Loss of PTEN induces microtentacles through PI3K-independent activation of cofilin

Suspension state affects the stemness of breast cancer cells by regulating the glycogen synthase kinase-3β

Circulating tumor cells (CTCs) are considered an important factor involved in tumor metastasis and can overcome mechanical interactions to gain the ability to distant metastasis. The previous study had shown that the suspension state could regulate the stemness of breast cancer cells (BCCs). However, the specific molecular mechanisms involved have not yet been explored clearly. In this study, MCF-7 and MDA-MBA-231 BCCs were cultured in suspension and adherent. The effect of suspension state on BCCs was further elucidated by observing suspension cell clusters, sorting CD44+/CD24- cell subpopulation and detecting self-renewal ability. Furthermore, it was found that glycogen synthase kinase-3β (GSK-3β) was significantly down-regulated in MCF-7 suspension cells along with the activation of the Wnt/β-catenin signaling, but the converse was true for MDA-MB-231 cells. Subsequently, GSK-3β was differentially expressed in MCF-7 suspension cells. The activation of the Wnt/β-catenin signaling, epithelial-mesenchymal transition (EMT) and stemness were all inhibited when GSK-3 was overexpressed in suspension MCF-7 cells. While GSK-3β was down-regulated, it further promoted the Wnt/β-catenin signaling, mesenchymal characteristic and stemness of MCF-7 cells. This study demonstrated that suspension state could activate the Wnt/β-catenin signaling by inhibiting GSK-3β to promote the stemness of epithelial BCCs, providing a therapeutic strategy for targeted CTCs.

Hydrogen Peroxide Induces α-Tubulin Detyrosination and Acetylation and Impacts Breast Cancer Metastatic Phenotypes

Levels of hydrogen peroxide are highly elevated in the breast tumor microenvironment compared to normal tissue. Production of hydrogen peroxide is implicated in the mechanism of action of many anticancer therapies. Several lines of evidence suggest hydrogen peroxide mediates breast carcinogenesis and metastasis, though the molecular mechanism remains poorly understood. This study elucidates the effects of exposure to elevated hydrogen peroxide on non-tumorigenic MCF10A mammary epithelial cells, tumorigenic MCF7 cells, and metastatic MDA-MB-231 breast cancer cells. Hydrogen peroxide treatment resulted in a dose- and time-dependent induction of two α-tubulin post-translational modifications-de-tyrosination and acetylation-both of which are markers of poor patient prognosis in breast cancer. Hydrogen peroxide induced the formation of tubulin-based microtentacles in MCF10A and MDA-MB-231 cells, which were enriched in detyrosinated and acetylated α-tubulin. However, the hydrogen peroxide-induced microtentacles did not functionally promote metastatic phenotypes of cellular reattachment and homotypic cell clustering. These data establish for the first time that microtentacle formation can be separated from the functions to promote reattachment and clustering, which indicates that there are functional steps that remain to be identified. Moreover, signals in the primary tumor microenvironment may modulate α-tubulin post-translational modifications and induce microtentacles; however, the functional consequences appear to be context-dependent.

Elevation of Cytoplasmic Calcium Suppresses Microtentacle Formation and Function in Breast Tumor Cells

Cytoskeletal remodeling in circulating tumor cells (CTCs) facilitates metastatic spread. Previous oncology studies examine sustained aberrant calcium (Ca²⁺) signaling and cytoskeletal remodeling scrutinizing long-term phenotypes such as tumorigenesis and metastasis. The significance of acute Ca²⁺ signaling in tumor cells that occur within seconds to minutes is overlooked. This study investigates rapid cytoplasmic Ca²⁺ elevation in suspended cells on actin and tubulin cytoskeletal rearrangements and the metastatic microtentacle (McTN) phenotype. The compounds Ionomycin and Thapsigargin acutely increase cytoplasmic Ca²⁺, suppressing McTNs in the metastatic breast cancer cell lines MDA-MB-231 and MDA-MB-436. Functional decreases in McTN-mediated reattachment and cell clustering during the first 24 h of treatment are not attributed to cytotoxicity. Rapid cytoplasmic Ca²⁺ elevation was correlated to Ca²⁺-induced actin cortex contraction and rearrangement via myosin light chain 2 and cofilin activity, while the inhibition of actin polymerization with Latrunculin A reversed Ca²⁺-mediated McTN suppression. Preclinical and phase 1 and 2 clinical trial data have established Thapsigargin derivatives as cytotoxic anticancer agents. The results from this study suggest an alternative molecular mechanism by which these compounds act, and proof-of-principle Ca²⁺-modulating compounds can rapidly induce morphological changes in free-floating tumor cells to reduce metastatic phenotypes.

Cofilin activation in pancreatic acinar cells plays a pivotal convergent role for mediating CCK-stimulated enzyme secretion and growth

Introduction: The actin regulatory protein, cofilin plays a key signaling role in many cells for numerous cellular responses including in proliferation, development, motility, migration, secretion and growth. In the pancreas it is important in islet insulin secretion, growth of pancreatic cancer cells and in pancreatitis. However, there are no studies on its role or activation in pancreatic acinar cells. Methods: To address this question, we studied the ability of CCK to activate cofilin in pancreatic acinar cells, AR42J cells and CCK₁-R transfected Panc-1 cells, the signaling cascades involved and its effect on enzyme secretion and MAPK activation, a key mediator of pancreatic growth. Results: CCK (0.3 and 100 nM), TPA, carbachol, Bombesin, secretin and VIP decreased phospho-cofilin (i.e., activate cofilin) and both phospho-kinetic and inhibitor studies of cofilin, LIM kinase (LIMK) and Slingshot Protein Phosphatase (SSH1) demonstrated these conventional activators of cofilin were not involved. Serine phosphatases inhibitors (calyculin A and okadaic acid), however inhibited CCK/TPA-cofilin activation. Studies of various CCK-activated signaling cascades showed activation of PKC/PKD, Src, PAK4, JNK, ROCK mediated cofilin activation, but not PI3K, p38, or MEK. Furthermore, using both siRNA and cofilin inhibitors, cofilin activation was shown to be essential for CCK-mediated enzyme secretion and MAPK activation. Conclusion: These results support the conclusion that cofilin activation plays a pivotal convergent role for various cell signaling cascades in CCK mediated growth/enzyme secretion in pancreatic acini.

