Cofilin promotes actin polymerization and defines the direction of cell motility

Rottlerin inhibits macropinocytosis of Porcine Reproductive and Respiratory Syndrome Virus through the PKCδ-Cofilin signaling pathway

Rottlerin exerts antiviral activity against various enveloped viruses, yet the mechanism by which it inhibits viral replication and the associated signaling pathways remains unclear. Here, we investigated the mechanisms for the antiviral effects of rottlerin against Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) in vitro. We demonstrate that PRRSV enters host cells via macropinocytosis. Rottlerin, a PKCδ inhibitor, partially inhibits PRRSV entry by decreasing actin polymerization, as evidenced by alterations in actin dynamics. LIM domain kinase 1 (LIMK1) is essential for PRRSV replication, and PRRSV infection-induced cofilin activation, which was reversed by rottlerin treatment. Our findings suggest that a subset of PRRSV utilizes PKCδ-mediated actin dynamics to enter cells via macropinocytosis, and that rottlerin is a potential antiviral molecule targeting this entry pathway.

F-actin in the cuticular plate and junctions of auditory hair cells is regulated by ADF and cofilin to allow for normal stereocilia bundle patterning and maintenance

Auditory hair cells, which convert sound-induced vibrations in the inner ear into neural signals, depend on multiple actin populations for normal function. Stereocilia are mechanosensory protrusions formed around a core of linear, crosslinked F-actin. They are anchored in the cuticular plate, which predominantly consists of randomly oriented actin filaments. A third actin population is found near hair cell junctions, consisting of both parallel and branched filaments. Actin depolymerizing factor (ADF) and cofilin-1 (CFL1) proteins disassemble actin filaments and are required to regulate F-actin in stereocilia, but their effect on cuticular plate and junctional actin populations is unclear. Here, we show that loss of ADF and CFL1 disrupts the patterning of stereocilia into orderly bundles and that this phenotype correlates with defective development of the cuticular plate and junctional actin populations. ADF/CFL1 continue to regulate these actin populations in mature cells, which is necessary for long-term maintenance of hair cell morphology.

3D printing cytoskeletal networks: ROS-induced filament severing leads to surge in actin polymerization

The cytoskeletal protein actin forms a spatially organized biopolymer network that plays a central role in many cellular processes. Actin filaments continuously assemble and disassemble, enabling cells to rapidly reorganize their cytoskeleton. Filament severing accelerates actin turnover, as both polymerization and depolymerization rates depend on the number of free filament ends - which severing increases. Here, we use light to control actin severing in vitro by locally generating reactive oxygen species (ROS) with photosensitive molecules such as fluorophores. We see that ROS sever actin filaments, which increases actin polymerization in our experiments. However, beyond a certain threshold, excessive severing leads to the disassembly of actin networks. Our experimental data is supported by simulations using a kinetic model of actin polymerization, which helps us understand the underlying dynamics. In cells, ROS are known to regulate the actin cytoskeleton, but the molecular mechanisms are poorly understood. Here we show that, in vitro, ROS directly affect actin reorganization.

Gastrodin Mitigates Ketamine-Induced Inhibition of F-Actin Remodeling and Cell Migration by Regulating the Rho Signaling Pathway

Background/Objects: Rho signaling plays a role in calcium-regulated cytoskeletal reorganization and cell movement, processes linked to neuronal function and cancer metastasis. Gastrodia elata, a traditional herbal medicine, can regulate glutamate-induced calcium influx in PC12 cells and influence cell function by modulating neuronal cytoskeleton remodeling via the monoaminergic system and Rho signaling. This study investigates the effects of gastrodin, a key component of Gastrodia elata, on Rho signaling, cytoskeleton remodeling, and cell migration in B35 and C6 cells. It also explores gastrodin's impact on Rho signaling in the prefrontal cortex of Sprague Dawley rats. Methods: B35 cells, C6 cells, and Sprague Dawley rats were treated with ketamine, gastrodin, or both. The expression of examined proteins from B35 cells, C6 cells, and the prefrontal cortex of Sprague Dawley rats were analyzed using immunoblotting. Immunofluorescent staining was applied to detect the phosphorylation of RhoGDI1. F-actin was stained using phalloidin-488 staining. Cell migration was analyzed using the Transwell and wound-healing assays. Results: Gastrodin reversed the ketamine-induced regulation of cell mobility inhibition, F-actin condensation, and Rho signaling modulation including Rho GDP dissociation inhibitor 1 (RhoGDI1); the Rho family protein (Ras homolog family member A (RhoA); cell division control protein 42 homolog (CDC42); Ras-related C3 botulinum toxin substrate 1(Rac1)); rho-associated, coiled-coil-containing protein kinase 1 (ROCK1); neural Wiskott-Aldrich syndrome protein (NWASP); myosin light chain 2 (MLC2); profilin1 (PFN1); and cofilin-1 (CFL1) in B35 and C6 cells. Similar modulations on Rho signaling were also observed in the prefrontal cortex of rats. Conclusions: Our findings show that gastrodin counteracts ketamine-induced disruptions in Rho signaling, cytoskeletal dynamics, and cell migration by regulating key components like RhoGDI1, ROCK1, MLC2, PFN1, and CFL1. This suggests the potential of gastrodin as a comprehensive regulator of cellular signaling.

Advances in understanding the roles of actin scaffolding and membrane trafficking in dendrite development

Dendritic morphology is typically highly branched, and the branching and synaptic abundance of dendrites can enhance the receptive range of neurons and the diversity of information received, thus providing the basis for information processing in the nervous system. Once dendritic development is aberrantly compromised or damaged, it may lead to abnormal connectivity of the neural network, affecting the function and stability of the nervous system and ultimately triggering a series of neurological disorders. Research on the regulation of dendritic developmental processes has flourished, and much progress is now being made in its regulatory mechanisms. Noteworthily, dendrites are characterized by an extremely complex dendritic arborization that cannot be attributed to individual protein functions alone, requiring a systematic analysis of the intrinsic and extrinsic signals and the coordinated roles among them. Actin cytoskeleton organization and membrane vesicle trafficking are required during dendrite development, with actin providing tracks for vesicles and vesicle trafficking in turn providing material for actin assembly. In this review, we focus on these two basic biological processes and discuss the molecular mechanisms and their synergistic effects underlying the morphogenesis of neuronal dendrites. We also offer insights and discuss strategies for the potential preventive and therapeutic treatment of neuropsychiatric disorders.

Beyond Glycolysis: Aldolase A Is a Novel Effector in Reelin-Mediated Dendritic Development

Reelin, a secreted glycoprotein, plays a crucial role in guiding neocortical neuronal migration, dendritic outgrowth and arborization, and synaptic plasticity in the adult brain. Reelin primarily operates through the canonical lipoprotein receptors apolipoprotein E receptor 2 (Apoer2) and very low-density lipoprotein receptor (Vldlr). Reelin also engages with noncanonical receptors and unidentified coreceptors; however, the effects of which are less understood. Using high-throughput tandem mass tag (TMT) liquid chromatography tandem mass spectrometry (LC-MS/MS)-based proteomics and gene set enrichment analysis (GSEA), we identified both shared and unique intracellular pathways activated by Reelin through its canonical and noncanonical signaling in primary murine neurons of either sex during dendritic growth and arborization. We observed pathway cross talk related to regulation of cytoskeleton, neuron projection development, protein transport, and actin filament-based process. We also found enriched gene sets exclusively by the noncanonical Reelin pathway including protein translation, mRNA metabolic process, and ribonucleoprotein complex biogenesis suggesting Reelin fine-tunes neuronal structure through distinct signaling pathways. A key discovery is the identification of aldolase A, a glycolytic enzyme and actin-binding protein, as a novel effector of Reelin signaling. Reelin induced de novo translation and mobilization of aldolase A from the actin cytoskeleton. We demonstrated that aldolase A is necessary for Reelin-mediated dendrite growth and arborization in primary murine neurons and mouse brain cortical neurons. Interestingly, the function of aldolase A in dendrite development is independent of its known role in glycolysis. Altogether, our findings provide new insights into the Reelin-dependent signaling pathways and effector proteins that are crucial for dendritic development.

