Thrombin Priming Promotes the Neuroprotective Effects of Human Wharton's Jelly-Derived Mesenchymal Stem Cells Via the HGF/AKT/STAT3 Signaling Pathway

Mesenchymal stem cells (MSCs) directly differentiate into neurons and endothelial cells after transplantation, and their secretome has considerable potential for treating brain injuries. Previous studies have suggested that the effects of MSCs priming with exposure to hypoxia, cytokines, growth factors, or chemical agents could optimize the paracrine potency and therapeutic potential of MSCs. Studies have suggested that thrombin-primed Wharton's Jelly-derived mesenchymal stem cells (Th.WJ-MSCs) significantly enhance the neuroprotective beneficial effects of naive MSCs in brain injury such as hypoxic-ischemic brain injury (HIE) and intraventricular hemorrhage (IVH). This study aimed to characterize WJ-MSCs in terms of stem cell markers, differentiation, cell proliferation, and paracrine factors by comparing naive and Th.WJ-MSCs. We demonstrated that compared with naive MSCs, Th.MSCs significantly enhanced the neuroprotective effects in vitro. Moreover, we identified differentially expressed proteins in the conditioned media of naive and Th.WJ-MSCs by liquid chromatography-tandem mass spectrometry analysis. Secretome analysis of the conditioned medium of WJ-MSCs revealed that such neuroprotective effects were mediated by paracrine effects with secretomes of Th.WJ-MSCs, and hepatocyte growth factor was identified as a key paracrine mediator. These results can be applied further in the preclinical and clinical development of effective and safe cell therapeutics for brain injuries such as HIE and IVH.

JAK2/STAT3 pathway mediates neuroprotective and pro-angiogenic treatment effects of adult human neural stem cells in middle cerebral artery occlusion stroke animal models

Mismatches between pre-clinical and clinical results of stem cell therapeutics for ischemic stroke limit their clinical applicability. To overcome these discrepancies, precise planning of pre-clinical experiments that can be translated to clinical trials and the scientific elucidation of treatment mechanisms is important. In this study, adult human neural stem cells (ahNSCs) derived from temporal lobe surgical samples were used (to avoid ethical and safety issues), and their therapeutic effects on ischemic stroke were examined using middle cerebral artery occlusion animal models. 5 × 10⁵ ahNSCs was directly injected into the lateral ventricle of contralateral brain hemispheres of immune suppressed rat stroke models at the subacute phase of stroke. Compared with the mock-treated group, ahNSCs reduced brain tissue atrophy and neurological sensorimotor and memory functional loss. Tissue analysis demonstrated that the significant therapeutic effects were mediated by the neuroprotective and pro-angiogenic activities of ahNSCs, which preserved neurons in ischemic brain areas and decreased reactive astrogliosis and microglial activation. The neuroprotective and pro-angiogenic effects of ahNSCs were validated in in vitro stroke models and were induced by paracrine factors excreted by ahNSCs. When the JAK2/STAT3 signaling pathway was inhibited by a specific inhibitor, AG490, the paracrine neuroprotective and pro-angiogenic effects of ahNSCs were reversed. This pre-clinical study that closely simulated clinical settings and provided treatment mechanisms of ahNSCs for ischemic stroke may aid the development of protocols for subsequent clinical trials of ahNSCs and the realization of clinically available stem cell therapeutics for ischemic stroke.

TACC3 Promotes Gastric Carcinogenesis by Promoting Epithelial-mesenchymal Transition Through the ERK/Akt/cyclin D1 Signaling Pathway

BACKGROUND/AIM

The present study investigated the oncogenic functions of TACC3 in the progression of gastric cancer (GC).

MATERIALS AND METHODS

We analysed TACC3 in relation to cell growth, invasion capability, expression of epithelial-mesenchymal transition (EMT)-related markers, and ERK/Akt/cyclin D1 signaling factors. The correlation between the immunohistochemically confirmed expression of TACC3 and clinical factors was also analyzed.

RESULTS

The increased proliferation and invasion of TACC3-over-expressing GC cells was accompanied by altered regulation of EMT-associated markers and activation of ERK/Akt/cyclin D1 signaling. Immunohistochemical analysis of TACC3 in human GC tissues revealed that its expression is correlated with aggressive characteristics and poor prognosis of intestinal-type GC.

