Rac regulates the interaction of fascin with protein kinase C in cell migration

Dynamic phosphorylation of Fascin-1 orchestrates microglial phagocytosis and neurological recovery after spinal cord injury

The persistence of myelin debris after spinal cord injury (SCI) constitutes a formidable barrier to axonal regeneration, remyelination, and functional recovery by initiating inflammatory cascades. Microglia, known for their superior phagocytic and degradative capabilities, are crucial in clearing myelin debris. Yet, the molecular mechanisms governing their function remain elusive. Our previous research has identified a sustained upregulation of Fascin-1, an actin-binding protein essential for phagocytosis, in Cx3cr1+ microglia after SCI. Here, we reveal that ablation of microglial Fascin-1 exacerbates neuronal loss and hampers motor recovery after SCI, correlating with diminished microglial phagocytic activity in Cx3cr1cre+/-;Fascin-1fl/fl mice. We demonstrated that dysregulated Fascin-1 phosphorylation impairs microglial phagocytosis, linked to the upstream Mas1/Protein kinase C gamma (PKCγ) axis. Pharmacologic activation of the Mas1/PKC axis to drive Fascin-1 phosphorylation in microglia restores phagocytic function, thereby alleviating neuronal loss and facilitating neurological recovery after SCI. Our findings underscore the critical role of Fascin-1 phosphorylation in microglial phagocytosis and highlight the Mas1/PKCγ axis as a promising therapeutic target for SCI.

The crucial role of fascin-1 in the pathogenesis, metastasis, and chemotherapeutic resistance of breast cancer

Breast cancer (BC) is the most common type of cancer in women to be diagnosed, and it is also the second leading cause of cancer death in women globally. It is the disease that causes the most life years adjusted for disability lost among women, making it a serious worldwide health issue. Understanding and interpreting carcinogenesis and metastatic pathways is critical for curing malignancy. Fascin-1 was recognized as an actin-bundling protein with parallel, rigid bundles as a result of the cross-linking of F-actin microfilaments. Increasing levels of fascin-1 have been associated with bad prognostic profiles, aggressiveness of clinical courses, and poor survival outcomes in a variety of human malignancies. Cancer cells that overexpress fascin-1 have higher capabilities for proliferation, invasion, migration, and metastasis. Fascin-1 is being considered as a potential target for therapy as well as a potential biomarker for diagnostics in a variety of cancer types. This review aims to provide an overview of the FSCN1 gene and its protein structure, elucidate its physiological and pathological roles, and throw light on its involvement in the initiation, development, and chemotherapeutic resistance of BC.

Protein Kinase C at the Crossroad of Mutations, Cancer, Targeted Therapy and Immune Response

The frequent PKC dysregulations observed in many tumors have made these enzymes natural targets for anticancer applications. Nevertheless, this considerable interest in the development of PKC modulators has not led to the expected therapeutic benefits, likely due to the complex biological activities regulated by PKC isoenzymes, often playing ambiguous and protective functions, further driven by the occurrence of mutations. The structure, regulation and functions of PKCs have been extensively covered in other publications. Herein, we focused on PKC alterations mostly associated with complete functional loss. We also addressed the modest yet encouraging results obtained targeting PKC in selected malignancies and the more frequent negative clinical outcomes. The reported observations advocate the need for more selective molecules and a better understanding of the involved pathways. Furthermore, we underlined the most relevant immune mechanisms controlled by PKC isoforms potentially impacting the immune checkpoint inhibitor blockade-mediated immune recovery. We believe that a comprehensive examination of the molecular features of the tumor microenvironment might improve clinical outcomes by tailoring PKC modulation. This approach can be further supported by the identification of potential response biomarkers, which may indicate patients who may benefit from the manipulation of distinctive PKC isoforms.

Cytoskeletal and Cytoskeleton-Associated Proteins: Key Regulators of Cancer Stem Cell Properties

Cancer stem cells (CSCs) are a subpopulation of cancer cells possessing stemness characteristics that are closely associated with tumor proliferation, recurrence and resistance to therapy. Recent studies have shown that different cytoskeletal components and remodeling processes have a profound impact on the behavior of CSCs. In this review, we outline the different cytoskeletal components regulating the properties of CSCs and discuss current and ongoing therapeutic strategies targeting the cytoskeleton. Given the many challenges currently faced in targeted cancer therapy, a deeper comprehension of the molecular events involved in the interaction of the cytoskeleton and CSCs will help us identify more effective therapeutic strategies to eliminate CSCs and ultimately improve patient survival.

Nuclear fascin regulates cancer cell survival

Fascin is an important regulator of F-actin bundling leading to enhanced filopodia assembly. Fascin is also overexpressed in most solid tumours where it supports invasion through control of F-actin structures at the periphery and nuclear envelope. Recently, fascin has been identified in the nucleus of a broad range of cell types but the contributions of nuclear fascin to cancer cell behaviour remain unknown. Here, we demonstrate that fascin bundles F-actin within the nucleus to support chromatin organisation and efficient DDR. Fascin associates directly with phosphorylated Histone H3 leading to regulated levels of nuclear fascin to support these phenotypes. Forcing nuclear fascin accumulation through the expression of nuclear-targeted fascin-specific nanobodies or inhibition of Histone H3 kinases results in enhanced and sustained nuclear F-actin bundling leading to reduced invasion, viability, and nuclear fascin-specific/driven apoptosis. These findings represent an additional important route through which fascin can support tumourigenesis and provide insight into potential pathways for targeted fascin-dependent cancer cell killing.

The role of fascin-1 in the pathogenesis, diagnosis and management of respiratory related cancers

Human cancer statistics report that respiratory related cancers such as lung, laryngeal, oral and nasopharyngeal cancers account for a large proportion of tumors, and tumor metastasis remains the major reason for patient death. The metastasis of tumor cells requires actin cytoskeleton remodeling, in which fascin-1 plays an important role. Fascin-1 can cross-link F-actin microfilaments into bundles and form finger-like cell protrusions. Some studies have shown that fascin-1 is overexpressed in human tumors and is associated with tumor growth, migration and invasion. The role of fascin-1 in respiratory related cancers is not very clear. The main purpose of this study was to provide an updated literature review on the role of fascin-1 in the pathogenesis, diagnosis and management of respiratory related cancers. These studies suggested that fascin-1 can serve as an emerging biomarker and potential therapeutic target, and has attracted widespread attention.

Two Sides of the Same Coin: Protein Kinase C γ in Cancer and Neurodegeneration

Protein kinase C (PKC) isozymes transduce myriad signals within the cell in response to the generation of second messengers from membrane phospholipids. The conventional isozyme PKCγ reversibly binds Ca2+ and diacylglycerol, which leads to an open, active conformation. PKCγ expression is typically restricted to neurons, but evidence for its expression in certain cancers has emerged. PKC isozymes have been labeled as oncogenes since the discovery that they bind tumor-promoting phorbol esters, however, studies of cancer-associated PKC mutations and clinical trial data showing that PKC inhibitors have worsened patient survival have reframed PKC as a tumor suppressor. Aberrant expression of PKCγ in certain cancers suggests a role outside the brain, although whether PKCγ also acts as a tumor suppressor remains to be established. On the other hand, PKCγ variants associated with spinocerebellar ataxia type 14 (SCA14), a neurodegenerative disorder characterized by Purkinje cell degeneration, enhance basal activity while preventing phorbol ester-mediated degradation. Although the basis for SCA14 Purkinje cell degeneration remains unknown, studies have revealed how altered PKCγ activity rewires cerebellar signaling to drive SCA14. Importantly, enhanced basal activity of SCA14-associated mutants inversely correlates with age of onset, supporting that enhanced PKCγ activity drives SCA14. Thus, PKCγ activity should likely be inhibited in SCA14, whereas restoring PKC activity should be the goal in cancer therapies. This review describes how PKCγ activity can be lost or gained in disease and the overarching need for a PKC structure as a powerful tool to predict the effect of PKCγ mutations in disease.

