The frequency of immortalization of human fibroblasts and mammary epithelial cells transfected with SV40 large T-antigen

Upregulated expression of lamin B receptor increases cell proliferation and suppresses genomic instability: implications for cellular immortalization

Mammalian somatic cells undergo terminal proliferation arrest after a limited number of cell divisions, a phenomenon termed cellular senescence. However, cells acquire the ability to proliferate infinitely (cellular immortalization) through multiple genetic alterations. Inactivation of tumor suppressor genes such as p53, RB and p16 is important for cellular immortalization, although additional molecular alterations are required for cellular immortalization to occur. Here, we aimed to gain insights into these molecular alterations. Given that cellular immortalization is the escape of cells from cellular senescence, genes that regulate cellular senescence are likely to be involved in cellular immortalization. Because senescent cells show altered heterochromatin organization, we investigated the implications of lamin A/C, lamin B1 and lamin B receptor (LBR), which regulate heterochromatin organization, in cellular immortalization. We employed human immortalized cell lines, KMST-6 and SUSM-1, and found that expression of LBR was upregulated upon cellular immortalization and downregulated upon cellular senescence. In addition, knockdown of LBR induced cellular senescence with altered chromatin configuration. Additionally, enforced expression of LBR increased cell proliferation likely through suppression of genome instability in human primary fibroblasts that expressed the simian virus 40 large T antigen (TAg), which inactivates p53 and RB. Furthermore, expression of TAg or knockdown of p53 led to upregulated LBR expression. These observations suggested that expression of LBR might be upregulated to suppress genome instability in TAg-expressing cells, and, consequently, its upregulated expression assisted the proliferation of TAg-expressing cells (i.e. p53/RB-defective cells). Our findings suggest a crucial role for LBR in the process of cellular immortalization.

Immortalization of mouse primary astrocytes

In cell culture studies, immortalized primary cells have become a useful tool to investigate the molecular and cellular functions of different types of cells. Several immortalization agents, such as human telomerase reverse transcriptase (hTERT) and Simian Virus 40 (SV40) T antigens, are commonly used for primary cell immortalization. Astrocytes, as the most abundant glial cell type in the central nervous system, are promising therapeutical targets for many neuronal disorders, such as Alzheimer's disease and Parkinson's disease. Immortalized primary astrocytes can provide useful information for astrocytes biology, astrocytes-neuron interactions, glial interactions and astrocytes-associated neuronal diseases. In this study, we successfully purified primary astrocytes with immuno-panning method and examined the astrocyte functions after immortalization through both hTERT and SV40 Large-T antigens. As expected, both immortalized astrocytes presented unlimited lifespan and highly expressed multiple astrocyte-specific markers. However, SV40 Large-T antigen, but not hTERT, immortalized astrocytes displayed fast ATP-induced calcium wave in culture. Hence, SV40 Large-T antigen could be a better choice for primary astrocyte immortalization, which closely mimics the cell biology of primary astrocytes in culture. In summary, the purification and immortalization of primary astrocytes presented in this study can be used for studying astrocyte biology under physiological and pathological conditions.

Establishment of a sheep immortalization cell line for generating and amplifying Orf virus recombinants

Orf virus (ORFV) causes highly contagious vesiculoulcerative pustular and skin lesions in ruminants like sheep. Developing ORFV-based recombinant vaccine is a potential way to combat Orf disease. Although ORFV could propagate in some kinds of primary cells, the proliferative capacity of primary cells is limited. Therefore, establishing immortalized stable cell line is an effective and affordable way for the production of live ORFV vaccine. In the present study, we introduced a telomerase reverse transcriptase (TERT) gene-expressing cassette into primary ovine fetal turbinate (OFTu) cells, then selected and expanded the cells, which was considered as immortalized OFTu cell line. Our results showed that TERT introduction has successfully expended the lifespan of OFTu cell line over 80 passages, without changing the cellular morphology, affecting chromosomes karyotype and inducing the cellular tumorigenic ability. Immortalized OFTu cell line-derived ORFV has caused similar levels of cytopathic effects (CPE), viral titers and viral particles when compared with the ORFV from primary OFTu cell. Importantly, immortalized OFTu cell line was suitable for generating gene-modified ORFV recombinant through homologous recombination, and for the amplification of ORFV recombinant. In summary, an immortalized OFTu cell line was established and characterized, which could be a powerful tool for preparing ORFV recombinant vaccines.

Telomere length as a biomarker of aging and diseases

As research related to healthspan and lifespan has become a hot topic, the necessity for a reliable and practical biomarker of aging (BoA), which can provide information about mortality and morbidity risk, along with remaining life expectancy, has increased. The chromosome terminus non-coding protective structure that prevents genomic instability is called a telomere. The continual shortening of telomeres, which affects their structure as well as function, is a hallmark of agedness. The aforementioned process is a potential cause of age-related diseases (ARDs), leading to a bad prognosis and a low survival rate, which compromise health and longevity. Hence, studies scrutinizing the BoAs often include telomere length (TL) as a prospective candidate. The results of these studies suggest that TL measurement can only provide an approximate appraisal of the aging rate, and its implementation into clinical practice and routine use as a BoA has many limitations and challenges. Nevertheless, measuring TL while determining other biomarkers can be used to assess biological age. This review focuses on the importance of telomeres in health, senescence, and diseases, as well as on summarizing the results and conclusions of previous studies evaluating TL as a potential BoA.