Human T-cell receptor triggering requires inactivation of Lim kinase-1 by Slingshot-1 phosphatase

Actin dynamics control early T-cell receptor (TCR) signalling during T-cell activation. However, the precise regulation of initial actin rearrangements is not completely understood. Here, we have investigated the regulatory role of the phosphatase Slingshot-1 (SSH1) in this process. Our data show that SSH1 rapidly polarises to nascent cognate synaptic contacts and later relocalises to peripheral F-actin networks organised at the mature immunological synapse. Knockdown of SSH1 expression by CRISPR/Cas9-mediated genome editing or small interfering RNA reveal a regulatory role for SSH1 in CD3ε conformational change, allowing Nck binding and proper downstream signalling and immunological synapse organisation. TCR triggering induces SSH1-mediated activation of actin dynamics through a mechanism mediated by Limk-1 inactivation. These data suggest that during early TCR activation, SSH1 is required for rapid F-actin rearrangements that mediate initial conformational changes of the TCR, integrin organisation and proximal signalling events for proper synapse organisation. Therefore, the SSH1 and Limk-1 axis is a key regulatory element for full T cell activation.

Filopodial protrusion driven by density-dependent Ena-TOCA-1 interactions

Filopodia are narrow actin-rich protrusions with important roles in neuronal development where membrane-binding adaptor proteins, such as I-BAR- and F-BAR-domain-containing proteins, have emerged as upstream regulators that link membrane interactions to actin regulators such as formins and proteins of the Ena/VASP family. Both the adaptors and their binding partners are part of diverse and redundant protein networks that can functionally compensate for each other. To explore the significance of the F-BAR domain-containing neuronal membrane adaptor TOCA-1 (also known as FNBP1L) in filopodia we performed a quantitative analysis of TOCA-1 and filopodial dynamics in Xenopus retinal ganglion cells, where Ena/VASP proteins have a native role in filopodial extension. Increasing the density of TOCA-1 enhances Ena/VASP protein binding in vitro, and an accumulation of TOCA-1, as well as its coincidence with Ena, correlates with filopodial protrusion in vivo. Two-colour single-molecule localisation microscopy of TOCA-1 and Ena supports their nanoscale association. TOCA-1 clusters promote filopodial protrusion and this depends on a functional TOCA-1 SH3 domain and activation of Cdc42, which we perturbed using the small-molecule inhibitor CASIN. We propose that TOCA-1 clusters act independently of membrane curvature to recruit and promote Ena activity for filopodial protrusion.

Beyond Glycolysis: Aldolase A is a Novel Effector in Reelin Mediated Dendritic Development

Reelin, a secreted glycoprotein, plays a crucial role in guiding neocortical neuronal migration, dendritic outgrowth and arborization, and synaptic plasticity in the adult brain. Reelin primarily operates through the canonical lipoprotein receptors apolipoprotein E receptor 2 (Apoer2) and very low-density lipoprotein receptor (Vldlr). Reelin also engages with non-canonical receptors and unidentified co-receptors; however, the effects of which are less understood. Using high-throughput tandem mass tag LC-MS/MS-based proteomics and gene set enrichment analysis, we identified both shared and unique intracellular pathways activated by Reelin through its canonical and non-canonical signaling in primary murine neurons during dendritic growth and arborization. We observed pathway crosstalk related to regulation of cytoskeleton, neuron projection development, protein transport, and actin filament-based process. We also found enriched gene sets exclusively by the non-canonical Reelin pathway including protein translation, mRNA metabolic process and ribonucleoprotein complex biogenesis suggesting Reelin fine-tunes neuronal structure through distinct signaling pathways. A key discovery is the identification of aldolase A, a glycolytic enzyme and actin binding protein, as a novel effector of Reelin signaling. Reelin induced de novo translation and mobilization of aldolase A from the actin cytoskeleton. We demonstrated that aldolase A is necessary for Reelin-mediated dendrite growth and arborization in primary murine neurons and mouse brain cortical neurons. Interestingly, the function of aldolase A in dendrite development is independent of its known role in glycolysis. Altogether, our findings provide new insights into the Reelin-dependent signaling pathways and effector proteins that are crucial for actin remodeling and dendritic development.

Significance

Reelin is an extracellular glycoprotein and exerts its function primarily by binding to the canonical lipoprotein receptors Apoer2 and Vldlr. Reelin is best known for its role in neuronal migration during prenatal brain development. Reelin also signals through a non-canonical pathway outside of Apoer2/Vldlr; however, these receptors and signal transduction pathways are less defined. Here, we examined Reelin's role during dendritic outgrowth in primary murine neurons and identified shared and distinct pathways activated by canonical and non-canonical Reelin signaling. We also found aldolase A as a novel effector of Reelin signaling, that functions independently of its known metabolic role, highlighting Reelin's influence on actin dynamics and neuronal structure and growth.

Mechanisms of actin disassembly and turnover

Cellular actin networks exhibit a wide range of sizes, shapes, and architectures tailored to their biological roles. Once assembled, these filamentous networks are either maintained in a state of polarized turnover or induced to undergo net disassembly. Further, the rates at which the networks are turned over and/or dismantled can vary greatly, from seconds to minutes to hours or even days. Here, we review the molecular machinery and mechanisms employed in cells to drive the disassembly and turnover of actin networks. In particular, we highlight recent discoveries showing that specific combinations of conserved actin disassembly-promoting proteins (cofilin, GMF, twinfilin, Srv2/CAP, coronin, AIP1, capping protein, and profilin) work in concert to debranch, sever, cap, and depolymerize actin filaments, and to recharge actin monomers for new rounds of assembly.

Engineering memory with an extrinsically disordered kinase

Synaptic plasticity plays a crucial role in memory formation by regulating the communication between neurons. Although actin polymerization has been linked to synaptic plasticity and dendritic spine stability, the causal link between actin polymerization and memory encoding has not been identified yet. It is not clear whether actin polymerization and structural changes in dendritic spines are a driver or a consequence of learning and memory. Using an extrinsically disordered form of the protein kinase LIMK1, which rapidly and precisely acts on ADF/cofilin, a direct modifier of actin, we induced long-term enlargement of dendritic spines and enhancement of synaptic transmission in the hippocampus on command. The activation of extrinsically disordered LIMK1 in vivo improved memory encoding and slowed cognitive decline in aged mice exhibiting reduced cofilin phosphorylation. The engineered memory by an extrinsically disordered LIMK1 supports a direct causal link between actin-mediated synaptic transmission and memory.

N-terminal α-amino SUMOylation of cofilin-1 is critical for its regulation of actin depolymerization

Small ubiquitin-like modifier (SUMO) typically conjugates to target proteins through isopeptide linkage to the ε-amino group of lysine residues. This posttranslational modification (PTM) plays pivotal roles in modulating protein function. Cofilins are key regulators of actin cytoskeleton dynamics and are well-known to undergo several different PTMs. Here, we show that cofilin-1 is conjugated by SUMO1 both in vitro and in vivo. Using mass spectrometry and biochemical and genetic approaches, we identify the N-terminal α-amino group as the SUMO-conjugation site of cofilin-1. Common to conventional SUMOylation is that the N-α-SUMOylation of cofilin-1 is also mediated by SUMO activating (E1), conjugating (E2), and ligating (E3) enzymes and reversed by the SUMO deconjugating enzyme, SENP1. Specific to the N-α-SUMOylation is the physical association of the E1 enzyme to the substrate, cofilin-1. Using F-actin co-sedimentation and actin depolymerization assays in vitro and fluorescence staining of actin filaments in cells, we show that the N-α-SUMOylation promotes cofilin-1 binding to F-actin and cofilin-induced actin depolymerization. This covalent conjugation by SUMO at the N-α amino group of cofilin-1, rather than at an internal lysine(s), serves as an essential PTM to tune cofilin-1 function during regulation of actin dynamics.

