Invadopodia: unique methods for measurement of extracellular matrix degradation in vitro

A MAP1B-cortactin-Tks5 axis regulates TNBC invasion and tumorigenesis

The microtubule-associated protein MAP1B has been implicated in axonal growth and brain development. We found that MAP1B is highly expressed in the most aggressive and deadliest breast cancer subtype, triple-negative breast cancer (TNBC), but not in other subtypes. Expression of MAP1B was found to be highly correlated with poor prognosis. Depletion of MAP1B in TNBC cells impairs cell migration and invasion concomitant with a defect in tumorigenesis. We found that MAP1B interacts with key components for invadopodia formation, cortactin, and Tks5, the latter of which is a PtdIns(3,4)P2-binding and scaffold protein that localizes to invadopodia. We also found that Tks5 associates with microtubules and supports the association between MAP1B and α-tubulin. In accordance with their interaction, depletion of MAP1B leads to Tks5 destabilization, leading to its degradation via the autophagic pathway. Collectively, these findings suggest that MAP1B is a convergence point of the cytoskeleton to promote malignancy in TNBC and thereby a potential diagnostic and therapeutic target for TNBC.

Ubiquitin-specific protease TRE17/USP6 promotes tumor cell invasion through the regulation of glycoprotein CD147 intracellular trafficking

Disordered expression and distribution of plasma membrane proteins at the cell surface leads to diverse malignant phenotypes in tumors, including cell invasion. The ubiquitin-specific protease TRE17/USP6, an oncogene identified in Ewing sarcoma, is highly expressed in several cancers and locally aggressive tumor-like lesions. We have previously demonstrated that TRE17 regulates the trafficking of plasma membrane proteins that enter cells via clathrin-independent endocytosis (CIE); TRE17 prevents CIE cargo proteins from being targeted to lysosomes for degradation by deubiquitylating them. However, functional insights into the effects of TRE17-mediated CIE cargo trafficking on cell invasion remain unknown. Here, we show that increased expression of TRE17 enhances invasiveness of the human sarcoma cell line HT-1080 by elevating the cell surface levels of the membrane glycoprotein CD147, which plays a central role in tumor progression. We demonstrate overexpression of TRE17 decreases ubiquitylated CD147, which is accompanied by suppression of CD147 transport to lysosomes, resulting in the stabilization and increase of cell surface-localized CD147. On the other hand, we show knockdown of TRE17 decreases cell surface CD147, which is coupled with reduced production of matrix metalloproteinases (MMPs), the enzymes responsible for extracellular matrix degradation. Furthermore, we demonstrate that inhibition of CD147 by a specific inhibitor alleviated the TRE17-promoted tumor cell invasion. We therefore propose a model for the pathogenesis of TRE17-driven tumors in which TRE17 increases CD147 at the cell surface by preventing its lysosomal degradation, which in turn enhances MMP synthesis and matrix degradation, thereby promoting tumor cell invasion.

Histone H3K9 methyltransferase SETDB1 augments invadopodia formation to promote tumor metastasis

Non-small cell lung cancer (NSCLC) is one of leading causes of cancer-related mortality worldwide, which harbors various accumulated genetic and epigenetic abnormalities. Histone methyltransferase SETDB1 is a pivotal epigenetic regulator whose focal amplification and upregulation are commonly detected in NSCLC. However, molecular mechanisms underlying the pro-oncogenic function of SETDB1 remain poorly characterized. Here, we demonstrate that SETDB1 augments the migration and invasion capabilities of NSCLC cells by reinforcing invadopodia formation and mediated ECM degradation. At the molecular level, SETDB1 suppresses the expression of FOXA2, a crucial tumor and metastasis suppressor via coordinated epigenetic mechanisms - SETDB1 not only catalyzes histone H3K9 methylation on FOXA2 genomic locus, but also recruits DNMT3A to regulate DNA methylation on CpG island. Consequently, depletion of Setdb1 in murine lung adenocarcinoma cells completely abolished their full and spontaneous metastatic capabilities in mouse xenograft models. These findings together establish the pro-metastasis activity of SETDB1 in NSCLC and elucidate the underlying cellular and molecular mechanisms.

Netrin-like domain of sFRP4, a Wnt antagonist inhibits stemness, metastatic and invasive properties by specifically blocking MMP-2 in cancer stem cells from human glioma cell line U87MG

Rapid proliferation, high stemness potential, high invasiveness and apoptotic evasion are the distinctive hallmarks of glioma malignancy. The dysregulation of the Wnt/β-catenin pathway is the key factor regulating glioma malignancy. Wnt antagonist, secreted frizzled-related protein 4 (sFRP4), which has a prominent pro-apoptotic role in glioma stem cells, has two functional domains, the netrin-like domain (NLD), and cysteine-rich domain (CRD) both of which contribute to apoptotic properties of the whole protein. However, there are no reports elucidating the specific effects of individual domains of sFRP4 in inhibiting the invasive properties of glioma. This study explores the efficacy of the domains of sFRP4 in inhibiting the key hallmarks of glioblastoma such as invasion, metastasis, and stemness. We overexpressed sFRP4 and its domains in the glioblastoma cell line, U87MG cells and observed that both CRD and NLD domains played prominent roles in attenuating cancer stem cell properties. Significantly, we could demonstrate for the first time that both NLD and CRD domains negatively impacted the key driver of metastasis and migration, the matrix metalloproteinase-2 (MMP-2). Mechanistically, compared to CRD, NLD domain suppressed MMP-2 mediated invasion more effectively in glioma cells as observed in matrigel invasion assay and a function-blocking antibody assay. Fluorescent matrix degradation assay further revealed that NLD reduces matrix degradation. NLD also significantly disrupted fibronectin assembly and decreased cell adhesion in another glioma cell line LN229. In conclusion, the NLD peptide of sFRP4 could be a potent short peptide therapeutic candidate for targeting MMP-2-mediated invasion in the highly malignant glioblastoma multiforme.

MT1-MMP recruits the ER-Golgi SNARE Bet1 for efficient MT1-MMP transport to the plasma membrane

Invasive cancer cells degrade and invade into the extracellular matrix by expressing the matrix metalloproteinase MT1-MMP at invadopodia. Miyagawa et al. show that MT1-MMP uses the ER-Golgi SNARE Bet1 to facilitate its own transport to the plasma membrane through their interaction in a cholesterol-rich milieu.

Metastasis is a major cause of cancer-related death. Membrane type 1–matrix metalloproteinase (MT1-MMP) is a critical protease for local invasion and metastasis. MT1-MMP is synthesized in the endoplasmic reticulum (ER) and transported in vesicles to invadopodia, specialized subdomains of the plasma membrane, through secretory and endocytic recycling pathways. The molecular mechanism underlying intracellular transport of MT1-MMP has been extensively studied, but is not fully understood. We show that MT1-MMP diverts the SNARE Bet1 from its function in ER-Golgi transport, to promote MT1-MMP trafficking to the cell surface, likely to invadopodia. In invasive cells, Bet1 is localized in MT1-MMP–positive endosomes in addition to the Golgi apparatus, and forms a novel SNARE complex with syntaxin 4 and endosomal SNAREs. MT1-MMP may also use Bet1 for its export from raft-like structures in the ER. Our results suggest the recruitment of Bet1 at an early stage after MT1-MMP expression promotes the exit of MT1-MMP from the ER and its efficient transport to invadopodia.

