Putting a new twist on actin: ADF/cofilins modulate actin dynamics

Regulation and signaling of the LIM domain kinases

The LIM domain kinases (LIMKs) are important actin cytoskeleton regulators. These proteins, LIMK1 and LIMK2, are nodes downstream of Rho GTPases and are the key enzymes that phosphorylate cofilin/actin depolymerization factors to regulate filament severing. They therefore perform an essential role in cascades that control actin depolymerization. Signaling of the LIMKs is carefully regulated by numerous inter- and intra-molecular mechanisms. In this review, we discuss recent findings that improve the understanding of LIM domain kinase regulation mechanisms. We also provide an up-to-date review of the role of the LIM domain kinases, their architectural features, how activity is impacted by other proteins, and the implications of these findings for human health and disease.

Cofilin-Mediated Filament Softening and Crosslinking Counterbalance to Enhance Actin Network Flexibility

Filamentous-actin (F-actin) crosslinking within the cell cytoskeleton mediates the transmission of mechanical forces, enabling changes in cell shape, as occurs during cell division and cell migration. Crosslinking by actin binding proteins (ABPs) generally increases the connectivity of the F-actin network, but also increases network rigidity. As a result, there is a narrow range in the concentration of crosslinker protein at which F-actin networks are both connected and labile. Another ABP, cofilin, severs F-actin filaments at high pH through increasing their bending flexibility and concentrating mechanical stress, inducing fragmentation. By contrast, at lower pH, cofilin increases filament flexibility yet does not sever. Instead, it forms disulfide bonds, which crosslink F-actin into bundles, and bundles into networks. Here, we combine light microscopy and rheology to determine the impact of two potentially opposing effects on the mechanics of F-actin networks-increased flexibility at the filament level, and increased connectivity at the network level. Indeed, by linear rheology, we find that these mechanisms are counterbalanced, such that cofilactin network moduli are only weakly dependent on cofilin concentration over a broad range, in contrast to the dramatic stiffening that occurs with F-actin crosslinking protein. Further, by nonlinear rheology, the network stiffens at a higher stress than crosslinking protein, indicative of a broader range in which the material remains flexible. These results may enable F-actin networks to increase connectivity without heavy penalties to rigidity, and thus provide a new route to modulating active polymer mechanics unseen using traditional F-actin accessory proteins.

TAZ is involved in breast cancer cell migration via regulating actin dynamics

Background

Cancer metastasis is dependent on cell migration. Several mechanisms, including epithelial-to-mesenchymal transition (EMT) and actin fiber formation, could be involved in cancer cell migration. As a downstream effector of the Hippo signaling pathway, transcriptional coactivator with PDZ-binding motif (TAZ) is recognized as a key mediator of the metastatic ability of breast cancer cells. We aimed to examine whether TAZ affects the migration of breast cancer cells through the regulation of EMT or actin cytoskeleton.

Methods

MCF-7 and MDA-MB-231 cells were treated with siRNA to attenuate TAZ abundance. Transwell migration assay and scratch wound healing assay were performed to study the effects of TAZ knockdown on cancer cell migration. Fluorescence microscopy was conducted to examine the vinculin and phalloidin. Semiquantitative immunoblotting and quantitative real-time PCR were performed to study the expression of small GTPases and kinases. Changes in the expression of genes associated with cell migration were examined through next-generation sequencing.

Results

TAZ-siRNA treatment reduced TAZ abundance in MCF-7 and MDA-MB-231 breast cancer cells, which was associated with a significant decrease in cell migration. TAZ knockdown increased the expression of fibronectin, but it did not exhibit the typical pattern of EMT progression. TGF-β treatment in MDA-MB-231 cells resulted in a reduction in TAZ and an increase in fibronectin levels. However, it paradoxically promoted cell migration, suggesting that EMT is unlikely to be involved in the decreased migration of breast cancer cells in response to TAZ suppression. RhoA, a small Rho GTPase protein, was significantly reduced in response to TAZ knockdown. This caused a decrease in the expression of the Rho-dependent downstream pathway, i.e., LIM kinase 1 (LIMK1), phosphorylated LIMK1/2, and phosphorylated cofilin, leading to actin depolymerization. Furthermore, myosin light chain kinase (MLCK) and phosphorylated MLC2 were significantly decreased in MDA-MB-231 cells with TAZ knockdown, inhibiting the assembly of stress fibers and focal adhesions.

Conclusion

TAZ knockdown inhibits the migration of breast cancer cells by regulating the intracellular actin cytoskeletal organization. This is achieved, in part, by reducing the abundance of RhoA and Rho-dependent downstream kinase proteins, which results in actin depolymerization and the disassembly of stress fibers and focal adhesions.

Differential sensitivity of ADF isovariants to a pH gradient promotes pollen tube growth

The actin cytoskeleton is one of the targets of the pH gradient in tip-growing cells, but how cytosolic pH regulates the actin cytoskeleton remains largely unknown. We here demonstrate that Arabidopsis ADF7 and ADF10 function optimally at different pH levels when disassembling actin filaments. This differential pH sensitivity allows ADF7 and ADF10 to respond to the cytosolic pH gradient to regulate actin dynamics in pollen tubes. ADF7 is an unusual actin-depolymerizing factor with a low optimum pH in in vitro actin depolymerization assays. ADF7 plays a dominant role in promoting actin turnover at the pollen tube apex. ADF10 has a typically high optimum pH in in vitro assays and plays a dominant role in regulating the turnover and organization of subapical actin filaments. Thus, functional specification and cooperation of ADF isovariants with different pH sensitivities enable the coordination of the actin cytoskeleton with the cytosolic pH gradient to support pollen tube growth.

A Haspin-ARHGAP11A axis regulates epithelial morphogenesis through Rho-ROCK dependent modulation of LIMK1-Cofilin

Throughout mitosis, a plethora of processes must be efficiently concerted to ensure cell proliferation and tissue functionality. The mitotic spindle does not only mediate chromosome segregation, but also defines the axis of cellular division, thus determining tissue morphology. Functional spindle orientation relies on precise actin dynamics, shaped in mitosis by the LIMK1-Cofilin axis. The kinase Haspin acts as a guardian of faithful chromosome segregation that ensures amphitelic chromosome attachment and prevents unscheduled cohesin cleavage. Here, we report an unprecedented role for Haspin in the determination of spindle orientation in mitosis. We show that, during mitosis, Haspin regulates Rho-ROCK activity through ARHGAP11A, a poorly characterized GAP, and that ROCK is in turn responsible for the mitotic activation of LIMK1 and stabilization of the actin cytoskeleton, thus supporting a functional spindle orientation. By exploiting 3D cell cultures, we show that this pathway is pivotal for the establishment of a morphologically functional tissue.

Neuroligin 2 governs synaptic morphology and function through RACK1-cofilin signaling in Drosophila

Neuroligins are transmembrane cell adhesion proteins well-known for their genetic links to autism spectrum disorders. Neuroligins can function by regulating the actin cytoskeleton, however the factors and mechanisms involved are still largely unknown. Here, using the Drosophila neuromuscular junction as a model, we reveal that F-Actin assembly at the Drosophila NMJ is controlled through Cofilin signaling mediated by an interaction between DNlg2 and RACK1, factors not previously known to work together. The deletion of DNlg2 displays disrupted RACK1-Cofilin signaling pathway with diminished actin cytoskeleton proteo-stasis at the terminal of the NMJ, aberrant NMJ structure, reduced synaptic transmission, and abnormal locomotion at the third-instar larval stage. Overexpression of wildtype and activated Cofilin in muscles are sufficient to rescue the morphological and physiological defects in dnlg2 mutants, while inactivated Cofilin is not. Since the DNlg2 paralog DNlg1 is known to regulate F-actin assembly mainly via a specific interaction with WAVE complex, our present work suggests that the orchestration of F-actin by Neuroligins is a diverse and complex process critical for neural connectivity.

