Low molecular weight cyclin E overexpression shortens mitosis, leading to chromosome missegregation and centrosome amplification

AURKB promotes colorectal cancer progression by triggering the phosphorylation of histone H3 at serine 10 to activate CCNE1 expression

Aurora kinase B (AURKB) initiates the phosphorylation of serine 10 on histone H3 (pH3S10), a crucial process for chromosome condensation and cytokinesis in mammalian mitosis. Nonetheless, the precise mechanisms through which AURKB regulates the cell cycle and contributes to tumorigenesis as an oncogenic factor in colorectal cancer (CRC) remain unclear. Here, we report that AURKB was highly expressed and positively correlated with Ki-67 expression in CRC. The abundant expression of AURKB promotes the growth of CRC cells and xenograft tumors in animal model. AURKB knockdown substantially suppressed CRC proliferation and triggered cell cycle arrest in G2/M phase. Interestingly, cyclin E1 (CCNE1) was discovered as a direct downstream target of AURKB and functioned synergistically with AURKB to promote CRC cell proliferation. Mechanically, AURKB activated CCNE1 expression by triggering pH3S10 in the promoter region of CCNE1. Furthermore, it was showed that the inhibitor specific for AURKB (AZD1152) can suppress CCNE1 expression in CRC cells and inhibit tumor cell growth. To conclude, this research demonstrates that AURKB accelerated the tumorigenesis of CRC through its potential to epigenetically activate CCNE1 expression, suggesting AURKB as a promising therapeutic target in CRC.

Small-molecule inhibition of kinesin KIF18A reveals a mitotic vulnerability enriched in chromosomally unstable cancers

Chromosomal instability (CIN) is a hallmark of cancer, caused by persistent errors in chromosome segregation during mitosis. Aggressive cancers like high-grade serous ovarian cancer (HGSOC) and triple-negative breast cancer (TNBC) have a high frequency of CIN and TP53 mutations. Here, we show that inhibitors of the KIF18A motor protein activate the mitotic checkpoint and selectively kill chromosomally unstable cancer cells. Sensitivity to KIF18A inhibition is enriched in TP53-mutant HGSOC and TNBC cell lines with CIN features, including in a subset of CCNE1-amplified, CDK4-CDK6-inhibitor-resistant and BRCA1-altered cell line models. Our KIF18A inhibitors have minimal detrimental effects on human bone marrow cells in culture, distinct from other anti-mitotic agents. In mice, inhibition of KIF18A leads to robust anti-cancer effects with tumor regression observed in human HGSOC and TNBC models at well-tolerated doses. Collectively, our results provide a rational therapeutic strategy for selective targeting of CIN cancers via KIF18A inhibition.

Targeting the DNA damage response beyond poly(ADP-ribose) polymerase inhibitors: novel agents and rational combinations

PURPOSE OF REVIEW

Poly(ADP-ribose) polymerase (PARP) inhibitors have transformed treatment paradigms in multiple cancer types defined by homologous recombination deficiency (HRD) and have become the archetypal example of synthetic lethal targeting within the DNA damage response (DDR). Despite this success, primary and acquired resistance to PARP inhibition inevitability threaten the efficacy and durability of response to these drugs. Beyond PARP inhibitors, recent advances in large-scale functional genomic screens have led to the identification of a steadily growing list of genetic dependencies across the DDR landscape. This has led to a wide array of novel synthetic lethal targets and corresponding inhibitors, which hold promise to widen the application of DDR inhibitors beyond HRD and potentially address PARP inhibitor resistance.

RECENT FINDINGS

In this review, we describe key synthetic lethal interactions that have been identified across the DDR landscape, summarize the early phase clinical development of the most promising DDR inhibitors, and highlight relevant combinations of DDR inhibitors with chemotherapy and other novel cancer therapies, which are anticipated to make an impact in rationally selected patient populations.

SUMMARY

The DDR landscape holds multiple opportunities for synthetic lethal targeting with multiple novel DDR inhibitors being evaluated on early phase clinical trials. Key challenges remain in optimizing the therapeutic window of ATR and WEE1 inhibitors as monotherapy and in combination approaches.

CDK4/6 inhibitors: mechanisms of resistance and potential biomarkers of responsiveness in breast cancer

Hormone receptor (HR)-positive, HER2-negative tumors represent the most common form of metastatic breast cancer (MBC), and endocrine therapy has been the mainstay treatment for several decades. Recently, a novel drug class called CDK4/6 inhibitors in combination with endocrine therapy have remarkably improved the outcome of patients with HR-positive, HER2-negative MBC by targeting the cell cycle machinery and overcoming aspects of endocrine resistance. Several potential cell-cycle-specific and nonspecific mechanisms of resistance to CDK4/6 inhibitors have been reported in recent studies. This review discusses potential resistance mechanisms to CDK4/6 inhibitors, the use of biomarkers to guide treatment for HR-positive, HER2-negative MBC and possible approaches to overcome resistance to CDK4/6 inhibitors.

EGFR amplification and outcome in a randomised phase III trial of chemotherapy alone or chemotherapy plus panitumumab for advanced gastro-oesophageal cancers

OBJECTIVE

Epidermal growth factor receptor (EGFR) inhibition may be effective in biomarker-selected populations of advanced gastro-oesophageal adenocarcinoma (aGEA) patients. Here, we tested the association between outcome and EGFR copy number (CN) in pretreatment tissue and plasma cell-free DNA (cfDNA) of patients enrolled in a randomised first-line phase III clinical trial of chemotherapy or chemotherapy plus the anti-EGFR monoclonal antibody panitumumab in aGEA (NCT00824785).

DESIGN

EGFR CN by either fluorescence in situ hybridisation (n=114) or digital-droplet PCR in tissues (n=250) and plasma cfDNAs (n=354) was available for 474 (86%) patients in the intention-to-treat (ITT) population. Tissue and plasma low-pass whole-genome sequencing was used to screen for coamplifications in receptor tyrosine kinases. Interaction between chemotherapy and EGFR inhibitors was modelled in patient-derived organoids (PDOs) from aGEA patients.

RESULTS

EGFR amplification in cfDNA correlated with poor survival in the ITT population and similar trends were observed when the analysis was conducted in tissue and plasma by treatment arm. EGFR inhibition in combination with chemotherapy did not correlate with improved survival, even in patients with significant EGFR CN gains. Addition of anti-EGFR inhibitors to the chemotherapy agent epirubicin in PDOs, resulted in a paradoxical increase in viability and accelerated progression through the cell cycle, associated with p21 and cyclin B1 downregulation and cyclin E1 upregulation, selectively in organoids from EGFR-amplified aGEA.

CONCLUSION

EGFR CN can be accurately measured in tissue and liquid biopsies and may be used for the selection of aGEA patients. EGFR inhibitors may antagonise the antitumour effect of anthracyclines with important implications for the design of future combinatorial trials.

Centrosome amplification: a quantifiable cancer cell trait with prognostic value in solid malignancies

Numerical and/or structural centrosome amplification (CA) is a hallmark of cancers that is often associated with the aberrant tumor karyotypes and poor clinical outcomes. Mechanistically, CA compromises mitotic fidelity and leads to chromosome instability (CIN), which underlies tumor initiation and progression. Recent technological advances in microscopy and image analysis platforms have enabled better-than-ever detection and quantification of centrosomal aberrancies in cancer. Numerous studies have thenceforth correlated the presence and the degree of CA with indicators of poor prognosis such as higher tumor grade and ability to recur and metastasize. We have pioneered a novel semi-automated pipeline that integrates immunofluorescence confocal microscopy with digital image analysis to yield a quantitative centrosome amplification score (CAS), which is a summation of the severity and frequency of structural and numerical centrosome aberrations in tumor samples. Recent studies in breast cancer show that CA increases across the disease progression continuum, while normal breast tissue exhibited the lowest CA, followed by cancer-adjacent apparently normal, ductal carcinoma in situ and invasive tumors, which showed the highest CA. This finding strengthens the notion that CA could be evolutionarily favored and can promote tumor progression and metastasis. In this review, we discuss the prevalence, extent, and severity of CA in various solid cancer types, the utility of quantifying amplified centrosomes as an independent prognostic marker. We also highlight the clinical feasibility of a CA-based risk score for predicting recurrence, metastasis, and overall prognosis in patients with solid cancers.

