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Tumour Invasion: A New Twist on Rac-Driven Mesenchymal Migration
Abstract
Elongated mesenchymal migration of cancer cells is driven by Rac1 activation mediated by the adaptor NEDD9 and the exchange factor DOCK3. A new study reports a role for the transcription factor Twist1 in inducing mesenchymal migration by relieving the suppression of NEDD9 and DOCK3 by the microRNA let-7i.
... YAP1-TEAD4 has been implicated in TIAM1-mediated activation of Rho-family GTPase RAC1, and thus, promotes tumour metastasis in breast cancer cells [54]. RAC has been linked to EMT [55]. Notably, RAC1 is also regulated by TWIST1, a highly active transcription factor in MES [55]. ...
... RAC has been linked to EMT [55]. Notably, RAC1 is also regulated by TWIST1, a highly active transcription factor in MES [55]. Similar findings have been reported in a mesenchymal subgroup of pancreatic neuroendocrine cancers with elevated YAP1 activity [56]. ...
Background:
Tumour heterogeneity in high-grade serous ovarian cancer (HGSOC) is a proposed cause of acquired resistance to treatment and high rates of relapse. Among the four distinct molecular subtypes of HGSOC, the mesenchymal subtype (MES) has been observed with high frequency in several study cohorts. Moreover, it exhibits aggressive characteristics with poor prognosis. The failure to adequately exploit such subtypes for treatment results in high mortality rates, highlighting the need for effective targeted therapeutic strategies that follow the idea of personalized medicine (PM).
Methods:
As a proof-of-concept, bulk and single-cell RNA data were used to characterize the distinct composition of the tumour microenvironment (TME), as well as the cell-cell communication and its effects on downstream transcription of MES. Moreover, transcription factor activity contextualized with causal inference analysis identified novel therapeutic targets with potential causal impact on transcription factor dysregulation promoting the malignant phenotype.
Findings:
Fibroblast and macrophage phenotypes are of utmost importance for the complex intercellular crosstalk of MES. Specifically, tumour-associated macrophages were identified as the source of interleukin 1 beta (IL1B), a signalling molecule with significant impact on downstream transcription in tumour cells. Likewise, signalling molecules tumour necrosis factor (TNF), transforming growth factor beta (TGFB1), and C-X-C motif chemokine 12 (CXCL12) were prominent drivers of downstream gene expression associated with multiple cancer hallmarks. Furthermore, several consistently hyperactivated transcription factors were identified as potential sources for treatment opportunities. Finally, causal inference analysis identified Yes-associated protein 1 (YAP1) and Nuclear Receptor Subfamily 2 Group F Member 6 (NR2F6) as novel therapeutic targets in MES, verified in an independent dataset.
Interpretation:
By utilizing a sophisticated bioinformatics approach, several candidates for treatment opportunities, including YAP1 and NR2F6 were identified. These candidates represent signalling regulators within the cellular network of the MES. Hence, further studies to confirm these candidates as potential targeted therapies in PM are warranted.
... Binary concepts like Epithelial to Mesenchymal Transition (EMT), and the reverse (MET), have been extensively studied in the fields of development and cancer (109). Our current understanding of cell motility in complex environments highlights that the initiation of invasion is not as simple as a transcriptional program switch and is heavily influenced by mechanochemical signaling and the plasticity it evokes. ...
... In a recent study, transformed cancerassociated fibroblasts (CAFs), were shown to facilitate tumor invasion through integrin αVβ3-dependent fibronectin secretion, which induced mechanical changes in the ECM through the contraction of collagen fibers (Figure 1) (105). The geometrical and mechanical ECM changes have been shown to affect the initial onset of invasion at the tumor-ECM interface (108,109). Reciprocally, stromal secretion of growth factors elicits changes in primary tumor cell behavior, resulting in tumor cell secretion of proteolytic enzymes, including MMPs (116,121) which have both catalytic and non-catalytic functions in melanoma invasion (32). Tumor-stromal crosstalk also plays a role in resistance to therapies where CAF-dependent ECM remodeling provides a therapeutic "safe-haven" for BRAF mutant melanoma from the BRAF inhibitor PLX4720 (122). ...
The importance of studying cancer cell invasion is highlighted by the fact that 90% of all cancer-related mortalities are due to metastatic disease. Melanoma metastasis is driven fundamentally by aberrant cell motility within three-dimensional or confined environments. Within this realm of cell motility, cytokines, growth factors, and their receptors are crucial for engaging signaling pathways, which both mediate crosstalk between cancer, stromal, and immune cells in addition to interactions with the surrounding microenvironment. Recently, the study of the mechanical biology of tumor cells, stromal cells and the mechanics of the microenvironment have emerged as important themes in driving invasion and metastasis. While current anti-melanoma therapies target either the MAPK signaling pathway or immune checkpoints, there are no drugs available that specifically inhibit motility and thus invasion and dissemination of melanoma cells during metastasis. One of the reasons for the lack of so-called "migrastatics" is that, despite decades of research, the precise biology of metastatic disease is still not fully understood. Metastatic disease has been traditionally lumped into a single classification, however what is now emergent is that the biology of melanoma metastasis is highly diverse, heterogeneous and exceedingly dynamic-suggesting that not all cases are created equal. The following mini-review discusses melanoma heterogeneity in the context of the emergent theme of mechanobiology and how it influences the tumor-stroma crosstalk during metastasis. Thus, highlighting future therapeutic options for migrastatics and mechanomedicines in the prevention and treatment of metastatic melanoma.
... Changes to the actin cytoskeleton are essential for the acquisition of migratory and invasive properties (Hanahan and Weinberg, 2000). Individual Rho GTPases are required for critical aspects of tumor cell migration and invasion (Vega and Ridley, 2008) and a tuned balance of Rho and Rac1 signaling is implicated in key aspects of cell motility (Sahai and Marshall, 2003;Pertz et al., 2006;Machacek et al., 2009;Sanz-Moreno, 2012). Recent evidence indicates that changes to nuclear structure influence cell migration simply by modulating nuclear plasticity to allow cell shape changes needed for squeezing through restricted spaces (Wolf et al., 2013), suggesting a role for Rac1 nuclear accumulation in this process. ...
... A converse GTP-loading pattern was observed for the cytosolic/ PM Rac1 pool, such that Rac1NES1 and Rac1NES1+2 mutants showed lower activation than Rac1WT and Rac1NES2 ( Figure 6B). These results likely reflect the well-established antagonism between Rac1 and RhoA (Pertz et al., 2006;Machacek et al., 2009;Sanz-Moreno, 2012). RhoA acts primarily to promote actomyosin contractile force generation through ROCK-mediated phosphorylation of regulatory myosin light chain (MLC; Rath and Olson, 2012). ...
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.
Copyright © 2015 Elsevier Inc. All rights reserved.
... Phosphorylated NEDD9 also physically interacts with SRC (10,303). Last, NEDD9 forms a complex with DOCK3, leading to RAC activation and initiation of mesenchymal like cell movement (259). Noncoding microRNAs also control EMT through transcriptional repression of genes governing epithelial identity (162,348). ...