Pelargonium sidoides extract mediates nephrotoxicity through mitochondrial malfunction and cytoskeleton destabilization

We investigated the cytotoxic effect of Pelargonium sidoides extract on Madin-Darby canine kidney (MDCK) cells. P. sidoides extract decreased the cell viability in a dose dependent manner (> 0.2%). The extract of P. sidoides decreased the mitochondrial action potential, increased the number of reactive oxygen species (ROS) inside the cell, and caused nicotinamide adenine dinucleotide hydride (NADH) to be released, all of which are signs of mitochondrial dysfunction. The results of unbiased mRNA sequencing showed that 0.3% P. sidoides extract upregulates the apoptosis-related gene (BBC3). This finding was supported by immunoblot analysis of apoptosis signal pathways, which included Bcl-2, Bax, cytochrome C (CytC), cleaved caspase 3 (CC3), cleaved caspase 7 (CC7), cleaved caspase 9 (CC9) and cleaved PARP (CP). It is interesting to note that the elevated levels of Bax, CytC, CC3, CC7, and CC9, as well as CP, were suppressed by N-acetyl-L-cysteine (NAC) pretreatment, which points to ROS-mediated apoptosis. The small GTPases, RhoA, and Rac1/cdc42-GTP-bound active form were all lowered when P. sidoides extract was used. Also, RhoA-related cytoskeleton signals (ROCK, p-LIMK1/2, p-cofilin) and Rac1/cdc42-related signals (N-WASP, WAVE-2) were inhibited by P. sidoides extract. NAC or RhoA/Rac1/cdc42 activator pretreatment reduced P. sidoides extract-induced actin destabilization. In this work, P. sidoides extract promotes apoptosis by causing mitochondrial dysfunction and cytoskeleton disassembly.

Actin polymerization and depolymerization in developing vertebrates

Development is a complex process that occurs throughout the life cycle. F-actin, a major component of the cytoskeleton, is essential for the morphogenesis of tissues and organs during development. F-actin is formed by the polymerization of G-actin, and the dynamic balance of polymerization and depolymerization ensures proper cellular function. Disruption of this balance results in various abnormalities and defects or even embryonic lethality. Here, we reviewed recent findings on the structure of G-actin and F-actin and the polymerization of G-actin to F-actin. We also focused on the functions of actin isoforms and the underlying mechanisms of actin polymerization/depolymerization in cellular and organic morphogenesis during development. This information will extend our understanding of the role of actin polymerization in the physiologic or pathologic processes during development and may open new avenues for developing therapeutics for embryonic developmental abnormalities or tissue regeneration.

Actin cytoskeleton in the control of vesicle transport, cytoplasmic organization, and pollen tube tip growth

Pollen tubes extend rapidly via tip growth. This process depends on a dynamic actin cytoskeleton, which has been implicated in controlling organelle movements, cytoplasmic streaming, vesicle trafficking, and cytoplasm organization in pollen tubes. In this update review, we describe the progress in understanding the organization and regulation of the actin cytoskeleton and the function of the actin cytoskeleton in controlling vesicle traffic and cytoplasmic organization in pollen tubes. We also discuss the interplay between ion gradients and the actin cytoskeleton that regulates the spatial arrangement and dynamics of actin filaments and the organization of the cytoplasm in pollen tubes. Finally, we describe several signaling components that regulate actin dynamics in pollen tubes.

Vascular mechanotransduction

This review aims to survey the current state of mechanotransduction in vascular smooth muscle cells (VSMCs) and endothelial cells (ECs), including their sensing of mechanical stimuli and transduction of mechanical signals that result in the acute functional modulation and longer-term transcriptomic and epigenetic regulation of blood vessels. The mechanosensors discussed include ion channels, plasma membrane-associated structures and receptors, and junction proteins. The mechanosignaling pathways presented include the cytoskeleton, integrins, extracellular matrix, and intracellular signaling molecules. These are followed by discussions on mechanical regulation of transcriptome and epigenetics, relevance of mechanotransduction to health and disease, and interactions between VSMCs and ECs. Throughout this review, we offer suggestions for specific topics that require further understanding. In the closing section on conclusions and perspectives, we summarize what is known and point out the need to treat the vasculature as a system, including not only VSMCs and ECs but also the extracellular matrix and other types of cells such as resident macrophages and pericytes, so that we can fully understand the physiology and pathophysiology of the blood vessel as a whole, thus enhancing the comprehension, diagnosis, treatment, and prevention of vascular diseases.

Activation of actin-depolymerizing factor by CDPK16-mediated phosphorylation promotes actin turnover in Arabidopsis pollen tubes

As the stimulus-responsive mediator of actin dynamics, actin-depolymerizing factor (ADF)/cofilin is subject to tight regulation. It is well known that kinase-mediated phosphorylation inactivates ADF/cofilin. Here, however, we found that the activity of Arabidopsis ADF7 is enhanced by CDPK16-mediated phosphorylation. We found that CDPK16 interacts with ADF7 both in vitro and in vivo, and it enhances ADF7-mediated actin depolymerization and severing in vitro in a calcium-dependent manner. Accordingly, the rate of actin turnover is reduced in cdpk16 pollen and the amount of actin filaments increases significantly at the tip of cdpk16 pollen tubes. CDPK16 phosphorylates ADF7 at Serine128 both in vitro and in vivo, and the phospho-mimetic mutant ADF7S128D has enhanced actin-depolymerizing activity compared to ADF7. Strikingly, we found that failure in the phosphorylation of ADF7 at Ser128 impairs its function in promoting actin turnover in vivo, which suggests that this phospho-regulation mechanism is biologically significant. Thus, we reveal that CDPK16-mediated phosphorylation up-regulates ADF7 to promote actin turnover in pollen.

Actin-microtubule cytoskeletal interplay mediated by MRTF-A/SRF signaling promotes dilated cardiomyopathy caused by LMNA mutations

Mutations in the lamin A/C gene (LMNA) cause dilated cardiomyopathy associated with increased activity of ERK1/2 in the heart. We recently showed that ERK1/2 phosphorylates cofilin-1 on threonine 25 (phospho(T25)-cofilin-1) that in turn disassembles the actin cytoskeleton. Here, we show that in muscle cells carrying a cardiomyopathy-causing LMNA mutation, phospho(T25)-cofilin-1 binds to myocardin-related transcription factor A (MRTF-A) in the cytoplasm, thus preventing the stimulation of serum response factor (SRF) in the nucleus. Inhibiting the MRTF-A/SRF axis leads to decreased α-tubulin acetylation by reducing the expression of ATAT1 gene encoding α-tubulin acetyltransferase 1. Hence, tubulin acetylation is decreased in cardiomyocytes derived from male patients with LMNA mutations and in heart and isolated cardiomyocytes from Lmna^{p.H222P/H222P} male mice. In Atat1 knockout mice, deficient for acetylated α-tubulin, we observe left ventricular dilation and mislocalization of Connexin 43 (Cx43) in heart. Increasing α-tubulin acetylation levels in Lmna^{p.H222P/H222P} mice with tubastatin A treatment restores the proper localization of Cx43 and improves cardiac function. In summary, we show for the first time an actin-microtubule cytoskeletal interplay mediated by cofilin-1 and MRTF-A/SRF, promoting the dilated cardiomyopathy caused by LMNA mutations. Our findings suggest that modulating α-tubulin acetylation levels is a feasible strategy for improving cardiac function.

PTEN Dual Lipid- and Protein-Phosphatase Function in Tumor Progression

Simple Summary

Phosphatase and tensin homolog deleted on chromosome ten (PTEN) is a multifunctional tumor suppressor with protein- and lipid-phosphatase activities. The inactivation of PTEN is commonly found in all human cancers and is correlated with tumor progression. PTEN-lipid-phosphatase activity has been well documented to dephosphorylate phosphatidylinositol-3, 4, 5-phosphate (PIP3), which hinders cell growth and survival by dampening the PI3K and AKT signaling activity. PTEN-protein-phosphatase activity is less well studied and understood. Recent studies have reported that PTEN-protein-phosphatase activity dephosphorylates the different proteins and acts in various cell functions. We here review the PTEN mutations and protein-phosphatase substrates in tumor progression. We aim to address the gap in our understanding as to how PTEN protein phosphatase contributes to its tumor-suppression functions.

