Pseudopodial actin dynamics control epithelial-mesenchymal transition in metastatic cancer cells

DNA methylation based biomarkers: practical considerations and applications

A biomarker is a molecular target analyzed in a qualitative or quantitative manner to detect and diagnose the presence of a disease, to predict the outcome and the response to a specific treatment allowing personalized tailoring of patient management. Biomarkers can belong to different types of biochemical molecules such as proteins, DNA, RNA or lipids, whereby protein biomarkers have been the most extensively studied and used, notably in blood-based protein quantification tests or immunohistochemistry. The rise of interest in epigenetic mechanisms has allowed the identification of a new type of biomarker, DNA methylation, which is of great potential for many applications. This stable and heritable covalent modification mostly affects cytosines in the context of a CpG dinucleotide in humans. It can be detected and quantified by a number of technologies including genome-wide screening methods as well as locus- or gene-specific high-resolution analysis in different types of samples such as frozen tissues and FFPE samples, but also in body fluids such as urine, plasma, and serum obtained through non-invasive procedures. In some cases, DNA methylation based biomarkers have proven to be more specific and sensitive than commonly used protein biomarkers, which could clearly justify their use in clinics. However, very few of them are at the moment used in clinics and even less commercial tests are currently available. The objective of this review is to discuss the advantages of DNA methylation as a biomarker, the practical considerations for their development, and their use in disease detection, prediction of outcome or treatment response, through multiple examples mainly focusing on cancer, but also to evoke their potential for complex diseases and prenatal diagnostics.

Coordinated expression of galectin-3 and caveolin-1 in thyroid cancer

Galectin-3 (Gal3) is the single most accurate marker for the diagnosis of differentiated thyroid cancer (DTC). Gal3 overrides the tumour suppressor activity of caveolin-1 (Cav1) and functions in concert with Cav1 to promote focal adhesion turnover and tumour cell migration and invasion. To study their coordinated role in progression of a human cancer, we investigated the expression of Gal3 and Cav1 in specimens of human benign thyroid lesions, DTC and anaplastic thyroid cancer (ATC). Gal3 and Cav1 expression is significantly associated with DTC and ATC, but not benign nodules. Essentially all Cav1-positive DTC cancers express Gal3, supporting the synergistic activity of these two proteins in DTC progression. Similarly, coordinated elevated Gal3/Cav1 expression was observed in three DTC-derived cell lines (papillary TCP1 and KTC1 and follicular FTC133) but only one (ACT1) of five ATC-derived cell lines. Using siRNA knockdown, Gal3 and Cav1 were shown to be required for RhoA GTPase activation, stabilization of focal adhesion kinase (FAK; a measure of focal adhesion signalling and turnover) and increased migration of the DTC cell lines studied, but not the ATC cell lines, including ACT1, which expresses elevated levels of Gal3 and Cav1. Co-expression of Gal3 and Cav1 in the T238 anaplastic cell line stabilized FAK-GFP in focal adhesions. Gal3 and Cav1 therefore function synergistically to promote focal adhesion signalling, migration and progression of DTC.

O-linked β-N-acetylglucosaminylation (O-GlcNAcylation) in primary and metastatic colorectal cancer clones and effect of N-acetyl-β-D-glucosaminidase silencing on cell phenotype and transcriptome

O-linked β-N-acetylglucosamine (O-GlcNAc) glycosylation is a regulatory post-translational modification occurring on the serine or threonine residues of nucleocytoplasmic proteins. O-GlcNAcylation is dynamically regulated by O-GlcNAc transferase and O-GlcNAcase (OGA), which are responsible for O-GlcNAc addition and removal, respectively. Although O-GlcNAcylation was found to play a significant role in several pathologies such as type II diabetes and neurodegenerative diseases, the role of O-GlcNAcylation in the etiology and progression of cancer remains vague. Here, we followed O-GlcNAcylation and its catalytic machinery in metastatic clones of human colorectal cancer and the effect of OGA knockdown on cellular phenotype and on the transcriptome. The colorectal cancer SW620 metastatic clone exhibited increased O-GlcNAcylation and decreased OGA expression compared with its primary clone, SW480. O-GlcNAcylation elevation in SW620 cells, through RNA interference of OGA, resulted in phenotypic alterations that included acquisition of a fibroblast-like morphology, which coincides with epithelial metastatic progression and growth retardation. Microarray analysis revealed that OGA silencing altered the expression of about 1300 genes, mostly involved in cell movement and growth, and specifically affected metabolic pathways of lipids and carbohydrates. These findings support the involvement of O-GlcNAcylation in various aspects of tumor cell physiology and suggest that this modification may serve as a link between metabolic changes and cancer.