Dorsal visual stream and LIMK1: hemideletion, haplotype, and enduring effects in children with Williams syndrome

BACKGROUND

Williams syndrome (WS), a rare neurodevelopmental disorder caused by hemizygous deletion of ~ 25 genes from chromosomal band 7q11.23, affords an exceptional opportunity to study associations between a well-delineated genetic abnormality and a well-characterized neurobehavioral profile. Clinically, WS is typified by increased social drive (often termed "hypersociability") and severe visuospatial construction deficits. Previous studies have linked visuospatial problems in WS with alterations in the dorsal visual processing stream. We investigated the impacts of hemideletion and haplotype variation of LIMK1, a gene hemideleted in WS and linked to neuronal maturation and migration, on the structure and function of the dorsal stream, specifically the intraparietal sulcus (IPS), a region known to be altered in adults with WS.

METHODS

We tested for IPS structural and functional changes using longitudinal MRI in a developing cohort of children with WS (76 visits from 33 participants, compared to 280 visits from 94 typically developing age- and sex-matched participants) over the age range of 5-22. We also performed MRI studies of 12 individuals with rare, shorter hemideletions at 7q11.23, all of which included LIMK1. Finally, we tested for effects of LIMK1 variation on IPS structure and imputed LIMK1 expression in two independent cohorts of healthy individuals from the general population.

RESULTS

IPS structural (p < 10-4 FDR corrected) and functional (p < .05 FDR corrected) anomalies previously reported in adults were confirmed in children with WS, and, consistent with an enduring genetic mechanism, were stable from early childhood into adulthood. In the short hemideletion cohort, IPS deficits similar to those in WS were found, although effect sizes were smaller than those found in WS for both structural and functional findings. Finally, in each of the two general population cohorts stratified by LIMK1 haplotype, IPS gray matter volume (pdiscovery < 0.05 SVC, preplication = 0.0015) and imputed LIMK1 expression (pdiscovery = 10-15, preplication = 10-23) varied according to LIMK1 haplotype.

CONCLUSIONS

This work offers insight into neurobiological and genetic mechanisms responsible for the WS phenotype and also more generally provides a striking example of the mechanisms by which genetic variation, acting by means of molecular effects on a neural intermediary, can influence human cognition and, in some cases, lead to neurocognitive disorders.

Cryo-EM structures of actin binding proteins as tool for drug discovery

Cellular actin dynamic is controlled by a plethora of actin binding proteins (ABPs), including actin nucleating, bundling, cross-linking, capping, and severing proteins. In this review, regulation of actin dynamics by ABPs will be introduced, and the role of the F-actin severing protein cofilin-1 and the F-actin bundling protein L-plastin in actin dynamics discussed in more detail. Since up-regulation of these proteins in different kinds of cancers is associated with malignant progression of cancer cells, we suggest the cryogenic electron microscopy (Cryo-EM) structure of F- actin with the respective ABP as template for in silico drug design to specifically disrupt the interaction of these ABPs with F-actin.

Chemoselective Caging of Carboxyl Groups for On-Demand Protein Activation with Small Molecules

Tools for on-demand protein activation enable impactful gain-of-function studies in biological settings. Thus far, however, proteins have been chemically caged at primarily Lys, Tyr, and Sec, typically through the genetic encoding of unnatural amino acids. Herein, we report that the preferential reactivity of diazo compounds with protonated acids can be used to expand this toolbox to solvent-accessible carboxyl groups with an elevated pKa value. As a model protein, we employed lysozyme (Lyz), which has an active-site Glu35 residue with a pKa value of 6.2. A diazo compound with a bioorthogonal self-immolative handle esterified Glu35 selectively, inactivating Lyz. The hydrolytic activity of the caged Lyz on bacterial cell walls was restored with two small-molecule triggers. The decaging was more efficient by small molecules than by esterases. This simple chemical strategy was also applied to a hemeprotein and an aspartyl protease, setting the stage for broad applicability.

Proteomic Markers for Mechanobiological Properties of Metastatic Cancer Cells

The major cause (more than 90%) of all cancer-related deaths is metastasis, thus its prediction can critically affect the survival rate. Metastases are currently predicted by lymph-node status, tumor size, histopathology and genetic testing; however, all these are not infallible, and obtaining results may require weeks. The identification of new potential prognostic factors will be an important source of risk information for the practicing oncologist, potentially leading to enhanced patient care through the proactive optimization of treatment strategies. Recently, the new mechanobiology-related techniques, independent of genetics, based on the mechanical invasiveness of cancer cells (microfluidic, gel indentation assays, migration assays etc.), demonstrated a high success rate for the detection of tumor cell metastasis propensity. However, they are still far away from clinical implementation due to complexity. Hence, the exploration of novel markers related to the mechanobiological properties of tumor cells may have a direct impact on the prognosis of metastasis. Our concise review deepens our knowledge of the factors that regulate cancer cell mechanotype and invasion, and incites further studies to develop therapeutics that target multiple mechanisms of invasion for improved clinical benefit. It may open a new clinical dimension that will improve cancer prognosis and increase the effectiveness of tumor therapies.

Cofilin promotes vasculogenic mimicry by regulating the actin cytoskeleton in human breast cancer cells

Vasculogenic mimicry (VM) is the formation of microvascular channels by cancer cells. VM requires cellular processes that are regulated by changes in cellular migration and morphology. Cofilin (CFL), a key regulator of actin depolymerization, has been reported to affect malignant phenotypes of cancer. We show that treatment with inhibitors of actin dynamics suppresses VM in MDA-MB-231 human breast cancer cells. We established CFL-knockout (KO) MDA-MB-231 cells and found that VM was attenuated in CFL-KO cells. Although the re-expression of wild-type CFL restored VM in CFL-KO cells, inactive phosphomimetic CFL failed to do so. Collectively, our results demonstrate that CFL is a critical regulator of VM and implicate CFL as a novel therapeutic target for breast cancer.

Impaired migration and premature differentiation underlie the neurological phenotype associated with PCDH12 loss of function

Protocadherins (PCDHs) are cell adhesion molecules that regulate many essential neurodevelopmental processes related to neuronal maturation, dendritic arbor formation, axon pathfinding, and synaptic plasticity. Bi-allelic loss-of-function variants in PCDH12 are associated with several neurodevelopmental disorders (NDDs) such as diencephalic-mesencephalic dysplasia syndrome, cerebral palsy, cerebellar ataxia, and microcephaly. Despite the highly deleterious outcome resulting from loss of PCDH12, little is known about its role during brain development and disease. Here, we show that PCDH12 loss severely impairs cerebral organoid development with reduced proliferative areas and disrupted laminar organization. 2D models further show that neural progenitor cells lacking PCDH12 prematurely exit cell cycle and differentiate earlier when compared to wildtype. Furthermore, we show that PCDH12 regulates neuronal migration through a mechanism requiring ADAM10-mediated ectodomain shedding and membrane recruitment of cytoskeleton regulators. Our data demonstrate a critical and broad involvement of PCDH12 in cortical development, revealing the pathogenic mechanisms underlying PCDH12-related NDDs.

Therapeutic potential of paeoniflorin in atherosclerosis: A cellular action and mechanism-based perspective

Epidemiological studies have shown that the incidence, prevalence and mortality of atherosclerotic cardiovascular disease (ASCVD) are increasing globally. Atherosclerosis is characterized as a chronic inflammatory disease which involves inflammation and immune dysfunction. P. lactiflora Pall. is a plant origin traditional medicine that has been widely used for the treatment of various diseases for more than a millennium in China, Japan and Korean. Paeoniflorin is a bioactive monomer extracted from P. lactiflora Pall. with anti-atherosclerosis effects. In this article, we comprehensively reviewed the potential therapeutic effects and molecular mechanism whereby paeoniflorin protects against atherosclerosis from the unique angle of inflammation and immune-related pathway dysfunction in vascular endothelial cells, smooth muscle cells, monocytes, macrophages, platelets and mast cells. Paeoniflorin, with multiple protective effects in atherosclerosis, has the potential to be used as a promising therapeutic agent for the treatment of atherosclerosis and its complications. We conclude with a detailed discussion of the challenges and future perspective of paeoniflorin in translational cardiovascular medicine.

