The high mobility group A2 protein epigenetically silences the Cdh1 gene during epithelial-to-mesenchymal transition.

The loss of the tumour suppressor E-cadherin (Cdh1) is a key event during tumourigenesis and epithelial-mesenchymal transition (EMT). Transforming growth factor-ß (TGFß) triggers EMT by inducing the expression of non-histone chromatin protein High Mobility Group A2 (HMGA2). We have previously shown that HMGA2, together with Smads, regulate a network of EMT-transcription factors (EMT-TFs) like Snail1, Snail2, ZEB1, ZEB2 and Twist1, most of which are well-known repressors of the Cdh1 gene. In this study, we show that the Cdh1 promoter is hypermethylated and epigenetically silenced in our constitutive EMT cell model, whereby HMGA2 is ectopically expressed in mammary epithelial NMuMG cells and these cells are highly motile and invasive. Furthermore, HMGA2 remodels the chromatin to favour binding of de novo DNA methyltransferase 3A (DNMT3A) to the Cdh1 promoter. E-cadherin expression could be restored after treatment with the DNA de-methylating agent 5-aza-2'-deoxycytidine. Here, we describe a new epigenetic role for HMGA2, which follows the actions that HMGA2 initiates via the EMT-TFs, thus achieving sustained silencing of E-cadherin expression and promoting tumour cell invasion.

Regulation of transcription factor Twist expression by the DNA architectural protein high mobility group A2 during epithelial-to-mesenchymal transition.

Deciphering molecular mechanisms that control epithelial-to-mesenchymal transition (EMT) contributes to our understanding of how tumor cells become invasive and competent for intravasation. We have established that transforming growth factor ß activates Smad proteins, which induce expression of the embryonic factor high mobility group A2 (HMGA2), which causes mesenchymal transition. HMGA2 associates with Smad complexes and induces expression of an established regulator of EMT, the zinc finger transcription factor Snail. We now show that HMGA2 can also induce expression of a second regulator of EMT, the basic helix-loop-helix transcription factor Twist. Silencing of endogenous Twist demonstrated that this protein acts in a partially redundant manner together with Snail. Double silencing of Snail and Twist reverts mesenchymal HMGA2-expressing cells to a more epithelial phenotype when compared with single silencing of Snail or Twist. Furthermore, HMGA2 can directly associate with A:T-rich sequences and promote transcription from the Twist promoter. The new evidence proposes a model whereby HMGA2 directly induces multiple transcriptional regulators of the EMT program and, thus, is a potential biomarker for carcinomas displaying EMT during progression to more advanced stages of malignancy.

A Journey on Extracellular Vesicles for Matrix Metalloproteinases: A Mechanistic Perspective.

Matrix metalloproteinases (MMPs) are key players in matrix remodeling and their function has been particularly investigated in cancer biology. Indeed, through extracellular matrix (ECM) degradation and shedding of diverse cell surface macromolecules, they are implicated in different steps of tumor development, from local expansion by growth to tissue invasion and metastasis. Interestingly, MMPs are also components of extracellular vesicles (EVs). EVs are membrane-limited organelles that cells release in their extracellular environment. These "secreted" vesicles are now well accepted players in cell-to-cell communication. EVs have received a lot of interest in recent years as they are also envisioned as sources of biomarkers and as potentially outperforming vehicles for the delivery of therapeutics. Molecular machineries governing EV biogenesis, cargo loading and delivery to recipient cells are complex and still under intense investigation. In this review, we will summarize the state of the art of our knowledge about the molecular mechanisms implicated in MMP trafficking and secretion. We focus on MT1-MMP, a major effector of invasive cell behavior. We will also discuss how this knowledge is of interest for a better understanding of EV-loading of MMPs. Such knowledge might be of use to engineer novel strategies for cancer treatment. A better understanding of these mechanisms could also be used to design more efficient EV-based therapies.

