Invasion of normal human fibroblasts induced by v-Fos is independent of proliferation, immortalization, and the tumor suppressors p16INK4a and p53

Compression-dependent microtubule reinforcement enables cells to navigate confined environments

Cells migrating through complex three-dimensional environments experience considerable physical challenges, including tensile stress and compression. To move, cells need to resist these forces while also squeezing the large nucleus through confined spaces. This requires highly coordinated cortical contractility. Microtubules can both resist compressive forces and sequester key actomyosin regulators to ensure appropriate activation of contractile forces. Yet, how these two roles are integrated to achieve nuclear transmigration in three dimensions is largely unknown. Here, we demonstrate that compression triggers reinforcement of a dedicated microtubule structure at the rear of the nucleus by the mechanoresponsive recruitment of cytoplasmic linker-associated proteins, which dynamically strengthens and repairs the lattice. These reinforced microtubules form the mechanostat: an adaptive feedback mechanism that allows the cell to both withstand compressive force and spatiotemporally organize contractility signalling pathways. The microtubule mechanostat facilitates nuclear positioning and coordinates force production to enable the cell to pass through constrictions. Disruption of the mechanostat imbalances cortical contractility, stalling migration and ultimately resulting in catastrophic cell rupture. Our findings reveal a role for microtubules as cellular sensors that detect and respond to compressive forces, enabling movement and ensuring survival in mechanically demanding environments.

Tensin3 interaction with talin drives the formation of fibronectin-associated fibrillar adhesions

The formation of healthy tissue involves continuous remodeling of the extracellular matrix (ECM). Whilst it is known that this requires integrin-associated cell-ECM adhesion sites (CMAs) and actomyosin-mediated forces, the underlying mechanisms remain unclear. Here, we examine how tensin3 contributes to the formation of fibrillar adhesions (FBs) and fibronectin fibrillogenesis. Using BioID mass spectrometry and a mitochondrial targeting assay, we establish that tensin3 associates with the mechanosensors such as talin and vinculin. We show that the talin R11 rod domain binds directly to a helical motif within the central intrinsically disordered region (IDR) of tensin3, whilst vinculin binds indirectly to tensin3 via talin. Using CRISPR knock-out cells in combination with defined tensin3 mutations, we show (i) that tensin3 is critical for the formation of α5β1-integrin FBs and for fibronectin fibrillogenesis, and (ii) the talin/tensin3 interaction drives this process, with vinculin acting to potentiate it.

Oral Senescence: From Molecular Biology to Clinical Research

Cellular senescence is an irreversible cell cycle arrest occurring following multiple rounds of cell division (replicative senescence) or in response to cellular stresses such as ionizing radiation, signaling imbalances and oxidative damage (stress-induced premature senescence). Even very small numbers of senescent cells can be deleterious and there is evidence that senescent cells are instrumental in a number of oral pathologies including cancer, oral sub mucous fibrosis and the side effects of cancer therapy. In addition, senescent cells are present and possibly important in periodontal disease and other chronic inflammatory conditions of the oral cavity. However, senescence is a double-edged sword because although it operates as a suppressor of malignancy in pre-malignant epithelia, senescent cells in the neoplastic environment promote tumor growth and progression. Many of the effects of senescent cells are dependent on the secretion of an array of diverse therapeutically targetable proteins known as the senescence-associated secretory phenotype. However, as senescence may have beneficial roles in wound repair, preventing fibrosis and stem cell activation the clinical exploitation of senescent cells is not straightforward. Here, we discuss biological mechanisms of senescence and we review the current approaches to target senescent cells therapeutically, including senostatics and senolytics which are entering clinical trials.

Direct evidence of cellular transformation by prion-like p53 amyloid infection

Tumor suppressor p53 mutations are associated with more than 50% of cancers. Aggregation and amyloid formation of p53 is also implicated in cancer pathogenesis, but direct evidence for aggregated p53 amyloids acting as an oncogene is lacking. Here, we conclusively demonstrate that wild-type p53 amyloid formation imparts oncogenic properties to non-cancerous cells. p53 amyloid aggregates were transferred through cell generations, contributing to enhanced survival, apoptotic resistance with increased proliferation and migration. The tumorigenic potential of p53 amyloid-transformed cells was further confirmed in mouse xenografts, wherein the tumors showed p53 amyloids. p53 disaggregation rescued the cellular transformation and inhibited tumor development in mice. We propose that wild-type p53 amyloid formation contributes to tumorigenesis and can be a potential target for therapeutic intervention. This article has an associated First Person interview with the first author of the paper.

