Lamellipodia Formation Research Articles

Cortical dynamics during cell motility are regulated by CRL3(KLHL21) E3 ubiquitin ligase.

Directed cell movement involves spatial and temporal regulation of the cortical microtubule (Mt) and actin networks to allow focal adhesions (FAs) to assemble at the cell front and disassemble at the rear. Mts are known to associate with FAs, but the mechanisms coordinating their dynamic interactions remain unknown. Here we show that the CRL3KLHL21 E3 ubiquitin ligase promotes cell migration by controlling Mt and FA dynamics at the cell cortex. Indeed, KLHL21 localizes to FA structures preferentially at the leading edge, and in complex with Cul3, ubiquitylates EB1 within its microtubule-interacting CH-domain. Cells lacking CRL3KLHL21 activity or expressing a non-ubiquitylatable EB1 mutant protein are unable to migrate and exhibit strong defects in FA dynamics, lamellipodia formation and cortical plasticity. Our study thus reveals an important mechanism to regulate cortical dynamics during cell migration that involves ubiquitylation of EB1 at focal adhesions.

SM22α inhibits lamellipodium formation and migration via Ras-Arp2/3 signaling in synthetic VSMCs.

We previously demonstrated that smooth muscle (SM) 22α promotes the migration activity in contractile vascular smooth muscle cells (VSMCs). Based on the varied functions exhibited by SM22α in different VSMC phenotypes, we investigated the effect of SM22α on VSMC migration under pathological conditions. The results demonstrated that SM22α overexpression in synthetic VSMCs inhibited platelet-derived growth factor (PDGF)-BB-induced cell lamellipodium formation and migration, which was different from its action in contractile cells. The results indicated two distinct mechanisms underlying inhibition of lamellipodium formation by SM22α, increased actin dynamic stability and decreased Ras activity via interference with interactions between Ras and guanine nucleotide exchange factor. The former inhibited actin cytoskeleton rearrangement in the cell cortex, while the latter significantly disrupted actin nucleation activation of the Arp2/3 complex. Baicalin, a herb-derived flavonoid compound, inhibited VSMC migration via upregulation of SM22α expression in vitro and in vivo. These data suggest that SM22α regulates lamellipodium formation and cell migration in a phenotype-dependent manner in VSMCs, which may be a new therapeutic target for vascular lesion formation.

Mst1 Kinase Regulates the Actin-Bundling Protein L-Plastin To Promote T Cell Migration

Exploring the mechanisms controlling lymphocyte trafficking is essential for understanding the function of the immune system and the pathophysiology of immunodeficiencies. The mammalian Ste20-like kinase 1 (Mst1) has been identified as a critical signaling mediator of T cell migration, and loss of Mst1 results in immunodeficiency disease. Although Mst1 is known to support T cell migration through induction of cell polarization and lamellipodial formation, the downstream effectors of Mst1 are incompletely defined. Mice deficient for the actin-bundling protein L-plastin (LPL) have phenotypes similar to mice lacking Mst1, including decreased T cell polarization, lamellipodial formation, and cell migration. We therefore asked whether LPL functions downstream of Mst1. The regulatory N-terminal domain of LPL contains a consensus Mst1 phosphorylation site at Thr(89) We found that Mst1 can phosphorylate LPL in vitro and that Mst1 can interact with LPL in cells. Removal of the Mst1 phosphorylation site by mutating Thr(89) to Ala impaired localization of LPL to the actin-rich lamellipodia of T cells. Expression of the T89A LPL mutant failed to restore migration of LPL-deficient T cells in vitro. Furthermore, expression of T89A LPL in LPL-deficient hematopoietic cells, using bone marrow chimeras, failed to rescue the phenotype of decreased thymic egress. These results identify LPL as a key effector of Mst1 and establish a novel mechanism linking a signaling intermediate to an actin-binding protein critical to T cell migration.

The novel model peptide, αAL14, regulates angiogenesis by inhibiting VEGFR 2-mediated signaling in HUVECs.