... NEDD9 expression in tumors also correlates positively with a poorer overall survival (196). NEDD9 expression is regulated in part by TGF- signaling, and NEDD9 mediates some TGF--induced EMT migratory phenotypes via regulation of effectors including SRC, FAK, and DOCK3/WAVE2 (3,22,109,164,222,259,304). In addition, NEDD9 interacts physically with TGF- signaling effectors such as SMAD3, SMAD6, and SMAD7, modulating their output [ Fig. 2B; (136, 177)]. ...
Bioinformatic approaches are intended to provide systems level insight into the complex biological processes that underlie serious diseases such as cancer. In this review we describe current bioinformatic resources, and illustrate how they have been used to study a clinically important example: epithelial-to-mesenchymal transition (EMT) in lung cancer. Lung cancer is the leading cause of cancer-related deaths and is often diagnosed at advanced stages, leading to limited therapeutic success. While EMT is essential during development and wound healing, pathological reactivation of this program by cancer cells contributes to metastasis and drug resistance, both major causes of death from lung cancer. Challenges of studying EMT include its transient nature, its molecular and phenotypic heterogeneity, and the complicated networks of rewired signaling cascades. Given the biology of lung cancer and the role of EMT, it is critical to better align the two in order to advance the impact of precision oncology. This task relies heavily on the application of bioinformatic resources. Besides summarizing recent work in this area, we use four EMT-associated genes, TGF-β (TGFB1), NEDD9/HEF1, β-catenin (CTNNB1) and E-cadherin (CDH1), as exemplars to demonstrate the current capacities and limitations of probing bioinformatic resources to inform hypothesis-driven studies with therapeutic goals.
... RAC1, a member of the Rho family of GTPases, is a key regulator of mesenchymal migration and phenotypic plasticity of cancer cells [32][33][34]. In the GTPbound activated state, RAC1 regulates actin cytoskeleton reorganization, lamellipodia formation, focal adhesion remodeling, and proteolytic degradation of ECM [25, 35,36]. ...
BRAF V600E mutation occurs in 46% of melanomas and drives high levels of ERK activity and ERK-dependent proliferation. However, BRAF V600E is insufficient to drive melanoma in GEMM models, and 82% of human benign nevi harbor BRAF V600E mutations. We show here that BRAF V600E inhibits mesenchymal migration by causing feedback inhibition of RAC1 activity. ERK pathway inhibition induces RAC1 activation and restores migration and invasion. In cells with BRAF V600E , mutant RAC1, overexpression of PREX1, PREX2, or PTEN inactivation restore RAC1 activity and cell motility. Together, these lesions occur in 48% of BRAF V600E melanomas. Thus, although BRAF V600E activation of ERK deregulates cell proliferation, it prevents full malignant transformation by causing feedback inhibition of cell migration. Secondary mutations are, therefore, required for tumorigenesis. One mechanism underlying tumor evolution may be the selection of lesions that rescue the deleterious effects of oncogenic drivers.
Statement of significance
BRAF V600E activation of ERK causes feedback inhibition of cell migration and invasion and thus blocks tumorigenesis. Secondary genetic lesions are required to rescue these processes and enable tumor development. Thus, oncogenic feedback can shape the details of tumor progression and, in doing so, selects for new mutations that may be therapeutic targets.
... Promotion of Akt activity by Bmi1 was also found to promote EMT by blocking GSK3β-mediated degradation of Snail in HNSCC and 9 breast cancer [137,138]. Twist and Bmi1 also mediate suppression of a micro-RNA, miR let-7i, which results in NEDD9 and DOCK3 overexpression and promotes mesenchymal motility in HNSCC, melanoma and breast cancer via Rac1 [139][140][141]. In many cases breast cancer metastasis may be under the control of balance between Akt1 and Akt2 and their link with MiR-200/Zeb/E-cadherin axis [142,143]. ...
Metastasis is a critical step in the process of carcinogenesis and a vast majority of cancer related mortalities result from metastat-ic disease that is resistant to current therapies. Cell migration and invasion are the first steps of the metastasis process, which mainly occurs by two important biological mechanisms i.e., cytoskeletal remodelling and Epithelial to Mesenchymal Transition (EMT). Akt (also known as Protein Kinase B) is a central signalling molecule of the PI3K-Akt signalling pathway. Aberrant acti-vation of this pathway has been identified in a wide range of cancers. Several studies have revealed that Akt actively engages with the migratory process in motile cells, including metastatic cancer cells. The downstream signalling mechanism of Akt in cell migration depends upon the tumour type, sites, and intracellular localisation of activated Akt. In this review, we focus on the role of Akt in the regulation of two events that control cell migration and invasion in various cancers including head and neck squamous cell carcinoma (HNSCC) and the status of PI3K-Akt pathway inhibitors in clinical trials in HNSCC.
... 35 DOCK3 acts as a cancer-promoting gene, contributing to adhesion, migration and invasion of tumor cells. 36,37 Previous findings revealed that MRI radiomic features may play important roles to distinguish Glioblastoma subtypes, become potential biomarkers of cancer, and even involve in some important molecular pathways. 17 Some scholars demonstrated radiomics features extracted from CT exhibited substantial heterogeneity and could predict survival for lung cancer, head and neck cancer patients, and were associated with gene-expression profiles or expression patterns. ...
Purpose:
Microvascular invasion (MVI) impairs long-term prognosis of patients with hepatocellular carcinoma (HCC). We aimed to develop a novel nomogram to predict MVI and patients' prognosis based on radiomic features of contrast-enhanced CT (CECT).
Patients and methods:
HCC patients who underwent curative resection were enrolled. The radiomic features were extracted from the region of tumor, and the optimal MVI-related radiomic features were selected and applied to construct radiomic signature (Rad-score). The prediction models were created according to the logistic regression and evaluated. Biomarkers were analyzed via q-PCR from randomly selected HCC patients. Correlations between biomarkers and radiomic signature were analyzed.
Results:
A total of 421 HCC patients were enrolled. A total of 1962 radiomic features were extracted from the region of tumor, and the 11 optimal MVI-related radiomic features showed a favor predictive ability with area under the curves (AUCs) of 0.796 and 0.810 in training and validation cohorts, respectively. Aspartate aminotransferase (AST), tumor number, alpha-fetoprotein (AFP) level, and radiomics signature were independent risk factors of MVI. The four factors were integrated into the novel nomogram, named as CRM, with AUCs of 0.767 in training cohort and 0.793 in validation cohort for predicting MVI, best among radiomics signature alone and clinical model. The nomogram was well-calibrated with favorable clinical value demonstrated by decision curve analysis and can divide patients into high- or low-risk subgroups of recurrence and mortality. In addition, gene BCAT1, DTGCU2, DOCK3 were analyzed via q-PCR and serum AFP were identified as having significant association with radiomics signature.
Conclusion:
The novel nomogram demonstrated good performance in preoperatively predicting the probability of MVI, which might guide clinical decision.
... miR-146a mediated down-regulation of direct targets INTαv and serine/threonine kinase RHOassociated, coiled-coil containing protein kinase 1 (ROCK1) affects motility, but not TG (116). ROCK1 mediates rounded cell migration, whereas INTαv is involved in mesenchymallike invasion characterized by cell polarization and membrane protrusion (121). ROCK1 is a major effector of small GTPase RHO A and regulates the actomyosin cytoskeleton promoting contractile force generation and plays a role in mobility, metastasis and angiogenesis (122,123). ...
