Centrosome abnormalities, genomic instability and carcinogenic progression

Differential expression of DNA repair genes and treatment outcome of chemoradiotherapy (CRT) in cervical cancer

Cervical cancer (CaCx) is the malignancy of uterine cervix which induce by human papillomavirus (HPV) infections. HPV infection starts with the induction of double-stranded breaks by increasing oxidative stress and modulation of DNA repair pathways. Deficiency in DNA repair pathways and accumulation of DNA damage increases mutation rates resulting in genomic instability and cancer development. Patients with HPV-associated CaCx display increased sensitivity to cisplatin-based chemoradiotherapy (CRT) and improved survival rates. However, the cellular mechanisms responsible for this characteristic difference are unclear. Here, we have evaluated expression of DNA repair genes in peripheral blood cells and correlated them with treatment outcomes. A total of 211 study subjects includes in the study comprised 103 CaCx patients and 108 healthy controls. All the study subjects were analyzed for the expression profile of DNA repair genes by using real-time PCR (RT-PCR). The differentially expressed DNA repair gene was correlated with the treatment outcome of CRT. OGG1, XRCC2, XRCC3, XRCC4 and XRCC6 genes were found to be significant (P=0.001) down-regulated as compared to controls. While XRCC5 and RAD51 showed significant up-regulated (P=0.024 and 0.041) in CaCx patients. XRCC6 was associated (P=0.033) with poor vital while up-regulated RAD51 showed slight association (P=0.075) with better vital with an increased 2.96- and 2.33-fold risk in the study population. In the case of overall survival, down-regulated XRCC4 was associated (P=0.042) with poor survival (27 months) with the least hazard ratio (0.56 HR). Down-regulated OGG1 involved BER, XRCC2 and XRCC3 in homologous recombination and XRCC4, XRCC5 and XRCC6 in Non-homologous end-joining repair, which showed a deficiency of DNA repair capacity resulting caused of an accumulation of DNA damage and genome instability. Impaired DNA repair gene expression is responsible for poor prognosis and survival in CaCx. Therefore, these gene expressions can be considered a potential prognostic, diagnostic and therapeutic biomarker for CaCx.

Toxoplasma gondii-induced host cellular cell cycle dysregulation is linked to chromosome missegregation and cytokinesis failure in primary endothelial host cells

Toxoplasma gondii is a zoonotic and intracellular parasite with fast proliferating properties leading to rapid host cell lysis. T. gondii modulates its host cell on numerous functional levels. T. gondii was previously reported to influence host cellular cell cycle and to dampen host cell division. By using primary endothelial host cells, we show for the first time that T. gondii tachyzoite infections led to increased host cell proliferation and to an enhanced number of multi-nucleated host cells. As detected on DNA content level, parasite infections induced a G2/M cell cycle arrest without affecting expression of G2-specific cyclin B1. In line, parasite-driven impairment mainly concerned mitotic phase of host cells by propagating several functional alterations, such as chromosome segregation errors, mitotic spindle alteration and blockage of cytokinesis progression, with the latter most likely being mediated by the downregulation of the Aurora B kinase expression.

The influence of ACYP2 polymorphisms on gastrointestinal cancer susceptibility in the Chinese Han population

BACKGROUND

Gastrointestinal cancer (GI cancer) is a type of cancer that has a high death rate. It has been reported that ACYP2 gene was associated with the development of gastric cancer and colorectal cancer, but it is not clear that the relationship between ACYP2 gene and GI cancer in Chinese Han population. This study aimed to investigate the association between polymorphisms of ACYP2 and GI cancer in the Chinese Han population.

METHODS

We used Agena MassARRAY to determine the genotypes of 1,160 GI cancer patients and 495 healthy controls. The correlation between ACYP2 variants and GI cancer risk was examined by logistic regression analysis.

RESULTS

We identified that rs6713088 (OR = 1.17, 95% CI: 1.00-1.36, p = 0.047), rs843711 (OR = 1.17, 95 CI: 1.01-1.36, p = 0.035), and rs11896604 (OR = 1.20, 95% CI: 1.00-1.45, p = 0.048) were correlated with an increased risk of GI cancer under allele model. Rs11125529 under the recessive model (OR = 2.05, 95% CI: 1.00-4.23, p = 0.038), rs843711 in recessive model (OR = 1.37, 95% CI: 1.04-1.82, p = 0.026), and rs11896604 under log-additive model (OR = 1.23, 95% CI: 1.01-1.51, p = 0.042) were associated with an increased risk of GI cancer.

CONCLUSION

Our study suggested that polymorphisms of ACYP2 gene might be associated with susceptibility to GI cancer.

Abnormal cleavage and developmental arrest of human preimplantation embryos in vitro

Despite improvements in culture conditions and laboratory techniques still only about 50% of human embryos reach the blastocyst stage of development in vitro. While many factors influence embryo development, aberrant cleavage divisions have only recently been shown to directly affect the genome in individual cells of human embryos resulting in chromosome loss, mosaicism and cell arrest. In this article we review the current literature in the area of aberrant cleavage in human embryos and its effect on blastocyst development. Further to this, we propose a series of common abnormal cleavage events, with particular attention to timing and frequency, and illustrate how these might influence a number of different embryo fates.

Novel insight into the function of tankyrase

Tankyrases are multifunctional poly(ADP-ribose) polymerases that regulate a variety of cellular processes, including Wnt signaling, telomere maintenance and mitosis regulation. Tankyrases interact with target proteins and regulate their interactions and stability through poly(ADP-ribosyl) ation. In addition to their roles in telomere maintenance and regulation of mitosis, tankyrase proteins regulate tumor suppressors, including AXIN, phosphatase and tensin homolog and angiomotin. Therefore, tankyrases may be effective targets for cancer treatment. Tankyrase inhibitors could affect a variety of carcinogenic pathways that promote uncontrolled proliferation, including Wnt, AKT, yes-associated protein, telomere maintenance and mitosis regulation. Recently, novel aspects of the function and mechanism of tankyrases have been reported, and a number of tankyrase inhibitors have been identified. A combination of conventional chemotherapy agents with tankyrase inhibitors may have synergistic anticancer effects. Therefore, it is expected that more advanced and improved tankyrase inhibitors will be developed, enabling novel therapeutic strategies against cancer and other tankyrase-associated diseases. The present review discusses tankyrase function and the role of tankyrase inhibitors in the treatment of cancer.