One-Two Punch Therapy for the Treatment of T-Cell Malignancies Involving p53-Dependent Cellular Senescence

T-cell malignancies are still difficult to treat due to a paucity of plans that target critical dependencies. Drug-induced cellular senescence provides a permanent cell cycle arrest during tumorigenesis and cancer development, particularly when combined with senolytics to promote apoptosis of senescent cells, which is an innovation for cancer therapy. Here, our research found that wogonin, a well-known natural flavonoid compound, not only had a potential to inhibit cell growth and proliferation but also induced cellular senescence in T-cell malignancies with nonlethal concentration. Transcription activity of senescence-suppression human telomerase reverse transcriptase (hTERT) and oncogenic C-MYC was suppressed in wogonin-induced senescent cells, resulting in the inhibition of telomerase activity. We also substantiated the occurrence of DNA damage during the wogonin-induced aging process. Results showed that wogonin increased the activity of senescence-associated β-galactosidase (SA-β-Gal) and activated the DNA damage response pathway mediated by p53. In addition, we found the upregulated expression of BCL-2 in senescent T-cell malignancies because of the antiapoptotic properties of senescent cells. Following up this result, we identified a BCL-2 inhibitor Navitoclax (ABT-263), which was highly effective in decreasing cell viability and inducing apoptotic cell death in wogonin-induced senescent cells. Thus, the “one-two punch” approach increased the sensibility of T-cell malignancies with low expression of BCL-2 to Navitoclax. In conclusion, our research revealed that wogonin possesses potential antitumor effects based on senescence induction, offering a better insight into the development of novel therapeutic methods for T-cell malignancies.

Simple Detection Methods for Senescent Cells: Opportunities and Challenges

Cellular senescence, the irreversible growth arrest of cells from conditional renewal populations combined with a radical shift in their phenotype, is a hallmark of ageing in some mammalian species. In the light of this, interest in the detection of senescent cells in different tissues and different species is increasing. However much of the prior work in this area is heavily slanted towards studies conducted in humans and rodents; and in these species most studies concern primary fibroblasts or cancer cell lines rendered senescent through exposure to a variety of stressors. Complex techniques are now available for the detailed analysis of senescence in these systems. But, rather than focussing on these methods this review instead examines techniques for the simple and reproducible detection of senescent cells. Intended primary for the non-specialist who wishes to quickly detect senescent cells in tissues or species which may lack a significant evidence base on the phenomenon it emphasises the power of the original techniques used to demonstrate the senescence of cells, their interrelationship with other markers and their potential to inform on the senescent state in new species and archival specimens.

The Role of Alternative RNA Splicing in the Regulation of hTERT, Telomerase, and Telomeres: Implications for Cancer Therapeutics

Alternative RNA splicing impacts the majority (>90%) of eukaryotic multi-exon genes, expanding the coding capacity and regulating the abundance of gene isoforms. Telomerase (hTERT) is a key example of a gene that is alternatively spliced during human fetal development and becomes dysregulated in nearly all cancers. Approximately 90% of human tumors use telomerase to synthesize de novo telomere repeats and obtain telomere-dependent cellular immortality. Paradigm shifting data indicates that hTERT alternative splicing, in addition to transcription, plays an important role in the regulation of active telomerase in cells. Our group and others are pursuing the basic science studies to progress this emerging area of telomerase biology. Recent evidence demonstrates that switching splicing of hTERT from the telomerase activity producing full-length hTERT isoform to alternatively spliced, non-coding isoforms may be a novel telomerase inhibition strategy to prevent cancer growth and survival. Thus, the goals of this review are to detail the general roles of telomerase in cancer development, explore the emerging regulatory mechanisms of alternative RNA splicing of the hTERT gene in various somatic and cancer cell types, define the known and potential roles of hTERT splice isoforms in cancer cell biology, and provide insight into new treatment strategies targeting hTERT in telomerase-positive cancers.

Establishment and characterization of an immortalized human chondrocyte cell line

OBJECTIVES

Following a specific number of mitotic divisions, primary chondrocytes undergo proliferative senescence, thwarting efforts to expand sufficient populations in vitro suitable to meet the needs of scientific research or medical therapies. Therefore, the human telomerase reverse transcriptase (TERT) was used to immortalize human chondrocyte and establish a cell line that escape from cellular senescence.

RESULTS

The human chondrocytes were successfully immortalized by ectopic stable expression of TERT. The established TERT-Chondrocyte cell line showed robust proliferation capacity, even in late passages up to P20, and displayed little cellular senescence. Moreover, TERT-Chondrocyte cells at 20th passage showed similar chondrocyte properties to normal chondrocytes at early passages.

CONCLUSIONS

Ectopic stable expression of TERT is an effective way to immortalized human chondrocyte. The immortalized chondrocytes displayed little cellular senescence, showed promise as an in vitro model to investigate osteoarthritis, and may be a promising resource for cell-based therapy for damaged cartilage.

