Liaisons between survivin and Plk1 during cell division and cell death

Toosendanin promotes prostate cancer cell apoptosis, ferroptosis and M1 polarization via USP39-mediated PLK1 deubiquitination

Toosendanin (TSN) can inhibit the malignant process of many cancers, and has the potential to be developed as an anti-tumor drug. However, the role and mechanism of TSN in prostate cancer (PCa) progression remain unclear. PCa cells (DU145 and LNCaP) were treated with TSN. Cell viability was detected by cell counting kit 8 assay. Cell proliferation, apoptosis and metastasis were assessed by colony formation assay, flow cytometry and transwell assay. Cell ferroptosis was evaluated by examining Fe2+, MDA and lipid-ROS levels. M1 polarization markers were analyzed by flow cytometry. Immunohistochemical staining, quantitative real-time PCR and western blot were used to detect ubiquitin-specific protease 39 (USP39) and polo-like kinase 1 (PLK1) expression. Cycloheximide treatment, Co-IP assay and ubiquitination assay were performed to confirm the regulation of USP39 on PLK1. In vivo experiments were employed to determine the effect of TSN and USP39 on PCa tumor growth. TSN treatment suppressed PCa cell proliferation, cell cycle, migration, and invasion, while enhanced apoptosis, ferroptosis, and M1 polarization. USP39 was upregulated in PCa tissues and cells, and its protein expression was reduced by TSN. USP39 overexpression reversed the regulation of TSN on PCa cell functions. PLK1 had elevated expression in PCa, and USP39 stabilized its protein expression by deubiquitination. USP39 knockdown inhibited PCa cell behaviors, and its regulation was abolished by PLK1 overexpression. Meanwhile, TSN reduced PCa tumor growth by regulating USP39/PLK1. TSN played anti-tumor role in PCa, which promoted PCa cell apoptosis, ferroptosis, and M1 polarization by inhibiting USP39/PLK1 axis.

AKT Inhibition Sensitizes to Polo-Like Kinase 1 Inhibitor Onvansertib in Prostate Cancer

Polo-like kinase 1 (PLK1) inhibitors have had limited antitumor efficacy as single agents, and focus of current efforts is on combination therapies. We initially confirmed that the PLK1-specific inhibitor onvansertib (ONV) could enhance responses to a PARP inhibitor (olaparib) in prostate cancer xenografts. To identify more effective combinations, we screened a library of bioactive compounds for efficacy in combination with ONV in LNCaP prostate cancer cells, which identified a series of compounds including multiple AKT inhibitors. We confirmed in vitro synergy between ONV and the AKT inhibitor ipatasertib (IPA) and found that the combination increased apoptosis. Mechanistic studies showed that ONV increased expression of the antiapoptotic protein SURVIVIN and that this was mitigated by IPA. Studies in three PTEN-deficient prostate cancer xenograft models showed that cotreatment with IPA and ONV led to significant tumor growth inhibition compared with monotherapies. Together, these in vitro and in vivo studies demonstrate that the efficacy of PLK1 antagonists can be enhanced by PARP or AKT inhibition and support further development of these combination therapies.

Survivin as a Therapeutic Target for the Treatment of Human Cancer

Survivin was initially identified as a member of the inhibitor apoptosis (IAP) protein family and has been shown to play a critical role in the regulation of apoptosis. More recent studies showed that survivin is a component of the chromosome passenger complex and acts as an essential mediator of mitotic progression. Other potential functions of survivin, such as mitochondrial function and autophagy, have also been proposed. Survivin has emerged as an attractive target for cancer therapy because its overexpression has been found in most human cancers and is frequently associated with chemotherapy resistance, recurrence, and poor survival rates in cancer patients. In this review, we discuss our current understanding of how survivin mediates various aspects of malignant transformation and drug resistance, as well as the efforts that have been made to develop therapeutics targeting survivin for the treatment of cancer.

Targeting survivin for cancer therapy: Strategies, small molecule inhibitors and vaccine based therapeutics in development

Survivin is a member of the family of inhibitors of apoptosis proteins (IAPs). It is involved in the normal mitotic process and acts as an anti-apoptotic molecule. While terminally differentiated normal tissues lack survivin, several human malignancies have significant protein levels. Resistance to chemotherapy and radiation in tumor cells is associated with survivin expression. Decreased tumor development, apoptosis, and increased sensitivity to chemotherapy and radiation are all effects of downregulating survivin expression or activity. As a prospective cancer treatment, small molecules targeting the transcription and translation of survivin and molecules that can directly bind with the survivin are being explored both in pre-clinical and clinics. Pre-clinical investigations have found and demonstrated the effectiveness of several small-molecule survivin inhibitors. Unfortunately, these inhibitors have also been shown to have off-target effects, which could limit their clinical utility. In addition to small molecules, several survivin peptide vaccines are currently under development. These vaccines are designed to elicit a cytotoxic T-cell response against survivin, which could lead to the destruction of tumor cells expressing survivin. Some survivin-based vaccines are advancing through Phase II clinical studies. Overall, survivin is a promising cancer drug target. However, challenges still need to be addressed before the survivin targeted therapies can be widely used in the clinics.

