Oncogenic function of microtubule end-binding protein 1 in breast cancer

End Binding Proteins: Drivers of Cancer Progression

Cancer, a complex and heterogeneous disease, continues to be a major global health concern. Despite advancements in diagnostics and therapeutics, the aggressive nature of certain cancers remain a significant challenge, necessitating a deeper understanding of the underlying molecular mechanisms driving their severity and progression. Cancer severity and progression depend on cellular properties such as cell migration, cell division, cell shape changes, and intracellular transport, all of which are driven by dynamic cellular microtubules. Dynamic properties of microtubules, in turn, are regulated by an array of proteins that influence their stability and growth. Among these regulators, End Binding (EB) proteins stand out as critical orchestrators of microtubule dynamics at their growing plus ends. Beyond their fundamental role in normal cellular functions, recent research has uncovered compelling evidence linking EB proteins to the pathogenesis of various diseases, including cancer progression. As the field of cancer research advances, the clinical implication of EB proteins role in cancer severity and aggressiveness become increasingly evident. This review aims to comprehensively explore the role of microtubule-associated EB proteins in influencing the severity and aggressiveness of cancer. We also discuss the potential significance of EB as a clinical biomarker for cancer diagnosis and prognosis and as a target for therapeutic intervention.

Rapid binding to protofilament edge sites facilitates tip tracking of EB1 at growing microtubule plus-ends

EB1 is a key cellular protein that delivers regulatory molecules throughout the cell via the tip-tracking of growing microtubule plus-ends. Thus, it is important to understand the mechanism for how EB1 efficiently tracks growing microtubule plus-ends. It is widely accepted that EB1 binds with higher affinity to GTP-tubulin subunits at the growing microtubule tip, relative to GDP-tubulin along the microtubule length. However, it is unclear whether this difference in affinity alone is sufficient to explain the tip-tracking of EB1 at growing microtubule tips. Previously, we found that EB1 binds to exposed microtubule protofilament-edge sites at a ~70 fold faster rate than to closed-lattice sites, due to diffusional steric hindrance to binding. Thus, we asked whether rapid protofilament-edge binding could contribute to efficient EB1 tip tracking. A computational simulation with differential EB1 on-rates based on closed-lattice or protofilament-edge binding, and with EB1 off-rates that were dependent on the tubulin hydrolysis state, robustly recapitulated experimental EB1 tip tracking. To test this model, we used cell-free biophysical assays, as well as live-cell imaging, in combination with a Designed Ankyrin Repeat Protein (DARPin) that binds exclusively to protofilament-edge sites, and whose binding site partially overlaps with the EB1 binding site. We found that DARPin blocked EB1 protofilament-edge binding, which led to a decrease in EB1 tip tracking on dynamic microtubules. We conclude that rapid EB1 binding to microtubule protofilament-edge sites contributes to robust EB1 tip tracking at the growing microtubule plus-end.

Tubulin Complexity in Cancer and Metastasis

Tubulin plays a fundamental role in cellular function and as the subject for microtubule-active agents in the treatment of ovarian cancer. Microtubule-binding proteins (e.g., tau, MAP1/2/4, EB1, CLIP, TOG, survivin, stathmin) and posttranslational modifications (e.g., tyrosination, deglutamylation, acetylation, glycation, phosphorylation, polyamination) further diversify tubulin functionality and may permit additional opportunities to understand microtubule behavior in disease and to develop microtubule-modifying approaches to combat ovarian cancer. Tubulin-based structures that project from suspended ovarian cancer cells known as microtentacles may contribute to metastatic potential of ovarian cancer cells and could represent an exciting novel therapeutic target.

TRP Channels Interactome as a Novel Therapeutic Target in Breast Cancer

Breast cancer is one of the most frequent cancer types worldwide and the first cause of cancer-related deaths in women. Although significant therapeutic advances have been achieved with drugs such as tamoxifen and trastuzumab, breast cancer still caused 627,000 deaths in 2018. Since cancer is a multifactorial disease, it has become necessary to develop new molecular therapies that can target several relevant cellular processes at once. Ion channels are versatile regulators of several physiological- and pathophysiological-related mechanisms, including cancer-relevant processes such as tumor progression, apoptosis inhibition, proliferation, migration, invasion, and chemoresistance. Ion channels are the main regulators of cellular functions, conducting ions selectively through a pore-forming structure located in the plasma membrane, protein–protein interactions one of their main regulatory mechanisms. Among the different ion channel families, the Transient Receptor Potential (TRP) family stands out in the context of breast cancer since several members have been proposed as prognostic markers in this pathology. However, only a few approaches exist to block their specific activity during tumoral progress. In this article, we describe several TRP channels that have been involved in breast cancer progress with a particular focus on their binding partners that have also been described as drivers of breast cancer progression. Here, we propose disrupting these interactions as attractive and potential new therapeutic targets for treating this neoplastic disease.

Proteomic Characterization of Cytoplasmic Lipid Droplets in Human Metastatic Breast Cancer Cells

One of the characteristic features of metastatic breast cancer is increased cellular storage of neutral lipid in cytoplasmic lipid droplets (CLDs). CLD accumulation is associated with increased cancer aggressiveness, suggesting CLDs contribute to metastasis. However, how CLDs contribute to metastasis is not clear. CLDs are composed of a neutral lipid core, a phospholipid monolayer, and associated proteins. Proteins that associate with CLDs regulate both cellular and CLD metabolism; however, the proteome of CLDs in metastatic breast cancer and how these proteins may contribute to breast cancer progression is unknown. Therefore, the purpose of this study was to identify the proteome and assess the characteristics of CLDs in the MCF10CA1a human metastatic breast cancer cell line. Utilizing shotgun proteomics, we identified over 1500 proteins involved in a variety of cellular processes in the isolated CLD fraction. Interestingly, unlike other cell lines such as adipocytes or enterocytes, the most enriched protein categories were involved in cellular processes outside of lipid metabolism. For example, cell-cell adhesion was the most enriched category of proteins identified, and many of these proteins have been implicated in breast cancer metastasis. In addition, we characterized CLD size and area in MCF10CA1a cells using transmission electron microscopy. Our results provide a hypothesis-generating list of potential players in breast cancer progression and offers a new perspective on the role of CLDs in cancer.

Microtubule-Associated Protein ATIP3, an Emerging Target for Personalized Medicine in Breast Cancer

Breast cancer is the leading cause of death by malignancy among women worldwide. Clinical data and molecular characteristics of breast tumors are essential to guide clinician’s therapeutic decisions. In the new era of precision medicine, that aims at personalizing the treatment for each patient, there is urgent need to identify robust companion biomarkers for new targeted therapies. This review focuses on ATIP3, a potent anti-cancer protein encoded by candidate tumor suppressor gene MTUS1, whose expression levels are markedly down-regulated in breast cancer. ATIP3 is a microtubule-associated protein identified both as a prognostic biomarker of patient survival and a predictive biomarker of breast tumors response to taxane-based chemotherapy. We present here recent studies pointing out ATIP3 as an emerging anti-cancer protein and a potential companion biomarker to be combined with future personalized therapy against ATIP3-deficient breast cancer.