Fibrogenic Lung Injury Induces Non-Cell-Autonomous Fibroblast Invasion

Pathologic accumulation of fibroblasts in pulmonary fibrosis appears to depend on their invasion through basement membranes and extracellular matrices. Fibroblasts from the fibrotic lungs of patients with idiopathic pulmonary fibrosis (IPF) have been demonstrated to acquire a phenotype characterized by increased cell-autonomous invasion. Here, we investigated whether fibroblast invasion is further stimulated by soluble mediators induced by lung injury. We found that bronchoalveolar lavage fluids from bleomycin-challenged mice or patients with IPF contain mediators that dramatically increase the matrix invasion of primary lung fibroblasts. Further characterization of this non-cell-autonomous fibroblast invasion suggested that the mediators driving this process are produced locally after lung injury and are preferentially produced by fibrogenic (e.g., bleomycin-induced) rather than nonfibrogenic (e.g., LPS-induced) lung injury. Comparison of invasion and migration induced by a series of fibroblast-active mediators indicated that these two forms of fibroblast movement are directed by distinct sets of stimuli. Finally, knockdown of multiple different membrane receptors, including platelet-derived growth factor receptor-β, lysophosphatidic acid 1, epidermal growth factor receptor, and fibroblast growth factor receptor 2, mitigated the non-cell-autonomous fibroblast invasion induced by bronchoalveolar lavage from bleomycin-injured mice, suggesting that multiple different mediators drive fibroblast invasion in pulmonary fibrosis. The magnitude of this mediator-driven fibroblast invasion suggests that its inhibition could be a novel therapeutic strategy for pulmonary fibrosis. Further elaboration of the molecular mechanisms that drive non-cell-autonomous fibroblast invasion consequently may provide a rich set of novel drug targets for the treatment of IPF and other fibrotic lung diseases.

Annotation enrichment analysis: an alternative method for evaluating the functional properties of gene sets

Gene annotation databases (compendiums maintained by the scientific community that describe the biological functions performed by individual genes) are commonly used to evaluate the functional properties of experimentally derived gene sets. Overlap statistics, such as Fishers Exact test (FET), are often employed to assess these associations, but don't account for non-uniformity in the number of genes annotated to individual functions or the number of functions associated with individual genes. We find FET is strongly biased toward over-estimating overlap significance if a gene set has an unusually high number of annotations. To correct for these biases, we develop Annotation Enrichment Analysis (AEA), which properly accounts for the non-uniformity of annotations. We show that AEA is able to identify biologically meaningful functional enrichments that are obscured by numerous false-positive enrichment scores in FET, and we therefore suggest it be used to more accurately assess the biological properties of gene sets.

P-Rex1 cooperates with PDGFRβ to drive cellular migration in 3D microenvironments

Expression of the Rac-guanine nucleotide exchange factor (RacGEF), P-Rex1 is a key determinant of progression to metastasis in a number of human cancers. In accordance with this proposed role in cancer cell invasion and metastasis, we find that ectopic expression of P-Rex1 in an immortalised human fibroblast cell line is sufficient to drive multiple migratory and invasive phenotypes. The invasive phenotype is greatly enhanced by the presence of a gradient of serum or platelet-derived growth factor, and is dependent upon the expression of functional PDGF receptor β. Consistently, the invasiveness of WM852 melanoma cells, which endogenously express P-Rex1 and PDGFRβ, is opposed by siRNA of either of these proteins. Furthermore, the current model of P-Rex1 activation is advanced through demonstration of P-Rex1 and PDGFRβ as components of the same macromolecular complex. These data suggest that P-Rex1 has an influence on physiological migratory processes, such as invasion of cancer cells, both through effects upon classical Rac1-driven motility and a novel association with RTK signalling complexes.

Scar/WAVE3 contributes to motility and plasticity of lamellipodial dynamics but not invasion in three dimensions

The Scar (suppressor of cAMP receptor)/WAVE [WASP (Wiskott-Aldrich syndrome protein) verprolin homologous] complex plays a major role in the motility of cells by activating the Arp2/3 complex, which initiates actin branching and drives protrusions. Mammals have three Scar/WAVE isoforms, which show some tissue-specific expression, but their functions have not been differentiated. In the present study we show that depletion of Scar/WAVE3 in the mammalian breast cancer cells MDA-MB-231 results in larger and less dynamic lamellipodia. Scar/WAVE3-depleted cells move more slowly but more persistently on a two-dimensional matrix and they typically only show one lamellipod. However, Scar/WAVE3 appears to have no role in driving invasiveness in a three-dimensional Matrigel™ invasion assay or a three-dimensional collagen invasion assay, suggesting that lamellipodial persistence as seen in two-dimensions is not crucial in three-dimensional environments.