Cyclin E expression is associated with high levels of replication stress in triple-negative breast cancer

Replication stress entails the improper progression of DNA replication. In cancer cells, including breast cancer cells, an important cause of replication stress is oncogene activation. Importantly, tumors with high levels of replication stress may have different clinical behavior, and high levels of replication stress appear to be a vulnerability of cancer cells, which may be therapeutically targeted by novel molecularly targeted agents. Unfortunately, data on replication stress is largely based on experimental models. Further investigation of replication stress in clinical samples is required to optimally implement novel therapeutics. To uncover the relation between oncogene expression, replication stress, and clinical features of breast cancer subgroups, we immunohistochemically analyzed the expression of a panel of oncogenes (Cyclin E, c-Myc, and Cdc25A,) and markers of replication stress (phospho-Ser33-RPA32 and γ-H2AX) in breast tumor tissues prior to treatment (n = 384). Triple-negative breast cancers (TNBCs) exhibited the highest levels of phospho-Ser33-RPA32 (P < 0.001 for all tests) and γ-H2AX (P < 0.05 for all tests). Moreover, expression levels of Cyclin E (P < 0.001 for all tests) and c-Myc (P < 0.001 for all tests) were highest in TNBCs. Expression of Cyclin E positively correlated with phospho-RPA32 (Spearman correlation r = 0.37, P < 0.001) and γ-H2AX (Spearman correlation r = 0.63, P < 0.001). Combined, these data indicate that, among breast cancers, replication stress is predominantly observed in TNBCs, and is associated with expression levels of Cyclin E. These results indicate that Cyclin E overexpression may be used as a biomarker for patient selection in the clinical evaluation of drugs that target the DNA replication stress response.

Cyclin E1 is a prognostic biomarker and potential therapeutic target in osteosarcoma

While amplified expressed cyclin E1 is a well-known tumorigenic factor and prognostic biomarker in several malignancies, its prognostic predictive potential and function in osteosarcoma is poorly understood. Here we reveal discrete expression pattern, correlation to clinicopathological characteristics and prognosis and overall function of cyclin E1 in osteosarcoma. Sixty-nine osteosarcoma patient tumor specimens were enrolled to construct a tissue microarray to evaluate cyclin E1 expression through immunohistochemical staining. Cyclin E1 expression in osteosarcoma cell lines and fresh tissues was assessed by Western blot. Cyclin E1 gene expression was evaluated using RNA sequencing data acquired from the public database. We correlated staining intensity to clinical characteristics. Cyclin E1 small interfering RNA was used to determine the effect of cyclin E1 silencing on osteosarcoma cell proliferation and chemotherapeutic sensitivity. Sixty-one percent of the osteosarcoma patient specimens in the tissue microarray had high cyclin E1 expression. Cyclin E1 gene was significantly highly expressed in osteosarcoma tissues and cell lines compared to normal tissues. The expression of cyclin E1 positively correlated with disease status, and inversely correlated to prognosis and response to neoadjuvant chemotherapy. The expression of cyclin E1 was an independent prognostic factor for osteosarcoma patients. In addition, silencing cyclin E1 expression in osteosarcoma cells significantly inhibited cell proliferation and increased sensitivity to chemotherapeutics. We conclude that cyclin E1 is overexpressed in osteosarcoma and is a promising biomarker for prognosis and chemotherapeutic response. We confirm aberrant cyclin E1 expression is a potent therapeutic target in osteosarcoma, and its selective inhibition is a rational treatment strategy for osteosarcoma.

Cyclin E2 Promotes Whole Genome Doubling in Breast Cancer

Genome doubling is an underlying cause of cancer cell aneuploidy and genomic instability, but few drivers have been identified for this process. Due to their physiological roles in the genome reduplication of normal cells, we hypothesised that the oncogenes cyclins E1 and E2 may be drivers of genome doubling in cancer. We show that both cyclin E1 (CCNE1) and cyclin E2 (CCNE2) mRNA are significantly associated with high genome ploidy in breast cancers. By live cell imaging and flow cytometry, we show that cyclin E2 overexpression promotes aberrant mitosis without causing mitotic slippage, and it increases ploidy with negative feedback on the replication licensing protein, Cdt1. We demonstrate that cyclin E2 localises with core preRC (pre-replication complex) proteins (MCM2, MCM7) on the chromatin of cancer cells. Low CCNE2 is associated with improved overall survival in breast cancers, and we demonstrate that low cyclin E2 protects from excess genome rereplication. This occurs regardless of p53 status, consistent with the association of high cyclin E2 with genome doubling in both p53 null/mutant and p53 wildtype cancers. In contrast, while cyclin E1 can localise to the preRC, its downregulation does not prevent rereplication, and overexpression promotes polyploidy via mitotic slippage. Thus, in breast cancer, cyclin E2 has a strong association with genome doubling, and likely contributes to highly proliferative and genomically unstable breast cancers.

CCNE1 Amplification as a Predictive Biomarker of Chemotherapy Resistance in Epithelial Ovarian Cancer

Ovarian cancer is the most-deadly gynecologic malignancy, with greater than 14,000 women expected to succumb to the disease this year in the United States alone. In the front-line setting, patients are treated with a platinum and taxane doublet. Although 40–60% of patients achieve complete clinical response to first-line chemotherapy, 25% are inherently platinum-resistant or refractory with a median overall survival of about one year. More than 80% of women afflicted with ovarian cancer will recur. Many attempts have been made to understand the mechanism of platinum and taxane based chemotherapy resistance. However, despite decades of research, few predictive markers of chemotherapy resistance have been identified. Here, we review the current understanding of one of the most common genetic alterations in epithelial ovarian cancer, CCNE1 (cyclin E1) amplification, and its role as a potential predictive marker of cytotoxic chemotherapy resistance. CCNE1 amplification has been identified as a primary oncogenic driver in a subset of high grade serous ovarian cancer that have an unmet clinical need. Understanding the interplay between cyclin E1 amplification and other common ovarian cancer genetic alterations provides the basis for chemotherapeutic resistance in CCNE1 amplified disease. Exploration of the effect of cyclin E1 amplification on the cellular machinery that causes dysregulated proliferation in cancer cells has allowed investigators to explore promising targeted therapies that provide the basis for emerging clinical trials.

Cul3 regulates cyclin E1 protein abundance via a degron located within the N-terminal region of cyclin E

Cyclin E and its binding partner Cdk2 control the G1/S transition in mammalian cells. Increased levels of cyclin E are found in some cancers. Additionally, proteolytic removal of the cyclin E N-terminus occurs in some cancers and is associated with increased cyclin E-Cdk2 activity and poor clinical prognosis. Cyclin E levels are tightly regulated and controlled in part through ubiquitin-mediated degradation initiated by one of two E3 ligases, Cul1 and Cul3. Cul1 ubiquitylates phosphorylated cyclin E, but the mechanism through which Cul3 ubiquitylates cyclin E is poorly understood. In experiments to ascertain how Cul3 mediates cyclin E destruction, we identified a degron on cyclin E that Cul3 targets for ubiquitylation. Recognition of the degron and binding of Cul3 does not require a BTB domain-containing adaptor protein. Additionally, this degron is lacking in N-terminally truncated cyclin E. Our results describe a mechanism whereby N-terminally truncated cyclin E can avoid the Cul3-mediated degradation pathway. This mechanism helps to explain the increased activity that is associated with the truncated cyclin E variants that occurs in some cancers.

Low-Molecular-Weight Cyclin E in Human Cancer: Cellular Consequences and Opportunities for Targeted Therapies

Cyclin E, a regulatory subunit of cyclin-dependent kinase 2 (CDK2), is central to the initiation of DNA replication at the G1/S checkpoint. Tight temporal control of cyclin E is essential to the coordination of cell-cycle processes and the maintenance of genome integrity. Overexpression of cyclin E in human tumors was first observed in the 1990s and led to the identification of oncogenic roles for deregulated cyclin E in experimental models. A decade later, low-molecular-weight cyclin E (LMW-E) isoforms were observed in aggressive tumor subtypes. Compared with full-length cyclin E, LMW-E hyperactivates CDK2 through increased complex stability and resistance to the endogenous inhibitors p21CIP1 and p27KIP1 LMW-E is predominantly generated by neutrophil elastase-mediated proteolytic cleavage, which eliminates the N-terminal cyclin E nuclear localization signal and promotes cyclin E's accumulation in the cytoplasm. Compared with full-length cyclin E, the aberrant localization and unique stereochemistry of LMW-E dramatically alters the substrate specificity and selectivity of CDK2, increasing tumorigenicity in experimental models. Cytoplasmic LMW-E, which can be assessed by IHC, is prognostic of poor survival and predicts resistance to standard therapies in patients with cancer. These patients may benefit from therapeutic modalities targeting the altered biochemistry of LMW-E or its associated vulnerabilities. Cancer Res; 78(19); 5481-91. ©2018 AACR.