SV40 and human mesothelioma

Simian virus 40 (SV40) is a DNA tumor virus capable of infecting and transforming human mesothelial (HM) cells in vitro. Hamsters injected intracardially to expose most tissue types to SV40 preferentially develop mesotheliomas. In humans, asbestos is the main cause of mesothelioma, and asbestos and SV40 are co-carcinogens in transforming HM cells in tissue culture and in causing mesothelioma in hamsters. Laser microdissection experiments conducted in the laboratory of Adi Gazdar demonstrated that SV40 was present specifically in the malignant mesothelioma cells and not in nearby stromal cells. Further experiments demonstrated that SV40 remains episomal in HM cells and astrocytes because of the production of a long antisense RNA that represses viral capsid protein production. Thus, the potent SV40 oncoprotein, T-antigen (Tag), is expressed, but because the capsid proteins are not produced, the cells are not lysed and, instead, become transformed. Together this evidence suggests that SV40 may contribute to the development of mesotheliomas in humans. However, epidemiological evidence to support this hypothesis is lacking. This chapter also summarizes the introduction of SV40, a monkey virus, into the human population as an unrecognized contaminant of early poliovaccines. In addition to mesotheliomas, SV40 now is linked with brain cancers, osteosarcomas, and lymphomas in humans. Explanations are provided for the apparent geographic variations in SV40 prevalence and for controversies about the role of SV40 in human cancer.

Cell Culture and Coculture for Oncological Research in Appropriate Microenvironments

With the increase in knowledge on the importance of the tumor microenvironment, cell culture models of cancers can be adapted to better recapitulate physiologically relevant situations. Three main microenvironmental factors influence tumor phenotype: the biochemical components that stimulate cells, the fibrous molecules that influence the stiffness of the extracellular matrix, and noncancerous cells like epithelial cells, fibroblasts, endothelial cells, and immune cells. Here we present methods for the culture of carcinomas in the presence of a matrix of specific stiffness, and for the coculture of tumors and fibroblasts as well as epithelial cells in the presence of matrix. Information is provided to help with choice and assessment of the matrix support and in working with serum-free medium. Using the example of a tissue chip recapitulating the environmental geometry of carcinomas, we also highlight the development of engineered platforms that provide exquisite control of cell culture parameters necessary in research and development. © 2019 by John Wiley & Sons, Inc.

Telomere biology and age-related diseases

Telomeres are the protective end caps of chromosomes and shorten with every cell division. Telomere length has been proposed as a biomarker of biological age and a risk factor for age-related diseases. Epidemiologic studies show an association between leukocyte telomere length (LTL) and mortality. There is solid evidence that links LTL with cardiovascular disease. Short telomeres promote atherosclerosis and impair the repair of vascular lesions. Alzheimer's disease patients have also a reduced LTL. Telomeres measured in tumor tissue from breast, colon and prostate are shorter than in healthy tissue from the same organ and the same patient. In healthy tissue directly adjacent to these tumors, telomeres are also shorter than in cells that are more distant from the cancerous lesion. A reduced telomere length in cancer tissue from breast, colon and prostate is associated with an advanced disease state at diagnosis, faster disease progression and poorer survival. By contrast, results regarding LTL and cancer are inconsistent. Furthermore, the majority of studies did not find significant associations between LTL, bone mineral density (BMD) and osteoporosis. The present manuscript gives an overview about our current understanding of telomere biology and reviews existing knowledge regarding the relationship between telomere length and age-related diseases.

Nonhistone targets of KAT2A and KAT2B implicated in cancer biology 1

Lysine acetylation is a critical post-translation modification that can impact a protein's localization, stability, and function. Originally thought to only occur on histones, we now know thousands of nonhistone proteins are also acetylated. In conjunction with many other proteins, lysine acetyltransferases (KATs) are incorporated into large protein complexes that carry out these modifications. In this review we focus on the contribution of two KATs, KAT2A and KAT2B, and their potential roles in the development and progression of cancer. Systems biology demands that we take a broad look at protein function rather than focusing on individual pathways or targets. As such, in this review we examine KAT2A/2B-directed nonhistone protein acetylations in cancer in the context of the 10 "Hallmarks of Cancer", as defined by Hanahan and Weinberg. By focusing on specific examples of KAT2A/2B-directed acetylations with well-defined mechanisms or strong links to a cancer phenotype, we aim to reinforce the complex role that these enzymes play in cancer biology.

Telomeres in cancer

Telomere shortening as a consequence of cell divisions during aging and chronic diseases associates with an increased cancer risk. Experimental data revealed that telomere shortening results in telomere dysfunction, which in turn affects tumorigenesis in two ways. First, telomere dysfunction suppresses tumor progression by the activation of DNA damage checkpoints, which induce cell cycle arrest (senescence) or apoptosis, as well as by inducing metabolic compromise and activation of immune responses directed against senescent cells. Second, telomere dysfunction promotes tumorigenesis by inducing chromosomal instability in tumor initiating cells, by inhibiting proliferative competition of non-transformed cells, and possibly, also by influencing tumor cell plasticity. The tumor promoting effects of telomere dysfunction are context dependent and require the loss of p53-dependent DNA damage checkpoints or other genetic modifiers that attenuate DNA damage responses possibly involving complex interactions of different genes. The activation of telomere stabilizing mechanisms appears as a subsequent step, which is required to enable immortal grotwh of emerging cancer cells. Here, we conceptually discuss our current knowledge and new, unpublished experimental data on telomere dependent influences on tumor initiation and progression.