The Arp2/3 activator WASH regulates α5β1-integrin-mediated invasive migration

The actin cytoskeleton provides scaffolding and physical force to effect fundamental processes such as motility, cytokinesis and vesicle trafficking. The Arp2/3 complex nucleates actin structures and contributes to endocytic vesicle invagination and trafficking away from the plasma membrane. Internalisation and directed recycling of integrins are major driving forces for invasive cell motility and potentially for cancer metastasis. Here, we describe a direct requirement for WASH and Arp2/3-mediated actin polymerisation on the endosomal membrane system for α5β1 integrin recycling. WASH regulates the trafficking of endosomal α5β1 integrin to the plasma membrane and is fundamental for integrin-driven cell morphology changes and integrin-mediated cancer cell invasion. Thus, we implicate WASH and Arp2/3-driven actin nucleation in receptor recycling leading to invasive motility.

Identification of a structural motif in the tumor-suppressive protein GRIM-19 required for its antitumor activity

We have previously isolated GRIM-19, a novel growth suppressor, using a genetic method. GRIM-19 ablates cell growth by inhibiting the transcription factor signal transducer and activator of transcription 3 (STAT3). Up-regulation of STAT3 and growth promotion were observed in a number of human tumors. Although the tumor-suppressive actions of GRIM-19 are known, the structural elements required for its antitumor actions are not understood. Mutational and protein sequence analyses identified a motif in the N terminus of GRIM-19 that exhibited similarity to certain RNA viral proteins. We show that disruption of specific amino acids within this motif cripples the antitumor actions of GRIM-19. These mutants fail to interact with STAT3 efficiently and consequently do not inhibit growth-promoting gene expression. More importantly, we show that a clinically observed mutation in the N terminus of GRIM-19 also weakened its interaction with STAT3 and antitumor action. Together, these studies identify a major role for the N terminus of GRIM-19 in mediating its tumor-suppressive actions.

c-Fos accelerates hepatocyte conversion to a fibroblastoid phenotype through ERK-mediated upregulation of paxillin-Serine178 phosphorylation

Transforming growth factor beta (TGF-beta) exerts an important role in the late steps of carcinogenesis by cooperating with Ras to induce cell motility and tumor invasion. The transcription complex AP-1 has been implicated in the regulation of genes involved in motility and invasion, by mechanisms not yet delineated. We utilized a model of immortalized human hepatocytes (IHH) overexpressing c-Fos (IHH-Fos) or not (IHH-C) to investigate the role of c-Fos on cell motility in response to a prolonged treatment with TGF-beta, EGF or a combination of both. Cotreatment with EGF and TGF-beta, but neither cytokine alone, induced the conversion of hepatocytes to a fibroblastoid phenotype and increased their motility in Boyden chambers. EGF/TGF-beta cotreatment induced a higher effect on ERK phosphorylation compared to TGF-beta treatment alone. It also induced an increase in total and phosphorylated Ser(178) paxillin, a protein previously implicated in cell motility. This response was inhibited by two specific MEK inhibitors, indicating the involvement of the ERK pathway in paxillin activation. Overexpression of c-Fos correlated with increased cell scattering and motility, higher levels of ERK activation and phospho Ser(178) paxillin, increased levels of EGF receptor (EGF-R) mRNA and higher EGF-R phosphorylation levels following EGF/TGF-beta cotreatment. Conversely, siRNA-mediated invalidation of c-Fos delayed the appearance of fibroblastoid cells, decreased EGF-R mRNA and downregulated ERK and Ser(178) paxillin phosphorylations, indicating that c-Fos activates hepatocyte motility through an EGF-R/ERK/paxillin pathway. Since c-Fos is frequently overexpressed in hepatocarcinomas, this newly identified mechanism might be involved in the progression of hepatic tumors in vivo.