Inhibition of angiogenesis has been focused on as a strategy for treating several diseases including cancer. In this study, a novel model peptide αAL14 was synthesized and used to identify its inhibitory effects on angiogenesis. The anti-angiogenic effects of αAL14 were investigated using vascular endothelial cells, HUVECs. αAL14 inhibited critical angiogenic processes including tubule formation, cell migration and cell invasion with no influence on cell proliferation in HUVECs. Activity of VEGFR2 was inhibited by αAL14 treatment in HUVECs. Additionally, activities of major subsequent downstream factors of VEGFR2 such as ERK, FAK and Akt were decreased. αAL14 affected expression of Rac1, Cdc42, Arp2 and WAVE2 which are involved in formation of lamellipodia. Moreover, αAL14 reduced NF-κB that can promote expression of several genes relating to cell invasion such as MMP2 and MMP9. Therefore, the results suggest that αAL14 has a potential to be developed as anti-angiogenic drug for treating diseases driven by abnormal angiogenesis.

The inhibitory effect of 7,7″-dimethoxyagastisflavone on the metastasis of melanoma cells via the suppression of F-actin polymerization.

7,7″-Dimethoxyagastisflavone (DMGF), a biflavonoid isolated from Taxus × media cv. Hicksii, induces apoptotic and autophagic cell death. However, whether DMGF suppresses tumor metastasis is unclear. The aim of this study was to investigate the anti-metastatic activities of DMGF on the metastatic processes of melanoma cells in vivo and in vitro. A transwell assay showed that DMGF could effectively attenuate the motility of B16F10 cells, and the results of real-time PCR revealed that DMGF also suppressed the expressions of matrix metalloproteinase-2 (MMP-2). Moreover, DMGF did not influence tube formation but inhibited the migration of endothelial cells. Furthermore, animal models were used to monitor the effects of DMGF on tumor metastasis, and all models showed that DMGF significantly suppressed the metastatic behaviors of B16F10 cells, including intravasation, colonization, and invasion of the lymphatic duct. In addition, DMGF could also reduce the densities of the blood vessels in the tumor area in vivo. Further investigation of the molecular mechanisms of anti-metastatic activity revealed that DMGF can down-regulate the levels of key modulators of the Cdc42/Rac1 pathway to interfere in F-actin polymerization and suppress the formation of lamellipodia by reducing the phosphorylation of CREB. These data suggested that DMGF presents anti-metastatic activities in B16F10 melanoma cells. Here, we demonstrated that DMGF can inhibit the metastasis of highly invasive melanoma cancer cells through the down-regulation of F-actin polymerization. Considering these findings, DMGF may be further developed to serve as a chemoprevention drug for patients with metastatic melanoma.

The effects of acoustic vibration on fibroblast cell migration

Cells are known to interact and respond to external mechanical cues and recent work has shown that application of mechanical stimulation, delivered via acoustic vibration, can be used to control complex cell behaviours. Fibroblast cells are known to respond to physical cues generated in the extracellular matrix and it is thought that such cues are important regulators of the wound healing process. Many conditions are associated with poor wound healing, so there is need for treatments/interventions, which can help accelerate the wound healing process. The primary aim of this research was to investigate the effects of mechanical stimulation upon the migratory and morphological properties of two different fibroblast cells namely; human lung fibroblast cells (LL24) and subcutaneous areolar/adipose mouse fibroblast cells (L929). Using a speaker-based system, the effects of mechanical stimulation (0–1600Hz for 5min) on the mean cell migration distance (μm) and actin organisation was investigated. The results show that 100Hz acoustic vibration enhanced cell migration for both cell lines whereas acoustic vibration above 100Hz was found to decrease cell migration in a frequency dependent manner. Mechanical stimulation was also found to promote changes to the morphology of both cell lines, particularly the formation of lamellipodia and filopodia. Overall lamellipodia was the most prominent actin structure displayed by the lung cell (LL24), whereas filopodia was the most prominent actin feature displayed by the fibroblast derived from subcutaneous areolar/adipose tissue. Mechanical stimulation at all the frequencies used here was found not to affect cell viability. These results suggest that low-frequency acoustic vibration may be used as a tool to manipulate the mechanosensitivity of cells to promote cell migration.