Cyclin E Overexpression Sensitizes Triple-Negative Breast Cancer to Wee1 Kinase Inhibition

PURPOSE

Poor prognosis in triple-negative breast cancer (TNBC) is due to an aggressive phenotype and lack of biomarker-driven targeted therapies. Overexpression of cyclin E and phosphorylated-CDK2 are correlated with poor survival in patients with TNBC, and the absence of CDK2 desensitizes cells to inhibition of Wee1 kinase, a key cell-cycle regulator. We hypothesize that cyclin E expression can predict response to therapies, which include the Wee1 kinase inhibitor, AZD1775.

EXPERIMENTAL DESIGN

Mono- and combination therapies with AZD1775 were evaluated in TNBC cell lines and multiple patient-derived xenograft (PDX) models with different cyclin E expression profiles. The mechanism(s) of cyclin E-mediated replicative stress were investigated following cyclin E induction or CRISPR/Cas9 knockout by a number of assays in multiple cell lines.

RESULTS

Cyclin E overexpression (i) is enriched in TNBCs with high recurrence rates, (ii) sensitizes TNBC cell lines and PDX models to AZD1775, (iii) leads to CDK2-dependent activation of DNA replication stress pathways, and (iv) increases Wee1 kinase activity. Moreover, treatment of cells with either CDK2 inhibitors or carboplatin leads to transient transcriptional induction of cyclin E (in cyclin E-low tumors) and result in DNA replicative stress. Such drug-mediated cyclin E induction in TNBC cells and PDX models sensitizes them to AZD1775 in a sequential treatment combination strategy.Conclusions: Cyclin E is a potential biomarker of response (i) for AZD1775 as monotherapy in cyclin E-high TNBC tumors and (ii) for sequential combination therapy with CDK2 inhibitor or carboplatin followed by AZD1775 in cyclin E-low TNBC tumors.

Does cyclin E and p57kıp2 expression have prognostic and survival value in colorectal adenocarcinoma?

INTRODUCTION

Colorectal cancer is still one of the main causes of cancer death in the world. There is a continous need for novel biomarkers for diagnose, treatment modalities and follow-up. Cyclin E and p57^KIP2 as the positive and negative regulators of cell cycle seem to be an important target for investigations.

MATERIALS AND METHODS

In a retrospective setting, primary colorectal adenocarcinoma cases examined in Mustafa Kemal University, School of Medicine, Pathology Department between 2008-2015 were reviewed. Immunohistochemical expressions of cyclin E and p57^KIP2 in 80 pairs of colorectal carcinoma and adjacent normal mucosal tissues were evaluated and the findings were compared with clinicopathological parameters and survival time.

RESULTS

There were no statistically significant difference between two groups both in cyclin E and p57^KIP2 stained tissues (P>0.05). There were 40 (50%) patients in high-expression group and 40 (50%) patients in low-expression group for cyclin E. p57^KIP2 was negative in 55 (68.75%) patients and positive in 25 (31.75%) patients. There were no statistically significant relation between p57^KIP2 and cyclin E expressions with clinicopathologic parameters defined as age, gender, lymphovascular invasion, perineural invasion, depth of invasion, nodal involvement, emergency in operation, perforation before operation and overall survival except that there was significant relation between p57^KIP2 expression and histological grade (P=0.012).

CONCLUSIONS

Immunohistochemical studies of cyclin E and p57^KIP2 should be performed with larger series of patients supported by more detailed technical research methods to be candidates as predictive markers for treatment modalities and prognostic factors.

Pathogenesis and heterogeneity of ovarian cancer

PURPOSE OF REVIEW

The most common type of ovarian cancer, high-grade serous ovarian carcinoma (HGSOC), was originally thought to develop from the ovarian surface epithelium. However, recent data suggest that the cells that undergo neoplastic transformation and give rise to the majority of HGSOC are from the fallopian tube. This development has impacted both translational research and clinical practice, revealing new opportunities for early detection, prevention, and treatment of ovarian cancer.

RECENT FINDINGS

Genomic studies indicate that approximately 50% of HGSOC are characterized by mutations in genes involved in the homologous recombination pathway of DNA repair, especially BRCA1 and BRCA2. Clinical trials have demonstrated successful treatment of homologous recombination-defective cancers with poly-ribose polymerase inhibitors through synthetic lethality. Recently, amplification of CCNE1 was found to be another major factor in HGSOC tumorigenesis, accounting for approximately 20% of all cases. Interestingly, amplification of CCNE1 and mutation of homologous recombination repair genes are mutually exclusive in HGSOC.

SUMMARY

The fallopian tube secretory cell is the cell of origin for the majority of ovarian cancers. Although it remains unclear what triggers neoplastic transformation of these cells, certain tumors exhibit loss of BRCA function or amplification of CCNE1. These alterations represent unique therapeutic opportunities in ovarian cancer.

Cyclin E overexpression as a biomarker for combination treatment strategies in inflammatory breast cancer

Inflammatory breast cancer (IBC) is a virulent form of breast cancer, and novel treatment strategies are urgently needed. Immunohistochemical analysis of tumors from women with a clinical diagnosis of IBC (n = 147) and those with non-IBC breast cancer (n = 2510) revealed that, whereas in non-IBC cases cytoplasmic cyclin E was highly correlated with poor prognosis (P < 0.001), in IBC cases both nuclear and cytoplasmic cyclin E were indicative of poor prognosis. These results underscored the utility of the cyclin E/CDK2 complex as a novel target for treatment. Because IBC cell lines were highly sensitive to the CDK2 inhibitors dinaciclib and meriolin 5, we developed a high-throughput survival assay (HTSA) to design novel sequential combination strategies based on the presence of cyclin E and CDK2. Using a 14-cell-line panel, we found that dinaciclib potentiated the activity of DNA-damaging chemotherapies treated in a sequence of dinaciclib followed by chemotherapy, whereas this was not true for paclitaxel. We also identified a signature of DNA repair–related genes that are downregulated by dinaciclib, suggesting that global DNA repair is inhibited and that prolonged DNA damage leads to apoptosis. Taken together, our findings argue that CDK2-targeted combinations may be viable strategies in IBC worthy of future clinical investigation.

Cytoplasmic Cyclin E Mediates Resistance to Aromatase Inhibitors in Breast Cancer

Purpose: Preoperative aromatase inhibitor (AI) therapy has demonstrated efficacy in hormone receptor (HR)-positive postmenopausal breast cancer. However, many patients have disease that is either intrinsically resistant to AIs or that responds initially but develops resistance after prolonged exposure. We have shown that patients with breast tumors expressing the deregulated forms of cyclin E [low molecular weight forms (LMW-E)] have poor overall survival. Herein, we hypothesize that LMW-E expression can identify HR-positive tumors that are unresponsive to neoadjuvant AI therapy due to the inability of AIs to induce a cytostatic effect.Experimental Design: LMW-E was examined in breast cancer specimens from 58 patients enrolled in the American College of Surgeons Oncology Group Z1031, a neoadjuvant AI clinical trial. The mechanisms of LMW-E-mediated resistance to AI were evaluated in vitro and in vivo using an inducible model system of cyclin E (full-length and LMW-E) in aromatase-overexpressing MCF7 cells.Results: Breast cancer recurrence-free interval was significantly worse in patients with LMW-E-positive tumors who received AI neoadjuvant therapy, compared with those with LMW-E negative tumors. Upon LMW-E induction, MCF7 xenografts were unresponsive to letrozole in vivo, resulting in increased tumor volume after treatment with AIs. LMW-E expression overcame cell-cycle inhibition by AIs in a CDK2/Rb-dependent manner, and inhibition of CDK2 by dinaciclib reversed LMW-E-mediated resistance, whereas treatment with palbociclib, a CDK4/6 inhibitor, did not.Conclusions: Collectively, these findings suggest that cell-cycle deregulation by LMW-E mediates resistance to AIs and a combination of CDK2 inhibitors and AIs may be an effective treatment in patients with HR-positive tumors that express LMW-E. Clin Cancer Res; 23(23); 7288-300. ©2017 AACR.

Neuropilin-1 mediates neutrophil elastase uptake and cross-presentation in breast cancer cells

Neutrophil elastase (NE) can be rapidly taken up by tumor cells that lack endogenous NE expression, including breast cancer, which results in cross-presentation of PR1, an NE-derived HLA-A2-restricted peptide that is an immunotherapy target in hematological and solid tumor malignancies. The mechanism of NE uptake, however, remains unknown. Using the mass spectrometry-based approach, we identify neuropilin-1 (NRP1) as a NE receptor that mediates uptake and PR1 cross-presentation in breast cancer cells. We demonstrated that soluble NE is a specific, high-affinity ligand for NRP1 with a calculated K_d of 38.7 nm Furthermore, we showed that NRP1 binds to the RRXR motif in NE. Notably, NRP1 knockdown with interfering RNA or CRISPR-cas9 system and blocking using anti-NRP1 antibody decreased NE uptake and, subsequently, susceptibility to lysis by PR1-specific cytotoxic T cells. Expression of NRP1 in NRP1-deficient cells was sufficient to induce NE uptake. Altogether, because NRP1 is broadly expressed in tumors, our findings suggest a role for this receptor in immunotherapy strategies that target cross-presented antigens.