Combined Inhibition of UBE2C and PLK1 Reduce Cell Proliferation and Arrest Cell Cycle by Affecting ACLY in Pan-Cancer

Various studies have shown that the cell-cycle-related regulatory proteins UBE2C, PLK1, and BIRC5 promote cell proliferation and migration in different types of cancer. However, there is a lack of in-depth and systematic research on the mechanism of these three as therapeutic targets. In this study, we found a positive correlation between the expression of UBE2C and PLK1/BIRC5 in the Cancer Genome Atlas (TCGA) database, revealing a potential combination therapy candidate for pan-cancer. Quantitative real-time PCR (qRT-PCR), Western blotting (WB), cell phenotype detection, and RNA-seq techniques were used to evidence the effectiveness of the combination candidate. We found that combined interference of UBE2C with PLK1 and UBE2C with BIRC5 affected metabolic pathways by significantly downregulating the mRNA expression of IDH1 and ACLY, which was related to the synthesis of acetyl-CoA. By combining the PLK1 inhibitor volasertib and the ACLY inhibitor bempedoic acid, it showed a higher synergistic inhibition of cell viability and higher synergy scores in seven cell lines, compared with those of other combination treatments. Our study reveals the potential mechanisms through which cell-cycle-related genes regulate metabolism and proposes a potential combined targeted therapy for patients with higher PLK1 and ACLY expression in pan-cancer.

The Involvement of Ubiquitination and SUMOylation in Retroviruses Infection and Latency

Retroviruses, especially the pathogenic human immunodeficiency virus type 1 (HIV-1), have severely threatened human health for decades. Retroviruses can form stable latent reservoirs via retroviral DNA integration into the host genome, and then be temporarily transcriptional silencing in infected cells, which makes retroviral infection incurable. Although many cellular restriction factors interfere with various steps of the life cycle of retroviruses and the formation of viral latency, viruses can utilize viral proteins or hijack cellular factors to evade intracellular immunity. Many post-translational modifications play key roles in the cross-talking between the cellular and viral proteins, which has greatly determined the fate of retroviral infection. Here, we reviewed recent advances in the regulation of ubiquitination and SUMOylation in the infection and latency of retroviruses, focusing on both host defense- and virus counterattack-related ubiquitination and SUMOylation system. We also summarized the development of ubiquitination- and SUMOylation-targeted anti-retroviral drugs and discussed their therapeutic potential. Manipulating ubiquitination or SUMOylation pathways by targeted drugs could be a promising strategy to achieve a "sterilizing cure" or "functional cure" of retroviral infection.

PLK1 and AURKB phosphorylate survivin differentially to affect proliferation in racially distinct triple-negative breast cancer

Protein diversity due to alternative mRNA splicing or post-translational modifications (PTMs) plays a vital role in various cellular functions. The mitotic kinases polo-like kinase 1 (PLK1) and Aurora B (AURKB) phosphorylate survivin, an inhibitor of apoptosis (IAP) family member, thereby regulating cell proliferation. PLK1, AURKB, and survivin are overexpressed in triple-negative breast cancer (TNBC), an aggressive breast cancer subtype. TNBC is associated with high proliferative capacity, high rates of distant metastasis, and treatment resistance. The proliferation-promoting protein survivin and its activating kinases, PLK1 and AURKB, are overexpressed in TNBC. In this study, we investigated the role of survivin phosphorylation in racial disparities in TNBC cell proliferation. Analysis of TCGA TNBC data revealed higher expression levels of PLK1 (P = 0.026) and AURKB (P = 0.045) in African Americans (AAs; n = 41) than in European Americans (EAs; n = 86). In contrast, no significant racial differences in survivin mRNA or protein levels were observed. AA TNBC cells exhibited higher p-survivin levels than EA TNBC cells. Survivin silencing using small interfering RNAs significantly attenuated cell proliferation and cell cycle progression in AA TNBC cells, but not in EA TNBC cells. In addition, PLK1 and AURKB inhibition with volasertib and barasertib significantly inhibited the growth of AA TNBC xenografts, but not of EA TNBC tumors. These data suggest that inhibition of PLK1 and AURKB suppresses cell proliferation and tumor growth, specifically in AA TNBC. These findings suggest that targeting survivin phosphorylation may be a viable therapeutic option for AA patients with TNBC.