Abstract 702: Serglycin promotes cell migration via modulating cytoskeleton reorganization and enhancing focal adhesion turnover

Abstract Serglycin (SRGN), a hematopoietic cell granule proteoglycan, has recently been shown to be overexpressed in several aggressive cancer types. In nasopharyngeal and hepatocellular carcinomas, elevated expression of SRGN was shown to correlate with poor prognosis. However, the molecular mechanisms underlying SRGN-mediated malignancies remain to be explored. In this study, we showed that SRGN is expressed at elevated levels in several lung cancer-derived cell lines. By gain-of-function and loss-of-function approaches, we showed that SRGN promoted NSCLC cell migration. SRGN modulated actin cytoskeleton reorganization and promoted lamellipodia and filopodia formation at the leading edge, facilitating a directional movement during wound closure in NSCLC cells. In consistence, increased levels of activated Rac1, which is required for lamellipodia formation, and CDC42, which is required for filopodia formation, were detected. Increased focal adhesion (FA) turnover, the process of continuous assembly and disassembly of adhesions, would lead to increased cell migration. We further showed that SRGN promoted Src activation, leading to increased phosphorylation of paxillin (PAX) at Y118 as well as reduced PAX/FAK complex formation, which were well-defined indicators of FA turnover. Taken together, these data suggested that SRGN promotes cell migration through inducing cytoskeleton reorganization and focal adhesion turnover. Citation Format: Jeou-Yuan Chen, Jing-You Guo. Serglycin promotes cell migration via modulating cytoskeleton reorganization and enhancing focal adhesion turnover. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 702.

A simple microfluidic device to study cell-scale endothelial mechanotransduction.

Atherosclerosis is triggered by chronic inflammation of arterial endothelial cells (ECs). Because atherosclerosis develops preferentially in regions where blood flow is disturbed and where ECs have a cuboidal morphology, the interplay between EC shape and mechanotransduction events is of primary interest. In this work we present a simple microfluidic device to study relationships between cell shape and EC response to fluid shear stress. Adhesive micropatterns are used to non-invasively control EC elongation and orientation at both the monolayer and single cell levels. The micropatterned substrate is coupled to a microfluidic chamber that allows precise control of the flow field, high-resolution live-cell imaging during flow experiments, and in situ immunostaining. Using micro particle image velocimetry, we show that cells within the chamber alter the local flow field so that the shear stress on the cell surface is significantly higher than the wall shear stress in regions containing no cells. In response to flow, we observe the formation of lamellipodia in the downstream portion of the EC and cell retraction in the upstream portion. We quantify flow-induced calcium mobilization at the single cell level for cells cultured on unpatterned surfaces or on adhesive lines oriented either parallel or orthogonal to the flow. Finally, we demonstrate flow-induced intracellular calcium waves and show that the direction of propagation of these waves is determined by cell polarization rather than by the flow direction. The combined versatility and simplicity of this microfluidic device renders it very useful for studying relationships between EC shape and mechanosensitivity.

Platelet-rich plasma promotes the migration and invasion of synovial fibroblasts in patients with rheumatoid arthritis