PTEN inhibits AMPK to control collective migration

Pten is one of the most frequently mutated tumour suppressor gene in cancer. PTEN is generally altered in invasive cancers such as glioblastomas, but its function in collective cell migration and invasion is not fully characterised. Herein, we report that the loss of PTEN increases cell speed during collective migration of non-tumourous cells both in vitro and in vivo. We further show that loss of PTEN promotes LKB1-dependent phosphorylation and activation of the major metabolic regulator AMPK. In turn AMPK increases VASP phosphorylation, reduces VASP localisation at cell-cell junctions and decreases the interjunctional transverse actin arcs at the leading front, provoking a weakening of cell-cell contacts and increasing migration speed. Targeting AMPK activity not only slows down PTEN-depleted cells, it also limits PTEN-null glioblastoma cell invasion, opening new opportunities to treat glioblastoma lethal invasiveness.

Pten is a tumour suppressor gene that is associated with highly invasive cancers such as glioblastoma. Here the authors show that PTEN loss results in increased migratory behaviour, which can be countered by targeting AMPK activity.

Microtubule disruption reduces metastasis more effectively than primary tumor growth

Clinical cancer imaging focuses on tumor growth rather than metastatic phenotypes. The microtubule-depolymerizing drug, Vinorelbine, reduced the metastatic phenotypes of microtentacles, reattachment and tumor cell clustering more than tumor cell viability. Treating mice with Vinorelbine for only 24 h had no significant effect on primary tumor survival, but median metastatic tumor survival was extended from 8 to 30 weeks. Microtentacle inhibition by Vinorelbine was also detectable within 1 h, using tumor cells isolated from blood samples. As few as 11 tumor cells were sufficient to yield 90% power to detect this 1 h Vinorelbine drug response, demonstrating feasibility with the small number of tumor cells available from patient biopsies. This study establishes a proof-of-concept that targeted microtubule disruption can selectively inhibit metastasis and reveals that existing FDA-approved therapies could have anti-metastatic actions that are currently overlooked when focusing exclusively on tumor growth.

TUBB3 is associated with PTEN, neuroendocrine differentiation, and castration resistance in prostate cancer

BACKGROUND

Tubulin-β3 encoded by the Tubulin-β3 (TUBB3) gene is a microtubule protein. Previous studies have shown that TUBB3 expression is upregulated in castration-resistant prostate cancer (CaP) and is involved in taxane resistance. However, the biological mechanism of TUBB3 involvement in the progression to castration-resistant CaP is not fully elucidated. This study aimed to analyze the expression and function of TUBB3 in localized and metastatic CaP.

METHODS

TUBB3 expression was determined using immunohistochemistry in localized and metastatic CaP. We also investigated the association between TUBB3, phosphatase and tensin homolog (PTEN), and neuroendocrine differentiation and examined the involvement of TUBB3 in new antiandrogen drugs (enzalutamide and apalutamide) resistance in metastatic CaP.

RESULTS

In 155 cases of localized CaP, immunohistochemistry showed that 5 (3.2%) of the CaP cases were positive for tubulin-β3. Kaplan-Meier analysis showed that high expression of tubulin-β3 was associated with poor prostate-specific antigen recurrence-free survival after radical prostatectomy. In 57 cases of metastatic CaP, immunohistochemistry showed that 14 (25%) cases were positive for tubulin-β3. Tubulin-β3 expression was higher in metastatic CaP than in localized CaP. High tubulin-β3 expression was correlated with negative PTEN expression. TUBB3 expression was increased in neuroendocrine CaP based on several public databases. PTEN knockout decreased the sensitivity to enzalutamide and apalutamide in 22Rv-1 cells. TUBB3 knockdown reversed the sensitivity to enzalutamide and apalutamide in PTEN-CRISPR 22Rv-1 cells. High expression of tubulin-β3 and negative expression of PTEN were significantly associated with poor overall survival in metastatic CaP treated with androgen deprivation therapy.

CONCLUSIONS

These results suggest that TUBB3 may be a useful predictive biomarker for survival and play an essential role in antiandrogen resistance in CaP.

Actin fence therapy with exogenous V12Rac1 protects against acute lung injury

High mortality in acute lung injury (ALI) results from sustained proinflammatory signaling by alveolar receptors, such as TNF-α receptor type 1 (TNFR1). Factors that determine the sustained signaling are not known. Unexpectedly, optical imaging of live alveoli revealed a major TNF-α–induced surge of alveolar TNFR1 due to a Ca²⁺-dependent mechanism that decreased the cortical actin fence. Mouse mortality due to inhaled LPS was associated with cofilin activation, actin loss, and the TNFR1 surge. The constitutively active form of the GTPase, Rac1 (V12Rac1), given intranasally (i.n.) as a noncovalent construct with a cell-permeable peptide, enhanced alveolar filamentous actin (F-actin) and blocked the TNFR1 surge. V12Rac1 also protected against ALI-induced mortality resulting from i.n. instillation of LPS or of Pseudomonas aeruginosa. We propose a potentially new therapeutic paradigm in which actin enhancement by exogenous Rac1 strengthens the alveolar actin fence, protecting against proinflammatory receptor hyperexpression, and therefore blocking ALI.