Redox-dependent regulation of end-binding protein 1 activity by glutathionylation

Cytoskeletal proteins are susceptible to glutathionylation under oxidizing conditions, and oxidative damage has been implicated in several neurodegenerative diseases. End-binding protein 1 (EB1) is a master regulator of microtubule plus-end tracking proteins (+TIPs) and is critically involved in the control of microtubule dynamics and cellular processes. However, the impact of glutathionylation on EB1 functions remains unknown. Here we reveal that glutathionylation is important for controlling EB1 activity and protecting EB1 from irreversible oxidation. In vitro biochemical and cellular assays reveal that EB1 is glutathionylated. Diamide, a mild oxidizing reagent, reduces EB1 comet number and length in cells, indicating the impairment of microtubule dynamics. Three cysteine residues of EB1 are glutathionylated, with mutations of these three cysteines to serines attenuating microtubule dynamics but buffering diamide-induced decrease in microtubule dynamics. In addition, glutaredoxin 1 (Grx1) deglutathionylates EB1, and Grx1 depletion suppresses microtubule dynamics and leads to defects in cell division orientation and cell migration, suggesting a critical role of Grx1-mediated deglutathionylation in maintaining EB1 activity. Collectively, these data reveal that EB1 glutathionylation is an important protective mechanism for the regulation of microtubule dynamics and microtubule-based cellular activities.

Targeting the cytoskeleton against metastatic dissemination

Cancer is a pathology characterized by a loss or a perturbation of a number of typical features of normal cell behaviour. Indeed, the acquisition of an inappropriate migratory and invasive phenotype has been reported to be one of the hallmarks of cancer. The cytoskeleton is a complex dynamic network of highly ordered interlinking filaments playing a key role in the control of fundamental cellular processes, like cell shape maintenance, motility, division and intracellular transport. Moreover, deregulation of this complex machinery contributes to cancer progression and malignancy, enabling cells to acquire an invasive and metastatic phenotype. Metastasis accounts for 90% of death from patients affected by solid tumours, while an efficient prevention and suppression of metastatic disease still remains elusive. This results in the lack of effective therapeutic options currently available for patients with advanced disease. In this context, the cytoskeleton with its regulatory and structural proteins emerges as a novel and highly effective target to be exploited for a substantial therapeutic effort toward the development of specific anti-metastatic drugs. Here we provide an overview of the role of cytoskeleton components and interacting proteins in cancer metastasis with a special focus on small molecule compounds interfering with the actin cytoskeleton organization and function. The emerging involvement of microtubules and intermediate filaments in cancer metastasis is also reviewed.

Tektin4 loss promotes triple-negative breast cancer metastasis through HDAC6-mediated tubulin deacetylation and increases sensitivity to HDAC6 inhibitor

Progression of triple-negative breast cancer (TNBC) constitutes a major unresolved clinical challenge, and effective targeted therapies are lacking. Because microtubule dynamics play pivotal roles in breast cancer metastasis, we performed RNA sequencing on 245 samples from TNBC patients to characterize the landscape of microtubule-associated proteins (MAPs). Here, our transcriptome analyses revealed that low expression of one MAP, tektin4, indicated poor patient outcomes. Tektin4 loss led to a marked increase in TNBC migration, invasion, and metastasis and a decrease in microtubule stability. Mechanistically, we identified a novel microtubule-associated complex containing tektin4 and histone deacetylase 6 (HDAC6). Tektin4 loss increased the interaction between HDAC6 and α-tubulin, thus decreasing microtubule stability through HDAC6-mediated tubulin deacetylation. Significantly, we found that tektin4 loss sensitized TNBC cells, xenograft models, and patient-derived organoid models to the HDAC6-selective inhibitor ACY1215. Furthermore, tektin4 expression levels were positively correlated with microtubule stability levels in clinical samples. Together, our findings uncover a metastasis suppressor function of tektin4 and support clinical development of HDAC6 inhibition as a new therapeutic strategy for tektin4-deficient TNBC patients.

Low concentrations of vorinostat decrease EB1 expression in GBM cells and affect microtubule dynamics, cell survival and migration

Glioblastoma multiform (GBM) is the most frequent primitive brain tumor with a high recurrence and mortality. Histone deacetylase inhibitors (HDACi) have evoked great interest because they are able to change transcriptomic profiles to promote tumor cell death but also induce side effects due to the lack of selectivity. We show in this paper new anticancer properties and mechanisms of action of low concentrations of vorinostat on various GBM cells which acts by affecting microtubule cytoskeleton in a non-histone 3 (H3) manner. Indeed, vorinostat induces tubulin acetylation and detyrosination, affects EB stabilizing cap on microtubule plus ends and suppresses microtubule dynamic instability. We previously identified EB1 overexpression as a marker of bad prognostic in GBM. Interestingly, we show for the first time to our knowledge, a strong decrease of EB1 expression in GBM cells by a drug. Altogether, our results suggest that low dose vorinostat, which is more selective for HDAC6 inhibition, could therefore represent an interesting therapeutic option for GBM especially in patients with EB1 overexpressing tumor with lower expected side effects. A validation of our hypothesis is needed during future clinical trials with this drug in GBM.

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

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

circSETD3 regulates MAPRE1 through miR-615-5p and miR-1538 sponges to promote migration and invasion in nasopharyngeal carcinoma

Circular RNAs (circRNAs) play an essential role in tumorigenesis and development. However, they have rarely been investigated in nasopharyngeal carcinoma (NPC). This study aimed to investigate the role of circRNA in the invasion and metastasis of NPC. We screened and verified the high expression of circSETD3 in NPC cell lines using RNA sequencing (RNA-Seq) and verified the results of NPC biopsy samples using real-time quantitative polymerase chain reaction (qRT-PCR) and in situ hybridization (ISH). In vivo and in vitro experiments indicated that circSETD3 could promote NPC cell invasion and migration. We compared the proteomic data of NPC cells before and after the overexpression or knockdown of circSETD3 in combination with bioinformatics prediction and experimental verification. It was found that circSETD3 competitively adsorbs to miR-615-5p and miR-1538 and negates their inhibitory effect on MAPRE1 mRNA, thereby upregulating the expression of MAPRE1. The upregulated MAPRE1 then inhibits the acetylation of α-tubulin, promotes the dynamic assembly of microtubules, and enhances the invasion and migration capabilities of NPC cells. The results of this study suggest that circSETD3 is a novel molecular marker and a potential target for NPC diagnosis and treatment.

Adenomatous polyposis coli-binding protein end-binding 1 promotes hepatocellular carcinoma growth and metastasis

This study was performed to determine the clinical significance of adenomatous polyposis coli (APC)-binding protein end-binding 1 (EB1) in hepatocellular carcinoma (HCC) and to characterize its biochemical role in comparison with previous reports. We performed immunohistochemical staining to detect EB1 expression in tissues from 235 patients with HCC and investigated its correlations with clinicopathological features and prognosis. We also investigated the roles of EB1 in cell proliferation, migration, and tumorigenesis in vitro and in vivo by siRNA- and CRISPR/Cas9-mediated modulation of EB1 expression in human HCC cell lines. The results showed that EB1 expression was significantly correlated with several important factors associated with tumor malignancy, including histological differentiation, portal vein invasion status, and intrahepatic metastasis. Patients with high EB1 expression in HCC tissue had poorer overall survival and higher recurrence rates than patients with low EB1 expression. EB1 knockdown and knockout in HCC cells reduced cell proliferation, migration, and invasion in vitro and inhibited tumor growth in vivo. Further, genes encoding Dlk1, HAMP, and SLCO1B3 that were differentially expressed in association with EB1 were identified using RNA microarray analysis. In conclusion, elevated expression of EB1 promotes tumor growth and metastasis of HCC. EB1 may serve as a new biomarker for HCC, and genes coexpressed with EB1 may represent potential targets for therapy.

