EN-RAGE production was significantly higher than in sarcoidosis (P < 0.01). (3) In the confocal laser scanning microscopic examination, the RAGE and EN-RAGE proteins were detected in lepromatous leprosy. These proteins are spatially colocalized along the cell surface, which is in agreement with their receptor-ligand interaction. (4) A comparable amount of EN-RAGE was detected in the serum of the MB and PB groups. Patients with the reaction showed a higher level of EN-RAGE than patients without the reaction in leprosy.

CONCLUSIONS

Our data suggest that in leprosy, RAGE and EN-RAGE may be involved in the proinflammatory process rather than the antimycobacterial activity, especially during the lepra reaction. The blockade of the interaction of RAGE and EN-RAGE at the early stage of the inflammatory process may minimize the inflammatory response and consequent tissue damage or the sequelae of leprosy.

Sphingosine 1-phosphate regulates cytoskeleton dynamics: implications in its biological response

The bioactive sphingolipid sphingosine 1-phosphate (S1P) elicits robust cytoskeletal rearrangement in a large variety of cell systems, mainly acting through a panel of specific cell surface receptors, named S1P receptors. Recent studies have begun to delineate the molecular mechanisms involved in the complex process responsible for cytoskeletal rearrangement following S1P ligation to its receptors. Notably, changes of cell shape and/or motility induced by S1P via cytoskeletal remodelling are functional to the biological action exerted by S1P which appears to be highly cell-specific. This review focuses on the current knowledge of the regulatory mechanisms of cytoskeleton dynamics elicited by S1P, with special emphasis on the relationship between cytoskeletal remodelling and the biological effects evoked by the sphingolipid in various cell types.

Knockdown of contactin-1 expression suppresses invasion and metastasis of lung adenocarcinoma

Numerous genetic changes are associated with cancer cell metastasis and invasion. In search for key regulators of invasion and metastasis, a panel of lung cancer cell lines with different invasive ability was screened. The gene for contactin-1 was found to play an essential role in tumor invasion and metastasis. Suppression of contactin-1 expression abolished the ability of lung adenocarcinoma cells to invade Matrigel in vitro as well as the polymerization of filamentous-actin and the formation of focal adhesion structures. Furthermore, knockdown of contactin-1 resulted in extensive inhibition of tumor metastasis and in increased survival in an animal model. RhoA but not Cdc42 or Rac1 was found to serve a critical role in contactin-1-mediated invasion and metastasis. Contactin-1-specific RNA interference resulted in loss of metastatic and invasive capacity in both in vitro and in vivo models. This loss was overturned by constitutive expression of the active form of RhoA. Contactin-1 was differentially expressed in tumor tissues, and its expression correlated with tumor stage, lymph node metastasis, and patient survival. Contactin-1 is proposed to function importantly in the invasion and metastasis of lung adenocarcinoma cells via RhoA-mediated mechanisms.

The VEGF-C/Flt-4 axis promotes invasion and metastasis of cancer cells

Flt-4, a VEGF receptor, is activated by its specific ligand, VEGF-C. The resultant signaling pathway promotes angiogenesis and/or lymphangiogenesis. This report provides evidence that the VEGF-C/Flt-4 axis enhances cancer cell mobility and invasiveness and contributes to the promotion of cancer cell metastasis. VEGF-C/Flt-4-mediated invasion and metastasis of cancer cells were found to require upregulation of the neural cell adhesion molecule contactin-1 through activation of the Src-p38 MAPK-C/EBP-dependent pathway. Examination of tumor tissues from various types of cancers revealed high levels of Flt-4 and VEGF-C expression that correlated closely with clinical metastasis and patient survival. The VEGF-C/Flt-4 axis, through upregulation of contactin-1, may regulate the invasive capacity in different types of cancer cells.