Microarray analysis verifies two distinct phenotypes of glioblastomas resistant to antiangiogenic therapy

PURPOSE

To identify mechanisms and mediators of resistance to antiangiogenic therapy in human glioblastoma.

EXPERIMENTAL DESIGN

We carried out microarray gene expression analysis and immunohistochemistry comparing 21 recurrent glioblastomas progressing during antiangiogenic treatment with VEGF neutralizing antibody bevacizumab to paired pretreatment tumors from the same patients.

RESULTS

Microarray analysis revealed that bevacizumab-resistant glioblastomas (BRG) had two clustering patterns defining subtypes that reflect radiographic growth patterns. Enhancing BRGs (EBRG) exhibited MRI enhancement, a long-established criterion for glioblastoma progression, and expressed mitogen-activated protein kinases, neural cell adhesion molecule-1 (NCAM-1), and aquaporin 4. Compared with their paired pretreatment tumors, EBRGs had unchanged vascularity and hypoxia, with increased proliferation. Nonenhancing BRGs (NBRG) exhibited minimal MRI enhancement but had FLAIR-bright expansion, a newer criterion for glioblastoma recurrence since the advent of antiangiogenic therapy, and expressed integrin α5, laminin, fibronectin1, and PDGFRβ. NBRGs had less vascularity, more hypoxia, and unchanged proliferation than their paired pretreatment tumors. Primary NBRG cells exhibited more stellate morphology with a 3-fold increased shape factor and were nearly 4-fold more invasive in Matrigel chambers than primary cells from EBRGs or bevacizumab-naive glioblastomas (P < 0.05).

CONCLUSION

Using microarray analysis, we found two resistance patterns during antiangiogenic therapy with distinct molecular profiles and radiographic growth patterns. These studies provide valuable biologic insight into the resistance that has limited antiangiogenic therapy to date.

The septin cytoskeleton facilitates membrane retraction during motility and blebbing

Septins assemble on the cortex and restore normal cell shape by retracting aberrantly protruding membranes and promoting cortical contraction during amoeboid motility.

Increasing evidence supports a critical role for the septin cytoskeleton at the plasma membrane during physiological processes including motility, formation of dendritic spines or cilia, and phagocytosis. We sought to determine how septins regulate the plasma membrane, focusing on this cytoskeletal element’s role during effective amoeboid motility. Surprisingly, septins play a reactive rather than proactive role, as demonstrated during the response to increasing hydrostatic pressure and subsequent regulatory volume decrease. In these settings, septins were required for rapid cortical contraction, and SEPT6-GFP was recruited into filaments and circular patches during global cortical contraction and also specifically during actin filament depletion. Recruitment of septins was also evident during excessive blebbing initiated by blocking membrane trafficking with a dynamin inhibitor, providing further evidence that septins are recruited to facilitate retraction of membranes during dynamic shape change. This function of septins in assembling on an unstable cortex and retracting aberrantly protruding membranes explains the excessive blebbing and protrusion observed in septin-deficient T cells.