Platelet-rich plasma (PRP) is blood plasma that has been enriched with platelets, and the number of platelets is correlated with rheumatoid activity. PRP is a concentrated source of autologous platelets, and contains several different growth factors and cytokines, including platelet‑derived growth factor, transforming growth factor‑β and insulin‑like growth factor‑1, which stimulate healing of bone and soft tissue. Rheumatoid arthritis (RA) is characterized by synovial hyperplasia, cell activation, articular inflammation and invasion of the synovium into the adjacent bone and cartilage. The adhesion of fibroblast‑like synoviocytes (FLSs) onto the extracellular matrix (ECM), migration and invasion are important for the erosion and destruction of the articular cartilage of patients with RA. The aim of the present study was to investigate the effects of PRP on the adhesion, migration and invasion of RA‑FLSs. Scratch and Transwell migration assays determined that PRP at a concentration of 2 and 5% significantly enhanced the migration ability of RA‑FLSs. Treatment of RA‑FLSs with 2and 5% PRP promoted the adhesion and invasion of the cells. Additionally, the immunofluorescence assay revealed that PRP induced a decrease in the number of centrally located stress fibers and led to an increase in the formation of filopodia and lamellipodia in the detectable leading edge protrusions in RA‑FLSs. In addition, reverse transcription‑quantitative polymerase chain reaction and western blot analysis determined that PRP upregulated the protein and mRNA expression levels of matrix metalloproteinase‑1 (MMP‑1). In conclusion, the promotion of RA‑FLS cell migration, invasion and adhesion on the ECM by PRP may be modulated through the upregulation of MMP‑1 expression and the induction of actin cytoskeletal reorganization.

PFA fixation enables artifact-free super-resolution imaging of the actin cytoskeleton and associated proteins.

ABSTRACTSuper-resolution microscopy (SRM) allows precise localization of proteins in cellular organelles and structures, including the actin cytoskeleton. Yet sample preparation protocols for SRM are rather anecdotal and still being optimized. Thus, SRM-based imaging of the actin cytoskeleton and associated proteins often remains challenging and poorly reproducible. Here, we show that proper paraformaldehyde (PFA)-based sample preparation preserves the architecture of the actin cytoskeleton almost as faithfully as gold-standard glutaraldehyde fixation. We show that this fixation is essential for proper immuno-based localization of actin-binding and actin-regulatory proteins involved in the formation of lamellipodia and ruffles, such as mDia1, WAVE2 and clathrin heavy chain, and provide detailed guidelines for the execution of our method. In summary, proper PFA-based sample preparation increases the multi-color possibilities and the reproducibility of SRM of the actin cytoskeleton and its associated proteins.

Stochastic modelling suggests that an elevated superoxide anion - hydrogen peroxide ratio can drive extravascular phagocyte transmigration by lamellipodium formation

Chemotaxis, integrates diverse intra- and inter-cellular molecular processes into a purposeful patho-physiological response; the operatic rules of which, remain speculative. Here, I surmise, that superoxide anion induced directional motility, in a responding cell, results from a quasi pathway between the stimulus, surrounding interstitium, and its biochemical repertoire. The epochal event in the mounting of an inflammatory response, is the extravascular transmigration of a phagocyte competent cell towards the site of injury, secondary to the development of a lamellipodium. This stochastic-to-markovian process conversion, is initiated by the cytosolic-ROS of the damaged cell, but is maintained by the inverse association of a de novo generated pool of self-sustaining superoxide anions and sub-critical hydrogen peroxide levels. Whilst, the exponential rise of O2.- is secondary to the focal accumulation of higher order lipid raft-Rac1/2-actin oligomers; O2.- mediated inactivation and redistribution of ECSOD, accounts for the minimal concentration of H2O2 that the phagocyte experiences. The net result of this reciprocal association between ROS/ RNS members, is the prolonged perturbation and remodeling of the cytoskeleton and plasma membrane, a prelude to chemotactic migration. The manuscript also describes the significance of stochastic modeling, in the testing of plausible molecular hypotheses of observable phenomena in complex biological systems.