Abstract

PTEN is the second most highly mutated tumor suppressor in cancer, following only p53. The PTEN protein functions as a phosphatase with lipid- and protein-phosphatase activity. PTEN-lipid-phosphatase activity dephosphorylates PIP3 to form PIP2, and it then antagonizes PI3K and blocks the activation of AKT, while its protein-phosphatase activity dephosphorylates different protein substrates and plays various roles in tumorigenesis. Here, we review the PTEN mutations and protein-phosphatase substrates in tumorigenesis and metastasis. Our purpose is to clarify how PTEN protein phosphatase contributes to its tumor-suppressive functions through PI3K-independent activities.

Paladin, overexpressed in colon cancer, is required for actin polymerisation and liver metastasis dissemination

Introduction

Colorectal cancer remains a public health issue and most colon cancer patients succumb to the development of metastases. Using a specific protocol of pressure-assisted interstitial fluid extrusion to recover soluble biomarkers, we identified paladin as a potential colon cancer liver metastases biomarker.

Methods

Using shRNA gene knockdown, we explored the biological function of paladin in colon cancer cells and investigated the phospho-proteome within colon cancer cells. We successively applied in vitro migration assays, in vivo metastasis models and co-immunoprecipitation experiments.

Results

We discovered that paladin is required for colon cancer cell migration and metastasis, and that paladin depletion altered the phospho-proteome within colon cancer cells. Data are available via ProteomeXchange with identifier PXD030803. Thanks to immunoprecipitation experiments, we demonstrated that paladin, was interacting with SSH1, a phosphatase involved in colon cancer metastasis. Finally, we showed that paladin depletion in cancer cells results in a less dynamic actin cytoskeleton.

Conclusions

Paladin is an undervalued protein in oncology. This study highlights for the first time that, paladin is participating in actin cytoskeleton remodelling and is required for efficient cancer cell migration.

Actin-Associated Proteins and Small Molecules Targeting the Actin Cytoskeleton

Actin-associated proteins (AAPs) act on monomeric globular actin (G-actin) and polymerized filamentous actin (F-actin) to regulate their dynamics and architectures which ultimately control cell movement, shape change, division; organelle localization and trafficking. Actin-binding proteins (ABPs) are a subset of AAPs. Since actin was discovered as a myosin-activating protein (hence named actin) in 1942, the protein has also been found to be expressed in non-muscle cells, and numerous AAPs continue to be discovered. This review article lists all of the AAPs discovered so far while also allowing readers to sort the list based on the names, sizes, functions, related human diseases, and the dates of discovery. The list also contains links to the UniProt and Protein Atlas databases for accessing further, related details such as protein structures, associated proteins, subcellular localization, the expression levels in cells and tissues, mutations, and pathology. Because the actin cytoskeleton is involved in many pathological processes such as tumorigenesis, invasion, and developmental diseases, small molecules that target actin and AAPs which hold potential to treat these diseases are also listed.

Genetic and molecular biology of gastric cancer among Iranian patients: an update

Background

There is a declining trend of gastric cancer (GC) incidence in the world during recent years that is related to the development of novel diagnostic methods. However, there is still a high ratio of GC mortality among the Iranian population that can be associated with late diagnosis. Despite various reports about the novel diagnostic markers, there is not any general and standard diagnostic panel marker for Iranian GC patients. Therefore, it is required to determine an efficient and general panel of molecular markers for early detection.

Main body of the abstract

In the present review, we summarized all of the reported markers until now among Iranian GC patients to pave the way for the determination of a population-based diagnostic panel of markers. In this regard, we categorized these markers in different groups based on their involved processes to know which molecular process is more frequent during the GC progression among Iranians.

Conclusion

We observed that the non-coding RNAs are the main factors involved in GC tumorigenesis in this population.

Stepwise synaptic plasticity events drive the early phase of memory consolidation

[Figure: see text].

Bidirectional role of dopamine in learning and memory-active forgetting

Dopaminergic neurons projecting from the Substantia Nigra to the Striatum play a critical role in motor functions while dopaminergic neurons originating in the Ventral Tegmental Area (VTA) and projecting to the Nucleus Accumbens, Hippocampus and other cortical structures regulate rewarding learning. While VTA mainly consists of dopaminergic neurons, excitatory (glutamate) and inhibitory (GABA) VTA-neurons have also been described: these neurons may also modulate and contribute to shape the final dopaminergic response, which is critical for memory formation. However, given the large amount of information that is handled daily by our brain, it is essential that irrelevant information be deleted. Recently, apart from the well-established role of dopamine (DA) in learning, it has been shown that DA plays a critical role in the intrinsic active forgetting mechanisms that control storage information, contributing to the deletion of a consolidated memory. These new insights may be instrumental to identify therapies for those disorders that involve memory alterations.

LINC01133 Inhibits Invasion and Promotes Proliferation in an Endometriosis Epithelial Cell Line

Endometriosis is a common gynecological disorder characterized by ectopic growth of endometrium outside the uterus and is associated with chronic pain and infertility. We investigated the role of the long intergenic noncoding RNA 01133 (LINC01133) in endometriosis, an lncRNA that has been implicated in several types of cancer. We found that LINC01133 is upregulated in ectopic endometriotic lesions. As expression appeared higher in the epithelial endometrial layer, we performed a siRNA knockdown of LINC01133 in an endometriosis epithelial cell line. Phenotypic assays indicated that LINC01133 may promote proliferation and suppress cellular migration, and affect the cytoskeleton and morphology of the cells. Gene ontology analysis of differentially expressed genes indicated that cell proliferation and migration pathways were affected in line with the observed phenotype. We validated upregulation of p21 and downregulation of Cyclin A at the protein level, which together with the quantification of the DNA content using fluorescence-activated cell sorting (FACS) analysis indicated that the observed effects on cellular proliferation may be due to changes in cell cycle. Further, we found testis-specific protein kinase 1 (TESK1) kinase upregulation corresponding with phosphorylation and inactivation of actin severing protein Cofilin, which could explain changes in the cytoskeleton and cellular migration. These results indicate that endometriosis is associated with LINC01133 upregulation, which may affect pathogenesis via the cellular proliferation and migration pathways.

HMT Exerts an Anticancer Effect by Targeting PAK-1

Heamatang (HMT) is a classic medicinal formula used in traditional Chinese and Korean medicine; it contains seven distinct components, mainly of herbal origin. HMT is used as an antiaging remedy, treating urinary disorders and increasing energy and vitality. However, the therapeutic applications of this formula have not been evaluated with evidence-based science. Therefore, we assessed HMT through various in vitro methods, including cell viability assay, fluorescence-activated cell sorting assay (FACS), Western blotting, migration assay, three-dimensional (3D) cell culture, siRNA-mediated PAK-1 knockdown, and crystal violet assays. HMT decreased PAK-1 expression in PC-3 cells and inhibited cell viability, growth, and motility. The inhibition of cell motility by HMT was correlated with PAK-1-mediated inhibition of Lim domain kinase (LIMK) and cofilin. HMT induced G1 arrest and apoptosis through the transcriptional regulation of cell cycle regulatory proteins and apoptosis-related proteins (increase in c-cas3 and inhibition of PARP and BCL-2). Moreover, HMT suppressed PAK-1 expression, leading to the inhibition of AKT activities. Finally, we showed that decursin was the active ingredient involved in the inhibitory effect of HMT on PAK-1. Our findings demonstrated that HMT exerts its anticancer influence through the inhibition of PAK-1. The HMT formula could be applied in various fields, including functional health food and pharmaceutical development.