Targeted Inhibition of O-Linked β-N-Acetylglucosamine Transferase as a Promising Therapeutic Strategy to Restore Chemosensitivity and Attenuate Aggressive Tumor Traits in Chemoresistant Urothelial Carcinoma of the Bladder

Acquisition of acquired chemoresistance during treatment cycles in urothelial carcinoma of the bladder (UCB) is the major cause of death through enhancing the risk of cancer progression and metastasis. Elevated glucose flux through the abnormal upregulation of O-linked β-N-acetylglucosamine (O-GlcNAc) transferase (OGT) controls key signaling and metabolic pathways regulating diverse cancer cell phenotypes. This study showed that OGT expression levels in two human UCB cell models with acquired resistance to gemcitabine and paclitaxel were significantly upregulated compared with those in parental cells. Reducing hyper-O-GlcNAcylation by OGT knockdown (KD) markedly facilitated chemosensitivity to the corresponding chemotherapeutics in both cells, and combination treatment with OGT-KD showed more severe growth defects in chemoresistant sublines. We subsequently verified the suppressive effects of OGT-KD monotherapy on cell migration/invasion in vitro and xenograft tumor growth in vivo in chemoresistant UCB cells. Transcriptome analysis of these cells revealed 97 upregulated genes, which were enriched in multiple oncogenic pathways. Our final choice of suspected OGT glycosylation substrate was VCAN, S1PR3, PDGFRB, and PRKCG, the knockdown of which induced cell growth defects. These findings demonstrate the vital role of dysregulated OGT activity and hyper-O-GlcNAcylation in modulating treatment failure and tumor aggression in chemoresistant UCB.

The Actin Bundling Protein Fascin-1 as an ACE2-Accessory Protein

We have previously shown that angiotensin-converting enzyme 2 (ACE2), an enzyme counterbalancing the deleterious effects of angiotensin type 1 receptor activation by production of vasodilatory peptides Angiotensin (Ang)-(1-9) and Ang-(1-7), is internalized and degraded in lysosomes following chronic Ang-II treatment. However, the molecular mechanisms involved in this effect remain unknown. In an attempt to identify the accessory proteins involved in this effect, we conducted a proteomic analysis in ACE2-transfected HEK293T cells. A single protein, fascin-1, was found to differentially interact with ACE2 after Ang-II treatment for 4 h. The interactions between fascin-1 and ACE2 were confirmed by confocal microscopy and co-immunoprecipitation. Overexpression of fascin-1 attenuates the effects of Ang-II on ACE2 activity. In contrast, downregulation of fascin-1 severely decreased ACE2 enzymatic activity. Interestingly, in brain homogenates from hypertensive mice, we observed a significant reduction of fascin-1, suggesting that the levels of this protein may change in cardiovascular diseases. In conclusion, we identified fascin-1 as an ACE2-accessory protein, interacting with the enzyme in an Ang-II dependent manner and contributing to the regulation of enzyme activity.

Hypoxia-induced Fascin-1 upregulation is regulated by Akt/Rac1 axis and enhances malignant properties of liver cancer cells via mediating actin cytoskeleton rearrangement and Hippo/YAP activation

In solid tumors, hypoxia facilitates malignant progression of cancer cells by triggering epithelial-mesenchymal transition (EMT) and cancer stemness. Fascin-1, an actin-bundling protein, takes part in the formation of many actin-based cellular structures. In the present study, we explored the potential functions of hypoxia-induced upregulation of Fascin-1 in liver cancer. Transcriptome RNA-sequencing was conducted to identify hypoxia-related genes. The potential functions of Fascin-1 were evaluated by western blot, transwell migration and invasion assays, sphere-formation assay, tumor xenograft growth, gelatin zymography analysis, immunofluorescence, cell viability assay, soft agar assay, and flow cytometry. We found that Fascin-1 was upregulated by hypoxia in liver cancer cell lines, elevated in liver cancer patients and correlated with larger tumor size, lymph node metastasis, distant metastasis, and shorter overall survival. Knockdown of Fascin-1 suppressed migration, invasion, EMT, stemness, and tumor xenograft growth of liver cancer cells under both normoxia and hypoxia conditions, while forced Fascin-1 expression showed opposite effects. Moreover, hypoxia-induced upregulation of Fascin-1 was regulated by the Akt/Rac1 signaling, and inhibition of Akt/Rac1 signaling by EHop-016 and MK-2206 restrained migration, invasion, EMT, and stemness of liver cancer cells under hypoxia. Furthermore, Fascin-1 knockdown suppressed MMP-2 and MMP-9 expression, impaired actin cytoskeleton rearrangement, inactivated Hippo/YAP signaling, and increased Sorafenib sensitivity in liver cancer cells. Our study provided a novel insight of Fascin-1 in regulating migration, invasion, EMT, and stemness of liver cancer cells under normoxia and hypoxia conditions.

Comprehensive Transcriptome and Pathway Analyses Revealed Central Role for Fascin in Promoting Triple-Negative Breast Cancer Progression

Recent years have witnessed major progress in development of novel therapeutic agents such as chemotherapy, targeted therapy and immune checkpoint inhibitors for breast cancer. However, cancer-related death remains high especially in triple-negative breast cancer (TNBC) due limited therapeutic options. Development of targeted therapies for TNBC requires better understanding of biology and signaling networks that promote disease progression. Fascin, an actin bundling protein, was identified as a key regulator of many signaling pathways that contribute to breast cancer progression. Herein, fascin ShRNA was used to generate stable fascin knockdown (FSCN1^KD) in the MDA-MB-231 TNBC cell line and then were subjected to comprehensive mRNA and miRNA transcriptome analysis. We identified 129 upregulated and 114 downregulated mRNA transcripts, while 14 miRNAs were differentially expressed in FSCN1^KD. Ingenuity pathway analysis (IPA) was used to predict the impact of differentially expressed transcripts on signaling pathways and functional categories and to construct miRNA-mRNA regulatory networks in the context of FSCN1 knockdown. Compared to FSCN1^KD, fascin-positive (FSCN1^CON) breast cancer cells showed enrichment in genes promoting cellular proliferation, migration, survival, DNA replication and repair. Expression of FSCN1^high (identified in BRCA dataset from TCGA) in conjunction with elevated expression of the top 10 upregulated or decreased expression of the top 10 downregulated genes (identified in our FSCN1^CON vs. FSCN1^KD) correlates with worst survival outcome. Taken together, these data confirmed fascin's role in promoting TNBC progression, and identified a novel opportunity for therapeutic interventions via targeting those FSCN1-related transcripts.

HDAC6 inhibitors sensitize non-mesenchymal triple-negative breast cancer cells to cysteine deprivation

Triple-negative breast cancer (TNBC) is a highly malignant type of breast cancer and lacks effective therapy. Targeting cysteine-dependence is an emerging strategy to treat the mesenchymal TNBC. However, many TNBC cells are non-mesenchymal and unresponsive to cysteine deprivation. To overcome such resistance, three selective HDAC6 inhibitors (Tubacin, CAY10603, and Tubastatin A), identified by epigenetic compound library screening, can synergize with cysteine deprivation to induce cell death in the non-mesenchymal TNBC. Despite the efficacy of HDAC6 inhibitor, knockout of HDAC6 did not mimic the synthetic lethality induced by its inhibitors, indicating that HDAC6 is not the actual target of HDAC6 inhibitor in this context. Instead, transcriptomic profiling showed that tubacin triggers an extensive gene transcriptional program in combination with erastin, a cysteine transport blocker. Notably, the zinc-related gene response along with an increase of labile zinc was induced in cells by the combination treatment. The disturbance of zinc homeostasis was driven by PKCγ activation, which revealed that the PKCγ signaling pathway is required for HDAC6 inhibitor-mediated synthetic lethality. Overall, our study identifies a novel function of HDAC6 inhibitors that function as potent sensitizers of cysteine deprivation and are capable of abolishing cysteine-independence in non-mesenchymal TNBC.