During the last years a considerable therapeutic progress in melanoma patients with the RAF V600E mutation via RAF/MEK pathway inhibition and immuno-therapeutic modalities has been witnessed. However, the majority of patients relapse after therapy. Therefore, a deeper understanding of the pathways driving oncogenicity and metastasis of melanoma is of paramount importance. In this review, we summarize microRNAs modulating tumor growth, metastasis, or both, in preclinical melanoma-related in vivo models and possible clinical impact in melanoma patients as modalities and targets for treatment of melanoma. We have identified miR-199a (ApoE, DNAJ4), miR-7-5p (RelA), miR-98a (IL6), miR-219-5p (BCL2) and miR-365 (NRP1) as possible targets to be scrutinized in further target validation studies.
... (Supplementary Figure 6A). Canonical Rac signaling results in enhanced cell migration and is a prerequisite for tumor invasion and metastasis (36,37). To determine if Rac inhibition would reduce cellular motility, Boyden chamber migration assays were conducted on HCT116 cells. ...
Resistance to chemotherapy represents a major limitation in the treatment of colorectal cancer. Novel strategies to circumvent resistance are critical to prolonging patient survival. Rac1b, a constitutively activated isoform of the small GTPase Rac1, is upregulated with disease progression and promotes cell proliferation and inhibits apoptosis by activation of NFκΒ signaling. Here, we show that Rac1b overexpression correlates with cancer stage and confirmed Rac1b expression is associated with increased growth through enhancing NFκB activity. Rac1b knockdown reduced cellular proliferation and reduced NFκB activity. Surprisingly, Rac1b expression and NFκB activity were upregulated in cells treated with chemotherapeutics, suggesting that Rac1b facilitates chemo-resistance through activation of NFκB signaling. Knockdown of Rac1b or Rac inhibtion increases the sensitivity of the cells to oxaliplatin. When used in combination, inhibition of Rac prevents the increase in NFκB activity associated with chemotherapy treatment and increases the sensitivity of the cells to oxaliplatin. While Rac inhibition or oxaliplatin treatment alone reduces the growth of colorectal cancer in vivo, combination therapy results in improved outcomes compared to single agents alone. We provide the first evidence that Rac1b expression confers resistance to chemotherapy in colorectal cancer. Additionally, we show that the use of a Rac inhibitor prevents chemoresistance by blocking activation of chemotherapy induced NFκB signaling providing a novel strategy to overcome resistance to chemotherapy in colorectal cancer.
... Rac1 is highly implicated in the regulation of various cellular functions like cell adhesion and cytoskeleton remodeling which majorly contribute to EMT process [112]. It was reported that the inhibition of Rac1 activity had greatly reduced the invasion as well as the proliferation of the human melanoma cells presenting the role of Rac1 in the melanoma metastasis and progression [113,114]. Few researchers have also reported the use of Zoledronic acid for the inhibition of ovarian cancer by preventing the activation of Rac1 [115]. They have conducted both in-vitro as well as in-vivo studies and found that treatment with Zoledronic acid could reduce the growth of the tumor, cell proliferation, and angiogenesis. ...
Cancer hallmarks help in understanding the diversity of various neoplasms. Epithelial cancers play an immense role in the tumor biology through Epithelial Mesenchymal Transition (EMT) process. Receptor tyrosine kinase as well as phosphatidyl ionositol-3 kinase pathways play an important role in the regulation of cell proliferation, survival, and differentiation during EMT. Till date, numerous studies have shown modulation in the expression profile of potential targets like CD44, EGFR, and Rac in epithelial cancers. CD44 interacts with EGFR and recruit other molecules which further activate the Rac pathway intermediates. This review mainly focused on modulation of genes like CD44, EGFR, and Rac pathway intermediates which play crucial role in the tumor progression, metastasis, proliferation, and invasion characteristics in epithelial cancers with EMT properties. Hence, targeting Rac pathway might be more strategically relevant approach in treating epithelial cancers.
... High levels of actomyosin contractility and lower levels of adhesion are characteristic of rounded amoeboid form of movement, in which blebs are used as functional protrusions. 3,4 Actomyosin contractility in amoeboid migration can be regulated either by Rho and downstream ROCK activity, or by Cdc42 through PAKs, [5][6][7][8] in both cases resulting in phosphorylation of MLC2 and therefore activating myosin II. 9 In contrast, elongated mesenchymal migrating cells use Rac-dependent actin polymerisation, and higher levels of integrin-dependent adhesion. [10][11][12] Intravital in vivo imaging studies have revealed how amoeboid migration is the fastest way of moving, being the preferred strategy used in the invasive fronts of melanomas and breast cancers. ...
Epithelial to mesenchymal transition is a common event during tumour dissemination. However, direct epithelial to amoeboid transition has not been characterized to date. Here we provide evidence that cells from hepatocellular carcinoma (HCC), a highly metastatic cancer, undergo epithelial to amoeboid transition in physiological environments, such as organoids or three-dimensional complex matrices. Furthermore, the NADPH oxidase NOX4 inhibits this transition and therefore suppresses efficient amoeboid bleb-based invasion. Moreover, NOX4 expression is associated with E-cadherin levels and inversely correlated with invasive features. NOX4 is necessary to maintain parenchymal structures, increase cell-cell and cell-to-matrix adhesion, and impair actomyosin contractility and amoeboid invasion. Importantly, NOX4 gene deletions are frequent in HCC patients, correlating with higher tumour grade. Contrary to that observed in mesenchymal cell types, here NOX4 suppresses Rho and Cdc42 GTPase expression and downstream actomyosin contractility. In HCC patients, NOX4 expression inversely correlates with RhoC and Cdc42 levels. Moreover, low expression of NOX4 combined with high expression of either RhoC or Cdc42 is associated with worse prognosis. Therefore, loss of NOX4 increases actomyosin levels and favours an epithelial to amoeboid transition contributing to tumour aggressiveness.Oncogene advance online publication, 12 December 2016; doi:10.1038/onc.2016.454.
... Cancer cell motility occurs through actin reorganization and control of integrin-directed cell migration via the actin cytoskeleton providing the possibility of regulating cancer cell invasion and metastasis [33]. The "mesenchymal" movement (elongated movement of cancer cells) requires activation of RAC1 [34,35], whereas rounded/amoeboid movement engages specific Cdc42 signaling pathways [36]. One of the ways RAC1 transduces signals is from integrins. ...