Pyr1-Mediated Pharmacological Inhibition of LIM Kinase Restores Synaptic Plasticity and Normal Behavior in a Mouse Model of Schizophrenia

The search for effective treatments for neuropsychiatric disorders is ongoing, with progress being made as brain structure and neuronal function become clearer. The central roles played by microtubules (MT) and actin in synaptic transmission and plasticity suggest that the cytoskeleton and its modulators could be relevant targets for the development of new molecules to treat psychiatric diseases. In this context, LIM Kinase - which regulates both the actin and MT cytoskeleton especially in dendritic spines, the post-synaptic compartment of the synapse - might be a good target. In this study, we analyzed the consequences of blocking LIMK1 pharmacologically using Pyr1. We investigated synaptic plasticity defects and behavioral disorders in MAP6 KO mice, an animal model useful for the study of psychiatric disorders, particularly schizophrenia. Our results show that Pyr1 can modulate MT dynamics in neurons. In MAP6 KO mice, chronic LIMK inhibition by long-term treatment with Pyr1 can restore normal dendritic spine density and also improves long-term potentiation, both of which are altered in these mice. Pyr1 treatment improved synaptic plasticity, and also reduced social withdrawal and depressive/anxiety-like behavior in MAP6 KO mice. Overall, the results of this study validate the hypothesis that modulation of LIMK activity could represent a new therapeutic strategy for neuropsychiatric diseases.

Nujiangexanthone A Inhibits Hepatocellular Carcinoma Metastasis via Down Regulation of Cofilin 1

Hepatocellular carcinoma (HCC) is one of the malignant tumors with poor prognosis. High expression level of cofilin 1 (CFL1) has been found in many types of cancers. However, the role of CFL1 in HCC hasn’t been known clearly. Here, we found that CFL1 was up regulated in human HCC and significantly associated with both overall survival and disease-free survival in HCC patients. Nujiangexanthone A (NJXA), the caged xanthones, isolated from gamboge plants decreased the expression of CFL1, which also inhibited the migration, invasion and metastasis of HCC cells in vitro and in vivo. Down regulation of CFL1 inhibited aggressiveness of HCC cells, which mimicked the effect of NJXA. Mechanism study indicated that, knockdown of CFL1 or treatment with NJXA increased the level of F-actin and disturbed the balance between F-actin and G-actin. In conclusion, our findings reveal the role of CFL1 in HCC metastasis through the CFL1/F-actin axis, and suggest that CFL1 may be a potential prognostic marker and a new therapeutic target. NJXA can effectively inhibit the metastasis of HCC cells by down regulating the expression of CFL1, which indicates the potential of NJXA for preventing metastasis in HCC.

Novel facets of glioma invasion

Malignant gliomas including Glioblastoma (GBM) are characterized by extensive diffuse tumor cell infiltration throughout the brain, which represents a major challenge in clinical disease management. While surgical resection is beneficial for patient outcome, it is well recognized that tumor cells at the invasive front or beyond stay behind and constitute a major source of tumor recurrence. Invasive glioma cells also represent a difficult therapeutic target since they are localized within normal functional brain areas with an intact blood brain barrier (BBB), thereby excluding most systemic drug treatments. Cell movement is mediated via the actin cytoskeleton where corresponding membrane protrusions play essential roles. This review provides an overview of the various paths of glioma cell invasion and underlines the specific aspects of the brain microenvironment. We highlight recent insight into tumor microtubes, neuro-glioma synapses and tumor metabolism which can regulate collective invasion processes. We also focus on the deregulation of actin cytoskeleton-related components in the context of glioma invasion, a deregulation that may be controlled by genomic alterations in tumor cells as well as by various external factors, including extracellular matrix (ECM) components and non-malignant stromal cells. Finally we critically assess the challenges and opportunities for therapeutically targeting glioma cell invasion.

Cavin1 Deficiency Causes Disorder of Hepatic Glycogen Metabolism and Neonatal Death by Impacting Fenestrations in Liver Sinusoidal Endothelial Cells

It has been reported that Cavin1 deficiency causes lipodystrophy in both humans and mice by affecting lipid metabolism. The ablation of Cavin1 in rodents also causes a significant deviation from Mendelian ratio at weaning in a background-dependent manner, suggesting the presence of undiscovered functions of Cavin1. In the current study, the results show that Cavin1 deficiency causes neonatal death in C57BL/6J mice by dampening the storage and mobilization of glycogen in the liver, which leads to lethal neonatal hypoglycemia. Further investigation by electron microscopy reveals that Cavin1 deficiency impairs the fenestration in liver sinusoidal endothelial cells (LSECs) and impacts the permeability of endothelial barrier in the liver. Mechanistically, Cavin1 deficiency inhibits the RhoA-Rho-associated protein kinase 2-LIM domain kinase-Cofilin signaling pathway and suppresses the dynamics of the cytoskeleton, and eventually causes the reduction of fenestrae in LSECs. In addition, the defect of fenestration in LSECs caused by Cavin1 deficiency can be rescued by treatment with the F-actin depolymerization reagent latrunculin A. In summary, the current study reveals a novel function of Cavin1 on fenestrae formation in LSECs and liver glycogen metabolism, which provide an explanation for the neonatal death of Cavin1 null mice and a potential mechanism for metabolic disorders in patients with Cavin1 mutation.

Mechanisms of Axon Elongation Following CNS Injury: What Is Happening at the Axon Tip?

After an injury to the central nervous system (CNS), functional recovery is limited by the inability of severed axons to regenerate and form functional connections with appropriate target neurons beyond the injury. Despite tremendous advances in our understanding of the mechanisms of axon growth, and of the inhibitory factors in the injured CNS that prevent it, disappointingly little progress has been made in restoring function to human patients with CNS injuries, such as spinal cord injury (SCI), through regenerative therapies. Clearly, the large number of overlapping neuron-intrinsic and -extrinsic growth-inhibitory factors attenuates the benefit of neutralizing any one target. More daunting is the distances human axons would have to regenerate to reach some threshold number of target neurons, e.g., those that occupy one complete spinal segment, compared to the distances required in most experimental models, such as mice and rats. However, the difficulties inherent in studying mechanisms of axon regeneration in the mature CNS in vivo have caused researchers to rely heavily on extrapolation from studies of axon regeneration in peripheral nerve, or of growth cone-mediated axon development in vitro and in vivo. Unfortunately, evidence from several animal models, including the transected lamprey spinal cord, has suggested important differences between regeneration of mature CNS axons and growth of axons in peripheral nerve, or during embryonic development. Specifically, long-distance regeneration of severed axons may not involve the actin-myosin molecular motors that guide embryonic growth cones in developing axons. Rather, non-growth cone-mediated axon elongation may be required to propel injured axons in the mature CNS. If so, it may be necessary to use other experimental models to promote regeneration that is sufficient to contact a critical number of target neurons distal to a CNS lesion. This review examines the cytoskeletal underpinnings of axon growth, focusing on the elongating axon tip, to gain insights into how CNS axons respond to injury, and how this might affect the development of regenerative therapies for SCI and other CNS injuries.

Cytoskeleton and Nucleotide Signaling in Glioma C6 Cells

This chapter describes signaling pathways, stimulated by the P2Y₂ nucleotide receptor (P2Y₂R), that regulate cellular processes dependent on actin cytoskeleton dynamics in glioma C6 cells. P2Y₂R coupled with G-proteins, in response to ATP or UTP, regulates the level of iphosphatidylinositol-4,5-bisphosphate (PIP₂) which modulates a variety of actin binding proteins and is involved in calcium response and activates Rac1 and RhoA proteins. The RhoA/ROCK signaling pathway plays an important role in contractile force generation needed for the assembly of stress fibers, focal adhesions and for tail retraction during cell migration. Blocking of this pathway by a specific Rho-kinase inhibitor induces changes in F-actin organization and cell shape and decreases the level of phosphorylated myosin II and cofilin. In glioma C6 cells these changes are reversed after UTP stimulation of P2Y₂R. Signaling pathways responsible for this compensation are calcium signaling which regulates MLC kinase activation via calmodulin, and the Rac1/PAK/LIMK cascade. Stimulation of the Rac1 mediated pathway via G_o proteins needs additional interaction between α_vβ₅ integrins and P2Y₂Rs. Calcium free medium, or growing of the cells in suspension, prevents Gα_o activation by P2Y₂ receptors. Rac1 activation is necessary for cofilin phosphorylation as well as integrin activation needed for focal complexes formation and stabilization of lamellipodium. Inhibition of positive Rac1 regulation prevents glioma C6 cells from recovery of control cell like morphology.