Emerging Role of Fascin-1 in the Pathogenesis, Diagnosis, and Treatment of the Gastrointestinal Cancers

Simple Summary

Gastrointestinal (GI) cancers, including esophageal, gastric, colorectal, liver, and pancreatic cancers, remain as one of the leading causes of death worldwide, with a large proportion accounting for fatalities related to metastatic disease. The active involvement of fascin-1 in forming membrane protrusions crucial for cellular movement has been identified as an important molecular mechanism behind the phenotypic switch from the localized to the metastatic tumor. Thus, fascin-1 expression status in the malignant tissue has been utilized as an important component in determining the patient’s clinicopathological outcomes. In this review, we provide an up-to-date literature review of the role of fascin-1 in the initiation and metastatic progression of GI tract cancers, its involvement in patients’ clinical outcomes, and its potential as a therapeutic target.

Abstract

Gastrointestinal (GI) cancers, including esophageal, gastric, colorectal, liver, and pancreatic cancers, remain as one of the leading causes of death worldwide, with a large proportion accounting for fatalities related to metastatic disease. Invasion of primary cancer occurs by the actin cytoskeleton remodeling, including the formation of the filopodia, stereocilia, and other finger-like membrane protrusions. The crucial step of actin remodeling in the malignant cells is mediated by the fascin protein family, with fascin-1 being the most active. Fascin-1 is an actin-binding protein that cross-links filamentous actin into tightly packed parallel bundles, giving rise to finger-like cell protrusions, thus equipping the cell with the machinery necessary for adhesion, motility, and invasion. Thus, fascin-1 has been noted to be a key component for determining patient diagnosis and treatment plan. Indeed, the overexpression of fascin-1 in GI tract cancers has been associated with a poor clinical prognosis and metastatic progression. Moreover, fascin-1 has received attention as a potential therapeutic target for metastatic GI tract cancers. In this review, we provide an up-to-date literature review of the role of fascin-1 in the initiation of GI tract cancers, metastatic progression, and patients’ clinical outcomes.

Fascin actin-bundling protein 1 in human cancer: promising biomarker or therapeutic target?

Fascin actin-bundling protein 1 (FSCN1) is a highly conserved actin-bundling protein that cross links F-actin microfilaments into tight, parallel bundles. Elevated FSCN1 levels have been reported in many types of human cancers and have been correlated with aggressive clinical progression, poor prognosis, and survival outcomes. The overexpression of FSCN1 in cancer cells has been associated with tumor growth, migration, invasion, and metastasis. Currently, FSCN1 is recognized as a candidate biomarker for multiple cancer types and as a potential therapeutic target. The aim of this study was to provide a brief overview of the FSCN1 gene and protein structure and elucidate on its actin-bundling activity and physiological functions. The main focus was on the role of FSCN1 and its upregulatory mechanisms and significance in cancer cells. Up-to-date studies on FSCN1 as a novel biomarker and therapeutic target for human cancers are reviewed. It is shown that FSCN1 is an unusual biomarker and a potential therapeutic target for cancer.

Fascin in Cell Migration: More Than an Actin Bundling Protein

Simple Summary

Cell migration is an essential biological process that regulates both development and diseases, such as cancer metastasis. Therefore, understanding the factors that promote cell migration is crucial. One of the factors known to regulate cell migration is the actin-binding protein, Fascin. Fascin is typically thought to promote cell migration through bundling actin to form migratory structures such as filopodia and invadapodia. However, Fascin has many other functions in the cell that may contribute to cell migration. How these novel functions promote cell migration and are regulated is still not well understood. Here, we review the structure of Fascin, the many functions of Fascin and how they may promote cell migration, how Fascin is regulated, and Fascin’s role in diseases such as cancer metastasis.

Abstract

Fascin, an actin-binding protein, regulates many developmental migrations and contributes to cancer metastasis. Specifically, Fascin promotes cell motility, invasion, and adhesion by forming filopodia and invadopodia through its canonical actin bundling function. In addition to bundling actin, Fascin has non-canonical roles in the cell that are thought to promote cell migration. These non-canonical functions include regulating the activity of other actin-binding proteins, binding to and regulating microtubules, mediating mechanotransduction to the nucleus via interaction with the Linker of the Nucleoskeleton and Cytoskeleton (LINC) Complex, and localizing to the nucleus to regulate nuclear actin, the nucleolus, and chromatin modifications. The many functions of Fascin must be coordinately regulated to control cell migration. While much remains to be learned about such mechanisms, Fascin is regulated by post-translational modifications, prostaglandin signaling, protein–protein interactions, and transcriptional means. Here, we review the structure of Fascin, the various functions of Fascin and how they contribute to cell migration, the mechanisms regulating Fascin, and how Fascin contributes to diseases, specifically cancer metastasis.

How does fascin promote cancer metastasis?

Fascin is an F-actin-bundling protein that cross-links individual actin filaments into straight and stiff bundles. Fascin overexpression in cancer is strongly associated with poor prognosis and metastatic progression across different cancer types. It is well established that fascin plays a causative role in promoting metastatic progression. We will review the recent progress in our understanding of mechanisms underlying fascin-mediated cancer metastasis. This review will cover the biochemical basis for fascin-bundling activity, the mechanisms by which cancer cells upregulate fascin expression and the mechanism underlying fascin-mediated cancer cell migration, invasion, and metastatic colonization. We propose that fascin has broad roles in both metastatic dissemination and metastatic colonization. Understanding these mechanisms will be crucial to the development of anti-metastasis therapeutics targeting fascin.

Curcumin downregulates the PI3K-AKT-mTOR pathway and inhibits growth and progression in head and neck cancer cells

Curcumin, a polyphenol isolated from the rhizome of Curcuma longa, has been studied because of its antioxidant, antimicrobial, and antiinflammatory properties. This study aimed to evaluate the effects of curcumin on head and neck cancer (HNC) cell lines and how it modulates the PI3K-AKT-mTOR signaling pathway. Dose-response curves for curcumin were established for hypopharynx carcinoma (FaDu), tongue carcinoma (SCC-9), and keratinocytes (HaCaT) cell lines and IC₅₀ values were calculated. Cell cycle and cell death were investigated through flow cytometry. Cytoskeleton organization was assessed through phalloidin+FITC staining. qPCR array and western blot were performed to analyze gene and protein expression. Curcumin reduced cell viability in a dose-dependent and selective manner, induced cell death on SCC-9 cells (necrosis/late apoptosis: 44% curcumin vs. 16.4% vehicle), and arrested cell cycle at phase G₂ /M on SCC-9 and FaDu (G₂ : SCC-9-19.1% curcumin vs. 13.4% vehicle; FaDu-37.8% curcumin vs. 12.9% vehicle). Disorganized cytoskeleton and altered cell morphology were observed. Furthermore, curcumin downregulated the PI3K-AKT-mTOR signaling pathway by modifying the expression of key genes and proteins. These findings highlight the promising therapeutic potential of curcumin to inhibit HNC growth and progression and to modulate the PI3K-AKT-mTOR pathway.