The acquisition of integrin-directed metastasis-associated (ID-MA) phenotypes by Triple-Negative Breast Cancer (TNBC) cells is caused by an upregulation of the Wnt-beta-catenin pathway (WP). We reported that WP is one of the salient genetic features of TNBC. RAC-GTPases, small G-proteins which transduce signals from cell surface proteins including integrins, have been implicated in tumorigenesis and metastasis by their role in essential cellular functions like motility. The collective percentage of alteration(s) in RAC1 in ER+ve BC was lower as compared to ER-ve BC (35% vs 57%) (brca/tcga/pub2015). High expression of RAC1 was associated with poor outcome for RFS with HR=1.48 [CI: 1.15-1.9] p=0.0019 in the Hungarian ER-veBC cohort. Here we examined how WP signals are transduced via RAC1 in the context of ID-MA phenotypes in TNBC. Using pharmacological agents (sulindac sulfide), genetic tools (beta-catenin siRNA), WP modulators (Wnt-C59, XAV939), RAC1 inhibitors (NSC23766, W56) and WP stimulations (LWnt3ACM, Wnt3A recombinant) in a panel of 6-7 TNBC cell lines, we studied fibronectin-directed (1) migration, (2) matrigel invasion, (3) RAC1 and Cdc42 activation, (4) actin dynamics (confocal microscopy) and (5) podia-parameters. An attenuation of WP, which (a) decreased cellular levels of beta-catenin, as well as its nuclear active-form, (b) decreased fibronectin-induced migration, (c) decreased invasion, (d) altered actin dynamics and (e) decreased podia-parameters was successful in blocking fibronectin-mediated RAC1/Cdc42 activity. Both Wnt-antagonists and RAC1 inhibitors blocked fibronectin-induced RAC1 activation and inhibited the fibronectin-induced ID-MA phenotypes following specific WP stimulation by LWnt3ACM as well as Wnt3A recombinant protein. To test a direct involvement of RAC1-activation in WP-mediated ID-MA phenotypes, we stimulated brain-metastasis specific MDA-MB231BR cells with LWnt3ACM. LWnt3ACM-stimulated fibronectin-directed migration was blocked by RAC1 inhibition in MDA-MB231BR cells. In the light of our previous report that WP upregulation causes ID-MA phenotypes in TNBC tumor cells, here we provide the first mechanism based evidence to demonstrate that WP upregulation signals ID-MA tumor cell phenotypes in a RAC1-GTPase dependent manner involving exchange-factors like TIAM1 and VAV2. Our study demonstrates for the first time that beta-catenin-RAC1 cascade signals integrin-directed metastasis-associated tumor cell phenotypes in TNBC.
... Neither LFNG nor NUMB did affect melanoma cell migration and invasion in vitro, while, interestingly, two key players of the integrin signaling, ITGAV and ROCK1, are affected by miR-146a. ROCK1 mediates "amoeboid," rounded cell migration, while ITGAV is involved in "mesenchymal-like" invasion, characterized by cell polarization and membrane protruding, two invasion strategies used by melanoma cells during dissemination (41). ROCK1 is poorly expressed in invasive human melanomas and cutaneous metastases, whereas miR-146a is enriched. ...
Unlabelled:
Malignant melanoma is the most aggressive form of skin cancer; therefore, it is crucial to disclose its underlying molecular mechanisms. MicroRNAs (miRNAs) are small endogenous noncoding RNAs able to posttranscriptionally downregulate the expression of direct target genes. Using a melanoma progression model, miR-146a was identified as a key double-acting player in melanoma malignancy. In fact, miR-146a is able to enhance tumor growth, while it suppresses dissemination. It was determined that miR-146a coordinated melanoma cell growth by its direct targets lunatic fringe (LFNG) and NUMB, which operate on the NOTCH/PTEN/Akt pathway; while inhibition of metastasis formation was linked to decreased expression of ITGAV and ROCK1. Relevantly, miR-146a expression correlated with melanoma recurrence and was enriched in both patient-derived melanoma and cutaneous metastasis specimens, while its direct targets were depleted. However, miR-146a levels drop in circulating tumor cells (CTCs), suggesting the necessity for miR-146a expression to fluctuate during tumor progression in order to favor tumor growth and allow dissemination. This study reconciles the contradictory biologic functions of miR-146a in melanoma progression and unravels distinct molecular mechanisms that need to be considered for therapeutic interventions.
Implications:
miR-146a controls melanoma progression in a dual way, promoting growth and inhibiting dissemination; however, it is poorly expressed in CTCs, resulting in overall tumor spreading and distant-site colonization. Mol Cancer Res; 14(6); 548-62. ©2016 AACR.
... Neither LFNG nor NUMB did affect melanoma cell migration and invasion in vitro, while, interestingly, two key players of the integrin signaling, ITGAV and ROCK1, are affected by miR-146a. ROCK1 mediates "amoeboid," rounded cell migration, while ITGAV is involved in "mesenchymal-like" invasion, characterized by cell polarization and membrane protruding, two invasion strategies used by melanoma cells during dissemination (41). ROCK1 is poorly expressed in invasive human melanomas and cutaneous metastases, whereas miR-146a is enriched. ...
Malignant melanoma is the most aggressive form of skin cancer therefore it is crucial to disclose its underlying molecular mechanisms. MicroRNAs (miRs) are small endogenous non-coding RNAs able to post-transcriptionally down-regulate the expression of direct target genes. Using a melanoma progression model, miR-146a was identified as a key double-acting player in melanoma malignancy. In fact, miR-146a is able to enhance tumor growth while it suppresses dissemination. It was determined that miR-146a coordinated melanoma cell growth by its direct targets lunatic fringe (LFNG) and NUMB which operate on the NOTCH/PTEN/Akt pathway; while, inhibition of metastasis formation was linked to decreased expression of ITGAV and ROCK1. Relevantly, miR-146a expression correlated with melanoma recurrence and was enriched in both patients-derived melanoma and cutaneous metastasis specimens, while its direct targets were depleted. However, miR-146a levels drop in Circulating Tumor Cells (CTCs), suggesting the necessity for miR-146 expression to fluctuate during tumor progression in order to favor tumor growth and allow dissemination. This study reconciles the contradictory biological functions of miR-146a in melanoma progression and unravels distinct molecular mechanisms that need to be considered for therapeutic interventions.
Implications:
miR-146a controls melanoma progression in a dual-way, promoting growth and inhibiting dissemination; however, it is poorly expressed in CTCs, resulting in overall tumor spreading and distant-site colonization.
... The antagonism between Rac1 and RhoA is well established ( Rottner et al. 1999) and may act as a regulatory switch between actin-and bleb-driven migration modes ( Parri and Chiarugi 2010). Cells with high Rac1 activity generally favor actin-driven mesenchymal migration ( Sanz-Moreno 2012) in agreement with central role of Rac1 in actin protrusion formation ( Steffen et al. 2004). Meanwhile, cells with high RhoA activity exhibit bleb-driven amoeboid migration ( Sahai and Marshall 2003) consistently with the modulatory role of this GTPase in actomyosin contractility. ...
Recently we described a new phenomenon of anodotropic pseudopod-like blebbing in U937 cells exposed to nanosecond pulsed electric field (nsPEF). In Ca(2+)-free buffer such exposure initiates formation of pseudopod-like blebs (PLBs), protrusive cylindrical cell extensions that are distinct from apoptotic and necrotic blebs. PLBs nucleate predominantly on anode-facing cell pole and extend toward anode during nsPEF exposure. Bleb extension depends on actin polymerization and availability of actin monomers. Inhibition of intracellular Ca(2+), cell contractility, and RhoA produced no effect on PLB initiation. Meanwhile, inhibition of WASP by wiskostatin causes dose-dependent suppression of PLB growth. Soon after the end of nsPEF exposure PLBs lose directionality of growth and then retract. Microtubule toxins nocodazole and paclitaxel did not show immediate effect on PLBs; however, nocodazole increased mobility of intracellular components during PLB extension and retraction. Retraction of PLBs is produced by myosin activation and the corresponding increase in PLB cortex contractility. Inhibition of myosin by blebbistatin reduces retraction while inhibition of RhoA-ROCK pathway by Y-27632 completely prevents retraction. Contraction of PLBs can produce cell translocation resembling active cell movement. Overall, the formation, properties, and life cycle of PLBs share common features with protrusions associated with ameboid cell migration. PLB life cycle may be controlled through activation of WASP by its upstream effectors such as Cdc42 and PIP2, and main ROCK activator-RhoA. Parallels between pseudopod-like blebbing and motility blebbing may provide new insights into their underlying mechanisms.