Anti-invasive and Anti-tumor Effects of Dryopteris crassirhizoma Extract by Disturbing Actin Polymerization

Aim. To evaluate the anti-invasive effect of ethanol extracts of rhizome of Dryopteris crassirhizoma (EEDC) in matrix invasion and formation of functional invadopodia and to determine the anti-tumor effect of EEDC in a mouse model of mandibular invasion by gingival squamous cell carcinoma (SCC). Methods. The rhizome of D crassirhizoma was extracted in ethanol. The anti-invasive effect of EEDC was analyzed with a Matrigel-coated transwell invasion and 3D culture system. Crucial factors related to the control of cancer cell invasion by EEDC were determined using a human protease array. Molecular evidence supporting the anti-invasive effect of EEDC in oral SCC (OSCC) cells used an invadopodia-mediated extracellular matrix (ECM) degradation; an in vivo athymic mouse model was also provided. Results. EEDC treatment (10 µg/mL) suppressed transwell migration and invasion of HSC-3 OSCC cells without cytotoxicity. Decreased levels of matrix metalloprotease (MMP)-7, kalikrein 10, cathepsin V, MMP-2, and cathepsin D were also found in EEDC-treated HSC-3 cells based on human protease array. The anti-invasive effects of EEDC involved the suppression of invadopodia-mediated ECM degradation via inhibition of globular-actin elongation. The anti-invasive effect resulting from disturbance of functional invadopodia formation by EEDC was observed even at a low concentration of 5 µg/mL. The phosphorylation of cortactin involved in functional invadopodia formation was decreased at EEDC concentrations that inhibited invadopodia formation. The anti-tumor effect of EEDC was also observed in a mouse xenograft model. Administration of EEDC resulted in inhibition of tumor growth and progression. Conclusions. EEDC represents a potential anti-invasive and anti-tumor agent in cancer control.

Hic-5 regulates Src-induced invadopodia rosette formation and organization

Fibroblasts transformed by the proto-oncogene Src form individual invadopodia that can spontaneously self-organize into large matrix-degrading superstructures called rosettes. However, the mechanisms by which the invadopodia can spatiotemporally reorganize their architecture is not well understood. Here, we show that Hic-5, a close relative of the scaffold protein paxillin, is essential for the formation and organization of rosettes in active Src-transfected NIH3T3 fibroblasts and cancer-associated fibroblasts. Live cell imaging, combined with domain-mapping analysis of Hic-5, identified critical motifs as well as phosphorylation sites that are required for the formation and dynamics of rosettes. Using pharmacological inhibition and mutant expression, we show that FAK kinase activity, along with its proximity to and potential interaction with the LD2,3 motifs of Hic-5, is necessary for rosette formation. Invadopodia dynamics and their coalescence into rosettes were also dependent on Rac1, formin, and myosin II activity. Superresolution microscopy revealed the presence of formin FHOD1 and INF2-mediated unbranched radial F-actin fibers emanating from invadopodia and rosettes, which may facilitate rosette formation. Collectively, our data highlight a novel role for Hic-5 in orchestrating the organization of invadopodia into higher-order rosettes, which may promote the localized matrix degradation necessary for tumor cell invasion.

PLD-dependent phosphatidic acid microdomains are signaling platforms for podosome formation

Local membrane phospholipid enrichment serves as docking platform for signaling proteins involved in many processes including cell adhesion and migration. Tissue-resident dendritic cells (DCs) assemble actomyosin-based structures called podosomes, which mediate adhesion and degradation of extracellular matrix for migration and antigen sampling. Recent evidence suggested the involvement of phospholipase D (PLD) and its product phosphatidic acid (PA) in podosome formation, but the spatiotemporal control of this process is poorly characterized. Here we determined the role of PLD1 and PLD2 isoforms in regulating podosome formation and dynamics in human primary DCs by combining PLD pharmacological inhibition with a fluorescent PA sensor and fluorescence microscopy. We found that ongoing PLD2 activity is required for the maintenance of podosomes, whereas both PLD1 and PLD2 control the early stages of podosome assembly. Furthermore, we captured the formation of PA microdomains accumulating at the membrane cytoplasmic leaflet of living DCs, in dynamic coordination with nascent podosome actin cores. Finally, we show that both PLD1 and PLD2 activity are important for podosome-mediated matrix degradation. Our results provide novel insight into the isoform-specific spatiotemporal regulation of PLD activity and further our understanding of the role of cell membrane phospholipids in controlling localized actin polymerization and cell protrusion.

Angiogenic and Immunologic Proteins Identified by Deep Proteomic Profiling of Human Retinal and Choroidal Vascular Endothelial Cells: Potential Targets for New Biologic Drugs

PURPOSE

Diseases that involve retinal or choroidal vascular endothelial cells are leading causes of vision loss: age-related macular degeneration, retinal ischemic vasculopathies, and noninfectious posterior uveitis. Proteins differentially expressed by these endothelial cell populations are potential drug targets. We used deep proteomic profiling to define the molecular phenotype of human retinal and choroidal endothelial cells at the protein level.

METHODS

Retinal and choroidal vascular endothelial cells were separately isolated from 5 human eye pairs by selection on CD31. Total protein was extracted and digested, and peptide fractions were analyzed by reverse-phase liquid chromatography tandem mass spectrometry. Peptide sequences were assigned to fragment ion spectra, and proteins were inferred from openly accessible protein databases. Protein abundance was determined by spectral counting. Publicly available software packages were used to identify proteins that were differentially expressed between human retinal and choroidal endothelial cells, and to classify proteins that were highly abundant in each endothelial cell population.

RESULTS

Human retinal and/or choroidal vascular endothelial cells expressed 5042 nonredundant proteins. Setting the differential expression false discovery rate at 0.05, 498 proteins of 3454 quantifiable proteins (14.4%) with minimum mean spectral counts of 2.5 were differentially abundant in the 2 cell populations. Retinal and choroidal endothelial cells were enriched in angiogenic proteins, and retinal endothelial cells were also enriched in immunologic proteins.

CONCLUSIONS

This work describes the different protein expression profiles of human retinal and choroidal vascular endothelial cells, and provides multiple candidates for further study as novel treatments or drug targets for posterior eye diseases. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

Catalytically defective receptor protein tyrosine kinase PTK7 enhances invasive phenotype by inducing MMP-9 through activation of AP-1 and NF-κB in esophageal squamous cell carcinoma cells

Protein tyrosine kinase 7 (PTK7), a member of the catalytically defective receptor protein tyrosine kinase family, is upregulated in various cancers including esophageal squamous cell carcinoma (ESCC). Here, we have explored the molecular mechanism of PTK7-dependent invasiveness in ESCC cells. PTK7 knockdown reduced gelatin degradation and MMP-9 secretion in cultures of ESCC TE-10 cells, and showed reduced levels of MMP9 mRNA using real-time RT-PCR and luciferase reporter assays. PTK7 knockdown decreased not only phosphorylation of NF-κB, IκB, ERK, and JNK, but also nuclear localization of NF-κB and AP-1 consisting of c-Fos and c-Jun. Activation of AP-1 and NF-κB requires PTK7-mediated activation of tyrosine kinases, including Src. In addition, NF-κB activation by PTK7 involves the PI3K/Akt signaling pathway. PTK7-mediated upregulation of MMP9 was also observed in other ESCC cell lines and in three-dimensional cultures of TE-10 cells. Moreover, MMP-9 expression positively correlated with PTK7 expression in ESCC tumor tissue. These findings demonstrate that PTK7 upregulates MMP9 through activation of AP-1 and NF-κB and, thus increases invasive properties of ESCC cells.