Intracellular Protein Photoactivation Using Sterically Bulky Caging

Methods for intracellular protein photoactivation have been studied to elucidate the spatial and temporal roles of proteins of interest. In this study, an intracellular protein photoactivation method was developed using sterically bulky caging. The protein of interest was modified with biotin via a photocleavable linker, and then conjugated with streptavidin to sterically block the protein surface for inactivation. The caged protein was transduced into cells and reactivated by light-induced degradation of the conjugates. A cytotoxic protein, saporin, was caged and photoactivated both in vitro and in living cells with this method. This method achieved control of the cytotoxic activity in an off-on manner, introducing cell death selectively at the designed location using light. This simple and versatile photoactivation method is a promising tool for studying spatio-temporal cellular events that are related to intracellular proteins of interest.

Inka2, a novel Pak4 inhibitor, regulates actin dynamics in neuronal development

The actin filament is a fundamental part of the cytoskeleton defining cell morphology and regulating various physiological processes, including filopodia formation and dendritic spinogenesis of neurons. Serine/threonine-protein kinase Pak4, an essential effector, links Rho GTPases to control actin polymerization. Previously, we identified the Inka2 gene, a novel mammalian protein exhibiting sequence similarity to Inka1, which serves as a possible inhibitor for Pak4. Although Inka2 is dominantly expressed in the nervous system and involved in focal-adhesion dynamics, its molecular role remains unclear. Here, we found that Inka2-iBox directly binds to Pak4 catalytic domain to suppress actin polymerization. Inka2 promoted actin depolymerization and inhibited the formation of cellular protrusion caused by Pak4 activation. We further generated the conditional knockout mice of the Inka2 gene. The beta-galactosidase reporter indicated the preferential Inka2 expression in the dorsal forebrain neurons. Cortical pyramidal neurons of Inka2^-/- mice exhibited decreased density and aberrant morphology of dendritic spines with marked activation/phosphorylation of downstream molecules of Pak4 signal cascade, including LIMK and Cofilin. These results uncovered the unexpected function of endogenous Pak4 inhibitor in neurons. Unlike Inka1, Inka2 is a critical mediator for actin reorganization required for dendritic spine development.

Actin filaments are an essential part of the cytoskeleton defining cell morphology and regulating various cellular processes, such as cell migration and synapse formation in the brain. Actin polymerization is controlled by the kinase activity of the Pak4 signaling cascade, including LIMK and Cofilin. Previously, we identified the Inka2 gene, which is strongly expressed in the mammalian central nervous system and a similar sequence as Inka1. Inka1 was reported to serve as a Pak4 inhibitor in cancer cell lines; however, the physiological function of Inka2 is unclear. In this study, we found that (i) Inka2 overexpression inhibits the formation of cell-protrusion caused by Pak4 activation; (ii) Inka2 directly binds to the catalytic domain of Pak4 to inhibit intracellular actin polymerization; (iii) Inka2 is specifically expressed in neurons in the forebrain region, including the cerebral cortex and hippocampus that are known to be essential for brain plasticity, such as learning and memory; and (iv) cortical neurons of Inka2-deficient mice showed decreased synapse formation and abnormal spine morphology, probably due to the marked phosphorylation of LIMK and Cofilin. These results indicate that Inka2 is an endogenous Pak4 inhibitor in neurons required for normal synapse formation through the modulation of actin reorganization.

Methamphetamine induces transcriptional changes in cultured HIV-infected mature monocytes that may contribute to HIV neuropathogenesis

HIV-associated neurocognitive impairment (HIV-NCI) persists in 15-40% of people with HIV (PWH) despite effective antiretroviral therapy. HIV-NCI significantly impacts quality of life, and there is currently no effective treatment for it. The development of HIV-NCI is complex and is mediated, in part, by the entry of HIV-infected mature monocytes into the central nervous system (CNS). Once in the CNS, these cells release inflammatory mediators that lead to neuroinflammation, and subsequent neuronal damage. Infected monocytes may infect other CNS cells as well as differentiate into macrophages, thus contributing to viral reservoirs and chronic neuroinflammation. Substance use disorders in PWH, including the use of methamphetamine (meth), can exacerbate HIV neuropathogenesis. We characterized the effects of meth on the transcriptional profile of HIV-infected mature monocytes using RNA-sequencing. We found that meth mediated an upregulation of gene transcripts related to viral infection, cell adhesion, cytoskeletal arrangement, and extracellular matrix remodeling. We also identified downregulation of several gene transcripts involved in pathogen recognition, antigen presentation, and oxidative phosphorylation pathways. These transcriptomic changes suggest that meth increases the infiltration of mature monocytes that have a migratory phenotype into the CNS, contributing to dysregulated inflammatory responses and viral reservoir establishment and persistence, both of which contribute to neuronal damage. Overall, our results highlight potential molecules that may be targeted for therapy to limit the effects of meth on HIV neuropathogenesis.

Coro1B and Coro1C regulate lamellipodia dynamics and cell motility by tuning branched actin turnover

Actin filament dynamics must be precisely controlled in cells to execute behaviors such as vesicular trafficking, cytokinesis, and migration. Coronins are conserved actin-binding proteins that regulate several actin-dependent subcellular processes. Here, we describe a new conditional knockout cell line for two ubiquitous coronins, Coro1B and Coro1C. These coronins, which strongly co-localize with Arp2/3-branched actin, require Arp2/3 activity for proper subcellular localization. Coronin null cells have altered lamellipodial protrusion dynamics due to increased branched actin density and reduced actin turnover within lamellipodia, leading to defective haptotaxis. Surprisingly, excessive cofilin accumulates in coronin null lamellipodia, a result that is inconsistent with the current models of coronin-cofilin functional interaction. However, consistent with coronins playing a pro-cofilin role, coronin null cells have increased F-actin levels. Lastly, we demonstrate that the loss of coronins increases accompanied by an increase in cellular contractility. Together, our observations reveal that coronins are critical for proper turnover of branched actin networks and that decreased actin turnover leads to increased cellular contractility.

β-cells retain a pool of insulin-containing secretory vesicles regulated by adherens junctions and the cadherin binding protein p120 catenin

The β-cells of the islets of Langerhans are the sole producers of insulin in the human body. In response to rising glucose levels, insulin-containing vesicles inside β-cells fuse with the plasma membrane and release their cargo. However, the mechanisms regulating this process are only partly understood. Previous evidence indicated reductions in α-catenin elevate insulin release, while reductions in β-catenin decrease insulin release. α- and β-catenin contribute to cellular regulation in a range of ways but one is as members of the adherens junction complex and these contribute to the development of cell polarity in b-cells. Therefore, we investigated the effects of adherens junctions on insulin release. We show in INS-1E β-cells knockdown of either E- or N-cadherin had only small effects on insulin secretion, but simultaneous knockout of both cadherins resulted in a significant increase in basal insulin release to the same level as glucose-stimulated release. This double knockdown also significantly attenuated levels of p120 catenin, a cadherin binding partner involved in regulating cadherin turnover. Conversely, reducing p120 catenin levels with siRNA destabilized both E- and N-cadherin, and this was also associated with an increase in levels of insulin secreted from INS-1E cells. Furthermore, there were also changes in these cells consistent with higher insulin release, namely reductions in levels of F-actin and increased intracellular free Ca²⁺ levels in response to KCl-induced membrane depolarization. Taken together, these data provide evidence that adherens junctions play important roles in retaining a pool of insulin secretory vesicles within the cell and establish a role for p120 catenin in regulating this process.