Partial thermal imidization of polyelectrolyte multilayer cell tethering surfaces (TetherChip) enables efficient cell capture and microtentacle fixation for circulating tumor cell analysis

The technical challenges of imaging non-adherent tumor cells pose a critical barrier to understanding tumor cell responses to the non-adherent microenvironments of metastasis, like the bloodstream or lymphatics. In this study, we optimized a microfluidic device (TetherChip) engineered to prevent cell adhesion with an optically-clear, thermal-crosslinked polyelectrolyte multilayer nanosurface and a terminal lipid layer that simultaneously tethers the cell membrane for improved spatial immobilization. Thermal imidization of the TetherChip nanosurface on commercially-available microfluidic slides allows up to 98% of tumor cell capture by the lipid tethers. Importantly, time-lapse microscopy demonstrates that unique microtentacles on non-adherent tumor cells are rapidly destroyed during chemical fixation, but tethering microtentacles to the TetherChip surface efficiently preserves microtentacle structure post-fixation and post-blood isolation. TetherChips remain stable for more than 6 months, enabling shipment to distant sites. The broad retention capability of TetherChips allows comparison of multiple tumor cell types, revealing for the first time that carcinomas beyond breast cancer form microtentacles in suspension. Direct integration of TetherChips into the Vortex VTX-1 CTC isolation instrument shows that live CTCs from blood samples are efficiently captured on TetherChips for rapid fixation and same-day immunofluorescence analysis. Highly efficient and unbiased label-free capture of CTCs on a surface that allows rapid chemical fixation also establishes a streamlined clinical workflow to stabilize patient tumor cell samples and minimize analytical variables. While current studies focus primarily on CTC enumeration, this microfluidic device provides a novel platform for functional phenotype testing in CTCs with the ultimate goal of identifying anti-metastatic, patient-specific therapies.

Microtubule-associated protein tau (MAPT) promotes bicalutamide resistance and is associated with survival in prostate cancer

INTRODUCTION

Microtubule-associated protein tau (MAPT), facilitates tubulin assembly and microtubule stabilization. Several studies have shown that overexpression of MAPT is linked to poor prognosis and is involved in taxane resistance in cancer. This study aimed to assess the expression and function of MAPT in prostate cancer (CaP).

METHODS

The expression of MAPT was determined using immunohistochemistry in CaP. We analyzed the interaction between MAPT, Phosphatase and Tensin Homolog (PTEN), and androgen receptor and investigated the role of MAPT in bicalutamide resistance.

RESULTS

Immunohistochemistry in 155 CaP cases showed that 15% of them were positive for MAPT. High MAPT expression was significantly orrelated with high Gleason score and high T stage. Kaplan-Meier analysis showed that the high MAPT expression was significantly associated with poor prostate-specific antigen recurrence survival after radical prostatectomy. There was an inverse correlation between MAPT and PTEN. In the CaP cell lines, knockout of PTEN increased the expression of MAPT, whereas knockdown of MAPT suppressed the expression of androgen receptor and increased the sensitivity to bicalutamide. Furthermore, immunohistochemical staining of MAPT showed that high MAPT expression was significantly associated with poor overall survival in 74 CaP patients who were treated with androgen deprivation therapy.

CONCLUSION

These results suggest that MAPT may be a promising predictive biomarker for survival and play an essential role in bicalutamide resistance in CaP.

A Premalignant Cell-Based Model for Functionalization and Classification of PTEN Variants

As sequencing becomes more economical, we are identifying sequence variations in the population faster than ever. For disease-associated genes, it is imperative that we differentiate a sequence variant as either benign or pathogenic, such that the appropriate therapeutic interventions or surveillance can be implemented. PTEN is a frequently mutated tumor suppressor that has been linked to the PTEN hamartoma tumor syndrome. Although the domain structure of PTEN and the functional impact of a number of its most common tumor-linked mutations have been characterized, there is a lack of information about many recently identified clinical variants. To address this challenge, we developed a cell-based assay that utilizes a premalignant phenotype of normal mammary epithelial cells lacking PTEN. We measured the ability of PTEN variants to rescue the spheroid formation phenotype of PTEN^-/- MCF10A cells maintained in suspension. As proof of concept, we functionalized 47 missense variants using this assay, only 19 of which have clear classifications in ClinVar. We utilized a machine learning model trained with annotated genotypic data to classify variants as benign or pathogenic based on our functional scores. Our model predicted with high accuracy that loss of PTEN function was indicative of pathogenicity. We also determined that the pathogenicity of certain variants may have arisen from reduced stability of the protein product. Overall, this assay outperformed computational predictions, was scalable, and had a short run time, serving as an ideal alternative for annotating the clinical significance of cancer-associated PTEN variants. SIGNIFICANCE: Combined three-dimensional tumor spheroid modeling and machine learning classifies PTEN missense variants, over 70% of which are currently listed as variants of uncertain significance. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/13/2775/F1.large.jpg.

Gauging the Impact of Cancer Treatment Modalities on Circulating Tumor Cells (CTCs)

The metastatic cascade consists of multiple complex steps, but the belief that it is a linear process is diminishing. In order to metastasize, cells must enter the blood vessels or body cavities (depending on the cancer type) via active or passive mechanisms. Once in the bloodstream and/or lymphatics, these cancer cells are now termed circulating tumor cells (CTCs). CTC numbers as well as CTC clusters have been used as a prognostic marker with higher numbers of CTCs and/or CTC clusters correlating with an unfavorable prognosis. However, we have very limited knowledge about CTC biology, including which of these cells are ultimately responsible for overt metastatic growth, but due to the fact that higher numbers of CTCs correlate with a worse prognosis; it would seem appropriate to either limit CTCs and/or their dissemination. Here, we will discuss the different cancer treatments which may inadvertently promote the mobilization of CTCs and potential CTC therapies to decrease metastasis.

Endothelial mitochondria determine rapid barrier failure in chemical lung injury

Acid aspiration, which can result from several etiologies, including postoperative complications, leads to direct contact of concentrated hydrochloric acid (HCl) with the alveolar epithelium. As a result, rapid endothelial activation induces alveolar inflammation, leading to life-threatening pulmonary edema. Because mechanisms underlying the rapid endothelial activation are not understood, here we determined responses in real time through optical imaging of alveoli of live mouse lungs. By alveolar micropuncture, we microinfused concentrated HCl in the alveolar lumen. As expected, acid contact with the epithelium caused rapid, but transient, apical injury. However, there was no concomitant membrane injury to the endothelium. Nevertheless, H2O2-mediated epithelial-endothelial paracrine signaling induced endothelial barrier failure, as detected by microvascular dextran leakage and lung water quantification. Remarkably, endothelial mitochondria regulated the barrier failure by activating uncoupling protein 2 (UCP2), thereby inducing transient mitochondrial depolarization that led to cofilin-induced actin depolymerization. Knockdown, or endothelium-targeted deletion of UCP2 expression, blocked these responses, including pulmonary edema. To our knowledge, these findings are the first to mechanistically implicate endothelial mitochondria in acid-induced barrier deterioration and pulmonary edema. We suggest endothelial UCP2 may be a therapeutic target for acid-induced acute lung injury.