Survivin in Breast Cancer: A Review

Breast cancer is the most frequently diagnosed cancer in women and ranks second among causes for cancer-related death in women. Gene technology has led to the recognition that breast cancer is a heterogeneous disease composed of different biological subtypes, and genetic profiling enables the response to chemotherapy to be predicted. This fact emphasizes the importance of selecting sensitive diagnostic and prognostic markers in the early disease stage and more efficient targeted treatments for this disease. One such prognostic marker appears to be survivin. Many studies have shown that survivin is strongly expressed in different types of cancers. Its overexpression has been demonstrated in breast cancer, and high activity of the survivin gene has been associated with a poor prognosis and worse survival rates.

Recent Progress on the Localization of PLK1 to the Kinetochore and Its Role in Mitosis

The accurate distribution of the replicated genome during cell division is essential for cell survival and healthy organismal development. Errors in this process have catastrophic consequences, such as birth defects and aneuploidy, a hallmark of cancer cells. PLK1 is one of the master kinases in mitosis and has multiple functions, including mitotic entry, chromosome segregation, spindle assembly checkpoint, and cytokinesis. To dissect the role of PLK1 in mitosis, it is important to understand how PLK1 localizes in the specific region in cells. PLK1 localizes at the kinetochore and is essential in spindle assembly checkpoint and chromosome segregation. However, how PLK1 localizes at the kinetochore remains elusive. Here, we review the recent literature on the kinetochore recruitment mechanisms of PLK1 and its roles in spindle assembly checkpoint and attachment between kinetochores and spindle microtubules. Together, this review provides an overview of how the local distribution of PLK1 could regulate major pathways in mitosis.

BIRC5 is a prognostic biomarker associated with tumor immune cell infiltration

BIRC5 is an immune-related gene that inhibits apoptosis and promotes cell proliferation. It is highly expressed in most tumors and leads to poor prognosis in cancer patients. This study aimed to analyze the relationship between the expression level of BIRC5 in different tumors and patient prognosis, clinical parameters, and its role in tumor immunity. Genes co-expressed with BIRC5 were analyzed, and functional enrichment analysis was performed. The relationship between BIRC5 expression and the immune and stromal scores of tumors in pan-cancer patients and the infiltration level of 22 tumor-infiltrating lymphocytes (TILs) was analyzed. The correlation of BIRC5 with immune checkpoints was conducted. Functional enrichment analysis showed that genes co-expressed with BIRC5 were significantly associated with the mitotic cell cycle, APC/C-mediated degradation of cell cycle proteins, mitotic metaphase, and anaphase pathways. Besides, the high expression of BIRC5 was significantly correlated with the expression levels of various DNA methyltransferases, indicating that BIRC5 regulates DNA methylation. We also found that BIRC5 was significantly correlated with multiple immune cells infiltrates in a variety of tumors. This study lays the foundation for future research on how BIRC5 modulates tumor immune cells, which may lead to the development of more effective targeted tumor immunotherapies.

Dual targeting of Polo-like kinase 1 and baculoviral inhibitor of apoptosis repeat-containing 5 in TP53-mutated hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC), often diagnosed at advanced stages without curative therapies, is the fifth most common malignant cancer and the second leading cause of cancer-related mortality. Polo-like kinase 1 (PLK1) is activated in the late G2 phase of the cell cycle and is required for entry to mitosis. Interestingly, PLK1 is overexpressed in many HCC patients and is highly associated with poor clinical outcome. Baculoviral inhibitor of apoptosis repeat-containing 5 (BIRC5) is also highly overexpressed in HCC and plays key roles in this malignancy.

AIM

To determine the expression patterns of PLK1 and BIRC5, as well as their correlation with p53 mutation status and patient clinical outcome.

METHODS

The expression patterns of PLK1 and BIRC5, and their correlation with p53 mutation status or patient clinical outcome were analyzed using a TCGA HCC dataset. Cell viability, cell apoptosis, and cell cycle arrest assays were conducted to investigate the efficacy of the PLK1 inhibitors volasertib and GSK461364 and the BIRC5 inhibitor YM155, alone or in combination. The in vivo efficacy of volasertib and YM155, alone or in combination, was assessed in p53-mutated Huh7-derived xenograft models in immune-deficient NSIG mice.