Overexpression of CFL1 in gastric cancer and the effects of its silencing by siRNA with a nanoparticle delivery system in the gastric cancer cell line

Gastric adenocarcinoma, like other cancers, is a multifactorial genetic disease, and metastasis of cancer cells is one of the main features of this illness. The expression levels of the CFL1 gene have been modulated in this pathway. Using small interfering RNA (siRNA) in the treatment of gastric cancer is considered a hopeful gene therapeutic approach. The present study reported the level of CFL1 genes between tumor and margin and healthy tissue of gastric cancer. Also, the features of a cationic nanoparticle with a polymer coating containing polyacrylic acid and polyethyleneimine that were used in the delivery of CFL1 siRNA, were shown. Then the cytotoxicity, cellular uptake, and gene silencing efficiency of this nanoparticle were evaluated with CFL1siRNA.

METHOD

In this study, the CFL1 gene expression was measured in 40 gastric adenocarcinoma, marginal and 15 healthy biopsy samples by a real-time polymerase chain reaction. Physicochemical characteristics, apoptosis, and inhibition of migration of the delivery of CFL1 siRNA by nanoparticle and lipofectamine were investigated in gastric cancer cells.

RESULT

The CFL1 expression was remarkably increased in gastric cancer tissues in comparison with the marginal samples and normal tissues (p < .05) and the biomarker index for CFL1 was obtained as 0.94, then this gene can be probably used as a biomarker for gastric cancer. After treatment of the AGS cell line by CFL1 siRNA, the CFL1 expression level of mRNA and migration in AGS cells were remarkably suppressed after transfection. Furthermore, the amount of apoptosis increased (p < .05).

CONCLUSION

Our results demonstrated that CFL1 downregulation in AGS cells can interdict cell migration. Finally, our outcomes propose that CFL1 can function as an oncogenic gene in gastric cancer and would be considered as a potential purpose of gene therapy for gastric cancer treatment.

The role of cofilin in age-related neuroinflammation

Aging brain becomes susceptible to neurodegenerative diseases due to the shifting of microglia and astrocyte phenotypes to an active “pro-inflammatory” state, causing chronic low-grade neuroinflammation. Despite the fact that the role of neuroinflammation during aging has been extensively studied in recent years, the underlying causes remain unclear. The identification of relevant proteins and understanding their potential roles in neuroinflammation can help explain their potential of becoming biomarkers in the aging brain and as drug targets for prevention and treatment. This will eventually reduce the chances of developing neurodegenerative diseases and promote healthier lives in the elderly. In this review, we have summarized the morphological and cellular changes in the aging brain, the effects of age-related neuroinflammation, and the potential role of cofilin-1 during neuroinflammation. We also discuss other factors contributing to brain aging and neuroinflammation.

Effects of Dexamethasone on Remodeling of the Hippocampal Synaptic Filamentous Actin Cytoskeleton in a Model of Pilocarpine-induced Status Epilepticus

The filamentous actin (F-actin) cytoskeleton is progressively damaged after status epilepticus (SE), which is related to delayed neuronal death, aberrant recurrent circuits and epileptogenesis. Glucocorticoids regulate dendritic spine remodeling by acting on glucocorticoid receptors and the dynamics of the F-actin cytoskeleton. Our previous study showed that administration of dexamethasone (DEX) in the latent period of the pilocarpine epileptic model reduces damage to the hippocampal filamentous actin cytoskeleton and the loss of hippocampal neurons and aids in maintaining the synaptic structures, but it is not sufficient to stop epileptogenesis. In this work, we focused on the role of glucocorticoids in regulating the hippocampal F-actin cytoskeleton during SE. We examined the abundance of synaptic F-actin, analyzed the hippocampal F-actin/G-actin (F/G) ratio and pCofilin, and evaluated the number of hippocampal neurons and pre/postsynaptic markers in pilocarpine-induced status epilepticus mice with or without administration of dexamethasone (DEX). We found that the latency of Stage 3 seizures increased, the mortality decreased, the damage to the synaptic F-actin cytoskeleton in the hippocampal subfields was significantly attenuated, and a greater number of postsynaptic structures were retained in the hippocampal subfields after treatment with DEX. These results indicate that treatment with dexamethasone stabilizes the synaptic F-actin cytoskeleton and reduces the damage to the brain due to SE. This approach is expected to be beneficial in alleviating delayed neuron damage and the process of epileptogenesis.

Forced Unfolding of Proteins Directs Biochemical Cascades

Many proteins in cells and in the extracellular matrix assemble into force-bearing networks, and some proteins clearly transduce mechanical stimuli into biochemical signals. Although structural mechanisms remain poorly understood, the designs of such proteins enable mechanical forces to either inhibit or facilitate interactions of protein domains with other proteins, including small molecules and enzymes, including proteases and kinases. Here, we review some of the structural proteins and processes that exhibit distinct modes of force-dependent signal conversion.

Coronin 1A depletion restores the nuclear stability and viability of Aip1/Wdr1-deficient neutrophils

Bowes et al. show that in zebrafish embryos deficient in the cofilin cofactor AIP1/Wdr1, neutrophils display F-actin as cytoplasmic aggregates, spatially uncoupled from active myosin, then undergo a progressive unwinding of their nucleus followed by eruptive cell death. This adverse phenotype is fully rescued by depletion of another cofilin cofactor, coronin 1A.

Actin dynamics is central for cells, and especially for the fast-moving leukocytes. The severing of actin filaments is mainly achieved by cofilin, assisted by Aip1/Wdr1 and coronins. We found that in Wdr1-deficient zebrafish embryos, neutrophils display F-actin cytoplasmic aggregates and a complete spatial uncoupling of phospho-myosin from F-actin. They then undergo an unprecedented gradual disorganization of their nucleus followed by eruptive cell death. Their cofilin is mostly unphosphorylated and associated with F-actin, thus likely outcompeting myosin for F-actin binding. Myosin inhibition reproduces in WT embryos the nuclear instability and eruptive death of neutrophils seen in Wdr1-deficient embryos. Strikingly, depletion of the main coronin of leukocytes, coronin 1A, fully restores the cortical location of F-actin, nuclear integrity, viability, and mobility of Wdr1-deficient neutrophils in vivo. Our study points to an essential role of actomyosin contractility in maintaining the integrity of the nucleus of neutrophils and a new twist in the interplay of cofilin, Wdr1, and coronin in regulating F-actin dynamics.

Remarkable structural transformations of actin bundles are driven by their initial polarity, motor activity, crosslinking, and filament treadmilling

Bundled actin structures play a key role in maintaining cellular shape, in aiding force transmission to and from extracellular substrates, and in affecting cellular motility. Recent studies have also brought to light new details on stress generation, force transmission and contractility of actin bundles. In this work, we are primarily interested in the question of what determines the stability of actin bundles and what network geometries do unstable bundles eventually transition to. To address this problem, we used the MEDYAN mechano-chemical force field, modeling several micron-long actin bundles in 3D, while accounting for a comprehensive set of chemical, mechanical and transport processes. We developed a hierarchical clustering algorithm for classification of the different long time scale morphologies in our study. Our main finding is that initially unipolar bundles are significantly more stable compared with an apolar initial configuration. Filaments within the latter bundles slide easily with respect to each other due to myosin activity, producing a loose network that can be subsequently severely distorted. At high myosin concentrations, a morphological transition to aster-like geometries was observed. We also investigated how actin treadmilling rates influence bundle dynamics, and found that enhanced treadmilling leads to network fragmentation and disintegration, while this process is opposed by myosin and crosslinking activities. Interestingly, treadmilling bundles with an initial apolar geometry eventually evolve to a whole gamut of network morphologies based on relative positions of filament ends, such as sarcomere-like organization. We found that apolar bundles show a remarkable sensitivity to environmental conditions, which may be important in enabling rapid cytoskeletal structural reorganization and adaptation in response to intracellular and extracellular cues.

