The centrosomal protein TACC3 controls paclitaxel sensitivity by modulating a premature senescence program

Investigation of differentially expressed genes related to cellular senescence between high-risk and non-high-risk groups in neuroblastoma

Object

This study aims to identify differentially expressed genes (DEGs) between high-risk and non-high-risk groups in neuroblastoma (NB), construct a prognostic model, and establish a risk score formula.

Materials and methods

The NB dataset GSE49710 (n = 498) from the GEO database served as the training cohort to select DEGs between high-risk and non-high-risk NB groups. Cellular senescence-related genes were obtained from the Aging Atlas database. Intersection genes from both datasets were identified as key genes of cellular senescence-related genes (SRGs). A prognostic model was constructed using Univariate Cox regression analysis and the Lasso algorithm with SRGs. Validation was performed using the E-MTAB-8248 cohort (n = 223). The expression levels of AURKA and CENPA were evaluated via RT-qPCR in two clinical NB sample groups.

Results

Eight SRGs were identified, and a prognostic model comprising five genes related to cellular senescence was constructed. AURKA and CENPA showed significant expression in clinical samples and were closely associated with cellular senescence.

Conclusion

The prognostic model consisted with five cellular senescence related genes effectively predicts the prognosis of NB patients. AURKA and CENPA represent promising targets in NB for predicting cellular senescence, offering potential insights for NB therapy.

TACC3: a multi-functional protein promoting cancer cell survival and aggressiveness

TACC3 is the most oncogenic member of the transforming acidic coiled-coil domain-containing protein (TACC) family. It is one of the major recruitment factors of distinct multi-protein complexes. TACC3 is localized to spindles, centrosomes, and nucleus, and regulates key oncogenic processes, including cell proliferation, migration, invasion, and stemness. Recently, TACC3 inhibition has been identified as a vulnerability in highly aggressive cancers, such as cancers with centrosome amplification (CA). TACC3 has spatiotemporal functions throughout the cell cycle; therefore, targeting TACC3 causes cell death in mitosis and interphase in cancer cells with CA. In the clinics, TACC3 is highly expressed and associated with worse survival in multiple cancers. Furthermore, TACC3 is a part of one of the most common fusions of FGFR, FGFR3-TACC3 and is important for the oncogenicity of the fusion. A detailed understanding of the regulation of TACC3 expression, its key partners, and molecular functions in cancer cells is vital for uncovering the most vulnerable tumors and maximizing the therapeutic potential of targeting this highly oncogenic protein. In this review, we summarize the established and emerging interactors and spatiotemporal functions of TACC3 in cancer cells, discuss the potential of TACC3 as a biomarker in cancer, and therapeutic potential of its inhibition.

TACC3 is an independent prognostic marker, and knockdown of TACC3 enhances the efficacy of CDK1 inhibitor RO3306 in liver cancer cells

The drug resistance of single-target therapy has gradually become an intractable clinical problem. Combination therapy may be an effective treatment to overcome or postpone drug resistance in cancer. Herein, we discussed the synergistic effect of transforming acidic coiled-coil containing protein 3 (TACC3) suppression and cyclin-dependent kinase 1 (CDK1) in hepatocellular carcinoma (HCC). The Cancer Genome Atlas database and bioinformatics methods were implemented to analyze the expression of CDK1 and TACC3, and predict the biological function of TACC3-related genes in HCC. In addition, in vitro experiments, including cell counting kit 8, transwell and flow cytometry were utilized to evaluate cell proliferation, migration, invasion, cell cycle arrest and apoptosis of HCC cells. Our results demonstrated that TACC3 is an unfavorable and independent prognostic factor to predict poor overall survival (OS) in HCC patients. Genetic inhibition of TACC3 exhibited a remarkable antineoplastic activity of HCC cell lines. Bioinformatic prediction proposed that CDK1 may be the main regulator of TACC3-related genes in HCC. In vitro experimental measurements suggested that a combination of si-TACC3 and CDK1 inhibitor synergistically inhibited cell proliferation and migration, and induced G2 cell cycle arrest and apoptosis of HepG2 or MHCC97H cells. In conclusion, our results revealed a prospective dual-target, TACC3 and CDK1, therapeutic strategy to improve the treatment of HCC.

Involvement of Bcl-2 Family Proteins in Tetraploidization-Related Senescence

The B-cell lymphoma 2 (Bcl-2) family of proteins is the main regulator of apoptosis. However, multiple emerging evidence has revealed that Bcl-2 family proteins are also involved in cellular senescence. On the one hand, the different expression of these proteins determines the entry into senescence. On the other hand, entry into senescence modulates the expression of these proteins, generally conferring resistance to apoptosis. With some exceptions, senescent cells are characterized by the upregulation of antiapoptotic proteins and downregulation of proapoptotic proteins. Under physiological conditions, freshly formed tetraploid cells die by apoptosis due to the tetraploidy checkpoint. However, suppression of Bcl-2 associated x protein (Bax), as well as overexpression of Bcl-2, favors the appearance and survival of tetraploid cells. Furthermore, it is noteworthy that our laboratory has shown that the joint absence of Bax and Bcl-2 antagonist/killer (Bak) favors the entry into senescence of tetraploid cells. Certain microtubule inhibitory chemotherapies, such as taxanes and vinca alkaloids, induce the generation of tetraploid cells. Moreover, the combined use of inhibitors of antiapoptotic proteins of the Bcl-2 family with microtubule inhibitors increases their efficacy. In this review, we aim to shed light on the involvement of the Bcl-2 family of proteins in the senescence program activated after tetraploidization and the possibility of using this knowledge to create a new therapeutic strategy targeting cancer cells.

Mechanisms of cancer cell death induction by paclitaxel: an updated review

Chemoresistance of cancer cells is a major problem in treating cancer. Knowledge of how cancer cells may die or resist cancer drugs is critical to providing certain strategies to overcome tumour resistance to treatment. Paclitaxel is known as a chemotherapy drug that can suppress the proliferation of cancer cells by inducing cell cycle arrest and induction of mitotic catastrophe. However, today, it is well known that paclitaxel can induce multiple kinds of cell death in cancers. Besides the induction of mitotic catastrophe that occurs during mitosis, paclitaxel has been shown to induce the expression of several pro-apoptosis mediators. It also can modulate the activity of anti-apoptosis mediators. However, certain cell-killing mechanisms such as senescence and autophagy can increase resistance to paclitaxel. This review focuses on the mechanisms of cell death, including apoptosis, mitotic catastrophe, senescence, autophagic cell death, pyroptosis, etc., following paclitaxel treatment. In addition, mechanisms of resistance to cell death due to exposure to paclitaxel and the use of combinations to overcome drug resistance will be discussed.

