Lamellipodia Formation Research Articles

Extracellular vesicles in diabetes mellitus induce alterations in endothelial cell morphology and migration

BackgroundInflammation-related atherosclerotic peripheral vascular disease is a major end organ complication of diabetes mellitus that results in devastating morbidity and mortality. Extracellular vesicles (EVs) are nano-sized particles that contain molecular cargo and circulate in the blood. Here, we examined EV protein cargo from diabetic individuals and whether these EVs cause functional changes in endothelial cells.MethodsWe quantified inflammatory protein levels in plasma-derived EVs from a longitudinal cohort of euglycemic and diabetic individuals and used in vitro endothelial cell biological assays to assess the functional effects of these EVs with samples from a cross-sectional cohort.ResultsWe found several significant associations between EV inflammatory protein levels and diabetes status. The angiogenic factor, vascular endothelial growth factor A (VEGF-A), was associated with diabetes status in our longitudinal cohort. Those with diabetes mellitus had higher EV VEGF-A levels compared to euglycemic individuals. Additionally, EV levels of VEGF-A were significantly associated with homeostatic model assessment of insulin resistance (HOMA-IR) and β-cell function (HOMA-B). To test whether EVs with different inflammatory cargo can demonstrate different effects on endothelial cells, we performed cell migration and immunofluorescence assays. We observed that EVs from diabetic individuals increased cell lamellipodia formation and migration when compared to EVs from euglycemic individuals.ConclusionsHigher levels of inflammatory proteins were found in EVs from diabetic individuals. Our data implicate EVs as playing important roles in peripheral vascular disease that occur in individuals with diabetes mellitus and suggest that EVs may serve as an informative diagnostic tool for the disease.

MicroRNA-1253 Regulation of WASF2 (WAVE2) and its Relevance to Racial Health Disparities.

The prevalence of hypertension among African Americans (AAs) in the US is among the highest of any demographic and affects over two-thirds of AA women. Previous data from our laboratory suggest substantial differential gene expression (DGE) of mRNAs and microRNAs (miRNAs) exists within peripheral blood mononuclear cells (PBMCs) isolated from AA and white women with or without hypertension. We hypothesized that DGE by race may contribute to racial differences in hypertension. In a reanalysis of our previous dataset, we found that the Wiskott–Aldrich syndrome protein Verprolin-homologous protein 2 (WASF2 (also known as WAVE2)) is differentially expressed in AA women with hypertension, along with several other members of the actin cytoskeleton signaling pathway that plays a role in cell shape and branching of actin filaments. We performed an in silico miRNA target prediction analysis that suggested miRNA miR-1253 regulates WASF2. Transfection of miR-1253 mimics into human umbilical vein endothelial cells (HUVECs) and human aortic endothelial cells (HAECs) significantly repressed WASF2 mRNA and protein levels (p < 0.05), and a luciferase reporter assay confirmed that miR-1253 regulates the WASF2 3′ UTR (p < 0.01). miR-1253 overexpression in HUVECs significantly increased HUVEC lamellipodia formation (p < 0.01), suggesting the miR-1253–WASF2 interaction may play a role in cell shape and actin cytoskeleton function. Together, we have identified novel roles for miR-1253 and WASF2 in a hypertension-related disparities context. This may ultimately lead to the discovery of additional actin-related genes which are important in the vascular-related complications of hypertension and influence the disproportionate susceptibility to hypertension among AAs in general and AA women in particular.

Genetic immunodeficiency and autoimmune disease reveals a WRC-independent role for Hem1 in mTORC2 regulation

Abstract Inborn errors of immunity (IEI) are genetic disorders that cause life-threatening infections, lymphoproliferation, autoimmunity, or combinations of these features. We describe five patients from four families with a novel IEI characterized by recurrent infections, atopic disease, lymphoproliferation, cytokine overproduction, and autoimmunity. All patients harbored loss-of-function (LOF) variants in the gene NCKAP1L, which encodes the hematopoietic-specific Hem1 protein. Hem1 is a required component of the WAVE regulatory complex (WRC), a critical mediator of Arp2/3-dependent actin polymerization. Three LOF mutations impair interactions between Hem1 and other WRC components, resulting in degradation of the complex. A fourth mutation in Hem1 (M371V) abrogates activation of the WRC by Arf1 GTPase, resulting in WRC deficiency. Loss of Hem1 function disrupts Arp2/3-dependent actin polymerization, immune synapse formation, lamellipodia formation, and migration. Diminished cortical actin barriers in Hem1-deficient cells enable increased degranulation, cytokine secretion, and immune hyperresponsiveness leading to lymphoproliferation. Surprisingly, Hem1 deficiency causes reduced mTORC2-mediated AKT phosphorylation independently of its role in the actin polymerization. Dysregulation of the mTORC2/AKT axis leads to impaired T cell proliferation and effector cytokine production upon T cell activation. Our data show that Hem1 governs two key regulatory complexes, the WRC and mTORC2, and provide a cellular explanation for the combined immunodeficiency and immune hyperresponsiveness observed in Hem1-deficient patients. This research was supported by the Intramural Research Program of the NIH, NIAID.

