Torsional stress generated by ADF/cofilin on cross-linked actin filaments boosts their severing.

Proteins of the actin depolymerizing factor (ADF)/cofilin family are the central regulators of actin filament disassembly. A key function of ADF/cofilin is to sever actin filaments. However, how it does so in a physiological context, where filaments are interconnected and under mechanical stress, remains unclear. Here, we monitor and quantify the action of ADF/cofilin in different mechanical situations by using single-molecule, single-filament, and filament network techniques, coupled to microfluidics. We find that local curvature favors severing, while tension surprisingly has no effect on cofilin binding and weakly enhances severing. Remarkably, we observe that filament segments that are held between two anchoring points, thereby constraining their twist, experience a mechanical torque upon cofilin binding. We find that this ADF/cofilin-induced torque does not hinder ADF/cofilin binding, but dramatically enhances severing. A simple model, which faithfully recapitulates our experimental observations, indicates that the ADF/cofilin-induced torque increases the severing rate constant 100-fold. A consequence of this mechanism, which we verify experimentally, is that cross-linked filament networks are severed by cofilin far more efficiently than nonconnected filaments. We propose that this mechanochemical mechanism is critical to boost ADF/cofilin's ability to sever highly connected filament networks in cells.

Cofilin-1-induced actin reorganization in stored platelets.

BACKGROUND: During platelet storage, there are extensive changes in cytoskeleton and phosphatidylserine exposure. The intrinsic mitochondrial pathway of apoptosis, activated in stored platelets, is a major mediator these changes. Cofilin-1 is an effector of actin reorganization. We examined the effect of cofilin-1 deficiency on cytoskeleton and phosphatidylserine exposure during storage and following activation of apoptosis. METHODS AND RESULTS: We assessed actin filaments by Alexa-647-phalloidin and phosphatidylserine exposure by fluorescein isothiocyanate-lactadherin by fluorescence microscopy. In fresh platelets, actin filaments are distributed in the subcortical region, and they do not express phosphatidylserine in the outer surface. In stored platelets, there is retraction of actin filaments from the subcortical region with increased phosphatidylserine expression. These changes are seen in 20% of platelets of 6 days old and increases further with storage. Treatment with ABT-737, which activates the mitochondrial apoptosis, induces similar cytoskeletal changes in actin filaments with increased phosphatidylserine. Cofilin-1 is activated in stored platelets as well as in ABT-737 treated platelets by dephosphorylation. In cofilin-1 deficient murine platelets actin filaments are abnormal and ABT-737 induces less phosphatidylserine. Despite these changes in vitro, platelet survival of cofilin-1 deficient platelets in mice was not significantly different from their wild-type controls. CONCLUSION: These results show that cofilin-1 plays a role in apoptosis-induced actin rearrangement and phosphatidylserine exposure during storage. Despite the defects in platelet cytoskeleton and phosphatidylserine exposure in cofilin-1-deficient platelets, the in vivo life span of platelets is similar to littermate controls, indicating multiple redundant pathways for the clearance of platelets in vivo.

Actin(g) on mitochondria - a role for cofilin1 in neuronal cell death pathways.

Actin dynamics, the coordinated assembly and disassembly of actin filaments (F-actin), are essential for fundamental cellular processes, including cell shaping and motility, cell division or organelle transport. Recent studies highlighted a novel role for actin dynamics in the regulation of mitochondrial morphology and function, for example, through mitochondrial recruitment of dynamin-related protein 1 (Drp1), a key factor in the mitochondrial fission machinery. Mitochondria are dynamic organelles, and permanent fission and fusion is essential to maintain their function in energy metabolism, calcium homeostasis and regulation of reactive oxygen species (ROS). Here, we summarize recent insights into the emerging role of cofilin1, a key regulator of actin dynamics, for mitochondrial shape and function under physiological conditions and during cellular stress, respectively. This is of peculiar importance in neurons, which are particularly prone to changes in actin regulation and mitochondrial integrity and function. In neurons, cofilin1 may contribute to degenerative processes through formation of cofilin-actin rods, and through enhanced mitochondrial fission, mitochondrial membrane permeabilization, and the release of cytochrome c. Overall, mitochondrial impairment induced by dysfunction of actin-regulating proteins such as cofilin1 emerge as important mechanisms of neuronal death with relevance to acute brain injury and neurodegenerative diseases, such as Parkinson's or Alzheimer's disease.