ILK silencing inhibits migration and invasion of more invasive glioblastoma cells by downregulating ROCK1 and Fascin-1

Glioblastoma multiforme (GBM) is the most aggressive type of brain tumor and it is associated with poor survival. Integrin-linked kinase (ILK) is a serine/threonine protein pseudo-kinase that binds to the cytoplasmic domains of β1 and β3 integrins and has been previously shown to promote invasion and metastasis in many cancer types, including GBM. However, little is known regarding the exact molecular mechanism implicating ILK in GBM aggressiveness. In this study, we used two brain cell lines, the non-invasive neuroglioma H4 cells, and the highly invasive glioblastoma A172 cells, which express ILK in much higher levels than H4. We studied the effect of ILK silencing on the metastatic behavior of glioblastoma cells in vitro and elucidate the underlying molecular mechanism. We showed that siRNA-mediated silencing of ILK inhibits cell migration and invasion of the highly invasive A172 cells while it does not affect the migratory and invasive capacity of H4 cells. These data were also supported by respective changes in the expression of Rho-associated kinase 1 (ROCK1), fascin actin-bundling protein 1 (FSCN1), and matrix metalloproteinase 13 (MMP13), which are known to regulate cell migration and invasion. Our findings were further corroborated by analyzing the Cancer Genome Atlas Glioblastoma Multiforme (TCGA-GBM) dataset. We conclude that ILK promotes glioblastoma cell invasion through activation of ROCK1 and FSCN1 in vitro, providing a more exact molecular mechanism for its action.

Rac1 Signaling: From Intestinal Homeostasis to Colorectal Cancer Metastasis

The small GTPase Rac1 has been implicated in a variety of dynamic cell biological processes, including cell proliferation, cell survival, cell-cell contacts, epithelial mesenchymal transition (EMT), cell motility, and invasiveness. These processes are orchestrated through the fine tuning of Rac1 activity by upstream cell surface receptors and effectors that regulate the cycling Rac1-GDP (off state)/Rac1-GTP (on state), but also through the tuning of Rac1 accumulation, activity, and subcellular localization by post translational modifications or recruitment into molecular scaffolds. Another level of regulation involves Rac1 transcripts stability and splicing. Downstream, Rac1 initiates a series of signaling networks, including regulatory complex of actin cytoskeleton remodeling, activation of protein kinases (PAKs, MAPKs) and transcription factors (NFkB, Wnt/β-catenin/TCF, STAT3, Snail), production of reactive oxygen species (NADPH oxidase holoenzymes, mitochondrial ROS). Thus, this GTPase, its regulators, and effector systems might be involved at different steps of the neoplastic progression from dysplasia to the metastatic cascade. After briefly placing Rac1 and its effector systems in the more general context of intestinal homeostasis and in wound healing after intestinal injury, the present review mainly focuses on the several levels of Rac1 signaling pathway dysregulation in colorectal carcinogenesis, their biological significance, and their clinical impact.

A Membrane Potential- and Calpain-Dependent Reversal of Caspase-1 Inhibition Regulates Canonical NLRP3 Inflammasome

The NLRP3 inflammasome senses a range of cellular disturbances, although no consensus exists regarding a common mechanism. Canonical NLRP3 activation is blocked by high extracellular K⁺, regardless of the activating signal. We report here that canonical NLRP3 activation leads to Ca²⁺ flux and increased calpain activity. Activated calpain releases a pool of Caspase-1 sequestered by the cytoskeleton to regulate NLRP3 activation. Using electrophysiological recording, we found that resting-state eukaryotic membrane potential (MP) is required for this calpain activity, and depolarization by high extracellular K⁺ or artificial hyperpolarization results in the inhibition of calpain. Therefore, the MP/Ca²⁺/calpain/ Caspase-1 axis acts as an independent regulatory mechanism for NLRP3 activity. This finding provides mechanistic insight into high K⁺-mediated inhibition of NLRP3 activation, and it offers an alternative model of NLRP3 inflammasome activation that does not involve K⁺ efflux.

Zhang et al. find that, in canonical NLRP inflammasome activation, calpain activity is essential for releasing caspase-1 from flightless-1 and the cytoskeleton. Membrane depolarization, such as under high extracellular K⁺ or hyperpolarization, impairs this activity. This work provides insight into extracellular K⁺ -mediated inhibition of the NLRP3 inflammasome.

Investigation of candidate molecular biomarkers for expression profile analysis of the Gene expression omnibus (GEO) in acute lymphocytic leukemia (ALL)

Much progress has been made in understanding the mechanism of acute lymphocytic leukemia (ALL). However, for adult ALL, there is still a lack of an effective treatment. In the present study, we first used the Gene Expression Omnibus (GEO) database to identify differentially expressed genes (DEGs) between ALL cell lines and Hodgkin and non-Hodgkin cell lines. Then, the GEO database was also used to detect the DEGs in acute lymphoblastic leukemia (Reh) cells transfected with a normal control or a constitutively active variant of the IkB kinase β. Finally, we found that three key DEGs (CCL5, FSCN1, and HS3ST1) are involved in proliferation and apoptosis according to Gene Ontology (GO) and Kyoto Encyclopedia of Genes Genomes (KEGG) pathway analyses. Finally, we determined that all three target genes that participate in proliferation and apoptosis are regulated via the NF-kB signaling pathway.

ΔNp63α suppresses cells invasion by downregulating PKCγ/Rac1 signaling through miR-320a

ΔNp63α, a member of the p53 family of transcription factors, is overexpressed in a number of cancers and plays a role in proliferation, differentiation, migration, and invasion. ΔNp63α has been shown to regulate several microRNAs that are involved in development and cancer. We identified miRNA miR-320a as a positively regulated target of ΔNp63α. Previous studies have shown that miR-320a is downregulated in colorectal cancer and targets the small GTPase Rac1, leading to a reduction in noncanonical WNT signaling and EMT, thereby inhibiting tumor metastasis and invasion. We showed that miR-320a is a direct target of ΔNp63α. Knockdown of ΔNp63α in HaCaT and A431 cells downregulates miR-320a levels and leads to a corresponding elevation in PKCγ transcript and protein levels. Rac1 phosphorylation at Ser71 was increased in the absence of ΔNp63α, whereas overexpression of ΔNp63α reversed S71 phosphorylation of Rac1. Moreover, increased PKCγ levels, Rac1 phosphorylation and cell invasion observed upon knockdown of ΔNp63α was reversed by either overexpressing miR-320a mimic or Rac1 silencing. Finally, silencing PKCγ or treatment with the PKC inhibitor Gö6976 reversed increased Rac1 phosphorylation and cell invasion observed upon silencing ΔNp63α. Taken together, our data suggest that ΔNp63α positively regulates miR-320a, thereby inhibiting PKCγ expression, Rac1 phosphorylation, and cancer invasion.

Mechanistic insights into Nav1.7-dependent regulation of rat prostate cancer cell invasiveness revealed by toxin probes and proteomic analysis

Voltage-gated sodium channels are involved in tumor metastasis, as potentiating or attenuating their activities affects the migration and invasion process of tumor cells. In the present study, we tested the effect of two peptide toxins, JZTX-I and HNTX-III which function as Nav1.7 activator and inhibitor, respectively, on the migration and invasion ability of prostate cancer (PCa) cell line Mat-LyLu. These two peptides showed opposite effects, and subsequently a comparative proteomic analysis characterized 64 differentially expressed membrane proteins from the JZTX-I- and HNTX-III-treated groups. Among these, 15 proteins were down-regulated and 49 proteins were up-regulated in the HNTX-III group. Bioinformatic analysis showed eight proteins are cytoskeleton proteins or related regulators, which might play important roles in the metastasis of Mat-LyLu cells. The altered expressions of four of these proteins, fascin, muskelin, annexin A2, and cofilin-1, were validated by western blot analysis. Further function network analysis of these proteins revealed that the Rho family GTPases RhoA and Rac1 might be of particular importance for the rat PCa cell invasion. Pharmacological data revealed that JZTX-I and HNTX-III could modulate the Rho signaling pathway in a Nav1.7-dependent manner. In summary, this study suggests that the Nav1.7-dependent regulation of Rho GTPase activity plays a vital role in Mat-LyLu cell migration and invasion and provides new insights into the treatment of PCa.