Metastasis is a critical step in the process of carcinogenesis and a vast majority of cancer-related mortalities result from metastatic disease that is resistant to current therapies. Cell migration and invasion are the first steps of the metastasis process, which mainly occurs by two important biological mechanisms, i.e., cytoskeletal remodelling and epithelial to mesenchymal transition (EMT). Akt (also known as protein kinase B) is a central signalling molecule of the PI3K-Akt signalling pathway. Aberrant activation of this pathway has been identified in a wide range of cancers. Several studies have revealed that Akt actively engages with the migratory process in motile cells, including metastatic cancer cells. The downstream signalling mechanism of Akt in cell migration depends upon the tumour type, sites, and intracellular localisation of activated Akt. In this review, we focus on the role of Akt in the regulation of two events that control cell migration and invasion in various cancers including head and neck squamous cell carcinoma (HNSCC) and the status of PI3K-Akt pathway inhibitors in clinical trials in metastatic cancers.
Circulating tumor cells (CTCs) play an important role in dissemination and metastases of mesenchymal tumors. Due to the rarity of these tumors and the absence of specific markers expressed by circulating mesenchymal tumor cells, the characterization of these cells is limited. Here, we provide an overview on the origin of mesenchymal tumor heterogeneity and dissemination. Moreover, recent progress has made it possible to isolate and characterize circulating mesenchymal tumor cells by size, and research studies have been looking for ideal markers for this type of cell. Furthermore, we know that the epithelial mesenchymal transition (EMT) is a key process in the progression of malignant cancer and is directly linked to the spread of CTCs. In contrast, the precise role of EMT-related processes in tumors originating from mesenchymal tissues is poorly explored. This chapter is a review of studies involving CTCs from mesenchymal tumors and mesenchymal-epithelial transition. It may open an area for future investigations and better understanding about CTCs and epithelial mesenchymal transition.
In vitro differentiation of stem cells into specific cell lineages provides a stable cell supply for cell therapy and tissue engineering. Therefore, understanding the mechanisms underlying such differentiation process is critical for generating committed lineage-specific cell progenies effectively. We previously developed a two-step protocol to differentiate mesenchymal stromal cells (MSCs) into hepatocyte-like cells. Since hepatic differentiation involves mesenchymal-epithelial transition (MET), we hypothesize that promoting MET could further accelerate the differentiation process. Ras-related C3 botulinum toxin substrate 1 (Rac1) is involved in actin polymerization and its role in MET was investigated in the study. Our results showed that inhibition of Rac1 activation by Rac1 specific inhibitor NSC23766 led to cells favoring epithelial morphology and being more packed during hepatic differentiation. In addition, Rac1 inhibition accelerated the upregulation of hepatic marker genes accompanied by more mature hepatic functions. Taken together, promotion of MET by inhibiting Rac1 accelerates the hepatic differentiation of MSCs. Our findings open a new prospect of directing the commitment of MSCs by manipulating cell morphology and cytoskeleton arrangement via small molecules. The results provide further insight into scaffold design for rapid production of MSC-differentiated hepatocytes.
Neural precursor expressed, developmentally down-regulated 9 (NEDD9), a member of the Cas family of signal transduction molecules, is amplified at the genetic level in melanoma, and elevated expression levels have been shown to correlate with melanoma progression and metastasis. NEDD9 interacts with the guanine nucleotide exchange factor DOCK3 to promote Rac activation and the elongated, mesenchymal-type of tumour cell invasion, but the molecular mechanisms through which NEDD9 promotes melanoma metastasis are not fully understood. We show that signalling through increased NEDD9 levels requires integrin β3 signalling, which leads to elevated phosphorylation of integrin β3. This results in increased Src and FAK but decreased ROCK signalling to drive elongated, mesenchymal-type invasion in environments that contain vitronectin. NEDD9 overexpression does not affect ROCK signalling through activation of RhoA but decreases ROCKII signalling through Src-dependent phosphorylation of a negative regulatory site Tyr722. In NEDD9-overexpressing melanoma cells, inhibition of Src with dasatinib results in a switch from Rac-driven elongated, mesenchymal-type invasion to ROCK-dependent rounded, amoeboid invasion. These findings brings into question whether dasatinib would work as a therapeutic agent to block melanoma invasion and metastasis. On the basis of the in vitro data presented here, a combination treatment of dasatinib and a ROCK inhibitor might be a better alternative in order to inhibit both elongated, mesenchymal-type and rounded, amoeboid motility.
Epithelial-mesenchymal transition (EMT), which is characterized by the suppression of the adhesion protein E-cadherin, is a crucial process that promotes metastasis and stem-like properties of cancer cells. However, the dissociation of cellular aggregates is not sufficient to explain why cancer cells move, and the motile nature of cancer cells undergoing EMT remains elusive. Here, we identify a mechanism in which the EMT inducer Twist1 elicits cancer cell movement through activation of RAC1. Twist1 cooperates with BMI1 to suppress let-7i expression, which results in upregulation of NEDD9 and DOCK3, leading to RAC1 activation and enabling mesenchymal-mode movement in three-dimensional environments. Moreover, the suppression of let-7i contributes to Twist1-induced stem-like properties. Clinically, activation of the Twist1-let-7i-NEDD9 axis in head and neck cancer patients correlates with tumour invasiveness and worse outcome. Our results uncover an essential mechanism to explain how Twist1 induces the motile stem-like cancer cell phenotype beyond simply suppressing E-cadherin.
Metastatic melanoma cells are highly adaptable to their in vivo microenvironment and can switch between protease-dependent mesenchymal and protease-independent amoeboid invasion to facilitate metastasis. Such adaptability can be visualized in vitro, when cells are cultured in conditions that recapitulate three-dimensional microenvironments. Using thick collagen layers in cell culture and in vivo extravasation assays, we found that pigment epithelium-derived factor (PEDF) suppressed lung extravasation of aggressive melanoma by coordinated regulation of cell shape and proteolysis. In cells grown on a thick collagen bed, PEDF overexpression and exogenous PEDF blocked the rapidly invasive, rounded morphology, and promoted an elongated, mesenchymal-like phenotype associated with reduced invasion. These changes in cell shape depended on decreased RhoA and increased Rac1 activation and were mediated by the up-regulation of Rac1-GEF, DOCK3 and down-regulation of Rac1-GAP, ARHGAP22. Surprisingly, we found that PEDF overexpression also blocked the trafficking of membrane-tethered, MT1-MMP to the cell surface through RhoA inhibition and Rac1 activation. In vivo, knockdown of Rac1 and DOCK3 or overexpression of MT1-MMP was sufficient to reverse the inhibitory effect of PEDF on extravasation. Using functional studies, we demonstrated that PEDF suppressed the rounded morphology and MT1-MMP surface localization through its antiangiongenic, 34-mer epitope and the recently identified PEDF receptor candidate, PNPLA2. Our findings unveil the coordinated regulation of cell shape and proteolysis and identify an unknown mechanism for PEDF's antimetastatic activity.