WDHD1 Leads to Cisplatin Resistance by Promoting MAPRE2 Ubiquitination in Lung Adenocarcinoma

Ubiquitin ligases have been shown to regulate drug sensitivity. This study aimed to explore the role of the ubiquitin ligase WD repeat and HMG-box DNA binding protein 1 (WDHD1) in regulating cisplatin sensitivity in lung adenocarcinoma (LUAD). A quantitative analysis of the global proteome identified differential protein expression between LUAD A549 cells and the cisplatin-resistant strain A549/DDP. Public databases revealed the relationship between ubiquitin ligase expression and the prognosis of patients with LUAD. Quantitative real-time polymerase chain reaction and Western blotting were used to estimate the WDHD1 expression levels. Analysis of public databases predicted the substrate of WDHD1. Western blotting detected the effect of WDHD1 on microtubule-associated protein RP/EB family member 2 (MAPRE2) and DSTN. Functional analysis of MAPRE2 verified the interaction between WDHD1 and MAPRE2, as well as the interacting sites by methyl-thiazolyl-tetrazolium assay and flow cytometry, immunoprecipitation, protein stability, and immunofluorescence. Cell and animal experiments confirmed the effect of WDHD1 and MAPRE2 on cisplatin sensitivity in LUAD. Clinical data evaluated the impact of WDHD1 expression level on cisplatin sensitivity. Quantitative analysis of the global proteome revealed ubiquitin-dependent protein catabolism to be more active in A549/DDP cells than in A549 cells. WDHD1 expression was higher in A549/DDP cells than in A549 cells, and knocking out WDHD1 increased the sensitivity of A549/DDP cells to cisplatin. WDHD1 overexpression negatively correlated with the overall survival of LUAD patients. We observed that MAPRE2 was upregulated when WDHD1 was knocked out. A MAPRE2 knockout in A549 cells resulted in increased cell viability while decreasing apoptosis when the A549 cells exposed to cisplatin. WDHD1 and MAPRE2 were found to interact in the nucleus, and WDHD1 promoted the ubiquitination of MAPRE2. Following cisplatin exposure, the WDHD1 and MAPRE2 knockout groups facilitated cell proliferation and migration, inhibited apoptosis in A549/DDP cells, decreased apoptosis, and increased tumor size and growth rate in animal experiments. Immunohistochemistry showed that Ki67 levels increased, and levels of apoptotic indicators significantly decreased in the WDHD1 and MAPRE2 knockout groups. Clinical data confirmed that WDHD1 overexpression negatively correlated with cisplatin sensitivity. Thus, the ubiquitin ligase WDHD1 induces cisplatin resistance in LUAD by promoting MAPRE2 ubiquitination.

Microtubule-associated tumor suppressors as prognostic biomarkers in breast cancer

PURPOSE

Breast cancer is the most common malignancy in women worldwide. Although important therapeutic progress was achieved over the past decade, this disease remains a public health problem. In light of precision medicine, the identification of new prognostic biomarkers in breast cancer is urgently needed to stratify populations of patients with poor clinical outcome who may benefit from new personalized therapies. The microtubule cytoskeleton plays a pivotal role in essential cellular functions and is an interesting target for cancer therapy. Microtubule assembly and dynamics are regulated by a wide range of microtubule-associated proteins (MAPs), some of which have oncogenic or tumor suppressor effects in breast cancer.

RESULTS

This review covers current knowledge on microtubule-associated tumor suppressors (MATS) in breast cancer and their potential value as prognostic biomarkers. We present recent studies showing that combinatorial expression of ATIP3 and EB1, two microtubule-associated biomarkers with tumor suppressor and oncogenic effects, respectively, improves breast cancer prognosis compared to each biomarker alone.

CONCLUSIONS

These findings are discussed regarding the increasing complexity of protein networks composed of MAPs that coordinate microtubule dynamics and functions. Further studies are warranted to evaluate the prognostic value of combined expression of different MATS and their interacting partners in breast cancer.

Genetic interactions between ANLN and KDR are prognostic for breast cancer survival

Single nucleotide polymorphisms (SNPs) are the most common genetic variation in mammalian cells with prognostic potential. Anillin-actin binding protein (ANLN) has been identified as being involved in PI3K/PTEN signaling, which is critical in cell life/death control, and kinase insert domain receptor (KDR) encodes a key receptor mediating the cancer angiogenesis/metastasis switch. Knowledge of the intrinsic connections between PI3K/PTEN and KDR signaling, which represent two critical transitions in carcinogenesis, led the present study to investigate the effects of the potential synergy between ANLN and KDR on breast cancer outcome and identify relevant SNPs driving such a synergy at the genetic level. The survival associations of SNPs from KDR and ANLN were assessed through pairwise interaction survival analysis, quantitative trait loci analysis, pathway enrichment analysis and network construction, and the interactions between ANLN and KDR were validated in vitro. It was found that both rare homozygotes in the ANLN:rs12535394 and KDR:rs11133360 SNP pair are prognostic of favorable breast cancer survival and underpin the prominent roles of the immune response in cancer state control. This study contributes to breast cancer prognosis and therapeutic design by providing genetic evidence of interactions between ANLN and KDR, and suggesting the prominent role of the immune response in driving the synergies between the cancer cell life/death and angiogenesis/metastasis transitions during carcinogenesis.

Phyllanthus taxodiifolius Beille suppresses microtubule dynamics and restricts glioblastoma aggressiveness

Glioblastoma is the most common and the most malignant form of brain tumor. This devastating tumor results in death within a year after diagnosis. Although the tumor mass can be surgically removed, glioma cells invade other areas in the brain leading to tumor recurrence and poor prognosis. Therefore, new agents that can overcome cancer cell invasion are urgently required. Phyllanthus taxodiifolius Beille (P. taxodiifolius), has been reported to have potent anti-cancer activities. However, its effects on glioblastoma cells and its underlying mechanisms have never been revealed. Here we investigated the effect and underlying mechanisms of P. taxodiifolius extract on aggressive properties of the glioblastoma, including adhesion, migration, and invasion. P. taxodiifolius extract disrupted adhesion, delayed migration and interfered with the invasion of glioblastoma cells. In addition, the extract suppressed microtubule dynamics as shown by live imaging of a microtubule plus tip protein and decreased focal adhesion by decreasing focal adhesion kinase activity. Our study is the first evidence showing that P. taxodiifolius extract suppresses invasive properties of glioblastoma cells by disrupting microtubule structure and interfering with microtubule dynamics, suggesting the possibility to further develop P. taxodiifolius and its bioactive compounds as an anti-cancer drug targeting microtubules in glioblastoma.

Clinical relevance of cytoskeleton associated proteins for ovarian cancer

PURPOSE

Ovarian cancer has a high mortality rate and up to now no reliable molecular prognostic biomarkers have been established. During malignant progression, the cytoskeleton is strongly altered. Hence we analyzed if expression of certain cytoskeleton-associated proteins is correlated with clinical outcome of ovarian cancer patients.