RESULTS

Our bioinformatics analysis using a TCGA HCC dataset revealed that PLK1 and BIRC5 were overexpressed in the same patient subset and their expression was highly correlated. The overexpression of both PLK1 and BIRC5 was more frequently detected in HCC with p53 mutations. High PLK1 or BIRC5 expression significantly correlated with poor clinical outcome. PLK1 inhibitors (volasertib and GSK461364) or a BIRC5 inhibitor (YM155) selectively targeted Huh7 cells with mutated p53, but not HepG2 cells with wild-type p53. The combination treatment of volasertib and YM155 synergistically inhibited the viability of Huh7 cells via apoptotic pathway. The efficacy of volasertib and YM155, alone or in combination, was validated in vivo in a Huh7-derived xenograft model.

CONCLUSION

PLK1 and BIRC5 are highly co-expressed in p53-mutated HCC and inhibition of both PLK1 and BIRC5 synergistically compromises the viability of p53-mutated HCC cells in vitro and in vivo.

Inhibition of Polo-like kinase 1 (PLK1) facilitates the elimination of HIV-1 viral reservoirs in CD4+ T cells ex vivo

Although combination antiretroviral therapy is effective in controlling HIV-1 infection, latent HIV-1 proviruses cannot be eliminated. HIV-1 reactivation induced by the mere use of latency-reversing agents is insufficient to render death of reservoir cells, indicating that certain intrinsic survival mechanisms exist. We report that Polo-like kinase 1 (PLK1) plays a critical role in survival of CD4+ T cells that undergo HIV-1 reactivation from latency or de novo infection. PLK1 is elevated in both scenarios, which requires HIV-1 Nef. HIV-1 enhances PLK1 SUMOylation, causing its nuclear translocation and protein stabilization. Inhibition or knockdown of PLK1 markedly facilitates death of HIV-1-infected CD4+ T cells. Furthermore, PLK1 inhibitors strikingly reduce the size of HIV-1 latent reservoirs in primary CD4+ T cells. Our findings demonstrate that HIV-1 infection hijacks PLK1 to prevent cell death induced by viral cytopathic effects, and that PLK1 is a promising target for chemical "killing" of HIV-1 reservoir cells.

A direct interaction between survivin and myosin II is required for cytokinesis

An acto-myosin contractile ring, which forms after anaphase onset and is highly regulated in time and space, mediates cytokinesis, the final step of mitosis. The chromosomal passenger complex (CPC), composed of Aurora-B kinase, INCENP, borealin and survivin (also known as BIRC5), regulates various processes during mitosis, including cytokinesis. It is not understood, however, how CPC regulates cytokinesis. We show that survivin binds to non-muscle myosin II (NMII), regulating its filament assembly. Survivin and NMII interact mainly in telophase, and Cdk1 regulates their interaction in a mitotic-phase-specific manner, revealing the mechanism for the specific timing of survivin-NMII interaction during mitosis. The survivin-NMII interaction is indispensable for cytokinesis, and its disruption leads to multiple mitotic defects. We further show that only the survivin homodimer binds to NMII, attesting to the biological importance for survivin homodimerization. We suggest a novel function for survivin in regulating the spatio-temporal formation of the acto-NMII contractile ring during cytokinesis and we elucidate the role of Cdk1 in regulating this process.This article has an associated First Person interview with the first author of the paper.

Correlation between SOX2 and Survivin clinical features in patients with salivary adenoid cystic carcinoma

OBJECTIVE

In this study, expression of cancer stem cells (CSCs)-related factor-Sex-determining region of Y chromosome-related high-mobility-group box 2 (SOX2) and anti-apoptotic specific factor- Survivin in salivary adenoid cystic carcinoma (SACC) was detected to provide important clues for effective SACC prevention and treatment by combining clinical pathological parameters analysis.

METHODS

Paraffin and fresh specimens were collected from SACC patients who underwent surgery at the Oral and Maxillofacial Surgery Department of Sichuan Academy of Medical Sciences & Sichuan Provincial People's Hospital. The experimental group was designed as SACC tissue, and the control group normal paracancerous normal gland tissue. (1) SOX2 and Survivin expression were detected using immunohistochemistry and analyzed by comnining clinical pathological parameter analysis. (2) mRNA and protein expression levels of SOX2 and Survivin were detected using RT-PCR, Western Blot.

RESULTS

1. Immunohistochemistry: (1) SOX2 was mainly expressed on the nucleus. The SOX2 positive rate was 28.57% in clinical stage I-II, and 76.92% in stage III-IV. (2) Survivin was mainly expressed in the cytoplasm. The Survivin positive rate was 61.90% in clinical stage I-II, and 76.92% in stage III-IV. (3) There was a clear correlation between SOX2 and Survivin. 2. RT-PCR and Western Blot: The mRNA and protein expression levels of SOX2 and Survivin were significantly higher in the experimental group than in the control group (P < 0.01).