A functional role of microRNAs (miRNAs or miRs) in neoplasia and metastasis is becoming clear, and the miR-200 family has received much attention for potentially regulating tumor progression. The miRNAs of this family have been shown to suppress epithelial-mesenchymal transition, and their down-regulation in some tumors promotes invasion and metastasis. Interestingly, while miR-200 is down-regulated in some cancers, it is up-regulated in others.
We show that levels of miR-200 are increased in melanoma cell lines compared to normal melanocytes and that miR-200 family members play a role in determining modes of tumor cell migration. Individual tumor cells can invade in either elongated, "mesenchymal-type" or rounded, "amoeboid-like" modes and these two modes of invasion are inter-convertible [1]. In melanoma cell lines, expression of miR-200 members does not suppress invasion but rather leads to a switch between modes of invasion. MicroRNA-200c results in a higher proportion of cells adopting the rounded, amoeboid-like mode of invasion, while miR-200a results in a protrusion-associated elongated mode of invasion. Functional target identification studies suggest that the morphological effects of miR-200c may be mediated by reduced expression of MARCKS, which has been linked to formation of cell protrusions. In contrast miR-200a reduces actomyosin contractility, a feature of rounded morphology.
Overall our findings call into question the general role of miR-200 in suppressing invasion and metastasis, and highlight novel distinguishing characteristics of individual miR-200 family members.
The epithelial-mesenchymal transition (EMT), one of the main mechanisms underlying development of cancer metastasis, induces stem-like properties in epithelial cells. Bmi1 is a polycomb-group protein that maintains self-renewal, and is frequently overexpressed in human cancers. Here, we show the direct regulation of BMI1 by the EMT regulator, Twist1. Furthermore, Twist1 and Bmi1 were mutually essential to promote EMT and tumour-initiating capability. Twist1 and Bmi1 act cooperatively to repress expression of both E-cadherin and p16INK4a. In patients with head and neck cancers, increased levels of both Twist1 and Bmi1 correlated with downregulation of E-cadherin and p16INK4a, and was associated with the worst prognosis. These results suggest that Twist1-induced EMT and tumour-initiating capability in cancer cells occurs through chromatin remodelling, which leads to unfavourable clinical outcomes.
Proteins of the CAS (Crk-associated substrate) family (BCAR1/p130Cas, NEDD9/HEF1/Cas-L, EFS/SIN and CASS4/HEPL) are integral players in normal and pathological cell biology. CAS proteins act as scaffolds to regulate protein complexes controlling migration and chemotaxis, apoptosis, cell cycle, and differentiation, and have more recently been linked to a role in progenitor cell function. Reflecting these complex functions, over-expression of CAS proteins has now been strongly linked to poor prognosis and increased metastasis in cancer, as well as resistance to first-line chemotherapeutics in multiple tumor types including breast and lung cancers, glioblastoma, and melanoma. Further, CAS proteins have also been linked to additional pathological conditions including inflammatory disorders, Alzheimer's and Parkinson's disease, as well as developmental defects. This review will explore the roles of the CAS proteins in normal and pathological states in the context of the many mechanistic insights into CAS protein function that have emerged in the past decade.
Here we use intravital imaging to demonstrate a reversible transition to a motile state as breast cancer cells spread. Imaging primary tumours revealed heterogeneity in cell morphology and motility. Two distinct modes of motility were observed: collective and single-celled. By monitoring the localization of Smad2 and the activity of a TGFbeta-dependent reporter gene during breast cancer cell dissemination, we demonstrate that TGFbeta signalling is transiently and locally activated in motile single cells. TGFbeta1 switches cells from cohesive to single cell motility through a transcriptional program involving Smad4, EGFR, Nedd9, M-RIP, FARP and RhoC. Blockade of TGFbeta signalling prevented cells moving singly in vivo but did not inhibit cells moving collectively. Cells restricted to collective invasion were capable of lymphatic invasion but not blood-borne metastasis. Constitutive TGFbeta signalling promoted single cell motility and intravasation but reduced subsequent growth in the lungs. Thus, transient TGFbeta signalling is essential for blood-borne metastasis.
Invasive tumor dissemination in vitro and in vivo involves the proteolytic degradation of ECM barriers. This process, however, is only incompletely attenuated by protease inhibitor-based treatment, suggesting the existence of migratory compensation strategies. In three-dimensional collagen matrices, spindle-shaped proteolytically potent HT-1080 fibrosarcoma and MDA-MB-231 carcinoma cells exhibited a constitutive mesenchymal-type movement including the coclustering of beta 1 integrins and MT1-matrix metalloproteinase (MMP) at fiber bindings sites and the generation of tube-like proteolytic degradation tracks. Near-total inhibition of MMPs, serine proteases, cathepsins, and other proteases, however, induced a conversion toward spherical morphology at near undiminished migration rates. Sustained protease-independent migration resulted from a flexible amoeba-like shape change, i.e., propulsive squeezing through preexisting matrix gaps and formation of constriction rings in the absence of matrix degradation, concomitant loss of clustered beta 1 integrins and MT1-MMP from fiber binding sites, and a diffuse cortical distribution of the actin cytoskeleton. Acquisition of protease-independent amoeboid dissemination was confirmed for HT-1080 cells injected into the mouse dermis monitored by intravital multiphoton microscopy. In conclusion, the transition from proteolytic mesenchymal toward nonproteolytic amoeboid movement highlights a supramolecular plasticity mechanism in cell migration and further represents a putative escape mechanism in tumor cell dissemination after abrogation of pericellular proteolysis.
Physical forces play important roles in regulating cell proliferation, differentiation, and death by activating intracellular signal transduction pathways. How cells sense mechanical stimulation, however, is largely unknown. Most studies focus on cellular membrane proteins such as ion channels, integrins, and receptors for growth factors as mechanosensory units. Here we show that mechanical stretch-induced c-Src protein tyrosine kinase activation is mediated through the actin filament-associated protein (AFAP). Distributed along the actin filaments, AFAP can directly active c-Src through binding to its Src homology 3 and/or 2 domains. Mutations at these specific binding sites on AFAP blocked mechanical stretch-induced c-Src activation. Therefore, mechanical force can be transmitted along the cytoskeleton, and interaction between cytoskeletal associated proteins and enzymes related to signal transduction may convert physical forces into biochemical reactions. Cytoskeleton deformation-induced protein-protein interaction via specific binding sites may represent a novel intracellular mechanism for cells to sense mechanical stimulation.
The mechanical environment crucially influences many cell functions. However, it remains largely mysterious how mechanical stimuli are transmitted into biochemical signals. Src is known to regulate the integrin-cytoskeleton interaction, which is essential for the transduction of mechanical stimuli. Using fluorescent resonance energy transfer (FRET), here we develop a genetically encoded Src reporter that enables the imaging and quantification of spatio-temporal activation of Src in live cells. We introduced a local mechanical stimulation to human umbilical vein endothelial cells (HUVECs) by applying laser-tweezer traction on fibronectin-coated beads adhering to the cells. Using the Src reporter, we observed a rapid distal Src activation and a slower directional wave propagation of Src activation along the plasma membrane. This wave propagated away from the stimulation site with a speed (mean +/- s.e.m.) of 18.1 +/- 1.7 nm s(-1). This force-induced directional and long-range activation of Src was abolished by the disruption of actin filaments or microtubules. Our reporter has thus made it possible to monitor mechanotransduction in live cells with spatio-temporal characterization. We find that the transmission of mechanically induced Src activation is a dynamic process that directs signals via the cytoskeleton to spatial destinations.