GRIM-19 inhibits v-Src-induced cell motility by interfering with cytoskeletal restructuring

GRIM-19 (Gene associated with Retinoid-Interferon-induced Mortality 19) is a novel tumor suppressor regulated by Interferon/retinoid combination. We have recently shown that GRIM-19 inhibits v-Src-induced oncogenic transformation and metastatic behavior of cells. Oncogenic v-Src induces cell motility by cytoskeletal remodeling especially the formation of podosomes and. Here we show that GRIM-19 inhibited the v-Src-induced cell motility by inhibiting cytoskeletal remodeling i.e., podosome formation. We also show that the N-terminus of GRIM-19 played a major role in this process and identified critical residues in this region. More importantly, we show that tumor-associated GRIM-19 mutations disrupted its ability to inhibit v-Src-induced cell motility. These actions appear to occur independently of STAT3, a known target of GRIM-19-mediated inhibition. Lastly, tumor-associated GRIM-19 mutants significantly lost their ability to control v-Src-induced metastases in vivo, indicating the biological and pathological significance of these observations.

Profiling distinct mechanisms of tumour invasion for drug discovery: imaging adhesion, signalling and matrix turnover

Recent advances in microscopic imaging technology, fluorescent reporter reagents, 3-dimensional (3D) cell models and multiparametric image analysis have enhanced our ability to model and understand complex cell physiology. Extension of these approaches to live cell, kinetic studies allows further spatial and temporal understanding of a multitude of dynamic functional events, including tumour cell invasion. Recent in vivo and 3D in vitro studies reveal how tumour cells utilize a diverse variety of mechanisms to permit invasion through 3D tissue environments. Such high degrees of diversity and plasticity between invasion mechanisms present a significant challenge to the successful treatment of malignant cancer. This review examines how advances in time-resolved imaging has contributed to the characterization of distinct modes of invasion and their associated molecular mechanisms. Specifically, we highlight the development of fluorescent reporter molecules and their incorporation into more predictive 3D in vitro and in vivo models, to enhance mechanistic analysis of tumour invasion. We also highlight the latest advances in kinetic imaging instrumentation applicable to in vitro and in vivo models of tumour invasion. We discuss how multiparametric image analysis can be used to interpret image data generated by these approaches. We further discuss how these approaches can be integrated into drug discovery pipelines to facilitate evaluation and selection of candidate drugs and novel pharmaceutical compositions, targeting multiple invasive mechanisms.

Chordoma and chondrosarcoma gene profile: implications for immunotherapy

Chordoma and chondrosarcoma are malignant bone tumors characterized by the abundant production of extracellular matrix. The resistance of these tumors to conventional therapeutic modalities has prompted us to delineate the gene expression profile of these two tumor types, with the expectation to identify potential molecular therapeutic targets. Furthermore the transcriptional profile of chordomas and chrondrosarcomas was compared to a wide variety of sarcomas as well as to that of normal tissues of similar lineage, to determine whether they express unique gene signatures among other tumors of mesenchymal origin, and to identify changes associated with malignant transformation. A HG-U133A Affymetrix Chip platform was used to determine the gene expression signature in 6 chordoma and 14 chondrosarcoma lesions. Validation of selected genes was performed by qPCR and immunohistochemistry (IHC) on an extended subset of tumors. By unsupervised clustering, chordoma and chondrosarcoma tumors grouped together in a genomic cluster distinct from that of other sarcoma types. They shared overexpression of many extracellular matrix genes including aggrecan, type II & X collagen, fibronectin, matrillin 3, high molecular weight-melanoma associated antigen (HMW-MAA), matrix metalloproteinase MMP-9, and MMP-19. In contrast, T Brachyury and CD24 were selectively expressed in chordomas, as were Keratin 8,13,15,18 and 19. Chondrosarcomas are distinguished by high expression of type IX and XI collagen. Because of its potential usefulness as a target for immunotherapy, the expression of HMW-MAA was analyzed by IHC and was detected in 62% of chordomas and 48% of chondrosarcomas, respectively. Furthermore, western blotting analysis showed that HMW-MAA synthesized by chordoma cell lines has a structure similar to that of the antigen synthesized by melanoma cells. In conclusion, chordomas and chondrosarcomas share a similar gene expression profile of up-regulated extracellular matrix genes. HMW-MAA represents a potential useful target to apply immunotherapy to these tumors.

Establishment and characterization of equine fibroblast cell lines transformed in vivo and in vitro by BPV-1: model systems for equine sarcoids

It is now widely recognized that BPV-1 and less commonly BPV-2 are the causative agents of equine sarcoids. Here we present the generation of equine cell lines harboring BPV-1 genomes and expressing viral genes. These lines have been either explanted from sarcoid biopsies or generated in vitro by transfection of primary fibroblasts with BPV-1 DNA. Previously detected BPV-1 genome variations in equine sarcoids are also found in sarcoid cell lines, and only variant BPV-1 genomes can transform equine cells. These equine cell lines are morphologically transformed, proliferate faster than parental cells, have an extended life span and can grow independently of substrate. These characteristics are more marked the higher the level of viral E5, E6 and E7 gene expression. These findings confirm that the virus has an active role in the induction of sarcoids and the lines will be invaluable for further studies on the role of BPV-1 in sarcoid pathology.