Chronophin coordinates cell leading edge dynamics by controlling active cofilin levels.

Cofilin, a critical player of actin dynamics, is spatially and temporally regulated to control the direction and force of membrane extension required for cell locomotion. In carcinoma cells, although the signaling pathways regulating cofilin activity to control cell direction have been established, the molecular machinery required to generate the force of the protrusion remains unclear. We show that the cofilin phosphatase chronophin (CIN) spatiotemporally regulates cofilin activity at the cell edge to generate persistent membrane extension. We show that CIN translocates to the leading edge in a PI3-kinase-, Rac1-, and cofilin-dependent manner after EGF stimulation to activate cofilin, promotes actin free barbed end formation, accelerates actin turnover, and enhances membrane protrusion. In addition, we establish that CIN is crucial for the balance of protrusion/retraction events during cell migration. Thus, CIN coordinates the leading edge dynamics by controlling active cofilin levels to promote MTLn3 cell protrusion.

Cofilin and Vangl2 cooperate in the initiation of planar cell polarity in the mouse embryo.

The planar cell polarity (PCP; non-canonical Wnt) pathway is required to orient the cells within the plane of an epithelium. Here, we show that cofilin 1 (Cfl1), an actin-severing protein, and Vangl2, a core PCP protein, cooperate to control PCP in the early mouse embryo. Two aspects of planar polarity can be analyzed quantitatively at cellular resolution in the mouse embryo: convergent extension of the axial midline; and posterior positioning of cilia on cells of the node. Analysis of the spatial distribution of brachyury(+) midline cells shows that the Cfl1 mutant midline is normal, whereas Vangl2 mutants have a slightly wider midline. By contrast, midline convergent extension fails completely in Vangl2 Cfl1 double mutants. Planar polarity is required for the posterior positioning of cilia on cells in the mouse node, which is essential for the initiation of left-right asymmetry. Node cilia are correctly positioned in Cfl1 and Vangl2 single mutants, but cilia remain in the center of the cell in Vangl2 Cfl1 double mutants, leading to randomization of left-right asymmetry. In both the midline and node, the defect in planar polarity in the double mutants arises because PCP protein complexes fail to traffic to the apical cell membrane, although other aspects of apical-basal polarity are unaffected. Genetic and pharmacological experiments demonstrate that F-actin remodeling is essential for the initiation, but not maintenance, of PCP. We propose that Vangl2 and cofilin cooperate to target Rab11(+) vesicles containing PCP proteins to the apical membrane during the initiation of planar cell polarity.

AIP1 acts with cofilin to control actin dynamics during epithelial morphogenesis.

During epithelial morphogenesis, cells not only maintain tight adhesion for epithelial integrity but also allow dynamic intercellular movement to take place within cell sheets. How these seemingly opposing processes are coordinated is not well understood. Here, we report that the actin disassembly factors AIP1 and cofilin are required for remodeling of adherens junctions (AJs) during ommatidial precluster formation in Drosophila eye epithelium, a highly stereotyped cell rearrangement process which we describe in detail in our live imaging study. AIP1 is enriched together with F-actin in the apical region of preclusters, whereas cofilin displays a diffuse and uniform localization pattern. Cofilin overexpression completely rescues AJ remodeling defects caused by AIP1 loss of function, and cofilin physically interacts with AIP1. Pharmacological reduction of actin turnover results in similar AJ remodeling defects and decreased turnover of E-cadherin, which also results from AIP1 deficiency, whereas an F-actin-destabilizing drug affects AJ maintenance and epithelial integrity. Together with other data on actin polymerization, our results suggest that AIP1 enhances cofilin-mediated actin disassembly in the apical region of precluster cells to promote remodeling of AJs and thus intercellular movement, but also that robust actin polymerization promotes AJ general adhesion and integrity during the remodeling process.

Genome-wide pathway analysis in neuroblastoma.