CCNE1 amplification and centrosome number abnormality in serous tubal intraepithelial carcinoma: further evidence supporting its role as a precursor of ovarian high-grade serous carcinoma

Aberration in chromosomal structure characterizes almost all cancers and has profound biological significance in tumor development. It can be facilitated by various mechanisms including overexpression of cyclin E1 and centrosome amplification. As ovarian high-grade serous carcinoma has pronounced chromosomal instability, in this study we sought to determine whether increased copy number of CCNE1 which encodes cyclin E1 and centrosome amplification (>2 copies) occurs in its putative precursor, serous tubal intraepithelial carcinoma. We found CCNE1 copy number gain/amplification in 8 (22%) of 37 serous tubal intraepithelial carcinomas and 12 (28%) of 43 high-grade serous carcinomas. There was a correlation in CCNE1 copy number between serous tubal intraepithelial carcinoma and high-grade serous carcinoma in the same patients (P<0.001). There was no significant difference in the percentage of CCNE1 gain/amplification between serous tubal intraepithelial carcinoma and high-grade serous carcinoma (P=0.61). Centrosome amplification was recorded in only 5 (14%) of 37 serous tubal intraepithelial carcinomas, and in 10 (40%) of 25 high-grade serous carcinomas. The percentage of cells with centrosome amplification was higher in high-grade serous carcinoma than in serous tubal intraepithelial carcinoma (P<0.001). Induced expression of cyclin E1 increased the percentage of fallopian tube epithelial cells showing centrosome amplification. Our findings suggest that gain/amplification of CCNE1 copy number occurs early in tumor progression and precedes centrosome amplification. The more prevalent centrosome amplification in high-grade serous carcinoma than in serous tubal intraepithelial carcinoma supports the view that serous tubal intraepithelial carcinoma precedes the development of many high-grade serous carcinomas.

Gamma-actin is involved in regulating centrosome function and mitotic progression in cancer cells

Reorganization of the actin cytoskeleton during mitosis is crucial for regulating cell division. A functional role for γ-actin in mitotic arrest induced by the microtubule-targeted agent, paclitaxel, has recently been demonstrated. We hypothesized that γ-actin plays a role in mitosis. Herein, we investigated the effect of γ-actin in mitosis and demonstrated that γ-actin is important in the distribution of β-actin and formation of actin-rich retraction fibers during mitosis. The reduced ability of paclitaxel to induce mitotic arrest as a result of γ-actin depletion was replicated with a range of mitotic inhibitors, suggesting that γ-actin loss reduces the ability of broad classes of anti-mitotic agents to induce mitotic arrest. In addition, partial depletion of γ-actin enhanced centrosome amplification in cancer cells and caused a significant delay in prometaphase/metaphase. This prolonged prometaphase/metaphase arrest was due to mitotic defects such as uncongressed and missegregated chromosomes, and correlated with an increased presence of mitotic spindle abnormalities in the γ-actin depleted cells. Collectively, these results demonstrate a previously unknown role for γ-actin in regulating centrosome function, chromosome alignment and maintenance of mitotic spindle integrity.

Cytoplasmic Cyclin E and Phospho-Cyclin-Dependent Kinase 2 Are Biomarkers of Aggressive Breast Cancer

Cyclin E and its co-activator, phospho-cyclin-dependent kinase 2 (p-CDK2), regulate G1 to S phase transition and their deregulation induces oncogenesis. Immunohistochemical assessments of these proteins in cancer have been reported but were based only on their nuclear expression. However, the oncogenic forms of cyclin E (low molecular weight cyclin E or LMW-E) in complex with CDK2 are preferentially mislocalized to the cytoplasm. Here, we used separate nuclear and cytoplasmic scoring systems for both cyclin E and p-CDK2 expression to demonstrate altered cellular accumulation of these proteins using immunohistochemical analysis. We examined the specificity of different cyclin E antibodies and evaluated their concordance between immunohistochemical and Western blot analyses in a panel of 14 breast cell lines. Nuclear versus cytoplasmic staining of cyclin E readily differentiated full-length from LMW-E, respectively. We also evaluated the expression of cyclin E and p-CDK2 in 1676 breast carcinoma patients by immunohistochemistry. Cytoplasmic cyclin E correlated strongly with cytoplasmic p-CDK2 (P < 0.0001), high tumor grade, negative estrogen/progesterone receptor status, and human epidermal growth factor receptor 2 positivity (all P < 0.0001). In multivariable analysis, cytoplasmic cyclin E plus phosphorylated CDK2 (as one variable) predicted breast cancer recurrence-free and overall survival. These results suggest that cytoplasmic cyclin E and p-CDK2 can be readily detected with immunohistochemistry and used as clinical biomarkers for aggressive breast cancer.

Centrosome amplification induces high grade features and is prognostic of worse outcomes in breast cancer

Background

Centrosome amplification (CA) has been reported in nearly all types of human cancer and is associated with deleterious clinical factors such as higher grade and stage. However, previous reports have not shown how CA affects cellular differentiation and clinical outcomes in breast cancer.

Methods

We analyzed centrosomes by immunofluorescence and compared to ploidy and chromosomal instability (CIN) as assessed by 6-chromosome FISH in a cohort of 362 breast cancers with median clinical follow-up of 8.4 years. Centrosomes were recognized by immunofluorescence using antibodies for pericentriolar material (PCM; pericentrin) and centrioles (polyglutamylated tubulin). CA was experimentally induced in cell culture by overexpression of polo-like kinase 4 (PLK4).

Results

CA is associated with reduced all-cause and breast cancer-specific overall survival and recurrence-free survival. CA correlates strongly with high-risk subtypes (e.g. triple negative) and higher stage and grade, and the prognostic nature of CA can be explained largely by these factors. A strong correlation between CA and high tumor ploidy demonstrates that chromosome and centrosome doubling often occur in concert. CA is proposed to be a method of inducing CIN via aberrant mitotic cell divisions; consonant with this, we observed a strong correlation between CA and CIN in breast cancers. However, some CA tumors had low levels of CIN, indicating that protective mechanisms are at play, such as centrosome clustering during mitosis. Intriguingly, some high-risk tumors have more acentriolar centrosomes, suggesting PCM fragmentation as another mechanism of CA. In vitro induction of CA in two non-transformed human cell lines (MCF10A and RPE) demonstrated that CA induces a de-differentiated cellular state and features of high-grade malignancy, supporting the idea that CA intrinsically causes high-grade tumors.

Conclusions

CA is associated with deleterious clinical factors and outcomes in breast cancer. Cell doubling events are the most prevalent causes of CA in cancer, although PCM fragmentation may be a secondary cause. CA promotes high-risk breast cancer in part by inducing high-grade features. These findings highlight the importance of centrosome aberrations in the biology of human breast cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2083-x) contains supplementary material, which is available to authorized users.

Cyclin E amplification, over-expression, and relapse-free survival in HER-2-positive primary breast cancer

Cyclin E is a well-characterized cell cycle regulator and an amplified oncogene in breast cancer. Over-expression of cyclin E has generally been associated with poor survival. Recent studies have shown an interaction between HER-2 (ERBB2) and cyclin E, but the exact mechanism is unknown. Interestingly, cyclin E over-expression has been associated with trastuzumab resistance. We studied cyclin E over-expression, CCNE1 amplification, and relapse-free survival in HER-2-positive primary breast cancers treated with and without trastuzumab therapy. Formalin-fixed paraffin-embedded tissue samples from 202 HER-2-positive breast carcinomas were studied. Expression levels of cyclin E and proliferation marker Ki-67 were determined using immunohistochemistry. Chromogenic in situ hybridization (CISH) with a gene-specific bacterial artificial chromosome (BAC) probe was used to analyze presence of CCNE1 amplification. Majority of HER-2-positive breast carcinomas exhibited nuclear staining for cyclin E protein. Cyclin E was highly expressed (≥50 % cells) in 37 % of cases. Incidence of CCNE1 amplification (≥6 gene copies/cell or clusters) was 8 %. Cyclin E amplification and over-expression were strongly associated with each other, grade, hormone receptors, and Ki-67. Neither high cyclin E expression nor CCNE1 amplification was associated with relapse-free survival (RFS) irrespective of short-term (9-week regimen) adjuvant trastuzumab therapy. These results confirm cyclin E and HER-2 gene co-amplification in a fraction of HER-2-positive breast cancers. Cyclin E is frequently over-expressed but appears to have limited value as a prognostic or predictive factor in HER-2-positive breast cancer regardless of trastuzumab therapy.