CONCLUSION

TACC3 contributes to gastric tumorigenesis by promoting EMT via the ERK/Akt/cyclin D1 signaling pathway. The correlation between TACC3 expression and multiple clinicopathological variables implies that its effective therapeutic targeting in GC will depend on the tumor subtype.

Human collagen alpha-2 type I stimulates collagen synthesis, wound healing, and elastin production in normal human dermal fibroblasts (HDFs)

Skin aging appears to be the result of overlapping intrinsic (including genetic and hormonal factors) and extrinsic (external environment including chronic light exposure, chemicals, and toxins) processes. These factors cause decreases in the synthesis of collagen type I and elastin in fibroblasts and increases in the melanin in melanocytes. Collagen Type I is the most abundant type of collagen and is a major structural protein in human body tissues. In previous studies, many products containing collagen derived from land and marine animals as well as other sources have been used for a wide range of purposes in cosmetics and food. However, to our knowledge, the effects of human collagen-derived peptides on improvements in skin condition have not been investigated. Here we isolate and identify the domain of a human COL1A2-derived protein which promotes fibroblast cell proliferation and collagen type I synthesis. This human COL 1A2-derived peptide enhances wound healing and elastin production. Finally, the human collagen alpha-2 type I-derived peptide (SMM) ameliorates collagen type I synthesis, cell proliferation, cell migration, and elastin synthesis, supporting a significant anti-wrinkle effect. Collectively, these results demonstrate that human collagen alpha-2 type I-derived peptides is practically accessible in both cosmetics and food, with the goal of improving skin condition.

De novo phosphorylation of H2AX by WSTF regulates transcription-coupled homologous recombination repair

Histone H2AX undergoes a phosphorylation switch from pTyr142 (H2AX-pY142) to pSer139 (γH2AX) in the DNA damage response (DDR); however, the functional role of H2AX-pY142 remains elusive. Here, we report a new layer of regulation involving transcription-coupled H2AX-pY142 in the DDR. We found that constitutive H2AX-pY142 generated by Williams-Beuren syndrome transcription factor (WSTF) interacts with RNA polymerase II (RNAPII) and is associated with RNAPII-mediated active transcription in proliferating cells. Also, removal of pre-existing H2AX-pY142 by ATM-dependent EYA1/3 phosphatases disrupts this association and requires for transcriptional silencing at transcribed active damage sites. The following recovery of H2AX-pY142 via translocation of WSTF to DNA lesions facilitates transcription-coupled homologous recombination (TC-HR) in the G1 phase, whereby RAD51 loading, but not RPA32, utilizes RNAPII-dependent active RNA transcripts as donor templates. We propose that the WSTF-H2AX-RNAPII axis regulates transcription and TC-HR repair to maintain genome integrity.

Pellino1 regulates reversible ATM activation via NBS1 ubiquitination at DNA double-strand breaks

DNA double-strand break (DSB) signaling and repair are critical for genome integrity. They rely on highly coordinated processes including posttranslational modifications of proteins. Here we show that Pellino1 (Peli1) is a DSB-responsive ubiquitin ligase required for the accumulation of DNA damage response proteins and efficient homologous recombination (HR) repair. Peli1 is activated by ATM-mediated phosphorylation. It is recruited to DSB sites in ATM- and γH2AX-dependent manners. Interaction of Peli1 with phosphorylated histone H2AX enables it to bind to and mediate the formation of K63-linked ubiquitination of NBS1, which subsequently results in feedback activation of ATM and promotes HR repair. Collectively, these results provide a DSB-responsive factor underlying the connection between ATM kinase and DSB-induced ubiquitination.

Occurrence of DNA double-strand break (DSB) repair is important for genome integrity. Here, the authors reveal that Pellino1 is a DSB-responsive ubiquitin ligase required for promoting the accumulation of ATM and MRN complex at DSB sites via NBS1 ubiquitination.