Tumor promoter PMA enhances kindlin-2 and decreases vimentin recruitment into cell adhesion sites

Phorbol diester PMA (phorbol 12-myristate 13-acetate) is a well-known promoter of tumor progression. PMA also regulates cell adhesion by several mechanisms including conformational activation of integrins and integrin clustering. Here, PMA was shown to induce lamellipodia formation and reorganization of the adhesion sites as well as actin and vimentin filaments independently of integrin preactivation. To further analyze the mechanism of PMA action, the protein composition in the α1β1 integrin/collagen IV adhesion sites was analyzed by mass spectrometry and proteomics. In four independent experiments we observed the reduced recruitment of vimentin in relation to integrin α1 subunit. This was in full agreement with the fact that we also detected the retraction of vimentin from cell adhesions by confocal microscopy. Furthermore, the accumulation of kindlin-2 into cell adhesions was significantly increased after PMA treatment. Kindlin-2 siRNA inhibited cell spreading as well as the formation of actin fibrils and cell adhesions, but did not prevent the effect of PMA on lamellipodia formation. Thus, kindlin-2 recruitment was considered to be a consequence rather than the primary cause for the loss of connection between vimentin and the adhesion sites.

Antibody neutralization of cell-surface gC1qR/HABP1/SF2-p32 prevents lamellipodia formation and tumorigenesis.

We previously demonstrated that cell-surface gC1qR is a key regulator of lamellipodia formation and cancer metastasis. Here, we screened a monoclonal mouse antibody against gC1qR to prevent cell migration by neutralizing cell-surface gC1qR. The anti-gC1qR antibody prevented growth factor-stimulated lamellipodia formation, cell migration and focal adhesion kinase activation by inactivating receptor tyrosine kinases (RTKs) in various cancer cells such as A549, MDA-MB-231, MCF7 and HeLa cells. The antibody neutralization of cell-surface gC1qR also inhibited angiogenesis because the anti-gC1qR antibody prevented growth factor-stimulated RTK activation, lamellipodia formation, cell migration and tube formation in HUVEC. In addition, we found that A549 tumorigenesis was reduced in a xenograft mouse model by following the administration of the anti-gC1qR antibody. With these data, we can conclude that the antibody neutralization of cell-surface gC1qR could be a good therapeutic strategy for cancer treatment.

Expression of a dynamin 2 mutant associated with Charcot-Marie-Tooth disease leads to aberrant actin dynamics and lamellipodia formation

Specific mutations in dynamin 2 are linked to Charcot-Marie-Tooth disease (CMT), an inherited peripheral neuropathy. However, the effects of these mutations on dynamin function, particularly in relation to the regulation of the actin cytoskeleton remain unclear. Here, selected CMT-associated dynamin mutants were expressed to examine their role in the pathogenesis of CMT in U2OS cells. Ectopic expression of the dynamin CMT mutants 555Δ3 and K562E caused an approximately 50% decrease in serum stimulation-dependent lamellipodia formation; however, only K562E caused aberrations in the actin cytoskeleton. Immunofluorescence analysis showed that the K562E mutation resulted in the disappearance of radially aligned actin bundles and the simultaneous appearance of F-actin clusters. Live-cell imaging analyses showed F-actin polymers of decreased length assembled into immobile clusters in K562E-expressing cells. The K562E dynamin mutant colocalized with the F-actin clusters, whereas its colocalization with clathrin-coated pit marker proteins was decreased. Essentially the same results were obtained using another cell line, HeLa and NG108-15 cells. The present study is the first to show the association of dynamin CMT mutations with aberrant actin dynamics and lamellipodia, which may contribute to defective endocytosis and myelination in Schwann cells in CMT.

The SHIP2 interactor Myo1c is required for cell migration in 1321 N1 glioblastoma cells

The phosphoinositide 5-phosphatases consist of several enzymes that have been shown to modulate cell migration and invasion. SHIP2, one family member, is known to interact with growth factor receptors and cytoskeletal proteins. In a human model of glioblastoma 1321 N1 cells, we recently identified Myo1c as a new interactor of SHIP2. This was shown in a complex of proteins also containing filamin A. We show here that SHIP2 localization at lamellipodia and ruffles is impaired in Myo1c depleted cells. In the absence of Myo1c, N1 cells tend to associate to form clusters. Cell migration is very much reduced in Myo1c depleted cells, concomitantly with a decrease in FAK Tyr397 phosphorylation, focal adhesion length and PI(4,5)P2 immunostaining. In N1 cells, Myo1c is thus important for lamellipodia formation to assemble a protein complex containing SHIP2 to facilitate cell migration.