Human papillomavirus and genome instability: from productive infection to cancer

Infection with high oncogenic risk human papillomavirus types is the etiological factor of cervical cancer and a major cause of other epithelial malignancies, including vulvar, vaginal, anal, penile and head and neck carcinomas. These agents affect epithelial homeostasis through the expression of specific proteins that deregulate important cellular signaling pathways to achieve efficient viral replication. Among the major targets of viral proteins are components of the DNA damage detection and repair machinery. The activation of many of these cellular factors is critical to process viral genome replication intermediates and, consequently, to sustain faithful viral progeny production. In addition to the important role of cellular DNA repair machinery in the infective human papillomavirus cycle, alterations in the expression and activity of many of its components are observed in human papillomavirus-related tumors. Several studies from different laboratories have reported the impact of the expression of human papillomavirus oncogenes, mainly E6 and E7, on proteins in almost all the main cellular DNA repair mechanisms. This has direct consequences on cellular transformation since it causes the accumulation of point mutations, insertions and deletions of short nucleotide stretches, as well as numerical and structural chromosomal alterations characteristic of tumor cells. On the other hand, it is clear that human papillomavirus-transformed cells depend on the preservation of a basal cellular DNA repair activity level to maintain tumor cell viability. In this review, we summarize the data concerning the effect of human papillomavirus infection on DNA repair mechanisms. In addition, we discuss the potential of exploiting human papillomavirus-transformed cell dependency on DNA repair pathways as effective antitumoral therapies.

RNAi screen reveals synthetic lethality between cyclin G-associated kinase and FBXW7 by inducing aberrant mitoses

Background:

F-box and WD40 repeat domain-containing 7 (FBXW7) is an E3 ubiquitin ligase involved in the ubiquitination and degradation of multiple oncogenic substrates. The tumour suppressor function is frequently lost in multiple cancers through genetic deletion and mutations in a broad range of tumours. Loss of FBXW7 functionality results in the stabilisation of multiple major oncoproteins, culminating in increased cellular proliferation and pro-survival pathways, cell cycle deregulation, chromosomal instability and altered metabolism. Currently, there is no therapy to specifically target FBXW7-deficient tumours.

Methods:

We performed a siRNA kinome screen to identify synthetically lethal hits to FBXW7 deficiency.

Results:

We identified and validated cyclin G-associated kinase (GAK) as a potential new therapeutic target. Combined loss of FBXW7 and GAK caused cell cycle defects, formation of multipolar mitoses and the induction of apoptosis. The synthetic lethal mechanism appears to be independent of clathrin-mediated receptor endocytosis function of GAK.

Conclusions:

These data suggest a putative therapeutic strategy for a large number of different types of human cancers with FBXW7 loss, many of which have a paucity of molecular abnormalities and treatment options.

Somatic Host Cell Alterations in HPV Carcinogenesis

High-risk human papilloma virus (HPV) infections cause cancers in different organ sites, most commonly cervical and head and neck cancers. While carcinogenesis is initiated by two viral oncoproteins, E6 and E7, increasing evidence shows the importance of specific somatic events in host cells for malignant transformation. HPV-driven cancers share characteristic somatic changes, including apolipoprotein B mRNA editing catalytic polypeptide-like (APOBEC)-driven mutations and genomic instability leading to copy number variations and large chromosomal rearrangements. HPV-associated cancers have recurrent somatic mutations in phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA) and phosphatase and tensin homolog (PTEN), human leukocyte antigen A and B (HLA-A and HLA-B)-A/B, and the transforming growth factor beta (TGFβ) pathway, and rarely have mutations in the tumor protein p53 (TP53) and RB transcriptional corepressor 1 (RB1) tumor suppressor genes. There are some variations by tumor site, such as NOTCH1 mutations which are primarily found in head and neck cancers. Understanding the somatic events following HPV infection and persistence can aid the development of early detection biomarkers, particularly when mutations in precancers are characterized. Somatic mutations may also influence prognosis and treatment decisions.

Direct Unequal Cleavages: Embryo Developmental Competence, Genetic Constitution and Clinical Outcome

Objective

To investigate the prevalence, developmental potential, chromosomal constitution and clinical outcome of embryos with direct unequal cleavages (DUC).

Design

A retrospective observational study.

Setting

Academic Institution.

Participant

21,261 embryos from 3,155 cycles cultured in EmbryoScope^®.

Results

The total incidence of DUCs per embryo occupying the first three cleavages were 26.1%. Depending of the cell stage, DUC rate was 9.8% at first cleavage (DUC-1), 9.1% at second cleavage (DUC-2), and 3.7% at third cleavage (DUC-3) with 3.6% of embryos exhibiting multiple DUCs (DUC-Plus). The occurrence of DUCs was not correlated with female gamete age or source. The incidence of DUC-1 was significantly higher in embryos fertilized by epididymal and testicular sperm (13.6% and 11.4%, respectively) compared to ejaculated sperm (9.1%, all p<0.05). The total incidences of DUCs were strongly correlated with the onset of blastomere multinucleation (MNB) during the first three divisions. In MNB embryos, DUCs incidence are two to three times more likely to develop when compared to non-MNB embryos (OR = 3.11, 95% CI [2.64, 3.67] at 1-cell stage, OR = 2.64, 95% CI [2.39, 2.91] at 2-cell stage and OR = 2.51, 95% CI [1.84, 3.43] at 4-cell stage). The blastocyst formation rates gradually decreased from 61.0% in non-DUC to 40.2% in DUC-3, 18.8% in DUC-2, 8.2% in DUC-1 and 5.6% in multiple DUC embryos (DUC-Plus). The known implantation rates (FH) for day 3 (D3) transfers were 12.42% (n = 3172) in Non-DUC embryos, 6.3% (n = 127) in DUC-3, and 2.7% (n = 260) in DUC-2 embryos. No live births resulted from either DUC-1 (n = 225) or DUC-Plus (n = 100) embryo transfers. For blastocyst transfers, lower implantation rates (33.3%) but similar live birth (LB) rates (40%) were observed if DUC blastocysts were transferred. Comparatively rates in Non-DUC blastocyst were 45.2% and 34.8%, respectively. The euploid rate gradually increased from DUC-1, -2, -3 to Non-DUC (13.3%, 19.5%, 33.3%, 45.6%, p<0.001) for D3 biopsied embryos. Interestingly, the trend of decreased euploidy disappeared in DUC D5/6 biopsied embryos and similar rates were exemplified in DUC (D5 56.3%, D6 35.6%) vs. non-DUC (D5 51.4%, D6 33.8%) embryos.

Conclusion

Blastocyst formation, implantation potential and euploid rate were significantly reduced in DUC embryos. DUC embryos should be deselected for D3 transfers, but should be culture to blastocyst stage for possible ET.