Cytotoxic and Antimetastatic Activity of Hesperetin and Doxorubicin Combination Toward Her2 Expressing Breast Cancer Cells

Objective:This study aimed to explore Hesperetin (Hst) potency as a co-chemotherapeutics agent combined with Doxorubicin (Dox), particularly cytotoxic and antimetastasis effects toward MCF-7/HER2 cells. Methods:The cytotoxic effects were measured under MTT assay. The flowcytometry analysis was used to examine the cell cycle modulation and apoptosis evidence, while the effect of migration was assayed by scratch wound healing assay. Western blotting and gelatin zymography were carried out to examine the expression level of proteins, HER2, and Rac1. Results:Under MTT assay, Hst and Dox exhibited to decrease cell viability in a dose-dependent manner with the IC50 value of 377 and 0,8 µM, respectively. The combination of Hst and Dox at the respective doses of 95 and 0,2 µM showed a synergistic effect with the combination index of 0,63. Flow cytometry analysis of Hst-Dox revealed that those compounds caused cell cycle arrest at the G2/M phase and induced apoptosis. Hst also decreased HER2 and Rac1 expression, as shown by western blot. Hst inhibited lamellipodia formation and cell migration, as indicated by microscopic observation and wound healing scratch assay. The antimetastatic activity of Hst was associated with the reduction of Rac1 and MMP9 expression as measured by gelatine zymography assay. Conclusion:These results indicated that the combination of Hst and Dox-induced cell cycle arrest, apoptosis, decreased HER2, Rac1, MMP9 expression, and cell migration. Thus, Hst may have the potential to be developed as a co-chemotherapeutic agent combined with doxorubicin toward HER2 overexpressing breast cancer cells.

RAC1-Dependent ORAI1 Translocation to the Leading Edge Supports Lamellipodia Formation and Directional Persistence

Tumor invasion requires efficient cell migration, which is achieved by the generation of persistent and polarized lamellipodia. The generation of lamellipodia is supported by actin dynamics at the leading edge where a complex of proteins known as the WAVE regulatory complex (WRC) promotes the required assembly of actin filaments to push the front of the cell ahead. By using an U2OS osteosarcoma cell line with high metastatic potential, proven by a xenotransplant in zebrafish larvae, we have studied the role of the plasma membrane Ca2+ channel ORAI1 in this process. We have found that epidermal growth factor (EGF) triggered an enrichment of ORAI1 at the leading edge, where colocalized with cortactin (CTTN) and other members of the WRC, such as CYFIP1 and ARP2/3. ORAI1-CTTN co-precipitation was sensitive to the inhibition of the small GTPase RAC1, an upstream activator of the WRC. RAC1 potentiated ORAI1 translocation to the leading edge, increasing the availability of surface ORAI1 and increasing the plasma membrane ruffling. The role of ORAI1 at the leading edge was studied in genetically engineered U2OS cells lacking ORAI1 expression that helped us to prove the key role of this Ca2+ channel on lamellipodia formation, lamellipodial persistence, and cell directness, which are required for tumor cell invasiveness in vivo.

Computational and in vitro Pharmacodynamics Characterization of 1A-116 Rac1 Inhibitor: Relevance of Trp56 in Its Biological Activity.