Effects of PTEN Loss and Activated KRAS Overexpression on Mechanical Properties of Breast Epithelial Cells

It has previously been shown that the simultaneous activation of PI3K (phosphatidylinositol 3-kinase) and Ras/MAPK (mitogen-activated protein kinases) pathways facilitate tumor growth despite only inducing cancer cell dormancy individually. Determining the impacts on cellular mechanics each pathway incites alone and in unison is critical to developing non-toxic cancer therapies for triple-negative breast cancers. PTEN (phosphatase and tensin homolog) knockout and activated KRAS (Kristen rat sarcoma viral oncogene homolog) overexpression in healthy MCF-10A human breast epithelial cells activated the PI3K and Ras/MAPK pathways, respectively. Cell stiffness and fluidity were simultaneously measured using atomic force microscopy. Results suggest that PTEN knockout reduced cell stiffness and increased cell fluidity independent of PI3K activation. Effects of activated KRAS overexpression on cell stiffness depends on rigidity of cell culture substrate. Activated KRAS overexpression also counteracts the effects of PTEN knockout.

Overexpressing TPTE2 (TPIP), a homolog of the human tumor suppressor gene PTEN, rescues the abnormal phenotype of the PTEN-/- mutant

One possible approach to normalize mutant cells that are metastatic and tumorigenic, is to upregulate a functionally similar homolog of the mutated gene. Here we have explored this hypothesis by generating an overexpressor of TPTE2 (TPIP), a homolog of PTEN, in PTEN-/- mutants, the latter generated by targeted mutagenesis of a human epithelial cell line. Overexpression of TPTE2 normalized phenotypic changes associated with the PTEN mutation. The PTEN-/- -associated changes rescued by overexpressing TPTE2 included 1) accelerated wound healing in the presence or absence of added growth factors (GFs), 2) increased division rates on a 2D substrate in the presence of GFs, 3) adhesion and viability on a 2D substrate in the absence of GFs, 4) viability in a 3D Matrigel model in the absence of GFs and substrate adhesion 5) loss of apoptosis-associated annexin V cell surface binding sites. The results justify further exploration into the possibility that upregulating TPTE2 by a drug may reverse metastatic and tumorigenic phenotypes mediated in part by a mutation in PTEN. This strategy may also be applicable to other tumorigenic mutations in which a homolog to the mutated gene is present and can substitute functionally.

Extracting microtentacle dynamics of tumor cells in a non-adherent environment

During metastasis, tumor cells dynamically change their cytoskeleton to traverse through a variety of non-adherent microenvironments, including the vasculature or lymphatics. Due to the challenges of imaging drift in non-adhered tumor cells, the dynamic cytoskeletal phenotypes are poorly understood. We present a new approach to analyze the dynamic cytoskeletal phenotypes of non-adhered cells that support microtentacles (McTNs), which are cell surface projections implicated in metastatic reattachment. Combining a recently-developed cell tethering method with a novel image analysis framework allowed McTN attribute extraction. Full cell outlines, number of McTNs, and distance of McTN tips from the cell body boundary were calculated by integrating a rotating anisotropic filtering method for identifying thin features with retinal segmentation and active contour algorithms. Tethered cells behave like free-floating cells; however tethering reduces cell drift and improves the accuracy of McTN measurements. Tethering cells does not significantly alter McTN number, but rather allows better visualization of existing McTNs. In drug treatment experiments, stabilizing tubulin with paclitaxel significantly increases McTN length, while destabilizing tubulin with colchicine significantly decreases McTN length. Finally, we quantify McTN dynamics by computing the time delay autocorrelations of 2 composite phenotype metrics (cumulative McTN tip distance, cell perimeter:cell body ratio). Our automated analysis demonstrates that treatment with paclitaxel increases total McTN amount and colchicine reduces total McTN amount, while paclitaxel also reduces McTN dynamics. This analysis method enables rapid quantitative measurement of tumor cell drug responses within non-adherent microenvironments, using the small numbers of tumor cells that would be available from patient samples.

Septin remodeling is essential for the formation of cell membrane protrusions (microtentacles) in detached tumor cells

Microtentacles are mostly microtubule-based cell protrusions that are formed by detached tumor cells. Here, we report that the formation of tumor cell microtentacles depends on the presence and dynamics of guanine nucleotide-binding proteins of the septin family, which are part of the cytoskeleton. In matrix-attached breast, lung, prostate and pancreas cancer cells, septins are associated with the cytosolic actin cytoskeleton. Detachment of cells causes redistribution of septins to the membrane, where microtentacle formation occurs. Forchlorfenuron, which inhibits septin functions, blocks microtentacle formation. The small GTPase Cdc42 and its effector proteins Borgs regulate septins and are essential for microtentacle formation. Dominant active and inactive Cdc42 inhibit microtentacle formation indicating that the free cycling of Cdc42 between its active and inactive state is essential for septin regulation and microtentacle formation. Cell attachment and aggregation models suggest that septins play an essential role in the metastatic behavior of tumor cells.

Slingshot-1L, a cofilin phosphatase, induces primary breast cancer metastasis

Slingshot (SSH) is a member of the conserved family of cofilin phosphatases that plays a critical role in cell membrane protrusion and migration by transforming inactive phosphorylated cofilin to an active form. SSH-like protein 1 (SSH-1L) expression is detected in various types of tumors; insulin induces the phosphatases activity of SSH-1L in a phosphoinositide 3-kinase-dependent manner. However, little is known about the expression and role of SSH-1L in breast cancer. Here, we analyzed 295 human breast cancer tissue specimens for SSH-1L expression by immunohistochemistry. The correlation between SSH-1L level and patients' clinical characteristics was analyzed with Pearson's χ² test. The function of SSH-1L was evaluated by gene knockdown and quantitative real-time polymerase chain reaction detection of cofilin expression in MDA-MB-231, MCF-7, and SK-BR-3 human breast cancer cell lines. SSH-1L expression was detected in 88.1% of tissue specimens by immunohistochemistry and was strongly associated with increased metastasis and mortality. Loss of SSH-1L expression decreased the nonphosphorylated, active form of cofilin in SK-BR-3 and MDA-MB-231 cell lines, which was associated with reduced cell motility. Accordingly, SSH-1L/cofilin signaling played a critical role in primary breast cancer metastasis and was a potential therapeutic target for breast cancer treatment.