Oncogenic potential of BEX4 is conferred by Polo-like kinase 1-mediated phosphorylation

The brain-expressed X-linked 4 (BEX4) gene has been recently identified as a mediator of microtubule hyperacetylation through sirtuin 2 inhibition and is highly overexpressed in human cancers. However, the gain-of-function molecular mechanism of the BEX4 gene in human cancers still needs to be elucidated. This study shows that BEX4 colocalizes and interacts with Polo-like kinase 1 (PLK1) at centrosomes, spindle poles, and midbodies, particularly during mitosis. Interestingly, PLK1-mediated phosphorylation upregulates the stability of BEX4 protein, and the PLK1-BEX4 interaction allows abnormal mitotic cells to adapt to aneuploidy rather than undergo apoptotic cell death. In summary, these results suggest that the oncogenicity of BEX4 is conferred by PLK1-mediated phosphorylation, and thus, the BEX4-PLK1 interaction is a novel oncogenic signal that enables the acquisition of chromosomal aneuploidy.

Combination Treatment of Polo-Like Kinase 1 and Tankyrase-1 Inhibitors Enhances Anticancer Effect in Triple-negative Breast Cancer Cells

BACKGROUND/AIM

Breast cancer is the most common malignant cancer type in women, and triple-negative breast cancer (TNBC) is an extremely aggressive subtype of breast cancer with poor prognosis rates. The present study investigated the antitumor effect of polo-like kinase 1 (PLK1) inhibitor in combination with the tankyrase-1 (TNKS1) inhibitor on TNBC cells.

MATERIALS AND METHODS

We evaluated the antitumor effects of combination therapy with PLK1 and TNKS1 inhibitor using cell viability analysis, apoptosis assay and transwell assay for cell invasion and migration in TNBC cells.

RESULTS

Combination treatment with PLK1 and TNKS1 inhibitors not only inhibited the invasion and migration capacity of TNBC cells, but also increased the apoptosis and cell death of TNBC cells. The viability of TNBC cells with low expression of β-catenin and high expression of PLK1 was not affected by treatment with PLK1 inhibitor. However, the combination treatment with the TNKS1 inhibitor significantly decreased cell invasion and migration and increased apoptosis.

CONCLUSION

Combination therapy of PLK1 and TNKS1 inhibitors may improve the therapeutic efficacy of the current treatment for TNBC.

Negative regulation of BRCA1 by transforming acidic coiled-coil protein 3 (TACC3)

In spite of the push to identify modifiers of BRCAness, it still remains unclear how tumor suppressor BRCA1 is lost in breast cancers in the absence of genetic or epigenetic aberrations. Mounting evidence indicates that the transforming acidic coiled-coil 3 (TACC3) plays an important role in the centrosome-microtubule network during mitosis and gene expression, and that deregulation of TACC3 is associated with breast cancer. However, the molecular mechanisms by which TACC3 contributes to breast cancer development have yet to be elucidated. Herein, we found that high levels of TACC3 in human mammary epithelial cells can cause genomic instability possibly in part through destabilizing BRCA1. We also found that high levels of TACC3 inhibited the interaction between BRCA1 and BARD1, thus subsequently allowing the BARD1-uncoupled BRCA1 to be destabilized by ubiquitin-mediated proteosomal pathway. Moreover, there is an inverse correlation between TACC3 and BRCA1 expression in breast cancer tissues. Overall, our findings provide a new insight into the role of TACC3 in genomic instability and breast tumorigenesis.

Pellino-1 confers chemoresistance in lung cancer cells by upregulating cIAP2 through Lys63-mediated polyubiquitination

Pellino-1 is an E3 ubiquitin ligase that mediates immune receptor signaling pathways. The role of Pellino-1 in oncogenesis of lung cancer was investigated in this study. Pellino-1 expression was increased in human lung cancer cell lines compared with non-neoplastic lung cell lines. Pellino-1 overexpression in human lung cancer cells, A549 and H1299 cells, increased the survival and colony forming ability. Pellino-1 overexpression in these cells also conferred resistance to cisplatin- or paclitaxel-induced apoptosis. In contrast, depletion of Pellino-1 decreased the survival of A549 and H1299 cells and sensitized these cells to cisplatin- and paclitaxel-induced apoptosis. Pellino-1 overexpression in A549 and H1299 cells upregulated the expression of inhibitor of apoptosis (IAP) proteins, including cIAP1 and cIAP2, while Pellino-1 depletion downregulated these molecules. Notably, Pellino-1 directly interacted with cIAP2 and stabilized cIAP2 through lysine63-mediated polyubiquitination via its E3 ligase activity. Pellino-1-mediated chemoresistance in lung cancer cells was dependent on the induction of cIAP2. Moreover, a strong positive correlation between Pellino-1 and the cIAP2 expression was observed in human lung adenocarcinoma tissues. Taken together, these results demonstrate that Pellino-1 contributes to lung oncogenesis through the overexpression of cIAP2 and promotion of cell survival and chemoresistance. Pellino-1 might be a novel oncogene and potential therapeutic target in lung cancer.