Rapamycin inhibits epithelial-to-mesenchymal transition of peritoneal mesothelium cells through regulation of Rho GTPases.

Epithelial-mesenchymal transition (EMT) of peritoneal mesothelial cells (PMCs) is a key process of peritoneal fibrosis. Rapamycin has been previously shown to inhibit EMT of PMCs and prevent peritoneal fibrosis. In this study, we investigated the undefined molecular mechanisms by which rapamycin inhibits EMT of PMCs. To define the protective effect of rapamycin, we initially used a rat PD model which was daily infused with 20 mL of 4.25% high glucose (HG) dialysis solution for 6 weeks to induce fibrosis. The HG rats showed decreased ultrafiltration volume and obvious fibroproliferative response, with markedly increased peritoneal thickness and higher expression of α-smooth muscle actin (α-SMA) and transforming growth factor-β1. Rapamycin significantly ameliorated those pathological changes. Next, we treated rat PMCs with HG to induce EMT and/or rapamycin for indicated time. Rapamycin significantly inhibited HG-induced EMT, which manifests as increased expression of α-SMA, fibronectin, and collagen I, decreased expression of E-cadherin, and increased mobility. HG increased the phosphorylation of PI3K, Akt, and mTOR. Importantly, rapamycin inhibits the RhoA, Rac1, and Cdc42 activated by HG. Moreover, rapamycin repaired the pattern of F-actin distribution induced by HG, reducing the formation of stress fiber, focal adhesion, lamellipodia, and filopodia. Thus, rapamycin shows an obvious protective effect on HG-induced EMT, by inhibiting the activation of Rho GTPases (RhoA, Rac1, and Cdc42).

Optogenetic toolkit reveals the role of Ca2+ sparklets in coordinated cell migration

Cell migration is controlled by various Ca(2+) signals. Local Ca(2+) signals, in particular, have been identified as versatile modulators of cell migration because of their spatiotemporal diversity. However, little is known about how local Ca(2+) signals coordinate between the front and rear regions in directionally migrating cells. Here, we elucidate the spatial role of local Ca(2+) signals in directed cell migration through combinatorial application of an optogenetic toolkit. An optically guided cell migration approach revealed the existence of Ca(2+) sparklets mediated by L-type voltage-dependent Ca(2+) channels in the rear part of migrating cells. Notably, we found that this locally concentrated Ca(2+) influx acts as an essential transducer in establishing a global front-to-rear increasing Ca(2+) gradient. This asymmetrical Ca(2+) gradient is crucial for maintaining front-rear morphological polarity by restricting spontaneous lamellipodia formation in the rear part of migrating cells. Collectively, our findings demonstrate a clear link between local Ca(2+) sparklets and front-rear coordination during directed cell migration.

PI3K p110β isoform synergizes with JNK in the regulation of glioblastoma cell proliferation and migration through Akt and FAK inhibition.

BackgroundGlioblastoma multiforme is the most aggressive malignant primary brain tumor, characterized by rapid growth and extensive infiltration to neighboring normal brain parenchyma. Both PI3K/Akt and JNK pathways are essential to glioblastoma cell survival, migration and invasion. Due to their hyperactivation in glioblastoma cells, PI3K and JNK are promising targets for glioblastoma treatment.MethodsTo investigate the combination effects of class IA PI3K catalytic isoforms (p110α, p110β and p110δ) and JNK inhibition on tumor cell growth and motility, glioblastoma cells and xenografts in nude mice were treated with isoform-selective PI3K inhibitors in combination with JNK inhibitor.ResultsWe showed that combined inhibition of these PI3K isoforms and JNK exerted divergent effects on the proliferation, migration and invasion of glioblastoma cells in vitro. Pharmacological inhibition of p110β or p110δ, but not p110α, displayed synergistic inhibitory effect with JNK inhibition on glioblastoma cell proliferation and migration through decreasing phosphorylation of Akt, FAK and zyxin, leading to blockade of lamellipodia and membrane ruffles formation. No synergistic effect on invasion was observed in all the combination treatment. In vivo, combination of p110β and JNK inhibitors significantly reduced xenograft tumor growth compared with single inhibitor alone.ConclusionConcurrent inhibition of p110β and JNK exhibited synergistic effects on suppressing glioblastoma cell proliferation and migration in vitro and xenograft tumor growth in vivo. Our data suggest that combined inhibition of PI3K p110β isoform and JNK may serve as a potent and promising therapeutic approach for glioblastoma multiforme.Electronic supplementary materialThe online version of this article (doi:10.1186/s13046-016-0356-5) contains supplementary material, which is available to authorized users.