METHODS

First, in silico analysis was performed using the cancer genome atlas (TCGA), the human expression atlas and Pubmed. Selected candidates were validated on 270 ovarian cancer patients by qRT-PCR and/or by western blotting.

RESULTS

In silico analysis revealed that mRNAs of 214 cytoskeleton-associated proteins are detectable in ovarian cancer tissue. Among these, we selected 17 proteins that participate in cancer disease progression and cytoskeleton modulation: KIF14, KIF20A, KIF18A, ASPM, CEP55, DLGAP5, MAP9, EB1, KATNA1, DIAPH1, ANLN, SCIN, CCDC88A, FSCN1, GSN, VASP and CDC42. The first ten candidates interact with microtubules (MTs) and the others bind to actin filaments. Validation on clinical samples of ovarian cancer patients revealed that the expression levels of DIAPH1, EB1, KATNA1, KIF14 and KIF18A significantly correlated with clinical and histological parameters of ovarian cancer. High DIAPH1, EB1, KATNA1 and KIF14 protein levels were associated with increased overall survival (OAS) of ovarian cancer patients, while high DIAPH1 and EB1 protein levels were also associated with low differentiation of respective tumors (G2/3). Moreover, DIAPH1 was the only protein, whose expression significantly correlated with increased recurrence-free interval (RFI).

CONCLUSION

Mainly the expression levels of the MT-associated proteins analyzed in this study, correlated with prolonged survival of ovarian cancer patients. From > 200 genes initially considered, 17 cytoskeletal proteins are involved in cancer progression according to the literature. Among these, four proteins significantly correlated with improved survival of ovarian cancer patients.

Combinatorial expression of microtubule-associated EB1 and ATIP3 biomarkers improves breast cancer prognosis

PURPOSE

The identification of molecular biomarkers for classification of breast cancer is needed to better stratify the patients and guide therapeutic decisions. The aim of this study was to investigate the value of MAPRE1 gene encoding microtubule-end binding proteins EB1 as a biomarker in breast cancer and evaluate whether combinatorial expression of MAPRE1 and MTUS1 gene encoding EB1-negative regulator ATIP3 may improve breast cancer diagnosis and prognosis.

METHODS

Probeset intensities for MAPRE1 and MTUS1 genes were retrieved from Exonhit splice array analyses of 45 benign and 120 malignant breast tumors for diagnostic purposes. Transcriptomic analyses (U133 Affymetrix array) of one exploratory cohort of 150 invasive breast cancer patients and two independent series of 130 and 155 samples were compared with clinical data of the patients for prognostic studies. A tissue microarray from an independent cohort of 212 invasive breast tumors was immunostained with anti-EB1 and anti-ATIP3 antibodies.

RESULTS

We show that MAPRE1 gene is a diagnostic and prognostic biomarker in breast cancer. High MAPRE1 levels correlate with tumor malignancy, high histological grade and poor clinical outcome. Combination of high-MAPRE1 and low-MTUS1 levels in tumors is significantly associated with tumor aggressiveness and reduced patient survival. IHC studies of combined EB1/ATIP3 protein expression confirmed these results.

CONCLUSIONS

These studies emphasize the importance of studying combinatorial expression of EB1 and ATIP3 genes and proteins rather than each biomarker alone. A population of highly aggressive breast tumors expressing high-EB1/low-ATIP3 may be considered for the development of new molecular therapies.

Apoptosis-linked gene 2 promotes breast cancer growth and metastasis by regulating the cytoskeleton

Breast cancer is the most prevalent cancer in women. Although it begins as local disease, breast cancer frequently metastasizes to the lymph nodes and distant organs. Therefore, novel therapeutic targets are needed for the management of this disease. Apoptosis-linked gene 2 (ALG-2) is a calcium-binding protein crucial for diverse physiological processes and has recently been implicated in cancer development. However, it remains unclear whether this protein is involved in the pathogenesis of breast cancer. Here, we demonstrate that the expression of ALG-2 is significantly upregulated in breast cancer tissues and is correlated with clinicopathological characteristics indicative of tumor malignancy. Our data further show that ALG-2 stimulates breast cancer growth and metastasis in mice. ALG-2 also promotes breast cancer cell proliferation, survival, and motility in vitro. Mechanistic data reveal that ALG-2 disrupts the localization of centrosome proteins, resulting in spindle multipolarity and chromosome missegregation. In addition, ALG-2 drives the polarization and migration of breast cancer cells by facilitating the rearrangement of microtubules and microfilaments. These findings reveal a critical role for ALG-2 in the pathogenesis of breast cancer and have important implications for its diagnosis and therapy.

Characterization of a novel EB1 acetylation site important for the regulation of microtubule dynamics and cargo recruitment

Microtubule plus ends undergo highly dynamic modifications to regulate different aspects of cellular activities. Most microtubule plus-end tracking proteins (+TIPs) are recruited to the microtubule ends by the master loading factor, end-binding protein 1 (EB1). These proteins coordinately regulate microtubule dynamics and cellular plasticity. Acetylation is known to modulate EB1 function; however, the molecular details of EB1 acetylation remain largely unclear. We mapped the acetylation pattern of EB1 and identified several previously uncharacterized sites of EB1 acetylation. We examined the effects of lysine-212 (K212) acetylation and found that acetylation of this site accelerates autophagy-mediated EB1 degradation. By time-lapse microscopy, we found that the acetylation-deficient K212R mutant increased the percentage of fast-growing and long-lived microtubules. Although K212 acetylation did not affect microtubule stability in vitro and the association of EB1 with microtubules, the K212R mutant significantly promoted microtubule regrowth in cells. Coimmunoprecipitation assays further revealed that the K212 site was critical for the recruitment of different +TIP cargoes. These data thus uncover a critical role for a novel EB1 acetylation site in regulating the dynamic structure of microtubules.

Identification of the potential crucial genes in invasive ductal carcinoma using bioinformatics analysis

Invasive ductal carcinoma (IDC) is a common histological type of breast cancer. The aim of this study was to identify the potential crucial genes associated with IDC and to provide valid biological information for further investigations. The gene expression profiles of GSE10780 which contained 42 histologically normal breast tissues and 143 IDC tissues were downloaded from the GEO database. Functional and pathway enrichment analysis of differentially expressed genes (DEGs) were performed and protein-protein interaction (PPI) network was analyzed using Cytoscape. In total, 999 DEGs were identified, including 667 up-regulated and 332 down-regulated DEGs. Gene ontology analysis demonstrated that most DEGs were significantly enriched in mitotic cell cycle, adhesion and protein binding process. Through PPI network analysis, a significant module was screened out, and the top 10 hub genes, CDK1, CCNB1, CENPE, CENPA, PLK1, CDC20, MAD2L1, HIST1H2BK, KIF2C and CCNA2 were identified from the PPI network. The expression levels of the 10 genes were validated in Oncomine database. KIF2C, MAD2L1 and PLK1 were associated with the overall survival. And we used cBioPortal to explore the genetic alterations of hub genes and potential drugs. In conclusion, the present study identified DEGs between normal and IDC samples, which could improve our understanding of the molecular mechanisms in the development of IDC, and these candidate genes might be used as therapeutic targets for IDC.