Why (multi)targeting of cyclin-dependent kinases is a promising therapeutic option for hormone-positive breast cancer and beyond

Estrogens, via induction of their specific receptors (e.g., ER-α), regulate cell proliferation, differentiation and morphogenesis in mammary epithelium. Cell-cycle progression is driven by activation of complexes consisting of cyclin-dependent kinases (CDKs) and cyclins, which also modulate the activity of ER-α. Loss of control over the cell-cycle results in accelerated cell division and malignant transformation. Thus, a reciprocal relation exists between estrogen signaling and cell proliferation. Based on these findings, a new concept was developed to reduce ER-α activity and bring the cell cycle in transformed cells to heel. Prevention of ER-α activation and control over the deregulated cell cycle was achieved by supplementation with pharmacological CDK inhibitors alone or in combination with selective antiestrogens.

Cyclin E1 plays a key role in balancing between totipotency and differentiation in human embryonic cells

STUDY HYPOTHESIS

We aimed to investigate if Cyclin E1 (CCNE1) plays a role in human embryogenesis, in particular during the early developmental stages characterized by a short cell cycle.

STUDY FINDING

CCNE1 is expressed in plenipotent human embryonic cells and plays a critical role during hESC derivation via the naïve state and, potentially, normal embryo development.

WHAT IS KNOWN ALREADY

A short cell cycle due to a truncated G1 phase has been associated with the high developmental capacity of embryonic cells. CCNE1 is a critical G1/S transition regulator. CCNE1 overexpression can cause shortening of the cell cycle and it is constitutively expressed in mouse embryonic stem cells and cancer cells.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

We investigated expression of CCNE1 in human preimplantation embryo development and embryonic stem cells (hESC). Functional studies included CCNE1 overexpression in hESC and CCNE1 downregulation in the outgrowths formed by plated human blastocysts. Analysis was performed by immunocytochemistry and quantitative real-time PCR. Mann-Whitney statistical test was applied.

MAIN RESULTS AND THE ROLE OF CHANCE

The CCNE1 protein was ubiquitously and constitutively expressed in the plenipotent cells of the embryo from the 4-cell stage up to and including the full blastocyst. During blastocyst expansion, CCNE1 was downregulated in the trophectoderm (TE) cells. CCNE1 shortly co-localized with NANOG in the inner cell mass (ICM) of expanding blastocysts, mimicking the situation in naïve hESC. In the ICM of expanded blastocysts, which corresponds with primed hESC, CCNE1 defined a subpopulation of cells different from NANOG/POU5F1-expressing pluripotent epiblast (EPI) cells and GATA4/SOX17-expressing primitive endoderm (PrE) cells. This CCNE1-positive cell population was associated with visceral endoderm based on transthyretin expression and marked the third cell lineage within the ICM, besides EPI and PrE, which had never been described before. We also investigated the role of CCNE1 by plating expanded blastocysts for hESC derivation. As a result, all the cells including TE cells re-gained CCNE1 and, consequently, NANOG expression, resembling the phenotype of naïve hESC. The inhibition of CCNE1 expression with siRNA blocked proliferation and caused degeneration of those plated cells.

LIMITATIONS, REASONS FOR CAUTION

The study is based on a limited number of good-quality human embryos donated to research.

WIDER IMPLICATIONS OF THE FINDINGS

Our study sheds light on the processes underlying the high developmental potential of early human embryonic cells. The CCNE1-positive plenipotent cell type corresponds with a phenotype that enables early human embryos to recover after fragmentation, cryodamage or (single cell) biopsy on day 3 for preimplantation genetic diagnosis. Knowledge on the expression and function of genes responsible for this flexibility will help us to better understand the undifferentiated state in stem cell biology and might enable us to improve technologies in assisted reproduction.

LARGE SCALE DATA

NA STUDY FUNDING AND COMPETING INTERESTS: This research is supported by grants from the Fund for Scientific Research - Flanders (FWO-Vlaanderen), the Methusalem (METH) of the VUB and Scientific Research Fond Willy Gepts of UZ Brussel. There are no competing interests.

Dependence of Human Colorectal Cells Lacking the FBW7 Tumor Suppressor on the Spindle Assembly Checkpoint

FBW7 (F-box and WD repeat domain containing 7), also known as FBXW7 or hCDC4, is a tumor suppressor gene mutated in a broad spectrum of cancer cell types. As a component of the SCF E3 ubiquitin ligase, FBW7 is responsible for specifically recognizing phosphorylated substrates, many important for tumor progression, and targeting them for ubiquitin-mediated degradation. Although the role of FBW7 as a tumor suppressor is well established, less well studied is how FBW7-mutated cancer cells might be targeted for selective killing. To explore this further, we undertook a genome-wide RNAi screen using WT and FBW7 knockout colorectal cell lines and identified the spindle assembly checkpoint (SAC) protein BUBR1, as a candidate synthetic lethal target. We show here that asynchronous FBW7 knockout cells have increased levels of mitotic APC/C substrates and are sensitive to knockdown of not just BUBR1 but BUB1 and MPS1, other known SAC components, suggesting a dependence of these cells on the mitotic checkpoint. Consistent with this dependence, knockdown of BUBR1 in cells lacking FBW7 results in significant cell aneuploidy and increases in p53 levels. The FBW7 substrate cyclin E was necessary for the genetic interaction with BUBR1. In contrast, the establishment of this dependence on the SAC requires the deregulation of multiple substrates of FBW7. Our work suggests that FBW7 knockout cells are vulnerable in their dependence on the mitotic checkpoint and that this may be a good potential target to exploit in FBW7-mutated cancer cells.

PKCiota promotes ovarian tumor progression through deregulation of cyclin E

The high frequency of relapse of epithelial ovarian tumors treated with standard chemotherapy has highlighted the necessity to identify targeted therapies that can improve patient outcomes. The dynamic relationship between Cyclin E and PKCiota frequent overexpression in high-grade ovarian tumors poses a novel pathway for therapeutic investigation. We hypothesized that a PI3K dependent signaling pathway activating PKCiota perpetuates cyclin E deregulation during ovarian tumorigenesis. We observed a positive correlation between PKCiota and cyclin E in a panel of 19 ovarian cancer cell lines. Modulation of cyclin E had no effect on PKCiota knockdown/overexpression however PKCiota differentially regulated cyclin E expression. In the serous ovarian cancer cells (IGROV, OVCAR-3), shPKCiota decreased proliferation, caused a G1 arrest, and significantly prolonged overall survival in xenograft mouse models. In vitro shPKCiota decreased the ability of IGROV cells to grow under anchorage independent conditions and form aberrant acini, which was dependent upon Ad-cyclin E or Ad-LMW-E expression. RPPA analysis of PKCiota wild-type, catalytic active, dominant negative protein isoforms strengthened the association between phospho-PKCiota levels and PI3K pathway activation. Inhibitors of PI3K coordinately decreased phospho-PKCiota and Cyclin E protein levels. In conclusion, we have identified a PI3K/PKCiota/Cyclin E signaling pathway as a therapeutic target during ovarian tumorigenesis.

VR23: A Quinoline-Sulfonyl Hybrid Proteasome Inhibitor That Selectively Kills Cancer via Cyclin E-Mediated Centrosome Amplification

The proteasome is clinically validated as a target for cancer therapeutics. However, proteasome-inhibitory agents that are cancer selective have yet to be developed. In this study, we report the identification of a safe and effective proteasome inhibitor with selective anticancer properties. We screened a chemical library constructed using a hybrid approach that incorporated a 4-piperazinylquinoline scaffold and a sulfonyl phamarcophore. From this library, we identified 7-chloro-4-(4-(2,4-dinitrophenylsulfonyl)piperazin-1-yl)quinoline (VR23) as a small molecule that potently inhibited the activities of trypsin-like proteasomes (IC50 = 1 nmol/L), chymotrypsin-like proteasomes (IC50 = 50-100 nmol/L), and caspase-like proteasomes (IC50 = 3 μmol/L). Data from molecular docking and substrate competition assays established that the primary molecular target of VR23 was β2 of the 20S proteasome catalytic subunit. Notably, VR23 was structurally distinct from other known proteasome inhibitors and selectively killed cancer cells by apoptosis, with little effect on noncancerous cells. Mechanistic investigations showed that cancer cells exposed to VR23 underwent an abnormal centrosome amplification cycle caused by the accumulation of ubiquitinated cyclin E. In combinations with the clinically approved chymotrypsin-like proteasome inhibitor bortezomib, VR23 produced a synergistic effect in killing multiple myeloma cells, including those that were resistant to bortezomib. VR23 was effective in vivo in controlling multiple myelomas and metastatic breast cancer cells, in the latter case also enhancing the antitumor activity of paclitaxel while reducing its side effects. Overall, our results identify VR23 as a structurally novel proteasome inhibitor with desirable properties as an anticancer agent.