The aim of this study was to identify candidate single-nucleotide polymorphisms (SNPs) that might play a role in susceptibility to neuroblastoma, elucidate their potential mechanisms, and generate SNP-to-gene-to-pathway hypotheses. A genome-wide association study (GWAS) dataset of neuroblastoma that included 442,976 SNPs from 1,627 neuroblastoma patients and 3,254 control subjects of European descent was used in this study. The identify candidate causal SNPs and pathways (ICSNPathway) analysis was applied to the GWAS dataset. ICSNPathway analysis identified 15 candidate SNPs, 10 genes, and 31 pathways, which revealed 10 hypothetical biological mechanisms. The strongest hypothetical biological mechanism was one wherein SNPrs40401 modulates the role of IL3 in several pathways and conditions, including the stem pathway, asthma (hsa05310), the dendritic cell pathway, and development (0.001 < p < 0.004; 0.001 < FDR < 0.033). The second strongest mechanism identified was that in which rs1048108 and rs16852600 alter the function of BARD1, which negatively regulates developmental process and modulates processes including cell development and programmed cell death (0.001 < p < 0.004; 0.001 < FDR < 0.033). The third mechanism identified was one wherein rs1939212 modulated CFL1, resulting in negative regulation of development, cell death, neural crest cell migration, and apoptosis (0.001 < p < 0.004; 0.001 < FDR < 0.033). By using the ICSNPathway to analyze neuroblastoma GWAS data, 15 candidate SNPs, 10 genes including IL3, BARD1, and CFL, and 31 pathways were identified that might contribute to the susceptibility of patients to neuroblastoma.

The actin-severing protein cofilin is downstream of neuregulin signaling and is essential for Schwann cell myelination.

Myelination is a complex process requiring coordination of directional motility and an increase in glial cell size to generate a multilamellar myelin sheath. Regulation of actin dynamics during myelination is poorly understood. However, it is known that myelin thickness is related to the abundance of neuregulin-1 (NRG1) expressed on the axon surface. Here we identify cofilin1, an actin depolymerizing and severing protein, as a downstream target of NRG1 signaling in rat Schwann cells (SCs). In isolated SCs, NRG1 promotes dephosphorylation of cofilin1 and its upstream regulators, LIM kinase (LIMK) and Slingshot-1 phosphatase (SSH1), leading to cofilin1 activation and recruitment to the leading edge of the plasma membrane. These changes are associated with rapid membrane expansion yielding a 35-50% increase in SC size within 30 min. Cofilin1-deficient SCs increase phosphorylation of ErbB2, ERK, focal adhesion kinase, and paxillin in response to NRG1, but fail to increase in size possibly due to stabilization of unusually long focal adhesions. Cofilin1-deficient SCs cocultured with sensory neurons do not myelinate. Ultrastructural analysis reveals that they unsuccessfully segregate or engage axons and form only patchy basal lamina. After 48 h of coculturing with neurons, cofilin1-deficient SCs do not align or elongate on axons and often form adhesions with the underlying substrate. This study identifies cofilin1 and its upstream regulators, LIMK and SSH1, as end targets of a NRG1 signaling pathway and demonstrates that cofilin1 is necessary for dynamic changes in the cytoskeleton needed for axon engagement and myelination by SCs.

Cofilin activation mediates Bax translocation to mitochondria during excitotoxic neuronal death.

During excitotoxic neuronal death, Bax translocates to the mitochondria where it plays an important role by contributing to the release of proapoptotic factors. However, how Bax translocates to the mitochondria during excitotoxicity remains poorly understood. Herein, our data suggest the presence of a novel signalling mechanism by which NMDA receptor stimulation promotes Bax translocation. This signalling pathway is triggered by dephosphorylation of cofilin. Once dephosphorylated, cofilin might interact physically with Bax acting as a carrier for it, translocating it to the mitochondria, where it contributes to mitochondrial membrane despolarization, permeabilization and to the release of apoptotic factors, thus leading to neuronal death. Lack-of-function studies indicate that only the Slingshot family of phosphatases, more specifically the enzyme Slingshot 1L phosphatase, but not cronophin participates in the cofilin activation process during excitotoxicity. Indeed, cofilin-mediated Bax translocation seems to be a key event in excitotoxic neuronal death as knock down of either cofilin or Slingshot 1L phosphatase has a marked neuroprotective effect on NMDA-mediated neuronal death. This novel biochemical pathway may therefore be a good target to develop future therapeutic molecules for neurodegenerative diseases.