In the last years, the development of new drugs in oncology has evolved notably. In particular, drug development has shifted from empirical screening of active cytotoxic compounds to molecularly targeted drugs blocking specific biologic pathways that drive cancer progression and metastasis. Using a rational design approach, our group has developed 1A-116 as a promising Rac1 inhibitor, with antitumoral and antimetastatic effects in several types of cancer. Rac1 is over activated in a wide range of tumor types and and it is one of the most studied proteins of the Rho GTPase family. Its role in actin cytoskeleton reorganization has effects on endocytosis, vesicular trafficking, cell cycle progression and cellular migration. In this context, the regulatory activity of Rac1 affects several key processes in the course of the cancer including invasion and metastasis. The purpose of this preclinical study was to focus on the mode of action of 1A-116, conducting an interdisciplinary approach with in silico bioinformatics tools and in vitro assays. Here, we demonstrate that the tryptophan 56 residue is necessary for the inhibitory effects of 1A-116 since this compound interferes with protein-protein interactions (PPI) of Rac1GTPase involving several GEF activators. 1A-116 is also able to inhibit the oncogenic Rac1P29S mutant protein, one of the oncogenic drivers found in sun-exposed melanoma. It also inhibits numerous Rac1-regulated cellular processes such as membrane ruffling and lamellipodia formation. These results deepen our knowledge of 1A-116 inhibition of Rac1 and its biological impact on cancer progression. They also represent a good example of how in silico analyses represent a valuable approach for drug development.

Transient lamellipodia predict sites of dendritic branch formation in hippocampal neurons.

Extensive branching creates the complex dendritic arbor of mammalian CNS neurons but capturing the complete process of branch formation with time-lapse recordings has been challenging. Here, we report that application of BMP7 to cultured hippocampal neurons accelerated dendritic growth sufficiently to document branches forming in less than 20h via frequent time-lapse imaging (10-min intervals). In these recordings, most branches emerged as collateral sprouts from the shaft of a parent branch. Analysis of the recordings showed that filopodia were abundant and formed transiently throughout the length of dendrites but among these, only a small subset occurred at sites where branches later emerged. Conversely, formation of lamellipodia was rare and coincided with sites where collateral branches emerged. This pattern suggests that lamellipodial structures act as an important intermediate form of cytoskeletal remodeling related to a cellular commitment to branch, whereas filopodia appear to be related to events prior to such commitment.

Inhibition of Src, SIRT1 or HDAC6 Reduces Transendothelial Migration of Acute Lymphoblastic Leukemia B cells

B‐cell acute lymphoblastic leukemia (B‐ALL) is the most common leukemia in children. B‐ALL cells have the ability to extravasate and infiltrate bone marrow and organs such as lungs, testis and central nervous system. Dynamic actin cytoskeletal remodeling is needed to accomplish transendothelial migration. Cortactin is an actin‐binding protein which accumulates in lamellipodia and invadopodia and regulates neutrophil transendothelial migration during inflammation. Cortactin is overexpressed in B‐cells of B‐ALL patients, and significantly correlates with bone marrow colonization, organ infiltration, drug resistance and disease relapse. Cortactin is a target of Src kinase, and the deacetylases SIRT1 and HDAC6 and as such is prone for post‐translational modifications that regulate its function and localization. Phosphorylation of cortactin at residue Y421 supports lamellipodia and invadopodia formation, whereas acetylation of cortactin diminishes its affinity for F‐actin and decreases cell migration. However, it remains to be explored whether these modifications are required for the migratory advantage that cortactin overexpression bestows on B‐ALL cells. Thus, in this project, we investigate: first, whether pharmacological inhibition of Src, HDAC6 and SIRT1 in leukemic B‐cells reduce transendothelial migration and bone marrow colonization; and second, whether these effects depend on cortactin overexpression. We found that cortactin is constitutively phosphorylated at Y421 in the pre‐B ALL cell line REH and that this phosphorylation is increased after CXCL12 stimulation over time. Of note, Src kinase inhibition with PP2 in leukemic B cells reduced phospho‐cortactin levels and impaired leukemic cell transmigration across HUVEC monolayers and BM organoid colonization. These data suggest that src‐mediated cortactin phosphorylation is required to trigger transmigration. This idea will be further corroborated using cortactin‐depleted REH cells. Moreover, SIRT1 inhibition with EX‐527 and HDAC6 inhibition with Tubastatin‐A also significantly reduced transendothelial migration and bone marrow organoid colonization suggesting that cortactin activation is also regulated by its acetylation status. Taken together, these findings highlight the importance of post‐translational modifications for the regulation of migratory processes of leukemic B cells. Future analysis of the underlying exact molecular mechanisms will contribute to a better understanding of B‐ALL disease progression.