Abstract 1119: Targeting tankyrases as a therapeutic strategy for triple-negative breast cancer

Tankyrases (TNKS1 and TNKS2) are members of the human poly(ADP-ribose) polymerase (PARP) family and catalyze PARsylation by using NAD+ as a substrate to modify various proteins in order to regulate various cellular processes including Wnt/β-catenin signaling. TNKS1 has been shown to be overexpressed and to be correlated with highly aggressive disease and prognosis in various types of human cancers. A small molecule inhibitor of TNKS1, XAV-939 has been proven to be a potent inhibitor of Wnt/β-catenin signaling by stabilizing Axin. However, the effect of tankyrase inhibitors as potential breast cancer therapy is still under investigation. In this study, we found that TNKS1 is highly expressed in breast cancer cell lines, particularly in triple-negative breast cancer (TNBC) cells and that the expression of TNKS1 correlates with anti-proliferative efficacy of tankyrase inhibitors, XAV-939 and JW55. Also, XAV-939 treatment suppressed cell migration and invasion capabilities and epithelial-mesenchymal transition (EMT) signaling in triple-negative breast cancer cell lines. Moreover, XAV-939 reduced expression of stemness markers. It was shown that polo-like kinase 1 (PLK1) functions as a positive regulator of TNKS1 protein stability. Interestingly, we found that combination treatment of XAV-939 with PLK inhibitor GW843682X significantly suppressed cell growth, clonogenic potential, migratory and invasive capabilities of breast cancer cells. The combination of XAV-939 with ionizing radiation (IR) also showed an additional therapeutic effect. Therefore, our findings highlight the important value of TNKS1 as a therapeutic target and suggest the potential for improving the clinical efficacies of tankyrase inhibitors in combination with either PLK inhibitors or radiotherapy for patients with triple-negative breast cancer.

Citation Format: Maya Mathew, Loredana Campo, Jung-Lye Kim, Geun-Hyoung Ha, Eun-Kyoung Breuer. Targeting tankyrases as a therapeutic strategy for triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1119. doi:10.1158/1538-7445.AM2017-1119

Oncogenic microtubule hyperacetylation through BEX4-mediated sirtuin 2 inhibition

Five brain-expressed X-linked (BEX) gene members (BEX1–5) are arranged in tandem on chromosome X, and are highly conserved across diverse species. However, little is known about the function and role of BEX. This study represents a first attempt to demonstrate the molecular details of a novel oncogene BEX4. Among BEX proteins, BEX4 localizes to microtubules and spindle poles, and interacts with α-tubulin (α-TUB) and sirtuin 2 (SIRT2). The overexpression of BEX4 leads to the hyperacetylation of α-TUB by inhibiting SIRT2-mediated deacetylation. Furthermore, we found BEX4 expression conferred resistance to apoptotic cell death but led to acquisition of aneuploidy, and also increased the proliferating potential and growth of tumors. These results suggest that BEX4 overexpression causes an imbalance between TUB acetylation and deacetylation by SIRT2 inhibition and induces oncogenic aneuploidy transformation.