Complement receptor-3 negatively regulates the phagocytosis of degenerated myelin through tyrosine kinase Syk and cofilin.

BACKGROUND: Intact myelin, which normally surrounds axons, breaks down in Wallerian degeneration following axonal injury and during neurodegenerative diseases such as multiple sclerosis. Clearance of degenerated myelin by phagocytosis is essential since myelin impedes repair and exacerbates damage. CR3 (complement receptor-3) is a principal phagocytic receptor in myelin phagocytosis. We studied how tyrosine kinase Syk (spleen tyrosine kinase) and cofilin control phagocytosis of degenerated myelin by CR3 in microglia and macrophages. Syk is a non-receptor tyrosine kinase that CR3 recruits to convey cellular functions. Cofilin is an actin-depolymerizing protein that controls F-actin (filamentous actin) remodeling (i.e., disassembly and reassembly) by shifting between active unphosphorylated and inactive phosphorylated states. RESULTS: Syk was continuously activated during prolonged phagocytosis. Phagocytosis increased when Syk activity and expression were reduced, suggesting that normally Syk down regulates CR3-mediated myelin phagocytosis. Levels of inactive p-cofilin (phosphorylated cofilin) decreased transiently during prolonged phagocytosis. In contrast, p-cofilin levels decreased continuously when Syk activity and expression were continuously reduced, suggesting that normally Syk advances the inactive state of cofilin. Observations also revealed inverse relationships between levels of phagocytosis and levels of inactive p-cofilin, suggesting that active unphosphorylated cofilin advances phagocytosis. Active cofilin could advance phagocytosis by promoting F-actin remodeling, which supports the production of membrane protrusions (e.g., filopodia), which, as we also revealed, are instrumental in myelin phagocytosis. CONCLUSIONS: CR3 both activates and downregulates myelin phagocytosis at the same time. Activation was previously documented. We presently demonstrate that downregulation is mediated through Syk, which advances the inactive phosphorylated state of cofilin. Self-negative control of phagocytosis by the phagocytic receptor can be useful in protecting phagocytes from excessive phagocytosis (i.e., "overeating") during extended exposure to particles that are destined for ingestion.

Regulation of AMPA receptor channels and synaptic plasticity by cofilin phosphatase Slingshot in cortical neurons.

Cofilin, the major actin depolymerizing factor, modulates actin dynamics that contribute to spine morphology, synaptic transmission and plasticity. Much evidence implicates the cofilin inactivation kinase LIMK in synaptic function, but little is known about the cofilin activation phosphatase Slingshot in this regard. In this study, we found that suppressing endogenous Slingshot with small RNA interference or function-blocking antibody led to a dramatic reduction of AMPA receptor-mediated excitatory postsynaptic currents (EPSCs) in cortical neurons. Perturbation of Slingshot function also diminished the ability to express synaptic plasticity. Inactivating cofilin or disturbing actin dynamics reduced AMPAR-EPSCs in a Slingshot-dependent manner. Moreover, surface GluR 1 and synaptic GluR2/3 clusters were reduced by Slingshot knockdown. Our data suggest that Slingshot plays a pivotal role in AMPAR trafficking and synaptic transmission by controlling actin cytoskeleton via cofilin activation.

Cofilin dysregulation alters actin turnover in frataxin-deficient neurons.

Abnormalities in actin cytoskeleton have been linked to Friedreich's ataxia (FRDA), an inherited peripheral neuropathy characterised by an early loss of neurons in dorsal root ganglia (DRG) among other clinical symptoms. Despite all efforts to date, we still do not fully understand the molecular events that contribute to the lack of sensory neurons in FRDA. We studied the adult neuronal growth cone (GC) at the cellular and molecular level to decipher the connection between frataxin and actin cytoskeleton in DRG neurons of the well-characterised YG8R Friedreich's ataxia mouse model. Immunofluorescence studies in primary cultures of DRG from YG8R mice showed neurons with fewer and smaller GCs than controls, associated with an inhibition of neurite growth. In frataxin-deficient neurons, we also observed an increase in the filamentous (F)-actin/monomeric (G)-actin ratio (F/G-actin ratio) in axons and GCs linked to dysregulation of two crucial modulators of filamentous actin turnover, cofilin-1 and the actin-related protein (ARP) 2/3 complex. We show how the activation of cofilin is due to the increase in chronophin (CIN), a cofilin-activating phosphatase. Thus cofilin emerges, for the first time, as a link between frataxin deficiency and actin cytoskeleton alterations.