MTORC2/Rac1 Pathway Predisposes Cancer Aggressiveness in IDH1-Mutated Glioma.

Isocitrate dehydrogenase (IDH) mutations are common genetic abnormalities in lower grade gliomas. The neomorphic enzyme activity of IDH mutants leads to tumor formation through epigenetic alteration, dysfunction of dioxygenases, and metabolic reprogramming. However, it remains elusive as to how IDH mutants regulate the pathways associated with oncogenic transformation and aggressiveness. In the present study, by using unbiased transcriptomic profiling, we showed that IDH1 mutations result in substantial changes in the gene sets that govern cellular motility, chemotaxis, and invasion. Mechanistically, rapamycin-insensitive companion of mammalian target of rapamycin (Rictor)/Ras-related C3 botulinum toxin substrate 1 (Rac1) signaling plays an essential role in the motility and proliferation of IDH1-mutated cells by prompting cytoskeleton reorganization, lamellipodia formation, and enhanced endocytosis. Targeting the Rictor/Rac1 pathway suppresses IDH1-mutated cells by limiting endocytosis and cell proliferation. Overall, our findings indicate a novel metabolic reprogramming mechanism of IDH1-mutated cells by exploiting metabolites from the extracellular milieu. Targeting the Rictor/Rac1 pathway could be an alternative therapeutic strategy for IDH1-mutated malignancies.

Antibacterial AZT derivative regulates metastasis of breast cancer cells

Antimicrobial peptides (AMP) with anticancer activity have drawn remarkable attention in modern treatments. However, long peptide length and protease instability are the most addressing factors, which hampers their further development as therapeutic agents. In view of this, herein, we designed and synthesized a series of AZT-based cationic small molecule incorporating a variety of hydrophobic groups and cationic charges, including amine and guanidine groups to mimic the amphipathic structure of AMPs. These compounds were evaluated for their antibacterial activity against Gram-positive and Gram-negative bacteria. Through an extensive structure activity relationship study (SAR), we identified ADG-2e as the most potent antibacterial agent, which exhibited remarkable potency against drug resistant bacterial strains such as MRSA and MDRPA. Further, ADG-2e was examined for their anti-metastatic ability by investigating the cancer cell migration and invasiveness through scratch wound-healing assay and transwell invasive assay, respectively. In addition, time-lapse cell tracking analysis also performed for analyzing the cell movement pattern. Treatment of ADG-2e against metastatic breast cancer cells (MDA-MB-231) suppressed tumor cell migration by multi-directional lamellipodium formation, indicating their anti-metastatic potential. Thus, our cationic AZT based small molecules may evolve as an appealing class of antibacterial agents with anti-metastasis potential.

IODVA1, a guanidinobenzimidazole derivative, targets Rac activity and Ras-driven cancer models.

We report the synthesis and preliminary characterization of IODVA1, a potent small molecule that is active in xenograft mouse models of Ras-driven lung and breast cancers. In an effort to inhibit oncogenic Ras signaling, we combined in silico screening with inhibition of proliferation and colony formation of Ras-driven cells. NSC124205 fulfilled all criteria. HPLC analysis revealed that NSC124205 was a mixture of at least three compounds, from which IODVA1 was determined to be the active component. IODVA1 decreased 2D and 3D cell proliferation, cell spreading and ruffle and lamellipodia formation through downregulation of Rac activity. IODVA1 significantly impaired xenograft tumor growth of Ras-driven cancer cells with no observable toxicity. Immuno-histochemistry analysis of tumor sections suggests that cell death occurs by increased apoptosis. Our data suggest that IODVA1 targets Rac signaling to induce death of Ras-transformed cells. Therefore, IODVA1 holds promise as an anti-tumor therapeutic agent.

The Nuclear Remodeling Induced by Helicobacter Cytolethal Distending Toxin Involves MAFB Oncoprotein.