Chemogenetic profiling reveals PP2A-independent cytotoxicity of proposed PP2A activators iHAP1 and DT-061

Protein phosphatase 2A (PP2A) is an abundant phosphoprotein phosphatase that acts as a tumor suppressor. For this reason, compounds able to activate PP2A are attractive anticancer agents. The compounds iHAP1 and DT-061 have recently been reported to selectively stabilize specific PP2A-B56 complexes to mediate cell killing. We were unable to detect direct effects of iHAP1 and DT-061 on PP2A-B56 activity in biochemical assays and composition of holoenzymes. Therefore, we undertook genome-wide CRISPR-Cas9 synthetic lethality screens to uncover biological pathways affected by these compounds. We found that knockout of mitotic regulators is synthetic lethal with iHAP1 while knockout of endoplasmic reticulum (ER) and Golgi components is synthetic lethal with DT-061. Indeed we showed that iHAP1 directly blocks microtubule assembly both in vitro and in vivo and thus acts as a microtubule poison. In contrast, DT-061 disrupts both the Golgi apparatus and the ER and lipid synthesis associated with these structures. Our work provides insight into the biological pathways perturbed by iHAP1 and DT-061 causing cellular toxicity and argues that these compounds cannot be used for dissecting PP2A-B56 biology.

Comprehensive Analysis Uncovers Prognostic and Immunogenic Characteristics of Cellular Senescence for Lung Adenocarcinoma

Cellular senescence plays a crucial role in tumorigenesis, development and immune modulation in cancers. However, to date, a robust and reliable cellular senescence-related signature and its value in clinical outcomes and immunotherapy response remain unexplored in lung adenocarcinoma (LUAD) patients. Through exploring the expression profiles of 278 cellular senescence-related genes in 936 LUAD patients, a cellular senescence-related signature (SRS) was constructed and validated as an independent prognostic predictor for LUAD patients. Notably, patients with high SRS scores exhibited upregulation of senescence-associated secretory phenotype (SASP) and an immunosuppressive phenotype. Further analysis showed that SRS combined with immune checkpoint expression or TMB served as a good predictor for patients’ clinical outcomes, and patients with low SRS scores might benefit from immunotherapy. Collectively, our findings demonstrated that SRS involved in the regulation of the tumor immune microenvironment through SASP was a robust biomarker for the immunotherapeutic response and prognosis in LUAD.

Transcriptional Profiles Reveal Deregulation of Lipid Metabolism and Inflammatory Pathways in Neurons Exposed to Palmitic Acid

The effects of the consumption of high-fat diets (HFD) have been studied to unravel the molecular pathways they are altering in order to understand the link between increased caloric intake, metabolic diseases, and the risk of cognitive dysfunction. The saturated fatty acid, palmitic acid (PA), is the main component of HFD and it has been found increased in the circulation of obese and diabetic people. In the central nervous system, PA has been associated with inflammatory responses in astrocytes, but the effects on neurons exposed to it have not been largely investigated. Given that PA affects a variety of metabolic pathways, we aimed to analyze the transcriptomic profile activated by this fatty acid to shed light on the mechanisms of neuronal dysfunction. In the current study, we profiled the transcriptome response after PA exposition at non-toxic doses in primary hippocampal neurons. Gene ontology and Reactome pathway analysis revealed a pattern of gene expression which is associated with inflammatory pathways, and importantly, with the activation of lipid metabolism that is considered not very active in neurons. Validation by quantitative RT-PCR (qRT-PCR) of Hmgcs2, Angptl4, Ugt8, and Rnf145 support the results obtained by RNAseq. Overall, these findings suggest that neurons are able to respond to saturated fatty acids changing the expression pattern of genes associated with inflammatory response and lipid utilization that may be involved in the neuronal damage associated with metabolic diseases.

TACC3 expression as a prognostic factor in aggressive types of adult T-cell leukemia/lymphoma patients

INTRODUCTION

Adult T-cell leukemia/lymphoma (ATLL) is a malignant peripheral T-cell neoplasm associated with human T-cell leukemia virus type-1 (HTLV-1). The acute and lymphoma subtypes are regarded as aggressive ATLLs, and the overall survival (OS) of patients remains poor. Transforming acidic coiled-coil-containing protein 3 (TACC3) regulates microtubules, which are associated with cancer-related proteins overexpressed in various cancers. Such a relationship has not been reported in hematopoietic tumors, including ATLL.

METHODS

We examined tissue microarrays of histological samples from 92 cases of aggressive ATLL and assessed clinical features, including TACC3 protein expression levels.

RESULTS

Compared with TACC3-low, TACC3-high ATLL patients were significantly older (P < .001), with a tendency toward pleomorphic variant over other morphological classifications (P = .019). TACC3-high patients (median survival time [MST] 10.6 months, confidence interval [CI] [6.27-15.6]) had poorer OS compared to TACC3-low patients (MST 20 months, CI [9.43-38.5]) (P = .0168). Moreover, multivariate analysis on TACC3 expression levels suggests that TACC3-high is an independent significant prognostic factor (HR, 1.700; 95% CI, 1.037-2.753; P = .0355).

CONCLUSION

Certain drugs that inhibit TACC3-overexpressing neoplastic cells are used clinically. Further studies might highlight a key role for TACC3 in the oncogenesis and progression of ATLL.

Centrosome dysfunction: a link between senescence and tumor immunity

Centrosome aberrations are hallmarks of human cancers and contribute to the senescence process. Structural and numerical centrosome abnormalities trigger mitotic errors, cellular senescence, cell death, genomic instability and/or aneuploidy, resulting in human disorders such as aging and cancer and affecting immunity. Interestingly, centrosome dysfunction promotes the secretion of multiple inflammatory factors that act as pivotal drivers of senescence and tumor immune escape. In this review, we summarize the forms of centrosome dysfunction and further discuss recent advances indicating that centrosome defects contribute to acceleration of senescence progression and promotion of tumor cell immune evasion in different ways.

Progress on small-molecule proteolysis-targeting chimeras

Proteolysis-targeting chimeras (PROTACs) have received much attention for their promising therapeutic intervention in recent years. These molecules, with the mechanism of simultaneous recruitment of target protein and an E3 ligase, can trigger the cellular ubiquitin–proteasome system to degrade the target proteins. This article systematically introduces the mechanism of small-molecule PROTACs, and summarized the research progress of small-molecule PROTACs. The prospect for further application and the problems to be solved are also discussed.