Myb overexpression overrides androgen depletion-induced cell cycle arrest and apoptosis in prostate cancer cells, and confers aggressive malignant traits: potential role in castration resistance

Myb, a cellular progenitor of v-Myb oncogenes, is amplified in prostate cancer and exhibits greater amplification frequency in hormone-refractory disease. Here, we have investigated the functional significance of Myb in prostate cancer. Our studies demonstrate Myb expression in all prostate cancer cell lines (LNCaP, C4-2, PC3 and DU145) examined, whereas it is negligibly expressed in normal/benign prostate epithelial cells (RWPE1 and RWPE2). Notably, Myb is significantly upregulated, both at transcript (>60-fold) and protein (>15-fold) levels, in castration-resistant (C4-2) cells as compared with androgen-dependent (LNCaP) prostate cancer cells of the same genotypic lineage. Using loss and gain of function approaches, we demonstrate that Myb promotes and sustains cell cycle progression and survival under androgen-supplemented and -deprived conditions, respectively, through induction of cyclins (A1, D1 and E1), Bcl-xL and Bcl2 and downregulation of p27 and Bax. Interestingly, Myb overexpression is also associated with enhanced prostate-specific antigen expression. Furthermore, our data show a role of Myb in enhanced motility and invasion and decreased homotypic interactions of prostate cancer cells. Myb overexpression is also associated with actin reorganization leading to the formation of filopodia-like cellular protrusions. Immunoblot analyses demonstrate gain of mesenchymal and loss of epithelial markers and vice versa, in Myb-overexpressing LNCaP and -silenced C4-2 cells, respectively, indicating a role of Myb in epithelial to mesenchymal transition. Altogether, our studies provide first experimental evidence for a functional role of Myb in growth and malignant behavior of prostate cancer cells and suggest a novel mechanism for castration resistance.

Application of SELDI-TOF-MS and LCM to screen protein markers for early diagnosis of liver metastasis of colorectal carcinoma

AIM: To screen protein markers for liver metastases of colorectal cancer using surface-enhanced laser desorption/ionization time-of-flight mass spectrometry protein chip (SELDI-TOF-MS) in combination with laser capture microdissection (LCM) technology.

METHODS: Normal colorectal cells, primary tumor cells and liver metastatic cells were obtained from 24 colorectal cancer patients with liver metastases using the LCM technology. Protein profiling was performed using SELDI-TOF-MS technology. Differentially expressed proteins were analyzed using Biomarker Wizard software and identified by querying the database.

RESULTS: Fifteen differentially expressed proteins were found between primary tumor cells and normal colorectal cells, of which 12 were up-regulated and 3 down-regulated. Nine differentially expressed proteins were found between liver metastatic cells and primary tumor cells, of which 5 were up-regulated and 4 down-regulated. Twenty differentially expressed proteins were identified by querying ExPasy protein database, including integral membrane protein 2C, DNA repair protein RAD51 homolog 4, cell cycle checkpoint protein RAD1, human epididymis protein 4, centromere protein R, and pleckstrin homology domain family member 3. Apoptosis regulator Bax-γ, S100A11, Raf kinase inhibitor protein (RKIP) and heat shock protein 27 (HSP-27) displayed most obvious differential expression among normal colorectal cells, primary tumor cells and liver metastatic cells (all P < 0. 01).

CONCLUSION: SELDI-TOF-MS technology combined with LCM may allow to screen highly sensitive and specific protein markers for colorectal cancer and liver metastases of colorectal cancer.

Mechanobiology of tumor invasion: engineering meets oncology

The physical sciences and engineering have introduced novel perspectives into the study of cancer through model systems, tools, and metrics that enable integration of basic science observations with clinical data. These methods have contributed to the identification of several overarching mechanisms that drive processes during cancer progression including tumor growth, angiogenesis, and metastasis. During tumor cell invasion - the first clinically observable step of metastasis - cells demonstrate diverse and evolving physical phenotypes that cannot typically be defined by any single molecular mechanism, and mechanobiology has been used to study the physical cell behaviors that comprise the "invasive phenotype". In this review, we discuss the continually evolving pathological characterization and in vitro mechanobiological characterization of tumor invasion, with emphasis on emerging physical biology and mechanobiology strategies that have contributed to a more robust mechanistic understanding of tumor cell invasion. These physical approaches may ultimately help to better predict and identify tumor metastasis.