The KDEL receptor signalling cascade targets focal adhesion kinase on focal adhesions and invadopodia

Membrane trafficking via the Golgi-localised KDEL receptor activates signalling cascades that coordinate both trafficking and other cellular functions, including autophagy and extracellular matrix degradation. In this study, we provide evidence that membrane trafficking activates KDEL receptor and the Src family kinases at focal adhesions of HeLa cells, where this phosphorylates ADP-ribosylation factor GTPase-activating protein with SH3 domain, ankyrin repeat and PH domain (ASAP)1 and focal adhesion kinase (FAK). Previous studies have reported extracellular matrix degradation at focal adhesions. Here, matrix degradation was not seen at focal adhesions, although it occurred at invadopodia, where it was increased by KDEL receptor activation. This activation of KDEL receptor at invadopodia of A375 cells promoted recruitment and phosphorylation of FAK on tyrosines 397 and 861. From the functional standpoint, FAK overexpression inhibited steady-state and KDEL-receptor-stimulated extracellular matrix degradation, whereas overexpression of the FAK-Y397F mutant only inhibited KDEL-receptor-stimulated matrix degradation. Finally, we show that the Src and FAK activated downstream of KDEL receptor are part of parallel signalling pathways. In conclusion, membrane-traffic-generated signalling via KDEL receptor activates Src not only at the Golgi complex, but also at focal adhesions. By acting on Src and FAK, KDEL receptor increases invadopodia-mediated matrix degradation.

Matrix Metalloproteinases -14, -9 and -2 are Localized to the Podosome and Involved in Podosome Development in the A7r5 Smooth Muscle Cell

Aim

The purpose of the study was to localize matrix metalloproteinase (MMP)-14, -9, and -2 in the A7r5 smooth muscle cell and to understand the interaction between these MMPs and the cytoskeleton. This interaction was observed under non-stimulating and phorbol 12, 13-dibutyrate (PDBu)-stimulating conditions.

Methods

Confocal microscopy was utilized to define the localizations of MMPs and tissue inhibitor of matrix metalloproteinases (TIMPs) in the A7r5 cell and to determine interaction between MMPs and the cytoskeleton. Under PDBu-stimulating conditions, the presence of MMP active forms and activity by gel zymography was evaluated in the A7r5 cell. Actin and microtubule-polymerization inhibitors were used to evaluate MMP interaction with the cytoskeleton and the cytoskeleton was observed on matrix and within a Type I collagen gel.

Results

MMP-14, -9, and -2 were localized to the podosome in the A7r5 smooth muscle cell and interactions were seen with these MMPs and the actin cytoskeleton. PDBu-stimulation induced increases in the protein abundance of the active forms of the MMPs and MMP-2 activity was increased. MMPs also interact with a-actin and not β-tubulin in the A7r5 cell. Galardin, also known as GM-6001, was shown to inhibit podosome formation and prevented MMP localization to the podosome. This broad spectrum MMP inhibitor also prevented collagen gel contraction and prevented cell adhesion and spreading of A7r5 cells within this collagen matrix.

Conclusion

MMPs are important in the formation and function of podosomes in the A7r5 smooth muscle cell. MMPs interact with a-actin and not β-tubulin in the A7r5 cell. Podosomes play an important role in cell migration and understanding the function of podosomes can lead to insights into cancer metastasis and cardiovascular disease.

Use of ethanol extracts of Terminalia chebula to prevent periodontal disease induced by dental plaque bacteria

BACKGROUND

The fruit of the Terminalia chebula tree has been widely used for the treatment of various disorders. Its anti-diabetic, anti-mutagenic, anti-oxidant, anti-bacterial, anti-fungal, and anti-viral effects have been studied. Dental plaque bacteria (DPB) are intimately associated with gingivitis and periodontitis. In the quest for materials that will prove useful in the treatment and prevention of periodontal disease, we investigated the preventive effects of an ethanol extract of Terminalia chebula (EETC) on DPB-induced inflammation and bone resorption.

METHODS

The anti-bacterial effect of EETC was analyzed using the disc diffusion method. The anti-inflammatory effect of EETC was determined by molecular biological analysis of the DPB-mediated culture cells. Prevention of osteoclastic bone resorption by EETC was explored using osteoclast formation and pit formation assays.

RESULTS

EETC suppressed the growth of oral bacteria and reduced the induction of inflammatory cytokines and proteases, abolishing the expression of PGE2 and COX-2 and inhibiting matrix damage. By stimulating the DPB-derived lipopolysaccharides, EETC inhibited both osteoclast formation in osteoclast precursors and RANKL expression in osteoblasts, thereby contributing to the prevention of bone resorption.

CONCLUSIONS

EETC may be a beneficial supplement to help prevent DPB-mediated periodontal disease.

In Vitro Methods to Study the Modulation of Migration and Invasion by Sphingosine-1-Phosphate

Sphingosine-1-phosphate (S1P) is a bioactive lipid that modulates migratory behavior of cells during embryonic development. In addition, S1P might promote tumor progression by enhancing migratory ability and invasiveness of tumor cells. Migration is a complex process that implies cytoskeletal reorganization and formation of structures that enable cell movement. Besides having similar requirements than migration, invasion also involves proteolytic degradation of extracellular matrix (ECM). Matrix metalloproteases (MMPs) have been identified to break down components of the ECM, allowing cancer cells to spread out of the primary tumor. In this chapter, we will describe different techniques to study migration and invasion induced by S1P. To this end, we include detailed protocols of end-point assays to study migration/invasion, and zymography assay to analyze MMP-2 and MMP-9 activity that were standardized in our laboratory in human melanoma cell lines.

A Golgi-based KDELR-dependent signalling pathway controls extracellular matrix degradation

We recently identified an endomembrane-based signalling cascade that is activated by the KDEL receptor (KDELR) on the Golgi complex. At the Golgi, the KDELR acts as a traffic sensor (presumably via binding to chaperones that leave the ER) and triggers signalling pathways that balance membrane fluxes between ER and Golgi. One such pathway relies on Gq and Src. Here, we examine if KDELR might control other cellular modules through this pathway. Given the central role of Src in extracellular matrix (ECM) degradation, we investigated the impact of the KDELR-Src pathway on the ability of cancer cells to degrade the ECM. We find that activation of the KDELR controls ECM degradation by increasing the number of the degradative structures known as invadopodia. The KDELR induces Src activation at the invadopodia and leads to phosphorylation of the Src substrates cortactin and ASAP1, which are required for basal and KDELR-stimulated ECM degradation. This study furthers our understanding of the regulatory circuitry underlying invadopodia-dependent ECM degradation, a key phase in metastases formation and invasive growth.

WIP and WICH/WIRE co-ordinately control invadopodium formation and maturation in human breast cancer cell invasion

Cancer cells form actin-rich degradative protrusions (invasive pseudopods and invadopodia), which allows their efficient dispersal during metastasis. Using biochemical and advanced imaging approaches, we demonstrate that the N-WASP-interactors WIP and WICH/WIRE play non-redundant roles in cancer cell invasion. WIP interacts with N-WASP and cortactin and is essential for invadopodium assembly, whereas WICH/WIRE regulates N-WASP activation to control invadopodium maturation and degradative activity. Our data also show that Nck interaction with WIP and WICH/WIRE modulates invadopodium maturation; changes in WIP and WICH/WIRE levels induce differential distribution of Nck. We show that WIP can replace WICH/WIRE functions and that elevated WIP levels correlate with high invasiveness. These findings identify a role for WICH/WIRE in invasiveness and highlight WIP as a hub for signaling molecule recruitment during invadopodium generation and cancer progression, as well as a potential diagnostic biomarker and an optimal target for therapeutic approaches.