STK31 is a cell-cycle regulated protein that contributes to the tumorigenicity of epithelial cancer cells

Serine/threonine kinase 31 (STK31) is one of the novel cancer/testis antigens for which its biological functions remain largely unclear. Here, we demonstrate that STK31 is overexpressed in many human colorectal cancer cell lines and tissues. STK31 co-localizes with pericentrin in the centrosomal region throughout all phases of the cell cycle. Interestingly, when cells undergo mitosis, STK31 also localizes to the centromeres, central spindle, and midbody. This localization behavior is similar to that of chromosomal passenger proteins, which are known to be the important players of the spindle assembly checkpoint. The expression of STK31 is cell cycle-dependent through the regulation of a putative D-box near its C-terminal region. Ectopically-expressed STK31-GFP increases cell migration and invasive ability without altering the proliferation rate of cancer cells, whereas the knockdown expression of endogenous STK31 by lentivirus-derived shRNA results in microtubule assembly defects that prolong the duration of mitosis and lead to apoptosis. Taken together, our results suggest that the aberrant expression of STK31 contributes to tumorigenicity in somatic cancer cells. STK31 might therefore act as a potential therapeutic target in human somatic cancers.

Clinical implication of centrosome amplification and expression of centrosomal functional genes in multiple myeloma

Background

Multiple myeloma (MM) is a low proliferative tumor of postgerminal center plasma cell (PC). Centrosome amplification (CA) is supposed to be one of the mechanisms leading to chromosomal instability. Also, CA is associated with deregulation of cell cycle, mitosis, DNA repair and proliferation. The aim of our study was to evaluate the prognostic significance and possible role of CA in pathogenesis and analysis of mitotic genes as mitotic disruption markers.

Design and methods

A total of 173 patients were evaluated for this study. CD138+ cells were separated by MACS. Immunofluorescent labeling of centrin was used for evaluation of centrosome amplification in PCs. Interphase FISH with cytoplasmic immunoglobulin light chain staining (cIg FISH) and qRT-PCR were performed on PCs.

Results

Based on the immunofluorescent staining results, all patients were divided into two groups: CA positive (38.2%) and CA negative (61.8%). Among the newly diagnosed patients, worse overall survival was indicated in the CA negative group (44/74) in comparison to the CA positive group (30/74) (P = 0.019).

Gene expression was significantly down-regulated in the CA positive group in comparison to CA negative in the following genes: AURKB, PLK4, TUBG1 (P < 0.05). Gene expression was significantly down-regulated in newly diagnosed in comparison to relapsed patients in the following genes: AURKA, AURKB, CCNB1, CCNB2, CETN2, HMMR, PLK4, PCNT, and TACC3 (P < 0.05).

Conclusions

Our findings indicate better prognosis for CA positive newly diagnosed patients. Considering revealed clinical and gene expression heterogeneity between CA negative and CA positive patients, there is a possibility to characterize centrosome amplification as a notable event in multiple myeloma pathogenesis.

The RhoD to centrosomal duplication

The main functional roles attributed to the centrosome, the major microtubule organizing center (MTOC) of metazoans, are related to cell locomotion, sensory perception and division. The role of vesicular trafficking in the regulation of the centrosome cycle has been largely unexplored. Recently, however, several studies have indicated the involvement of molecules and/or complexes of the trafficking routes in centrosome positioning, duplication and regulation. Functional screens have revealed communication between the outer nuclear envelope, the Golgi apparatus, the endosomal recycling compartment and centrosomes, while other studies underline the involvement of the ESCRT complex proteins in centrosome function. In this commentary, we discuss our recent study, which shows the involvement of an endosomal Rho protein, namely RhoD, in centrosome duplication and possible links between the centrosome's structural and functional integrity to vesicular trafficking.

mRNA and DNA detection of human papillomaviruses in women of all ages attending two colposcopy clinics

OBJECTIVE

HPV infection is a common finding, especially in young women while the majority of infections are cleared within a short time interval. The aim of this study was to examine the efficacy of HPV DNA and mRNA testing in a population attending colposcopy units of two University hospitals.

METHODS

1173 liquid based cervical samples from two colposcopy clinics were tested for HPV DNA positivity using a commercial typing kit and HPV E6/E7 mRNA positivity with a flow cytometry based commercial kit. Statistic measures were calculated for both molecular tests and morphological cytology and colposcopy diagnosis according to histology results.

RESULTS

HPV DNA, high-risk HPV DNA, HPV16 or 18 DNA and HPV mRNA was detected in 55.5%, 50.6%, 20.1% and 29.7% of the cervical smears respectively. Concordance between the DNA and the mRNA test was 71.6% with their differences being statistically significant. Both tests' positivity increased significantly as lesion grade progressed and both displayed higher positivity rates in samples from women under 30 years old. mRNA testing displayed similar NPV, slightly lower sensitivity but significantly higher specificity and PPV than DNA testing, except only when DNA positivity for either HPV16 or 18 was used.

CONCLUSIONS

Overall mRNA testing displayed higher clinical efficacy than DNA testing, either when used as a reflex test or as an ancillary test combined with morphology. Due to enhanced specificity of mRNA testing and its comparable sensitivity in ages under 25 or 30 years old, induction of mRNA testing in young women could be feasible if a randomized trial verifies these results.

Phosphoregulation of the RNA-binding protein Hu antigen R (HuR) by Cdk5 affects centrosome function

Hu antigen R (HuR) is an mRNA-binding protein belonging to the ELAV family. It is highly expressed in cancer and involved in cell survival and proliferation. The impact of post-translational regulation of HuR and resulting cellular effects are poorly understood. In the current report, we describe a direct interaction between HuR and Cdk5 in glioma. We determined that Cdk5 specifically phosphorylates HuR at the serine 202 residue in the unique hinge region. The molecular consequences of this interaction are an altered HuR ability to bind, stabilize, and promote translation of mRNAs. At the cellular level, the anomalous HuR phosphorylation at this site evokes robust defects in centrosome duplication and cohesion as well as arrest of cell cycle progression. Subcellular fractionation and immunofluorescence technique confirm a direct integration of HuR and Cdk5 with centrosomes. We propose that HuR stores mRNA in the centrosome and that HuR phosphorylation by Cdk5 controls de novo protein synthesis in near proximity to centrosomes and, thus, impacts centrosome function.