CONCLUSION

(1) The mRNA and protein expression level of SOX2 and Survivin was significantly higher in SACC tissues than in paracancerous normal salivary gland tissues, indicating that both of the two are tissue-specific and may become SACC oncogenes. (2) SOX2 and Survivin are significantly correlated in expression, which may coorinatively participate in SACC incidence and development.

Survivin at a glance

Survivin (also known as BIRC5) is an evolutionarily conserved eukaryotic protein that is essential for cell division and can inhibit cell death. Normally it is only expressed in actively proliferating cells, but is upregulated in most, if not all cancers; consequently, it has received significant attention as a potential oncotherapeutic target. In this Cell Science at a Glance article and accompanying poster, we summarise our knowledge of survivin 21 years on from its initial discovery. We describe the structure, expression and function of survivin, highlight its interactome and conclude by describing anti-survivin strategies being trialled.

Playing polo during mitosis: PLK1 takes the lead

Polo-like kinase 1 (PLK1), the prototypical member of the polo-like family of serine/threonine kinases, is a pivotal regulator of mitosis and cytokinesis in eukaryotes. Many layers of regulation have evolved to target PLK1 to different subcellular structures and to its various mitotic substrates in line with its numerous functions during mitosis. Collective work is starting to illuminate an important set of substrates for PLK1: the mitotic kinases that together ensure the fidelity of the cell division process. Amongst these, recent developments argue that PLK1 regulates the activity of the histone kinases Aurora B and Haspin to define centromere identity, of MPS1 to initiate spindle checkpoint signaling, and of BUB1 and its pseudokinase paralog BUBR1 to coordinate spindle checkpoint activation and inactivation. Here, we review the recent work describing the regulation of these kinases by PLK1. We highlight common themes throughout and argue that a major mitotic function of PLK1 is as a master regulator of these key kinases.

Nuclear survivin promoted by acetylation is associated with the aggressive phenotype of oral squamous cell carcinoma

Defects in apoptotic pathway contribute to development and progression of oral cancer. Survivin, a member of the inhibitors of apoptosis protein (IAP) family, is increased in many types of cancers. However, it is unclear whether increased survivin is associated with oral squamous cell carcinomas (OSCC), and what mechanisms may involve in. In this study, we examined survivin expression in OSCC compared with normal oral tissues via immunohistochemical staining. The results showed that, not only total survivin is increased in OSCCs, but also the subcellular location of survivin is changed in OSCCs compared with normal oral tissues. In most of normal oral tissues, survivin staining was either negative, or cytoplasmic positive/nuclear negative; whereas in most of OSCC tissues, survivin staining was nuclear positive. Statistic analysis indicates that nuclear survivin, rather than total or cytoplasmic one, correlates with tumor TNM stage and differentiation grade. Consistently, in vitro analysis showed that survivin is in cytoplasm in normal human oral kinotinocyte (HOK) cells; whereas it is in nucleus in OSCC HN6 cells. Importantly, treatment of HOK cells with HDAC inhibitor Trichostatin A (TSA) induces survivin acetylation and promotes its nuclear localization. Moreover, nuclear survivin in OSCC cells was acetylated at K129 in its C-terminal, suggesting that the acetylation is important for nuclear location of survivin. Our study demonstrates that it is nuclear survivin, rather than total or cytoplasmic one, associates with TNM stage and tumor grade of OSCC. Thus, we propose nuclear survivin as a prognostic marker for the progression of OSCC.

Decoding Polo-like kinase 1 signaling along the kinetochore-centromere axis

Protein kinase signaling along the kinetochore-centromere axis is crucial to assure mitotic fidelity, yet the details of its spatial coordination are obscure. Here, we examined how pools of human Polo-like kinase 1 (Plk1) within this axis control signaling events to elicit mitotic functions. To do this, we restricted active Plk1 to discrete subcompartments within the kinetochore-centromere axis using chemical genetics and decoded functional and phosphoproteomic signatures of each. We observe distinct phosphoproteomic and functional roles, suggesting that Plk1 exists and functions in discrete pools along this axis. Deep within the centromere, Plk1 operates to assure proper chromosome alignment and segregation. Thus, Plk1 at the kinetochore is a conglomerate of an observable bulk pool coupled with additional functional pools below the threshold of microscopic detection or resolution. Although complex, this multiplicity of locales provides an opportunity to decouple functional and phosphoproteomic signatures for a comprehensive understanding of Plk1's kinetochore functions.