Tubgcp3 Is Required for Retinal Progenitor Cell Proliferation During Zebrafish Development

The centrosomal protein γ-tubulin complex protein 3 (Tubgcp3/GCP3) is required for the assembly of γ-tubulin small complexes (γ-TuSCs) and γ-tubulin ring complexes (γ-TuRCs), which play critical roles in mitotic spindle formation during mitosis. However, its function in vertebrate embryonic development is unknown. Here, we generated the zebrafish tubgcp3 mutants using the CRISPR/Cas9 system and found that the tubgcp3 mutants exhibited the small eye phenotype. Tubgcp3 is required for the cell cycle progression of retinal progenitor cells (RPCs), and its depletion caused cell cycle arrest in the mitotic (M) phase. The M-phase arrested RPCs exhibited aberrant monopolar spindles and abnormal distributed centrioles and γ-tubulin. Moreover, these RPCs underwent apoptosis finally. Our study provides the in vivo model for the functional study of Tubgcp3 and sheds light on the roles of centrosomal γ-tubulin complexes in vertebrate development.

Oncogenic driver FGFR3-TACC3 is dependent on membrane trafficking and ERK signaling

Fusion proteins resulting from chromosomal translocations have been identified as oncogenic drivers in many cancers, allowing them to serve as potential drug targets in clinical practice. The genes encoding FGFRs, Fibroblast Growth Factor Receptors, are commonly involved in such translocations, with the FGFR3-TACC3 fusion protein frequently identified in many cancers, including glioblastoma, cervical cancer, bladder cancer, nasopharyngeal carcinoma, and lung adenocarcinoma among others. FGFR3-TACC3 retains the entire extracellular domain and most of the kinase domain of FGFR3, with its C-terminal domain fused to TACC3. We examine here the effects of targeting FGFR3-TACC3 to different subcellular localizations by appending either a nuclear localization signal (NLS) or a myristylation signal, or by deletion of the normal signal sequence. We demonstrate that the oncogenic effects of FGFR3-TACC3 require either entrance to the secretory pathway or plasma membrane localization, leading to overactivation of canonical MAPK/ERK pathways. We also examined the effects of different translocation breakpoints in FGFR3-TACC3, comparing fusion at TACC3 exon 11 with fusion at exon 8. Transformation resulting from FGFR3-TACC3 was not affected by association with the canonical TACC3-interacting proteins Aurora-A, clathrin, and ch-TOG. We have shown that kinase inhibitors for MEK (Trametinib) and FGFR (BGJ398) are effective in blocking cell transformation and MAPK pathway upregulation. The development of personalized medicines will be essential in treating patients who harbor oncogenic drivers such as FGFR3-TACC3.

Elevated Expression of Transforming Acidic Coiled-Coil Containing Protein 3 (TACC3) Is Associated With a Poor Prognosis in Osteosarcoma

BACKGROUND

Transforming acidic coiled-coil containing protein 3 (TACC3) is expressed during the mitotic phase of nuclear division and regulates microtubules. Recently, high TACC3 expression in tumor cells of various cancers including soft tissue sarcoma has been reported. However, its role in osteosarcoma remains unknown. Because we have few prognostic markers for survival in osteosarcoma, we wanted to investigate the potential role of TACC3 in human osteosarcoma and determine if it is associated with survival.

QUESTIONS/PURPOSES

(1) Is there a relationship between TACC3 expression and clinicopathologic characteristics such as sex, age (< 20 or ≥ 20 years), histologic type (osteoblastic or others), tumor location (femur or others), American Joint Committee on Cancer staging system (AJCC stage IIA or IIB), tumor necrosis percentage after chemotherapy (< 90% or ≥ 90%), p53 expression (low or high), and Ki-67 expression (low or high)? (2) Is TACC3 expression associated with event-free and overall survival in patients with osteosarcoma?

METHODS

Forty-six conventional patients with osteosarcoma were treated at our institution from 1989 to 2013. Patients were excluded because of unresectable primary site (two patients) and no chemotherapy (two patients). Patients with metastasis at the initial visit (five patients), without pretreatment biopsy samples (two patients), or clinical charts (two patients) were also excluded. The left 33 patients who received neoadjuvant and adjuvant chemotherapy, which consisted of cisplatin/doxorubicin/methotrexate or cisplatin/doxorubicin/methotrexate/ifosfamide, and completed surgical resection with histologic wide tumor margins. Primary tumor samples before chemotherapy were used in this study. We investigated TACC3 expression using immunohistochemical staining and statistically analyzed the TACC3 expression, clinicopathologic characteristics, and event-free and overall survival in patients with osteosarcoma.

RESULTS

High TACC3 expression was observed in 19 of 33 osteosarcoma specimens (58%), and this was associated with larger tumor size (ie, AJCC stage IIB in this study; p = 0.002), higher p53 expression (p = 0.007), and higher Ki-67 expression (p = 0.002). The estimated metastasis-free survival at 5 years was 21% (95% confidence interval [CI], 7%-41%) in patients with high TACC3 expression and 79% (95% CI, 47%-93%) in patients with low TACC3 expression (p < 0.001), and the estimated overall survival at 5 years was 34% (95% CI, 13%-56%) in patients with high TACC3 expression and 86% (95% CI, 54%-96%) in patients with low TACC3 expression (p < 0.001). Furthermore, high TACC3 expression was an independent poor prognostic factor for metastasis-free survival with a hazard ratio of 3.89 (95% CI, 1.07-19.78; p = 0.039) as well as overall survival with 4.41 (95% CI, 1.01-32.97; p = 0.049).

CONCLUSIONS

High TACC3 expression was associated with aggressive clinicopathologic features and unfavorable prognosis in these patients with osteosarcoma. Our preliminary results suggest that further analysis about mutation or an inactive form of TACC3 would be useful to understand the mechanism of abnormal TACC3 expression in patients with osteosarcoma. If these findings are substantiated in larger studies, TACC3 might be useful for predicting survival and a potential therapeutic target for osteosarcoma.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Overexpression of TACC3 in Breast Cancer Associates With Poor Prognosis

Increasing evidences suggest that transforming acidic coiled-coil protein 3 (TACC3) is associated with various types of human cancer. However, the expression of TACC3 in breast cancer tissues remains largely unknown. To identify whether TACC3 can serve as a biomarker for the diagnosis and prognosis of breast cancer, quantitative polymerase chain reaction, western blotting, and immunohistochemistry staining were utilized to detect the expression of TACC3. The mRNA and protein levels of TACC3 in breast cancer samples were novelty higher compared with nontumorous breast tissues. Immunohistochemistry results revealed TACC3 expression was significantly correlated to lymphoid nodal metastasis (P=0.035) and HER-2 status (P=0.021). The patients with high expression of TACC3 had a significantly poor prognosis compared with patients with low expression (P=0.017), especially in the patients with pathological tumor size 2-4 status (P=0.028). Furthermore, multivariate analysis indicated that TACC3 expression was an independent prognostic factor for breast cancer patients (P=0.029). This study, first, suggested TACC3 might be an important molecular marker for diagnosis and prognosis of breast cancer.