Aneuploidy and tumorigenesis

Aneuploidy is a prominent phenotype of cancer. It refers to deviations from the normal number of chromosomes in a cell, as a result of whole-chromosome loss or gain. In most cases, aneuploidy is caused by mitotic errors due to defects in the mechanisms that have evolved to ensure faithful chromosome segregation, such as the spindle assembly checkpoint (SAC). The observation that SAC-deficient mice are tumor prone demonstrates that this checkpoint is important in suppressing tumor formation and suggests that aneuploidy can induce tumorigenesis. In this review, we will summarize our current knowledge about the cause of aneuploidy and discuss the cellular response to aneuploidy in the context of tumorigenesis.

Centrosomal Nlp is an oncogenic protein that is gene-amplified in human tumors and causes spontaneous tumorigenesis in transgenic mice

Disruption of mitotic events contributes greatly to genomic instability and results in mutator phenotypes. Indeed, abnormalities of mitotic components are closely associated with malignant transformation and tumorigenesis. Here we show that ninein-like protein (Nlp), a recently identified BRCA1-associated centrosomal protein involved in microtubule nucleation and spindle formation, is an oncogenic protein. Nlp was found to be overexpressed in approximately 80% of human breast and lung carcinomas analyzed. In human lung cancers, this deregulated expression was associated with NLP gene amplification. Further analysis revealed that Nlp exhibited strong oncogenic properties; for example, it conferred to NIH3T3 rodent fibroblasts the capacity for anchorage-independent growth in vitro and tumor formation in nude mice. Consistent with these data, transgenic mice overexpressing Nlp displayed spontaneous tumorigenesis in the breast, ovary, and testicle within 60 weeks. In addition, Nlp overexpression induced more rapid onset of radiation-induced lymphoma. Furthermore, mouse embryonic fibroblasts (MEFs) derived from Nlp transgenic mice showed centrosome amplification, suggesting that Nlp overexpression mimics BRCA1 loss. These findings demonstrate that Nlp abnormalities may contribute to genomic instability and tumorigenesis and suggest that Nlp might serve as a potential biomarker for clinical diagnosis and therapeutic target.

Cullin 1 functions as a centrosomal suppressor of centriole multiplication by regulating polo-like kinase 4 protein levels

Abnormal centrosome and centriole numbers are frequently detected in tumor cells where they can contribute to mitotic aberrations that cause chromosome missegregation and aneuploidy. The molecular mechanisms of centriole overduplication in malignant cells, however, are poorly characterized. Here, we show that the core SKP1-cullin-F-box component cullin 1 (CUL1) localizes to maternal centrioles and that CUL1 is critical for suppressing centriole overduplication through multiplication, a recently discovered mechanism whereby multiple daughter centrioles form concurrently at single maternal centrioles. We found that this activity of CUL1 involves the degradation of Polo-like kinase 4 (PLK4) at maternal centrioles. PLK4 is required for centriole duplication and strongly stimulates centriole multiplication when aberrantly expressed. We found that CUL1 is critical for the degradation of active PLK4 following deregulation of cyclin E/cyclin-dependent kinase 2 activity, as is frequently observed in human cancer cells, as well as for baseline PLK4 protein stability. Collectively, our results suggest that CUL1 may function as a tumor suppressor by regulating PLK4 protein levels and thereby restraining excessive daughter centriole formation at maternal centrioles.

Early detection of cervical carcinomas: finding an overall approach

BACKGROUND

Infection with human papillomavirus (HPV) is a necessary, but not sufficient condition for the emergence of cervical cancer. Cervical cancer develops over several years through a series of precursor lesions that can be detected by cytological screening. The majority of these lesions, however, regress spontaneously. The challenge of cancer screening is to detect those patients who are at high risk of tumor progression.

METHODS

Selective literature review on cervical cancer screening in light of current guidelines and recommendations.

RESULTS AND CONCLUSION

Since the recently introduced vaccination against HPV does not provide full protection against cervical cancer, screening programs must continue. HPV vaccination and early detection of cervical carcinomas should be organized into a combined prevention program with systematic documentation, quality control, and active invitation to participate. It is assumed that the reduction in prevalence of precancerous lesions as a result of vaccination will have a negative impact on the efficiency of cytological early detection. Therefore, the existing screening procedures should be optimized and complemented by new techniques. Already available for screening is the detection of HPV DNA. Further promising biomarkers are currently being investigated in international studies, but no conclusions on their potential efficacy can yet be drawn.

Studying chromosome instability in the mouse

Aneuploidy has long been recognized as one of the hallmarks of cancer. It nonetheless remains uncertain whether aneuploidy occurring early in the development of a cancer is a primary cause of oncogenic transformation, or whether it is an epiphenomenon that arises from a general breakdown in cell cycle control late in tumorigenesis. The accuracy of chromosome segregation is ensured both by the intrinsic mechanics of mitosis and by an error-checking spindle assembly checkpoint. Many cancers show altered expression of proteins involved in the spindle checkpoint or in proteins implicated in other mitotic processes. To understand the role of aneuploidy in the initiation and progression of cancer, a number of spindle checkpoint genes have been disrupted in mice, most through conventional gene targeting (to create germ-line knockouts). We describe the consequence of these mutations with respect to embryonic development, tumor progression and an unexpected link to premature aging; readers are referred elsewhere [1] for a discussion of other cell cycle regulators.

When the genome plays dice: circumvention of the spindle assembly checkpoint and near-random chromosome segregation in multipolar cancer cell mitoses

Background

Normal cell division is coordinated by a bipolar mitotic spindle, ensuring symmetrical segregation of chromosomes. Cancer cells, however, occasionally divide into three or more directions. Such multipolar mitoses have been proposed to generate genetic diversity and thereby contribute to clonal evolution. However, this notion has been little validated experimentally.

Principal Findings

Chromosome segregation and DNA content in daughter cells from multipolar mitoses were assessed by multiphoton cross sectioning and fluorescence in situ hybridization in cancer cells and non-neoplastic transformed cells. The DNA distribution resulting from multipolar cell division was found to be highly variable, with frequent nullisomies in the daughter cells. Time-lapse imaging of H2B/GFP-labelled multipolar mitoses revealed that the time from the initiation of metaphase to the beginning of anaphase was prolonged and that the metaphase plates often switched polarity several times before metaphase-anaphase transition. The multipolar metaphase-anaphase transition was accompanied by a normal reduction of cellular cyclin B levels, but typically occurred before completion of the normal separase activity cycle. Centromeric AURKB and MAD2 foci were observed frequently to remain on the centromeres of multipolar ana-telophase chromosomes, indicating that multipolar mitoses were able to circumvent the spindle assembly checkpoint with some sister chromatids remaining unseparated after anaphase. Accordingly, scoring the distribution of individual chromosomes in multipolar daughter nuclei revealed a high frequency of nondisjunction events, resulting in a near-binomial allotment of sister chromatids to the daughter cells.