Enterohepatic Helicobacters, such as Helicobacter hepaticus and Helicobacter pullorum, are associated with several intestinal and hepatic diseases. Their main virulence factor is the cytolethal distending toxin (CDT). In the present study, whole genome microarray-based identification of differentially expressed genes was performed in vitro in HT-29 intestinal cells while following the ectopic expression of the active CdtB subunit of H. hepaticus CDT. A CdtB-dependent upregulation of the V-maf musculoaponeurotic fibrosarcoma oncogene homolog B (MAFB) gene encoding the MAFB oncoprotein was found, as well as the CdtB-dependent regulation of several MAFB target genes. The transduction and coculture experiments confirmed MAFB mRNA and protein induction in response to CDT and its CdtB subunit in intestinal and hepatic cell lines. An analysis of MAFB protein subcellular localization revealed a strong nuclear and perinuclear localization in the CdtB-distended nuclei in intestinal and hepatic cells. MAFB was also detected at the cell periphery of the CdtB-induced lamellipodia in some cells. The silencing of MAFB changed the cellular response to CDT with the formation of narrower lamellipodia, a reduction of the increase in nucleus size, and the formation of less γH2AX foci, the biomarker for DNA double-strand breaks. Taken together, these data show that the CDT of enterohepatic Helicobacters modulates the expression of the MAFB oncoprotein, which is translocated in the nucleus and is associated with the remodeling of the nuclei and actin cytoskeleton.

Abstract B48: PI3Kδ-specific inhibitors may act as adjuvants in the immunotherapy of glioblastoma

Abstract Glioblastoma is the most devastating form of primary brain tumor. Despite surgery, radiotherapy, and concomitant temozolomide chemotherapy, the survival rate remains disappointing. Multiple factors including a diverse array of signaling pathways play significant roles in glioblastoma pathogenesis. Of note, the phosphoinositide 3-kinase (PI3K) signaling pathway is often aberrant in glioblastoma, leading to uncontrolled cell proliferation, migration, and invasion into nearby normal brain tissues. The PI3Kδ isoform, predominantly found in leukocytes, is expressed in a number of tumors including glioblastoma. We had previously shown that PI3Kδ is also expressed in glioma cells such as the U87-MG cell line. Using siRNA knockdown technique, we demonstrated that it is important in glioma cell migration and invasion. Interestingly, its expression has been reported to associate with glioma cell resistance to erlotinib. To further study the mechanistic role of PI3Kδ in glioma pathogenesis, we created two knockout cell strains of U87-MG by CRISPR-Cas9 technology. We performed global transcriptome and pathway analysis comparing the parent cell line U87-MG with these knockout cell strains. Our results showed that the mRNA expression of Pleckstrin 2 (PLEK2) is dramatically reduced in PI3Kδ knockout cells. This is confirmed by quantitative RT-PCR. Western blot analysis showed that PLEK2 protein level is reduced by more than 90% and the phosphorylation of Akt at 308, but not 473, is also reduced. PLEK2 contributes to lamellipodia formation and cell spreading via actin cytoskeleton rearrangement, ultimately affecting cell migration and invasion. Our recent findings further strengthen the important role of PI3Kδ in glioma cell motility. It has been shown recently that inhibition of PI3Kα/δ directly enhances effector CD8+ T-cell activity. Thus, use of PI3Kδ-specific inhibitors may reduce expression of PLEK2 thereby reduces glioma cell migration and at the same time promotes antitumor immunity. PI3Kδ inhibitors may also be used as adjuvants together with immune checkpoint inhibitors such as pembrolizumab to prolong the survival of glioblastoma patients. Citation Format: Zulfikar Azam, Shao Wei, Tony To. PI3Kδ-specific inhibitors may act as adjuvants in the immunotherapy of glioblastoma [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr B48.

Optogenetic Rac1 engineered from membrane lipid-binding RGS-LOV for inducible lamellipodia formation.

We report the construction of a single-component optogenetic Rac1 (opto-Rac1) to control actin polymerization by dynamic membrane recruitment. Opto-Rac1 is a fusion of wildtype human Rac1 small GTPase to the C-terminal region of BcLOV4, a LOV (light-oxygen-voltage) photoreceptor that rapidly binds the plasma membrane upon blue-light activation via a direct electrostatic interaction with anionic membrane phospholipids. Translocation of the fused wildtype Rac1 effector permits its activation by GEFs (guanine nucleotide exchange factors) and consequent actin polymerization and lamellipodia formation, unlike in existing single-chain systems that operate by allosteric photo-switching of constitutively active Rac1 or the heterodimerization-based (i.e. two-component) membrane recruitment of a Rac1-activating GEF. Opto-Rac1 induction of lamellipodia formation was spatially restricted to the patterned illumination field and was efficient, requiring sparse stimulation duty ratios of ∼1-2% (at the sensitivity threshold for flavin photocycling) to cause significant changes in cell morphology. This work exemplifies how the discovery of LOV proteins of distinct signal transmission modes can beget new classes of optogenetic tools for controlling cellular function.