The aggressive clinical behavior of melanoma suggests that the developmental origins of melanocytes in the neural crest might be relevant to their metastatic propensity. Here we show that primary human melanocytes, transformed using a specific set of introduced genes, form melanomas that frequently metastasize to multiple secondary sites, whereas human fibroblasts and epithelial cells transformed using an identical set of genes generate primary tumors that rarely do so. Notably, these melanomas have a metastasis spectrum similar to that observed in humans with melanoma. These observations indicate that part of the metastatic proclivity of melanoma is attributable to lineage-specific factors expressed in melanocytes and not in other cell types analyzed. Analysis of microarray data from human nevi shows that the expression pattern of Slug, a master regulator of neural crest cell specification and migration, correlates with those of other genes that are important for neural crest cell migrations during development. Moreover, Slug is required for the metastasis of the transformed melanoma cells. These findings indicate that melanocyte-specific factors present before neoplastic transformation can have a pivotal role in governing melanoma progression.
Genomes of human cancer cells are characterized by numerous chromosomal aberrations of uncertain pathogenetic significance. Here, in an inducible mouse model of melanoma, we characterized metastatic variants with an acquired focal chromosomal amplification that corresponds to a much larger amplification in human metastatic melanomas. Further analyses identified Nedd9, an adaptor protein related to p130CAS, as the only gene within the minimal common region that exhibited amplification-associated overexpression. A series of functional, biochemical, and clinical studies established NEDD9 as a bona fide melanoma metastasis gene. NEDD9 enhanced invasion in vitro and metastasis in vivo of both normal and transformed melanocytes, functionally interacted with focal adhesion kinase and modulated focal contact formation, and exhibited frequent robust overexpression in human metastatic melanoma relative to primary melanoma. Thus, comparative oncogenomics has enabled the identification and facilitated the validation of a highly relevant cancer gene governing metastatic potential in human melanoma.
Contractile actin cortex is involved in cell morphogenesis, movement, and cytokinesis, but its organization and assembly are poorly understood. During blebbing, the membrane detaches from the cortex and inflates. As expansion ceases, contractile cortex re-assembles under the membrane and drives bleb retraction. This cycle enabled us to measure the temporal sequence of protein recruitment to the membrane during cortex reassembly and to explore dependency relationships. Expanding blebs were devoid of actin, but proteins of the erythrocytic submembranous cytoskeleton were present. When expansion ceased, ezrin was recruited to the membrane first, followed by actin, actin-bundling proteins, and, finally, contractile proteins. Complete assembly of the contractile cortex, which was organized into a cagelike mesh of filaments, took approximately 30 s. Cytochalasin D blocked recruitment of actin and alpha-actinin, but had no effect on membrane association of ankyrin B and ezrin. Ezrin played no role in actin nucleation, but was essential for tethering the membrane to the cortex. The Rho pathway was important for cortex assembly in blebs.
The morphological term 'amoeboid' migration subsumes a number of rather distinct biophysical modes of cellular locomotion that range from blebbing motility to entirely actin-polymerization-based gliding. Here, we discuss the diverse principles of force generation and force transduction that lead to the distinct amoeboid phenotypes. We argue that shifting the balance between actin protrusion, actomyosin contraction, and adhesion to the extracellular substrate can explain the different modes of amoeboid movement and that blebbing and gliding are barely extreme variants of one common migration strategy. Depending on the cell type, physiological conditions or experimental manipulation, amoeboid cells can adopt the distinct mechanical modes of amoeboid migration.
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Melanoma cells can switch between an elongated mesenchymal-type and a rounded amoeboid-type migration mode. The rounded 'amoeboid' form of cell movement is driven by actomyosin contractility resulting in membrane blebbing. Unlike elongated A375 melanoma cells, rounded A375 cells do not display any obvious morphological front-back polarisation, although polarisation is thought to be a prerequisite for cell movement. We show that blebbing A375 cells are polarised, with ezrin (a linker between the plasma membrane and actin cytoskeleton), F-actin, myosin light chain, plasma membrane, phosphatidylinositol (4,5)-bisphosphate and β1-integrin accumulating at the cell rear in a uropod-like structure. This structure does not have the typical protruding shape of classical leukocyte uropods, but, as for those structures, it is regulated by protein kinase C. We show that the ezrin-rich uropod-like structure (ERULS) is an inherent feature of polarised A375 cells and not a consequence of cell migration, and is necessary for cell invasion. Furthermore, we demonstrate that membrane blebbing is reduced at this site, leading to a model in which the rigid ezrin-containing structure determines the direction of a moving cell through localised inhibition of membrane blebbing.
The morphological term 'amoeboid' migration subsumes a number of rather distinct biophysical modes of cellular locomotion that range from blebbing motility to entirely actin-polymerization-based gliding. Here, we discuss the diverse principles of force generation and force transduction that lead to the distinct amoeboid phenotypes. We argue that shifting the balance between actin protrusion, actomyosin contraction, and adhesion to the extracellular substrate can explain the different modes of amoeboid movement and that blebbing and gliding are barely extreme variants of one common migration strategy. Depending on the cell type, physiological conditions or experimental manipulation, amoeboid cells can adopt the distinct mechanical modes of amoeboid migration.
The motility of cancer cells in 3D matrices is of two types: mesenchymal motility, in which the cells are elongated and amoeboid motility, in which the cells are round. Amoeboid motility is driven by an actomyosin-based contractile force, which is regulated by the Rho/ROCK pathway. However, the molecular mechanisms underlying the motility of elongated cells remain unknown. Here, we show that the motility of elongated cells is regulated by Rac signaling through the WAVE2/Arp2/3-dependent formation of elongated pseudopodia and cell-substrate adhesion in 3D substrates. The involvement of Rac signaling in cell motility was different in cell lines that displayed an elongated morphology in 3D substrates. In U87MG glioblastoma cells, most of which exhibit mesenchymal motility, inhibition of Rac signaling blocked the invasion of these cells in 3D substrates. In HT1080 fibrosarcoma cells, which display mixed cell motility involving both elongated and rounded cells, inhibition of Rac1 signaling not only blocked mesenchymal motility but also caused a mesenchymal-amoeboid transition. Additionally, Rac1 and RhoA signaling regulated the mesenchymal and amoeboid motility in these cells, respectively, and the inhibition of both pathways dramatically decreased cell invasion. Hence, we could conclude that Rac1 and RhoA signaling simultaneously regulate cell invasion in 3D matrices.
Tumor cells exhibit two different modes of individual cell movement. Mesenchymal-type movement is characterized by an elongated cellular morphology and requires extracellular proteolysis. In amoeboid movement, cells have a rounded morphology, are less dependent on proteases, and require high Rho-kinase signaling to drive elevated levels of actomyosin contractility. These two modes of cell movement are interconvertible. We show that mesenchymal-type movement in melanoma cells is driven by activation of the GTPase Rac through a complex containing NEDD9, a recently identified melanoma metastasis gene, and DOCK3, a Rac guanine nucleotide exchange factor. Rac signals through WAVE2 to direct mesenchymal movement and suppress amoeboid movement through decreasing actomyosin contractility. Conversely, in amoeboid movement, Rho-kinase signaling activates a Rac GAP, ARHGAP22, that suppresses mesenchymal movement by inactivating Rac. We demonstrate tight interplay between Rho and Rac in determining different modes of tumor cell movement, revealing how tumor cells switch between different modes of movement.