miR-30e controls DNA damage-induced stress responses by modulating expression of the CDK inhibitor p21WAF1/CIP1 and caspase-3

MicroRNAs (miRNAs), a class of small non-coding RNAs that usually cause gene silencing by translational repression or degradation of mRNAs, are implicated in DNA damage-induced stress responses. To identify senescence-associated miRNAs, we performed microarray analyses using wild-type and p53-deficient HCT116 colon carcinoma cells that following gamma-irradiation (γIR) are driven into senescence and apoptosis, respectively. Several miRNAs including miR-30e were found upregulated in a p53-dependent manner specifically in senescent cells, but not in apoptotic cells. Overexpression of miR-30e in HCT116 cells not only inhibited γIR-, etoposide- or miR-34a-induced caspase-3-like DEVDase activities and cell death, but greatly accelerated and augmented their senescent phenotype. Consistently, procaspase-3 protein, but not mRNA decreased in the presence of miR-30e, whereas expression of the cyclin-dependent kinase inhibitor p21 increased both at the mRNA and protein level. Performing luciferase reporter gene assays, we identified the 3′-UTR of the caspase-3 mRNA as a direct miR-30e target. In contrast, although miR-30e was unable to bind to the p21 mRNA, it increased expression of a luciferase construct containing the p21 promoter, suggesting that the miR-30e-mediated upregulation of p21 occurs indirectly at the transcriptional level. Interestingly, despite suppressing procaspase-3 expression, miR-30e was unable to protect RKO colon carcinoma cells from DNA damage-induced death or to induce senescence, as miR-30e completely fails to upregulate p21 in these cells. These data suggest that miR-30e functions in a cell type-dependent manner as an important molecular switch for DNA damage-induced stress responses and may thus represent a target of therapeutic value.

Clinicopathological and prognostic value of transforming acidic coiled-coil-containing protein 3 (TACC3) expression in soft tissue sarcomas

Transforming acidic coiled-coil-containing protein 3 (TACC3), a microtubule regulator, is associated with various cancers. However, the relationship between TACC3 and soft tissue sarcomas (STS) remains unclear. We investigated the expression of TACC3 in 136 STS patient samples using immunohistochemical (IHC) staining, and the statistical associations between TACC3 expression and clinicopathological characteristics were evaluated. Additionally, the expression levels of the tumor suppressor p53 and of the cell proliferation marker Ki-67 were also assessed by IHC. High TACC3 expression was detected in 94/136 of STS cases (69.1%), and significantly correlated with higher grade according to the French Fédération Nationale des Centres de Lutte Contre le Cancer system (P<0.0001), poorer tumor differentiation (P<0.0001), increased mitotic counts (P<0.0001), advanced stage per American Joint Committee on Cancer guidelines (P<0.0001), higher p53 expression (P = 0.0487), higher Ki-67 expression (P<0.0001), and undergoing postoperative therapy (P = 0.0001). Disease-free survival (DFS) and overall survival (OS) of patients with high TACC3 expression were significantly shorter (P<0.0001 and P<0.0001, respectively). On multivariate analyses, high TACC3 expression was an independent negative prognostic factor for both DFS and OS (hazard ratio [HR]: 3.074; P = 0.0235 and HR: 8.521; P = 0.0415, respectively). Our results suggest that TACC3 is an independent prognostic factor and may be a novel therapeutic target for the treatment of STS.

Mitotic Spindle Assembly and Genomic Stability in Breast Cancer Require PI3K-C2α Scaffolding Function

Proper organization of the mitotic spindle is key to genetic stability, but molecular components of inter-microtubule bridges that crosslink kinetochore fibers (K-fibers) are still largely unknown. Here we identify a kinase-independent function of class II phosphoinositide 3-OH kinase α (PI3K-C2α) acting as limiting scaffold protein organizing clathrin and TACC3 complex crosslinking K-fibers. Downregulation of PI3K-C2α causes spindle alterations, delayed anaphase onset, and aneuploidy, indicating that PI3K-C2α expression is required for genomic stability. Reduced abundance of PI3K-C2α in breast cancer models initially impairs tumor growth but later leads to the convergent evolution of fast-growing clones with mitotic checkpoint defects. As a consequence of altered spindle, loss of PI3K-C2α increases sensitivity to taxane-based therapy in pre-clinical models and in neoadjuvant settings.

TACC3 as an independent prognostic marker for solid tumors: a systematic review and meta-analysis

Recent studies have showed that the transforming acidic coiled coil 3 (TACC3), was aberrantly up-regulated in various solid tumors and was reported to be correlated with unfavorable prognosis in cancer patients. This study aimed to examine the relationship between TACC3 and relevant clinical outcomes. Pubmed, Web of Science, Embase and Cochrane Library were systematically searched to obtain all eligible articles. Pooled hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated to evaluate the influence of TACC3 expression on overall survival (OS) and disease-free survival (DFS) in solid tumors patients. A total of 1943 patients from 11 articles were included. The result indicated that a significantly shorter OS was observed in patients with high expression level of TACC3 (HR=1.90, 95% CI=1.63-2.23). In the subgroup analysis, the association was also observed in patients with cancers of digestive system (HR=1.85, 95% CI=1.53-2.24). Statistical significance was also observed in subgroup meta-analysis stratified by the cancer type, analysis type and sample size. Furthermore, poorer DFS was observed in patients with high expression level of TACC3 (HR=2.67, 95% CI=2.10-3.40). Additionally, the pooled odds ratios (ORs) showed that increased TACC3 expression was also related to positive lymph node metastasis (OR=1.68, 95% CI=1.26-2.25), tumor differentiation (OR=1.90, 95% CI=1.25-2.88) and TNM stage (OR=1.66, 95% CI=1.25-2.20). In conclusion, the increased expression level of TACC3 was associated with unfavorable prognosis, suggesting that it was a valuable prognosis biomarker or a promising therapeutic target of solid tumors. Further studies should be conducted to confirm the clinical utility of TACC3 in human solid tumors.