Akap350 Recruits Eb1 to The Spindle Poles, Ensuring Proper Spindle Orientation and Lumen Formation in 3d Epithelial Cell Cultures

The organization of epithelial cells to form hollow organs with a single lumen requires the accurate three-dimensional arrangement of cell divisions. Mitotic spindle orientation is defined by signaling pathways that provide molecular links between specific spots at the cell cortex and astral microtubules, which have not been fully elucidated. AKAP350 is a centrosomal/Golgi scaffold protein, implicated in the regulation of microtubule dynamics. Using 3D epithelial cell cultures, we found that cells with decreased AKAP350 expression (AKAP350KD) formed polarized cysts with abnormal lumen morphology. Analysis of mitotic cells in AKAP350KD cysts indicated defective spindle alignment. We established that AKAP350 interacts with EB1, a microtubule associated protein that regulates spindle orientation, at the spindle poles. Decrease of AKAP350 expression lead to a significant reduction of EB1 levels at spindle poles and astral microtubules. Conversely, overexpression of EB1 rescued the defective spindle orientation induced by deficient AKAP350 expression. The specific delocalization of the AKAP350/EB1complex from the centrosome decreased EB1 levels at astral microtubules and lead to the formation of 3D-organotypic structures which resembled AKAP350KD cysts. We conclude that AKAP350 recruits EB1 to the spindle poles, ensuring EB1 presence at astral microtubules and proper spindle orientation during epithelial morphogenesis.

EB1 phosphorylation mediates the functions of ASK1 in pancreatic cancer development

Pancreatic cancer has a poor prognosis due to its rapid rate of metastasis and frequent late-stage diagnosis. An improved understanding of the molecular mechanisms underlying this disease is urgently needed to promote the development of improved diagnostic tools and more effective therapies. Apoptosis signal-regulating kinase 1 (ASK1) has been shown to be overexpressed in pancreatic cancer and to promote the proliferation of pancreatic cancer cells in a kinase activity-dependent manner. However, the molecular mechanisms by which ASK1 promotes cell proliferation remain to be elucidated. In this study, we report that the phosphorylation of end-binding protein 1 (EB1) at threonine 206 (pT206-EB1), which is catalyzed by ASK1, is increased in pancreatic cancer tissues. We further find that the level of pT206-EB1 correlates with that of ASK1 in cancer tissues. Additionally, ASK1 localizes to spindle poles, and knockdown of ASK1 results in the formation of multipolar spindles. Moreover, we show that depletion of ASK1 or disruption of EB1 phosphorylation inhibits spindle microtubule dynamics in pancreatic cancer cells. Collectively, these findings suggest that EB1 phosphorylation mediates the functions of ASK1 in pancreatic cancer development.

Regulation of paclitaxel activity by microtubule-associated proteins in cancer chemotherapy

Microtubules, highly dynamic components of the cytoskeleton, participate in diverse cellular activities such as mitosis, cell migration, and intracellular trafficking. Dysregulation of microtubule dynamics contributes to the development of serious diseases, including cancer. The dynamic properties and functions of microtubule network are regulated by microtubule-associated proteins. Paclitaxel, an anti-microtubule agent of the taxane family, has shown a success in clinical treatment of many cancer patients. However, the variable response activity of patients and acquired resistance to paclitaxel limit the clinical use of the drug. Accumulating studies show that microtubule-associated proteins can regulate paclitaxel sensitivity in a wide range of cancer types. In this review, we will describe the roles of various microtubule-associated proteins in the regulation of paclitaxel in cancers. Particularly, we will focus on the modulation of centrosomal proteins in paclitaxel resistance. Improved understandings of how these proteins act might predict treatment responses and provide insights into more rational chemotherapeutic regimens in clinical practice.

EB1 protein alteration characterizes sporadic but not ulcerative colitis associated colorectal cancer

Background

While carcinogenesis in Sporadic Colorectal Cancer (SCC) has been thoroughly studied, less is known about Ulcerative Colitis associated Colorectal Cancer (UCC). This study aimed to identify and validate differentially expressed proteins between clinical samples of SCC and UCC to elucidate new insights of UCC/SCC carcinogenesis and progression.

Results

Multiplex-fluorescence two-dimensional gel electrophoresis (2-D DIGE) and mass spectrometry identified 67 proteoforms representing 43 distinct proteins. After analysis by Ingenuity Pathway Analysis^® (IPA), subsequent Western blot validation proofed the differential expression of Heat shock 27 kDA protein 1 (HSPB1) and Microtubule-associated protein R/EB family, member 1 (EB1) while the latter one showed also expression differences by immunohistochemistry.

Materials and Methods

Fresh frozen tissue of UCC (n = 10) matched with SCC (n = 10) was investigated. Proteins of cancerous intestinal mucosal cells were obtained by Laser Capture Microdissection (LCM) and compared by 2-D DIGE. Significant spots were identified by mass spectrometry. After IPA, three proteins [EB1, HSPB1, and Annexin 5 (ANXA5)] were chosen for further validation by Western blotting and tissue microarray-based immunohistochemistry.

Conclusions

This study identified significant differences in protein expression of colorectal carcinoma cells from UCC patients compared to patients with SCC. Particularly, EB1 was validated in an independent clinical cohort.

Regulation of end-binding protein EB1 in the control of microtubule dynamics

The regulation of microtubule dynamics is critical to ensure essential cell functions, such as proper segregation of chromosomes during mitosis or cell polarity and migration. End-binding protein 1 (EB1) is a plus-end-tracking protein (+TIP) that accumulates at growing microtubule ends and plays a pivotal role in the regulation of microtubule dynamics. EB1 autonomously binds an extended tubulin-GTP/GDP-Pi structure at growing microtubule ends and acts as a molecular scaffold that recruits a large number of regulatory +TIPs through interaction with CAP-Gly or SxIP motifs. While extensive studies have focused on the structure of EB1-interacting site at microtubule ends and its role as a molecular platform, the mechanisms involved in the negative regulation of EB1 have only started to emerge and remain poorly understood. In this review, we summarize recent studies showing that EB1 association with MT ends is regulated by post-translational modifications and affected by microtubule-targeting agents. We also present recent findings that structural MAPs, that have no tip-tracking activity, physically interact with EB1 to prevent its accumulation at microtubule plus ends. These observations point out a novel concept of "endogenous EB1 antagonists" and emphasize the importance of finely regulating EB1 function at growing microtubule ends.

Phosphorylation of EB1 regulates the recruitment of CLIP-170 and p150glued to the plus ends of astral microtubules

Phosphorylation of end-binding protein 1 (EB1), a key member of microtubule plus end-tracking proteins (+TIPs), by apoptosis signal-regulating kinase 1 (ASK1) has been demonstrated to promote the stability of astral microtubules during mitosis by stimulating the binding of EB1 to microtubule plus ends. However, the roles of other members of the +TIPs family in ASK1/EB1-mediated regulation of astral microtubules are unknown. Herein, we show that ASK1-mediated phosphorylation of EB1 enhances the localization of cytoplasmic linker protein 170 (CLIP-170) and p150glued to the plus ends of astral microtubules. Depletion of ASK1 or expression of phospho-deficient or phospho-mimetic EB1 mutants results in changes in the levels of plus-end localized CLIP-170 or p150glued. Mechanistic studies reveal that EB1 phosphorylation promotes its interactions with CLIP-170 and p150glued, thereby recruiting these +TIPs to microtubules. Structural analysis suggests that serine-40 is the primary phosphorylation site on EB1 that exerts these effects. Together, these findings provide novel insight into the molecular mechanisms that regulate the interactions of EB1 with other +TIPs.