Cofilin-1 and phosphoglycerate kinase 1 as promising indicators for glioma radiosensibility and prognosis

Glioma is a primary malignancy in central nervous system. Radiotherapy has been used as one of the standard treatments for glioma for decades. Since radioresistance can reduce the curative efficacy of radiotherapy in glioma, investigating the cause of radioresistance and predicting the tumour radiosensibility appeared particularly important. We previously reported that CFL1 and PGK1 are over-expressed in radioresistant U251 glioma cells. In this study, the level of CFL1 and PGK1 of 113 glioma tissues were measured by ELISA method. The relevance of the expression of these two proteins to radiosensibility was analyzed by mean test and multivariate logistic regression. The survival analysis was carried out in 85 irradiated patients and 105 followed-up patients respectively. The relationship between protein expression and clinical parameters was explored in overall 113 patients, and the correlation between CFL1 and PGK1 were determined as well. Our results showed that the expression of CFL1 and PGK1 were significantly higher (P < 0.001) in radioresistant patients than others. The multivariate Logistic regression demonstrated that the expression of CFL1 (p < 0.001) and PGK1 (p < 0.001) were associated with radioresistance in glioma. The multivariate Cox regression in overall survival suggested that CFL1 level or PGK1 level could be the independent prognosis factor for poor prognosis in 113 glioma patients. In addition, CFL1 expression was positively correlated with PGK1 expression in glioma. The results suggested that as promising indicators, CFL1 and PGK1 could be used to evaluate glioma radiosensibility and prognosis. These two proteins could also be the potential therapeutic targets of glioma.

Cytoskeletal organization in microtentacles

Microtentacles are thin, flexible cell protrusions that have recently been described and whose presence enhances efficient attachment of circulating cells. They are found on circulating tumor cells and can be induced on a wide range of breast cancer cell lines, where they are promoted by factors that either stabilize microtubules or destabilize the actin cytoskeleton. Evidence suggests that they are relevant to the metastatic spread of cancer, so understanding their structure and formation may lead to useful therapies. Microtentacles are formed by microtubules and contain vimentin intermediate filaments, but beyond this, there is little information about their ultrastructure. We have used electron microscopy of high pressure frozen sections and tomography of cryo-prepared intact cells, along with super resolution fluorescence microscopy, to provide the first ultrastructural insights into microtubule and intermediate filament arrangement within microtentacles. By scanning electron microscopy it was seen that microtentacles form within minutes of addition of drugs that stabilize microtubules and destabilize actin filaments. Mature microtentacles were found to be well below one micrometer in diameter, tapering gradually to below 100nm at the distal ends. They also contained frequent branches and bulges suggestive of heterogeneous internal structure. Super resolution fluorescence microscopy and examination of sectioned samples showed that the microtubules and intermediate filaments can occupy different areas within the microtentacles, rather than interacting intimately as had been expected. Cryo-electron tomography of thin regions of microtentacles revealed densely packed microtubules and absence of intermediate filaments. The number of microtubules ranged from several dozen in some areas to just a few in the thinnest regions, with none of the regular arrangement found in axonemes. Improved understanding of the mechanism of microtentacle formation, as well as the resultant structure, will be valuable in developing therapies against metastasis, if the hypothesized role of microtentacles in metastasis is confirmed. This work provides a significant step in this direction.

Analysis of microtubule growth dynamics arising from altered actin network structure and contractility in breast tumor cells

The periphery of epithelial cells is shaped by opposing cytoskeletal physical forces generated predominately by two dynamic force generating systems-growing microtubule ends push against the boundary from the cell center, and the actin cortex contracts the attached plasma membrane. Here we investigate how changes to the structure and dynamics of the actin cortex alter the dynamics of microtubules. Current drugs target actin polymerization and contraction to reduce cell division and invasiveness; however, the impacts on microtubule dynamics remain incompletely understood. Using human MCF-7 breast tumor cells expressing GFP-tagged microtubule end-binding-protein-1 (EB1) and coexpression of cytoplasmic fluorescent protein mCherry, we map the trajectories of growing microtubule ends and cytoplasmic boundary respectively. Based on EB1 tracks and cytoplasmic boundary outlines, we calculate the speed, distance from cytoplasmic boundary, and straightness of microtubule growth. Actin depolymerization with Latrunculin-A reduces EB1 growth speed as well as allows the trajectories to extend beyond the cytoplasmic boundary. Blebbistatin, a direct myosin-II inhibitor, reduced EB1 speed and yielded less straight EB1 trajectories. Inhibiting signaling upstream of myosin-II contractility via the Rho-kinase inhibitor, Y-27632, altered EB1 dynamics differently from Blebbistatin. These results indicate that reduced actin cortex integrity can induce distinct alterations in microtubule dynamics. Given recent findings that tumor stem cell characteristics are increased by drugs which reduce actin contractility or stabilize microtubules, it remains important to clearly define how cytoskeletal drugs alter the interactions between these two filament systems in tumor cells.

Cofilin-1 and Other ADF/Cofilin Superfamily Members in Human Malignant Cells

Identification of actin-depolymerizing factor homology (ADF-H) domains in the structures of several related proteins led first to the formation of the ADF/cofilin family, which then expanded to the ADF/cofilin superfamily. This superfamily includes the well-studied cofilin-1 (Cfl-1) and about a dozen different human proteins that interact directly or indirectly with the actin cytoskeleton, provide its remodeling, and alter cell motility. According to some data, Cfl-1 is contained in various human malignant cells (HMCs) and is involved in the formation of malignant properties, including invasiveness, metastatic potential, and resistance to chemotherapeutic drugs. The presence of other ADF/cofilin superfamily proteins in HMCs and their involvement in the regulation of cell motility were discovered with the use of various OMICS technologies. In our review, we discuss the results of the study of Cfl-1 and other ADF/cofilin superfamily proteins, which may be of interest for solving different problems of molecular oncology, as well as for the prospects of further investigations of these proteins in HMCs.