Role of cofilin­1 in arsenic trioxide­induced apoptosis of NB4­R1 cells.

All­trans retinoic acid (ATRA) and arsenic trioxide (As2O3) are currently first­line treatments for acute promyelocytic leukemia (APL). However, a number of patients with APL are resistant to ATRA but still sensitive to As2O3, and the underlying mechanisms of this remain unclear. In the present study, two­dimensional gel electrophoresis, mass spectrometry and other proteomic methods were applied to screen and identify the differentially expressed proteins between the retinoic acid­sensitive cell lines and drug­resistant cell lines. The results demonstrated that in retinoic acid­resistant NB4­R1 cells, the protein expression of cofilin­1 was markedly increased compared with that in the drug­sensitive NB4 cells. Subsequently, the effects of cofilin­1 on As2O3­induced apoptosis in NB4­R1 cells were further investigated. The results revealed that cell viability was markedly suppressed and apoptosis was increased in the As2O3­treated NB4­R1 cells, with increased expression levels of cleaved­poly (ADP­ribose) polymerase and cleaved­caspase 12. Cofilin­1 expression was significantly decreased at both the mRNA and protein levels in the As2O3­treated group compared with the control. Western blotting further revealed that As2O3 treatment decreased the cytoplasmic cofilin­1 level but increased its expression in the mitochondrion. However, the opposite effects of As2O3 on the cytochrome C distribution were found in NB4­R1 cells. This suggested that As2O3 can induce the transfer of cofilin­1 from the cytoplasm to mitochondria and trigger the release of mitochondrial cytochrome C in NB4­R1 cells. Moreover, cofilin­1 knockdown by its specific short hairpin RNA significantly suppressed As2O3­induced NB4­R1 cell apoptosis and inhibited the release of mitochondrial cytochrome C. Whereas, overexpression of cofilin­1 using a plasmid vector carrying cofilin­1 increased the release of cytochrome C into the cytoplasm from the mitochondria in As2O3­treated NB4­R1 cells. In conclusion, cofilin­1 played a role in As2O3­induced NB4­R1 cell apoptosis and it might be a novel target for APL treatment.

Biochemical and genetic analyses provide insight into the structural and mechanistic properties of actin filament disassembly by the Aip1p cofilin complex in Saccharomyces cerevisiae.

Explication of the Aip1p/cofilin/actin filament complex may lead to a more detailed understanding of the mechanisms by which Aip1p and cofilin collaborate to rapidly disassemble filaments. We further characterized the actin-Aip1p interface through a random mutagenic screen of ACT1, identifying a novel Aip1p interaction site on actin. This finding is consistent with our current ternary complex model and offers insights into how Aip1p may disturb intersubunit contacts within an actin filament. In addition, site-directed mutagenesis aimed at interfering with salt bridge interactions at the predicted Aip1p-cofilin interface revealed hyperactive alleles of cof1 and aip1 that support the ternary complex model and suggest that conformational changes in cofilin structure may be transmitted to actin filaments, causing increased destabilization. Furthermore, these data support an active role for Aip1p in promoting actin filament turnover.

Cofilin increases the torsional flexibility and dynamics of actin filaments.