Conclusion

The capability of multipolar mitoses to circumvent the spindle assembly checkpoint system typically results in a near-random distribution of chromosomes to daughter cells. Spindle multipolarity could thus be a highly efficient generator of genetically diverse minority clones in transformed cell populations.

Analysis of centrosome overduplication in correlation to cell division errors in high-risk human papillomavirus (HPV)-associated anal neoplasms

High-risk HPV-associated anal neoplasms are difficult to treat and biomarkers of malignant progression are needed. A hallmark of carcinogenic progression is genomic instability, which is frequently associated with cell division errors and aneuploidy. The HPV-16 E7 oncoprotein has been previously shown to rapidly induce centriole and centrosome overduplication and to cooperate with HPV-16 E6 in the induction of abnormal multipolar mitoses. Based on this function, it has been suggested that HPV-16 E7 may act as a driving force for chromosomal instability. However, a detailed analysis of centrosome overduplication in primary HPV-associated neoplasms has not been performed so far. Here, we determined the frequency of centrosome overduplication in HPV-associated anal lesions using a recently identified marker for mature maternal centrioles, Cep170. We detected centrosome overduplication in a small but significant fraction of cells. Remarkably, centrosome overduplication, but not aberrant centrosome numbers per se or centrosome accumulation, correlated significantly with the presence of cell division errors. In addition, our experiments revealed that in particular pseudo-bipolar mitoses may play a role in the propagation of chromosomal instability in high-risk HPV-associated tumors. These results provide new insights into the role of centrosome aberrations in cell division errors and encourage further studies on centrosome overduplication as a predictive biomarker of malignant progression in HPV-associated anal lesions.

Physical status of multiple human papillomavirus genotypes in flow-sorted cervical cancer cells

Multiple human papilloma virus (HPV) infections have been detected in cervical cancer. To investigate the significance of multiple HPV infections, we studied their prevalence in cancer samples from a low-risk (Dutch) and a high-risk (Surinamese) population and the correlation of HPV infection with tumor cell aneuploidy. SPF(10) LiPA was used for HPV detection in formalin-fixed cervical carcinoma samples from 96 Dutch and 95 Surinamese patients. Samples with HPV type 16 or 18 infections were sorted by flow cytometry, and fluorescence in situ hybridization was performed on the diploid and aneuploid subpopulations to detect HPV 16 and 18 genotypes simultaneously. Multiple HPV infections were present in 11 of 80 (13.8%) Dutch and 17 of 77 (22.1%) Surinamese carcinomas. Three cases had an HPV 16 and HPV 18 coinfection: in two cases, integrated HPV copies of HPV 16 or 18 were detected in the aneuploid fraction, and in one case both HPV 16 and 18 were present solely as episomes. Based on our findings, multiple HPV infections are present in cervical cancer samples from both high- and low-risk populations. Furthermore, multiple HPV types can be present in an episomal state in both diploid and aneuploid tumor cells, but integrated HPV genomes are detectable only in the aneuploid tumor cell subpopulations.

Centrosome and retroviruses: the dangerous liaisons

Centrosomes are the major microtubule organizing structures in vertebrate cells. They localize in close proximity to the nucleus for the duration of interphase and play major roles in numerous cell functions. Consequently, any deficiency in centrosome function or number may lead to genetic instability. Several viruses including retroviruses such as, Foamy Virus, HIV-1, JSRV, M-PMV and HTLV-1 have been shown to hamper centrosome functions for their own profit, but the outcomes are very different. Foamy viruses, HIV-1, JSRV, M-PMV and HTLV-1 use the cellular machinery to traffic towards the centrosome during early and/or late stages of the infection. In addition HIV-1 Vpr protein alters the cell-cycle regulation by hijacking centrosome functions. Enthrallingly, HTLV-1 Tax expression also targets the functions of the centrosome, and this event is correlated with centrosome amplification, aneuploidy and transformation.

RNA polymerase II transcription is required for human papillomavirus type 16 E7- and hydroxyurea-induced centriole overduplication

Aberrant centrosome numbers are detected in virtually all human cancers where they can contribute to chromosomal instability by promoting mitotic spindle abnormalities. Despite their widespread occurrence, the molecular mechanisms that underlie centrosome amplification are only beginning to emerge. Here, we present evidence for a novel regulatory circuit involved in centrosome overduplication that centers on RNA polymerase II (pol II). We found that human papillomavirus type 16 E7 (HPV-16 E7)- and hydroxyurea (HU)-induced centriole overduplication are abrogated by alpha-amanitin, a potent and specific RNA pol II inhibitor. In contrast, normal centriole duplication proceeded undisturbed in alpha-amanitin-treated cells. Centriole overduplication was significantly reduced by siRNA-mediated knock down of CREB-binding protein (CBP), a transcriptional co-activator. We identified cyclin A2 as a key transcriptional target of RNA pol II during HU-induced centriole overduplication. Collectively, our results show that ongoing RNA pol II transcription is required for centriole overduplication whereas it may be dispensable for normal centriole duplication. Given that many chemotherapeutic agents function through inhibition of transcription, our results may help to develop strategies to target centrosome-mediated chromosomal instability for cancer therapy and prevention.

A mutation in the centriole-associated protein centrin causes genomic instability via increased chromosome loss in Chlamydomonas reinhardtii

BACKGROUND

The role of centrioles in mitotic spindle function remains unclear. One approach to investigate mitotic centriole function is to ask whether mutation of centriole-associated proteins can cause genomic instability.

RESULTS

We addressed the role of the centriole-associated EF-hand protein centrin in genomic stability using a Chlamydomonas reinhardtii centrin mutant that forms acentriolar bipolar spindles and lacks the centrin-based rhizoplast structures that join centrioles to the nucleus. Using a genetic assay for loss of heterozygosity, we found that this centrin mutant showed increased genomic instability compared to wild-type cells, and we determined that the increase in genomic instability was due to a 100-fold increase in chromosome loss rates compared to wild type. Live cell imaging reveals an increased rate in cell death during G1 in haploid cells that is consistent with an elevated rate of chromosome loss, and analysis of cell death versus centriole copy number argues against a role for multipolar spindles in this process.

CONCLUSION

The increased chromosome loss rates observed in a centrin mutant that forms acentriolar spindles suggests a role for centrin protein, and possibly centrioles, in mitotic fidelity.