Matrix rigidity differentially regulates invadopodia activity through ROCK1 and ROCK2

ROCK activity increases due to ECM rigidity in the tumor microenvironment and promotes a malignant phenotype via actomyosin contractility. Invasive migration is facilitated by actin-rich adhesive protrusions known as invadopodia that degrade the ECM. Invadopodia activity is dependent on matrix rigidity and contractile forces suggesting that mechanical factors may regulate these subcellular structures through ROCK-dependent actomyosin contractility. However, emerging evidence indicates that the ROCK1 and ROCK2 isoforms perform different functions in cells suggesting that alternative mechanisms may potentially regulate rigidity-dependent invadopodia activity. In this study, we found that matrix rigidity drives ROCK signaling in cancer cells but that ROCK1 and ROCK2 differentially regulate invadopodia activity through separate signaling pathways via contractile (NM II) and non-contractile (LIMK) mechanisms. These data suggest that the mechanical rigidity of the tumor microenvironment may drive ROCK signaling through distinct pathways to enhance the invasive migration required for cancer progression and metastasis.

Lysophosphatidic acid activates the RhoA and NF-κB through Akt/IκBα signaling and promotes prostate cancer invasion and progression by enhancing functional invadopodia formation

We have demonstrated previously that increased RhoA and nuclear factor (NF)-κB activities are associated with increased PC-3 prostate cancer cell invasion and that lysophosphatidic acid (LPA) significantly increases cancer invasion through RhoA and NF-κB activation. In this study, we identified the intermediate signaling molecules and specialized cell structures which are activated by LPA, resulting in enhanced cellular invasion. LPA-induced Akt and IκBα signaling pathways were necessary for RhoA and NF-κB activation, and these LPA effects were abolished by RhoA inhibition. Mice injected with PC-3 cells expressing dominant-negative RhoA N19 developed significantly less tumor growth compared with those injected with control (pcDNA 3.1). In addition, LPA treatment increased functional invadopodia formation. Activation of RhoA and NF-κB through the Akt and IκBα signaling pathway was required for LPA-stimulated gelatin degradation activity. LPA administration increased tumor growth and osteolytic lesions in a mouse xenograft model. These results indicate that LPA promotes PC-3 cell invasion by increasing functional invadopodia formation via upregulating RhoA and NF-κB signaling which contributes to prostate cancer progression. Therefore, the LPA and RhoA-NF-κB signaling axis may represent key molecular targets to inhibit prostate cancer invasion and progression.

Identification of AMPK Phosphorylation Sites Reveals a Network of Proteins Involved in Cell Invasion and Facilitates Large-Scale Substrate Prediction

AMP-activated protein kinase (AMPK) is a central energy gauge that regulates metabolism and has been increasingly involved in non-metabolic processes and diseases. However, AMPK's direct substrates in non-metabolic contexts are largely unknown. To better understand the AMPK network, we use a chemical genetics screen coupled to a peptide capture approach in whole cells, resulting in identification of direct AMPK phosphorylation sites. Interestingly, the high-confidence AMPK substrates contain many proteins involved in cell motility, adhesion, and invasion. AMPK phosphorylation of the RHOA guanine nucleotide exchange factor NET1A inhibits extracellular matrix degradation, an early step in cell invasion. The identification of direct AMPK phosphorylation sites also facilitates large-scale prediction of AMPK substrates. We provide an AMPK motif matrix and a pipeline to predict additional AMPK substrates from quantitative phosphoproteomics datasets. As AMPK is emerging as a critical node in aging and pathological processes, our study identifies potential targets for therapeutic strategies.

Significance of caveolin-1 and matrix metalloproteinase 14 gene expression in canine mammary tumours

Canine mammary tumours (CMTs) are the most common neoplasms affecting female dogs. There is an urgent need for molecular biomarkers that can detect early stages of the disease in order to improve accuracy of CMT diagnosis. The aim of this study was to examine whether caveolin-1 (Cav-1) and matrix metalloproteinase 14 (MMP14) are associated with CMT histological malignancy and invasion. Sixty-five benign and malignant CMT samples and six normal canine mammary glands were analysed using quantitative reverse transcription-polymerase chain reaction. Cav-1 and MMP14 genes were highly expressed in CMT tissues compared to normal tissues. Cav-1 especially was overexpressed in malignant and invasive CMT tissues. When a CMT cell line was cultured on fluorescent gelatin-coated coverslips, localisation of Cav-1 was observed at invadopodia-mediated degradation sites of the gelatin matrix. These findings suggest that Cav-1 may be involved in CMT invasion and that the markers may be useful for estimating CMT malignancy.

αII-spectrin regulates invadosome stability and extracellular matrix degradation

Invadosomes are actin-rich adhesion structures involved in tissue invasion and extracellular matrix (ECM) remodelling. αII-Spectrin, an ubiquitous scaffolding component of the membrane skeleton and a partner of actin regulators (ABI1, VASP and WASL), accumulates highly and specifically in the invadosomes of multiple cell types, such as mouse embryonic fibroblasts (MEFs) expressing SrcY527F, the constitutively active form of Src or activated HMEC-1 endothelial cells. FRAP and live-imaging analysis revealed that αII-spectrin is a highly dynamic component of invadosomes as actin present in the structures core. Knockdown of αII-spectrin expression destabilizes invadosomes and reduces the ability of the remaining invadosomes to digest the ECM and to promote invasion. The ECM degradation defect observed in spectrin-depleted-cells is associated with highly dynamic and unstable invadosome rings. Moreover, FRAP measurement showed the specific involvement of αII-spectrin in the regulation of the mobile/immobile β3-integrin ratio in invadosomes. Our findings suggest that spectrin could regulate invadosome function and maturation by modulating integrin mobility in the membrane, allowing the normal processes of adhesion, invasion and matrix degradation. Altogether, these data highlight a new function for spectrins in the stability of invadosomes and the coupling between actin regulation and ECM degradation.

Mechanical interplay between invadopodia and the nucleus in cultured cancer cells

Invadopodia are actin-rich membrane protrusions through which cells adhere to the extracellular matrix and degrade it. In this study, we explored the mechanical interactions of invadopodia in melanoma cells, using a combination of correlative light and electron microscopy. We show here that the core actin bundle of most invadopodia interacts with integrin-containing matrix adhesions at its basal end, extends through a microtubule-rich cytoplasm, and at its apical end, interacts with the nuclear envelope and indents it. Abolishment of invadopodia by microtubules or src inhibitors leads to the disappearance of these nuclear indentations. Based on the indentation profile and the viscoelastic properties of the nucleus, the force applied by invadopodia is estimated to be in the nanoNewton range. We further show that knockdown of the LINC complex components nesprin 2 or SUN1 leads to a substantial increase in the prominence of the adhesion domains at the opposite end of the invadopodia. We discuss this unexpected, long-range mechanical interplay between the apical and basal domains of invadopodia, and its possible involvement in the penetration of invadopodia into the matrix.

Rac1 nucleocytoplasmic shuttling drives nuclear shape changes and tumor invasion

Nuclear membrane microdomains are proposed to act as platforms for regulation of nuclear function, but little is known about the mechanisms controlling their formation. Organization of the plasma membrane is regulated by actin polymerization, and the existence of an actin pool in the nucleus suggests that a similar mechanism might operate here. We show that nuclear membrane organization and morphology are regulated by the nuclear level of active Rac1 through actin polymerization-dependent mechanisms. Rac1 nuclear export is mediated by two internal nuclear export signals and through its interaction with nucleophosmin-1 (B23), which acts as a Rac1 chaperone inside the nucleus. Rac1 nuclear accumulation alters the balance between cytosolic Rac1 and Rho, increasing RhoA signaling in the cytoplasm and promoting a highly invasive phenotype. Nuclear Rac1 shuttling is a finely tuned mechanism for controlling nuclear shape and organization and cell invasiveness.