FGFR3-TACC3 cancer gene fusions cause mitotic defects by removal of endogenous TACC3 from the mitotic spindle

Fibroblast growth factor receptor 3-transforming acidic coiled-coil containing protein 3 (FGFR3-TACC3; FT3) is a gene fusion resulting from rearrangement of chromosome 4 that has been identified in many cancers including those of the urinary bladder. Altered FGFR3 signalling in FT3-positive cells is thought to contribute to cancer progression. However, potential changes in TACC3 function in these cells have not been explored. TACC3 is a mitotic spindle protein required for accurate chromosome segregation. Errors in segregation lead to aneuploidy, which can contribute to cancer progression. Here we show that FT3-positive bladder cancer cells have lower levels of endogenous TACC3 on the mitotic spindle, and that this is sufficient to cause mitotic defects. FT3 is not localized to the mitotic spindle, and by virtue of its TACC domain, recruits endogenous TACC3 away from the spindle. Knockdown of the fusion gene or low-level overexpression of TACC3 partially rescues the chromosome segregation defects in FT3-positive bladder cancer cells. This function of FT3 is specific to TACC3 as inhibition of FGFR3 signalling does not rescue the TACC3 level on the spindle in these cancer cells. Models of FT3-mediated carcinogenesis should, therefore, include altered mitotic functions of TACC3 as well as altered FGFR3 signalling.

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.

MicroRNA-15b regulates mitochondrial ROS production and the senescence-associated secretory phenotype through sirtuin 4/SIRT4

Mammalian sirtuins are involved in the control of metabolism and life-span regulation. Here, we link the mitochondrial sirtuin SIRT4 with cellular senescence, skin aging, and mitochondrial dysfunction. SIRT4 expression significantly increased in human dermal fibroblasts undergoing replicative or stress-induced senescence triggered by UVB or gamma-irradiation. In-vivo, SIRT4 mRNA levels were upregulated in photoaged vs. non-photoaged human skin. Interestingly, in all models of cellular senescence and in photoaged skin, upregulation of SIRT4 expression was associated with decreased levels of miR-15b. The latter was causally linked to increased SIRT4 expression because miR-15b targets a functional binding site in the SIRT4 gene and transfection of oligonucleotides mimicking miR-15b function prevented SIRT4 upregulation in senescent cells. Importantly, increased SIRT4 negatively impacted on mitochondrial functions and contributed to the development of a senescent phenotype. Accordingly, we observed that inhibition of miR-15b, in a SIRT4-dependent manner, increased generation of mitochondrial reactive oxygen species, decreased mitochondrial membrane potential, and modulated mRNA levels of nuclear encoded mitochondrial genes and components of the senescence-associated secretory phenotype (SASP). Thus, miR-15b is a negative regulator of stress-induced SIRT4 expression thereby counteracting senescence associated mitochondrial dysfunction and regulating the SASP and possibly organ aging, such as photoaging of human skin.

PKCι depletion initiates mitotic slippage-induced senescence in glioblastoma

Cellular senescence is a tumor suppressor mechanism where cells enter a permanent growth arrest following cellular stress. Oncogene-induced senescence (OIS) is induced in non-malignant cells following the expression of an oncogene or inactivation of a tumor suppressor. Previously, we have shown that protein kinase C iota (PKCι) depletion induces cellular senescence in glioblastoma cells in the absence of a detectable DNA damage response. Here we demonstrate that senescent glioblastoma cells exhibit an aberrant centrosome morphology. This was observed in basal levels of senescence, in p21-induced senescence, and in PKCι depletion-induced senescence. In addition, senescent glioblastoma cells are polyploid, Ki-67 negative and arrest at the G1/S checkpoint, as determined by expression of cell cycle regulatory proteins. These markers are all consistent with cells that have undergone mitotic slippage. Failure of the spindle assembly checkpoint to function properly can lead to mitotic slippage, resulting in the premature exit of mitotic cells into the G1 phase of the cell cycle. Although in G1, these cells have the replicated DNA and centrosomal phenotype of a cell that has entered mitosis and failed to divide. Overall, we demonstrate that PKCι depletion initiates mitotic slippage-induced senescence in glioblastoma cells. To our knowledge, this is the first evidence of markers of mitotic slippage directly in senescent cells by co-staining for senescence-associated β-galactosidase and immunofluorescence markers in the same cell population. We suggest that markers of mitotic slippage be assessed in future studies of senescence to determine the extent of mitotic slippage in the induction of cellular senescence.

Aurora-A Kinase: A Potent Oncogene and Target for Cancer Therapy

The Aurora kinase family is comprised of three serine/threonine kinases, Aurora-A, Aurora-B, and Aurora-C. Among these, Aurora-A and Aurora-B play central roles in mitosis, whereas Aurora-C executes unique roles in meiosis. Overexpression or gene amplification of Aurora kinases has been reported in a broad range of human malignancies, pointing to their role as potent oncogenes in tumorigenesis. Aurora kinases therefore represent promising targets for anticancer therapeutics. A number of Aurora kinase inhibitors (AKIs) have been generated; some of which are currently undergoing clinical evaluation. Recent studies have unveiled novel unexpected functions of Aurora kinases during cancer development and the mechanisms underlying the anticancer actions of AKIs. In this review, we discuss the most recent advances in Aurora-A kinase research and targeted cancer therapy, focusing on the oncogenic roles and signaling pathways of Aurora-A kinases in promoting tumorigenesis, the recent preclinical and clinical AKI data, and potential alternative routes for Aurora-A kinase inhibition.

High expression of TACC3 in esophageal squamous cell carcinoma correlates with poor prognosis

To analyze the expression of the transforming acidic coiled-coil protein 3 (TACC3) in esophageal squamous cell carcinoma (ESCC) samples, and to identify whether TACC3 can serve as a biomarker for the diagnosis and prognosis of ESCC, qPCR, western blotting and immunohistochemistry staining (IHC) were utilized to detect the expression of TACC3. Furthermore, cell growth, colony formation, migration ability and the epithelial-mesenchymal transition markers of ESCC cells in which TACC3 were knocked-down were measured. The mRNA and protein levels of TACC3 were higher in ESCC specimens compared to non-tumorous esophageal epithelial tissues. IHC results revealed TACC3 expression was significantly correlated to differentiation (p = 0.017) and lymphoid nodal status (p = 0.028). The patients with high-expression of TACC3 had a significantly poor prognosis compared to those of low-expression (p = 0.017), especially in the patients at stages I–II (p = 0.028). Multivariate analysis indicated that TACC3 expression was an independent prognostic factor for ESCC patients (p = 0.025). Knockdown of TACC3 inhibited the ability of cell proliferation, colony formation and migration. This study first identifies TACC3 not only as a useful biomarker for diagnose and prognosis of ESCC, but also as a potential therapeutic target for patients with ESCC.