Counting actin in contractile rings reveals novel contributions of cofilin and type II myosins to fission yeast cytokinesis

Cytokinesis by animals, fungi, and amoebas depends on actomyosin contractile rings, which are stabilized by continuous turnover of actin filaments. Remarkably little is known about the amount of polymerized actin in contractile rings, so we used low concentrations of GFP-Lifeact to count total polymerized actin molecules in the contractile rings of live fission yeast cells. Contractile rings of wild-type cells accumulated polymerized actin molecules at 4900/min to a peak number of ∼198,000 followed by a loss of actin at 5400/min throughout ring constriction. In adf1-M3 mutant cells with cofilin that severs actin filaments poorly, contractile rings accumulated polymerized actin at twice the normal rate and eventually had almost twofold more actin along with a proportional increase in type II myosins Myo2, Myp2, and formin Cdc12. Although 30% of adf1-M3 mutant cells failed to constrict their rings fully, the rest lost actin from the rings at the wild-type rates. Mutations of type II myosins Myo2 and Myp2 reduced contractile ring actin filaments by half and slowed the rate of actin loss from the rings.

Recent Advances in Protein Caging Tools for Protein Photoactivation

In biosciences and biotechnologies, it is recently critical to promote research regarding the regulation of the dynamic functions of proteins of interest. Light-induced control of protein activity is a strong tool for a wide variety of applications because light can be spatiotemporally irradiated in high resolutions. Therefore, synthetic, semi-synthetic, and genetic engineering techniques for photoactivation of proteins have been actively developed. In this review, the conventional approaches will be outlined. As a solution for overcoming barriers in conventional ones, our recent approaches in which proteins were chemically modified with biotinylated caging reagents are introduced to photo-activate a variety of proteins without genetic engineering and elaborate optimization. This review mainly focuses on protein caging and describes the concepts underlying the development of reported approaches that can contribute to the emergence of both novel protein photo-regulating methods and their killer applications.

Graphene Enhances Actin Filament Assembly Kinetics and Modulates NIH-3T3 Fibroblast Cell Spreading

Actin plays critical roles in various cellular functions, including cell morphogenesis, differentiation, and movement. The assembly of actin monomers into double-helical filaments is regulated in surrounding microenvironments. Graphene is an attractive nanomaterial that has been used in various biomaterial applications, such as drug delivery cargo and scaffold for cells, due to its unique physical and chemical properties. Although several studies have shown the potential effects of graphene on actin at the cellular level, the direct influence of graphene on actin filament dynamics has not been studied. Here, we investigate the effects of graphene on actin assembly kinetics using spectroscopy and total internal reflection fluorescence microscopy. We demonstrate that graphene enhances the rates of actin filament growth in a concentration-dependent manner. Furthermore, cell morphology and spreading are modulated in mouse embryo fibroblast NIH-3T3 cultured on a graphene surface without significantly affecting cell viability. Taken together, these results suggest that graphene may have a direct impact on actin cytoskeleton remodeling.

LIM Kinases in Osteosarcoma Development

Tumorigenesis is a long-term and multistage process that often leads to the formation of metastases. During this pathological course, two major events appear to be crucial: primary tumour growth and metastatic expansion. In this context, despite research and clinical advances during the past decades, bone cancers remain a leading cause of death worldwide among paediatric cancer patients. Osteosarcomas are the most common malignant bone tumours in children and adolescents. Notwithstanding advances in therapeutic treatments, many patients succumb to these diseases. In particular, less than 30% of patients who demonstrate metastases at diagnosis or are poor responders to chemotherapy survive 5 years after initial diagnosis. LIM kinases (LIMKs), comprising LIMK1 and LIMK2, are common downstream effectors of several signalization pathways, and function as a signalling node that controls cytoskeleton dynamics through the phosphorylation of the cofilin family proteins. In recent decades, several reports have indicated that the functions of LIMKs are mainly implicated in the regulation of actin microfilament and the control of microtubule dynamics. Previous studies have thus identified LIMKs as cancer-promoting regulators in multiple organ cancers, such as breast cancer or prostate cancer. This review updates the current understanding of LIMK involvement in osteosarcoma progression.

Dynamic Landscape of Extracellular Vesicle-Associated Proteins Is Related to Treatment Response of Patients with Metastatic Breast Cancer

Breast cancer is the leading cause of cancer death in women. The majority of these deaths are due to disease metastasis, in which cancer cells disseminate to multiple organs and disrupt vital physiological functions. It is widely accepted that breast cancer cells secrete extracellular vesicles (EVs), which contain dynamic molecular cargo that act as versatile mediators of intercellular communication. Therefore, Evs. secreted by breast cancer cells could be involved in the development of metastatic disease and resistance to treatment. Moreover, changes in EV cargo could reflect the effects of therapy on their parent tumor cells. The aim of this feasibility study was to quantitatively profile the proteomes of Evs. isolated from blood samples taken from treatment sensitive and resistant metastatic breast cancer patients to identify proteins associated with responses. Three serial blood samples were collected from three patients with metastatic breast cancer receiving systemic therapy including a responder, a non-responder, and a mixed-responder. Evs. were isolated from plasma using size exclusion chromatography and their protein cargo was prepared for tandem mass tag (TMT)-labelling and quantitative analyses using two-dimensional high-performance liquid chromatography followed by tandem mass spectrometry. After filtering, we quantitatively identified 286 proteins with high confidence using a q value of 0.05. Of these, 149 were classified as EV associated candidate proteins and 137 as classical, high abundant plasma proteins. After comparing EV protein abundance between the responder and non-responder, we identified 35 proteins with unique de-regulated abundance patterns that was conserved at multiple time points. We propose that this proof-of-concept approach can be used to identify proteins which have potential as predictors of metastatic breast cancer response to treatment.

Pharmacology, Toxicology, and Metabolism of Sennoside A, A Medicinal Plant-Derived Natural Compound

Sennoside A (SA) is a natural dianthrone glycoside mainly from medicinal plants of Senna and Rhubarb, and used as a folk traditional irritant laxative and slimming health food. Accumulating evidences suggest that SA possesses numerous pharmacological properties, such as laxative, anti-obesity, hypoglycemic, hepatoprotective, anti-fibrotic, anti-inflammatory, anti-tumor, anti-bacterial, anti-fungal, anti-viral, and anti-neurodegenerative activities. These pharmacological effects lay the foundation for its potential application in treating a variety of diseases. However, numerous published studies suggest that a long-term use of SA in large doses may have some adverse effects, including the occurrence of melanosis coli and carcinogenesis of colon cancer, thereby limiting its clinical use. It remains to be established whether SA or its metabolites are responsible for the pharmacological and toxicity effects. In this review, the latest advances in the pharmacology, toxicology, and metabolism of SA were summarizedbased on its biological characteristics and mechanism.

Neurobiological Opportunities in Diabetic Polyneuropathy

This review highlights a selection of potential translational directions for the treatment of diabetic polyneuropathy (DPN) currently irreversible and without approved interventions beyond pain management. The list does not include all diabetic targets that have been generated over several decades of research but focuses on newer work. The emphasis is firstly on approaches that support the viability and growth of peripheral neurons and their ability to withstand a barrage of diabetic alterations. We include a section describing Schwann cell targets and finally how mitochondrial damage has been a common element in discussing neuropathic damage. Most of the molecules and pathways described here have not yet reached clinical trials, but many trials have been negative to date. Nonetheless, these failures clear the pathway for new thoughts over reversing DPN.

Triggering biological processes: methods and applications of photocaged peptides and proteins

There has been a significant push in recent years to deploy fundamental knowledge and methods of photochemistry toward biological ends. Photoreactive groups have enabled chemists to activate biological function using the concept of photocaging. By granting spatiotemporal control over protein activation, these photocaging methods are fundamental in understanding biological processes. Peptides and proteins are an important group of photocaging targets that present conceptual and technical challenges, requiring precise chemoselectivity in complex polyfunctional environments. This review focuses on recent advances in photocaging techniques and methodologies, as well as their use in living systems. Photocaging methods include genetic and chemical approaches that require a deep understanding of structure-function relationships based on subtle changes in primary structure. Successful implementation of these ideas can shed light on important spatiotemporal aspects of living systems.