Immune complexes stimulate CCR7-dependent dendritic cell migration to lymph nodes

Antibodies are critical for defense against a variety of microbes, but they may also be pathogenic in some autoimmune diseases. Many effector functions of antibodies are mediated by Fcγ receptors (FcγRs), which are found on most immune cells, including dendritic cells (DCs)-important antigen-presenting cells that play a central role in inducing antigen-specific tolerance or immunity. Following antigen acquisition in peripheral tissues, DCs migrate to draining lymph nodes via the lymphatics to present antigen to T cells. Here we demonstrate that FcγR engagement by IgG immune complexes (ICs) stimulates DC migration from peripheral tissues to the paracortex of draining lymph nodes. In vitro, IC-stimulated mouse and human DCs showed greater directional migration in a chemokine (C-C) ligand 19 (CCL19) gradient and increased chemokine (C-C) receptor 7 (CCR7) expression. Using intravital two-photon microscopy, we observed that local administration of IC resulted in dermal DC mobilization. We confirmed that dermal DC migration to lymph nodes depended on CCR7 and increased in the absence of the inhibitory receptor FcγRIIB. These observations have relevance to autoimmunity because autoantibody-containing serum from humans with systemic lupus erythematosus (SLE) and from a mouse model of SLE also increased dermal DC migration in vivo, suggesting that this process may occur in lupus, potentially driving the inappropriate localization of autoantigen-bearing DCs.

WIP is necessary for matrix invasion by breast cancer cells

Actin filament assembly and reorganisation during cell migration and invasion into extracellular matrices is a well-documented phenomenon. Among actin-binding proteins regulating its polymerisation, the members of the WASP (Wiskott Aldrich Syndrome Protein) family are generally thought to play the most significant role in supporting cell invasiveness. In situ, cytosolic N-WASP (neural WASP) is associated with a partner protein termed WIP (WASP Interacting Protein) that is bound to the N-terminal domain of N-WASP. Despite much effort, rather little is known about the role of WIP in regulating N-WASP and consequent actin-filament assembly. Even less is known about the function of WIP within the specialised cell adhesion and attachment structures known as podosomes and invadopodia. In particular, whilst the interaction of WIP with known participants in the development and maturation of invadopodia such as N-WASP, the Arp2/3 complex and cortactin has been described, little is known concerning the direct contribution of WIP to invadopodia and its potential role as a regulator of cancer cell invasion. In this report, we use 2D and 3D culture systems to describe the role played by WIP in modulating the morphology and invasiveness of metastatic breast cancer cells in vitro, as well as its effect on the process of mesenchymal-epithelial transition (MET) seen in these cells. We demonstrate that WIP is necessary for invadopodium formation and matrix degradation by basal breast cancer cells, but not sufficient to induce invasiveness in luminal cells.

Phosphatidylinositol 5-phosphate regulates invasion through binding and activation of Tiam1

PtdIns5P is a lipid messenger acting as a stress-response mediator in the nucleus, and known to maintain cell activation through traffic alterations upon bacterial infection. Here, we show that PtdIns5P regulates actin dynamics and invasion via recruitment and activation of the exchange factor Tiam1 and Rac1. Restricted Rac1 activation results from the binding of Tiam1 DH-PH domains to PtdIns5P. Using an assay that mimics Rac1 membrane anchoring by using Rac1-His and liposomes containing Ni(2+)-NTA modified lipids, we demonstrate that intrinsic Tiam1 DH-PH activity increases when Rac1 is anchored in a PtdIns5P-enriched environment. This pathway appears to be general since it is valid in different pathophysiological models: receptor tyrosine kinase activation, bacterial phosphatase IpgD expression and the invasive NPM-ALK(+) lymphomas. The discovery that PtdIns5P could be a keystone of GTPases and cytoskeleton spatiotemporal regulation opens important research avenues towards unravelling new strategies counteracting cell invasion.

Cellular traction stresses mediate extracellular matrix degradation by invadopodia

During tumorigenesis, matrix rigidity can drive oncogenic transformation via altered cellular proliferation and migration. Cells sense extracellular matrix (ECM) mechanical properties with intracellular tensile forces generated by actomyosin contractility. These contractile forces are transmitted to the matrix surface as traction stresses, which mediate mechanical interactions with the ECM. Matrix rigidity has been shown to increase proteolytic ECM degradation by cytoskeletal structures known as invadopodia that are critical for cancer progression, suggesting that cellular contractility promotes invasive behavior. However, both increases and decreases in traction stresses have been associated with metastatic behavior. Therefore, the role of cellular contractility in invasive migration leading to metastasis is unclear. To determine the relationship between cellular traction stresses and invadopodia activity, we characterized the invasive and contractile properties of an aggressive carcinoma cell line utilizing polyacrylamide gels of different rigidities. We found that ECM degradation and traction stresses were linear functions of matrix rigidity. Using calyculin A to augment myosin contractility, we also found that traction stresses were strongly predictive of ECM degradation. Overall, our data suggest that cellular force generation may play an important part in invasion and metastasis by mediating invadopodia activity in response to the mechanical properties of the tumor microenvironment.

The matricellular protein CCN5 regulates podosome function via interaction with integrin αvβ 3

CCN proteins play crucial roles in cell motility, matrix turnover, and proliferation. In particular, CCN5 plays a role in cell motility and proliferation in several cell types; however, no functional binding proteins for CCN5 have been identified. In this study we report that CCN5 binds to the cell surface receptor integrin αvβ3 in vascular smooth muscle cells. Furthermore, this interaction takes place in podosomes, organelles known to degrade matrix and mediate motility. We show that CCN5 regulates the ability of podosomes to degrade matrix, but does not affect podosome formation. The level of CCN5 present in a podosome negatively correlates with its ability to degrade matrix. Conversely, knockdown of CCN5 greatly enhances the matrix-degrading ability of podosomes. These findings suggest that the antimotility effects of CCN5 may be mediated through the direct interaction of CCN5 and integrin αvβ3 in podosomes and the concomitant suppression of matrix degradation that is required for cell migration.

Tks5 and SHIP2 regulate invadopodium maturation, but not initiation, in breast carcinoma cells

BACKGROUND

Tks5 regulates invadopodium formation, but the precise timing during invadopodium lifetime (initiation, stabilization, maturation) when Tks5 plays a role is not known.

RESULTS

We report new findings based on high-resolution spatiotemporal live-cell imaging of invadopodium precursor assembly. Cortactin, N-WASP, cofilin, and actin arrive together to form the invadopodium precursor, followed by Tks5 recruitment. Tks5 is not required for precursor initiation but is needed for precursor stabilization, which requires the interaction of the phox homology (PX) domain of Tks5 with PI(3,4)P2. During precursor formation, PI(3,4)P2 is uniformly distributed but subsequently starts accumulating at the precursor core 3-4 min after core initiation, and conversely, PI(3,4,5)P3 gets enriched in a ring around the precursor core. SHIP2, a 5'-inositol phosphatase, localizes at the invadopodium core and regulates PI(3,4)P2 levels locally at the invadopodium. The timing of SHIP2 arrival at the invadopodium precursor coincides with the onset of PI(3,4)P2 accumulation. Consistent with its late arrival, we found that SHIP2 inhibition does not affect precursor formation but does cause decreases in mature invadopodia and matrix degradation, whereas SHIP2 overexpression increases matrix degradation.

CONCLUSIONS

Together, these findings lead us to propose a new sequential model that provides novel insights into molecular mechanisms underlying invadopodium precursor initiation, stabilization, and maturation into a functional invadopodium.