Pharmacologic regulation of AMPK in breast cancer affects cytoskeletal properties involved with microtentacle formation and re-attachment

The presence of tumor cells in the circulation is associated with a higher risk of metastasis in patients with breast cancer. Circulating breast tumor cells use tubulin-based structures known as microtentacles (McTNs) to re-attach to endothelial cells and arrest in distant organs. McTN formation is dependent on the opposing cytoskeletal forces of stable microtubules and the actin network. AMP-activated protein kinase (AMPK) is a cellular metabolic regulator that can alter actin and microtubule organization in epithelial cells. We report that AMPK can regulate the cytoskeleton of breast cancer cells in both attached and suspended conditions. We tested the effects of AMPK on microtubule stability and the actin-severing protein, cofilin. AMPK inhibition with compound c increased both microtubule stability and cofilin activation, which also resulted in higher McTN formation and re-attachment. Conversely, AMPK activation with A-769662 decreased microtubule stability and cofilin activation with concurrent decreases in McTN formation and cell re-attachment. This data shows for the first time that AMPK shifts the balance of cytoskeletal forces in suspended breast cancer cells, which affect their ability to form McTNs and re-attach. These results support a model where AMPK activators may be used therapeutically to reduce the metastatic efficiency of breast tumor cells.

The combinatorial activation of the PI3K and Ras/MAPK pathways is sufficient for aggressive tumor formation, while individual pathway activation supports cell persistence

A high proportion of human tumors maintain activation of both the PI3K and Ras/MAPK pathways. In basal-like breast cancer (BBC), PTEN expression is decreased/lost in over 50% of cases, leading to aberrant activation of the PI3K pathway. Additionally, BBC cell lines and tumor models have been shown to exhibit an oncogenic Ras-like gene transcriptional signature, indicating activation of the Ras/MAPK pathway. To directly test how the PI3K and Ras/MAPK pathways contribute to tumorigenesis, we deleted PTEN and activated KRas within non-tumorigenic MCF-10A breast cells. Neither individual mutation was sufficient to promote tumorigenesis, but the combination promoted robust tumor growth in mice. However, in vivo bioluminescence reveals that each mutation has the ability to promote a persistent phenotype. Inherent in the concept of tumor cell dormancy, a stage in which residual disease is present but remains asymptomatic, viable cells with each individual mutation can persist in vivo during a period of latency. The persistent cells were excised from the mice and showed increased levels of the cell cycle arrest proteins p21 and p27 compared to the aggressively growing PTEN−/−KRAS(G12V) cells. Additionally, when these persistent cells were placed into growth-promoting conditions, they were able to re-enter the cell cycle and proliferate. These results highlight the potential for either PTEN loss or KRAS activation to promote cell survival in vivo, and the unique ability of the combined mutations to yield rapid tumor growth. This could have important implications in determining recurrence risk and disease progression in tumor subtypes where these mutations are common.

Integrative genomic and functional analysis of human oral squamous cell carcinoma cell lines reveals synergistic effects of FAT1 and CASP8 inactivation

Oral squamous cell carcinoma (OSCC) is genetically highly heterogeneous, which contributes to the challenges of treatment. To create an in vitro model that accurately reflects this heterogeneity, we generated a panel of HPV-negative OSCC cell lines. By whole exome sequencing of the lines and matched patient blood samples, we demonstrate that the mutational spectrum of the lines is representative of primary OSCC in The Cancer Genome Atlas. We show that loss of function mutations in FAT1 (an atypical cadherin) and CASP8 (Caspase 8) frequently occur in the same tumour. OSCC cells with inactivating FAT1 mutations exhibited reduced intercellular adhesion. Knockdown of FAT1 and CASP8 individually or in combination in OSCC cells led to increased cell migration and clonal growth, resistance to Staurosporine-induced apoptosis and, in some cases, increased terminal differentiation. The OSCC lines thus represent a valuable resource for elucidating the impact of different mutations on tumour behaviour.

Anti-cancer effect of ursolic acid activates apoptosis through ROCK/PTEN mediated mitochondrial translocation of cofilin-1 in prostate cancer

Ursolic acid is a type of pentacyclic triterpene compound with multiple pharmacological activities including cancer resistance, protection from liver injury, antisepsis, anti-inflammation and antiviral activity. The present study aimed to investigate the anticancer effect of ursolic acid. Ursolic acid activates cell apoptosis and its pro-apoptotic mechanism remains to be fully elucidated. Cell Counting kit-8 assays, flow cytometric analysis and analysis of caspase-3 and caspase-9 activity were used to estimate the anticancer effect of ursolic acid on DU145 prostate cancer cells. The protein expression of cytochrome c, rho-associated protein kinase (ROCK), phosphatase and tensin homolog (PTEN) and cofilin-1 were examined using western blot analysis. In the present study, ursolic acid significantly suppressed cell growth and induced apoptosis, as well as increasing caspase-3 and caspase-9 activities of DU145 cells. Furthermore, cytoplasmic and mitochondrial cytochrome c protein expression was significantly activated and suppressed, respectively, by ursolic acid. Ursolic acid significantly suppressed the ROCK/PTEN signaling pathway and inhibited cofilin-1 protein expression in DU145 cells. The results of the present study indicate that the anticancer effect of ursolic acid activates cell apoptosis through ROCK/PTEN mediated mitochondrial translocation of cofilin-1 in prostate cancer.