Discovery of Centrosomal Protein 70 as an Important Player in the Development and Progression of Breast Cancer

Centrosome abnormalities have been implicated in the development and progression of breast cancer. However, the molecular players involved in the above processes remain largely uncharacterized. Herein, we identify centrosomal protein 70 (Cep70) as an important factor that mediates breast cancer growth and metastasis. Cep70 is up-regulated in breast cancer tissues and cell lines, and its expression is closely correlated with several clinicopathologic variables associated with breast cancer progression. Mechanistic studies reveal that the up-regulation of Cep70 in breast cancer occurs at the mRNA level and is independent of gene amplification. Cep70 promotes breast cancer cell proliferation and colony formation in vitro and increases tumor growth in mice. In addition, Cep70 stimulates breast cancer cell migration and invasion in vitro. Bioluminescence imaging analysis further shows that Cep70 enhances breast cancer lung metastasis in mice. Together, these results demonstrate a critical role for Cep70 in the development and progression of breast cancer and have important implications in the diagnosis and therapy of this malignancy.

Apoptosis signal-regulating kinase 1 exhibits oncogenic activity in pancreatic cancer

Pancreatic cancer has an extremely grim prognosis, with an overall 5-year survival rate less than 5%, as a result of its rapid metastasis and late diagnosis. To combat this disease, it is crucial to better understand the molecular mechanisms that contribute to its pathogenesis. Herein, we report that apoptosis signal-regulating kinase 1 (ASK1) is overexpressed in pancreatic cancer tissues and that its expression correlates with the histological grade of pancreatic cancer. The expression of ASK1 is also elevated in pancreatic cancer cell lines at both protein and mRNA levels. In addition, ASK1 promotes the proliferation and stimulates the tumorigenic capacity of pancreatic cancer cells. These functions of ASK1 are abrogated by pharmacological inhibition of its kinase activity or by introduction of a kinase-dead mutation, suggesting that the kinase activity of ASK1 is required for its role in pancreatic cancer. However, the alteration of ASK1 expression or activity does not significantly affect the migration or invasion of pancreatic cancer cells. Collectively, these findings reveal a critical role for ASK1 in the development of pancreatic cancer and have important implications for the diagnosis and treatment of this malignancy.

Interaction of microtubules with the actin cytoskeleton via cross-talk of EB1-containing +TIPs and γ-actin in epithelial cells

Actin microfilaments and microtubules are both highly dynamic cytoskeleton components implicated in a wide range of intracellular processes as well as cell-cell and cell-substrate interactions. The interactions of actin filaments with the microtubule system play an important role in the assembly and maintenance of 3D cell structure. Here we demonstrate that cytoplasmic actins are differentially distributed in relation to the microtubule system. LSM, 3D-SIM, proximity ligation assay (PLA) and co-immunoprecipitation methods applied in combination with selective depletion of β- or γ-cytoplasmic actins revealed a selective interaction between microtubules and γ-, but not β-cytoplasmic actin via the microtubule +TIPs protein EB1. EB1-positive comet distribution analysis and quantification have shown more effective microtubule growth in the absence of β-actin. Our data represent the first demonstration that microtubule +TIPs protein EB1 interacts mainly with γ-cytoplasmic actin in epithelial cells.

Negative regulation of EB1 turnover at microtubule plus ends by interaction with microtubule-associated protein ATIP3

The regulation of microtubule dynamics is critical to ensure essential cell functions. End binding protein 1 (EB1) is a master regulator of microtubule dynamics that autonomously binds an extended GTP/GDP-Pi structure at growing microtubule ends and recruits regulatory proteins at this location. However, negative regulation of EB1 association with growing microtubule ends remains poorly understood. We show here that microtubule-associated tumor suppressor ATIP3 interacts with EB1 through direct binding of a non-canonical proline-rich motif. Results indicate that ATIP3 does not localize at growing microtubule ends and that in situ ATIP3-EB1 molecular complexes are mostly detected in the cytosol. We present evidence that a minimal EB1-interacting sequence of ATIP3 is both necessary and sufficient to prevent EB1 accumulation at growing microtubule ends in living cells and that EB1-interaction is involved in reducing cell polarity. By fluorescence recovery of EB1-GFP after photobleaching, we show that ATIP3 silencing accelerates EB1 turnover at microtubule ends with no modification of EB1 diffusion in the cytosol. We propose a novel mechanism by which ATIP3-EB1 interaction indirectly reduces the kinetics of EB1 exchange on its recognition site, thereby accounting for negative regulation of microtubule dynamic instability. Our findings provide a unique example of decreased EB1 turnover at growing microtubule ends by cytosolic interaction with a tumor suppressor.

End Binding 1 (EB1) overexpression in oral lesions and cancer: A biomarker of tumor progression and poor prognosis

INTRODUCTION

Oral squamous cell carcinoma (OSCC) patients are at high risk of loco-regional recurrence and despite the improvement in treatment strategy, 5-year survival rates are about 50%. Identification of patients at high risk of recurrence may enable rigorous personalized post-treatment management. In an earlier proteomics study we observed overexpression of End Binding Protein (EB1) in OSCC. In the present study we investigated the diagnostic and prognostic significance of alterations in expression of EB1 in oral cancer.

METHODS

In this retrospective study, the expression of EB1 protein was evaluated in 259 OSCCs, 41 dysplasia, 166 hyperplasia and 126 normal tissues using immunohistochemistry and correlated with clinical-pathological parameters and prognosis of OSCC patients over a follow-up period of up to 91months.

RESULTS

Significantly higher expression of cytoplasmic EB1 was observed in hyperplasia [p<0.001, OR=7.2, 95% CI=4.1-12.8], dysplasia (p<0.001, OR=21.8, CI=8.8-50.2) and OSCCs (p<0.001, OR=10.1, CI=5.8-17.4) in comparison with normal mucosa. Univariate analysis revealed cytoplasmic EB1 association with tumor grade, tumor size and recurrence of the disease. Kaplan Meier survival analysis of EB1 expression showed significantly reduced disease free survival (DFS) (p=0.003). Notably, OSCC patients showing cytoplasmic EB1 overexpression demonstrated significantly reduced DFS (p=0.004, HR=2.1).

CONCLUSION

EB1 overexpression is an early event in oral tumorigenesis and cytoplasmic EB1 accumulation is associated with poor prognosis and tumor recurrence in OSCC patients.

Cep70 overexpression stimulates pancreatic cancer by inducing centrosome abnormality and microtubule disorganization

The centrosome is crucial for mitotic fidelity, and centrosome aberrations are associated with genomic instability and tumorigenesis. The centrosomal protein Cep70 has been reported to play a role in various cellular activities. However, whether this protein is involved in pathological processes remains unknown. In this study, we demonstrate that Cep70 is highly expressed in pancreatic cancer tissues. Cep70 expression correlates with clinicopathological parameters of pancreatic cancer, including histological grade, pathological tumor node metastasis stage, lymph node metastasis, and carbohydrate antigen 19-9 level. Depletion of Cep70 significantly suppresses pancreatic cancer cell proliferation and promotes apoptotic cell death, and exogenous expression of Cep70 can rescue the above effects. Cep70 also stimulates colony formation in soft agar and enhances tumor growth in mice. Our data further show that ectopic expression of Cep70 in pancreatic cancer cells results in the mislocalization of centrosomal proteins, including γ-tubulin and pericentrin, and the formation of intracellular aggregates. In addition, Cep70 overexpression leads to microtubule disorganization and the formation of multipolar spindles during mitosis. Our study thus unravels a critical role for Cep70 in pancreatic cancer and suggests Cep70 as a potential biomarker and therapeutic target for this deadly disease.