Self-incompatibility in Papaver pollen: programmed cell death in an acidic environment

Self-incompatibility (SI) is a genetically controlled mechanism that prevents self-fertilization and thus encourages outbreeding and genetic diversity. During pollination, most SI systems utilize cell-cell recognition to reject incompatible pollen. Mechanistically, one of the best-studied SI systems is that of Papaver rhoeas (poppy), which involves the interaction between the two S-determinants, a stigma-expressed secreted protein (PrsS) and a pollen-expressed plasma membrane-localized protein (PrpS). This interaction is the critical step in determining acceptance of compatible pollen or rejection of incompatible pollen. Cognate PrpS-PrsS interaction triggers a signalling network causing rapid growth arrest and eventually programmed cell death (PCD) in incompatible pollen. In this review, we provide an overview of recent advances in our understanding of the major components involved in the SI-induced PCD (SI-PCD). In particular, we focus on the importance of SI-induced intracellular acidification and consequences for protein function, and the regulation of soluble inorganic pyrophosphatase (Pr-p26.1) activity by post-translational modification. We also discuss attempts to identify protease(s) involved in the SI-PCD process. Finally, we outline future opportunities made possible by the functional transfer of the P. rhoeas SI system to Arabidopsis.

Mechanobiology of mice cervix: expression profile of mechano-related molecules during pregnancy

There is a known reciprocation between the chronic exertion of force on tissue and both increased tissue density (e.g., bone) and hypertrophy (e.g., heart). This can also be seen in cervical tissue where the excessive gravitational forces associated with multiple fetal pregnancies promote preterm births. While there is a well-known regulation of cervical remodeling (CR) by sex steroid hormones and growth factors, the role of mechanical force is less appreciated. Using proteome-wide technology, we previously provided evidence for the presence of and alteration in mechano-related signaling molecules in the mouse cervix during pregnancy. Here, we profile the expression of select cytoskeletal factors (filamin-A, gelsolin, vimentin, actinin-1, caveolin-1, transgelin, keratin-8, profilin-1) and their associated signaling molecules [focal adhesion kinase (FAK) and the Rho GTPases CDC42, RHOA, and RHOB] in cervices of pregnant mice by real-time PCR and confocal immunofluorescence microscopy. Messenger RNA and protein levels increased for each of these 12 factors, except for 3 (keratin-8, profilin-1, RHOA) that decreased during the course of pregnancy and this corresponded with an increase in gravitational force exerted by the fetus on the cervix. We therefore conclude that size or weight of the growing fetus likely plays a key role in CR through mechanotransduction processes.

The mysteries of remote memory

Long-lasting memories form the basis of our identity as individuals and lie central in shaping future behaviours that guide survival. Surprisingly, however, our current knowledge of how such memories are stored in the brain and retrieved, as well as the dynamics of the circuits involved, remains scarce despite seminal technical and experimental breakthroughs in recent years. Traditionally, it has been proposed that, over time, information initially learnt in the hippocampus is stored in distributed cortical networks. This process-the standard theory of memory consolidation-would stabilize the newly encoded information into a lasting memory, become independent of the hippocampus, and remain essentially unmodifiable throughout the lifetime of the individual. In recent years, several pieces of evidence have started to challenge this view and indicate that long-lasting memories might already ab ovo be encoded, and subsequently stored in distributed cortical networks, akin to the multiple trace theory of memory consolidation. In this review, we summarize these recent findings and attempt to identify the biologically plausible mechanisms based on which a contextual memory becomes remote by integrating different levels of analysis: from neural circuits to cell ensembles across synaptic remodelling and epigenetic modifications. From these studies, remote memory formation and maintenance appear to occur through a multi-trace, dynamic and integrative cellular process ranging from the synapse to the nucleus, and represent an exciting field of research primed to change quickly as new experimental evidence emerges.This article is part of a discussion meeting issue 'Of mice and mental health: facilitating dialogue between basic and clinical neuroscientists'.

Actin Bundles in The Pollen Tube

The angiosperm pollen tube delivers two sperm cells into the embryo sac through a unique growth strategy, named tip growth, to accomplish fertilization. A great deal of experiments have demonstrated that actin bundles play a pivotal role in pollen tube tip growth. There are two distinct actin bundle populations in pollen tubes: the long, rather thick actin bundles in the shank and the short, highly dynamic bundles near the apex. With the development of imaging techniques over the last decade, great breakthroughs have been made in understanding the function of actin bundles in pollen tubes, especially short subapical actin bundles. Here, we tried to draw an overall picture of the architecture, functions and underlying regulation mechanism of actin bundles in plant pollen tubes.

Study of cofilin 1 gene expression in colorectal cancer

Background

Colorectal cancer (CRC) is one of the most prevalent malignancies worldwide. Cofilin is a key regulatory protein in the dynamics of actin filaments. Previous studies have shown cofilin 1's major role in cell migration process and its role in tumor cell migration and invasion. Therefore, cofilin 1 may have the potential as a novel diagnostic tumor marker in various cancers. In this study, differential expression of CFL1 in CRC tissues in comparison with adjacent non-tumor tissues was investigated and the diagnostic value of this protein in CRC was evaluated.

Methods

Synthesized cDNA from extracted RNAs of 30 patients were subjected to qRT-PCR to quantify relative expression of cofilin 1. The relationship between cofilin 1 expression and clinicopathological features of patients were studied too.

Results

The study showed significant upregulation of cofilin 1 in CRC tissue samples compared to adjacent non-tumor tissue samples (P<0.05). The receiver operating characteristic curve analysis showed higher area under the curve (0.85). There was no significant correlation between cofilin 1 expression levels and clinicopathological features of patients.

Conclusions

According to the obtained results, cofilin 1 can serve as a candidate for clinically useful diagnostic biomarker or therapeutic target for CRC.

Cofilin-1 phosphorylation catalyzed by ERK1/2 alters cardiac actin dynamics in dilated cardiomyopathy caused by lamin A/C gene mutation

Hyper-activation of extracellular signal-regulated kinase (ERK) 1/2 contributes to heart dysfunction in cardiomyopathy caused by mutations in the lamin A/C gene (LMNA cardiomyopathy). The mechanism of how this affects cardiac function is unknown. We show that active phosphorylated ERK1/2 directly binds to and catalyzes the phosphorylation of the actin depolymerizing factor cofilin-1 on Thr25. Cofilin-1 becomes active and disassembles actin filaments in a large array of cellular and animal models of LMNA cardiomyopathy. In vivo expression of cofilin-1, phosphorylated on Thr25 by endogenous ERK1/2 signaling, leads to alterations in left ventricular function and cardiac actin. These results demonstrate a novel role for cofilin-1 on actin dynamics in cardiac muscle and provide a rationale on how increased ERK1/2 signaling leads to LMNA cardiomyopathy.

Overexpression of SSH1 in gastric adenocarcinoma and its correlation with clinicopathological features

Background

Gastric adenocarcinoma is known to be the fourth most common cancer type and the second cause of cancer-related deaths. Movement and invasion of cancer cells is one of the major characteristics of the cancer phenotype that various types of network regulate this. Expression levels of slingshot diphosphatase 1 (SSH1) gene has been modulated in this pathway. SSH1 acts as a dephosphorylation and activator of cofilin that this regulating and activating by SSH1 can play a major role in the mobility and migration of the cell. The aim of this study was to compare the expression level of SSH1 genes between tumor and corresponding adjacent non tumor gastric tissues and healthy tissue of gastric adenocarcinoma.

Methods

In this study, mRNA of 40 gastric adenocarcinoma and corresponding adjacent non tumor gastric tissues and 15 healthy biopsy samples was extracted, then after cDNA synthesis, real-time polymerase chain reaction was performed to measure gene expression.