A PREVIOUSLY UNKNOWN UNIQUE CHALLENGE FOR INHIBITORS OF SYK ATP-BINDING SITE: ROLE OF SYK AS A CELL CYCLE CHECKPOINT REGULATOR

The identification of SYK as a molecular target in B-lineage leukemia/lymphoma cells prompted the development of SYK inhibitors as a new class of anti-cancer drug candidates. Here we report that induction of the SYK gene expression in human cells causes a significant down-regulation of evolutionarily conserved genes associated with mitosis and cell cycle progression providing unprecedented evidence that SYK is a master regulator of cell cycle regulatory checkpoint genes in human cells. We further show that SYK regulates the G₂ checkpoint by physically associating with and inhibiting the dual-specificity phosphatase CDC25C via phosphorylation of its S216 residue. SYK depletion by RNA interference or treatment with the chemical SYK inhibitor prevented nocodazole-treated human cell lines from activating the G₂ checkpoint via CDC25C S216-phosphorylation and resulted in polyploidy. Our study provides genetic and biochemical evidence that spleen tyrosine kinase (SYK) has a unique role in the activation of the G₂ checkpoint in both non-lymphohematopoietic and B-lineage lymphoid cells. This previously unknown role of SYK as a cell cycle checkpoint regulator represents an unforeseen and significant challenge for inhibitors of SYK ATP binding site.

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SYK is a cell cycle regulatory kinase that phosphorylates CDC25C at S216

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SYK is a master regulator of cell cycle regulatory checkpoint genes in human cells

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Inhibitors of SYK ATP binding site may increase the risk for secondary cancer

Cyclin E1 deregulation occurs early in secretory cell transformation to promote formation of fallopian tube-derived high-grade serous ovarian cancers

The fallopian tube is now generally considered the dominant site of origin for high-grade serous ovarian carcinoma. However, the molecular pathogenesis of fallopian tube-derived serous carcinomas is poorly understood and there are few experimental studies examining the transformation of human fallopian tube cells. Prompted by recent genomic analyses that identified cyclin E1 (CCNE1) gene amplification as a candidate oncogenic driver in high-grade serous ovarian carcinoma, we evaluated the functional role of cyclin E1 in serous carcinogenesis. Cyclin E1 was expressed in early- and late-stage human tumor samples. In primary human fallopian tube secretory epithelial cells, cyclin E1 expression imparted malignant characteristics to untransformed cells if p53 was compromised, promoting an accumulation of DNA damage and altered transcription of DNA damage response genes related to DNA replication stress. Together, our findings corroborate the hypothesis that cyclin E1 dysregulation acts to drive malignant transformation in fallopian tube secretory cells that are the site of origin of high-grade serous ovarian carcinomas.

Resistance to CDK2 inhibitors is associated with selection of polyploid cells in CCNE1-amplified ovarian cancer

PURPOSE

Amplification of cyclin E1 (CCNE1) is associated with poor outcome in breast, lung, and other solid cancers, and is the most prominent structural variant associated with primary treatment failure in high-grade serous ovarian cancer (HGSC). We have previously shown that CCNE1-amplified tumors show amplicon-dependent sensitivity to CCNE1 suppression. Here, we explore targeting CDK2 as a novel therapeutic strategy in CCNE1-amplified cancers and mechanisms of resistance.

EXPERIMENTAL DESIGN

We examined the effect of CDK2 suppression using RNA interference and small-molecule inhibitors in SK-OV-3, OVCAR-4, and OVCAR-3 ovarian cancer cell lines. To identify mechanisms of resistance, we derived multiple, independent resistant sublines of OVCAR-3 to CDK2 inhibitors. Resistant cells were extensively characterized by gene expression and copy number analysis, fluorescence-activated cell sorting profiling and conventional karyotyping. In addition, we explored the relationship between CCNE1 amplification and polyploidy using data from primary tumors.

RESULTS

We validate CDK2 as a therapeutic target in CCNE1-amplified cells by showing selective sensitivity to suppression, either by gene knockdown or using small-molecule inhibitors. In addition, we identified two resistance mechanisms, one involving upregulation of CDK2 and another novel mechanism involving selection of polyploid cells from the pretreatment tumor population. Our analysis of genomic data shows that polyploidy is a feature of cancer genomes with CCNE1 amplification.

CONCLUSIONS

These findings suggest that cyclinE1/CDK2 is an important therapeutic target in HGSC, but that resistance to CDK2 inhibitors may emerge due to upregulation of CDK2 target protein and through preexisting cellular polyploidy.

Genomic instability and colon carcinogenesis: from the perspective of genes

Colon cancer is the second most lethal cancer; approximately 600,000 people die of it annually in the world. Colon carcinogenesis generally follows a slow and stepwise process of accumulation of mutations under the influence of environmental and epigenetic factors. To adopt a personalized (tailored) cancer therapy approach and to improve current strategies for prevention, diagnosis, prognosis, and therapy overall, advanced understanding of molecular events associated with colon carcinogenesis is necessary. A contemporary approach that combines genetics, epigenomics, and signaling pathways has revealed many genetic/genomic alterations associated with colon cancer progression and their relationships to a genomic instability phenotype prevalent in colon cancer. In this review, we describe the relationship between gene mutations associated with colon carcinogenesis and a genomic instability phenotype, and we discuss possible clinical applications of genomic instability studies. Colon carcinogenesis is associated with frequent mutations in several pathways that include phosphatidylinositol 3-kinase, adenomatous polyposis coli, p53 (TP53), F-box and WD repeat domain containing 7, transforming growth factor-β, chromosome cohesion, and K-RAS. These genes frequently mutated in pathways affecting colon cancer were designated colon cancer (CAN) genes. Aberrations in major colon CAN genes have a causal relationship to genomic instability. Conversely, genomic instability itself plays a role in colon carcinogenesis in experimental settings, as demonstrated in transgenic mouse models with high genomic instability. Thus, there is a feedback-type relationship between CAN gene mutations and genomic instability. These genetic/genomic studies have led to emerging efforts to apply the knowledge to colon cancer prognosis and to targeted therapy.

In the wrong place at the wrong time: does cyclin mislocalization drive oncogenic transformation?

Cyclin-dependent kinases (CDKs) are regulated by both cyclin abundance and cyclin localization. Increased cyclin expression in cancer was first observed two decades ago, and its role in pathogenesis has been investigated in great depth. This Opinion article focuses on the spatial deregulation of cyclin expression and its potential link to oncogenesis. It describes the contexts in which particular cyclins have been reported to be mislocalized in neoplasia, reviews the mechanisms underlying the dynamic subcellular localization of CDK-cyclin complexes in normal cells, and discusses how these controls can be disrupted in cancer. It also outlines the mechanisms by which cyclin mislocalization might disrupt cell cycle control and interfere with faithful chromosome segregation. Finally, it discusses the extent to which cyclin mislocalization might facilitate tumorigenesis in human cancer.

Cyclin E2 induces genomic instability by mechanisms distinct from cyclin E1

Cyclins E1 drives the initiation of DNA replication, and deregulation of its periodic expression leads to mitotic delay associated with genomic instability. Since it is not known whether the closely related protein cyclin E2 shares these properties, we overexpressed cyclin E2 in breast cancer cells. This did not affect the duration of mitosis, nor did it cause an increase in p107 association with CDK2. In contrast, cyclin E1 overexpression led to inhibition of the APC complex, prolonged metaphase and increased p107 association with CDK2. Despite these different effects on the cell cycle, elevated levels of either cyclin E1 or E2 led to hallmarks of genomic instability, i.e., an increased proportion of abnormal mitoses, micronuclei and chromosomal aberrations. Cyclin E2 induction of genomic instability by a mechanism distinct from cyclin E1 indicates that these two proteins have unique functions in a cancer setting.