The clinical significance of transforming acidic coiled-coil protein 3 expression in non-small cell lung cancer

The relationship between TACC3, a member of the transforming acidic coiled-coil proteins (TACCs) family, and lung carcinoma remains unclear. The present study was designed to explore the prognostic and clinical significance of TACC3 in non-small cell lung cancer (NSCLC). An immunohistochemistry (IHC) assay was performed to analyze the expression of TACC3 in 195 lung cancer cases. The mRNA and protein levels of TACC3 were examined by quantitative reverse transcription-PCR or western blotting. The correlation between TACC3 expression and clinicopathological factors was analyzed by χ2 analysis and Fisher's exact test. Kaplan-Meier analysis and the Cox proportional hazards model were used to examine the correlation of prognostic outcomes with TACC3. The results showed that the levels of TACC3 mRNA and total protein were higher in lung cancer lesions than paired non-cancerous tissues. IHC analysis revealed that TACC3 was highly expressed in 94 (48.2%) cases. The expression of TACC3 was strongly correlated with smoking status, histological classification, differentiation, cytokeratin 19 fragment levels, T stage and the clinical stage of NSCLC patients. Univariate and multivariate analyses demonstrated that TACC3 is a useful biomarker for NSCLC prognosis. The low TACC3 expression group exhibited better progression-free survival (PFS) among patients who received anti-microtubule chemotherapy. In conclusion, the results showed that a high level of TACC3 expression was correlated with advanced clinicopathological classifications, poor overall survival (OS) and poor recurrence-free survival (RFS) in NSCLC patients. Our findings indicate that TACC3 is a potential prognostic marker and therapeutic target for NSCLC.

High expression of transforming acidic coiled coil-containing protein 3 strongly correlates with aggressive characteristics and poor prognosis of gastric cancer

Transforming acidic coiled coil-containing protein 3 (TACC3) is well understood to regulate mitotic spindle dynamics and centrosome integrity during mitosis. TACC3 has been suggested to be deregulated in a variety of human malignancies and may be involved in the process of cancer progression. The aim of the present study was to determine the status of TACC3 expression in gastric cancer (GC) and to clarify its clinical/prognostic significance. In the present study, we applied quantitative PCR (qPCR) and western blotting to examine TACC3 mRNA/protein expression in paired GC tissues and matched adjacent non-malignant tissues. Immunohistochemistry (IHC) was performed on a large cohort of 186 postoperative GC samples. Chi-square test, Kaplan-Meier analysis and Cox regression modelling were used to analyse the data. Upregulated mRNA and protein expression levels of TACC3 were observed in the majority of the GC tissues based on qPCR and western blotting compared to the adjacent non-cancerous gastric tissues. Specific IHC staining for TACC3 was predominantly identified in the cytoplasm of the cancer cells. A high expression of TACC3 was detected in 102 of the 186 (54.8%) tissue samples and was significantly associated with the extracapsular extension of the tumour (P<0.001), tumour relapse (P<0.001) and shortened overall survival in GC (P<0.001). Further analysis demonstrated that the TACC3 expression level stratified the patient outcome in stage II (P=0.040), stage III (P<0.001), T3/4 (P<0.001), N positive (P<0.001) and poorly differentiated/undifferentiated tumour subgroups (P<0.001). The Cox regression analysis suggested that a high expression of TACC3 was an independent prognostic factor for GC patients. The measurement of TACC3 protein expression may be beneficial for predicting clinical outcomes for GC patients.

The mesh is a network of microtubule connectors that stabilizes individual kinetochore fibers of the mitotic spindle

Kinetochore fibers (K-fibers) of the mitotic spindle are force-generating units that power chromosome movement during mitosis. K-fibers are composed of many microtubules that are held together throughout their length. Here, we show, using 3D electron microscopy, that K-fiber microtubules (MTs) are connected by a network of MT connectors. We term this network ‘the mesh’. The K-fiber mesh is made of linked multipolar connectors. Each connector has up to four struts, so that a single connector can link up to four MTs. Molecular manipulation of the mesh by overexpression of TACC3 causes disorganization of the K-fiber MTs. Optimal stabilization of K-fibers by the mesh is required for normal progression through mitosis. We propose that the mesh stabilizes K-fibers by pulling MTs together and thereby maintaining the integrity of the fiber. Our work thus identifies the K-fiber meshwork of linked multipolar connectors as a key integrator and determinant of K-fiber structure and function.

DOI:http://dx.doi.org/10.7554/eLife.07635.001

Before a cell divides, its genetic material must be copied and then equally distributed between the newly formed daughter cells. In the cells of plants, animals, and fungi, a structure known as the spindle pulls the two copies of the chromosomes apart. The spindle is made up of a network of long, protein filaments called microtubules, and the bundles of microtubules that attach to the chromosomes are referred to as ‘K-fibers’.

K-fibers are organized in a way that provides strength. These bundles of microtubules are held together throughout their entire length and, in 2011, it was suggested that a group of proteins including one called TACC3 could cross-link adjacent microtubules within K-fibers. However, it remained unclear how these proteins achieved this.

Now, Nixon et al.—including several of the researchers involved in the 2011 work—have used a technique called 3D electron tomography to analyze what holds the K-fibers together in human cells. This analysis revealed struts or connectors that hold together adjacent microtubules within K-fibers. These connectors can vary in size and a single connector can link up to four microtubules. This means that, in a three-dimensional view, the connectors appear as a ‘mesh’ between the microtubules in the bundle.

Nixon et al. then increased the levels of the TACC3 protein and found that the K-fibers became disorganized. The spacing of the microtubules with the K-fibers was reduced so that they were more tightly packed than normal. These observations suggest that ‘the mesh’ influences the microtubule spacing within a K-fiber.

Nixon et al. analyzed how disorganized K-fibers affected dividing cells and found that it took longer for the chromosomes to move to the newly forming daughter cells. This suggests that cells must maintain optimal levels of TACC3 to ensure that the K-fibers can effectively separate the chromosomes. Further work is needed to identify the other proteins and molecules that make up the mesh.