αvβ5 Integrin Sustains Growth of Human Pre-B Cells through an RGD-independent Interaction with a Basic Domain of the CD23 Protein

CD23 is a type II transmembrane glycoprotein synthesized by hematopoietic cells that has biological activity in both membrane-bound and freely soluble forms, acting via a number of receptors, including integrins. We demonstrate here that soluble CD23 (sCD23) sustains growth of human B cell precursors via an RGD-independent interaction with the alphavbeta5 integrin. The integrin recognizes a tripeptide motif in a small disulfide-bonded loop at the N terminus of the lectin head region of CD23, centered around Arg(172), Lys(173), and Cys(174) (RKC). This RKC motif is present in all forms of sCD23 with cytokine-like activity, and cytokine activity is independent of the lectin head, an "inverse RGD" motif, and the CD21 and IgE binding sites. RKC-containing peptides derived from this region of CD23 bind alphavbeta5 and are biologically active. The binding and activity of these peptides is unaffected by inclusion of a short peptide containing the classic RGD sequence recognized by integrins, and, in far-Western analyses, RKC-containing peptides bind to the beta subunit of the alphavbeta5 integrin. The interaction between alphavbeta5 and sCD23 indicates that integrins deliver to cells important signals initiated by soluble ligands without the requirement for interactions with RGD motifs in their common ligands. This mode of integrin signaling may not be restricted to alphavbeta5.

EGF-R regulates MMP function in fibroblasts through MAPK and AP-1 pathways

EGF-R regulates cell proliferation, migration, and invasion in fibroblasts. However, the connection of EGF-R with downstream signaling pathways mediating these responses has remained elusive. Here we provide genetic and biochemical evidence that EGF-R- and AP-1-mediated signals are required for MMP expression and collagen contraction in fibroblasts. In EGF-R (-/-) mouse embryonal fibroblasts, basal and inducible expression of several MMPs, including MMP-2, -3, and -14 is impaired in comparison to wild-type counterparts. The loss of MMP expression is associated with a suppression of EGF-induced Erk and Jnk activities, and AP-1 DNA-binding and transactivation capacities. While inhibition of Jnk mainly prevents EGF-induced phosphorylation of c-Jun, inhibition of Erk pathway suppresses both the expression and phosphorylation of c-Jun and c-Fos proteins. Moreover, the expression of MMP-3 and -14, and collagen contraction is partially prevented by Mek/Erk and Jnk inhibitors. However, Jnk inhibitor also suppresses cell growth independently of EGF-R activity. The central role of AP-1 as a mediator of EGF-R signaling in fibroblasts is emphasized by the finding that expression of a dominant negative c-Jun downregulates the expression of MMP-3. Conversely, expression of a constitutively active Mek1 can induce MMP-3 expression independently of upstream signals. The results indicate that ERK pathway and AP-1 are downstream effectors of the EGF-R-mediated MMP-3 expression and collagen contraction in fibroblasts.

p120-catenin is required for the collective invasion of squamous cell carcinoma cells via a phosphorylation-independent mechanism

Loss of E-cadherin-mediated cell-cell junctions has been correlated with cancer cell invasion and poor patient survival. p120-catenin has emerged as a key player in promoting E-cadherin stability and adherens junction integrity and has been proposed as a potential invasion suppressor by preventing release of cells from the constraints imposed by cadherin-mediated cell-cell adhesion. However, it has been proposed that tyrosine phosphorylation of p120 may contribute to cadherin-dependent junction disassembly during invasion. Here, we use small interfering RNA (siRNA) in A431 cells to show that knockdown of p120 promotes two-dimensional migration of cells. In contrast, p120 knockdown impairs epidermal growth factor-induced A431 invasion into three-dimensional matrix gels or in organotypic culture, whereas re-expression of siRNA-resistant p120, or a p120 isoform that cannot be phosphorylated on tyrosine, restores the collective mode of invasion employed by A431 cells in vitro. Thus, p120 promotes A431 cell invasion in a phosphorylation-independent manner. We show that the collective invasion of A431 cells depends on the presence of cadherin-mediated (P- and E-cadherin) cell-cell contacts, which are lost in cells where p120 expression is knocked down. Furthermore, membranous p120 is maintained in invasive squamous cell carcinomas in tumours suggesting that p120 may be important for the collective invasion of tumours cells in vivo.