Progesterone triggers Rho kinase-cofilin axis during in vitro and in vivo endometrial decidualization

STUDY QUESTION

Can a combination of the focussed protein kinase assays and a wide-scale proteomic screen pinpoint novel, clinically relevant players in decidualization in vitro and in vivo?

SUMMARY ANSWER

Rho-dependent protein kinase (ROCK) activity is elevated in response to the combined treatment with progesterone and 8-Br-cAMP during in vitro decidualization, mirrored by increase of ROCK2 mRNA and protein levels and the phosphorylation levels of its downstream target Cofilin-1 (CFL1) in secretory versus proliferative endometrium.

WHAT IS KNOWN ALREADY

Decidualization is associated with extensive changes in gene expression profile, proliferation, metabolism and morphology of endometrium, yet only a few underlying molecular pathways have been systematically explored. In vitro decidualization of endometrial stromal cells (ESCs) can be reportedly induced using multiple protocols with variable physiological relevance. In our previous studies, cyclic AMP (cAMP)/cAMP-dependent protein kinase (PKA)/prolactin axis that is classically upregulated during decidualization showed dampened activation in ESCs isolated from polycystic ovary syndrome (PCOS) patients as compared to controls.

STUDY DESIGN, SIZE, DURATION

In vitro decidualization studies were carried out in passage 2 ESCs isolated from controls (N = 15) and PCOS patients (N = 9). In parallel, lysates of non-cultured ESCs isolated from proliferative (N = 4) or secretory (N = 4) endometrial tissue were explored. The observed trends were confirmed using cryo-cut samples of proliferative (N = 3) or secretory endometrium (N = 3), and in proliferative or secretory full tissue samples from controls (N = 8 and N = 9, respectively) or PCOS patients (N = 10 for both phases).

PARTICIPANTS/MATERIALS, SETTING, METHODS

The activities of four target kinases were explored using kinase-responsive probes and selective inhibitors in lysates of in vitro decidualized ESCs and non-cultured ESCs isolated from tissue at different phases of the menstrual cycle. In the latter lysates, wide-scale proteomic and phosphoproteomic studies were further carried out. ROCK2 mRNA expression was explored in full tissue samples from controls or PCOS patients. The immunofluorescent staining of phosphorylated CFL1 was performed in full endometrial tissue samples, and in the in vitro decidualized fixed ESCs from controls or PCOS patients. Finally, the cellular migration properties were explored in live in vitro decidualized ESCs.

MAIN RESULTS AND THE ROLE OF CHANCE

During in vitro decidualization, the activities of PKA, protein kinase B (Akt/PKB), and ROCK are increased while the activity of casein kinase 2 (CK2) is decreased; these initial trends are observable after 4-day treatment (P < 0.05) and are further augmented following the 9-day treatment (P < 0.001) with mixtures containing progesterone and 8-Br-cAMP or forskolin. The presence of progesterone is necessary for activation of ROCK, yet it is dispensable in the case of PKA and Akt/PKB; in comparison to controls, PCOS patient-derived ESCs feature dampened response to progesterone. In non-cultured ESCs isolated from secretory vs proliferative phase tissue, only activity of ROCK is increased (P < 0.01). ROCK2 protein levels are slightly elevated in secretory versus proliferative ESCs (relative mean standard deviation < 50%), and ROCK2 mRNA is elevated in mid-secretory versus proliferative full tissue samples (P < 0.05) obtained from controls but not PCOS patients. Activation of ROCK2 downstream signalling results in increase of phospho-S3 CFL1 in secretory endometrium (P < 0.001) as well as in vitro decidualized ESCs (P < 0.01) from controls but not PCOS patients. ROCK2-triggered alterations in the cytoskeleton are reflected by the significantly decreased motility of in vitro decidualized ESCs (P < 0.05).

LARGE SCALE DATA

Proteomic and phosphoproteomic data are available via ProteomeXchange with identifier PXD026243.

LIMITATIONS, REASONS FOR CAUTION

The number of biological samples was limited. The duration of protocol for isolation of non-cultured ESCs from tissue can potentially affect phosphorylation pathways in cells, yet the possible artefacts were minimized by the identical treatment of proliferative and secretory samples.

WIDER IMPLICATIONS OF THE FINDINGS

The study demonstrated the benefits of combining the focussed kinase activity assay with wide-scale phosphoproteomics and showed the need for detailed elaboration of the in vitro decidualization protocols. ROCK was identified as the novel target of interest in decidualization, which requires closer attention in further studies-including the context of decidualization-related subfertility and infertility.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by the Estonian Ministry of Education and Research, and the Estonian Research Council (PRG1076, PRG454, PSG230 and PSG608), Enterprise Estonia (EU48695), Horizon 2020 innovation grant (ERIN, Grant no. EU952516) of the European Commission, the COMBIVET ERA Chair, H2020-WIDESPREAD-2018-04 (Grant agreement no. 857418), the Academy of Finland (Project grants 315921 and 321763), the Finnish Medical Foundation and The Sigrid Juselius Foundation. The authors confirm that they have no conflict of interest with respect to the content of this article.

Sirolimus Suppresses Phosphorylation of Cofilin and Reduces Interstitial Septal Thickness in Sporadic Lymphangioleiomyomatosis

Sporadic lymphangioleiomyomatosis (S-LAM) is a rare lung disease characterized by the proliferation of smooth muscle-like LAM cells and progressive cystic destruction. Sirolimus, a mammalian target of rapamycin (mTOR) inhibitor, has a proven efficacy in patients with LAM. However, the therapeutic mechanisms of sirolimus in LAM remain unclear. We aimed to evaluate sirolimus-related lung parenchymal changes and the potential effect in LAM cells and modulating pathological cystic destruction. Lung specimens were examined for histopathological changes by HMB45 staining and compared the LAM patients treated with and without sirolimus. We detected the overexpression of mTOR, HMB45, and phosphorylation of cofilin (p-cofilin) in LAM patients. Sirolimus showed efficacy in patients with LAM, who exhibited a reduced expression of mTOR and p-cofilin as well as reduced interstitial septal thickness. In addition, sirolimus suppresses mTOR and p-cofilin, thus suppressing the migration and proliferation of LAM cells isolated from the patient's lung tissue. This study demonstrates that interstitial septal thickness, as determined by histological structural analysis. Sirolimus effectively reduced the expression of p-cofilin and interstitial septal thickness, which may be a novel mechanism by sirolimus. Moreover, we develop a new method to isolate and culture the LAM cell, which can test the possibility of medication in vitro and impact this current study has on the LAM field. The development of approaches to interfere with mTOR-cofilin1-actin signaling may result in an option for S-LAM therapy.

Morphofunctional programming of microglia requires distinct roles of type II myosins

The ramified morphology of microglia and the dynamics of their membrane protrusions are essential for their functions in central nervous system development, homeostasis, and disease. Although their ability to change and control shape critically depends on the actin and actomyosin cytoskeleton, the underlying regulatory mechanisms remain largely unknown. In this study, we systematically analyzed the actomyosin cytoskeleton and regulators downstream of the small GTPase RhoA in the control of microglia shape and function. Our results reveal that (i) Myh9 controls cortical tension levels and affects microglia protrusion formation, (ii) cofilin-mediated maintenance of actin turnover regulates microglia protrusion extension, and (iii) Myh10 influences microglia inflammatory activation. Overall we uncover molecular pathways that regulate microglia morphology and identify type-II myosins as important regulators of microglia biology with differential roles in the control of cell shape (Myh9) and functions (Myh10).