LncRNAs regulate the cytoskeleton and related Rho/ROCK signaling in cancer metastasis

Some of the key steps in cancer metastasis are the migration and invasion of tumor cells; these processes require rearrangement of the cytoskeleton. Actin filaments, microtubules, and intermediate filaments involved in the formation of cytoskeletal structures, such as stress fibers and pseudopodia, promote the invasion and metastasis of tumor cells. Therefore, it is important to explore the mechanisms underlying cytoskeletal regulation. The ras homolog family (Rho) and Rho-associated coiled-coil containing protein serine/threonine kinase (ROCK) signaling pathway is involved in the regulation of the cytoskeleton. Moreover, long noncoding RNAs (lncRNAs) have essential roles in tumor migration and guide gene regulation during cancer progression. LncRNAs can regulate the cytoskeleton directly or may influence the cytoskeleton via Rho/ROCK signaling during tumor migration. In this review, we focus on the regulatory association between lncRNAs and the cytoskeleton and discuss the pathways and mechanisms involved in the regulation of cancer metastasis.

Rho GTPases as therapeutic targets in cancer (Review)

Rho GTPases are key molecular switches controlling the transduction of external signals to cytoplasmic and nuclear effectors. In the last few years, the development of genetic and pharmacological tools has allowed a more precise definition of the specific roles of Rho GTPases in cancer. The aim of the present review is to describe the cellular functions regulated by these proteins with focus in deregulated signals present in malignant tumors. Finally, we describe the state of the art in search of different experimental therapeutic strategies with Rho GTPases as molecular targets.

Expression of protein kinase C gamma promotes cell migration in colon cancer

Despite extensive efforts, Protein Kinase Cs (PKCs) have proven to be an intractable target in cancer therapies. Traditionally it was accepted that PKCs act as tumour promoters, however new research suggests that PKCs may play an important role in the suppression of cancer. A challenge in targeting PKCs is the limited data available in patient samples. One of the PKC isozymes, PKC gamma, is thought to be present only in the brain and has been largely neglected in the context of cancer. Analysis of gene expression levels of PKC gamma in patient matched normal and colon cancer tissue samples revealed an up-regulation of the gene in the cancer tissue of 54% of the patients examined. Mechanistically we demonstrate that a reduction in the levels of PKC gamma in the colon cancer cells inhibits cell migration and foci formation. Further to this, we observe an increase in cell adhesion and proliferation following the reduction of PKC gamma levels in the cell. Thus, PKC gamma plays a key role in colon cancer; making it an important isozyme that needs to be reconsidered in the context of cancer therapies.

The origin and evolution of cell types

Cell types are the basic building blocks of multicellular organisms and are extensively diversified in animals. Despite recent advances in characterizing cell types, classification schemes remain ambiguous. We propose an evolutionary definition of a cell type that allows cell types to be delineated and compared within and between species. Key to cell type identity are evolutionary changes in the 'core regulatory complex' (CoRC) of transcription factors, that make emergent sister cell types distinct, enable their independent evolution and regulate cell type-specific traits termed apomeres. We discuss the distinction between developmental and evolutionary lineages, and present a roadmap for future research.

Fascin1 in carcinomas: Its regulation and prognostic value

Previous cell biological studies demonstrate that the actin bundling protein fascin1 regulates cell motility, migration and invasion. Human studies demonstrate that fascin1 is upregulated in many epithelial cancers. This review gives a brief overview of the role of fascin1 in cell migration and invasion, but focuses mainly on the regulation and clinical relevance of fascin1 in epithelial cancers. Here, we propose fascin1 as a potent prognostic biomarker for breast, colorectal, esophageal cancers and head and neck squamous cell carcinomas. Fascin1 may also be an attractive drug target against these carcinomas in the future, but more studies are needed.

Impact of Posttranslational Modifications on the Anticancer Activity of Hsp90 Inhibitors

Molecular chaperones are essential for guarding proteins that are indispensable for normal cellular functions. Heat shock protein 90 (Hsp90) is a vital molecular chaperone in eukaryotes that participates in stabilizing and activating approximately 200 target proteins, called "clients," many of which are involved in signal transduction pathways. Cancer cells however utilize Hsp90 to chaperone an array of mutated and overexpressed oncoproteins to protect them from misfolding and degradation. Therefore, Hsp90 is an attractive target in cancer therapy. Hsp90 chaperone function relies on ATP binding and hydrolysis, which in turn guides its carefully orchestrated conformational changes. This chaperone cycle is fine-tuned by another group of proteins called co-chaperones. They are able to accelerate or decelerate the cycle, allowing Hsp90 to chaperone different clients. Posttranslational modifications (PTMs) can also regulate the chaperone cycle at an epigenetic level thereby tailoring Hsp90 function to suit a specific cell type or environmental condition. Recent evidence suggests that inhibition of the enzymes that catalyze the PTM of Hsp90 can act synergistically with Hsp90 inhibitors, providing a novel therapeutic strategy to enhance the efficacy of Hsp90 inhibitors in cancer cells.

Genetic variations in the PRKCG gene and osteosarcoma risk in a Chinese population: a case-control study

Osteosarcoma is a common malignant tumor, which exists widely in the bone of children and adolescents. Protein kinase C gamma (PRKCG) gene, which encodes γPKC, plays important roles in tumor promotion, cell proliferation, differentiation, and migration. The objective of the present study was to investigate the relationship between PRKCG polymorphisms and the risk of osteosarcoma. Five tag single nucleotide polymorphisms (SNPs) of PRKCG were retrieved from the HapMap database and genotyped by the method of SNapShot in a hospital-based study containing 388 patients and 388 healthy individuals. Odds ratios (ORs) and their 95 % confidence intervals (CIs) were used to evaluate the association SPSS 20.0 statistical software package was used to analyze statistical data. Our results suggested that the T/C variant of rs454006 located in the intron 3 region of PRKCG gene was significantly associated with an increased risk of osteosarcoma (CC vs. TT, OR = 1.91; 95 % CI 1.29-2.85; P = 0.001; CC vs. TT+TC, OR = 2.14, 95 % CI = 1.48-3.09, P = 0.001; C vs. T, OR = 1.32, 95 % CI = 1.08-1.62, P = 0.008). Similarly, the rs3745406 T/C variant can also elevate the risk of osteosarcoma in the dominant model (OR = 1.45, 95 % CI = 1.08-1.96, P = 0.014), homozygous model (OR = 1.68, 95 % CI = 1.10-2.59, P = 0.002), and allelic model (OR = 1.31, 95 % CI = 1.07-1.61, P = 0.009). However, there were no significant differences in genotypes and allele frequencies of rs2547362 (T>C), rs8103851 (C>G), and rs2242245 (T>C) SNPs between osteosarcoma patients and healthy controls. The results showed that carrier of rs454006*C allele and rs3745406*C might elevate the risk of osteosarcoma. Further studies are needed to validate the coalition between PRKCG gene polymorphisms and risk of osteosarcoma relying on a larger population that included the participants in different ethnicity and hospital.

Single-nucleotide polymorphisms of the PRKCG gene and osteosarcoma susceptibility

The objective of this study was to explore the relationship between single-nucleotide polymorphisms (SNPs) of the protein kinase C gamma (PRKCG) gene and osteosarcoma susceptibility in Chinese Han population. A total of 610 cases of osteosarcoma patients and 610 healthy individuals were enrolled in this study. TaqMan method was used to compare genotypes and the allelic distribution frequency of three SNPs (rs454006, rs2242245, and rs8103851) in the PRKGG gene between osteosarcoma patients and healthy individuals. Osteosarcoma patients were grouped according to different clinical parameters (age, gender, pathological types, tumor location, Enneking staging, tumor metastasis and treatment) to compare genotype and allele frequency among different groups as well as to explore the relationship between gene polymorphisms and different clinical parameters. The rs454006 polymorphisms of the PRKCG gene include the CC, CT, and TT genotypes. The differences in genotype frequency and allele frequency between osteosarcoma patients and healthy individuals were significant (both P < 0.001). There was no significant different between osteosarcoma patients and healthy individuals in rs8103851 and rs2242245 polymorphisms of the PRKCG gene (both P > 0.05). The differences of the rs8103851 genotype frequency and allele frequency in patients with metastatic osteosarcoma and patients without metastasis were significant (both P < 0.001). The distribution frequencies of the CG and GG genotypes as well as the G allele in patients with metastatic osteosarcoma were higher than in patients without metastasis. The genotype frequency and allele frequency of rs454006 and rs2242245 did not correlate with clinical parameters. The rs454006 polymorphism of the PRKCG gene correlated to osteosarcoma susceptibility and might increase the risk of osteosarcoma. The rs8103851 correlated to metastatic osteosarcoma and could be risk factors for metastatic osteosarcoma.