ROCK inhibition promotes microtentacles that enhance reattachment of breast cancer cells

The presence of circulating tumor cells (CTCs) in blood predicts poor patient outcome and CTC frequency is correlated with higher risk of metastasis. Recently discovered, novel microtubule-based structures, microtentacles, can enhance reattachment of CTCs to the vasculature. Microtentacles are highly dynamic membrane protrusions formed in detached cells and occur when physical forces generated by the outwardly expanding microtubules overcome the contractile force of the actin cortex. Rho-associated kinase (ROCK) is a major regulator of actomyosin contractility and Rho/ROCK over-activation is implicated in tumor metastasis. ROCK inhibitors are gaining popularity as potential cancer therapeutics based on their success in reducing adherent tumor cell migration and invasion. However, the effect of ROCK inhibition on detached cells in circulation is largely unknown. In this study, we use breast tumor cells in suspension to mimic detached CTCs and show that destabilizing the actin cortex through ROCK inhibition in suspended cells promotes the formation of microtentacles and enhances reattachment of cells from suspension. Conversely, increasing actomyosin contraction by Rho over-activation reduces microtentacle frequency and reattachment. Although ROCK inhibitors may be effective in reducing adherent tumor cell behavior, our results indicate that they could inadvertently increase metastatic potential of non-adherent CTCs by increasing their reattachment efficacy.

Formation of Nanotube-Like Protrusions, Regulation of Septin Organization and Re-guidance of Vesicle Traffic by Depolymerization of the Actin Cytoskeleton Induced by Binary Bacterial Protein Toxins

A large group of bacterial protein toxins, including binary ADP-ribosylating toxins, modify actin at arginine-177, thereby actin polymerization is blocked and the actin cytoskeleton is redistributed. Modulation of actin functions largely affects other components of the cytoskeleton, especially microtubules and septins. Here, recent findings about the functional interconnections of the actin cytoskeleton with microtubules and septins, affected by bacterial toxins, are reviewed.

Neuron navigator 2 overexpression indicates poor prognosis of colorectal cancer and promotes invasion through the SSH1L/cofilin-1 pathway

Background

Neuron navigator 2 (NAV2) encodes a member of the neuron navigator gene family, which plays a role in tumorigenesis and cell migration. However, the prognostic value of NAV2 expression in colorectal cancer (CRC) patients and the potential pathway through which NAV2 promotes migration and invasion in CRC cell lines is poorly understood.

Methods

The expression level of NAV2 was detected in CRC tissues from two different CRC cohorts by immunohistochemistry, qRT-PCR and Western blotting; the correlation between NAV2 expression and clinicopathological characters was analyzed, and the prognostic value of NAV2 expression was analyzed using a Cox regression model. CRC cell lines with NAV2 knocked out were used to validate the function and potential pathway used by NAV2 to promote CRC cell migration and invasion.

Results

The results showed that NAV2 was overexpressed in CRC tissues, and it was closely correlated with depth of invasion, and lymph and distant metastasis. Multivariate analysis indicated that high NAV2 expression was a poor prognostic indicator of recurrence-free survival and overall survival in CRC patients. Furthermore, Cox regression analysis revealed that high NAV2 expression integrated with high tumor budding grade was a powerful independent predictive factor of CRC clinical outcome. In vitro and in vivo assays demonstrated that knockdown of NAV2 led to reduced migration and invasion of cancer cells, and the process involved the regulation of F-actin polymerization through the SSH1L/cofilin-1 pathway.

Conclusion

Based on these findings, NAV2 could serve as both a prognostic biomarker and a potential therapeutic target for patients with NAV2-positive CRC.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-015-0237-3) contains supplementary material, which is available to authorized users.

Loss of the obscurin-RhoGEF downregulates RhoA signaling and increases microtentacle formation and attachment of breast epithelial cells

Obscurins are RhoGEF-containing proteins whose downregulation has been implicated in the development and progression of breast cancer. Herein, we aim to elucidate the mechanism for increased motility of obscurin-deficient cells. We show that shRNA-mediated obscurin downregulation in MCF10A cells leads to >50% reduction in RhoA activity relative to scramble control (shCtrl), as well as decreased phosphorylation of RhoA effectors, including myosin light chain phosphatase, myosin light chain, lim kinase, and cofilin, in both attached and suspended cells. These alterations result in decreased actomyosin contractility, allowing suspended cells to escape detachment-induced apoptosis. Moreover, ~40% of shObsc-expressing cells, but only ~10% of shCtrl-expressing cells, extend microtentacles, tubulin-based projections that mediate the attachment of circulating tumor cells to endothelium. Indeed, we show that MCF10A cells expressing shObsc attach in vitro more readily than shCtrl cells, an advantage that persists following taxane exposure. Overall, our data suggest that loss of obscurins may represent a substantial selective advantage for breast epithelial cells during metastasis, and that treatment with paclitaxel may exacerbate this advantage by preferentially allowing obscurin-deficient, stem-like cells to attach to the endothelium of distant sites, a first step towards colonizing metastatic tumors.

α-Tubulin acetylation elevated in metastatic and basal-like breast cancer cells promotes microtentacle formation, adhesion, and invasive migration

Metastatic cases of breast cancer pose the primary challenge in clinical management of this disease, demanding the identification of effective therapeutic strategies that remain wanting. In this study, we report that elevated levels of α-tubulin acetylation are a sufficient cause of metastatic potential in breast cancer. In suspended cell culture conditions, metastatic breast cancer cells exhibited high α-tubulin acetylation levels that extended along microtentacle (McTN) protrusions. Mutation of the acetylation site on α-tubulin and enzymatic modulation of this posttranslational modification exerted a significant impact on McTN frequency and the reattachment of suspended tumor cells. Reducing α-tubulin acetylation significantly inhibited migration but did not affect proliferation. In an analysis of more than 140 matched primary and metastatic tumors from patients, we found that acetylation was maintained and in many cases increased in lymph node metastases compared with primary tumors. Proteomic analysis of an independent cohort of more than 390 patient specimens further documented the relationship between increased α-tubulin acetylation and the aggressive behaviors of basal-like breast cancers, with a trend toward increased risk of disease progression and death in patients with high-intensity α-tubulin acetylation in primary tumors. Taken together, our results identify a tight correlation between acetylated α-tubulin levels and aggressive metastatic behavior in breast cancer, with potential implications for the definition of a simple prognostic biomarker in patients with breast cancer.