Pellino 1 promotes lymphomagenesis by deregulating BCL6 polyubiquitination

The signal-responsive E3 ubiquitin ligase pellino 1 (PELI1) regulates TLR and T cell receptor (TCR) signaling and contributes to the maintenance of autoimmunity; however, little is known about the consequence of mutations that result in upregulation of PELI1. Here, we developed transgenic mice that constitutively express human PELI1 and determined that these mice have a shorter lifespan due to tumor formation. Constitutive expression of PELI1 resulted in ligand-independent hyperactivation of B cells and facilitated the development of a wide range of lymphoid tumors, with prominent B cell infiltration observed across multiple organs. PELI1 directly interacted with the oncoprotein B cell chronic lymphocytic leukemia (BCL6) and induced lysine 63-mediated BCL6 polyubiquitination. In samples from patients with diffuse large B cell lymphomas (DLBCLs), PELI1 expression levels positively correlated with BCL6 expression, and PELI1 overexpression was closely associated with poor prognosis in DLBCLs. Together, these results suggest that increased PELI1 expression and subsequent induction of BCL6 promotes lymphomagenesis and that this pathway may be a potential target for therapeutic strategies to treat B cell lymphomas.

Abstract 5086: BEX protein attenuates the mitotic checkpoint and induces preneoplastic aneuploidy

The mitotic checkpoint plays a critical role in preventing chromosome missegregation and the adaptation of aneuploid cells. BubR1 kinase is a member of the mitotic checkpoint machinery. To understand the function of BubR1-mediated mitotic checkpoint, we have screened a novel BubR1-interating protein, BEX, by performing yeast two-hybrid systems. Here, we show that overexpression of BEX protein with sustained spindle poison results in a production of aneuploid cells and less apoptotic cell death. Inhibition of BubR1 expression increases aneuploid cell populations, whereas knockdown of both BEX and BubR1 avoid polyploidy by undergoing apoptosis in BubR1-depleted aneuploid cells. In addition, forced BEX expression significantly induces the colony forming potential and accelerates the proliferation rate. Interestingly, BEX is localized on X chromosome, and seems to be selectively expressed at cancer cells and tissues. These results indicate that BEX expression leads to mitotic dysfunction, and contributes to unstable chromosome aneuploid cells to be preneoplastically adapted.

Citation Format: Jin-Kwan Lee, Geun-Hyoung Ha, Janet Lee, Chang-Woo Lee. BEX protein attenuates the mitotic checkpoint and induces preneoplastic aneuploidy. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5086. doi:10.1158/1538-7445.AM2014-5086

TACC3 is essential for EGF-mediated EMT in cervical cancer

The third member of transforming acidic coiled-coil protein (TACC) family, TACC3, has been shown to be an important player in the regulation of centrosome/microtubule dynamics during mitosis and found to be deregulated in a variety of human malignancies. Our previous studies have suggested that TACC3 may be involved in cervical cancer progression and chemoresistance, and its overexpression can induce epithelial-mesenchymal transition (EMT) by activating the phosphatidylinositol 3-kinase (PI3K)/Akt and extracellular signal-regulated protein kinases (ERKs) signal transduction pathways. However, the upstream mechanisms of TACC3-mediated EMT and its functional/clinical importance in human cervical cancer remain elusive. Epidermal growth factor (EGF) has been shown to be a potent inducer of EMT in cervical cancer and associated with tumor invasion and metastasis. In this study, we found that TACC3 is overexpressed in cervical cancer and can be induced upon EGF stimulation. The induction of TACC3 by EGF is dependent on the tyrosine kinase activity of the EGF receptor (EGFR). Intriguingly, depletion of TACC3 abolishes EGF-mediated EMT, suggesting that TACC3 is required for EGF/EGFR-driven EMT process. Moreover, Snail, a key player in EGF-mediated EMT, is found to be correlated with the expression of TACC3 in cervical cancer. Collectively, our study highlights a novel function for TACC3 in EGF-mediated EMT process and suggests that targeting of TACC3 may be an attractive strategy to treat cervical cancers driven by EGF/EGFR signaling pathways.

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.