We have measured the effects of cofilin on the conformation and dynamics of actin filaments labeled at Cys374 with erythrosin-iodoacetemide (ErIA), using time-resolved phosphorescence anisotropy (TPA). Cofilin quenches the phosphorescence intensity of actin-bound ErIA, indicating that binding changes the local environment of the probe. The cofilin concentration-dependence of the phosphorescence intensity is sigmoidal, consistent with cooperative actin filament binding. Model-independent analysis of the anisotropies indicates that cofilin increases the rates of the microsecond rotational motions of actin. In contrast to the reduction in phosphorescence intensity, the changes in the rates of rotational motions display non-nearest-neighbor cooperative interactions and saturate at substoichiometric cofilin binding densities. Detailed analysis of the TPA decays indicates that cofilin decreases the torsional rigidity (C) of actin, increasing the thermally driven root-mean-square torsional angle between adjacent filament subunits from approximately 4 degrees (C = 2.30 x 10(-27) Nm2 radian(-1)) to approximately 17 degrees (C = 0.13 x 10(-27) Nm2 radian(-1)) at 25 degrees C. We favor a mechanism in which cofilin binding shifts the equilibrium between thermal ErIA-actin filament conformers, and facilitates two distinct structural changes in actin. One is local in nature, which affects the structure of actin's C terminus and is likely to mediate nearest-neighbor cooperative binding and filament severing. The second is a change in the internal dynamics of actin, which displays non-nearest-neighbor cooperativity and increases the torsional flexibility of filaments. The long-range effects of cofilin on the torsional dynamics of actin may accelerate P(i) release from filaments and modulate interactions with other regulatory actin filament binding proteins.

The role of cofilin-l in vulvar squamous cell carcinoma: A marker of carcinogenesis, progression and targeted therapy.

Numerous studies have revealed that cofilin-l (CFL1) is associated with cancer cell migration and invasion in various types of tumor tissues. We investigated the roles of CFL1 in vulvar squamous cell carcinoma (VSCC). CFL1 expression was detected in VSCC and normal vulvar tissues using immunohistochemistry and western blotting. The vulvar carcinoma SW962 cell line was transfected with CFL1 small interfering RNA (siRNA) and exposed to periplocoside. We then assessed changes in cell proliferation, apoptosis, invasion and metastasis. We detected changes in CFL1 mRNA and protein expression by RT-PCR and western blotting, and alterations in protein expression of various relevant molecules by western blotting. CFL1 expression was found to be significantly upregulated in the VSCC tissues compared with the normal vulvar tissues by immunohistochemistry and western blotting (P<0.05) and was positively correlated with International Federation of Gynecology and Obstetrics (FIGO) stage, differentiation and lymphatic metastasis (P<0.05). After CFL1 knockdown by siRNA transfection, SW962 cells exhibited a decrease in growth, G1 phase cell cycle arrest, induction of apoptotic, low invasion and metastasis, and disrupted lamellipodium formation. We found that the protein expression of Bcl-xL, cyclin A1, MMP2, MMP9 and STAT3 was decreased, while expression of Bax was increased. Periplocoside inhibited SW962 cell growth, promoted apoptosis, suppressed invasion and migration, and lamellipodium formation. Periplocoside exposure resulted in lower CFL1, Bcl-xL, cyclin A1, MMP2, MMP9 and STAT3 levels, but a higher Bax level compared with the control group. We demonstrated that abnormal CFL1 expression may affect vulvar carcinogenesis and subsequent progression. CFL1 silencing by siRNA significantly inhibited VSCC cell progression, which suggests that CFL1 is a potential therapeutic target for vulvar cancer. Periplocoside, which was utilized in the present study for the clinical treatment of vulvar cancer, showed strong antitumor effects by suppression of CFL1 expression.

Two mouse cofilin isoforms, muscle-type (MCF) and non-muscle type (NMCF), interact with F-actin with different efficiencies.

Two cofilin isoforms, a muscle-type (MCF) and a non-muscle-type (NMCF), are co-expressed in developing mammalian skeletal and cardiac muscles. To clarify how they are involved in the actin filament dynamics during myofibrillogenesis, we examined their localization in muscle tissues and cultured muscle cells using immunocytochemical methods, and their interaction with F-actin in vitro. NMCF was mostly detected in a diffuse pattern in the cytoplasm but MCF was partly localized to the striated structures in myofibrils. The location of chicken cofilin, a homologue of MCF, in the I-bands of myofibrils was determined by an immunocytochemical method. It is suggested that MCF could be associated with actin filaments in muscle cells more efficiently than NMCF. Using purified recombinant MCF and NMCF, their interaction with F-actin was examined in vitro by a cosedimentation assay method. We observed that MCF was precipitated with F-actin more effectively than NMCF. When MCF and NMCF were simultaneously incubated with F-actin, MCF was preferentially associated with F-actin. MCF and NMCF inhibited the interaction of F-actin with tropomyosin, but the former suppressed the actin-tropomyosin interaction more strongly than the latter. These results suggest that MCF interacts with F-actin with higher affinity than NMCF, and although both of them are involved in the regulation of actin assembly in developing myotubes, the two proteins may play somewhat different roles.