Assessment of in Vitro Applicability of Reversibly Immortalized NKNT-3 Cells and Clonal Derivatives

In vitro applications of human hepatocytes, such as bioartificial livers and toxicity assays, require thoroughly testing of human cell lines prior to using them as alternative cell sources. The reversibly immortalized NKNT-3 cell line was reported to show clear in vivo functionality. Here, NKNT-3 cells were tested for their in vitro applicability. Low-passage (P2) and high-passage (P28) NKNT-3 cells and clonal derivatives were characterized for reversion of immortalization, heterogeneity, and hepatic functionality. Reversion with reduced expression of immortalizing agent could be established. However, during culturing the cells lost the capacity to be selected for completed reversion. The phenotypic instability is probably associated with heterogeneity in the culture, as clonal derivatives of P2 cells varied in morphology, growth, and reversion characteristics. The mRNA levels of genes related with hepatic differentiation increased 4–20-fold after reversion. However, the levels never exceeded 0.1% of that detected in liver and no urea production nor ammonia elimination was detected. Additionally, activities of different cytochrome P450s were limited. In conclusion, the NKNT-3 culture is heterogeneous and unstable and the in vitro functionality is relatively low. These findings emphasize that in vivo testing of hepatic cell lines is little informative for predicting their value for in vitro applications.

A novel method for banking stem cells from human exfoliated deciduous teeth: lentiviral TERT immortalization and phenotypical analysis

Background

Stem cells from human exfoliated deciduous teeth (SHED) have recently attracted attention as novel multipotential stem cell sources. However, their application is limited due to in vitro replicative senescence. Ectopic expression of telomerase reverse transcriptase (TERT) is a promising strategy for overcoming this replicative senescence. Nevertheless, its potential application and the phenotype as well as tumorigenicity have never been assessed in SHED.

Methods

TERT expression was stably restored in SHED (TERT-SHED) isolated from healthy children aged 6–8 years using lentiviral transduction with a puromycin selection marker. The expression of TERT was detected using reverse transcription polymerase chain reaction, Western blot and immunofluorescence. Surface markers of SHED were detected by flow cytometry. Enzyme-linked immunosorbent assay was used to assess senescence-associated β-galactosidase, while CCK-8 methods were used to examine the proliferation capacity of SHED and TERT-SHED at different passages. Moreover, multilineage differentiation, karyotype, colony formation in soft agar, and tumor formation in nude mice of SHED and TERT-SHED were also examined.

Results

Lentiviral transduction induced stable TERT expression even in SHED at the 40th passage. TERT-SHED showed robust proliferation capacity and low concentration of β-galactosidase. Although they had some different biomarkers than early passage SHED, TERT-SHED at late passage showed similar mutilineage differentiation as TERT at early passage. Moreover, TERT-SHED at late passage showed normal karyotype, no soft agar colony formation, and no tumor formation in nude mice.

Conclusions

TERT-immortalized SHED may be a promising resource for stem-cell therapy, although attention should be paid to the biological behavior of the cells.

Nuclear Factor κB1/RelA Mediates Inflammation in Human Lung Epithelial Cells at Atmospheric Oxygen Levels

Oxygen levels range from 2% to 9% in vivo. Atmospheric O2 levels (21%) are known to induce cell proliferation defects and cellular senescence in primary cell cultures. However, the mechanistic basis of the deleterious effects of higher O2 levels is not fully understood. On the other hand, immortalized cells including cancer cell lines, which evade cellular senescence are normally cultured at 21% O2 and the effects of higher O2 on these cells are understudied. Here, we addressed this problem by culturing immortalized human bronchial epithelial (BEAS-2B) cells at ambient atmospheric, 21% O2 and lower, 10% O2. Our results show increased inflammatory response at 21% O2 but not at 10% O2. We found higher RelA binding at the NF-κB1/RelA target gene promoters as well as upregulation of several pro-inflammatory cytokines in cells cultured at 21% O2. RelA knockdown prevented the upregulation of the pro-inflammatory cytokines at 21% O2, suggesting NF-κB1/RelA as a major mediator of inflammatory response in cells cultured at 21% O2. Interestingly, unlike the 21% O2 cultured cells, exposure of 10% O2 cultured cells to H2O2 did not elicit inflammatory response, suggesting increased ability to tolerate oxidative stress in cells cultured at lower O2 levels.

Karyotype alteration generates the neoplastic phenotypes of SV40-infected human and rodent cells

BACKGROUND

Despite over 50 years of research, it remains unclear how the DNA tumor viruses SV40 and Polyoma cause cancers. Prevailing theories hold that virus-coded Tumor (T)-antigens cause cancer by inactivating cellular tumor suppressor genes. But these theories don't explain four characteristics of viral carcinogenesis: (1) less than one in 10,000 infected cells become cancer cells, (2) cancers have complex individual phenotypes and transcriptomes, (3) recurrent tumors without viral DNA and proteins, (4) preneoplastic aneuploidies and immortal neoplastic clones with individual karyotypes.