Transforming growth factor-beta employs HMGA2 to elicit epithelial-mesenchymal transition.

Epithelial-mesenchymal transition (EMT) occurs during embryogenesis, carcinoma invasiveness, and metastasis and can be elicited by transforming growth factor-beta (TGF-beta) signaling via intracellular Smad transducers. The molecular mechanisms that control the onset of EMT remain largely unexplored. Transcriptomic analysis revealed that the high mobility group A2 (HMGA2) gene is induced by the Smad pathway during EMT. Endogenous HMGA2 mediates EMT by TGF-beta, whereas ectopic HMGA2 causes irreversible EMT characterized by severe E-cadherin suppression. HMGA2 provides transcriptional input for the expression control of four known regulators of EMT, the zinc-finger proteins Snail and Slug, the basic helix-loop-helix protein Twist, and inhibitor of differentiation 2. We delineate a pathway that links TGF-beta signaling to the control of epithelial differentiation via HMGA2 and a cohort of major regulators of tumor invasiveness and metastasis. This network of signaling/transcription factors that work sequentially to establish EMT suggests that combinatorial detection of these proteins could serve as a new tool for EMT analysis in cancer patients.

EB1 Restricts Breast Cancer Cell Invadopodia Formation and Matrix Proteolysis via FAK.

Regulation of microtubule dynamics by plus-end tracking proteins (+TIPs) plays an essential role in cancer cell migration. However, the role of +TIPs in cancer cell invasion has been poorly addressed. Invadopodia, actin-rich protrusions specialized in extracellular matrix degradation, are essential for cancer cell invasion and metastasis, the leading cause of death in breast cancer. We, therefore, investigated the role of the End Binding protein, EB1, a major hub of the +TIP network, in invadopodia functions. EB1 silencing increased matrix degradation by breast cancer cells. This was recapitulated by depletion of two additional +TIPs and EB1 partners, APC and ACF7, but not by the knockdown of other +TIPs, such as CLASP1/2 or CLIP170. The knockdown of Focal Adhesion Kinase (FAK) was previously proposed to similarly promote invadopodia formation as a consequence of a switch of the Src kinase from focal adhesions to invadopodia. Interestingly, EB1-, APC-, or ACF7-depleted cells had decreased expression/activation of FAK. Remarkably, overexpression of wild type FAK, but not of FAK mutated to prevent Src recruitment, prevented the increased degradative activity induced by EB1 depletion. Overall, we propose that EB1 restricts invadopodia formation through the control of FAK and, consequently, the spatial regulation of Src activity.

iASPP contributes to cell cortex rigidity, mitotic cell rounding, and spindle positioning.

iASPP is a protein mostly known as an inhibitor of p53 pro-apoptotic activity and a predicted regulatory subunit of the PP1 phosphatase, which is often overexpressed in tumors. We report that iASPP associates with the microtubule plus-end binding protein EB1, a central regulator of microtubule dynamics, via an SxIP motif. iASPP silencing or mutation of the SxIP motif led to defective microtubule capture at the cortex of mitotic cells, leading to abnormal positioning of the mitotic spindle. These effects were recapitulated by the knockdown of the membrane-to-cortex linker Myosin-Ic (Myo1c), which we identified as a novel partner of iASPP. Moreover, iASPP or Myo1c knockdown cells failed to round up upon mitosis because of defective cortical stiffness. We propose that by increasing cortical rigidity, iASPP helps cancer cells maintain a spherical geometry suitable for proper mitotic spindle positioning and chromosome partitioning.

A proximity-labeling proteomic approach to investigate invadopodia molecular landscape in breast cancer cells.