Constitutive K-RasG12D activation of ERK2 specifically regulates 3D invasion of human pancreatic cancer cells via MMP-1

Pancreatic ductal adenocarcinomas (PDAC) are highly invasive and metastatic neoplasms commonly unresponsive to current drug therapy. Overwhelmingly, PDAC harbors early constitutive, oncogenic mutations in K-Ras(G12D) that exist prior to invasion. Histologic and genetic analyses of human PDAC biopsies also exhibit increased expression of extracellular signal-regulated kinase (ERK) 1/2 and proinvasive matrix metalloproteinases (MMP), indicators of poor prognosis. However, the distinct molecular mechanisms necessary for K-Ras/ERK1/2 signaling and its influence on MMP-directed stromal invasion in primary human pancreatic ductal epithelial cells (PDEC) have yet to be elucidated in three-dimensions. Expression of oncogenic K-Ras(G12D) alone in genetically defined PDECs reveals increased invadopodia and epithelial-to-mesenchymal transition markers, but only when cultured in a three-dimensional model incorporating a basement membrane analog. Activation of ERK2, but not ERK1, also occurs only in K-Ras(G12D)-mutated PDECs cultured in three-dimensions and is a necessary intracellular signaling event for invasion based upon pharmacologic and short hairpin RNA (shRNA) inhibition. Increased active invasion of K-Ras(G12D) PDECs through the basement membrane model is associated with a specific microarray gene expression signature and induction of MMP endopeptidases. Specifically, MMP-1 RNA, its secreted protein, and its proteolytic cleavage activity are amplified in K-Ras(G12D) PDECs when assayed by real-time quantitative PCR, ELISA, and fluorescence resonance energy transfer (FRET). Importantly, shRNA silencing of MMP-1 mimics ERK2 inhibition and disrupts active, vertical PDEC invasion. ERK2 isoform and MMP-1 targeting are shown to be viable strategies to attenuate invasion of K-Ras(G12D)-mutated human pancreatic cancer cells in a three-dimensional tumor microenvironment.

The emerging functions of septins in metazoans

Septins form a subfamily of highly related GTP-binding proteins conserved from eukaryotic protists to mammals. In most cases, septins function in close association with cell membranes and the actin and microtubule cytoskeleton to regulate a wide variety of key cellular processes. Further underscoring their importance, septin abnormalities are associated with several human diseases. Remarkably, septins have the ability to polymerize into assemblies of different sizes in vitro and in vivo. In cells, these structures act in the formation of diffusion barriers and scaffolds that maintain subcellular polarity. Here, we focus on the emerging roles of vertebrate septins in ciliogenesis, neurogenesis, tumorigenesis and host-pathogen interactions, and discuss whether unifying themes underlie the molecular function of septins in health and disease.

Actin-depolymerizing factor homology domain: a conserved fold performing diverse roles in cytoskeletal dynamics

Actin filaments form contractile and protrusive structures that play central roles in many processes such as cell migration, morphogenesis, endocytosis, and cytokinesis. During these processes, the dynamics of the actin filaments are precisely regulated by a large array of actin-binding proteins. The actin-depolymerizing factor homology (ADF-H) domain is a structurally conserved protein motif, which promotes cytoskeletal dynamics by interacting with monomeric and/or filamentous actin, and with the Arp2/3 complex. Despite their structural homology, the five classes of ADF-H domain proteins display distinct biochemical activities and cellular roles, only parts of which are currently understood. ADF/cofilin promotes disassembly of aged actin filaments, whereas twinfilin inhibits actin filament assembly via sequestering actin monomers and interacting with filament barbed ends. GMF does not interact with actin, but instead binds Arp2/3 complex and promotes dissociation of Arp2/3-mediated filament branches. Abp1 and drebrin are multidomain proteins that interact with actin filaments and regulate the activities of other proteins during various actin-dependent processes. The exact function of coactosin is currently incompletely understood. In this review article, we discuss the biochemical functions, cellular roles, and regulation of the five groups of ADF-H domain proteins.