RESULTS

As an alternative theory we propose that viral carcinogenesis is a form of speciation, initiated by virus-induced aneuploidy. Since aneuploidy destabilizes the karyotype by unbalancing thousands of genes it catalyzes chain reactions of karyotypic and transcriptomic evolutions. Eventually rare karyotypes evolve that encode cancer-specific autonomy of growth. The low probability of forming new autonomous cancer-species by random karyotypic and transcriptomic variations predicts individual and clonal cancers. Although cancer karyotypes are congenitally aneuploid and thus variable, they are stabilized or immortalized by selections for variants with cancer-specific autonomy. Owing to these inherent variations cancer karyotypes are heterogeneous within clonal margins. To test this theory we analyzed karyotypes and phenotypes of SV40-infected human, rat and mouse cells developing into neoplastic clones. In all three systems we found (1) preneoplastic aneuploidies, (2) neoplastic clones with individual clonal but flexible karyotypes and phenotypes, which arose from less than one in 10,000 infected cells, survived over 200 generations, but were either T-antigen positive or negative, (3) spontaneous and drug-induced variations of neoplastic phenotypes correlating 1-to-1 with karyotypic variations.

CONCLUSIONS

Since all 14 virus-induced neoplastic clones tested contained individual clonal karyotypes and phenotypes, we conclude that these karyotypes have generated and since maintained these neoplastic clones. Thus SV40 causes cancer indirectly, like carcinogens, by inducing aneuploidy from which new cancer-specific karyotypes evolve automatically at low rates. This theory explains the (1) low probability of carcinogenesis per virus-infected cell, (2) the individuality and clonal flexibility of cancer karyotypes, (3) recurrence of neoplasias without viral T-antigens, and (4) the individual clonal karyotypes, transcriptomes and immortality of virus-induced neoplasias - all unexplained by current viral theories.

CDDO-Me protects normal lung and breast epithelial cells but not cancer cells from radiation

Although radiation therapy is commonly used for treatment for many human diseases including cancer, ionizing radiation produces reactive oxygen species that can damage both cancer and healthy cells. Synthetic triterpenoids, including CDDO-Me, act as anti-inflammatory and antioxidant modulators primarily by inducing the transcription factor Nrf2 to activate downstream genes containing antioxidant response elements (AREs). In the present series of experiments, we determined if CDDO-Me can be used as a radioprotector in normal non-cancerous human lung and breast epithelial cells, in comparison to lung and breast cancer cell lines. A panel of normal non-cancerous, partially cancer progressed, and cancer cell lines from both lung and breast tissue was exposed to gamma radiation with and without pre-treatment with CDDO-Me. CDDO-Me was an effective radioprotector when given ∼18 hours before radiation in epithelial cells (average dose modifying factor (DMF) = 1.3), and Nrf2 function was necessary for CDDO-Me to exert these radioprotective effects. CDDO-Me did not protect cancer lines tested from radiation-induced cytotoxicity, nor did it protect experimentally transformed human bronchial epithelial cells (HBECs) with progressive oncogenic manipulations. CDDO-Me also protected human lymphocytes against radiation-induced DNA damage. A therapeutic window exists in which CDDO-Me protects normal cells from radiation by activating the Nrf2 pathway, but does not protect experimentally transformed or cancer cell lines. This suggests that use of this oral available, non-toxic class of drug can protect non-cancerous healthy cells during radiotherapy, resulting in better outcomes and less toxicity for patients.

Ras regulates kinesin 13 family members to control cell migration pathways in transformed human bronchial epithelial cells

We show that expression of the microtubule depolymerizing kinesin KIF2C is induced by transformation of immortalized human bronchial epithelial cells by expression of K-Ras^G12V and knockdown of p53. Further investigation demonstrates that this is due to the K-Ras/ERK1/2 MAPK pathway, as loss of p53 had little effect on KIF2C expression. In addition to KIF2C, we also found that the related kinesin KIF2A is modestly upregulated in this model system; both proteins are expressed more highly in many lung cancer cell lines compared to normal tissue. As a consequence of their depolymerizing activity, these kinesins increase dynamic instability of microtubules. Depletion of either of these kinesins impairs the ability of cells transformed with mutant K-Ras to migrate and invade matrigel. However, depletion of these kinesins does not reverse the epithelial-mesenchymal transition caused by mutant K-Ras. Our studies indicate that increased expression of microtubule destabilizing factors can occur during oncogenesis to support enhanced migration and invasion of tumor cells.

A targeted RNAi screen of the breast cancer genome identifies KIF14 and TLN1 as genes that modulate docetaxel chemosensitivity in triple-negative breast cancer

PURPOSE

To identify biomarkers within the breast cancer genome that may predict chemosensitivity in breast cancer.

EXPERIMENTAL DESIGN

We conducted an RNA interference (RNAi) screen within the breast cancer genome for genes whose loss-of-function enhanced docetaxel chemosensitivity in an estrogen receptor-negative, progesterone receptor-negative, and Her2-negative (ER-, PR-, and Her2-, respectively) breast cancer cell line, MDA-MB-231. Top candidates were tested for their ability to modulate chemosensitivity in 8 breast cancer cell lines and to show in vivo chemosensitivity in a mouse xenograft model.