Effect of drugs affecting microtubular assembly on microtubules, phospholipid synthesis and physiological indices (signalling, growth, motility and phagocytosis) inTetrahymena pyriformis

Structural changes of microtubules, incorporation of radioactively labelled components into phospholipids, cell motility, growth and phagocytosis were studied under the effect of four drugs affecting microtubular assembly: colchicine, nocodazole, vinblastine and taxol. Although the first three agents influence microtubules in the direction of depolymerization and the fourth stabilizes them, their effects on the structure of microtubules cannot be explained by this. Using confocal microscopy after an acetylated anti-tubulin label, in nocodazole- and colchicine-treated cells, the basal body cages disappear and longitudinal microtubules (LM) became thinner without changing transversal microtubules (TM). After taxol treatment LM also became thinner, however TM disappeared. Under the effect of vinblastine TM became thinner, without influencing LM. These drugs influence the incorporation of components ([(3)H]-serine, [(3)H]-palmitic acid and (32)P) into phospholipids, however their effect is equivocal and cannot be consequently coupled with the effect on the microtubules. Nocodazole, vinblastine and taxol significantly reduced the cell's motility, however colchicine did so to a lesser degree. Vinblastine and nocodazole totally inhibited, and taxol significantly decreased cell growth, while colchicine in a lower concentration increased the multiplication of cells. Phagocytosis was not significantly influenced after 1 min, but after 5 min all the agents studied (except colchicine) significantly inhibited phagocytosis. After 15 and 30 min each molecule caused highly significant inhibition. The experiments demonstrate that drugs affecting microtubular assembly dynamics influence differently the diverse (longitudinal, transversal etc.) microtubular systems of Tetrahymena and also differently influence microtubule-dependent physiological processes. The latter are more dependent on microtubular dynamics than are changes in phospholipid signalling.

Polarity and motility of large polymer-actin complexes

The polarity of polymer-actin complexes obtained by mixing F-actin with synthetic polymers carrying positive charges such as poly(L-lysine), x,y-ionene bromide polymers, and poly(N-[3-(dimethylamino)propyl]acrylamide) (PDMAPAA-Q) have been investigated. Actin complexes formed with poly(L-lysine) and PDMAPAA-Q, which carry charges on their side chains, show a higher polarity than those formed with x,y-ionene bromide polymers, which have charges on their chain backbones. All these polymer-actin complex gels show motility on the surfaces coated with myosin by coupling to adenosine 5'-triphosphate hydrolysis. A linear correlation between the polarity of polymer-actin complex gels and the motility is observed.

Actin polymerization in the equatorial and postacrosomal regions of guinea pig spermatozoa during the acrosome reaction is regulated by G proteins

The acrosome reaction (AR) is an exocytotic process of spermatozoa, and an absolute requirement for fertilization. During AR, actin polymerization is necessary in the equatorial and postacrosomal regions of guinea pig sperm for spermatozoa incorporation deep into the egg cytoplasm, but not for plasma membrane (PM) fusion nor the early steps of egg activation. To identify the mechanisms involved in this sperm actin polymerization, we searched for the protein members, known to be involved in a highly conserved model, that may apply to any cellular process in which de novo actin polymerization occurs from G protein activation. WASP, Arp 2/3, profilins I and II, and Cdc42, RhoA and RhoB GTPases were localized by indirect immunofluorescence (IIF) in guinea pig spermatozoa and their presence corroborated by Western blotting. WASP and profilin II were translocated to the postacrosomal region (Arp2/3 already were there) in long-term capacitated and acrosome-reacted spermatozoa, at the same time as actin polymerization occurred. These events were inhibited by GDP-beta-S and promoted by lysophosphatidic acid (LPA) and GTP-gamma-S, a small GTPase inhibitor and two activators, respectively. By immunoprecipitation, Cdc42-WASp association was identified in capacitated but not in noncapacitated gametes. Polymerized actin in the postacrosomal region is apparently anchored both to the postacrosomal perinuclear theca region and the overlying PM. Results suggest that GTPases are involved in sperm actin polymerization, in the postacrosomal region and the mechanism for polymerization might fit a previously proposed model (Mullins, 2000: Curr Opin Cell Biol 12:91-96).