PLCγ1-PKCγ signaling-mediated Hsp90α plasma membrane translocation facilitates tumor metastasis

The 90-kDa heat shock protein (Hsp90α) has been identified on the surface of cancer cells, and is implicated in tumor invasion and metastasis, suggesting that it is a potentially important target for tumor therapy. However, the regulatory mechanism of Hsp90α plasma membrane translocation during tumor invasion remains poorly understood. Here, we show that Hsp90α plasma membrane expression is selectively upregulated upon epidermal growth factor (EGF) stimulation, which is a process independent of the extracellular matrix. Abrogation of EGF-mediated activation of phospholipase (PLCγ1) by its siRNA or inhibitor prevents the accumulation of Hsp90α at cell protrusions. Inhibition of the downstream effectors of PLCγ1, including Ca(2+) and protein kinase C (PKCγ), also blocks the membrane translocation of Hsp90α, while activation of PKCγ leads to increased levels of cell-surface Hsp90α. Moreover, overexpression of PKCγ increases extracellular vesicle release, on which Hsp90α is present. Furthermore, activation or overexpression of PKCγ promotes tumor cell motility in vitro and tumor metastasis in vivo, whereas a specific neutralizing monoclonal antibody against Hsp90α inhibits such effects, demonstrating that PKCγ-induced Hsp90α translocation is required for tumor metastasis. Taken together, our study provides a mechanistic basis for the role for the PLCγ1-PKCγ pathway in regulating Hsp90α plasma membrane translocation, which facilitates tumor cell motility and promotes tumor metastasis.

The regulatory mechanism of a client kinase controlling its own release from Hsp90 chaperone machinery through phosphorylation

It is believed that the stability and activity of client proteins are passively regulated by the Hsp90 (heat-shock protein 90) chaperone machinery, which is known to be modulated by its intrinsic ATPase activity, co-chaperones and post-translational modifications. However, it is unclear whether client proteins themselves participate in regulation of the chaperoning process. The present study is the first example to show that a client kinase directly regulates Hsp90 activity, which is a novel level of regulation for the Hsp90 chaperone machinery. First, we prove that PKCγ (protein kinase Cγ) is a client protein of Hsp90α, and, that by interacting with PKCγ, Hsp90α prevents PKCγ degradation and facilitates its cytosol-to-membrane translocation and activation. A threonine residue set, Thr¹¹⁵/Thr⁴²⁵/Thr⁶⁰³, of Hsp90α is specifically phosphorylated by PKCγ, and, more interestingly, this threonine residue set serves as a ‘phosphorylation switch’ for Hsp90α binding or release of PKCγ. Moreover, phosphorylation of Hsp90α by PKCγ decreases the binding affinity of Hsp90α towards ATP and co-chaperones such as Cdc37 (cell-division cycle 37), thereby decreasing its chaperone activity. Further investigation demonstrated that the reciprocal regulation of Hsp90α and PKCγ plays a critical role in cancer cells, and that simultaneous inhibition of PKCγ and Hsp90α synergistically prevents cell migration and promotes apoptosis in cancer cells.

The present study is the first example to show that a client directly regulates Hsp90 activity, which is a novel level of regulation for the Hsp90 chaperone machinery.

Fascin regulates the migration of subventricular zone-derived neuroblasts in the postnatal brain

After birth, stem cells in the subventricular zone (SVZ) generate neuroblasts that migrate along the rostral migratory stream (RMS) to become interneurons in the olfactory bulb (OB). This migration is a fundamental event controlling the proper integration of new neurons in a pre-existing synaptic network. Many regulators of neuroblast migration have been identified; however, still very little is known about the intracellular molecular mechanisms controlling this process. Here, we show that the actin-bundling protein fascin is highly upregulated in mouse SVZ-derived migratory neuroblasts. Fascin-1ko mice display an abnormal RMS and a smaller OB. Bromodeoxyuridine labeling experiments show that lack of fascin significantly impairs neuroblast migration, but does not appear to affect cell proliferation. Moreover, fascin depletion substantially alters the polarized morphology of rat neuroblasts. Protein kinase C (PKC)-dependent phosphorylation of fascin on Ser39 regulates its actin-bundling activity. In vivo postnatal electroporation of phosphomimetic (S39D) or nonphosphorylatable (S39A) fascin variants followed by time-lapse imaging of brain slices demonstrates that the phospho-dependent modulation of fascin activity ensures efficient neuroblast migration. Finally, fluorescence lifetime imaging microscopy studies in rat neuroblasts reveal that the interaction between fascin and PKC can be modulated by cannabinoid signaling, which controls neuroblast migration in vivo. We conclude that fascin, whose upregulation appears to mark the transition to the migratory neuroblast stage, is a crucial regulator of neuroblast motility. We propose that a tightly regulated phospho/dephospho-fascin cycle modulated by extracellular signals is required for the polarized morphology and migration in neuroblasts, thus contributing to efficient neurogenesis.

PKC mediates fluctuant ERK-paxillin signaling for hepatocyte growth factor-induced migration of hepatoma cell HepG2

Hepatocyte growth factor (HGF) is critical for triggering metastasis of hepatocellular carcinoma cell (HCC). Extracellular signal-regulated kinase (ERK) mediates HGF-induced cell migration via focal adhesion signaling. Protein kinase C (PKC) is a negative regulator of ERK activation, however, both PKC and ERK were required for HGF-induced cell migration. To address this intriguing issue, the signal mechanisms for HGF-induced HepG2 cell migration were investigated in a long-term fashion. HGF-induced phosphorylations of ERK, Src (at Tyr 416) and paxillin (at Ser178 and Tyr31) were up and down for 3 times within 24h. HGF also induced fluctuant PKC activation and Rac degradation. Consistently, HGF induced intermittent actin polarization within 24h, which can be blocked by the inhibitors of PKC (Bisindolymaleimide) and ERK. Inhibitor studies revealed that ERK was required for HGF-induced paxillin phosphorylation at Ser178, whereas PKC and Rac-1 may suppress HGF-induced phosphorylation of ERK and paxillin (at Ser178) and upregulate phosphorylation of paxillin at Tyr31. Based on shRNA technique, PKCα and δ were responsible for suppressing HGF-induced phosphorylation of ERK and paxillin (at Ser178), whereas PKC ε and ζ were required for phosphorylation of paxillin at Tyr31. The HGF-induced fluctuant signaling is reminiscent of c-Met endocytosis. Using Concanavalin A, an inhibitor of endocytosis, we found that c-Met endocytosis was required for PKC to suppress ERK phosphorylation. Moreover, HGF-induced c-Met degradation was also fluctuant, which can be prevented by Bisindolymaleimide. In conclusion, PKC is critical for mediating HGF-induced fluctuant ERK-paxillin signaling during cell migration, probably via triggering endosomal degradation of c-Met.

Actin binding proteins: their ups and downs in metastatic life

In order to metastasize away from the primary tumor site and migrate into adjacent tissues, cancer cells will stimulate cellular motility through the regulation of their cytoskeletal structures. Through the coordinated polymerization of actin filaments, these cells will control the geometry of distinct structures, namely lamella, lamellipodia and filopodia, as well as the more recently characterized invadopodia. Because actin binding proteins play fundamental functions in regulating the dynamics of actin polymerization, they have been at the forefront of cancer research. This review focuses on a subset of actin binding proteins involved in the regulation of these cellular structures and protrusions, and presents some general principles summarizing how these proteins may remodel the structure of actin. The main body of this review aims to provide new insights into how the expression of these actin binding proteins is regulated during carcinogenesis and highlights new mechanisms that may be initiated by the metastatic cells to induce aberrant expression of such proteins.