Results

According to REST analysis, the relative expression of SSH1 was significantly increased in gastric cancer tissues compared to the corresponding adjacent non tumor gastric tissue samples and normal tissue. Nevertheless, the result revealed no substantial correlation between the expression levels of SSH1 with clinical features. The biomarker index for SSH1 was obtained as 0.89.

Conclusions

The results obtained from investigating SSH1 expression are indicative of significant changes in the expression of this gene in gastric adenocarcinoma. This gene can also be used as a biomarker for gastric cancer.

Solution structure and dynamics of glia maturation factor from Caenorhabditis elegans

BACKGROUND

The GMF class of the ADF-H domain family proteins regulate actin dynamics by binding to the Arp2/3 complex and F-actin through their Site-1 and Site-2, respectively. CeGMF of C. elegans is analogous to GMFγ of human and mouse and is 138 amino acids in length.

METHODS

We have characterized the solution structure and dynamics of CeGMF by solution NMR spectroscopy and its thermal stability by DSC.

RESULTS

The solution structure of CeGMF shows canonical ADF-H fold with two additional β-strands in the β4-β5 loop region. The Site-1 of CeGMF is well formed and residues of all three regions of Site-1 show dynamic flexibility. However, the β4-β5 loop of Site-2 is less inclined towards the C-terminal, as the latter is truncated by four residues in comparison to GMF isoforms of human and mouse. Regions of Site-2 show motions on ns-ps timescale, but dynamic flexibility of β4-β5 loop is low in comparison to corresponding F-loop region of ADF/cofilin UNC-60B. A general difference in packing of α3 and α1 between GMF and ADF/cofilins was noticed. Additionally, thermal stability of CeGMF was significantly higher than its ADF/cofilin homologs.

CONCLUSION

We have presented the first solution structure of GMF from C. elegans, which highlights the structural differences between the Site-2 of CeGMF and mammalian GMF isoforms. Further, we have seen the differences in structure, dynamics, and thermal stability of GMF and ADF/cofilin.

GENERAL SIGNIFICANCE

This study provides a useful insight to structural and dynamics factors that define the specificity of GMF towards Arp2/3 complex.

Utilizing proteomics to understand and define hypertension: where are we and where do we go?

INTRODUCTION

Hypertension is a complex and multifactorial cardiovascular disorder. With different mechanisms contributing to a different extent to an individual's blood pressure, the discovery of novel pathogenetic principles of hypertension is challenging. However, there is an urgent and unmet clinical need to improve prevention, detection, and therapy of hypertension in order to reduce the global burden associated with hypertension-related cardiovascular diseases. Areas covered: Proteomic techniques have been applied in reductionist experimental models including angiotensin II infusion models in rodents and the spontaneously hypertensive rat in order to unravel mechanisms involved in blood pressure control and end organ damage. In humans proteomic studies mainly focus on prediction and detection of organ damage, particularly of heart failure and renal disease. While there are only few proteomic studies specifically addressing human primary hypertension, there are more data available in hypertensive disorders in pregnancy, such as preeclampsia. We will review these studies and discuss implications of proteomics on precision medicine approaches. Expert commentary: Despite the potential of proteomic studies in hypertension there has been moderate progress in this area of research. Standardized large-scale studies are required in order to make best use of the potential that proteomics offers in hypertension and other cardiovascular diseases.

Structure, dynamics, and biochemical characterization of ADF/cofilin Twinstar from Drosophilamelanogaster

BACKGROUND

Twinstar is an ADF/cofilin family protein, which is expressed by the tsr gene in Drosophila melanogaster. Twinstar is one of the main regulators of actin cytoskeleton remodelling and is essential for vital cellular processes like cytokinesis and endocytosis.

METHODS

We have characterized the structure and dynamics of Twinstar by solution NMR spectroscopy, the interaction of Twinstar with rabbit muscle actin by ITC, and biochemical activities of Twinstar through different biochemical assays using fluorescence spectroscopy and ultra-centrifugation.

RESULTS

The solution structure of Twinstar shows characteristic ADF-H fold with well-formed G/F-site and F-site for interaction with actin. The structure possesses an extended F-loop, which is rigid at the base, but flexible towards its apical region. Twinstar shares similar dynamics for the G/F-site with C. elegans homologs, UNC-60A and UNC-60B. However, the dynamics of its F-loop are different from its C. elegans homologs. Twinstar shows strong affinity for ADP-G-Actin and ATP-G-Actin with K_ds of ~7.6 nM and ~0.4 μM, respectively. It shows mild F-actin depolymerizing activity and stable interaction with F-actin with a K_d of ~5.0 μM. It inhibits the rate of the nucleotide exchange in a dose dependent manner.

CONCLUSION

On the basis of structure, dynamics, and biochemical activity, Twinstar can be taken to execute its biochemical role by facilitating directional growth and maintenance of length of actin filaments.

GENERAL SIGNIFICANCE

This study characterizes the structure, backbone dynamics, and biochemical activities of Twinstar of Drosophila, which provides an insight into the regulation of actin dynamics in the member of phylum insecta.

Actin polymerization contributes to enhanced pulmonary vasoconstrictor reactivity after chronic hypoxia

Chronic hypoxia (CH) augments basal and endothelin-1 (ET-1)-induced pulmonary vasoconstrictor reactivity through reactive oxygen species (ROS) generation and RhoA/Rho kinase (ROCK)-dependent myofilament Ca²⁺ sensitization. Because ROCK promotes actin polymerization and the actin cytoskeleton regulates smooth muscle tension, we hypothesized that actin polymerization is required for enhanced basal and ET-1-dependent vasoconstriction after CH. To test this hypothesis, both end points were monitored in pressurized, endothelium-disrupted pulmonary arteries (fourth-fifth order) from control and CH (4 wk at 0.5 atm) rats. The actin polymerization inhibitors cytochalasin and latrunculin attenuated both basal and ET-1-induced vasoconstriction only in CH vessels. To test whether CH directly alters the arterial actin profile, we measured filamentous actin (F-actin)-to-globular actin (G-actin) ratios by fluorescent labeling of F-actin and G-actin in fixed pulmonary arteries and actin sedimentation assays using homogenized pulmonary artery lysates. We observed no difference in actin polymerization between groups under baseline conditions, but ET-1 enhanced actin polymerization in pulmonary arteries from CH rats. This response was blunted by the ROS scavenger tiron, the ROCK inhibitor fasudil, and the mDia (RhoA effector) inhibitor small-molecule inhibitor of formin homology domain 2. Immunoblot analysis revealed an effect of CH to increase both phosphorylated (inactive) and total levels of the actin disassembly factor cofilin but not phosphorylated cofilin-to-total cofilin ratios. We conclude that actin polymerization contributes to increased basal pulmonary arterial constriction and ET-1-induced vasoconstrictor reactivity after CH in a ROS- and ROCK-dependent manner. Our results further suggest that enhanced ET-1-mediated actin polymerization after CH is dependent on mDia but independent of changes in the phosphorylated cofilin-to-total cofilin ratio. NEW & NOTEWORTHY This research is the first to demonstrate a role for actin polymerization in chronic hypoxia-induced basal pulmonary arterial constriction and enhanced agonist-induced vasoconstrictor activity. These results suggest that a reactive oxygen species-Rho kinase-actin polymerization signaling pathway mediates this response and may provide a mechanistic basis for the vasoconstrictor component of pulmonary hypertension.