Characterization of E-cadherin-dependent and -independent events in a new model of c-Fos-mediated epithelial–mesenchymal transition

Fos proteins have been implicated in control of tumorigenesis-related genetic programs including invasion, angiogenesis, cell proliferation and apoptosis. In this study, we demonstrate that c-Fos is able to induce mesenchymal transition in murine tumorigenic epithelial cell lines. Expression of c-Fos in MT1TC1 cells led to prominent alterations in cell morphology, increased expression of mesenchymal markers, vimentin and S100A4, DNA methylation-dependent down-regulation of E-cadherin and abrogation of cell-cell adhesion. In addition, c-Fos induced a strong beta-catenin-independent proliferative response in MT1TC1 cells and stimulated cell motility, invasion and adhesion to different extracellular matrix proteins. To explore whether loss of E-cadherin plays a role in c-Fos-mediated mesenchymal transition, we expressed wild-type E-cadherin and two different E-cadherin mutants in MT1TC1/c-fos cells. Expression of wild-type E-cadherin restored epithelioid morphology and enhanced cellular levels of catenins. However, exogenous E-cadherin did not influence expression of c-Fos-dependent genes, only partly suppressed growth of MT1TC1/c-fos cells and produced no effect on c-Fos-stimulated cell motility and invasion in matrigel. On the other hand, re-expression of E-cadherin specifically negated c-Fos-induced adhesion to collagen type I, but not to laminin or fibronectin. Of interest, mutant E-cadherin which lacks the ability to form functional adhesive complexes had an opposite, potentiating effect on cell adhesion to collagen I. These data suggest that cell adhesion to collagen I is regulated by the functional state of E-cadherin. Overall, our data demonstrate that, with the exception of adhesion to collagen I, c-Fos is dominant over E-cadherin in relation to the aspects of mesenchymal transition assayed in this study.

p38gamma mitogen-activated protein kinase integrates signaling crosstalk between Ras and estrogen receptor to increase breast cancer invasion

Ras is believed to stimulate invasion and growth by different effector pathways, and yet, the existence of such effectors under physiologic conditions has not been shown. Estrogen receptor (ER), on the other hand, is both anti-invasive and proliferative in human breast cancer, with mechanisms for these paradoxical actions remaining largely unknown. Our previous work showed an essential role of p38gamma mitogen-activated protein kinase in Ras transformation in rat intestinal epithelial cells, and here, we show that p38gamma integrates invasive antagonism between Ras and ER to increase human breast cancer invasion without affecting their proliferative activity. Ras positively regulates p38gamma expression, and p38gamma in turn mediates Ras nonmitogenic signaling to increase invasion. Expression of the Ras/p38gamma axis, however, is trans-suppressed by ER that inhibits invasion and stimulates growth also by distinct mechanisms. Analysis of ER and its cytoplasmic localized mutant reveals that ER additionally binds to p38gamma protein, leading to its specific down-regulation in the nuclear compartment. A p38gamma-antagonistic activity of ER was further shown in a panel of breast cancer cell lines and was shown independent of estrogens by both ER depletion and ER expression. These results revealed that both Ras and ER use distinct pathways to regulate breast cancer growth and invasion, and that p38gamma specifically integrates their antagonistic activity to stimulate cell invasion. Selective targeting of p38gamma-dependent invasion pathways may be a novel strategy to control breast cancer progression.

Transcription factors control invasion: AP-1 the first among equals

Metastasis, the aggressive spread of a malignant tumor to distant organs, is a major cause of death in cancer patients. Despite this critical role in cancer outcomes, the molecular mechanisms that control this process are just beginning to be understood. Metastasis is largely dependent upon the ability of tumor cells to invade the barrier formed by the basement membrane and to migrate through neighboring tissues. This review will summarize the evidence that tumor cell invasion is the result of oncogene-mediated signal transduction pathways that control the expression of a specific set of genes that together mediate tumor cell invasion. We focus on the role of the transcription factor AP-1 to both induce the expression of genes that function as invasion effectors and repress other genes that function as invasion suppressors. This identifies AP-1 as a critical regulator of a complex program of gene expression that defines the invasive phenotype.