Chromosomal instability in oral cancer cells

Chromosomal instability is a common feature of human tumors, including oral cancer. Although a tumor karyotype may remain quite stable over time, chromosomal instability can lead to 'variations on a theme' of a clonal cell population, often with each cell within a tumor possessing a different karyotype. Thus, chromosomal instability appears to be an important acquired feature of tumor cells, since propagation of such a diverse cell population may facilitate evasion of standard therapies. There are several sources of chromosomal instability, although the primary causes appear to be defects in chromosomal segregation, telomere stability, cell-cycle checkpoint regulation, and the repair of DNA damage. Our understanding of the biological basis of chromosomal instability in cancer cells is increasing rapidly, and we are finding that the seemingly unrelated origins of this phenomenon may actually be related through the complex network of cellular signaling pathways. Here, we review the general causes of chromosomal instability in human tumors. Specifically, we address the state of our knowledge regarding chromosomal instability in oral cancer, and discuss various mechanisms that enhance the ability of cancer cells within a tumor to express heterogeneous karyotypes. In addition, we discuss the clinical relevance of factors associated with chromosomal instability as they relate to tumor prognosis and therapy.

Mitotic Infidelity and Centrosome Duplication Errors in Cells Overexpressing Tripeptidyl-Peptidase II

The oligopeptidase tripeptidyl-peptidase II (TPP II) is up-regulated Burkitt's lymphoma (BL) cells that overexpress the c-myc proto-oncogene and is required for their growth and survival. Here we show that overexpression of TPP II induces accelerated growth and resistance to apoptosis in human embryonic kidney 293 cells. This correlates with the appearance of multiple chromosomal aberrations, numerical and structural centrosome abnormalities, and multipolar cell divisions. Similar mitotic aberrations were also observed in a panel of BL lines and were suppressed, in parallel with TPP II down-regulation, upon reversion of BL-like characteristics in EBV-immortalized B lymphocytes carrying a tetracycline-regulated c-myc. Functional TPP II knockdown by small interfering RNA expression in BL cells caused the appearance of giant polynucleated cells that failed to complete cell division. Collectively, these data point to a role of TPP II in the regulation of centrosome homeostasis and mitotic fidelity suggesting that this enzyme may be a critical player in the induction and/or maintenance of genetic instability in malignant cells.

DNA aneuploidy and integration of human papillomavirus type 16 e6/e7 oncogenes in intraepithelial neoplasia and invasive squamous cell carcinoma of the cervix uteri

PURPOSE

Increasingly deregulated expression of the E6-E7 oncogenes of high-risk human papillomaviruses (HR-HPVs) has been identified as the major transforming factor in the pathogenesis of cervical dysplasia and derived cancers. The expression of these genes in epithelial stem cells first results in chromosomal instability and induces chromosomal aneuploidy. It is speculated that this subsequently favors integration of HR-HPV genomes into cellular chromosomes. This in turn leads to expression of viral cellular fusion transcripts and further enhanced expression of the E6-E7 oncoproteins. Chromosomal instability and aneuploidization thus seems to precede and favor integration of HR-HPV genomes.

EXPERIMENTAL DESIGN

To prove this sequential concept, we analyzed here the sequence of events of DNA aneuploidization and integration in a series of HPV-16-positive cervical dysplastic lesions and carcinomas. Eighty-five punch biopsies of HPV-16-positive cervical lesions (20 CIN1/2, 50 CIN3, and 15 CxCa) were analyzed for DNA ploidy by DNA flow cytometry and for integration of HPV E6/E7 oncogenes using the amplification of papillomavirus oncogene transcripts assay, a reverse transcription-PCR method to detect integrate-derived human papillomavirus oncogene transcripts.

RESULTS

DNA aneuploidy and viral genome integration were both associated with increasing dysplasia (P < 0.001, chi(2) test for trend). In addition, DNA aneuploidy was associated with increased viral integration (P < 0.01, Fisher's exact test). Nineteen of 20 (95%) lesions with integrated viral genomes had aneuploid cell lines; however, only 19 of 32 (59%) lesions with aneuploid cell lines had integrated viral genomes.

CONCLUSIONS

These data support the hypothesis that aneuploidization precedes integration of HR-HPV genomes in the progression of cervical dysplasia. Accordingly, deregulated viral oncogene expression appears to result first in chromosomal instability and aneuploidization and is subsequently followed by integration of HR-HPV genomes in the affected cell clones.

[Viral carcinogenesis of head and neck tumors]

Approximately 15% of malignant diseases are caused by infectious agents. Human papilloma viruses (HPV) can be frequently found in oral carcinomas, especially tonsillar cancer. A group of HPV-infected tumors shows clear signs for a virally induced transformation process: high-risk HPVs can be detected in all tumor cells, the viral oncogenes E6 and E7 are constantly expressed and lead to upregulation of cellular p16(INK4a), a cyclin-dependent kinase inhibitor. The patients frequently lack typical risk factors associated with head and neck cancers such as drinking and smoking. Epstein-Barr viruses (EBV) are associated with lymphoproliferative disorders and cause nasopharyngeal carcinoma (NPC). NPC has a high incidence in some East Asian countries. In this review, the molecular pathogenesis of HPV- and EBV-associated malignancies are described and the clinical relevance of the presented findings is discussed.

Short duration of elevated vIRF-1 expression during lytic replication of human herpesvirus 8 limits its ability to block antiviral responses induced by alpha interferon in BCBL-1 cells

Human herpesvirus 8 (HHV-8) encodes multiple proteins that disrupt the host antiviral response, including viral interferon (IFN) regulatory factor 1 (vIRF-1). The product of the vIRF-1 gene blocks responses to IFN when overexpressed by transfection, but the functional consequence of vIRF-1 that is expressed during infection with HHV-8 is not known. These studies demonstrate that BCBL-1 cells that were latently infected with HHV-8 expressed low levels of vIRF-1 that were associated with PML bodies, whereas much higher levels of vIRF-1 were transiently expressed during the lytic phase of HHV-8 replication. The low levels of vIRF-1 that were associated with PML bodies were insufficient to block alpha IFN (IFN-alpha)-induced alterations in gene expression, whereas cells that expressed high levels of vIRF-1 were resistant to some changes induced by IFN-alpha, including the expression of the double-stranded-RNA-activated protein kinase. High levels of vIRF-1 were expressed for only a short period during the lytic cascade, so many cells with HHV-8 in the lytic phase responded to IFN-alpha with increased expression of antiviral genes and enhanced apoptosis. Furthermore, the production of infectious virus was severely compromised when IFN-alpha was present early during the lytic cascade. These studies indicate that the transient expression of high levels of vIRF-1 is inadequate to subvert many of the antiviral effects of IFN-alpha so that IFN-alpha can effectively induce apoptosis and block production of infectious virus when present early in the lytic cascade of HHV-8.