Differential Tks5 isoform expression contributes to metastatic invasion of lung adenocarcinoma

Metastasis accounts for the vast majority of cancer-related deaths, yet the molecular mechanisms that drive metastatic spread remain poorly understood. Here we report that Tks5, which has been linked to the formation of proteolytic cellular protrusions known as invadopodia, undergoes an isoform switch during metastatic progression in a genetically engineered mouse model of lung adenocarcinoma. Nonmetastatic primary tumor-derived cells predominantly expressed a short isoform, Tks5short, while metastatic primary tumor- and metastasis-derived cells acquired increased expression of the full-length isoform Tks5long. This elevation of Tks5long to Tks5short ratio correlated with a commensurate increase in invadopodia activity in metastatic cells compared with nonmetastatic cells. Further characterization of these isoforms by knockdown and overexpression experiments demonstrated that Tks5long promoted invadopodia in vitro and increased metastasis in transplant models and an autochthonous model of lung adenocarcinoma. Conversely, Tks5short decreased invadopodia stability and proteolysis, acting as a natural dominant-negative inhibitor to Tks5long. Importantly, high Tks5long and low Tks5short expressions in human lung adenocarcinomas correlated with metastatic disease and predicted worse survival of early stage patients. These data indicate that tipping the Tks5 isoform balance to a high Tks5long to Tks5short ratio promotes invadopodia-mediated invasion and metastasis.

Impact of flavonoids on matrix metalloproteinase secretion and invadopodia formation in highly invasive A431-III cancer cells

Metastasis is a major cause of mortality in cancer patients. Invadopodia are considered to be crucial structures that allow cancer cells to penetrate across the extracellular matrix (ECM) by using matrix metalloproteinases (MMPs). Previously, we isolated a highly invasive A431-III subline from parental A431 cells by Boyden chamber assay. The A431-III cells possess higher invasive and migratory abilities, elevated levels of MMP-9 and an enhanced epithelial-mesenchymal transition (EMT) phenotype. In this study, we discovered that A431-III cells had an increased potential to form invadopodia and an improved capacity to degrade ECM compared with the original A431 cells. We also observed enhanced phosphorylation levels of cortactin and Src in A431-III cells; these phosphorylated proteins have been reported to be the main regulators of invadopodia formation. Flavonoids, almost ubiquitously distributed in food plants and plant food products, have been documented to exhibit anti-tumor properties. Therefore, it was of much interest to explore the effects of flavonoid antioxidants on the metastatic activity of A431-III cells. Exposure of A431-III cells to two potent dietary flavonoids, namely luteolin (Lu) and quercetin (Qu), caused inhibition of invadopodia formation and decrement in ECM degradation. We conclude that Lu and Qu attenuate the phosphorylation of cortactin and Src in A431-III cells. As a consequence, there ensues a disruption of invadopodia generation and the suppression of MMP secretion. These changes, in concert, bring about a reduction in metastasis.

Signaling inputs to invadopodia and podosomes

Remodeling of extracellular matrix (ECM) is a fundamental cell property that allows cells to alter their microenvironment and move through tissues. Invadopodia and podosomes are subcellular actin-rich structures that are specialized for matrix degradation and are formed by cancer and normal cells, respectively. Although initial studies focused on defining the core machinery of these two structures, recent studies have identified inputs from both growth factor and adhesion signaling as crucial for invasive activity. This Commentary will outline the current knowledge on the upstream signaling inputs to invadopodia and podosomes and their role in governing distinct stages of these invasive structures. We discuss invadopodia and podosomes as adhesion structures and highlight new data showing that invadopodia-associated adhesion rings promote the maturation of already-formed invadopodia. We present a model in which growth factor stimulation leads to phosphoinositide 3-kinase (PI3K) activity and formation of invadopodia, whereas adhesion signaling promotes exocytosis of proteinases at invadopodia.

Epigallocatechin-3 gallate inhibits cancer invasion by repressing functional invadopodia formation in oral squamous cell carcinoma

Although the polyphenol EGCG has various beneficial biological effects, its effect on cytoskeletal activities during cancer invasion is not well defined, and the precise molecular mechanisms are largely unknown. Here, we provide molecular evidence on the anti-invasion effect of EGCG in OSCC cells using an in vitro 3-D culture system and in vivo athymic mouse model. Briefly, EGCG exerted an inhibitory effect on the Matrigel-based Transwell invasion and migration of OSCC cells. These effects were not due to decreased cell viability or adhesion capacity to ECM. EGCG-treated OSCC cells possessed fully extended actin fibers without invadopodia, indicating a loss of ECM degradation capacity. Decreased phosphorylation of Src, CTTN, and FAK also followed EGCG treatment. Additionally, EGCG reduced activation of RhoA in dominant-negative RhoA N19 and constitutively active RhoA Q63E cells, and inhibited the invasive capability of these cells in the 3-D cell growth model. Furthermore, the administration of EGCG led to substantial inhibition of tumor growth and activation of invadopodial proteins in the tumor tissues of mice inoculated with OSCC cells. The data indicate the potential value of EGCG as an invadopodia-targeted anti-invasive agent in cancer therapy.

Palladin promotes invasion of pancreatic cancer cells by enhancing invadopodia formation in cancer-associated fibroblasts

The stromal compartment surrounding epithelial-derived pancreatic tumors is thought to have a key role in the aggressive phenotype of this malignancy. Emerging evidence suggests that cancer-associated fibroblasts (CAFs), the most abundant cells in the stroma of pancreatic tumors, contribute to the tumor's invasion, metastasis and resistance to therapy, but the precise molecular mechanisms that regulate CAFs behavior are poorly understood. In this study, we utilized immortalized human pancreatic CAFs to investigate molecular pathways that control the matrix-remodeling and invasion-promoting activity of CAFs. We showed previously that palladin, an actin-associated protein, is expressed at high levels in CAFs of pancreatic tumors and other solid tumors, and also in an immortalized line of human CAFs. In this study, we found that short-term exposure of CAFs to phorbol esters reduced the number of stress fibers and triggered the appearance of individual invadopodia and invadopodial rosettes in CAFs. Molecular analysis of invadopodia revealed that their composition resembled that of similar structures (that is, invadopodia and podosomes) described in other cell types. Pharmacological inhibition and small interfering RNA knockdown experiments demonstrated that protein kinase C, the small GTPase Cdc42 and palladin were necessary for the efficient assembly of invadopodia by CAFs. In addition, GTPase activity assays showed that palladin contributes to the activation of Cdc42. In mouse xenograft experiments using a mixture of CAFs and tumor cells, palladin expression in CAFs promoted the rapid growth and metastasis of human pancreatic tumor cells. Overall, these results indicate that high levels of palladin expression in CAFs enhance their ability to remodel the extracellular matrix by regulating the activity of Cdc42, which in turn promotes the assembly of matrix-degrading invadopodia in CAFs and tumor cell invasion. Together, these results identify a novel molecular signaling pathway that may provide new molecular targets for the inhibition of pancreatic cancer metastasis.

A novel 3D fibril force assay implicates src in tumor cell force generation in collagen networks

New insight into the biomechanics of cancer cell motility in 3D extracellular matrix (ECM) environments would significantly enhance our understanding of aggressive cancers and help identify new targets for intervention. While several methods for measuring the forces involved in cell-matrix interactions have been developed, previous to this study none have been able to measure forces in a fibrillar environment. We have developed a novel assay for simultaneously measuring cell mechanotransduction and motility in 3D fibrillar environments. The assay consists of a controlled-density fibrillar collagen gel atop a controlled-stiffness polyacrylamide (PAA) surface. Forces generated by living cells and their migration in the 3D collagen gel were measured with the 3D motion of tracer beads within the PAA layer. Here, this 3D fibril force assay is used to study the role of the invasion-associated protein kinase Src in mechanotransduction and motility. Src expression and activation are linked with proliferation, invasion, and metastasis, and have been shown to be required in 2D for invadopodia membranes to direct and mediate invasion. Breast cancer cell line MDA-MD-231 was stably transfected with GFP-tagged constitutively active Src or wild-type Src. In 3D fibrillar collagen matrices we found that, relative to wild-type Src, constitutively active Src: 1) increased the strength of cell-induced forces on the ECM, 2) did not significantly change migration speed, and 3) increased both the duration and the length, but not the number, of long membrane protrusions. Taken together, these results support the hypothesis that Src controls invasion by controlling the ability of the cell to form long lasting cellular protrusions to enable penetration through tissue barriers, in addition to its role in promoting invadopodia matrix-degrading activity.