Abstract 4302: TACC3 promotes EMT through the up-regulation of PI3K/Akt and ERK signaling pathways

Transforming acidic coiled-coil protein 3 (TACC3) is a member of TACC family, essential for the maintenance of centrosome integrity and the regulation of microtubule assembly and spindle stability during mitosis. In addition to its function in mitosis, TACC3 has been shown to be involved in controlling cell growth, differentiation and transcriptional regulation. Interestingly, deregulated expression of TACC3 has been found in many human cancers, including breast, ovary, bladder, glioblastoma and non-small cell lung cancer. Moreover, our previous microarray analysis suggested that overexpression of TACC3 may be associated with the progression, metastasis and chemoresistance of cervical cancer. Although these findings indicate that TACC3 may play an important role in human cancer, the fundamental molecular mechanisms underlying how TACC3 contributes to cancer initiation, progression and metastasis, and its clinical significance remain elusive. Here, we explored the significance of TACC3 in cervical cancer. Using cervical cancer tissue microarrays, we found that TACC3 is overexpressed in cervical cancer compared with normal cervix. By modulating the expression of TACC3, we found that overexpression of TACC3 leads to changes in cell morphology, proliferation, transforming capability, migratory/invasive behavior as well as the expression of epithelial-mesenchymal transition (EMT)-related markers. Moreover, phosphatidylinositol 3-kinase (PI3K)/Akt and extracellular signal-regulated protein kinases (ERKs) signaling pathways are critical for TACC3-mediated EMT process. Notably, depletion of TACC3 is sufficient to suppress EMT phenotype. Our findings, therefore, identify a novel mechanism that promotes EMT, possibly leading to a more malignant and metastatic tumor phenotype as well as a potential biomarker for diagnosis, prognosis and therapy for cervical cancer.

Citation Format: Geun-Hyoung Ha, Jong-Sup Park, Eun-Kyoung Y. Breuer. TACC3 promotes EMT through the up-regulation of PI3K/Akt and ERK signaling pathways. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4302. doi:10.1158/1538-7445.AM2013-4302

Cyclin-dependent kinase 4 signaling acts as a molecular switch between syngenic differentiation and neural transdifferentiation in human mesenchymal stem cells

Multipotent mesenchymal stem/stromal cells (MSCs) are capable of differentiating into a variety of cell types from different germ layers. However, the molecular and biochemical mechanisms underlying the transdifferentiation of MSCs into specific cell types still need to be elucidated. In this study, we unexpectedly found that treatment of human adipose- and bone marrow-derived MSCs with cyclin-dependent kinase (CDK) inhibitor, in particular CDK4 inhibitor, selectively led to transdifferentiation into neural cells with a high frequency. Specifically, targeted inhibition of CDK4 expression using recombinant adenovial shRNA induced the neural transdifferentiation of human MSCs. However, the inhibition of CDK4 activity attenuated the syngenic differentiation of human adipose-derived MSCs. Importantly, the forced regulation of CDK4 activity showed reciprocal reversibility between neural differentiation and dedifferentiation of human MSCs. Together, these results provide novel molecular evidence underlying the neural transdifferentiation of human MSCs; in addition, CDK4 signaling appears to act as a molecular switch from syngenic differentiation to neural transdifferentiation of human MSCs.

TACC3 promotes epithelial-mesenchymal transition (EMT) through the activation of PI3K/Akt and ERK signaling pathways

Transforming acidic coiled-coil protein 3 (TACC3) is a member of the TACC family, essential for mitotic spindle dynamics and centrosome integrity during mitosis. Mounting evidence suggests that deregulation of TACC3 is associated with various types of human cancer. However, the molecular mechanisms by which TACC3 contributes to the development of cancer remain largely unknown. Here, we propose a novel mechanism by which TACC3 regulates epithelial-mesenchymal transition (EMT). By modulating the expression of TACC3, we found that overexpression of TACC3 leads to changes in cell morphology, proliferation, transforming capability, migratory/invasive behavior as well as the expression of EMT-related markers. Moreover, phosphatidylinositol 3-kinase (PI3K)/Akt and extracellular signal-regulated protein kinases (ERKs) signaling pathways are critical for TACC3-mediated EMT process. Notably, depletion of TACC3 is sufficient to suppress EMT phenotype. Collectively, our findings identify TACC3 as a driver of tumorigenesis as well as an inducer of oncogenic EMT and highlight its overexpression as a potential therapeutic target for preventing EMT-associated tumor progression and invasion.