Mitotic activity of survivin is regulated by acetylation at K129

Survivin is a cancer-associated protein regulated by multiple factors, including acetylation at K129 within its C-terminal α-helical tail. Acetylation of survivin is being pursued as a potential prognostic marker in breast cancer. This modification at K129 may cause nuclear accumulation of survivin in interphase cells; however, whether this affects its essential role during mitosis has not been addressed. We posited whether mimicking acetylation of survivin at K129 alters its activity during mitosis. Fluorescence microscopy and time-lapse imaging showed that, mutating this site to an alanine to act as a constitutive acetyl mimetic, K129A, causes defects in chromosome segregation and cytokinesis. As a non-acetylatable version, K129R, also has difficulty during mitotic exit, we conclude that cyclical acetylation and deacetylation is required for fully functional survivin during mitosis.

Volasertib suppresses tumor growth and potentiates the activity of cisplatin in cervical cancer

Volasertib (BI 6727), a highly selective and potent inhibitor of PLK1, has shown broad antitumor activities in the preclinical and clinical studies for the treatment of several types of cancers. However, the anticancer effect of volasertib on cervical cancer cells is still unknown. In the present study, we show that volasertib can markedly induce cell growth inhibition, cell cycle arrest at G2/M phase and apoptosis with the decreased protein expressions of PLK1 substrates survivin and wee1 in human cervical cancer cells. Furthermore, volasertib also enhances the intracellular reactive oxidative species (ROS) levels, and pretreated with ROS scavenger N-acety-L-cysteine totally blocks ROS generation but partly reverses volasertib-induced apoptosis. In addition, volasertib significantly potentiates the activity of cisplatin to inhibit the growth of cervical cancer in vitro and in vivo. In brief, volasertib suppresses tumor growth and potentiates the activity of cisplatin in cervical cancer, suggesting the combination of volasertib and cisplatin may be a promising strategy for the treatment of patients with cervical cancer.

The Aurora B Kinase in Chromosome Bi-Orientation and Spindle Checkpoint Signaling

Aurora B, a member of the Aurora family of serine/threonine protein kinases, is a key player in chromosome segregation. As part of a macromolecular complex known as the chromosome passenger complex, Aurora B concentrates early during mitosis in the proximity of centromeres and kinetochores, the sites of attachment of chromosomes to spindle microtubules. There, it contributes to a number of processes that impart fidelity to cell division, including kinetochore stabilization, kinetochore–microtubule attachment, and the regulation of a surveillance mechanism named the spindle assembly checkpoint. In the regulation of these processes, Aurora B is the fulcrum of a remarkably complex network of interactions that feed back on its localization and activation state. In this review, we discuss the multiple roles of Aurora B during mitosis, focusing in particular on its role at centromeres and kinetochores. Many details of the network of interactions at these locations remain poorly understood, and we focus here on several crucial outstanding questions.

Silencing of Survivin Expression Leads to Reduced Proliferation and Cell Cycle Arrest in Cancer Cells

Survivin is an anti-apoptotic gene that is overexpressed in most human tumors. RNA interference using short interfering RNA (siRNA) can be used to specifically inhibit survivin expression. Tumor cells were treated with a newly designed survivin siRNA, which was modified with 2′-OMe. Cellular survivin mRNA and protein levels were determined by real-time qRT-PCR and Western blot, respectively. Cell cycle and apoptosis were determined by flow cytometry. Cell proliferation was measured by MTT assay. Our data showed that the novel survivin-targeted siRNA could efficiently knockdown the expression of survivin and inhibit cell proliferation. Survivin mRNA was reduced by 95% after 48h treatment with 20nM siRNA. In addition, the siRNA could markedly arrest the cell cycle at the G2/M checkpoint and induce cellular apoptosis in a dose-dependent manner. The percentage of apoptotic cells reached 50% when treated with 40nM siRNA. In conclusion, we have identified a novel chemically modified siRNA against survivin that is highly efficient and delineated its mechanism of action, thus demonstrating a potential therapeutic role for this molecule in cancer. Further evaluation of this siRNA for therapeutic activity is warranted.

Polo-like kinase-1 triggers histone phosphorylation by Haspin in mitosis

Histone modifications coordinate the chromatin localization of key regulatory factors in mitosis. For example, mitotic phosphorylation of Histone H3 threonine-3 (H3T3ph) by Haspin creates a binding site for the chromosomal passenger complex (CPC). However, how these histone modifications are spatiotemporally controlled during the cell cycle is unclear. Here we show that Plk1 binds to Haspin in a Cdk1-phosphorylation-dependent manner. Reducing Plk1 activity decreases the phosphorylation of Haspin and inhibits H3T3ph, particularly in prophase, suggesting that Plk1 is required for initial activation of Haspin in early mitosis. These studies demonstrate that Plk1 can positively regulate CPC recruitment in mitosis.