Cancer cell metabolism regulates extracellular matrix degradation by invadopodia

Transformed cancer cells have an altered metabolism, characterized by a shift towards aerobic glycolysis, referred to as 'the Warburg phenotype'. A change in flux through mitochondrial OXPHOS and cytosolic pathways for ATP production and a gain of capacity for biomass production in order to sustain the needs for altered growth and morphodynamics are typically involved in this global rewiring of cancer cell metabolism. Characteristically, these changes in metabolism are accompanied by enhanced uptake of nutrients like glucose and glutamine. Here we focus on the relationship between cell metabolism and cell dynamics, in particular the formation and function of invadopodia, specialized structures for focal degradation of the extracellular matrix. Since we recently found presence of enzymes that are active in glycolysis and associated pathways in invadopodia, we hypothesize that metabolic adaptation and invadopodia formation are linked processes. We give an overview on the background for this idea and show for the first time that extracellular matrix degradation by invadopodia can be differentially manipulated, without effects on cell proliferation, by use of metabolic inhibitors or changes in nutrient composition of cell culture media. We conclude that cell metabolism and carbohydrate availability, especially pyruvate, are involved in fuelling of invadopodia formation and activity.

Nicotinic acetylcholine receptor mediates nicotine-induced actin cytoskeletal remodeling and extracellular matrix degradation by vascular smooth muscle cells

Cigarette smoking is a significant risk factor for atherosclerosis, which involves the invasion of vascular smooth muscle cells (VSMCs) from the media to intima. A hallmark of many invasive cells is actin cytoskeletal remodeling in the form of podosomes, accompanied by extracellular matrix (ECM) degradation. A7r5 VSMCs form podosomes in response to PKC activation. In this study, we found that cigarette smoke extract, nicotine, and the cholinergic agonist, carbachol, were similarly effective in inducing the formation of podosome rosettes in A7r5 VSMCs. α-Bungarotoxin and atropine experiments confirmed the involvement of nicotinic acetylcholine receptors (nAChRs). Western blotting and immunofluorescence experiments revealed the aggregation of nAChRs at podosome rosettes. Cycloheximide experiments and media exchange experiments suggested that autocrine factor(s) and intracellular phenotypic modulation are putative mechanisms. In situ zymography experiments indicated that, in response to PKC activation, nicotine-treated cells degraded ECM near podosome rosettes, and possibly endocytose ECM fragments to intracellular compartments. Invasion assay of human aortic smooth muscle cells indicated that nicotine and PKC activation individually and synergistically enhanced cell invasion through ECM. Results from this study suggest that nicotine enhances the ability of VSMCs to degrade and invade ECM. nAChR activation, actin cytoskeletal remodeling and phenotypic modulation are possible mechanisms.

Role of the retinal vascular endothelial cell in ocular disease

Retinal endothelial cells line the arborizing microvasculature that supplies and drains the neural retina. The anatomical and physiological characteristics of these endothelial cells are consistent with nutritional requirements and protection of a tissue critical to vision. On the one hand, the endothelium must ensure the supply of oxygen and other nutrients to the metabolically active retina, and allow access to circulating cells that maintain the vasculature or survey the retina for the presence of potential pathogens. On the other hand, the endothelium contributes to the blood-retinal barrier that protects the retina by excluding circulating molecular toxins, microorganisms, and pro-inflammatory leukocytes. Features required to fulfill these functions may also predispose to disease processes, such as retinal vascular leakage and neovascularization, and trafficking of microbes and inflammatory cells. Thus, the retinal endothelial cell is a key participant in retinal ischemic vasculopathies that include diabetic retinopathy and retinopathy of prematurity, and retinal inflammation or infection, as occurs in posterior uveitis. Using gene expression and proteomic profiling, it has been possible to explore the molecular phenotype of the human retinal endothelial cell and contribute to understanding of the pathogenesis of these diseases. In addition to providing support for the involvement of well-characterized endothelial molecules, profiling has the power to identify new players in retinal pathologies. Findings may have implications for the design of new biological therapies. Additional progress in this field is anticipated as other technologies, including epigenetic profiling methods, whole transcriptome shotgun sequencing, and metabolomics, are used to study the human retinal endothelial cell.

Regulation of synaptojanin 2 5'-phosphatase activity by Src

Synaptojanin 2 (SYNJ2) is a phosphatidylinositol (PI) phosphatase that controls two distinct functions, clathrin-mediated endocytosis and tumor cell invadopodia formation and invasion. Here, we identify a number of novel SYNJ2 binding partners, several of which have previously been shown to be necessary for invadopodia formation or clathrin-mediated endocytosis. We focus on Src family kinases. We found that Src phosphorylates SYNJ2 on Tyr⁴⁹⁰, thereby stimulating SYNJ2 5′-phosphatase activity in vitro. We also provide evidence that Src-mediated phosphorylation of SYNJ2 contributes to invadopodia formation.

The small GTPase RhoG mediates glioblastoma cell invasion

Background

The invasion of glioblastoma cells into regions of the normal brain is a critical factor that limits current therapies for malignant astrocytomas. Previous work has identified roles for the Rho family guanine nucleotide exchange factors Trio and Vav3 in glioblastoma invasion. Both Trio and Vav3 act on the small GTPase RhoG. We therefore examined the role of RhoG in the invasive behavior of glioblastoma cells.

Results

We found that siRNA-mediated depletion of RhoG strongly inhibits invasion of glioblastoma cells through brain slices ex vivo. In addition, depletion of RhoG has a marginal effect on glioblastoma cell proliferation, but significantly inhibits glioblastoma cell survival in colony formation assays. We also observed that RhoG is activated by both HGF and EGF, two factors that are thought to be clinically relevant drivers of glioblastoma invasive behavior, and that RhoG is overexpressed in human glioblastoma tumors versus non-neoplastic brain. In search of a mechanism for the contribution of RhoG to the malignant behavior of glioblastoma cells, we found that depletion of RhoG strongly inhibits activation of the Rac1 GTPase by both HGF and EGF. In line with this observation, we also show that RhoG contributes to the formation of lamellipodia and invadopodia, two functions that have been shown to be Rac1-dependent.

Conclusions

Our functional analysis of RhoG in the context of glioblastoma revealed a critical role for RhoG in tumor cell invasion and survival. These results suggest that targeting RhoG-mediated signaling presents a novel avenue for glioblastoma therapy.

Rab5c promotes AMAP1-PRKD2 complex formation to enhance β1 integrin recycling in EGF-induced cancer invasion

EGF signaling activates Rab5c and promotes the intracellular association of AMAP1 and PRKD2 to enhance β1 integrin recycling and promote the invasiveness of breast cancer cells.

Epidermal growth factor receptor (EGFR) signaling is one of the crucial factors in breast cancer malignancy. Breast cancer cells often overexpress Arf6 and its effector, AMAP1/ASAP1/DDEF1; in these cells, EGFR signaling may activate the Arf6 pathway to induce invasion and metastasis. Active recycling of some integrins is crucial for invasion and metastasis. Here, we show that the Arf6–AMAP1 pathway links to the machinery that recycles β1 integrins, such as α3β1, to promote cell invasion upon EGFR stimulation. We found that AMAP1 had the ability to bind directly to PRKD2 and hence to make a complex with the cytoplasmic tail of the β1 subunit. Moreover, GTP-Rab5c also bound to AMAP1, and activation of Rab5c by EGFR signaling was necessary to promote the intracellular association of AMAP1 and PRKD2. Our results suggest a novel mechanism by which EGFR signaling promotes the invasiveness of some breast cancer cells via integrin recycling.