Sterically Bulky Caging of Transferrin for Photoactivatable Intracellular Delivery

Photoactivatable ligand proteins are potentially useful for light-induced intracellular delivery of therapeutic and diagnostic cargos through receptor-mediated cellular uptake. Here, we report the simple and effective caging of transferrin (Tf), a representative ligand protein with cellular uptake ability, which has been used in the delivery of various cargos. Tf was modified with several biotin molecules through a photocleavable linker, and then the biotinylated Tf (bTf) was conjugated with the biotin-binding protein, streptavidin (SA), to provide steric hindrance to block the interaction with the Tf receptor. Without exposure to light, the cellular uptake of the bTf-SA complex was effectively inhibited. In response to light exposure, the complex was degraded with the release of Tf, leading to cellular uptake of Tf. Similarly, the cellular uptake of Tf-doxorubicin (Dox) conjugates could be suppressed by caging with biotinylation and SA binding, and the intracellular delivery of Dox could be triggered in a light-dependent manner. The intracellularly accumulated Dox decreased the cell viability to 25% because of the cell growth inhibitory effect of Dox. These results provided proof of principle that the caged Tf can be employed as a photoactivatable molecular device for the intracellular delivery of cargos.

Arginine-dependent immune responses

A growing body of evidence indicates that, over the course of evolution of the immune system, arginine has been selected as a node for the regulation of immune responses. An appropriate supply of arginine has long been associated with the improvement of immune responses. In addition to being a building block for protein synthesis, arginine serves as a substrate for distinct metabolic pathways that profoundly affect immune cell biology; especially macrophage, dendritic cell and T cell immunobiology. Arginine availability, synthesis, and catabolism are highly interrelated aspects of immune responses and their fine-tuning can dictate divergent pro-inflammatory or anti-inflammatory immune outcomes. Here, we review the organismal pathways of arginine metabolism in humans and rodents, as essential modulators of the availability of this semi-essential amino acid for immune cells. We subsequently review well-established and novel findings on the functional impact of arginine biosynthetic and catabolic pathways on the main immune cell lineages. Finally, as arginine has emerged as a molecule impacting on a plethora of immune functions, we integrate key notions on how the disruption or perversion of arginine metabolism is implicated in pathologies ranging from infectious diseases to autoimmunity and cancer.

Coactosin Promotes F-Actin Protrusion in Growth Cones Under Cofilin-Related Signaling Pathway

During brain development, axon outgrowth and its subsequent pathfinding are reliant on a highly motile growth cone located at the tip of the axon. Actin polymerization that is regulated by actin-depolymerizing factors homology (ADF-H) domain-containing family drives the formation of lamellipodia and filopodia at the leading edge of growth cones for axon guidance. However, the precise localization and function of ADF-H domain-containing proteins involved in axon extension and retraction remain unclear. We have previously shown that transcripts and proteins of coactosin-like protein 1 (COTL1), an ADF-H domain-containing protein, are observed in neurites and axons in chick embryos. Coactosin overexpression analysis revealed that this protein was localized to axonal growth cones and involved in axon extension in the midbrain. We further examined the specific distribution of coactosin and cofilin within the growth cone using superresolution microscopy, structured illumination microscopy, which overcomes the optical diffraction limitation and is suitable to the analysis of cellular dynamic movements. We found that coactosin was tightly associated with F-actin bundles at the growth cones and that coactosin overexpression promoted the expansion of lamellipodia and extension of growth cones. Coactosin knockdown in oculomotor neurons resulted in an increase in the levels of the inactive, phosphorylated form of cofilin and dysregulation of actin polymerization and axonal elongation, which suggests that coactosin promoted axonal growth in a cofilin-dependent manner. Indeed, the application of a dominant-negative form of LIMK1, a downstream effector of GTPases, reversed the effect of coactosin knockdown on axonal growth by enhancing cofilin activity. Combined, our results indicate that coactosin functions promote the assembly of protrusive actin filament arrays at the leading edge for growth cone motility.

Nyap1 Regulates Multipolar-Bipolar Transition and Morphology of Migrating Neurons by Fyn Phosphorylation during Corticogenesis

The coordination of cytoskeletal regulation is a prerequisite for proper neuronal migration during mammalian corticogenesis. Neuronal tyrosine-phosphorylated adaptor for the phosphoinositide 3-kinase 1 (Nyap1) is a member of the Nyap family of phosphoproteins, which has been studied in neuronal morphogenesis and is involved in remodeling of the actin cytoskeleton. However, the precise role of Nyap1 in neuronal migration remains unknown. Here, overexpression and knockdown of Nyap1 in the embryonic neocortex of mouse by in utero electroporation-induced abnormal morphologies and multipolar-bipolar transitions of migrating neurons. The level of phosphorylated Nyap1 was crucial for neuronal migration and morphogenesis in neurons. Furthermore, Nyap1 regulated neuronal migration as a downstream target of Fyn, a nonreceptor protein-tyrosine kinase that is a member of the Src family of kinases. Importantly, Nyap1 mediated the role of Fyn in the multipolar-bipolar transition of migrating neurons. Taken together, these results suggest that cortical radial migration is regulated by a molecular hierarchy of Fyn via Nyap1.

Two-photon absorption enhancement for organic acceptor molecules with QD antennas

The photophysics of an inorganic/organic hybrid system was studied by time-resolved optical spectroscopy, focusing on the goal of increasing the two-photon efficiency of photoresponsive systems. The hybrid system consists of CdS/ZnS core/shell quantum dots (QDs) as energy donor and coumarin derivatives as energy acceptor molecules. The spectral overlap of QD emission and coumarin 343 absorption promotes a Förster resonance energy tranfer (FRET) mechanism leading to a FRET efficiency up to nearly 90%. Additionally, time-correlated single photon counting showed a faster fluorescence decay while acceptor molecules were attached to the QD surface. Femtosecond transient absorption measurements demonstrated an ultrafast FRET reaction. Importantly, FRET was observed also after two-photon excitation of the QDs indicating that the chosen QDs can act as two-photon antennas.

The multiple roles of actin-binding proteins at invadopodia

Invadopodia are actin-rich membrane protrusions that facilitate cancer cell dissemination by focusing on proteolytic activity and clearing paths for migration through physical barriers, such as basement membranes, dense extracellular matrices, and endothelial cell junctions. Invadopodium formation and activity require spatially and temporally regulated changes in actin filament organization and dynamics. About three decades of research have led to a remarkable understanding of how these changes are orchestrated by sequential recruitment and coordinated activity of different sets of actin-binding proteins. In this chapter, we provide an update on the roles of the actin cytoskeleton during the main stages of invadopodium development with a particular focus on actin polymerization machineries and production of pushing forces driving extracellular matrix remodeling.

Actin at stereocilia tips is regulated by mechanotransduction and ADF/cofilin

Stereocilia on auditory sensory cells are actin-based protrusions that mechanotransduce sound into an electrical signal. These stereocilia are arranged into a bundle with three rows of increasing length to form a staircase-like morphology that is required for hearing. Stereocilia in the shorter rows, but not the tallest row, are mechanotransducing because they have force-sensitive channels localized at their tips. The onset of mechanotransduction during mouse postnatal development refines stereocilia length and width. However, it is unclear how actin is differentially regulated between stereocilia in the tallest row of the bundle and the shorter, mechanotransducing rows. Here, we show actin turnover is increased at the tips of mechanotransducing stereocilia during bundle maturation. Correspondingly, from birth to postnatal day 6, these stereocilia had increasing amounts of available actin barbed ends, where monomers can be added or lost readily, as compared with the non-mechanotransducing stereocilia in the tallest row. The increase in available barbed ends depended on both mechanotransduction and MYO15 or EPS8, which are required for the normal specification and elongation of the tallest row of stereocilia. We also found that loss of the F-actin-severing proteins ADF and cofilin-1 decreased barbed end availability at stereocilia tips. These proteins enriched at mechanotransducing stereocilia tips, and their localization was perturbed by the loss of mechanotransduction, MYO15, or EPS8. Finally, stereocilia lengths and widths were dysregulated in Adf and Cfl1 mutants. Together, these data show that actin is remodeled, likely by a severing mechanism, in response to mechanotransduction.