Calpain 2 and Src dependence distinguishes mesenchymal and amoeboid modes of tumour cell invasion: a link to integrin function

Cancer cells can invade three-dimensional matrices by distinct mechanisms, recently defined by their dependence on extracellular proteases, including matrix metalloproteinases. Upon treatment with protease inhibitors, some tumour cells undergo a 'mesenchymal to amoeboid' transition that allows invasion in the absence of pericellular proteolysis and matrix degradation. We show here that in HT1080 cells, this transition is associated with weakened integrin-dependent adhesion, consistently reduced cell surface expression of the alpha2beta1 integrin collagen receptor and impaired signalling downstream, as judged by reduced autophosphorylation of focal adhesion kinase (FAK). On examining cancer cells that use defined invasion strategies, we show that distinct from mesenchymal invasion, amoeboid invasion is independent of intracellular calpain 2 proteolytic activity that is usually needed for turnover of integrin-linked adhesions during two-dimensional planar migration. Moreover, an inhibitor of Rho/ROCK signalling, which specifically impairs amoeboid-like invasion, restores cell surface expression of alpha2beta1 integrin, downstream FAK autophosphorylation and calpain 2 sensitivity--features of mesenchymal invasion. These findings link weakened integrin function to a lack of requirement for calpain 2-mediated integrin adhesion turnover during amoeboid invasion. In keeping with the need for integrin adhesion turnover, mesenchymal invasion is uniquely sensitive to Src inhibitors. Thus, the need for a major pathway that controls integrin adhesion turnover defines and distinguishes cancer cell invasion strategies.

AP-1 differentially expressed proteins Krp1 and fibronectin cooperatively enhance Rho-ROCK-independent mesenchymal invasion by altering the function, localization, and activity of nondifferentially expressed proteins

The transcription factor AP-1, which is composed of Fos and Jun family proteins, plays an essential role in tumor cell invasion by altering gene expression. We report here that Krp1, the AP-1 up-regulated protein that has a role in pseudopodial elongation in v-Fos-transformed rat fibroblast cells, forms a novel interaction with the nondifferentially expressed actin binding protein Lasp-1. Krp1 and Lasp-1 colocalize with actin at the tips of pseudopodia, and this localization is maintained by continued AP-1 mediated down-regulation of fibronectin that in turn suppresses integrin and Rho-ROCK signaling and allows pseudopodial protrusion and mesenchyme-like invasion. Mutation analysis of Lasp-1 demonstrates that its SH3 domain is necessary for pseudopodial extension and invasion. The results support the concept of an AP-1-regulated multigenic invasion program in which proteins encoded by differentially expressed genes direct the function, localization, and activity of proteins that are not differentially expressed to enhance the invasiveness of cells.

Invasion is a genetic program regulated by transcription factors

The invasive and metastatic behaviour of tumours impacts crucially on the clinical management of cancer. Accordingly, it is important to understand the regulation of tumour cell invasiveness. Genetic analysis of worms, Drosophila and mice has provided evidence that invasion is a genetic pathway regulated by transcription factors that are often implicated in tumour cell invasion. Recent evidence has revealed much concerning the role of one particular transcription factor, AP1, which is involved in the regulation of a multigenic invasion program in which upregulated and downregulated genes function as invasion effectors and suppressors, respectively. Differentially expressed genes cooperatively enhance pseudopod elongation during the mesenchymal mode of invasion by altering the function, localisation and activity of non-differentially expressed proteins.

Mobile classification in microarray experiments

In a homogeneous group of samples, there are genes whose expression variations can be attributed to factors other than experimental errors. These factors can include natural biological oscillations or metabolic processes. These genes are rarely classified as 'interesting' based on their variability profile. However, their dynamic behaviour can tease out important clues about naturally occurring biological processes in the organism under study and can be used for group classification. Dynamical discriminate function analysis was developed on the concept that stable classification parameters (roots) can be derived from highly variable gene-expression data. Stability of these combinations implies a strongly compensatory relationship that may divulge functional interconnections.

Similarities and differences between the E5 oncoproteins of bovine papillomaviruses type 1 and type 4: cytoskeleton, motility and invasiveness in E5-transformed bovine and mouse cells

Bovine papillomaviruses (BPVs) are oncogenic viruses. In cattle, BPV-1/2 is associated with urinary bladder cancer and BPV-4 with upper GI tract cancer. BPV E5 is a small hydrophobic protein localised in the endoplasmic reticulum (ER) and Golgi apparatus (GA). E5 is the major transforming protein of BPVs, capable of inducing cell transformation in cultured mouse fibroblasts and, in cooperation with E7, in primary bovine cells. E5-induced cell transformation is accompanied by activation of several cellular protein kinases, including growth factor receptors, and alkalinisation of endosomes and GA. We have reported that BPV E5 causes swelling and fragmentation of the GA and extensive vacuolisation of the cytoplasm. We now show that E5 from both BPV-1 and BPV-4 disturbs the actin cytoskeleton and focal adhesions in transformed bovine cells, where these morphological and behavioural characteristics are accompanied by hyperphosphorylation of the cellular phosphotyrosine kinase c-src. Both BPV-1 and BPV-4 E5 increase the motility of transformed mouse cells, but only BPV-1 E5 causes transformed mouse cells to penetrate a matrigel matrix. BPV-1 transformed mouse cells, but not BPV-4 transformed mouse cells, have hyperhpsphorylated c-src.