Septin 9 isoform expression, localization and epigenetic changes during human and mouse breast cancer progression

Introduction

Altered expression of Septin 9 (SEPT9), a septin coding for multiple isoform variants, has been observed in several carcinomas, including colorectal, head and neck, ovarian and breast, compared to normal tissues. The mechanisms regulating its expression during tumor initiation and progression in vivo and the oncogenic function of its different isoforms remain elusive.

Methods

Using an integrative approach, we investigated SEPT9 at the genetic, epigenetic, mRNA and protein levels in breast cancer. We analyzed a panel of breast cancer cell lines, human primary tumors and corresponding tumor-free areas, normal breast tissues from reduction mammoplasty patients, as well as primary mammary gland adenocarcinomas derived from the polyoma virus middle T antigen, or PyMT, mouse model. MCF7 clones expressing individual GFP-tagged SEPT9 isoforms were used to determine their respective intracellular distributions and effects on cell migration.

Results

An overall increase in gene amplification and altered expression of SEPT9 were observed during breast tumorigenesis. We identified an intragenic alternative promoter at which methylation regulates SEPT9_v3 expression. Transfection of specific GFP-SEPT9 isoforms in MCF7 cells indicates that these isoforms exhibit differential localization and affect migration rates. Additionally, the loss of an uncharacterized SEPT9 nucleolar localization is observed during tumorigenesis.

Conclusions

In this study, we found conserved in vivo changes of SEPT9 gene amplification and overexpression during human and mouse breast tumorigenesis. We show that DNA methylation is a prominent mechanism responsible for regulating differential SEPT9 isoform expression and that breast tumor samples exhibit distinctive SEPT9 intracellular localization. Together, these findings support the significance of SEPT9 as a promising tool in breast cancer detection and further emphasize the importance of analyzing and targeting SEPT9 isoform-specific expression and function.

Septin roles in tumorigenesis

Septins are a family of cytoskeleton related proteins consisting of 14 members that associate and interact with actin and tubulin. From yeast to humans, septins maintain a conserved role in cytokinesis and they are also involved in a variety of other cellular functions including chromosome segregation, DNA repair, migration and apoptosis. Tumorigenesis entails major alterations in these processes. A substantial body of literature reveals that septins are overexpressed, downregulated or generate chimeric proteins with MLL in a plethora of solid tumors and in hematological malignancies. Thus, members of this gene family are emerging as key players in tumorigenesis. The analysis of septins during cancer initiation and progression is challenged by the presence of many family members and by their potential to produce numerous isoforms. However, the development and application of advanced technologies is allowing for a more detailed analysis of septins during tumorigenesis. Specifically, such applications have led to the establishment and validation of SEPT9 as a biomarker for the early detection of colorectal cancer. This review summarizes the current knowledge on the role of septins in tumorigenesis, emphasizing their significance and supporting their use as potential biomarkers in various cancer types.

3D models of epithelial-mesenchymal transition in breast cancer metastasis: high-throughput screening assay development, validation, and pilot screen

Despite advancements in therapies developed for the treatment of cancer, patient prognosis and mortality rates have improved minimally, and metastasis remains the primary cause of cancer mortality worldwide. An underlying mechanism promoting metastasis in many types of cancer is epithelial-mesenchymal transition (EMT). Here the authors report a novel 3D model of EMT and metastatic breast cancer suitable for high-throughput screening (HTS) drug discovery. The primary assay incorporates the expression of the prognostic biomarker vimentin, as a luciferase reporter of EMT, in basil-like/triple-negative MDA-MB-231 breast carcinoma spheroids. Using this model, the authors developed a number of known antitumor agents as control modulators of EMT. U0126, PKC412, PF2341066, dasatinib, and axitinib downregulated vimentin expression by 70% to 90% as compared to untreated spheroids. Counterassays were developed to measure spheroid viability and the invasive potential of MDA-MB-231 spheroids after small-molecule treatment and used to confirm hits from primary screening. Finally, the authors conducted a pilot screen to validate this model for HTS using a purified library of marine secondary metabolites. From 230 compounds screened, they obtained a Z' score of 0.64, indicative of an excellent assay, and confirmed 4 hits, including isonaamidine B, papuamine, mycalolide E, and jaspamide. This HTS model demonstrates the potential to identify small-molecule modulators of EMT that could be used to discover novel antimetastatic agents for the treatment of cancer.