Quantitative measurement of invadopodia-mediated extracellular matrix proteolysis in single and multicellular contexts

Cellular invasion into local tissues is a process important in development and homeostasis. Malregulated invasion and subsequent cell movement is characteristic of multiple pathological processes, including inflammation, cardiovascular disease and tumor cell metastasis. Focalized proteolytic degradation of extracellular matrix (ECM) components in the epithelial or endothelial basement membrane is a critical step in initiating cellular invasion. In tumor cells, extensive in vitro analysis has determined that ECM degradation is accomplished by ventral actin-rich membrane protrusive structures termed invadopodia. Invadopodia form in close apposition to the ECM, where they moderate ECM breakdown through the action of matrix metalloproteinases (MMPs). The ability of tumor cells to form invadopodia directly correlates with the ability to invade into local stroma and associated vascular components. Visualization of invadopodia-mediated ECM degradation of cells by fluorescent microscopy using dye-labeled matrix proteins coated onto glass coverslips has emerged as the most prevalent technique for evaluating the degree of matrix proteolysis and cellular invasive potential. Here we describe a version of the standard method for generating fluorescently-labeled glass coverslips utilizing a commercially available Oregon Green-488 gelatin conjugate. This method is easily scaled to rapidly produce large numbers of coated coverslips. We show some of the common microscopic artifacts that are often encountered during this procedure and how these can be avoided. Finally, we describe standardized methods using readily available computer software to allow quantification of labeled gelatin matrix degradation mediated by individual cells and by entire cellular populations. The described procedures provide the ability to accurately and reproducibly monitor invadopodia activity, and can also serve as a platform for evaluating the efficacy of modulating protein expression or testing of anti-invasive compounds on extracellular matrix degradation in single and multicellular settings.

Functional invadopodia formation through stabilization of the PDPN transcript by IMP-3 and cancer-stromal crosstalk for PDPN expression

We previously reported that insulin-like growth factor-II mRNA-binding protein-3 (IMP-3) depletion (IMP-3(Δ)) was shown to inhibit invadopodia formation and extracellular matrix degradation capacity in oral squamous cell carcinoma (OSCC) cells. In this study, we found that IMP-3(Δ) cells significantly downregulated the podoplanin (PDPN) level, which resulted in a loss of extracellular matrix degradation activity, although invadopodia was still thriving. From RNA in situ hybridization using a digoxigenin-labeled 3'UTR recognition probe of PDPN and reporter assay with 3'UTR of the PDPN gene cloned downstream from the luciferase reporter gene, we revealed that IMP-3 depletion was shown to be downregulated, which most probably lowered PDPN gene expression by reducing mRNA stabilization. In a xenograft model, PDPN depletion was the cause of a decrease in tumor volume and regional infiltration into nearby stroma. Taken together, transforming growth factor beta 1 increased PDPN expression, which potentiated cancer invasion through increased invadopodia formation and extracellular matrix degradation in the low invasive OSCC cell line. Reciprocally, interleukin-1 beta secreted by OSCC cells, stimulated transforming growth factor beta 1 secretion from stromal fibroblasts to induce PDPN expression in OSCC cells. In addition, a retrospective investigation of OSCC patients found that IMP-3 and PDPN expression significantly correlated with lymph node metastasis of OSCC patients. Moreover, co-expression of IMP-3 and PDPN were frequently detected both in primary and lymph nodes metastatic OSCC cells using immunohistochemical dual staining. Thus, the IMP-3-PDPN axis may be a sensitive target molecule in anti-invadopodia therapy for the treatment of metastatic cancers.

Adhesion rings surround invadopodia and promote maturation

Invasion and metastasis are aggressive cancer phenotypes that are highly related to the ability of cancer cells to degrade extracellular matrix (ECM). At the cellular level, specialized actin-rich structures called invadopodia mediate focal matrix degradation by serving as exocytic sites for ECM-degrading proteinases. Adhesion signaling is likely to be a critical regulatory input to invadopodia, but the mechanism and location of such adhesion signaling events are poorly understood. Here, we report that adhesion rings surround invadopodia shortly after formation and correlate strongly with invadopodium activity on a cell-by-cell basis. By contrast, there was little correlation of focal adhesion number or size with cellular invadopodium activity. Prevention of adhesion ring formation by inhibition of RGD-binding integrins or knockdown (KD) of integrin-linked kinase (ILK) reduced the number of ECM-degrading invadopodia and reduced recruitment of IQGAP to invadopodium actin puncta. Furthermore, live cell imaging revealed that the rate of extracellular MT1-MMP accumulation at invadopodia was greatly reduced in both integrin-inhibited and ILK-KD cells. Conversely, KD of MT1-MMP reduced invadopodium activity and dynamics but not the number of adhesion-ringed invadopodia. These results suggest a model in which adhesion rings are recruited to invadopodia shortly after formation and promote invadopodium maturation by enhancing proteinase secretion. Since adhesion rings are a defining characteristic of podosomes, similar structures formed by normal cells, our data also suggest further similarities between invadopodia and podosomes.

Hic-5 promotes invadopodia formation and invasion during TGF-β-induced epithelial-mesenchymal transition

The focal adhesion protein Hic-5 acts through RhoC to promote TGF-β–stimulated invadopodia formation, cell migration, and invasion.

Transforming growth factor β (TGF-β)–stimulated epithelial–mesenchymal transition (EMT) is an important developmental process that has also been implicated in increased cell invasion and metastatic potential of cancer cells. Expression of the focal adhesion protein Hic-5 has been shown to be up-regulated in epithelial cells in response to TGF-β. Herein, we demonstrate that TGF-β–induced Hic-5 up-regulation or ectopic expression of Hic-5 in normal MCF10A cells promoted increased extracellular matrix degradation and invasion through the formation of invadopodia. Hic-5 was tyrosine phosphorylated in an Src-dependent manner after TGF-β stimulation, and inhibition of Src activity or overexpression of a Y38/60F nonphosphorylatable mutant of Hic-5 inhibited matrix degradation and invasion. RhoC, but not RhoA, was also required for TGF-β– and Hic-5–induced matrix degradation. Hic-5 also induced matrix degradation, cell migration, and invasion in the absence of TGF-β via Rac1 regulation of p38 MAPK. These data identify Hic-5 as a critical mediator of TGF-β–stimulated invadopodia formation, cell migration, and invasion.

The biomechanical properties of 3d extracellular matrices and embedded cells regulate the invasiveness of cancer cells

The malignancy of tumors depends on the biomechanical properties of cancer cells and their microenvironment, which enable cancer cells to migrate through the connective tissue, transmigrate through basement membranes and endothelial monolayers and form metastases in targeted organs. The current focus of cancer research is still based on biological capabilities such as molecular genetics and gene signaling, but these approaches ignore the mechanical nature of the invasion process of cancer cells. This review will focus on how structural, biochemical and mechanical properties of extracellular matrices (ECMs), and adjacent cells regulate the invasiveness of cancer cells. In addition, it presents how cancer cells create their own microenvironment by restructuring of the ECM and by interaction with stromal cells, which then further contribute to the progression of cancer disease. Finally, this review will point out that mechanical properties are a critical determinant for the efficiency of cancer cell invasion and the progression of cancer which might affect the future development of new cancer treatments.