RAS and TGF-β exert antagonistic effects on extracellular matrix gene expression and fibroblast transformation

Ras, Raf, and Fos function as components in a signal transduction pathway that is constitutively active in many cancers. Many of the changes that underlie cell transformation arise through changes in gene expression. We have used gene expression profiling of 3T3 cells transformed by Ras, Raf, and Fos to define the common and distinct targets of transcriptional control by each of these oncogenes. In this analysis, the most strongly conserved feature of cell transformation at the transcriptional level is the transcriptional repression of genes that encode components of the extracellular matrix (ECM). TGF-beta treatment of fibroblasts is known to increase production of ECM, suggesting that TGF-beta might selectively reverse some of the gene expression changes that occur during cell transformation. Using gene expression profiling of the TGF-beta response, we show that the ability of TGF-beta to reverse the changes in gene expression brought about by cellular transformation is essentially confined to genes that encode components of the ECM and the cytoskeleton. This selective reversal of transformation-induced changes in gene expression is associated with partial reversal of many parameters of cell transformation. The results demonstrate a correlation between gene repression by the Ras/Raf/ERK signaling pathway, gene activation by the TGF-beta signaling pathway, and the transformed phenotype in fibroblasts.

Fos-Related Antigen 1 Modulates Malignant Features of Glioma Cells

Malignant gliomas, and high-grade gliomas (HGG) in particular, are nonmetastasizing but locally infiltrating, hypervascularized brain tumors of poor prognosis. We found previously that a c-fos-inducible vascular endothelial growth factor D is ubiquitously up-regulated in HGG grade IV, glioblastoma multiforme, and that glioblastoma multiforme overexpress Fos-related antigen 1 (Fra-1) rather than the c-Fos. We have thus become interested in the role Fra-1 may play in malignant glioma progression/maintenance, because Fra-1 has the capacity to modulate transcription of a variety of target genes. In this work, we have analyzed the biological effects of ectopic Fra-1 expression or Fra-1 knockdown in malignant glioma cells. Ectopic Fra-1 induced prominent phenotypic changes in all three malignant glioma cell lines examined: H4, U-87 MG, and A-172 MG. These changes were reflected in cells becoming more elongated with larger number of cellular processes. Furthermore, Fra-1 transgene caused H4 cells, which do not form tumor xenografts, to regain tumorigenic capacity. The genotype of these cells changed too, because 50 of 1,056 genes examined became either up-regulated or down-regulated. Conversely, Fra-1 knockdown altered prominently the morphology, anchorage-independent growth, tumorigenic potential, and Fra-1 effector expression, such as vascular endothelial growth factor D, in HGG cells. For example, cells transfected with antisense fra-1 showed shorter cellular processes than the control cells that did not grow in agar, and their tumorigenic potential was significantly diminished. Thus, Fra-1 may likely play an important role in the maintenance/progression of malignant gliomas and potentially represents a new target for therapeutic interventions.

Invasion of v-FosFBR-transformed cells is dependent upon histone deacetylase activity and suppression of histone deacetylase regulated genes

Transformation of fibroblasts with the v-fos oncogene produces a highly invasive phenotype that is mediated by changes in gene expression. Inhibition of histone deacetylase (HDAC) activity with trichostatin A (TSA) or valproic acid (VPA) at concentrations that do not affect morphology, motility, chemotaxis or proliferation, strongly inhibits invasion and results in the re-expression of a significant proportion of those genes that are downregulated in the v-Fos-transformed cells. Independent expression of three of these re-expressed genes, (Ring1 and YY1 binding protein (RYBP); protocadherin gamma subfamily C,3 (PCDHGC3); and signal transducer and activator of transcription 6 (STAT6)) in Fos-transformed cells, has no effect on morphology, motility, chemotaxis or proliferation, but strongly inhibits invasion. Therefore, we conclude that the ability of v-Fos-transformed cells to invade is dependent upon repression of gene expression through either direct or indirect HDAC activity.