Cofilin signaling in hemin-induced microglial activation and inflammation

Intracerebral hemorrhage (ICH) is the most severe form of stroke and is further exacerbated by the secondary injury involving inflammatory response due to the activation of microglia. This secondary injury is partly due to the toxic effects of hemin, an endogenous breakdown product of hemoglobin. Cofilin, an actin depolymerizing factor, controls actin dynamics and has been previously shown to be involved in mediating neuronal cell death in ischemic conditions and during bacterial lipopolysaccharide induced microglial activation. There are limited studies regarding the deleterious effects of extremely high concentrations of hemin released during ICH and its effects on microglia and subsequent cofilin response. Therefore, investigations were conducted to study the effects of hemin on microglial activation induced inflammation and the critical role of cofilin in mediating the response. We observed that hemin treated microglia had a concentration dependent increase in cofilin expression and NO production. There were increased levels of iNOS, TNF-α, HO1, Nrf2, Wfs-1, XBP-1 and spliced XBP-1 observed in response to hemin treatment and the signaling was found to be partly mediated by cofilin. Acute hemin treatment did not evoke Ca2+ signaling and long-term treatment of hemin also resulted in the failure of microglial response to acetylcholine-evoked Ca2+ signaling. Knockdown of cofilin by siRNA also reduced acetylcholine-evoked Ca2+ signaling. These studies demonstrate that cofilin signaling is important in hemin-induced inflammation, oxidative stress, ER stress, microglial migration, and the ability to evoke Ca2+ signaling. Therefore, cofilin inhibition could be a potential therapy in brain injuries triggered by hemin toxicity in conditions like ICH.

The transcription factor HOXB7 regulates ERK kinase activity and thereby stimulates the motility and invasiveness of pancreatic cancer cells

HOX genes encode transcription factors that function as sequence-specific transcription factors that are involved in cellular proliferation, differentiation, and death. The aim of this study was to investigate the role of a HOX family protein, HOXB7, in the motility and invasiveness of pancreatic cancer cells. We previously identified a HOXB7 transcript that is one of a number of transcripts that are preferentially translated in membrane protrusions in pancreatic cancer cells. Immunocytochemistry showed that HOXB7 was localized to the cell protrusions of migrating pancreatic cancer cells. Knockdown of HOXB7 by transfection with HOXB7-specific siRNA decreased these protrusions and inhibited the motility and invasiveness of the cells. Transfection of a HOXB7-rescue construct into the HOXB7-knockdown cells restored peripheral actin structures in cell protrusions and abrogated the HOXB7 knockdown-induced decrease in cell protrusions. It is generally accepted that the Rho family of GTPases regulate the organization of actin filaments and contribute to the formation of cell protrusions. The levels of the active Rho GTPases were not influenced by HOXB7 in the cells; however, HOXB7 knockdown decreased the level of phosphorylated ERK1/2. This inactivation of ERK1/2 decreased cell protrusions, thereby inhibiting the invasiveness of pancreatic cancer cells. Further investigation showed that HOXB7/ERK1/2 signaling selectively stimulated JNK and HSP27 phosphorylation and thereby increased the motility and invasiveness of pancreatic cancer cells. These results suggested that HOXB7 stimulates ERK1/2 phosphorylation and provided evidence that HOXB7, besides its role in transcriptional regulation, also promotes cell motility and invasiveness.

Redox regulation of the actin cytoskeleton and its role in the vascular system

The actin cytoskeleton is critical for form and function of vascular cells, serving mechanical, organizational and signaling roles. Because many cytoskeletal proteins are sensitive to reactive oxygen species, redox regulation has emerged as a pivotal modulator of the actin cytoskeleton and its associated proteins. Here, we summarize work implicating oxidants in altering actin cytoskeletal proteins and focus on how these alterations affect cell migration, proliferation and contraction of vascular cells. Finally, we discuss the role of oxidative modification of the actin cytoskeleton in vivo and highlight its importance for vascular diseases.

Enhanced Depolymerization of Actin Filaments by ADF/Cofilin and Monomer Funneling by Capping Protein Cooperate to Accelerate Barbed-End Growth

A living cell’s ability to assemble actin filaments in intracellular motile processes is directly dependent on the availability of polymerizable actin monomers, which feed polarized filament growth [1, 2]. Continued generation of the monomer pool by filament disassembly is therefore crucial. Disassemblers like actin depolymerizing factor (ADF)/cofilin and filament cappers like capping protein (CP) are essential agonists of motility [3, 4, 5, 6, 7, 8], but the exact molecular mechanisms by which they accelerate actin polymerization at the leading edge and filament turnover has been debated for over two decades [9, 10, 11, 12]. Whereas filament fragmentation by ADF/cofilin has long been demonstrated by total internal reflection fluorescence (TIRF) [13, 14], filament depolymerization was only inferred from bulk solution assays [15]. Using microfluidics-assisted TIRF microscopy, we provide the first direct visual evidence of ADF’s simultaneous severing and rapid depolymerization of individual filaments. Using a conceptually novel assay to directly visualize ADF’s effect on a population of pre-assembled filaments, we demonstrate how ADF’s enhanced pointed-end depolymerization causes an increase in polymerizable actin monomers, thus promoting faster barbed-end growth. We further reveal that ADF-enhanced depolymerization synergizes with CP’s long-predicted “monomer funneling” [16] and leads to skyrocketing of filament growth rates, close to estimated lamellipodial rates. The “funneling model” hypothesized, on thermodynamic grounds, that at high enough extent of capping, the few non-capped filaments transiently grow much faster [15], an effect proposed to be very important for motility. We provide the first direct microscopic evidence of monomer funneling at the scale of individual filaments. These results significantly enhance our understanding of the turnover of cellular actin networks.

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ADF enhances barbed- and pointed-end depolymerization of actin filaments

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Capping protein funnels monomers from all pointed ends to the few non-capped barbed ends

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ADF and capping protein synergy leads to skyrocketing of filament elongation rates

Diversity of actin architecture in human osteoclasts: network of curved and branched actin supporting cell shape and intercellular micrometer-level tubes

Osteoclasts are multinucleated bone-resorbing cells with a dynamic actin cytoskeleton. Osteoclasts are derived from circulating mononuclear precursors. Confocal and stimulated emission depletion (STED) super-resolution microscopy was used to investigate peripheral blood-derived human osteoclasts cultured on glass surfaces. STED and confocal microscopy demonstrated that the actin was curved and branched, for instance, in the vicinity of membrane ruffles. The overall architecture of the curved actin network extended from the podosomes to the top of the cell. The other novel finding was that a micrometer-level tube containing actin bridged the osteoclasts well above the level of the culture glass. The actin filaments of the tubes originated from the network of curved actin often surrounding a group of nuclei. Furthermore, nuclei were occasionally located inside the tubes. Our findings demonstrated the accumulation of c-Src, cortactin, cofilin, and actin around nuclei suggesting their role in nuclear processes such as the locomotion of nuclei. ARP2/3 labeling was abundant at the substratum level of osteoclasts and in the branched actin network, where it localized to the branching points. We speculate that the actin-containing tubes of osteoclasts may provide a means of transportation of nuclei, e.g., during the fusion of osteoclasts. These novel findings can pave the way for future studies aiming at the elucidation of the differentiation of multinucleated osteoclasts.

Promoting Glucose Transporter-4 Vesicle Trafficking along Cytoskeletal Tracks: PAK-Ing Them Out

Glucose is the principal cellular energy source in humans and maintenance of glucose homeostasis is critical for survival. Glucose uptake into peripheral skeletal muscle and adipose tissues requires the trafficking of vesicles containing glucose transporter-4 (GLUT4) from the intracellular storage compartments to the cell surface. Trafficking of GLUT4 storage vesicles is initiated via the canonical insulin signaling cascade in skeletal muscle and fat cells, as well as via exercise-induced contraction in muscle cells. Recent studies have elucidated steps in the signaling cascades that involve remodeling of the cytoskeleton, a process that underpins the mechanical movement of GLUT4 vesicles. This review is focused upon an alternate phosphoinositide-3 kinase-dependent pathway involving Ras-related C3 botulinum toxin substrate 1 signaling through the p21-activated kinase p21-activated kinase 1 and showcases related signaling events that co-regulate both the depolymerization and re-polymerization of filamentous actin. These new insights provide an enriched understanding into the process of glucose transport and yield potential new targets for interventions aimed to improve insulin sensitivity and remediate insulin resistance, pre-diabetes, and the progression to type 2 diabetes.