[Obtaining of the affinity purified antibodies against survivin for the structure functional study of the protein]

Tumor-associated protein survivin is the bifunctional protein which can participate either in cell division regulation or in apoptosis inhibition depending on its localization and structure state. The aim of this work was to obtain monospecific antibodies useful for investigation of protein structure and functional features. Six affinity purified antibodies directed to different protein regions were obtained. The ability of antibodies obtained to detect survivin in tumor cells and breast cancer tissues was studied. It was shown that antibodies to (1-22) and (95-105) survivin fragments have the highest specific activity. In western-blot antibodies to (1-22) region predominantly binds with survivin-containing complex, which may be the survivin dimer as we suppose, while antibodies to (95-105) region detects only monomeric form of the protein. Breast cancer tissues study demonstrated that survivin monomer presents only in the tumor core tissues, while survivin-containing complex is expressed both in tumor core and tumor periphery tissues. It was shown that antibodies to (1-22) fragment detect predominantly nuclear survivin, which participates in mitosis regulation, while antibodies to (95-105) fragment gave nucleoplasm and cytoplasm staining at all stages of cell cycle. Thereby antibodies obtained are the useful tool for structure-functional study of survivin.

Survivin - biology and potential as a therapeutic target in oncology

Survivin is a member of the inhibitor-of-apoptosis proteins (IAPs) family; its overexpression has been widely demonstrated to occur in various types of cancer. Overexpression of survivin also correlates with tumor progression and induces anticancer drug resistance. Interestingly, recent studies reveal that survivin exhibits multiple pro-mitotic and anti-apoptotic functions; the differential functions of survivin seem to be caused by differential subcellular localization, phosphorylation, and acetylation of this molecule. In this review, the complex expression regulations and post-translational modifications of survivin are discussed. This review also discusses how recent discoveries improve our understanding of survivin biology and also create opportunities for developing differential-functioned survivin-targeted therapy. Databases such as PubMed, Scopus® (Elsevier, New York, NY, USA), and SciFinder® (CAS, Columbus, OH, USA) were used to search for literature in the preparation of this review.

Function of survivin in trophoblastic cells of the placenta

BACKGROUND

Preeclampsia is one of the leading causes of maternal and perinatal mortality and morbidity worldwide and its pathogenesis is not totally understood. As a member of the chromosomal passenger complex and an inhibitor of apoptosis, survivin is a well-characterized oncoprotein. Its roles in trophoblastic cells remain to be defined.

METHODS

The placental samples from 16 preeclampsia patients and 16 well-matched controls were included in this study. Real-time PCR, immunohistochemistry and Western blot analysis were carried out with placental tissues. Primary trophoblastic cells from term placentas were isolated for Western blot analysis. Cell proliferation, cell cycle analysis and immunofluorescence staining were performed in trophoblastic cell lines BeWo, JAR and HTR-8/SVneo.

RESULTS

The survivin gene is reduced but the protein amount is hardly changed in preeclamptic placentas, compared to control placentas. Upon stress, survivin in trophoblastic cells is phosphorylated on its residue serine 20 by protein kinase A and becomes stabilized, accompanied by increased heat shock protein 90. Depletion of survivin induces chromosome misalignment, abnormal centrosome integrity, and reduced localization and activity of Aurora B at the centromeres/kinetochores in trophoblastic metaphase cells.

CONCLUSIONS

Our data indicate that survivin plays pivotal roles in cell survival and proliferation of trophoblastic cells. Further investigations are required to define the function of survivin in each cell type of the placenta in the context of proliferation, differentiation, apoptosis, angiogenesis, migration and invasion.

Exploring the role of post-translational modifications on protein-protein interactions with survivin

Survivin is a member of the inhibitor of apoptosis protein (IAP) family with crucial roles in apoptosis and cell cycle regulation. Post-translational modifications (PTMs) have a ubiquitous role in the regulation of a diverse range of proteins' cellular functions and survivin is not an exception. Phosphorylation, acetylation and ubiquitination seem to regulate survivin anti-apoptotic and mitotic roles and also its nuclear localization. In the present review we explore the role of PTMs on protein-protein interactions focused on survivin to provide new insights into the functions and cell localization of this IAP in pathophysiological conditions, which might help the envisioning of novel targeted therapies for diseases characterized by impaired survivin activity. Protein-protein interaction analysis was performed with bioinformatics tools based on published data aiming to give an integrated perspective of this IAP's role in the cell.