A MAPK-Driven Feedback Loop Suppresses Rac Activity to Promote RhoA-Driven Cancer Cell Invasion.

Cell migration in 3D microenvironments is fundamental to development, homeostasis and the pathobiology of diseases such as cancer. Rab-coupling protein (RCP) dependent co-trafficking of α5β1 and EGFR1 promotes cancer cell invasion into fibronectin (FN) containing extracellular matrix (ECM), by potentiating EGFR1 signalling at the front of invasive cells. This promotes a switch in RhoGTPase signalling to inhibit Rac1 and activate a RhoA-ROCK-Formin homology domain-containing 3 (FHOD3) pathway and generate filopodial actin-spike protrusions which drive invasion. To further understand the signalling network that drives RCP-driven invasive migration, we generated a Boolean logical model based on existing network pathways/models, where each node can be interrogated by computational simulation. The model predicted an unanticipated feedback loop, whereby Raf/MEK/ERK signalling maintains suppression of Rac1 by inhibiting the Rac-activating Sos1-Eps8-Abi1 complex, allowing RhoA activity to predominate in invasive protrusions. MEK inhibition was sufficient to promote lamellipodia formation and oppose filopodial actin-spike formation, and led to activation of Rac and inactivation of RhoA at the leading edge of cells moving in 3D matrix. Furthermore, MEK inhibition abrogated RCP/α5β1/EGFR1-driven invasive migration. However, upon knockdown of Eps8 (to suppress the Sos1-Abi1-Eps8 complex), MEK inhibition had no effect on RhoGTPase activity and did not oppose invasive migration, suggesting that MEK-ERK signalling suppresses the Rac-activating Sos1-Abi1-Eps8 complex to maintain RhoA activity and promote filopodial actin-spike formation and invasive migration. Our study highlights the predictive potential of mathematical modelling approaches, and demonstrates that a simple intervention (MEK-inhibition) could be of therapeutic benefit in preventing invasive migration and metastasis.

Screening and target identification of bioactive compounds that modulate cell migration and autophagy

Cell migration is a fundamental step for embryonic development, wound repair, immune responses, and tumor cell invasion and metastasis. It is well known that protrusive structures, namely filopodia and lamellipodia, can be observed at the leading edge of migrating cells. The formation of these structures is necessary for cell migration; however, the molecular mechanisms behind the formation of these structures remain largely unclear. Therefore, bioactive compounds that modulate protrusive structures are extremely powerful tools for studying the mechanisms behind the formation of these structures and subsequent cell migration. Therefore, we have screened for bioactive compounds that inhibit the formation of filopodia, lamellipodia, or cell migration from natural products, and attempted to identify the target molecules of our isolated compounds. Additionally, autophagy is a bulk, non-specific protein degradation system that is involved in the pathogenesis of cancer and neurodegenerative disorders. Recent extensive studies have revealed the molecular mechanisms of autophagy, however, they also remain largely unclear. Thus, we also have screened for bioactive compounds that modulate autophagy, and identified the target molecules. In the present article, we introduce the phenotypic screening system and target identification of four bioactive compounds.