Systematic review of genomic integration sites of human papillomavirus genomes in epithelial dysplasia and invasive cancer of the female lower genital tract

Cancers of the anogenital tract as well as some head and neck cancers are caused by persistent infections with high-risk type human papillomaviruses (HPVs). Two viral oncogenes, E6 and E7, induce severe chromosomal instability associated with centrosome aberrations, anaphase bridges, chromosome lagging, and breaking. This occurs early in preneoplastic lesions, when the viral genome still persists in an episomal state. In most invasive cancers and also in a few high-grade dysplastic lesions, however, integration of high-risk HPV genomes into the host genome is observed. Integration seems to be a direct consequence of chromosomal instability and an important molecular event in the progression of preneoplastic lesions. Disruption or deregulation of defined critical cellular gene functions by insertional mutagenesis by integrated HPV genome fragments has been hypothesized as one major promoting factor in the pathogenesis of HPV-associated cancers. This hypothesis was based on the detection of HPV integration events in the area of tumor-relevant genes in few cases. Here, we reviewed >190 reported integration loci with respect to changes in the viral structure and the targeted genomic locus. This analysis confirms that HPV integration sites are randomly distributed over the whole genome with a clear predilection for genomic fragile sites. No evidence for targeted disruption or functional alteration of critical cellular genes by the integrated viral sequences could be found.

Loss of CCAAT/enhancer binding protein delta promotes chromosomal instability

The transcription factor CCAAT/enhancer binding protein delta (Cebpd, also known as C/EBPdelta, CRP3, CELF, NF-IL6beta) is implicated in diverse cellular functions such as the acute phase response, adipocyte differentiation, learning and memory, and mammary epithelial cell growth control. Here, we report that lack of Cebpd causes genomic instability and centrosome amplifications in primary embryonic fibroblasts derived from 129S1 mice. Upon spontaneous immortalization, Cebpd-deficient fibroblasts acquire transformed features such as impaired contact inhibition and reduced serum dependence. These data identify a novel role for Cebpd in the maintenance of chromosomal stability and suggest a potential tumor suppressor function in vivo.

Excessive centrosome abnormalities without ongoing numerical chromosome instability in a Burkitt's lymphoma

Numerical and structural centrosome abnormalities are detected in various human malignancies and have been implicated in the formation of multipolar mitoses, chromosome missegregation, and chromosomal instability. Despite this association between centrosome abnormalities and cancerous growth, a causative role of centrosome aberrations in generating chromosomal instability and aneuploidy has not been universally established. We report here excessive numerical and structural centrosome abnormalities in a malignant Burkitt's lymphoma harboring the characteristic t(8;14) chromosomal translocation. Using conventional karyotyping and fluorescence in situ hybridization (FISH), we detected no signs of ongoing numerical chromosome instability, although the tumor displayed sporadic multipolar metaphases. These findings demonstrate that centrosome abnormalities are not a universal surrogate marker for chromosomal instability in malignant tumors. Moreover, our results suggest a model in which additional cellular alterations may be required to promote centrosome-related mitotic defects in tumor cells.

A comprehensive analysis of HPV integration loci in anogenital lesions combining transcript and genome-based amplification techniques

Persistent infections with high-risk human papillomaviruses (HPVs) induce dysplastic lesions of the lower genital tract. Some of these lesions eventually progress to invasive cancers, particularly of the uterine cervix. In many advanced preneoplastic cervical lesions and most derived carcinomas, HPV genomes are found to be integrated into the host cell chromosomes. Although HPV integration seems to play an important role in the progression of cervical dysplasia, the underlying mechanisms are still unclear. To investigate the pathogenic role of genomic integration of HPV genomes in greater detail, we analysed integration sites of HPV16 and 18 genomes in 21 anogenital precancerous and cancerous lesions using a ligation-mediated chain reaction (DIPS) and the recently described amplification of papilloma virus oncogene transcripts (APOT) assay. On the genomic level, only singular integration events were observed in individual neoplastic cell clones. At many integration sites, a short overlap between HPV and genomic sequences was observed, suggesting that the integration of HPV genomes is mediated by nonhomologous sequence-specific recombination. APOT analysis revealed that the majority of integrated HPV genomes was actively transcribed. These data suggest that in the progression of cervical preneoplasia to invasive carcinomas, integration of viral genomes occurs only at single or few chromosomal loci in a given cell clone. Disruption of cellular genes might support malignant transformation in rare cases; however, it is not a pathogenic prerequisite. The main function of HPV integration seems to be the stabilization of oncogene transcription.

Detection of human papillomavirus in Chinese esophageal squamous cell carcinoma and its adjacent normal epithelium

AIM: To investigate the putative role of human papillomavirus (HPV) infection in the carcinogenesis of esophageal squamous cell carcinoma in China.

METHODS: Twenty-three esophageal squamous cell carcinoma samples and the distal normal epithelium from Shanxi Province, and 25 more esophageal squamous cell carcinoma samples from Anyang city, two areas with a high incidence of esophageal cancer in China, were detected for the existence of HPV-16 DNA by PCR, mRNA in situ hybridization (ISH) and immunohistochemistry (IHC) targeting HPV-16 E6 gene.

RESULTS: There were approximately 64% (31/48) patients having HPV-16 DNA in tumor samples, among them nearly two-thirds (19/31) samples were detected with mRNA expression of HPV-16 E6. However, in the normal esophageal epithelium from cancer patients, the DNA and mRNA of HPV-16 were found with much less rate: 34.7% (8/23) and 26.1% (6/23) respectively. In addition, at protein level detected by IHC assay, 27.1% (13/48) tumor samples had virus oncoprotein E6 expression, while only one case of normal epithelium was found positive.

CONCLUSION: HPV infection, especially type 16, should be considered as a risk factor for esophageal malignancies in China.