RESULTS

From ranking chemosensitivity of 328 short hairpin RNA (shRNA) MDA-MB-231 cell lines (targeting 133 genes with known somatic mutations in breast cancer), we focused on the top two genes, kinesin family member 14 (KIF14) and talin 1 (TLN1). KIF14 and TLN1 loss-of-function significantly enhanced chemosensitivity in four triple-negative breast cancer (TNBC) cell lines (MDA-MB-231, HCC38, HCC1937, and Hs478T) but not in three hormone receptor-positive cell lines (MCF7, T47D, and HCC1428) or normal human mammary epithelial cells (HMEC). Decreased expression of KIF14, but not TLN1, also enhanced docetaxel sensitivity in a Her2-amplified breast cancer cell line, SUM190PT. Higher KIF14 and TLN1 expressions are found in TNBCs compared with the other clinical subtypes. Mammary fat pad xenografts of KIF14- and TLN1-deficient MDA-MB-231 cells revealed reduced tumor mass compared with control MDA-MB-231 cells after chemotherapy. KIF14 expression is also prognostic of relapse-free and overall survival in representative breast cancer expression arrays.

CONCLUSION

KIF14 and TLN1 are modulators of response to docetaxel and potential therapeutic targets in TNBC.

hTERT extends the life of human fibroblasts without compromising type I interferon signaling

Primary cells are often used to study viral replication and host-virus interactions as their antiviral pathways have not been altered or inactivated; however, their use is restricted by their short lifespan. Conventional methods to extend the life of primary cultures typically utilize viral oncogenes. Many of these oncogenes, however, perturb or inactivate cellular antiviral pathways, including the interferon (IFN) response. It has been previously shown that expression of the telomerase reverse transcriptase (TERT) gene extends the life of certain cell types. The effect that TERT expression has on the innate antiviral response to RNA- and DNA-containing viruses has not been examined. In the current study, we introduced the human TERT (hTERT) gene into a primary human embryonic lung (HEL-299) cell strain, which is known to respond to the type I IFN, IFN-β. We show that the resulting HEL-TERT cell line is capable of replicating beyond 100 population doublings without exhibiting signs of senescence. Treatment with IFN-β resulted in the upregulation of four model IFN stimulated genes (ISGs) in HEL-299 and HEL-TERT cells. Both cell lines supported the replication of herpes simplex virus type 1 (HSV-1) and vesicular stomatitis virus (VSV) and impaired the replication of both viruses upon IFN-β pretreatment. Introduction of the viral oncoprotein, simian virus 40 (SV40) large T-antigen, which is frequently used to immortalize cells, largely negated this effect. Taken together, our data indicate that expression of hTERT does not alter type 1 IFN signaling and/or the growth of two viruses, making this cell line a useful reagent for studying viral replication and virus-cell interactions.

[The influence of compound aITEL1296 on telomerase activity and the growth of cancer cells]

Telomerase is a ribonucleoprotein that synthesizes telomeric repeats and identified as a promising target for anticancer therapy. Here we describe a new compound aITEL1296 as a potent telomerase inhibitor. Its inhibitory activity was a bit higher (IC50 = 0,19 +/- 0,02 ng/ml) than that of BIBR1532, one of the most potent telomerase inhibitors known to date. Besides telomerase inhibition aITEL1296 activated apoptotic mechanisms and effectively suppressed proliferation of tumor cell lines (GI50 = 5,0 +/- 0,2 ng/ml for most sensitive cell line LnCap) but not normal fibroblast cell line.

Telomere-driven tetraploidization occurs in human cells undergoing crisis and promotes transformation of mouse cells

Human cancers with a subtetraploid karyotype are thought to originate from tetraploid precursors, but the cause of tetraploidization is unknown. We previously documented endoreduplication in mouse cells with persistent telomere dysfunction or genome-wide DNA damage. We now report that endoreduplication and mitotic failure occur during telomere crisis in human fibroblasts and mammary epithelial cells and document the role of p53 and Rb in repressing tetraploidization. Using an inducible system to generate transient telomere damage, we show that telomere-driven tetraploidization enhances the tumorigenic transformation of mouse cells. Similar to human solid cancers, the resulting tumors evolved subtetraploid karyotypes. These data establish that telomere-driven tetraploidization is induced by critically short telomeres and has the potential to promote tumorigenesis in early cancerous lesions.

Organ aging and susceptibility to cancer may be related to the geometry of the stem cell niche

Telomere loss at each cell replication limits the proliferative capacity of normal cells, including adult stem cells. Entering replicative senescence protects dividing cells from neoplastic transformation, but also contributes to aging of the tissue. Recent experiments have shown that intestinal mouse stem cells divide symmetrically, at random make decisions to remain stem cells or to differentiate, and gradually lose telomeric DNA. A cell's decision whether to differentiate or to remain a stem cell depends on the local cellular and chemical environment and thus tissue architecture is expected to play role in cell proliferation dynamics. To take into account the structure of the stem cell niche in determining its proliferative potential and susceptibility to cancer, a theoretical model is introduced and the niche proliferative potential is quantified for different architectures. The niche proliferative potential is quantitatively related to the proliferative potential of the individual stem cells for different structural classes of the stem cell niche. Stem cells at the periphery of a niche are under pressure to divide and to differentiate, as well as to maintain the stem cell niche boundary, and thus the geometry of the stem cell niche is expected to play a role in determining the stem cell division sequence and differentiation. Smaller surface-to-volume ratio is associated with higher susceptibility to cancer, higher tissue renewal capacity, and decreased aging rate. Several testable experimental predictions are discussed, as well the presence of stochastic effects.