Nε-Carboxymethyl-Lysine Negatively Regulates Foam Cell Migration via the Vav1/Rac1 Pathway.

Background Macrophage-derived foam cells play a central role in atherosclerosis, and their ultimate fate includes apoptosis, promotion of vascular inflammation, or migration to other tissues. Nε-Carboxymethyl-lysine (CML), the key active component of advanced glycation end products, induced foam cell formation and apoptosis. Previous studies have shown that the Vav1/Rac1 pathway affects the macrophage cytoskeleton and cell migration, but its role in the pathogenesis of diabetic atherosclerosis is unknown. Methods and Results In this study, we used anterior tibiofibular vascular samples from diabetic foot amputation patients and accident amputation patients, and histological and cytological tests were performed using a diabetic ApoE−/− mouse model and primary peritoneal macrophages, respectively. The results showed that the atherosclerotic plaques of diabetic foot amputation patients and diabetic ApoE−/− mice were larger than those of the control group. Inhibition of the Vav1/Rac1 pathway reduced vascular plaques and promoted the migration of macrophages to lymph nodes. Transwell and wound healing assays showed that the migratory ability of macrophage-derived foam cells was inhibited by CML. Cytoskeletal staining showed that advanced glycation end products inhibited the formation of lamellipodia in foam cells, and inhibition of the Vav1/Rac1 pathway restored the formation of lamellipodia. Conclusion CML inhibits the migration of foam cells from blood vessels via the Vav1/Rac1 pathway, and this process affects the formation of lamellipodia.

Inhibitory effects of ceramide kinase on Rac1 activation, lamellipodium formation, cell migration, and metastasis of A549 lung cancer cells

Ceramide kinase (CerK) phosphorylates ceramide to ceramide-1-phosphate (C1P), a bioactive sphingolipid. Since the mechanisms responsible for regulating the proliferation and migration/metastasis of cancer cells by the CerK/C1P pathway remain unclear, we conducted the present study. The knockdown of CerK in A549 lung and MCF-7 breast cancer cells (shCerK cells) increased the formation of lamellipodia, which are membrane protrusions coupled with cell migration. Mouse embryonic fibroblasts prepared from CerK-null mice also showed an enhanced formation of lamellipodia. The overexpression of CerK inhibited lamellipodium formation in A549 cells. The knockdown of CerK increased the number of cells having lamellipodia with Rac1 and the levels of active Rac1-GTP form, whereas the overexpression of CerK decreased them. CerK was located in lamellipodia after the epidermal growth factor treatment, indicating that CerK functioned there to inhibit Rac1. The migration of A549 cells was negatively regulated by CerK. An intravenous injection of A549-shCerK cells into nude mice resulted in markedly stronger metastatic responses in the lungs than an injection of control cells. The in vitro growth of A549 cells and in vivo expansion after the injection into mouse flanks were not affected by the CerK knockdown. These results suggest that the activation of CerK/C1P pathway has inhibitory roles on lamellipodium formation, migration, and metastasis of A549 lung cancer cells.

New role of the antidepressant imipramine as a Fascin1 inhibitor in colorectal cancer cells

Serrated adenocarcinoma (SAC) is more invasive, has worse outcomes than conventional colorectal carcinoma (CRC), and is characterized by frequent resistance to anti-epidermal growth factor receptor (EGFR) and overexpression of fascin1, a key protein in actin bundling that plays a causative role in tumor invasion and is overexpressed in different cancer types with poor prognosis. In silico screening of 9591 compounds, including 2037 approved by the Food and Drug Administration (FDA), was performed, and selected compounds were analyzed for their fascin1 binding affinity by differential scanning fluorescence. The results were compared with migrastatin as a typical fascin1 inhibitor. In silico screening and differential scanning fluorescence yielded the FDA-approved antidepressant imipramine as the most evident potential fascin1 blocker. Biophysical and different in vitro actin-bundling assays confirm this activity. Subsequent assays investigating lamellipodia formation and migration and invasion of colorectal cancer cells in vitro using 3D human tissue demonstrated anti-fascin1 and anti-invasive activities of imipramine. Furthermore, expression profiling suggests the activity of imipramine on the actin cytoskeleton. Moreover, in vivo studies using a zebrafish invasion model showed that imipramine is tolerated, its anti-invasive and antimetastatic activities are dose-dependent, and it is associated with both constitutive and induced fascin1 expression. This is the first study that demonstrates an antitumoral role of imipramine as a fascin1 inhibitor and constitutes a foundation for a molecular targeted therapy for SAC and other fascin1-overexpressing tumors.