Hyper-mitogenic drive coexists with mitotic incompetence in senescent cells

When the cell cycle is arrested, even though growth-promoting pathways such as mTOR are still active, then cells senesce. For example, induction of either p21 or p16 arrests the cell cycle without inhibiting mTOR, which, in turn, converts p21/p16-induced arrest into senescence (geroconversion). Here we show that geroconversion is accompanied by dramatic accumulation of cyclin D1 followed by cyclin E and replicative stress. When p21 was switched off, senescent cells (despite their loss of proliferative potential) progressed through S phase, and levels of cyclins D1 and E dropped. Most cells entered mitosis and then died, either during mitotic arrest or after mitotic slippage, or underwent endoreduplication. Next, we investigated whether inhibition of mTOR would prevent accumulation of cyclins and loss of mitotic competence in p21-arrested cells. Both nutlin-3, which inhibits mTOR in these cells, and rapamycin suppressed geroconversion during p21-induced arrest, decelerated accumulation of cyclins D1 and E and decreased replicative stress. When p21 was switched off, cells successfully progressed through both S phase and mitosis. Also, senescent mouse embryonic fibroblasts (MEFs) overexpressed cyclin D1. After release from cell cycle arrest, senescent MEFs entered S phase but could not undergo mitosis and did not proliferate. We conclude that cellular senescence is characterized by futile hyper-mitogenic drive associated with mTOR-dependent mitotic incompetence.

Tumor suppressor activity of CBX7 in lung carcinogenesis

The generation of knockout mice for the Cbx7 gene validates the tumor suppressor role of CBX7, whose expression is lost in several human malignancies. Indeed, these mice developed liver and lung adenomas and carcinomas. Cyclin E overexpression due to the lack of Cbx7 negative regulation of its expression likely accounts for the phenotype of the Cbx7-KO mice. A similar mechanism is likely involved in human lung carcinogenesis, since cyclin E upregulation associated with the loss of CBX7 expression has been observed in most of the human lung carcinomas analyzed.

Low molecular weight cyclin E is associated with p27-resistant, high-grade, high-stage and invasive bladder cancer

Expression of low molecular weight (LMW) isoforms of cyclin E is a strong predictor of poor outcome in patients with breast cancer. The purpose of this study was to examine the expression of full-length and LMW cyclin E in bladder cancer cell lines and patient tumors. We used western blotting, immunoprecipitation and kinase assays to examine the expression and activity of key cell cycle-regulatory proteins in various human bladder cell lines, both tumorigenic and non-tumorigenic. We also analyzed cyclin E expression, kinase activity and immune complex binding partners in 43 tissue samples from grade 2 and 3 transitional cell carcinomas. Cyclin E was overexpressed and LMW isoforms were present only in bladder cancer cells. Overexpression of LMW isoforms of cyclin E and increased cyclin E kinase activity were both significantly associated with tumorigenicity of the bladder cell lines (p = 0.005 and 0.022, respectively). Binding of the cyclin-dependent kinase inhibitors p21 and p27 to LMW cyclin E did not inhibit the kinase activity of cyclin E and cyclin-dependent kinase 2 in primary tumor samples overexpressing LMW cyclin E. Full-length and LMW cyclin E were significantly overexpressed in grade 3 tumors compared with grade 2 tumors (p = 0.004). Finally, LMW cyclin E levels were significantly associated with a non-papillary growth pattern (p = 0.031) and invasiveness (p = 0.021) of the bladder tumors and poor overall survival (p = 0.06). These results suggest that LMW cyclin E can be used as a new prognostic marker for bladder cancer.

LMW-E/CDK2 deregulates acinar morphogenesis, induces tumorigenesis, and associates with the activated b-Raf-ERK1/2-mTOR pathway in breast cancer patients

Elastase-mediated cleavage of cyclin E generates low molecular weight cyclin E (LMW-E) isoforms exhibiting enhanced CDK2-associated kinase activity and resistance to inhibition by CDK inhibitors p21 and p27. Approximately 27% of breast cancers express high LMW-E protein levels, which significantly correlates with poor survival. The objective of this study was to identify the signaling pathway(s) deregulated by LMW-E expression in breast cancer patients and to identify pharmaceutical agents to effectively target this pathway. Ectopic LMW-E expression in nontumorigenic human mammary epithelial cells (hMECs) was sufficient to generate xenografts with greater tumorigenic potential than full-length cyclin E, and the tumorigenicity was augmented by in vivo passaging. However, cyclin E mutants unable to interact with CDK2 protected hMECs from tumor development. When hMECs were cultured on Matrigel, LMW-E mediated aberrant acinar morphogenesis, including enlargement of acinar structures and formation of multi-acinar complexes, as denoted by reduced BIM and elevated Ki67 expression. Similarly, inducible expression of LMW-E in transgenic mice generated hyper-proliferative terminal end buds resulting in enhanced mammary tumor development. Reverse-phase protein array assay of 276 breast tumor patient samples and cells cultured on monolayer and in three-dimensional Matrigel demonstrated that, in terms of protein expression profile, hMECs cultured in Matrigel more closely resembled patient tissues than did cells cultured on monolayer. Additionally, the b-Raf-ERK1/2-mTOR pathway was activated in LMW-E-expressing patient samples, and activation of this pathway was associated with poor disease-specific survival. Combination treatment using roscovitine (CDK inhibitor) plus either rapamycin (mTOR inhibitor) or sorafenib (a pan kinase inhibitor targeting b-Raf) effectively prevented aberrant acinar formation in LMW-E-expressing cells by inducing G1/S cell cycle arrest. LMW-E requires CDK2-associated kinase activity to induce mammary tumor formation by disrupting acinar development. The b-Raf-ERK1/2-mTOR signaling pathway is aberrantly activated in breast cancer and can be suppressed by combination treatment with roscovitine plus either rapamycin or sorafenib.

The involvement of MCT-1 oncoprotein in inducing mitotic catastrophe and nuclear abnormalities

Centrosome amplification and chromosome abnormality are frequently identified in neoplasia and tumorigenesis. However, the mechanisms underlying these defects remain unclear. We here identify that MCT-1 is a centrosomal oncoprotein involved in mitosis. Knockdown of MCT-1 protein results in intercellular bridging, chromosome mis-congregation, cytokinesis delay, and mitotic death. Introduction of MCT-1 oncogene into the p53 deficient cells (MCT-1-p53), the mitotic checkpoint kinases and proteins are deregulated synergistically. These biochemical alterations are accompanied with increased frequencies of cytokinesis failure, multi-nucleation, and centrosome amplification in subsequent cell cycle. As a result, the incidences of polyploidy and aneuploidy are progressively induced by prolonged cell cultivation or further promoted by sustained spindle damage on MCT-1-p53 background. These data show that the oncoprotein perturbs centrosome structure and mitotic progression, which provide the molecular aspect of chromsomal abnormality in vitro and the information for understanding the stepwise progression of tumors under oncogenic stress.

The impact of multi-targeted cyclin-dependent kinase inhibition in breast cancer cells: clinical implications

INTRODUCTION

The progression of the mammalian cell cycle is driven by the transient activation of complexes consisting of cyclins and cyclin-dependent kinases (CDKs). Loss of control over the cell cycle results in accelerated cell division and malignant transformation and can be caused by the upregulation of cyclins, the aberrant activation of CDKs or the inactivation of cellular CDK inhibitors. For these reasons, cell cycle regulators are regarded as very promising therapeutic targets for the treatment of human malignancies.

AREAS COVERED

This review covers the structures and anti-breast cancer activity of selected pharmacological pan-specific CDK inhibitors. Multi-targeted CDK inhibitors affect CDKs involved in the regulation of both cell cycle progression and transcriptional control. The inhibition of CDK7/CDK9 has a serious impact on the activity of RNA polymerase II; when its carboxy-terminal domain is unphosphorylated, it is unable to recruit the cofactors required for transcriptional elongation, resulting in a global transcriptional block. Multi-targeted inhibition of CDKs represses anti-apoptotic proteins and thus promotes the induction of apoptosis. Moreover, the inhibition of CDK7 in estrogen receptor (ER)-positive breast cancer cells prevents activating phosphorylation of ER-α.

EXPERT OPINION

These diverse modes of action make multi-targeted CDK inhibitors promising drugs for the treatment of breast cancers.

A clinical overview of centrosome amplification in human cancers

The turn of the 21st century had witnessed a surge of interest in the centrosome and its causal relation to human cancer development - a postulate that has existed for almost a century. Centrosome amplification (CA) is frequently detected in a growing list of human cancers, both solid and haematological, and is a candidate "hallmark" of cancer cells. Several lines of evidence support the progressive involvement of CA in the transition from early to advanced stages of carcinogenesis, being also found in pre-neoplastic lesions and even in histopathologically-normal tissue. CA constitutes the major mechanism leading to chromosomal instability and aneuploidy, via the formation of multipolar spindles and chromosomal missegregation. Clinically, CA may translate to a greater risk for initiation of malignant transformation, tumour progression, chemoresistance and ultimately, poor patient prognosis. As mechanisms underlying CA are progressively being unravelled, the centrosome has emerged as a novel candidate target for cancer treatment. This Review summarizes mainly the clinical studies performed to date focusing on the mechanisms underlying CA in human neoplasia, and highlights the potential utility of centrosomes in the diagnosis, prognosis and treatment of human cancers.