Tumor cells can move in a three-dimensional (3D) environment in either mesenchymal-type or amoeboid modes. In mesenchymal-type movement, cells have an elongated morphology with Rac-induced protrusions at the leading edge. Amoeboid cells have high levels of actomyosin contractility, and movement is associated with deformation of the cell body through the matrix without proteolysis. Because signaling pathways that control the activation of GTPases for amoeboid movement are poorly understood, we sought to identify regulators of amoeboid movement by screening an siRNA library targeting guanine nucleotide exchange factors (GEFs) for Rho-family GTPases.
We identified DOCK10, a Cdc42 GEF, as a key player in amoeboid migration; accordingly, we find that expression of activated Cdc42 induces a mesenchymal-amoeboid transition and increases cell invasion. Silencing DOCK10 expression promotes conversion to mesenchymal migration and is associated with decreased MLC2 phosphorylation and increased Rac1 activation. Consequently, abrogating DOCK10 and Rac1 expression suppresses both amoeboid and mesenchymal migration and results in decreased invasion. We show that the Cdc42 effectors N-WASP and Pak2 are required for the maintenance of the rounded-amoeboid phenotype. Blocking Cdc42 results in loss of mesenchymal morphology, arguing that Cdc42 is also involved in mesenchymal morphology through different activation and effector pathways.
Previous work has identified roles of Rho and Rac signaling in tumor cell movement, and we now elucidate novel roles of Cdc42 signaling in amoeboid and mesenchymal movement and tumor cell invasion.
Cell migration has been studied extensively by manipulating and observing cells bathed in putative chemotactic or chemokinetic agents on planar substrates. This environment differs from that in vivo and, consequently, the cells can behave abnormally. Embryo slices provide an optically accessible system for studying cellular navigation pathways during development. We extended this system to observe the migration of muscle precursors from the somite into the forelimb, their cellular morphology, and the localization of green fluorescent protein (GFP)-tagged adhesion-related molecules under normal and perturbed conditions.
Muscle precursors initiated migration synchronously and migrated in broad, rather than highly defined, regions. Bursts of directed migration were followed by periods of meandering or extension and retraction of cell protrusions. Although paxillin did not localize to discernible intracellular structures, we found that alpha-actinin localized to linear, punctate structures, and the alpha5 integrin to some focal complexes and/or vesicle-like concentrations. Alterations in the expression of adhesion molecules inhibited migration. The muscle precursors migrating in situ formed unusually large, long-lived protrusions that were polarized in the direction of migration. Unlike wild-type Rac, a constitutively active Rac localized continuously around the cell surface and promoted random protrusive activity and migration.
The observation of cellular migration and the dynamics of molecular organization at high temporal and spatial resolution in situ is feasible. Migration from the somite to the wing bud is discontinuous and not highly stereotyped. In situ, local activation of Rac appears to produce large protrusions, which in turn, leads to directed migration. Adhesion can also regulate migration.
The tyrosine kinase c-src associates with the platelet-derived growth factor (PDGF) receptor. Overexpression of wild-type c-src, a kinase-negative c-src mutant, and v-src in microvascular endothelial cells modulated the mitogenic effect of PDGF, suggesting that c-src kinase activity inhibits PDGF signals. Analyses of cell morphology in two-dimensional culture revealed changes in cell shape and size induced by the overexpression of c-src proteins. Investigations in three-dimensional culture unveiled a modulatory role of c-src during in vitro angiogenesis. Overexpression of c-src resulted in an increased diameter of tube-like structures, and the number of branching segments was decreased. Expression of the kinase-negative c-src mutant resulted in abortive tube formation consisting of disconnected multicellular fragments. These results indicate that the c-src tyrosine kinase exerts regulatory effects on endothelial proliferation, size, and cytoskeletal organization in two-dimensional culture and on the formation of a differentiated multicellular network in three-dimensional culture.
Rho family GTPases regulate the cytoskeleton and cell migration and are frequently overexpressed in tumours. Here, we identify two modes of tumour-cell motility in 3D matrices that involve different usage of Rho signalling. Rho signalling through ROCK promotes a rounded bleb-associated mode of motility that does not require pericellular proteolysis. This form of motility requires ezrin, which is localized in the direction of cell movement. In contrast, elongated cell motility is associated with Rac-dependent F-actin-rich protrusions and does not require Rho, ROCK or ezrin function. Combined blockade of extracellular proteases and ROCK negates the ability of tumour cells to switch between modes of motility and synergises to prevent tumour cell invasion.
To evaluate the frequency of distant metastases (DM) and to determine the ability of certain clinical and pathologic factors to predict the development of distant metastases.
Retrospective analysis.
University hospital.
A total of 1972 patients with oral, oropharyngeal, hypopharyngeal, and laryngeal squamous cell carcinomas who were treated from 1981 to 1998 and who were not diagnosed as having DM at the time of initial treatment.
We evaluated the frequency of DM and the influence of different variables in their appearance.
A total of 181 patients (9.2%) (95% confidence interval, 7.9%-10.5%) developed DM. Younger age (<45 years), hypopharyngeal localization, an advanced T stage and/or N stage tumor according to the TNM staging system, high histologic grade, and locoregional control were found to be significantly associated with the risk of DM at both univariate and multivariate analyses.
The incidence of DM in subjects with head and neck squamous cell carcinoma is relatively low. The risk of DM is influenced by age, site of primary cancer, local and/or regional extension, grading, and achievement of locoregional control.
Despite identification of the genes responsible for autosomal dominant polycystic kidney disease (PKD) and autosomal recessive PKD (ARPKD), the precise functions of their cystoprotein products remain unknown. Recent data suggested that multimeric cystoprotein complexes initiate aberrant signaling cascades in PKD, and common components of these signaling pathways may be therapeutic targets. This study identified c-Src (pp60(c-Src)) as one such common signaling intermediate and sought to determine whether Src activity plays a role in cyst formation. With the use of the nonorthologous BPK murine model and the orthologous PCK rat model of ARPKD, greater Src activity was found to correlate with disease progression. Inhibition of Src activity with the pharmacologic inhibitor SKI-606 resulted in amelioration of renal cyst formation and biliary ductal abnormalities in both models. Furthermore, the effects of Src inhibition in PCK kidneys suggest that the ErbB2 and B-Raf/MEK/ERK pathways are involved in Src-mediated signaling in ARPKD and that this occurs without reducing elevated cAMP. These data suggest that Src inhibition may provide therapeutic benefit in PKD.
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New Hunts House, Guy's Campus, King's College London, London SE1 1UL
Randall Division of Cell and Molecular
Biophysics, School of Biomedical and Health
Sciences, New Hunts House, Guy's Campus,
King's College London, London SE1 1UL, UK.
E-mail: victoria.sanz_moreno@kcl.ac.uk
DOI: 10.1016/j.cub.2012.04.024
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