Attention-Deficit/Hyperactivity Disorder-like Phenotype in a Mouse Model with Impaired Actin Dynamics.

BACKGROUND: Actin depolymerizing proteins of the actin depolymerizing factor (ADF)/cofilin family are essential for actin dynamics, which is critical for synaptic function. Two ADF/cofilin family members, ADF and n-cofilin, are highly abundant in the brain, where they are present in excitatory synapses. Previous studies demonstrated the relevance of n-cofilin for postsynaptic plasticity, associative learning, and anxiety. These studies also suggested overlapping functions for ADF and n-cofilin. METHODS: We performed pharmacobehavioral, electrophysiologic, and electron microscopic studies on ADF and n-cofilin single mutants and double mutants (named ACC mice) to characterize the importance of ADF/cofilin activity for synapse physiology and mouse behavior. RESULTS: The ACC mice, but not single mutants, exhibited hyperlocomotion, impulsivity, and impaired working memory. Hyperlocomotion and impulsive behavior were reversed by methylphenidate, a psychostimulant commonly used for the treatment of attention-deficit/hyperactivity disorder (ADHD). Also, ACC mice displayed a disturbed morphology of striatal excitatory synapses, accompanied by strongly increased glutamate release. Blockade of dopamine or glutamate transmission resulted in normal locomotion. CONCLUSIONS: Our study reveals that ADHD can result from a disturbed balance between excitation and inhibition in striatal circuits, providing novel insights into the mechanisms underlying this neurobehavioral disorder. Our results link actin dynamics to ADHD, suggesting that mutations in actin regulatory proteins may contribute to the etiology of ADHD in humans.

Aß Influences Cytoskeletal Signaling Cascades with Consequences to Alzheimer's Disease.

Abnormal signal transduction events can impact upon the cytoskeleton, affecting the actin and microtubule networks with direct relevance to Alzheimer's disease (AD). Cytoskeletal anomalies, in turn, promote atypical neuronal responses, with consequences for cellular organization and function. Neuronal cytoskeletal modifications in AD include neurofibrillary tangles, which result from aggregates of hyperphosphorylated tau protein. The latter is a microtubule (MT)-binding protein, whose abnormal phosphorylation leads to MT instability and consequently provokes irregularities in the neuronal trafficking pathways. Early stages of AD are also characterized by synaptic dysfunction and loss of dendritic spines, which correlate with cognitive deficit and impaired brain function. Actin dynamics has a prominent role in maintaining spine plasticity and integrity, thus providing the basis for memory and learning processes. Hence, factors that disrupt both actin and MT network dynamics will compromise neuronal function and survival. The peptide Aß is the major component of senile plaques and has been described as a pivotal mediator of neuronal dystrophy and synaptic loss in AD. Here, we review Aß-mediated effects on both MT and actin networks and focus on the relevance of the elicited cytoskeletal signaling events targeted in AD pathology.

Cofilin recruits F-actin to SPCA1 and promotes Ca2+-mediated secretory cargo sorting.

The actin filament severing protein cofilin-1 (CFL-1) is required for actin and P-type ATPase secretory pathway calcium ATPase (SPCA)-dependent sorting of secretory proteins at the trans-Golgi network (TGN). How these proteins interact and activate the pump to facilitate cargo sorting, however, is not known. We used purified proteins to assess interaction of the cytoplasmic domains of SPCA1 with actin and CFL-1. A 132-amino acid portion of the SPCA1 phosphorylation domain (P-domain) interacted with actin in a CFL-1-dependent manner. This domain, coupled to nickel nitrilotriacetic acid (Ni-NTA) agarose beads, specifically recruited F-actin in the presence of CFL-1 and, when expressed in HeLa cells, inhibited Ca(2+) entry into the TGN and secretory cargo sorting. Mutagenesis of four amino acids in SPCA1 that represent the CFL-1 binding site also affected Ca(2+) import into the TGN and secretory cargo sorting. Altogether, our findings reveal the mechanism of CFL-1-dependent recruitment of actin to SPCA1 and the significance of this interaction for Ca(2+) influx and secretory cargo sorting.