Altered Actin Dynamics in Cell Migration of GNE Mutant Cells

Cell migration is an essential cellular process that requires coordination of cytoskeletal dynamics, reorganization, and signal transduction. The actin cytoskeleton is central in maintaining the cellular structure as well as regulating the mechanisms of cell motility. Glycosylation, particularly sialylation of cell surface proteins like integrins, regulates signal transduction from the extracellular matrix to the cytoskeletal network. The activation of integrin by extracellular cues leads to recruitment of different focal adhesion complex proteins (Src, FAK, paxillin, etc.) and activates the signal including Rho GTPases for the regulation of actin assembly and disassembly. During cell migration, the assembly and disassembly of actin filament provides the essential force for the cell to move. Abnormal sialylation can lead to actin signaling dysfunction leading to aberrant cell migration, one of the main characteristics of cancer and myopathies. In the present study, we have reported altered F-actin to G-actin ratios in GNE mutated cells. These cells exhibit pathologically relevant mutations of GNE (UDP N-acetylneuraminic 2-epimerase/N-acetylmannosamine kinase), a key sialic acid biosynthetic enzyme. It was found that GNE neither affects the actin polymerization nor binds directly to actin. However, mutation in GNE resulted in increased binding of α-actinin to actin filaments. Further, through confocal imaging, GNE was found to be localized in focal adhesion complex along with paxillin. We further elucidated that mutation in GNE resulted in upregulation of RhoA protein and Cofilin activity is downregulated, which could be rescued with Rhosin and chlorogenic acid, respectively. Lastly, mutant in GNE reduced cell migration as implicated from wound healing assay. Our study indicates that molecules altering Cofilin function could significantly revert the cell migration defect due to GNE mutation in sialic acid-deficient cells. We propose cytoskeletal proteins to be alternate drug targets for disorders associated with GNE such as GNE myopathy.

Targeting the cytoskeleton against metastatic dissemination

Cancer is a pathology characterized by a loss or a perturbation of a number of typical features of normal cell behaviour. Indeed, the acquisition of an inappropriate migratory and invasive phenotype has been reported to be one of the hallmarks of cancer. The cytoskeleton is a complex dynamic network of highly ordered interlinking filaments playing a key role in the control of fundamental cellular processes, like cell shape maintenance, motility, division and intracellular transport. Moreover, deregulation of this complex machinery contributes to cancer progression and malignancy, enabling cells to acquire an invasive and metastatic phenotype. Metastasis accounts for 90% of death from patients affected by solid tumours, while an efficient prevention and suppression of metastatic disease still remains elusive. This results in the lack of effective therapeutic options currently available for patients with advanced disease. In this context, the cytoskeleton with its regulatory and structural proteins emerges as a novel and highly effective target to be exploited for a substantial therapeutic effort toward the development of specific anti-metastatic drugs. Here we provide an overview of the role of cytoskeleton components and interacting proteins in cancer metastasis with a special focus on small molecule compounds interfering with the actin cytoskeleton organization and function. The emerging involvement of microtubules and intermediate filaments in cancer metastasis is also reviewed.

Cofilin: A Promising Protein Implicated in Cancer Metastasis and Apoptosis

Cofilin is an actin-binding protein that regulates filament dynamics and depolymerization. The over-expression of cofilin is observed in various cancers, cofilin promotes cancer metastasis by regulating cytoskeletal reorganization, lamellipodium formation and epithelial-to-mesenchymal transition. Clinical treatment of cancer regarding cofilin has been explored in aspects of tumor cells apoptosis and cofilin related miRNAs. This review addresses the structure and phosphorylation of cofilin and describes recent findings regarding the function of cofilin in regulating cancer metastasis and apoptosis in tumor cells.

In Vitro Models for Studying Tumor Progression

Beyond cell proliferation, one of the most outstanding characteristics of the cancerous cells that promotes the tumoral progression is their high capacity to migrate and invade the surrounding healthy tissue. These cellular processes (migration and invasion) are critical steps to metastasis. Metastatic progression of the tumors is often the leading cause of morbidity and mortality in cancer patients. Critical genes and cell signaling pathways involved in cell migration and invasion of tumor cells have been identified, and several clinical efforts to alleviate cancer are focused on them; however, once the tumor has metastasized, it is extremely difficult to stop the progression of very aggressive forms of cancer such as glioblastomas. Therefore, it is crucial to elucidate the specific molecular mechanisms underlying tumor progression. In this chapter, we describe some methods to study tumor progression by assessing migration and cell invasion in 2D and 3D cell culture conditions.

Thermally Triggered, Cell-Specific Enzymatic Glyco-Editing: In Situ Regulation of Lectin Recognition and Immune Response on Target Cells

In situ glyco-editing on the cell surface can endow cellular glycoforms with new structures and properties; however, the lack of cell specificity and dependence on cells' endogenous functions plague the revelation of cellular glycan recognition properties and hamper the application of glyco-editing in complicated authentic biosystems. Herein, we develop a thermally triggered, cell-specific glyco-editing method for regulation of lectin recognition on target live cells in both single- and cocultured settings. The method relies on the aptamer-mediated anchoring of microgel-encapsulated neuraminidase on target cells and subsequent thermally triggered enzyme release for localized sialic acid (Sia) trimming. This temperature-based enzyme accessibility modulation strategy exempts genetic or metabolic engineering operations and, thus for the first time, enables tumor-specific desialylation on complicated tissue slices. The proposed method also provides an unprecedented opportunity to potentiate the innate immune response of natural killer cells toward target tumor cells through thermally triggered cell-specific desialylation, which paves the way for in vivo glycoimmune-checkpoint-targeted cancer therapeutic intervention.

Outlining cell interaction and inflammatory cytokines on UV-photofunctionalized mixed-phase TiO2 thin film

Photofunctionalization mediated by ultraviolet (UV) light seems to be a promising approach to improve the physico-chemical characteristics and the biological response of titanium (Ti) dental implants. Seeing that photofunctionalization is able to remove carbon from the surface, besides to promote reactions on the titanium dioxide (TiO₂) layer, coating the Ti with a stable TiO₂ film could potentialize the UV effect. Thus, here we determined the impact of UV-photofunctionalized mixed-phase (anatase and rutile) TiO₂ films on the physico-chemical properties of Ti substrate and cell biology. Mixed-phase TiO₂ films were grown by radiofrequency magnetron sputtering on commercially pure titanium (cpTi) discs, and samples were divided as follow: cpTi (negative control), TiO₂ (positive control), cpTi UV, TiO₂ UV (experimental). Photofunctionalization was performed using UVA (360 nm - 40 W) and UVC (250 nm - 40 W) lamps for 48 h. Surfaces were analyzed in terms of morphology, topography, chemical composition, crystalline phase, wettability and surface free energy. Pre-osteoblastic cells (MC3T3E1) were used to assess cell morphology and adhesion, metabolism, mineralization potential and cytokine secretion (IFN-γ, TNF-α, IL-4, IL-6 and IL-17). TiO₂-coated surfaces exhibited granular surface morphology and greater roughness. Photofunctionalization increased wettability (p < 0.05) and surface free energy (p < 0.001) on both surface conditions. TiO₂-treated groups featured normal cell morphology and spreading, and greater cellular metabolic activity at 2 and 4 days (p < 0.05), whereas UV-photofunctionalized surfaces enhanced cell metabolism, cell adhered area, and calcium deposition (day 14) (p < 0.05). In general, assessed proteins were found slightly affected by either UV or TiO₂ treatments. Altogether, our findings suggest that UV-photofunctionalized TiO₂ surface has the potential to improve pre-osteoblastic cell differentiation and the ability of cells to form mineral nodules by modifying Ti physico-chemical properties towards a more stable context. UV-modified surfaces modulate the secretion of key inflammatory markers.