Characterization of hTERT-immortalized caprine mammary epithelial cells

The aim of this article is to demonstrate and characterize caprine mammary epithelial cells (CMC) immortalized with human telomerase reverse transcriptase (hTERT) gene. Five immortalized CMCs were assigned to either myoepithelial or luminal epithelial groups based on their morphology and expression of cell lineage-specific intermediate filaments. Telomeric repeat amplification protocol revealed various telomerase activities in CMCs associated with their distinct proliferation potential. Karyotypic analysis showed three CMCs retained their modal Capra hircus chromosome number (2n = 60), whereas the remaining two CMCs were abnormal at 2n = 19 and 2n = 36. CMCs with abnormal karyotypes lost p53 protein after chemical-induced DNA damage and showed anchorage-independent growth in soft agar assay. In terms of functional differentiation, luminal CMCs organized into alveolus-like structures when grown in Matrigel. Furthermore, αs1- and β-casein gene was induced in luminal CMCs in response to lacto-hormones stimulation. Together these results showed that hTERT-immortalized CMCs retained major characteristics of mammary epithelial cells, and stability of the genome is required for maintaining normal mammary epithelium function. Application of CMCs can provide valuable models to study alveologenesis and lactogenesis of mammary epithelium and test the feasibility of recombinant constructs designed for the generation of transgenic livestock.

Immortalized cells as experimental models to study cancer

The development of cancer is a multi-step process in which normal cells sustain a series of genetic alterations that together program the malignant phenotype. Much of our knowledge of cancer biology results from the detailed study of specimens and cell lines derived from patient tumors. While these approaches continue to yield critical information regarding the identity, number, and types of alterations found in human tumors, further progress in understanding the molecular basis of malignant transformation depends upon the generation and use of increasingly sophisticated experimental models of cancer. Over the past several years, the recognition that telomeres and telomerase play essential roles in regulating cell lifespan now permits the development of new models of human cancer. Here we review recent progress in the use of immortalized human cells as a foundation for understanding the molecular basis of cancer.

Use of exogenous hTERT to immortalize primary human cells

A major obstacle to the immortalization of primary human cells and the establishment of human cell lines is telomere-controlled senescence. Telomere-controlled senescence is caused by the shortening of telomeres that occurs each time somatic human cells divide. The enzyme telomerase can prevent the erosion of telomeres and block the onset of telomere-controlled senescence, but its expression is restricted to the early stages of embryonic development, and in the adult, to rare cells of the blood, skin and digestive track. However, we and others have shown that the transfer of an exogenous hTERT cDNA, encoding the catalytic subunit of human telomerase, can be used to prevent telomere shortening, overcome telomere-controlled senescence, and immortalize primary human cells. Most importantly, hTERT alone can immortalize cells without causing cancer-associated changes or altering phenotypic properties. Primary human cells that have so far been established by the forced expression of hTERT alone include fibroblasts, retinal pigmented epithelial cells, endothelial cells, oesophageal squamous cells, mammary epithelial cells, keratinocytes, osteoblasts, and Nestin-positive cells of the pancreas. In this article, we discuss the use of hTERT to immortalize of human cells, the properties of hTERT-immortalized cells, and their applications to cancer research and tissue engineering.

Establishment of an erythroid cell line from primary CD36+ erythroid progenitor cells

OBJECTIVE

Most continuous cell lines with erythroid characteristics are derived from patients with myelogenous leukemia or erythroleukemia. Among them, a few cell lines have been reported to be positive for CD36. We tried to establish a continuous erythroid cell line from the primary CD36(+) erythroid progenitor cells (EPCs) by the lentivirus-mediated gene transduction system.

MATERIALS AND METHODS

A lentiviral vector carrying SV40T, hTERT, or the human papillomavirus type 16 (HPV16) E6 and E7 (E6/E7) viral oncogenes, was introduced into CD36(+) EPCs, singularly or combined. Transformed cells were characterized in terms of histology, phenotype, karyotype, and gene expression profile.

RESULTS

The lentiviral vector carrying HPV16 E6/E7 genes successfully transformed CD36(+) EPCs, creating a continuous cell line, CD36E. Immunophenotype analysis revealed that the CD36E cells had characteristics of erythroid progenitors, among which about 27% of the cell population produced hemoglobin. Colony-forming cell assay demonstrated that the CD36E cells were capable of forming erythroid colonies. Using cytokines or chemical agents, attempts were made to induce differentiation of the CD36E cells but were ineffective, indicating the irreversible erythroid lineage commitment of the cells. The gene expression profile of the CD36E cells displayed a marked difference from that of the CD36(+) EPCs.

CONCLUSIONS

The continuous CD36E cell line is an erythroid progenitor cell line possessing the ability to produce hemoglobin. The CD36E cell line would be an excellent tool for applied research involving erythroid lineage cells and comparative studies with primary CD36(+) EPCs.