The +TIP coordinating protein EB1 is highly dynamic and diffusive on microtubules, sensitive to GTP analog, ionic strength, and EB1 concentration

Using single-molecule fluorescence microscopy, we investigated the dynamics of dye-labeled EB1, a +TIP microtubule binding protein. To promote EB1 binding along the entire microtubule length, we formed microtubules using the nonhydrolyzable GTP analogs GMPCPP and GTPγS. Through precise tracking of the motions of individual dye-labeled proteins, we found EB1 to be highly dynamic and continuously diffusive while bound to a microtubule, with a diffusion coefficient and characteristic binding lifetime that were sensitive to both the choice of GTP analog and the buffer ionic strength. Using fluorescence-based equilibrium binding measurements, we found EB1 binding to be cooperative and also sensitive to GTP analog and ionic strength. By tracking the motion of a small number of individually-labeled EB1 proteins within a bath of unlabeled EB1 proteins, we determined the effects of increasing the total EB1 concentration on binding and dynamics. We found that the diffusion coefficient decreased with increasing EB1 concentration, which may be due at least in part, to the cooperativity of EB1 binding. Our results may have important consequences for the assembly and organization of the growing microtubule plus-end.

End-binding 1 protein overexpression correlates with glioblastoma progression and sensitizes to Vinca-alkaloids in vitro and in vivo

End-binding 1 protein (EB1) is a key player in the regulation of microtubule (MT) dynamics. Here, we investigated the role of EB1 in glioblastoma (GBM) tumor progression and its potential predictive role for response to Vinca-alkaloid chemotherapy. Immunohistological analysis of the 109 human GBM cases revealed that EB1 overexpression correlated with poor outcome including progression-free survival and overall survival. Downregulation of EB1 by shRNA inhibited cell migration and proliferation in vitro. Conversely, EB1 overexpression promoted them and accelerated tumor growth in orthotopically-transplanted nude mice. Furthermore, EB1 was largely overexpressed in stem-like GBM6 that display in vivo a higher tumorigenicity with a more infiltrative pattern of migration than stem-like GBM9. GBM6 showed strong and EB1-dependent migratory potential. The predictive role of EB1 in the response of GBM cells to chemotherapy was investigated. Vinflunine and vincristine increased survival of EB1-overexpressing U87 bearing mice and were more effective to inhibit cell migration and proliferation in EB1-overexpressing clones than in controls. Vinca inhibited the increase of MT growth rate and growth length induced by EB1 overexpression. Altogether, our results show that EB1 expression level has a prognostic value in GBM, and that Vinca-alkaloid chemotherapy could improve the treatment of GBM patients with EB1-overexpressing tumor.

Microtubule-Binding Proteins as Promising Biomarkers of Paclitaxel Sensitivity in Cancer Chemotherapy

Microtubules, tirelessly animated and highly dynamic structures, are vital for most cellular processes and their intricacies are still being revealed even after a century since their discovery. The importance of microtubules as chemotherapeutic targets cannot be overstated, and their clinical role is unlikely to abate in the near future. Indeed, improved understanding of microtubule biology could herald a new epoch of anticancer drug design by permitting fine-tuning of microtubule-targeting agents, the clinical utility of which is presently often limited by primary or acquired resistance. Paclitaxel, one such agent belonging to the taxane family, has proven a resoundingly successful treatment for many cancer patients; however, for too many others with paclitaxel-refractory tumors, the drug has offered nothing but side effects. Accumulating evidence suggests that microtubule-binding proteins (MBPs) can regulate paclitaxel sensitivity in a wide range of cancer types. Improved understanding of how these proteins can be assayed to predict treatment responses or manipulated pharmacologically to improve clinical outcomes could transform modern chemotherapy and is urgently awaited.

Identification of novel microtubule-binding proteins by taxol-mediated microtubule stabilization and mass spectrometry analysis

Microtubule-binding proteins (MBPs) are structurally and functionally diverse regulators of microtubule-mediated cellular processes. Alteration of MBPs has been implicated in the pathogenesis of human diseases, including cancer. MBPs can stabilize or destabilize microtubules or move along microtubules to transport various cargoes. In addition, MBPs can control microtubule dynamics through direct interaction with microtubules or coordination with other proteins. To better understand microtubule structure and function, it is necessary to identify additional MBPs. In this study, we isolated microtubules and MBPs from mammalian cells by a taxol-based method and then profiled a panel of MBPs by mass spectrometry. We discovered a number of previously uncharacterized MBPs, including several membrane-associated proteins and proteins involved in post-translational modifications, in addition to several structural components. These results support the notion that microtubules have a wide range of functions and may undergo more exquisite regulation than previously recognized.

ROS-mediated EB1 phosphorylation through Akt/GSK3β pathway: implication in cancer cell response to microtubule-targeting agents

Microtubule-targeting agents (MTAs) are largely administered in adults and children cancers. Better deciphering their mechanism of action is of prime importance to develop more convenient therapy strategies. Here, we addressed the question of how reactive oxygen species (ROS) generation by mitochondria can be necessary for MTA efficacy. We showed for the first time that EB1 associates with microtubules in a phosphorylation-dependent manner, under control of ROS. By using phospho-defective mutants, we further characterized the Serine 155 residue as critical for EB1 accumulation at microtubule plus-ends, and both cancer cell migration and proliferation. Phosphorylation of EB1 on the Threonine 166 residue triggered opposite effects, and was identified as a requisite molecular switch in MTA activities. We then showed that GSK3β activation was responsible for MTA-triggered EB1 phosphorylation, resulting from ROS-mediated inhibition of upstream Akt. We thus disclosed here a novel pathway by which generation of mitochondrial ROS modulates microtubule dynamics through phosphorylation of EB1, improving our fundamental knowledge about this oncogenic protein, and pointing out the need to re-examine the current dogma of microtubule targeting by MTAs. The present work also provides a strong mechanistic rational to the promising therapeutic strategies that currently combine MTAs with anti-Akt targeted therapies.