Rho GTPases in platelet function

The Rho family of GTP binding proteins, also commonly referred to as the Rho GTPases, are master regulators of the platelet cytoskeleton and platelet function. These low-molecular-weight or 'small' GTPases act as signaling switches in the spatial and temporal transduction, and amplification of signals from platelet cell surface receptors to the intracellular signaling pathways that drive platelet function. The Rho GTPase family members RhoA, Cdc42 and Rac1 have emerged as key regulators in the dynamics of the actin cytoskeleton in platelets and play key roles in platelet aggregation, secretion, spreading and thrombus formation. Rho GTPase regulators, including GEFs and GAPs and downstream effectors, such as the WASPs, formins and PAKs, may also regulate platelet activation and function. In this review, we provide an overview of Rho GTPase signaling in platelet physiology. Previous studies of Rho GTPases and platelets have had a shared history, as platelets have served as an ideal, non-transformed cellular model to characterize Rho function. Likewise, recent studies of the cell biology of Rho GTPase family members have helped to build an understanding of the molecular regulation of platelet function and will continue to do so through the further characterization of Rho GTPases as well as Rho GAPs, GEFs, RhoGDIs and Rho effectors in actin reorganization and other Rho-driven cellular processes.

Drosophila Fascin is a novel downstream target of prostaglandin signaling during actin remodeling

Prostaglandins (PGs) regulate the actin cytoskeleton. However, their mechanisms of action are unknown. Use of Drosophila oogenesis—specifically nurse cell dumping—as a model shows that PGs regulate the actin bundler Fascin to control parallel actin filament bundle formation and cortical actin integrity.

Although prostaglandins (PGs)—lipid signals produced downstream of cyclooxygenase (COX) enzymes—regulate actin cytoskeletal dynamics, their mechanisms of action are unknown. We previously established Drosophila oogenesis, in particular nurse cell dumping, as a new model to determine how PGs regulate actin remodeling. PGs, and thus the Drosophila COX-like enzyme Pxt, are required for both the parallel actin filament bundle formation and the cortical actin strengthening required for dumping. Here we provide the first link between Fascin (Drosophila Singed, Sn), an actin-bundling protein, and PGs. Loss of either pxt or fascin results in similar actin defects. Fascin interacts, both pharmacologically and genetically, with PGs, as reduced Fascin levels enhance the effects of COX inhibition and synergize with reduced Pxt levels to cause both parallel bundle and cortical actin defects. Conversely, overexpression of Fascin in the germline suppresses the effects of COX inhibition and genetic loss of Pxt. These data lead to the conclusion that PGs regulate Fascin to control actin remodeling. This novel interaction has implications beyond Drosophila, as both PGs and Fascin-1, in mammalian systems, contribute to cancer cell migration and invasion.

Fascin controls neuronal class-specific dendrite arbor morphology

The branched morphology of dendrites represents a functional hallmark of distinct neuronal types. Nonetheless, how diverse neuronal class-specific dendrite branches are generated is not understood. We investigated specific classes of sensory neurons of Drosophila larvae to address the fundamental mechanisms underlying the formation of distinct branch types. We addressed the function of fascin, a conserved actin-bundling protein involved in filopodium formation, in class III and class IV sensory neurons. We found that the terminal branchlets of different classes of neurons have distinctive dynamics and are formed on the basis of molecularly separable mechanisms; in particular, class III neurons require fascin for terminal branching whereas class IV neurons do not. In class III neurons, fascin controls the formation and dynamics of terminal branchlets. Previous studies have shown that transcription factor combinations define dendrite patterns; we find that fascin represents a downstream component of such programs, as it is a major effector of the transcription factor Cut in defining class III-specific dendrite morphology. Furthermore, fascin defines the morphological distinction between class III and class IV neurons. In fact, loss of fascin function leads to a partial conversion of class III neurons to class IV characteristics, while the reverse effect is obtained by fascin overexpression in class IV neurons. We propose that dedicated molecular mechanisms underlie the formation and dynamics of distinct dendrite branch types to elicit the accurate establishment of neuronal circuits.

A novel Rho-dependent pathway that drives interaction of fascin-1 with p-Lin-11/Isl-1/Mec-3 kinase (LIMK) 1/2 to promote fascin-1/actin binding and filopodia stability

Background

Fascin-1 is an actin crosslinking protein that is important for the assembly of cell protrusions in neurons, skeletal and smooth muscle, fibroblasts, and dendritic cells. Although absent from most normal adult epithelia, fascin-1 is upregulated in many human carcinomas, and is associated with poor prognosis because of its promotion of carcinoma cell migration, invasion, and metastasis. Rac and Cdc42 small guanine triphosphatases have been identified as upstream regulators of the association of fascin-1 with actin, but the possible role of Rho has remained obscure. Additionally, experiments have been hampered by the inability to measure the fascin-1/actin interaction directly in intact cells. We investigated the hypothesis that fascin-1 is a functional target of Rho in normal and carcinoma cells, using experimental approaches that included a novel fluorescence resonance energy transfer (FRET)/fluorescence lifetime imaging (FLIM) method to measure the interaction of fascin-1 with actin.

Results

Rho activity modulates the interaction of fascin-1 with actin, as detected by a novel FRET method, in skeletal myoblasts and human colon carcinoma cells. Mechanistically, Rho regulation depends on Rho kinase activity, is independent of the status of myosin II activity, and is not mediated by promotion of the fascin/PKC complex. The p-Lin-11/Isl-1/Mec-3 kinases (LIMK), LIMK1 and LIMK2, act downstream of Rho kinases as novel binding partners of fascin-1, and this complex regulates the stability of filopodia.

Conclusions

We have identified a novel activity of Rho in promoting a complex between fascin-1 and LIMK1/2 that modulates the interaction of fascin-1 with actin. These data provide new mechanistic insight into the intracellular coordination of contractile and protrusive actin-based structures. During the course of the study, we developed a novel FRET method for analysis of the fascin-1/actin interaction, with potential general applicability for analyzing the activities of actin-binding proteins in intact cells.

Proteomic analysis of PKCγ-related proteins in the spinal cord of morphine-tolerant rats

Background

Morphine tolerance is a common drawback of chronic morphine exposure, hindering use of this drug. Studies have shown that PKCã may play a key role in the development of morphine tolerance, although the mechanisms are not fully known.

Methodology/Principal Findings

In a rat model of morphine tolerance, PKCã knockdown in the spinal cord was successfully carried out using RNA interference (RNAi) with lentiviral vector-mediated short hairpin RNA of PKCã (LV-shPKCã). Spinal cords (L4-L5) were obtained surgically from morphine-tolerant (MT) rats with and without PKCã knockdown, for comparative proteomic analysis. Total proteins from the spinal cords (L4-L5) were extracted and separated using two-dimensional gel electrophoresis (2DGE); 2D gel images were analyzed with PDQuest software. Seven differential gel-spots were observed with increased spot volume, and 18 spots observed with decreased spot volume. Among these, 13 differentially expressed proteins (DEPs) were identified with matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS), comparing between MT rats with and without PKCã knockdown. The DEPs identified have roles in the cytoskeleton, as neurotrophic factors, in oxidative stress, in ion metabolism, in cell signaling, and as chaperones. Three DEPs (GFAP, FSCN and GDNF) were validated with Western blot analysis, confirming the DEP data. Furthermore, using immunohistochemical analysis, we reveal for the first time that FSCN is involved in the development of morphine tolerance.

Conclusions/Significance

These data cast light on the proteins associated with the PKCã activity during morphine tolerance, and hence may contribute to clarification of the mechanisms by which PKCã influences MT.