DOI:http://dx.doi.org/10.7554/eLife.07635.002

Cancer cell death induced by novel small molecules degrading the TACC3 protein via the ubiquitin-proteasome pathway

The selective degradation of target proteins with small molecules is a novel approach to the treatment of various diseases, including cancer. We have developed a protein knockdown system with a series of hybrid small compounds that induce the selective degradation of target proteins via the ubiquitin–proteasome pathway. In this study, we designed and synthesized novel small molecules called SNIPER(TACC3)s, which target the spindle regulatory protein transforming acidic coiled-coil-3 (TACC3). SNIPER(TACC3)s induce poly-ubiquitylation and proteasomal degradation of TACC3 and reduce the TACC3 protein level in cells. Mechanistic analysis indicated that the ubiquitin ligase APC/C^CDH1 mediates the SNIPER(TACC3)-induced degradation of TACC3. Intriguingly, SNIPER(TACC3) selectively induced cell death in cancer cells expressing a larger amount of TACC3 protein than normal cells. These results suggest that protein knockdown of TACC3 by SNIPER(TACC3) is a potential strategy for treating cancers overexpressing the TACC3 protein.

Pulling it together: The mitotic function of TACC3

Transforming acidic coiled coil 3 (TACC3) is a non-motor microtubule-associated protein (MAP) that is important for mitotic spindle stability and organization. The exact mechanism by which TACC3 acts at microtubules to stabilize the spindle has been unclear. However, several recent studies identified that the TACC3 complex at microtubules contains clathrin in addition to its previously identified binding partner, colonic and hepatic tumor overexpressed gene (ch-TOG). In this complex, phosphorylated TACC3 interacts directly with both ch-TOG and clathrin heavy chain, promoting accumulation of all complex members at the mitotic spindle. This complex stabilizes kinetochore fibers within the spindle by forming cross-bridges that link adjacent microtubules in these bundles. So, TACC3 is an adaptor that recruits ch-TOG and clathrin to mitotic microtubules, in an Aurora A kinase-regulated manner. In this mini-review we will describe the recent advances in the understanding of TACC 3 function and present a model that pulls together these new data with previous observations.

Curcumin-induced Aurora-A suppression not only causes mitotic defect and cell cycle arrest but also alters chemosensitivity to anticancer drugs

Overexpression of oncoprotein Aurora-A increases drug resistance and promotes lung metastasis of breast cancer cells. Curcumin is an active anticancer compound in turmeric and curry. Here we observed that Aurora-A protein and kinase activity were reduced in curcumin-treated human breast chemoresistant nonmetastatic MCF-7 and highly metastatic cancer MDA-MB-231 cells. Curcumin acts in a similar manner to Aurora-A small interfering RNA (siRNA), resulting in monopolar spindle formation, S and G2/M arrest, and cell division reduction. Ectopic Aurora-A extinguished the curcumin effects. The anticancer effects of curcumin were enhanced by Aurora-A siRNA and produced additivity and synergism effects in cell division and monopolar phenotype, respectively. Combination treatment with curcumin overrode the chemoresistance to four Food and Drug Administration (FDA)-approved anticancer drugs (ixabepilone, cisplatin, vinorelbine, or everolimus) in MDA-MB-231 cells, which was characterized by a decrease in cell viability and the occurrence of an additivity or synergy effect. Ectopic expression of Aurora-A attenuated curcumin-enhanced chemosensitivity to these four tested drugs. A similar benefit of curcumin was observed in MCF-7 cells treated with ixabepilone, the primary systemic therapy to patients with invasive breast cancer (stages IIA-IIIB) before surgery. Antagonism effect was observed when MCF-7 cells were treated with curcumin plus cisplatin, vinorelbine or everolimus. Curcumin-induced enhancement in chemosensitivity was paralleled by significant increases (additivity or synergy effect) in apoptosis and cell cycle arrest at S and G2/M phases, the consequences of Aurora-A inhibition. These results suggest that a combination of curcumin with FDA-approved anticancer drugs warrants further assessment with a view to developing a novel clinical treatment for breast cancer.

Role of centrosomal adaptor proteins of the TACC family in the regulation of microtubule dynamics during mitotic cell division

During the mitotic division cycle, cells pass through an extensive microtubule rearrangement process where microtubules forming the mitotic spindle apparatus are dynamically instable. Several centrosomal- and microtubule-associated proteins are involved in the regulation of microtubule dynamics and stability during mitosis. Here, we focus on members of the transforming acidic coiled coil (TACC) family of centrosomal adaptor proteins, in particular TACC3, in which their subcellular localization at the mitotic spindle apparatus is controlled by Aurora-A kinase-mediated phosphorylation. At the effector level, several TACC-binding partners have been identified and characterized in greater detail, in particular, the microtubule polymerase XMAP215/ch-TOG/CKAP5 and clathrin heavy chain (CHC). We summarize the recent progress in the molecular understanding of these TACC3 protein complexes, which are crucial for proper mitotic spindle assembly and dynamics to prevent faulty cell division and aneuploidy. In this regard, the (patho)biological role of TACC3 in development and cancer will be discussed.

The centrosomal adaptor TACC3 and the microtubule polymerase chTOG interact via defined C-terminal subdomains in an Aurora-A kinase-independent manner

The cancer-associated, centrosomal adaptor protein TACC3 (transforming acidic coiled-coil 3) and its direct effector, the microtubule polymerase chTOG (colonic and hepatic tumor overexpressed gene), play a crucial function in centrosome-driven mitotic spindle assembly. It is unclear how TACC3 interacts with chTOG. Here, we show that the C-terminal TACC domain of TACC3 and a C-terminal fragment adjacent to the TOG domains of chTOG mediate the interaction between these two proteins. Interestingly, the TACC domain consists of two functionally distinct subdomains, CC1 (amino acids (aa) 414-530) and CC2 (aa 530-630). Whereas CC1 is responsible for the interaction with chTOG, CC2 performs an intradomain interaction with the central repeat region of TACC3, thereby masking the TACC domain before effector binding. Contrary to previous findings, our data clearly demonstrate that Aurora-A kinase does not regulate TACC3-chTOG complex formation, indicating that Aurora-A solely functions as a recruitment factor for the TACC3-chTOG complex to centrosomes and proximal mitotic spindles. We identified with CC1 and CC2, two functionally diverse modules within the TACC domain of TACC3 that modulate and mediate, respectively, TACC3 interaction with chTOG required for spindle assembly and microtubule dynamics during mitotic cell division.

Cellular senescence or EGFR signaling induces Interleukin 6 (IL-6) receptor expression controlled by mammalian target of rapamycin (mTOR)

Interleukin 6 (IL-6) signaling plays a role in inflammation, cancer, and senescence. Here, we identified soluble IL-6 receptor (sIL-6R) as a member of the senescence-associated secretory phenotype (SASP). Senescence-associated sIL-6R upregulation was mediated by mammalian target of rapamycin (mTOR). sIL-6R was mainly generated by a disintegrin and metalloprotease 10 (ADAM10)-dependent ectodomain shedding to enable IL-6 trans-signaling. In vivo, heterozygous PTEN-knockout mice exhibited higher mTOR activity and increased sIL-6R levels. Moreover, aberrant EGF receptor (EGFR) activation triggered IL-6 synthesis. In analogy to senescence, EGFR-induced activation of mTOR also induced IL-6R expression and sIL-6R generation. Hence, mTOR activation reprograms IL-6 non-responder cells into IL-6 responder cells. Our data suggest that mTOR serves as a central molecular switch to facilitate cellular IL-6 classic and trans-signaling via IL-6R upregulation with direct implications for cellular senescence and tumor development.