Metastatic progression is the leading cause of mortality in breast cancer. Invasive tumor cells develop invadopodia to travel through basement membranes and the interstitial matrix. Substantial efforts have been made to characterize invadopodia molecular composition. However, their full molecular identity is still missing due to the difficulty in isolating them. To fill this gap, we developed a non-hypothesis driven proteomic approach based on the BioID proximity biotinylation technology, using the invadopodia-specific protein Tks5α fused to the promiscuous biotin ligase BirA* as bait. In invasive breast cancer cells, Tks5α fusion concentrated to invadopodia and selectively biotinylated invadopodia components, in contrast to a fusion which lacked the membrane-targeting PX domain (Tks5ß). Biotinylated proteins were isolated by affinity capture and identified by mass spectrometry. We identified known invadopodia components, revealing the pertinence of our strategy. Furthermore, we observed that Tks5 newly identified close neighbors belonged to a biologically relevant network centered on actin cytoskeleton organization. Analysis of Tks5ß interactome demonstrated that some partners bound Tks5 before its recruitment to invadopodia. Thus, the present strategy allowed us to identify novel Tks5 partners that were not identified by traditional approaches and could help get a more comprehensive picture of invadopodia molecular landscape.

Peptide screen identifies a new NADPH oxidase inhibitor: impact on cell migration and invasion.

The NADPH oxidase proteins catalyse the formation of superoxide anion which act as signalling molecules in physiological and pathological processes. Nox1-dependent NADPH oxidase is expressed in heart, lung, colon, blood vessels and brain. Different strategies involving Nox1 inhibition based on diphenylene iodonium derivatives are currently tested for colorectal cancer therapy. Here, after peptides screening on Nox1-dependent NADPH oxidase assay in HT-29 cells, we identify a peptide (referred to as NF02), cell-active, that potently block Nox1-dependent reactive oxygen species generation. Study of DEPMPO adduct formation by electron paramagnetic resonance showed that NF02 has no superoxide scavenging activity and no impact on cellular reactive oxygen species-producing enzymes such xanthine oxidase. NF02 was not cytotoxic, inhibited reactive oxygen species production of reconstituted Nox1/Noxo1/Noxa1 complex in HEK293 and did not decrease Nox2 dependent cellular NADPH oxidase reactive oxygen species production. Finally, NF02 inhibited cell migration and invasion of colorectal cancer cells which is consistent with the described impact of Nox1 inhibitors on cell migration. NF02 peptide is a new NADPH oxidase inhibitor specific for Nox1 over Nox2 and xanthine oxidase which might represent a useful Nox1 tool with potential therapeutic insights.

Analysis of Epithelial-Mesenchymal Transition Induced by Transforming Growth Factor ß.

In recent years, the importance of the cell biological process of epithelial-mesenchymal transition (EMT) has been established via an exponentially growing number of reports. EMT has been documented during embryonic development, tissue fibrosis, and cancer progression in vitro, in animal models in vivo and in human specimens. EMT relates to many molecular and cellular alterations that occur when epithelial cells undergo a switch in differentiation that generates mesenchymal-like cells with newly acquired migratory and invasive properties. In addition, EMT relates to a nuclear reprogramming similar to the one occurring in the generation of induced pluripotent stem cells. Via such a process, EMT is gradually established to promote the generation and maintenance of adult tissue stem cells which under disease states such as cancer, are known as cancer stem cells. EMT is induced by developmental growth factors, oncogenes, radiation, and hypoxia. A prominent growth factor that causes EMT is transforming growth factor ß (TGF-ß).A series of molecular and cellular techniques can be applied to define and characterize the state of EMT in diverse biological samples. These methods range from DNA and RNA-based techniques that measure the expression of key EMT regulators and markers of epithelial or mesenchymal differentiation to functional assays of cell mobility, invasiveness and in vitro stemness. This chapter focuses on EMT induced by TGF-ß and provides authoritative protocols and relevant reagents and citations of key publications aiming at assisting newcomers that enter this prolific area of biomedical sciences, and offering a useful reference tool to pioneers and aficionados of the field.

The RhoE/ROCK/ARHGAP25 signaling pathway controls cell invasion by inhibition of Rac activity.