Corrigendum]Phosphorylation of cortactin by cyclin-dependent kinase5 modulates actin bundling by the dynamin 1-cortactin ring-like complex and formation of filopodia and lamellipodia in NG108-15 glioma-derived cells.

Subsequently to the publication of the above article, the authors have realized that the second‑listed author, The Mon La, had not been properly credited as one of the co‑writers of the paper. Therefore, the Authors' Contributions of the Declarations section of the article should have read as follows: Authors' contributions HY, KTa and TML designed the research and wrote the paper. HY, TA, YM, EO and TT performed mutant protein construction, protein purification and actin bundling experiments. TA and YM performed electron microscopy. EO, TML, KS and KF performed immunofluorescent microscopy, cell migration assay and analyzed data. FYW and KTo identified phosphorylation sites by MALDI‑MS. All authors read and approved the final manuscript. The authors apologize to the readership of the Journal for the misinformation in this regard, and for any inconvenience caused. [the original article was published in International Journal of Oncology 54: 550‑558, 2019; DOI: 10.3892/ijo.2018.4663].

Partial loss of actin nucleator actin-related protein 2/3 activity triggers blebbing in primary T lymphocytes.

T lymphocytes utilize amoeboid migration to navigate effectively within complex microenvironments. The precise rearrangement of the actin cytoskeleton required for cellular forward propulsion is mediated by actin regulators, including the actin‐related protein 2/3 (Arp2/3) complex, a macromolecular machine that nucleates branched actin filaments at the leading edge. The consequences of modulating Arp2/3 activity on the biophysical properties of the actomyosin cortex and downstream T cell function are incompletely understood. We report that even a moderate decrease of Arp3 levels in T cells profoundly affects actin cortex integrity. Reduction in total F‐actin content leads to reduced cortical tension and disrupted lamellipodia formation. Instead, in Arp3‐knockdown cells, the motility mode is dominated by blebbing migration characterized by transient, balloon‐like protrusions at the leading edge. Although this migration mode seems to be compatible with interstitial migration in three‐dimensional environments, diminished locomotion kinetics and impaired cytotoxicity interfere with optimal T cell function. These findings define the importance of finely tuned, Arp2/3‐dependent mechanophysical membrane integrity in cytotoxic effector T lymphocyte activities.

Platelet lamellipodium formation is not required for thrombus formation and stability

AbstractDuring platelet spreading, the actin cytoskeleton undergoes rapid rearrangement, forming filopodia and lamellipodia. Controversial data have been published on the role of lamellipodia in thrombus formation and stability. The Wiskott-Aldrich syndrome protein-family verprolin-homologous protein (WAVE)-regulatory complex, which has been shown in other cells to drive lamellipodium formation by enhancing actin nucleation via the actin-related protein 2/3 (Arp2/3) complex, is activated by Ras-related C3 botulinum toxin substrate 1 (Rac1) interaction with the WAVE complex subunit cytoplasmic fragile X mental retardation 1–interacting protein 1 (Cyfip1). We analyzed Cyfip1flox/floxPf4-Cre mice to investigate the role of Cyfip1 in platelet function. These mice displayed normal platelet counts and a slight reduction in platelet volume. Activation of mutant platelets was only moderately reduced to all tested agonists as measured by αIIbβ3 integrin activation and P-selectin surface exposure. However, lamellipodium formation of mutant platelets was completely abolished on different matrices. Nevertheless, Cyfip1-deficient platelets formed stable thrombi on collagen fibers ex vivo and in 2 models of occlusive arterial thrombosis in vivo. Similarly, the hemostatic function and maintenance of vascular integrity during inflammation of the skin and lung were unaltered in the mutant mice. Investigation of platelet morphology in an induced thrombus under flow revealed that platelets rather form filopodia in the thrombus shell, and are flattened with filopodium-like structures when in direct contact to collagen fibers at the bottom of the thrombus. We provide for the first time direct evidence that platelet lamellipodium formation is not required for stable thrombus formation, and that morphological changes of platelets differ between a static spreading assay and thrombus formation under flow.