The chromosomal passenger complex (CPC): from easy rider to the godfather of mitosis

Successful cell division requires the precise and timely coordination of chromosomal, cytoskeletal and membrane trafficking events. These processes are regulated by the competing actions of protein kinases and phosphatases. Aurora B is one of the most intensively studied kinases. In conjunction with inner centromere protein (INCENP), borealin (also known as Dasra) and survivin it forms the chromosomal passenger complex (CPC). This complex targets to different locations at differing times during mitosis, where it regulates key mitotic events: correction of chromosome-microtubule attachment errors; activation of the spindle assembly checkpoint; and construction and regulation of the contractile apparatus that drives cytokinesis. Our growing understanding of the CPC has seen it develop from a mere passenger riding on the chromosomes to one of the main controllers of mitosis.

Digitoxin and its analogs as novel cancer therapeutics

A growing body of evidence indicates that digitoxin cardiac glycoside is a promising anticancer agent when used at therapeutic concentrations. Digitoxin has a prolonged half-life and a well-established clinical profile. New scientific avenues have shown that manipulating the chemical structure of the saccharide moiety of digitoxin leads to synthetic analogs with increased cytotoxic activity. However, the anticancer mechanism of digitoxin or synthetic analogs is still subject to study while concerns about digitoxin's cardiotoxicity preclude its clinical application in cancer therapeutics. This review focuses on digitoxin and its analogs, and their cytotoxicity against cancer cells. Moreover, a new perspective on the pharmacological aspects of digitoxin and its analogs is provided to emphasize new research directions for developing potent chemotherapeutic drugs.

Threonine 48 in the BIR domain of survivin is critical to its mitotic and anti-apoptotic activities and can be phosphorylated by CK2 in vitro

In this study we report that the protein kinase CK2 phosphorylates survivin specifically on threonine 48 (T48) within its BIR domain, and that T48 is critical to both the mitotic and anti-apoptotic roles of survivin. Interestingly, during mitosis T48 mutants localise normally, but are unable to support cell growth when endogenous survivin is removed by siRNA. In addition, while overexpression of survivin normally confers inhibition of TRAIL-mediated apoptosis, this protection is abolished by mutation of T48. Furthermore in interphase cells depletion of endogenous survivin causes redistribution of T48 mutants from the cytoplasm to the nucleus and treatment of cells expressing survivin-GFP with the CK2 inhibitor TBB phenocopies this nuclear redistribution. Finally, we show T48 mutants have increased affinity for borealin, and that this association and cell proliferation can be restored by introduction of a second mutation at T97. To our knowledge these data are the first to identify T48 as a key regulatory site on survivin, and CK2 as a mediator of its mitotic and anti-apoptotic functions.

Is survivin the potential Achilles' heel of cancer?

Survivin, the smallest member of the inhibitors of apoptosis proteins (IAPs), plays an important role in the control of apoptosis, cell division, and cell migration/metastasis. Survivin is expressed and required for normal fetal development but is then generally no longer present in most adult tissues. However, reexpression of survivin is observed in numerous human cancers where presence of the protein is associated with enhanced proliferation, metastasis, poor prognosis, and decreased patient survival. Given the relatively selective expression in cancer cells, but not in normal tissue (tumor-associated antigen), and its importance in tumor cell biology, survivin has emerged as an attractive target for cancer treatment. Here, we discuss some aspects of survivin biology by focusing on why the protein appears to be so important for cancer cells and then discuss strategies that harness this dependence to eradicate tumors and situate survivin as a potential Achilles' heel of cancer.

Survivin and IAP proteins in cell-death mechanisms

From the realization that cell number homoeostasis is fundamental to the biology of all metazoans, and that deregulation of this process leads to human diseases, enormous interest has been devoted over the last two decades to map the requirements of cell death and cell survival. This effort has led to tangible progress, and we can now chart with reasonable accuracy complex signalling circuitries controlling cell-fate decisions. Some of this knowledge has translated into novel therapeutics, and the outcome of these strategies, especially in cancer, is eagerly awaited. However, the function of cell-death modifiers have considerably broadened over the last few years, and these molecules are increasingly recognized as arbiters of cellular homoeostasis, from cell division, to intracellular signalling to cellular adaptation. This panoply of functions is best exemplified by members of the IAP (inhibitor of apoptosis) gene family, molecules originally narrowly defined as endogenous caspase inhibitors, but now firmly positioned at the crossroads of multiple normal and transformed cellular responses.