Overexpression of cyclin E isoforms correlates with poor prognosis in rectal cancer

AIMS

To investigate the expression of cyclin E isoforms in rectal cancer and its relations to clinicopathological factors and survival.

MATERIALS AND METHODS

Cyclin E expression was assessed by Western blot in 360 resected rectal cancer patients of stage I to III. Multivariate analysis was applied to indicate the independent prognostic markers in this cohort.

RESULTS

Nineteen percent, 24% or 29% patients exhibited elevated levels of full-length (FL) cyclin E, low-molecular-weight (LMW) cyclin E or total cyclin E in their tumors respectively. Significant correlation was observed between cyclin E expression with blood vessel invasion, deeply invasive tumors, histology grade and lymph node metastasis. Moreover, patients with high levels of LMW-cyclin E or total cyclin E had a poorer 5-year overall survival than did patients with low levels of LMW-cyclin E or total cyclin E. In multivariate analysis, both the LMW-cyclin E and total cyclin E, but not FL-cyclin E, remained independent prognostic indicators in both patients with stage I to III and in those with early stage. Patients with elevated LMW- or total cyclin E levels had a hazard ratio for death from rectal cancer of 6.302 (95% CI, 1.903-17.81, p = 0.001) or 4.332 (95% CI, 1.298-16.362, p = 0.001).

CONCLUSION

Overexpression of the LMW-cyclin E or total cyclin E is a strong predictor for poorer survival in patients with rectal cancer. Therefore, evaluating cyclin E expression may provide useful prognostic information for resectable rectal cancer patients.

Targeting low molecular weight cyclin E (LMW-E) in breast cancer

Low molecular weight cyclin E (LMW-E) plays an important oncogenic role in breast cancer. LMW-E, which is not found in normal tissue, can promote the formation of aggressive tumors and can lead to increased genomic instability and tumorigenesis. Additionally, breast cancer patients whose tumors express LMW-E have a very poor prognosis. Therefore, we investigated LMW-E as a potential specific target for treatment either alone or in combination therapy. We hypothesized that because LMW-E binds to CDK2 more efficiently than full length cyclin E, resulting in increased activity, CDK inhibitors could be used to target tumors with LMW-E bound to CDK2. To test the hypothesis, an inducible full length and LMW-E MCF7-Tet-On system was established. Cyclin E (full length (EL) or LMW-E) is only expressed upon induction of the transgene. The doubling times of cells were unchanged when the transgenes were induced. However, upon induction, the kinase activity associated with LMW-E was much higher than that in the EL induced cells or any of the uninduced cells. Additionally only the LMW-E induced cells underwent chromosome aberrations and increased polyploidy. By examining changes in proliferation and survival in cells with induced full length and LMW-E, CDK inhibitors alone were determined to be insufficient to specifically inhibit LMW-E expressing cells. However, in combination with doxorubicin, the CDK inhibitor, roscovitine (seliciclib, CYC202), synergistically led to increased cell death in LMW-E expressing cells. Clinically, the combination of CDK inhibitors and chemotherapy such as doxorubicin provides a viable personalized treatment strategy for those breast cancer patients whose tumors express the LMW-E.

Cdk2 is required for breast cancer mediated by the low-molecular-weight isoform of cyclin E

Cyclin E activates Cdk2, controls centrosome duplication, and regulates histone gene transcription. Cyclin E is deregulated in cancer and appears as low-molecular-weight (LMW) isoforms that correlate strongly with decreased survival in breast cancer patients. Transgenic mice overexpressing LMW-cyclin E have increased incidence of mammary tumors and distant metastasis when compared with mice that had full-length cyclin E. To specifically test the requirement for Cdk2 in LMW-cyclin E-mediated mammary tumorigenesis, we generated transgenic mice, which expressed LMW-cyclin E in a Cdk2-deficient background. We found that mammary gland development proceeds relatively normally in these animals, indicating that Cdk2 kinase activity is largely dispensable for this process. However, Cdk2-deficient mice were completely resistant to LMW-cyclin E-mediated mammary tumors. Cdk2 wild-type or heterozygous mice succumbed to mammary tumors with mean latencies of 16 and 19.5 months, respectively, but Cdk2 nullizygous littermates did not display tumors through 24 months. Similarly, continuous administration of two different Cdk inhibitors significantly delayed LMW-cyclin E-induced mammary tumor progression. Triple transgenic mice generated in a p53 heterozygous background also displayed no tumors. Finally, we found that Cdk2 silencing induced cell death in LMW-overexpressing breast cancer cell lines, but not in cell lines lacking LMW expression. Our findings establish a requirement for Cdk2 in LMW-cyclin E-mediated mammary tumorigenesis, arguing that human breast tumors overexpressing LMW-cyclin E are prime candidates for anti-Cdk2 therapy.

Screening of differentially expressed low-abundance proteins among serum samples from patients with different HBV-related hepatic diseases by SELDI-TOF-MS

AIM: To screen differentially expressed low-abundance proteins among serum samples from patients with different HBV-related hepatic diseases and to evaluate their possible value in the diagnosis of these diseases.

METHODS: The surface-enhanced laser desorption or ionization time-of-flight mass spectroscopy (SELDI-TOF-MS) was used to screen differentially expressed proteins among serum samples, in which high-abundance proteins had been removed with acetonitrile, collected from patients with asymptomatic chronic hepatitis B (ASC), chronic hepatitis B (CHB), liver cirrhosis (LC), hepatocellular carcinoma (HCC), and normal controls. Diagnostic models for each disease were then established with differentially expressed proteins. Protein databases were searched to predict the possible structure and function of differentially expressed proteins.

RESULTS: Compared with the normal control group, 63 differentially expressed protein peaks were detected in the ASC group, of which 29 were up-regulated and 34 down-regulated (P < 0.05); 57 in the CHB group, of which 29 up-regulated and 34 down-regulated; 68 in the LC group, of which 33 up-regulated and 35 down-regulated; and 74 in the HCC group, of which 28 up-regulated and 46 down-regulated. A peak with a m/z of 15 889.8 corresponded to a protein whose expression was up-regulated gradually in an order of healthy controls, ASC, CHB and LC patients, and its expression level in the HCC group was lower than those in the CHB group and LC group. The expression of a protein with a m/z of 11 742.2 was higher in the LC group and HCC group than in other groups, and its expression was gradually increased in an order of healthy controls, CHB, and LC patients, or in another order of healthy controls, CHB, and HCC patients. The sensitivity and specificity using the protein peak at 11 742.2 for diagnosis of LC were 90% and 86.67% and for HCC were 93.33% and 83.33%, respectively.

CONCLUSION: Ten protein peaks with m/z values of 8 709.7, 13 759.8, 14 004.0, 15 361.89, 16 072.3, 2 746.8, 3 449.1, 3 941.06, 4 098.3, and 9 445.5 correspond to proteins that might be involved in HBV infection. The protein peak with a m/z of 15 889.8 might be used as a biomarker for early diagnosis of HBV-related liver cirrhosis, while that with a m/z of 11 742.2 might be an important biomarker for the development of HBV-related liver cirrhosis or HCC.

Cyclin E deregulation impairs mitotic progression through premature activation of Cdc25C

The cyclin E-cyclin-dependent kinase 2 (CDK2) complex accelerates entry into the S phase of the cell cycle and promotes polyploidy, which may contribute to genomic instability in cancer cells. The effect of low molecular weight isoforms of cyclin E (LMW-E) overexpression on mitotic progression and its link to genomic instability were the focus of this study. Here, we show that full-length cyclin E (EL) and LMW-E overexpression impairs the G(2)-M transition differently by targeting dual-specificity phosphatase Cdc25C activity. We identify Cdc25C as an interaction partner and substrate for cyclin E/CDK2 kinase. Specifically, the cyclin E/CDK2 complex phosphorylates Cdc25C on Ser(214), leading to its premature activation, which coincides with higher cyclin B/CDK1 and Polo-like kinase 1 (PLK1) activities in an S-phase-enriched population that result in faster mitotic entry. Whereas EL overexpression leads to hyperactivation of Cdc25C, cyclin B/CDK1, and PLK1 in a G(2)-M-enriched population, LMW-E overexpression causes premature inactivation of Cdc25C and PLK1, leading to faster mitotic exit. In addition, LMW-E-overexpressing cells showed a reduction in the mitotic index in the presence of a spindle poison and faster degradation of cyclin B, suggesting an increased rate of mitotic slippage and adaptation to the spindle checkpoint. Lastly, downregulation of Cdc25C inhibits LMW-E-mediated chromosome missegregation, anaphase bridges, and centrosome amplification. These results suggest that the high levels of LMW-E isoforms found in breast cancer may contribute to cellular transformation and genomic instability by impairing mitotic progression involving Cdc25C.