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of skeletal muscle origin in children and adolescents. Among RMS subtypes, alveolar rhabdomyosarcoma (ARMS), which is characterized by the presence of the PAX3-FOXO1A or PAX7-FOXO1A chimeric oncogenic transcription factor, is associated with poor prognosis and a strong risk of metastasis compared with the embryonal subtype (ERMS). To identify molecular pathways involved in ARMS aggressiveness, we first characterized the migratory behavior of cell lines derived from ARMS and ERMS biopsies using a three-dimensional spheroid cell invasion assay. ARMS cells were more invasive than ERMS cells and adopted an ellipsoidal morphology to efficiently invade the extracellular matrix. Moreover, the invasive potential of ARMS cells depended on ROCK activity, which is regulated by the GTPase RhoE. Specifically, RhoE expression was low in ARMS biopsies, and its overexpression in ARMS cells reduced their invasion potential. Conversely, ARHGAP25, a GTPase-activating protein for Rac, was up-regulated in ARMS biopsies. Moreover, we found that ARHGAP25 inhibits Rac activity downstream of ROCKII and is required for ARMS cell invasion. Our results indicate that the RhoE/ROCK/ARHGAP25 signaling pathway promotes ARMS invasive potential and identify these proteins as potential therapeutic targets for ARMS treatment.

P-cadherin promotes collective cell migration via a Cdc42-mediated increase in mechanical forces.

Collective cell migration (CCM) is essential for organism development, wound healing, and metastatic transition, the primary cause of cancer-related death, and it involves cell-cell adhesion molecules of the cadherin family. Increased P-cadherin expression levels are correlated with tumor aggressiveness in carcinoma and aggressive sarcoma; however, how P-cadherin promotes tumor malignancy remains unknown. Here, using integrated cell biology and biophysical approaches, we determined that P-cadherin specifically induces polarization and CCM through an increase in the strength and anisotropy of mechanical forces. We show that this mechanical regulation is mediated by the P-cadherin/ß-PIX/Cdc42 axis; P-cadherin specifically activates Cdc42 through ß-PIX, which is specifically recruited at cell-cell contacts upon CCM. This mechanism of cell polarization and migration is absent in cells expressing E- or R-cadherin. Thus, we identify a specific role of P-cadherin through ß-PIX-mediated Cdc42 activation in the regulation of cell polarity and force anisotropy that drives CCM.

HMGA2 and Smads co-regulate SNAIL1 expression during induction of epithelial-to-mesenchymal transition.

Epithelial-mesenchymal transition (EMT) is important during embryonic cell layer movement and tumor cell invasiveness. EMT converts adherent epithelial cells to motile mesenchymal cells, favoring metastasis in the context of cancer progression. Transforming growth factor-beta (TGF-beta) triggers EMT via intracellular Smad transducers and other signaling proteins. We previously reported that the high mobility group A2 (HMGA2) gene is required for TGF-beta to elicit EMT in mammary epithelial cells. In the present study we investigated the molecular mechanisms by which HMGA2 induces EMT. We found that HMGA2 regulates expression of many important repressors of E-cadherin. Among these, we analyzed in detail the zinc-finger transcription factor SNAIL1, which plays key roles in tumor progression and EMT. We demonstrate that HMGA2 directly binds to the SNAIL1 promoter and acts as a transcriptional regulator of SNAIL1 expression. Furthermore, we observed that HMGA2 cooperates with the TGF-beta/Smad pathway in regulating SNAIL1 gene expression. The mechanism behind this cooperation involves physical interaction between these factors, leading to an increased binding of Smads to the SNAIL1 promoter. SNAIL1 seems to play the role of a master effector downstream of HMGA2 for induction of EMT, as SNAIL1 knock-down partially reverts HMGA2-induced loss of epithelial differentiation. The data propose that HMGA2 acts in a gene-specific manner to orchestrate the transcriptional network necessary for the EMT program.