+TIP EB1 downregulates paclitaxel‑induced proliferation inhibition and apoptosis in breast cancer cells through inhibition of paclitaxel binding on microtubules

Microtubule plus‑end‑binding protein (+TIP) EB1 has been shown to be upregulated in breast cancer cells and promote breast tumor growth in vivo. However, its effect on the cellular actions of microtubule‑targeted drugs in breast cancer cells has remained poorly understood. By using cellular and biochemical assays, we demonstrate that EB1 plays a critical role in regulating the sensitivity of breast cancer cells to anti‑microtubule drug, paclitaxel (PTX). Cell viability assays revealed that EB1 expression in the breast cancer cell lines correlated with the reduction of their sensitivity to PTX. Knockdown of EB1 by enzymatically‑prepared siRNA pools (esiRNAs) increased PTX‑induced cytotoxicity and sensitized cells to PTX‑induced apoptosis in three breast cancer cell lines, MCF‑7, MDA MB‑231 and T47D. Apoptosis was associated with activation of caspase‑9 and an increase in the cleavage of poly(ADP‑ribose) polymerase (PARP). p53 and Bax were upregulated and Bcl2 was downregulated in the EB1‑depleted PTX‑treated MCF‑7 cells, indicating that the apoptosis occurs via a p53‑dependent pathway. Following its upregulation, the nuclear accumulation of p53 and its association with cellular microtubules were increased. EB1 depletion increased PTX‑induced microtubule bundling in the interphase cells and induced formation of multiple spindle foci with abnormally elongated spindles in the mitotic MCF‑7 cells, indicating that loss of EB1 promotes PTX‑induced stabilization of microtubules. EB1 inhibited PTX‑induced microtubule polymerization and diminished PTX binding to microtubules in vitro, suggesting that it modulates the binding sites of PTX at the growing microtubule ends. Results demonstrate that EB1 downregulates inhibition of PTX‑induced proliferation and apoptosis in breast cancer cells through a mechanism in which it impairs PTX‑mediated stabilization of microtubule polymerization and inhibits PTX binding on microtubules.

Mechanical effects of EB1 on microtubules depend on GTP hydrolysis state and presence of paclitaxel

Using the nonhydrolyzable GTP analog GMPCPP and the slowly hydrolyzable GTPγS, we polymerize microtubules that recapitulate the end binding behavior of the plus end interacting protein (+TIP) EB1 along their entire length, and use these to investigate the impact of EB1 binding on microtubule mechanics. To measure the stiffness of single filaments, we use a spectral analysis method to determine the ensemble of shapes adopted by a freely diffusing, fluorescently labeled microtubule. We find that the presence of EB1 can stiffen microtubules in a manner that depends on the hydrolysis state of the tubulin-bound nucleotide, as well as the presence of the small-molecule stabilizer paclitaxel. We find that the magnitude of the EB1-induced stiffening is not proportional to the EB1-microtubule binding affinity, suggesting that the stiffening effect does not arise purely from an increase in the total amount of bound EB1. Additionally, we find that EB1 binds cooperatively to microtubules in manner that depends on tubulin-bound nucleotide state.

Microtubule-associated protein Mdp3 promotes breast cancer growth and metastasis

Breast cancer is the most prevalent cancer in women worldwide with a high mortality rate, and the identification of new biomarkers and targets for this disease is greatly needed. Here we present evidence that microtubule-associated protein (MAP) 7 domain-containing protein 3 (Mdp3) is highly expressed in clinical samples and cell lines of breast cancer. The expression of Mdp3 correlates with clinicopathological parameters indicating breast cancer malignancy. In addition, Mdp3 promotes breast cancer cell proliferation and motility in vitro and stimulates breast cancer growth and metastasis in mice. Mechanistic studies reveal that γ-tubulin interacts with and recruits Mdp3 to the centrosome and that the centrosomal localization of Mdp3 is required for its activity to promote breast cancer cell proliferation and motility. These findings suggest a critical role for Mdp3 in the growth and metastasis of breast cancer and may have important implications for the management of this disease.

End-binding protein 1 stimulates paclitaxel sensitivity in breast cancer by promoting its actions toward microtubule assembly and stability

Paclitaxel is a microtubule-targeting agent widely used for the treatment of many solid tumors. However, patients show variable sensitivity to this drug, and effective diagnostic tests predicting drug sensitivity remain to be investigated. Herein, we show that the expression of end-binding protein 1 (EB1), a regulator of microtubule dynamics involved in multiple cellular activities, in breast tumor tissues correlates with the pathological response of tumors to paclitaxel-based chemotherapy. In vitro cell proliferation assays reveal that EB1 stimulates paclitaxel sensitivity in breast cancer cell lines. Our data further demonstrate that EB1 increases the activity of paclitaxel to cause mitotic arrest and apoptosis in cancer cells. In addition, microtubule binding affinity analysis and polymerization/depolymerization assays show that EB1 enhances paclitaxel binding to microtubules and stimulates the ability of paclitaxel to promote microtubule assembly and stabilization. These findings thus reveal EB1 as a critical regulator of paclitaxel sensitivity and have important implications in breast cancer chemotherapy.

End-binding protein 1 (EB1) up-regulation is an early event in colorectal carcinogenesis

End-binding protein (EB1) is a microtubule protein that binds to the tumor suppressor adenomatous polyposis coli (APC). While EB1 is implicated as a potential oncogene, its role in cancer progression is unknown. Therefore, we analyzed EB1/APC expression at the earliest stages of colorectal carcinogenesis and in the uninvolved mucosa ("field effect") of human and animal tissue. We also performed siRNA-knockdown in colon cancer cell lines. EB1 is up-regulated in early and field carcinogenesis in the colon, and the cellular/nano-architectural effect of EB1 knockdown depended on the genetic context. Thus, dysregulation of EB1 is an important early event in colon carcinogenesis.

CYLD coordinates with EB1 to regulate microtubule dynamics and cell migration

Cylindromatosis (CYLD), a deubiquitinase involved in inflammation and tumorigenesis via the modulation of cell signaling, has recently been identified as a critical regulator of microtubule dynamics. CYLD has also been shown to stimulate cell migration and thereby contribute to normal physiological processes. However, it remains elusive how the regulation of microtubule dynamic properties by CYLD is connected to its role in mediating cell migration. In this study, we performed yeast 2-hybrid screening with CYLD as bait and identified 7 CYLD-interacting proteins, including end-binding protein 1 (EB1). The CYLD-EB1 interaction was confirmed both in cells and in vitro, and these 2 proteins colocalized at the plus ends of microtubules. Interestingly, the association of CYLD with EB1 was significantly increased upon the stimulation of cell migration. CYLD coordinated with EB1 to orchestrate tail retraction, centrosome reorientation, and leading-edge microtubule stabilization in migratory cells. In addition, CYLD acted in concert with EB1 to regulate microtubule assembly in vitro, microtubule nucleation at the centrosome, and microtubule growth at the cell periphery. These data provide mechanistic insights into the actions of CYLD in the regulation of microtubule dynamics and cell migration. These findings also support the notion that coordinated actions of microtubule-binding proteins are critical for microtubule-mediated cellular events.

Regulation of tumor angiogenesis by the microtubule-binding protein CLIP-170

Angiogenesis, the expansion of preexisting blood vessels, is a complex process required for tumor growth and metastasis. Although current antiangiogenic strategies have shown promising results in several cancer types, identification of additional antiangiogenic targets is required to improve the therapeutic response. Herein, we show that the microtubule-binding protein CLIP-170 (cytoplasmic linker protein of 170 kDa) is highly expressed in breast tumor samples and correlates positively with blood vessel density. Depletion of CLIP-170 significantly impaired vascular endothelial tube formation and sprouting in vitro and inhibited breast tumor growth in mice by decreasing tumor vascularization. Our data further show that CLIP-170 is important for the migration but not the proliferation of vascular endothelial cells. In addition, CLIP-170 promotes the polarization of endothelial cells in response to the angiogenic stimulus. These findings thus demonstrate a critical role for CLIP-170 in tumor angiogenesis and suggest its potential as a novel antiangiogenic target.