Slug enhances invasion ability of pancreatic cancer cells through upregulation of matrix metalloproteinase-9 and actin cytoskeleton remodeling

Slug, a member of the Snail family of transcription factors, has a crucial role in the regulation of epithelial-mesenchymal transition (EMT) by suppressing several epithelial markers and adhesion molecules, including E-cadherin. A recent study demonstrated that no relationship exists between Slug and E-cadherin in pancreatic cancer. Another study showed that in malignant mesothelioma effusions Slug was associated with matrix metalloproteinase (MMP) expression, but that there was no association with E-cadherin. F-ascin is an actin-bundling protein involved in filopodia assembly and cancer invasion and metastasis of multiple epithelial cancer types. In this study, we investigated Slug, E-cadherin, and MMP-9 expression using immunohistochemistry in 60 patients with pancreatic cancer and their correlation with carcinoma invasion and metastasis. Additionally, we observed the effects of Slug on invasion and metastasis in the pancreatic cancer cell line PANC-1. Alterations in Slug, MMP-9, and E-cadherin were determined by RT-PCR, western blot, and immunohistochemistry. Alterations in MMP-9 and F-actin cytoskeleton were determined by immunofluorescence staining, flow cytometry (FCM), or gelatin zymography. Slug, E-cadherin, and MMP-9 expression in pancreatic cancer was significantly associated with lymph node metastases and we found a significant correlation between Slug and MMP-9 expression; however, no significant correlation was observed between Slug and E-cadherin expression. Slug transfection significantly increased invasion and metastasis in PANC-1 cells and orthotopic tumor of mouse in vivo, and significantly upregulated and activated MMP-9; however, there was no effect on E-cadherin expression. Slug promoted the formation of lamelliopodia or filopodia in PANC-1 cells. The intracellular F-actin and MMP-9 was increased and relocated to the front of the extending pseudopodia from the perinuclear pool in Slug-transfected PANC-1 cells. These results suggest that Slug promotes migration and invasion of PANC-1 cells, which may correlate with the reorganization of MMP-9 and remodeling of the F-actin cytoskeleton, but not with E-cadherin expression.

Epithelial and mesenchymal phenotypic switchings modulate cell motility in metastasis

The most ominous stage of cancer progression is metastasis, or the dissemination of carcinoma cells from the primary site into distant organs. Metastases are often resistant to current extirpative therapies and even the newest biological agents cure only a small subset of patients. Therefore a greater understanding of tumor biology that integrates properties intrinsic to carcinomas with tissue environmental modulators of behavior is needed. In no aspect of tumor progression is this more evident than the acquisition of cell motility that is critical for both escape from the primary tumor and colonization. In this overview, we discuss how this behavior is modified by carcinoma cell phenotypic plasticity that is evidenced by reversible switching between epithelial and mesenchymal phenotypes. The presence or absence of intercellular adhesions mediate these switches and dictate the receptivity towards signals from the extracellular milieu. These signals, which include soluble growth factors, cytokines, and extracellular matrix embedded with matrikines and matricryptines will be discussed in depth. Finally, we will describe a new mode of discerning the balance between epithelioid and mesenchymal movement.

RNA purification from tumor cell protrusions using porous polycarbonate filters

Actin-rich cellular protrusions or pseudopodia form via local actin filament polymerization and branching and represent a variety of polarized cellular domains including lamellipodia, filipodia, and neuronal growth cones. RNA localization and local protein translation in these domains are important for various cellular processes. RNA transport and local synthesis have been implicated in cell migration and tumor cell metastasis as well as in neuronal plasticity in neurons. Characterization of the mRNAs present in these domains is key to understanding the functional role of mRNA translocation and local protein translation in cellular processes. We describe here a method to segregate pseudopodia of metastatic cancer cells from the cell body using porous polycarbonate filters. This approach enables the purification and identification of RNAs and proteins in these protrusive cellular domains.