Functional role of Meox2 during the epithelial cytostatic response to TGF-beta.

Transforming growth factor beta (TGF-beta) suppresses epithelial cell growth. We have identified a new target gene of the TGF-beta/Smad pathway, Meox2, encoding the homeodomain transcription factor that is known to regulate endothelial cell proliferation and muscle development. Knockdown of endogenous Meox2 by RNA interference prevented the TGF-beta1-induced cytostatic response. Moreover, ectopic Meox2 suppressed epithelial cell proliferation in cooperation with TGF-beta1, and mediated induction of the cell cycle inhibitor gene p21. Transcriptional induction of p21 by Meox2 required a distal region of the p21 promoter that spans the p53-binding site. We show that Meox2 can form protein complexes with Smads leading to cooperative regulation of p21 gene expression. Finally, we found that in cell models that undergo both cell cycle arrest and epithelial-mesenchymal transition (EMT), ectopic Meox2 failed to induce EMT and inhibited the proper EMT response to TGF-beta. Thus, Meox2 is primarily involved in the TGF-beta tumor suppressor pathway.

Functional analysis of the TFIID-specific yeast TAF4 (yTAF(II)48) reveals an unexpected organization of its histone-fold domain.

Yeast TFIID comprises the TATA binding protein and 14 TBP-associated factors (TAF(II)s), nine of which contain histone-fold domains (HFDs). The C-terminal region of the TFIID-specific yTAF4 (yTAF(II)48) containing the HFD shares strong sequence similarity with Drosophila (d)TAF4 (dTAF(II)110) and human TAF4 (hTAF(II)135). A structure/function analysis of yTAF4 demonstrates that the HFD, a short conserved C-terminal domain (CCTD), and the region separating them are all required for yTAF4 function. Temperature-sensitive mutations in the yTAF4 HFD alpha2 helix or the CCTD can be suppressed upon overexpression of yTAF12 (yTAF(II)68). Moreover, coexpression in Escherichia coli indicates direct yTAF4-yTAF12 heterodimerization optimally requires both the yTAF4 HFD and CCTD. The x-ray crystal structure of the orthologous hTAF4-hTAF12 histone-like heterodimer indicates that the alpha3 region within the predicted TAF4 HFD is unstructured and does not correspond to the bona fide alpha3 helix. Our functional and biochemical analysis of yTAF4, rather provides strong evidence that the HFD alpha3 helix of the TAF4 family lies within the CCTD. These results reveal an unexpected and novel HFD organization in which the alpha3 helix is separated from the alpha2 helix by an extended loop containing a conserved functional domain.

Crystal structure of a subcomplex of human transcription factor TFIID formed by TATA binding protein-associated factors hTAF4 (hTAF(II)135) and hTAF12 (hTAF(II)20).

The crystal structure is presented of a complex formed by the interacting domains from two subunits of the general transcription factor TFIID, the human TATA binding protein-associated factors hTAF4 (hTAF(II)135) and hTAF12 (hTAF(II)20). In agreement with predictions, hTAF12 forms a histone fold that is very similar to that of histone H2B, yet unexpected differences are observed between the structures of the hTAF12 interaction domain of hTAF4 and histone H2A. Most importantly, the hTAF4 fragment forms only the first two helices of a classical histone fold, which are followed by a 26-residue disordered region. This indicates that either full-length TAF4 contains an unusually long connecting loop between its second and third helix, and this helix is not required for stable interaction with TAF12, or that TAF4 represents a novel class of partial histone fold motifs. Structural models and structure-based sequence alignments support a role for TAF4b and hSTAF42/yADA1 as alternative partners for TAF12 and are consistent with the formation of nucleosome-like histone-fold octamers through interaction of TAF12 with a TAF6-TAF9 tetramer, yet argue against involvement of TAF12-containing histone-fold pairs in DNA binding.