The hsSsu72 phosphatase is a cohesin-binding protein that regulates the resolution of sister chromatid arm cohesion

Cohesin is a multiprotein complex that establishes sister chromatid cohesion from S phase until mitosis or meiosis. In vertebrates, sister chromatid cohesion is dissolved in a stepwise manner: most cohesins are removed from the chromosome arms via a process that requires polo-like kinase 1 (Plk1), aurora B and Wapl, whereas a minor amount of cohesin, found preferentially at the centromere, is cleaved by separase following its activation by the anaphase-promoting complex/cyclosome. Here, we report that our budding yeast two-hybrid assay identified hsSsu72 phosphatase as a Rad21-binding protein. Additional experiments revealed that Ssu72 directly interacts with Rad21 and SA2 in vitro and in vivo, and associates with sister chromatids in human cells. Interestingly, depletion or mutational inactivation of Ssu72 phosphatase activity caused the premature resolution of sister chromatid arm cohesion, whereas the overexpression of Ssu72 yielded high resistance to this resolution. Interestingly, it appears that Ssu72 regulates the cohesion of chromosome arms but not centromeres, and acts by counteracting the phosphorylation of SA2. Thus, our study provides important new evidence, suggesting that Ssu72 is a novel cohesin-binding protein capable of regulating cohesion between sister chromatid arms.

p53 Activation in Response to Mitotic Spindle Damage Requires Signaling via BubR1-Mediated Phosphorylation

The mitotic spindle checkpoint plays a crucial role in regulating accurate chromosome segregation and preventing the adaptation of multiploid progeny cells. Recent reports have indicated that the induction of p53 by mitotic checkpoint activation is essential for protecting cells from abnormal chromosome ploidization caused by mitotic failure. However, although studies have shown that p53 deficiencies arrest mitosis, compromise apoptosis, and may cause profound aneuploidy, the molecular mechanisms leading to p53 induction following mitotic checkpoint activation remain unknown. Here, we show that the BubR1 mitotic checkpoint kinase interacts with p53 both in vitro and in vivo, with higher levels of interaction in mitotic cells. This interaction contributes to p53 phosphorylation. Silencing of BubR1 expression reduces the phosphorylation and stability of p53, whereas exogenous introduction of BubR1 proteins into BubR1-depleted cells recovers p53 stability. In addition, inhibition of BubR1 expression in the presence of a microtubule inhibitor accelerates chromosomal instability and polyploidy in p53-null cells. These results collectively suggest that p53 activation in response to mitotic spindle damage requires signaling via BubR1-mediated phosphorylation.

Transcriptional Abnormality of the hsMAD2 Mitotic Checkpoint Gene Is a Potential Link to Hepatocellular Carcinogenesis

MAD2 is localized to kinetochores of unaligned chromosomes, where it inactivates the anaphase-promoting complex/cyclosome, thus contributing to the production of a diffusible anaphase inhibitory signal. Disruption of MAD2 expression leads to defects in the mitotic checkpoint, chromosome missegregation, and tumorigenesis. However, the mechanism by which deregulation and/or abnormality of hsMAD2 expression remains to be elucidated. Here, we clone and analyze a approximately 0.5 kb fragment upstream of hsMAD2 and show that this fragment acts as a strong promoter. Transcriptional dysfunction of hsMAD2 is frequently observed in hepatocellular carcinoma cells, and down-regulation of hsMAD2 protein expression is correlated with transcriptional silencing of the hsMAD2 promoter by hypermethylation. These results imply a relationship between transcriptional abnormality of this mitotic checkpoint gene and mitotic abnormality in human cancers.

WD repeat-containing mitotic checkpoint proteins act as transcriptional repressors during interphase

WD repeats are implicated in protein-protein interactions and regulate a wide variety of cellular functions, including chromatin remodeling and transcription. The WD repeats of the Bub3 and Cdc20 kinetochore proteins are important for the physical interactions of these proteins with Mad2 and BubR1 to yield a kinetochore protein complex capable of delaying anaphase by inhibiting ubiquitin ligation via the anaphase-promoting complex/cyclosome. Here, we show that Bub3 and Cdc20 form a complex with histone deacetylases; this interaction appears to confer transcriptional repressor activity in a heterologous DNA-binding context. In addition, inhibition of Bub3 and Cdc20 expression significantly impairs interphase cell cycle. These results indicate that Bub3 and Cdc20 play additional roles in the integration of cell cycle arrest as transcriptional repressors.