Transforming acidic coiled-coil proteins (TACCs) in human cancer

Fine-tuned regulation of the centrosome/microtubule dynamics during mitosis is essential for faithful cell division. Thus, it is not surprising that deregulations in this dynamic network can contribute to genomic instability and tumorigenesis. Indeed, centrosome loss or amplification, spindle multipolarity and aneuploidy are often found in a majority of human malignancies, suggesting that defects in centrosome and associated microtubules may be directly or indirectly linked to cancer. Therefore, future research to identify and characterize genes required for the normal centrosome function and microtubule dynamics may help us gain insight into the complexity of cancer, and further provide new avenues for prognostic, diagnostics and therapeutic interventions. Members of the transforming acidic coiled-coil proteins (TACCs) family are emerging as important players of centrosome and microtubule-associated functions. Growing evidence indicates that TACCs are involved in the progression of certain solid tumors. Here, we will discuss our current understanding of the biological function of TACCs, their relevance to human cancer and possible implications for cancer management.

Oncogenic FGFR3 gene fusions in bladder cancer

FGF receptor 3 (FGFR3) is activated by mutation or over-expression in many bladder cancers. Here, we identify an additional mechanism of activation via chromosomal re-arrangement to generate constitutively activated fusion genes. FGFR3–transforming acid coiled coil 3 (TACC3) fusions resulting from 4p16.3 re-arrangements and a t(4;7) that generates a FGFR3-BAI1-associated protein 2-like 1 (BAIAP2L1) fusion were identified in 4 of 43 bladder tumour cell lines and 2 of 32 selected tissue samples including the tumour from which one of the cell lines was derived. These are highly activated and transform NIH-3T3 cells. The FGFR3 component is identical in all cases and lacks the final exon that includes the phospholipase C gamma 1 (PLCγ1) binding site. Expression of the fusions in immortalized normal human urothelial cells (NHUC) induced activation of the mitogen-activated protein kinase pathway but not PLCγ1. A protein with loss of the terminal region alone was not as highly activated as the fusion proteins, indicating that the fusion partners are essential. The TACC3 fusions retain the TACC domain that mediates microtubule binding and the BAIAP2L1 fusion retains the IRSp53/MIM domain (IMD) that mediates actin binding and Rac interaction. As urothelial cell lines with FGFR3 fusions are extremely sensitive to FGFR-selective agents, the presence of a fusion gene may aid in selection of patients for FGFR-targeted therapy.

Centrosome aberrations associated with cellular senescence and p53 localization at supernumerary centrosomes

Centrosome overduplication or amplification has been observed in many human cancers and in premalignant tissue, but the mechanisms leading to such centrosome aberrations are not fully understood. We previously showed that abnormal mitotic cells with supernumerary centrosomes increase with replicative senescence in human fibroblasts, especially in a polyploid subpopulation. This study examines localization of p53 protein at centrosomes in mitotic cells, which is often observed in association with DNA damage response, to investigate a possible association between p53 localization and numerical centrosome aberrations induced by cellular senescence. Cultures at later passages or the 4th day after exposure to H(2)O(2) showed increased frequencies of mitotic cells with supernumerary centrosomes, especially in a polyploid subpopulation. Immunohistochemical analysis frequently showed p53-positive foci in mitotic cells, and some were localized at centrosomes. The number of p53-positive foci in mitotic cells and its localization to centrosomes increased with replicative and premature senescence. Supernumerary centrosomes showed higher frequencies of p53 localization compared to normally duplicated centrosomes. Centrosome-associated p53 protein was phosphorylated at Ser15. These data suggest a possible association between localization of p53 protein and numerical centrosome aberrations in replicatively or prematurely senescent cells.

Multiple cancer testis antigens function to support tumor cell mitotic fidelity

While the expression of genes that are normally involved in spermatogenesis is frequently detected in tumors, the extent to which these gene products are required for neoplastic behaviors is unclear. To begin to address their functional relevance to tumorigenesis, we identified a cohort of proteins which display synthetic lethality with paclitaxel in non-small-cell lung cancer and whose expression is biased toward testes and tumors. Remarkably, these testis proteins, FMR1NB, NXF2, MAGEA5, FSIP1, and STARD6, are required for accurate chromosome segregation in tumor cells. Their individual depletion enhances the generation of multipolar spindles, increases mitotic transit time, and induces micronucleation in response to an otherwise innocuous dose of paclitaxel. The underlying basis for abnormal mitosis is an alteration in microtubule function, as their depletion increases microtubule cytaster formation and disrupts microtubule stability. Given these observations, we hypothesize that reactivated testis proteins may represent unique tumor cell vulnerabilities which, if targeted, could enhance responsiveness to antimitotic therapy. Indeed, we demonstrate that combining paclitaxel with a small-molecule inhibitor of the gametogenic and tumor cell mitotic protein TACC3 leads to enhanced centrosomal abnormalities, activation of death programs, and loss of anchorage-independent growth.

Disruption of Tacc3 function leads to in vivo tumor regression

The formation of the bipolar spindle is responsible for accurate chromosomal segregation during mitosis. The dynamic instability of microtubules has an important role in this process, and has been shown to be an effective target for cancer chemotherapy. Several agents that target non-microtubule mitotic proteins, including the motor protein Eg5, Aurora kinases and Polo-like kinases, are currently being developed as chemotherapeutic drugs. However, because the efficacies of these drugs remain elusive, new molecular targets that have essential roles in tumor cells are desired. Here, we provide in vivo evidence that transforming acidic coiled-coil-3 (Tacc3) is a potential target for cancer chemotherapy. Using MRI, we showed that Tacc3 loss led to the regression of mouse thymic lymphoma in vivo, which was accompanied by massive apoptosis. By contrast, normal tissues, including the thymus, showed no overt abnormalities, despite high Tacc3 expression. in vitro analysis indicated that Tacc3 depletion induced multi-polar spindle formation, which led to mitotic arrest, followed by apoptosis. Similar responses have been observed in Burkitt's lymphoma and T-ALL. These results show that Tacc3 is a vulnerable component of the spindle assembly in lymphoma cells and is a promising cancer chemotherapy target.