Computerized video time-lapse (CVTL) analysis of the fate of giant cells produced by X-irradiating EJ30 human bladder carcinoma cells

This study was designed to examine the viability and proliferation of uninucleated and multinucleated giant cells formed after 6 Gy X irradiation. The pedigrees of 102 individual EJ30 giant cells present 5 days after irradiation were analyzed from time-lapse movies captured over 6.3 days from 100 fields (100x). Pedigree analysis enabled us to study the proliferation of giant cells. The average starting size (area) of the giant cells (14500 +/- 9100 microm(2)) was approximately 25 times larger than the normal-sized cells observed after irradiation (560 +/- 200 microm(2)). From a total of 76 pedigrees of uninucleated giant cells, 42 had giant cells that either died or were arrested, while 34 divided at least once and produced progeny that divided again (five three times and three four times) before the progeny died or were arrested. Twenty-four pedigrees contained progeny that were lost from observation after dividing at least once. While most progeny continued to have giant cell morphology, two uninucleated giant cells ultimately produced progeny that contained two normal-sized cells. From a total of 26 multinucleated giant cells, only three divided. Two divided only once, but one produced progeny that divided two times. In all, 37 out of 102 giant cells divided at least once; eight of these divided four or five times with two of these pedigrees ultimately producing two normal-sized daughter cells. These results suggest that a small fraction of giant cells might be potentially clonogenic.

Human papillomaviruses and centrosome duplication errors: modeling the origins of genomic instability

The majority of human cancers are genomically unstable, often with gains or losses of whole chromosomes. In high-risk human papillomavirus (HPV)-associated cervical neoplasia, the two HPV-encoded oncoproteins E6 and E7 have been implicated in mitotic infidelity by their ability to induce centrosome-related mitotic disturbances. However, the mechanisms by which HPV E6 and E7 subvert centrosome homeostasis are strikingly different. Whereas the E7 oncoprotein rapidly drives centrosome duplication errors in cells that appear phenotypically normal, expression of the HPV E6 oncoprotein results in an accumulation of supernumerary centrosomes in multinucleated cells. The primary centrosome duplication defect in HPV E7 expressing cells may be linked to the ability of E7 to disrupt regulatory nodes that govern both the host cell division cycle machinery and the initiation of centrosome duplication. Most importantly, the E7 oncoprotein has been shown to dysregulate cdk2 activity, a major determinant for the initiation of centrosome duplication. HPV-induced centrosome abnormalities, multipolar mitoses, and aneuploidy often occur at early stages during cervical carcinogenesis and increase with malignant conversion. These findings suggest that HPV oncoprotein-induced chromosomal instability increases the risk for genetic changes that may ultimately facilitate carcinogenic progression.

The mechanism regulating the dissociation of the centrosomal protein C-Nap1 from mitotic spindle poles

The centrosomal protein C-Nap1 is thought to play an important role in centrosome cohesion during interphase of the cell cycle. At the onset of mitosis, when centrosomes separate for bipolar spindle formation, C-Nap1 dissociates from centrosomes. Here we report the results of experiments aimed at determining whether the dissociation of C-Nap1 from mitotic centrosomes is triggered by proteolysis or phosphorylation. Specifically, we analyzed both the cell cycle regulation of endogenous C-Nap1 and the fate of exogenously expressed full-length C-Nap1. Western blot analyses suggested a reduction in the endogenous C-Nap1 level during M phase, but studies using proteasome inhibitors and destruction assays performed in Xenopus extracts argue against ubiquitin-dependent degradation of C-Nap1. Instead, our data indicate that the mitotic C-Nap1 signal is reduced as a consequence of M-phase-specific phosphorylation. Overexpression of full-length C-Nap1 in human U2OS cells caused the formation of large structures that embedded the centrosome and impaired its microtubule nucleation activity. Remarkably, however, these centrosome-associated structures did not interfere with cell division. Instead, centrosomes were found to separate from these structures at the onset of mitosis, indicating that a localized and cell-cycle-regulated activity can dissociate C-Nap1 from centrosomes. A prime candidate for this activity is the centrosomal protein kinase Nek2, as the formation of large C-Nap1 structures was substantially reduced upon co-expression of active Nek2. We conclude that the dissociation of C-Nap1 from mitotic centrosomes is regulated by localized phosphorylation rather than generalized proteolysis.

Centrosome overduplication, increased ploidy and transformation in cells expressing endoplasmic reticulum-associated cyclin A2

Cyclin A2 is predominantly, but not exclusively, localized in the nucleus from G1/S transition onwards. It is degraded when cells enter mitosis after nuclear envelope breakdown. We previously showed that a fusion protein (S2A) between the hepatitis B virus (HBV) surface antigen protein and a non-degradable fragment of human cyclin A2 (Delta152) resides in the endoplasmic reticulum membranes, escapes degradation and transforms normal rat fibroblasts. The present study investigates whether cytoplasmic cyclin A2 may play a role in oncogenesis. We show that the sequestration of non-degradable cyclin A2-Delta152 by a cellular ER targeting domain (PRL-A2) leads to cell transformation when coexpressed with activated Ha-ras. REF52 cells constitutively expressing PRL-A2 are found to have a high incidence of multinucleate giant cells, polyploidy and abnormal centrosome numbers, giving rise to the nucleation of multipolar spindles. Injection of these cells into athymic nude mice causes tumors, even in the absence of a cooperating Ha-ras oncogene. These results demonstrate that, independently of any viral context, an intracellular redistribution of non-degradable cyclin A2 is capable of deregulating the normal cell cycle to the point where it promotes aneuploidy and cancer.

Biological activities and molecular targets of the human papillomavirus E7 oncoprotein

The human papillomavirus (HPV) E7 protein is one of only two viral proteins that remain expressed in HPV-associated human cancers. HPV E7 proteins share structural and functional similarities with oncoproteins encoded by other small DNA tumor viruses such as adenovirus E1A and SV40 large tumor antigen. The HPV E7 protein plays an important role in the viral life cycle by subverting the tight link between cellular differentiation and proliferation in normal epithelium, thus allowing the virus to replicate in differentiating epithelial cells that would have normally withdrawn from the cell division cycle. The transforming activities of E7 largely reflect this important function.

Centrosome abnormalities and genomic instability by episomal expression of human papillomavirus type 16 in raft cultures of human keratinocytes

Primary human keratinocytes with ectopic expression of high-risk human papillomavirus (HPV) E6 and E7 oncoproteins display abnormal centrosome numbers, multipolar mitoses, and aneusomy. However, it has not been explored whether these abnormalities can occur in cells containing HPV episomes where E6 and E7 expression is under viral transcriptional control. Here, we demonstrate that centrosome abnormalities and genomic instability occur in organotypic raft cultures of human keratinocytes with episomal HPV-16 even at low copy numbers. We conclude that HPV-16 DNA, when maintained as an episome, can disturb centrosome homeostasis and subvert genomic integrity of the host cell during early stages of the viral infection.