Novel roles for ERK5 and cofilin as critical mediators linking ERα-driven transcription, actin reorganization, and invasiveness in breast cancer

Cancer cell motility and invasiveness are fundamental characteristics of the malignant phenotype and are regulated through diverse signaling networks involving kinases and transcription factors. This study establishes an estrogen receptor (ERα)/MAPK (ERK5)/cofilin (CFL1) network that specifies the degree of breast cancer cell aggressiveness through coupling of actin reorganization and hormone receptor-mediated transcription. Using dominant negative and constitutively active forms, as well as small-molecule inhibitors of extracellular signal-regulated kinase (ERK)5 and MAP-ERK kinase (MEK)5, it was revealed that hormone activation of ERα determined the subcellular localization of ERK5, which functions as a coregulator of ERα-dependent gene transcription. Notably, ERK5 acted in concert with the actin remodeling protein, CFL1, and upon hormone exposure, both localized to active nuclear transcriptional hubs as verified by immunofluorescence and proximity ligation assays. Both ERK5 and CFL1 facilitated PAF1 recruitment to the RNA Pol II complex and both were required for regulation of gene transcription. In contrast, in cells lacking ERα, ERK5 and CFL1 localized to cytoplasmic membrane regions of high actin remodeling, promoting cell motility and invasion, thereby revealing a mechanism likely contributing to the generally poorer prognosis of patients with ERα-negative breast cancer. Thus, this study uncovers the dynamic interplay of nuclear receptor-mediated transcription and actin reorganization in phenotypes of breast cancer aggressiveness.

IMPLICATIONS

Identification of the ER/ERK5/CFL1 axis suggests new prognostic biomarkers and novel therapeutic avenues to moderate cancer aggressiveness.

βIII-tubulin overexpression is an independent predictor of prostate cancer progression tightly linked to ERG fusion status and PTEN deletion

Evidence suggests that class III β-tubulin (βIII-tubulin) may represent a prognostic and predictive molecular marker in prostate cancer. βIII-Tubulin expression was determined by IHC in 8179 prostate cancer specimens in a TMA format. Results were compared with tumor phenotype, biochemical recurrence, v-ets avian erythroblastosis virus E26 oncogene homolog (ERG) status, and deletions on PTEN, 3p13, 5q21, and 6q15. βIII-Tubulin expression was detectable in 25.6% of 8179 interpretable cancers. High βIII-tubulin expression was strongly associated with both TMPRSS2:ERG rearrangement and ERG expression (P < 0.0001 each). High βIII-tubulin expression was tightly linked to high Gleason grade, advanced pT stage, and early prostate-specific antigen (PSA) recurrence in all cancers (P < 0.0001 each), but also in the subgroups of ERG-negative and ERG-positive cancers. When all tumors were analyzed, the prognostic role of βIII-tubulin expression was independent of Gleason grade, pT stage, pN stage, surgical margin status, and preoperative PSA. Independent prognostic value became even more evident if the analysis was limited to preoperatively available features, such as biopsy specimen Gleason grade, preoperative PSA, cT stage, and βIII-tubulin expression (P < 0.0001 each). βIII-Tubulin expression was associated with PTEN (P < 0.0001) when all tumors were analyzed, but also in the subgroups of ERG-negative and ERG-positive cancers. βIII-Tubulin expression is an independent prognostic parameter. The significant associations with key genomic alterations of prostate cancer, such as TMPRSS2:ERG fusions and PTEN deletions, suggest interactions with several pivotal pathways involved in prostate cancer.

Curcumin targets breast cancer stem-like cells with microtentacles that persist in mammospheres and promote reattachment

Cancer stem-like cells (CSC) and circulating tumor cells (CTC) have related properties associated with distant metastasis, but the mechanisms through which CSCs promote metastasis are unclear. In this study, we report that breast cancer cell lines with more stem-like properties display higher levels of microtentacles (McTN), a type of tubulin-based protrusion of the plasma cell membrane that forms on detached or suspended cells and aid in cell reattachment. We hypothesized that CSCs with large numbers of McTNs would more efficiently attach to distant tissues, promoting metastatic efficiency. The naturally occurring stem-like subpopulation of the human mammary epithelial (HMLE) cell line presents increased McTNs compared with its isogenic non-stem-like subpopulation. This increase was supported by elevated α-tubulin detyrosination and vimentin protein levels and organization. Increased McTNs in stem-like HMLEs promoted a faster initial reattachment of suspended cells that was inhibited by the tubulin-directed drug, colchicine, confirming a functional role for McTNs in stem cell reattachment. Moreover, live-cell confocal microscopy showed that McTNs persist in breast stem cell mammospheres as flexible, motile protrusions on the surface of the mammosphere. Although exposed to the environment, they also function as extensions between adjacent cells along cell-cell junctions. We found that treatment with the breast CSC-targeting compound curcumin rapidly extinguished McTN in breast CSC, preventing reattachment from suspension. Together, our results support a model in which breast CSCs with cytoskeletal alterations that promote McTNs can mediate attachment and metastasis but might be targeted by curcumin as an antimetastatic strategy.

Cofilin activation during podosome belt formation in osteoclasts

Podosomes are dynamic actin-based structures found constitutively in cells of monocytic origin such as macrophages, dendritic cells and osteoclasts. They have been involved in osteoclast cell adhesion, motility and matrix degradation, and all these functions rely on the ability of podosomes to form supra-molecular structures called podosome belts or sealing zones on mineralized substrates. Podosomes contain two distinct domains, an actin-rich core enriched in actin polymerization regulators, surrounded by a ring of signaling and plaque molecules. The organization of podosome arrays into belts is linked to actin dynamics. Cofilin is an actin-severing protein that is known to regulate cytoskeleton architecture and cell migration. Cofilin is present in lamellipodia and invadopodia where it regulates actin polymerization. In this report, we show that cofilin is a novel component of the podosome belt, the mature osteoclast adhesion structure. Time-course analysis demonstrated that cofilin is activated during primary osteoclast differentiation, at the time of podosome belt assembly. Immunofluorescence studies reveal a localization of active cofilin in the podosome core structure, whereas phosphorylated, inactive cofilin is concentrated in the podosome cloud. Pharmacological studies unraveled the role of a specific cofilin phosphatase to achieve cofilin activation during osteoclast differentiation. We ruled out the implication of PP1/PP2A and PTEN in this process, and rather provided evidence for the involvement of SSH1. In summary, our data involve cofilin as a regulator of podosome organization that is activated during osteoclast differentiation by a RANKL-mediated signaling pathway targeting the SSH1 phosphatase.