Fascin promotes filopodia formation independent of its role in actin bundling

Mutation of a critical residue of fascin eliminates the protein’s actin-bundling activity but maintains its positive role in filopodia formation

Fascin is an evolutionarily conserved actin-binding protein that plays a key role in forming filopodia. It is widely thought that this function involves fascin directly bundling actin filaments, which is controlled by an N-terminal regulatory serine residue. In this paper, by studying cellular processes in Drosophila melanogaster that require fascin activity, we identify a regulatory residue within the C-terminal region of the protein (S289). Unexpectedly, although mutation (S289A) of this residue disrupted the actin-bundling capacity of fascin, fascin S289A fully rescued filopodia formation in fascin mutant flies. Live imaging of migrating macrophages in vivo revealed that this mutation restricted the localization of fascin to the distal ends of filopodia. The corresponding mutation of human fascin (S274) similarly affected its interaction with actin and altered filopodia dynamics within carcinoma cells. These data reveal an evolutionarily conserved role for this regulatory region and unveil a function for fascin, uncoupled from actin bundling, at the distal end of filopodia.

The microtubule-associated protein EB1 maintains cell polarity through activation of protein kinase C

The plus-ends of microtubules target the cell cortex to modulate actin protrusion dynamics and polarity, but little is known of the molecular mechanism that couples the interaction. EB1 protein associates with the plus-ends of microtubules, placing EB1 in an ideal spatial position to mediate microtubule-actin cross talk. The objective of the current study was to further understand intracellular signaling involved in EB1-dependent cell polarity and motility. B16F10 mouse melanoma cells were depleted of EB1 protein using short hair-pin RNA interference. Correlative live cell-immunofluorescence microscopy was performed to determine localization of WAVE2 and IQGAP1 to protruding versus retracting edges. EB1 knock down caused poor subcellular separation of WAVE2 and IQGAP1, and overall decreased localization. Activation of PKC corrected defects in WAVE2 and IQGAP1 localization, cell spreading and cell shape to levels observed in control cells, but did not correct defects in cell migration. Consistent with these findings, decreased PKC phosphorylation was observed in EB1 knock down cells. These findings support a model where EB1 protein links microtubules to actin protrusion and cell polarity through signaling pathways involving PKC.

Life at the leading edge

Cell migration requires sustained forward movement of the plasma membrane at the cell's front or "leading edge." To date, researchers have uncovered four distinct ways of extending the membrane at the leading edge. In lamellipodia and filopodia, actin polymerization directly pushes the plasma membrane forward, whereas in invadopodia, actin polymerization couples with the extracellular delivery of matrix-degrading metalloproteases to clear a path for cells through the extracellular matrix. Membrane blebs drive the plasma membrane forward using a combination of actomyosin-based contractility and reversible detachment of the membrane from the cortical actin cytoskeleton. Each protrusion type requires the coordination of a wide spectrum of signaling molecules and regulators of cytoskeletal dynamics. In addition, these different protrusion methods likely act in concert to move cells through complex environments in vivo.

Fascin-1 expression correlates with repression of E-cadherin expression in hepatocellular carcinoma cells and augments their invasiveness in combination with matrix metalloproteinases

Expression of fascin-1, an actin bundling protein, is a poor prognostic factor in hepatocellular carcinoma (HCC). However, its biological role in HCC cells remains unclear. Using human HCC tissues and cell lines HLE, Hep3B, and Huh7, we investigated whether fascin-1 is involved in epithelial-mesenchymal transition (EMT) and increases invasiveness, thus serving as a promoter of cancer aggressiveness. Immunohistochemical analysis revealed that fascin-1 expression in 19% of primary HCCs was associated with repression of E-cadherin expression, indicating EMT. In vitro, HLE cells showed high fascin-1 expression, loss of E-cadherin, and efficient invasion through Matrigel. Knockdown of fascin-1 significantly repressed invasiveness of the HLE cells and slightly induced E-cadherin expression. In contrast, Huh7 cells had low fascin-1 levels, high E-cadherin expression, and were expectedly non-invasive. However, forced overexpression of fascin-1 conferred only modest invasiveness without E-cadherin repression, indicating that fascin-1 alone cannot effectively stimulate invasiveness or EMT. Furthermore, Hep3B cells were non-invasive despite high fascin-1 expression. Nevertheless, fascin-1 overexpression dramatically increased the migratory potential of Huh7 cells. We then evaluated matrix metalloproteinases (MMPs) 2 and 9 from the HCC cell lines. Significant MMP secretion was only found in HLE cells. Although MMP levels were not elevated in fascin-1-overexpressing Huh7 cells, their invasiveness was remarkably augmented by coculture with HLE cells, and was suppressed in the presence of an MMP inhibitor. In conclusion, we propose that fascin-1 primarily acts as a migration factor associated with EMT in HCC cells and facilitates their invasiveness in combination with MMPs.

ATP enhances neuronal differentiation of PC12 cells by activating PKCα interactions with cytoskeletal proteins

PKCα is a key mediator of the neuronal differentiation controlled by NGF and ATP. However, its downstream signaling pathways remain to be elucidated. To identify the signaling partners of PKCα, we analyzed proteins coimmunoprecipitated with this enzyme in PC12 cells differentiated with NGF and ATP and compared them with those obtained with NGF alone or growing media. Mass spectrometry analysis (LC-MS/MS) identified plectin, peripherin, filamin A, fascin, and β-actin as potential interacting proteins. The colocalization of PKCα and its interacting proteins increased when PC12 cells were differentiated with NGF and ATP. Peripherin and plectin organization and the cortical remodeling of β-actin were dramatically affected when PKCα was down-regulated, suggesting that all three proteins might be functional targets of ATP-dependent PKCα signaling. Taken together, these data demonstrate that PKCα is essential for controlling the neuronal development induced by NGF and ATP and interacts with the cytoskeletal components at two levels: assembly of the intermediate filament peripherin and organization of cortical actin.

The actin-cytoskeleton pathway and its potential role in inflammatory bowel disease-associated human colorectal cancer

INTRODUCTION

To improve our understanding of the various clinical phenotypes in inflammatory bowel disease (IBD)-associated colorectal cancer (CRC) and provide potential targets for early diagnosis and future therapy, we sought to identify new candidate genes and molecular pathways involved in the pathogenesis and progression of this disorder. Recent evidence has implicated the actin-cytoskeleton pathway in the development of metastatic sporadic CRC through cytoskeletal proteins such as fascin-1. We hereby propose that similar genetic polymorphisms and mutations among regulatory genes of the actin-cytoskeleton pathway may also be associated with increased dysplasia, carcinogenesis, and susceptibility for invasion and metastasis in IBD-associated CRC, as compared with sporadic CRC.

MATERIALS AND METHODS

To test this hypothesis, we identified three patients with IBD-associated CRC. We subsequently retrieved normal, dysplastic, and cancerous tissue from within the same surgical colonic specimen. Messenger RNA was subsequently isolated from fresh frozen tissue, and oligonucleotide arrays were carried out to identify genes that were differentially expressed between the three various tissue types (normal, dysplasia, and cancer). By utilizing the same specimen to obtain each of the three various tissue types, we excluded intersubject variability during the analysis. Finally, we performed bioinformatic interaction pathway analysis using the "Ingenuity Pathway Analysis" software.

RESULTS

Computerized pathway analysis revealed that the actin-cytoskeleton pathway was significantly dysregulated in the progression of normal cells, via dysplasia, to IBD-associated CRC (p < 0.05). Significantly up-regulated genes identified in the analysis included the fibroblast growth factor, Abelson interactor gene-2, profilin-2, and radixin genes. Conversely, the diaphanous homolog gene appeared to be significantly down-regulated.

CONCLUSION

Via the dysregulation of these five genes within the actin-cytoskeleton pathway, we propose that this molecular pathway provides a potential mechanism for the malignant transformation and progression of normal tissue, via dysplasia, to IBD-associated CRC.