Resistance to experimental tumorigenesis in cells of a long-lived mammal, the naked mole-rat (Heterocephalus glaber)

The naked mole-rat (NMR, Heterocephalus glaber) is a long-lived mammal in which spontaneous cancer has not been observed. To investigate possible mechanisms for cancer resistance in this species, we studied the properties of skin fibroblasts from the NMR following transduction with oncogenes that cause cells of other mammalian species to form malignant tumors. Naked mole-rat fibroblasts were transduced with a retrovirus encoding SV40 large T antigen and oncogenic Ras(G12V). Following transplantation of transduced cells into immunodeficient mice, cells rapidly entered crisis, as evidenced by the presence of anaphase bridges, giant cells with enlarged nuclei, multinucleated cells, and cells with large number of chromosomes or abnormal chromatin material. In contrast, similarly transduced mouse and rat fibroblasts formed tumors that grew rapidly without crisis. Crisis was also observed after > 40 population doublings in SV40 TAg/Ras-expressing NMR cells in culture. Crisis in culture was prevented by additional infection of the cells with a retrovirus encoding hTERT (telomerase reverse transcriptase). SV40 TAg/Ras/hTERT-expressing NMR cells formed tumors that grew rapidly in immunodeficient mice without evidence of crisis. Crisis could also be induced in SV40 TAg/Ras-expressing NMR cells by loss of anchorage, but after hTERT transduction, cells were able to proliferate normally following loss of anchorage. Thus, rapid crisis is a response of oncogene-expressing NMR cells to growth in an in vivo environment, which requires anchorage independence, and hTERT permits cells to avoid crisis and to achieve malignant tumor growth. The unique reaction of NMR cells to oncogene expression may form part of the cancer resistance of this species.

Loss of MTG16a (CBFA2T3), a novel rDNA repressor, leads to increased ribogenesis and disruption of breast acinar morphogenesis

Human MTG16a (CBFA2T3), a chromatin repressor with nucleolar localization, was described to act as a suppressor of breast tumourigenesis. Here we show that MTG16a is a novel ribosomal gene repressor, which can counteract MYC-driven activation of ribosomal RNA (rRNA) transcription. We also show that either knocking down MTG16a by RNA interference, or sequestering MTG16a outside the nucleolus of human breast epithelial cells, hampers acinar morphogenesis concomitant with up-regulation of rRNA synthesis and increased ribogenesis. This is the first demonstration that loss of MTG16a function in the nucleolus of breast epithelial cells can induce morphological and molecular changes typical of breast cancer initiation.

Immortalization of human precartilaginous stem cells by transfecting SV40Tag

Immortalized human precartilaginous stem cells (IPSCs) were established to provide stable cell resource for the study of the molecular mechanism of gene targeting on the differentiation of PSCs. Plasmid pCMVSV40T/PUR containing simian virus 40 large T antigen gene (SV40Tag) was transfected into human PSCs by using lipofectin transfection. Colonies were isolated by puromycin selection and expanded by multiple passages. Immunohistochemistry, RT-PCR and Southern blotting were used to identify the transfected cells and to detect the expression and integration of SV40Tag in expanded cell lines. The positive colonies were isolated and subcultured, designated immortalized precartilaginous stem cells (IPSCs), which were confirmed as fibroblast growth factor receptor-3 (FGFR-3) positive cells by immunohistochemistry and RT-PCR. SV40Tag cDNA was found in cultured IPSCs of passage 8 by Southern blotting, and the expressions of SV40Tag mRNA and protein were confirmed by RT-PCR. These findings suggested that IPSCs strain with SV40Tag was constructed successfully.

Altered states of telomere deprotection and the two-stage mechanism of replicative aging

The molecular distinctions between mortality stages 1 (M1; senescence) and 2 (M2; crisis) of human replicative aging are ill defined. We demonstrate a qualitative difference between telomeric end associations at M1 and the end fusions that produce dicentric chromosomes and breakage-fusion cycles. Knockdown of ligase IV sufficient to completely inhibit radiation-induced dicentric chromosome formation had no effect on the frequency of telomere associations (TAs), establishing that TAs are not covalent conventional nonhomologous end-joining (NHEJ) products. TAs preceded and were more numerous than dicentric chromosomes. Cells initially tolerated dicentric chromosomes without dying, but eventually, a combination of too many TAs and dicentrics/complex chromosomal rearrangements resulted in apoptosis. We propose a working model in which end associations represent abortive DNA repair intermediates when the number of telomeric repeats is too small to completely inhibit DNA damage signaling but is sufficient to prevent the final covalent ligation step of NHEJ and induces the M1 checkpoint arrest in normal human cells. Rather than being all-or-none, telomere deprotection would thus proceed first through TAs before additional shortening leads to dicentric chromosomes. M2/crisis involves both qualitative changes (a shift from TAs to TAs plus dicentric chromosomes) and quantitative changes (an increase in the number of dysfunctional telomeres).

Telomerase deficiency affects the formation of chromosomal translocations by homologous recombination in Saccharomyces cerevisiae

Telomerase is a ribonucleoprotein complex required for the replication and protection of telomeric DNA in eukaryotes. Cells lacking telomerase undergo a progressive loss of telomeric DNA that results in loss of viability and a concomitant increase in genome instability. We have used budding yeast to investigate the relationship between telomerase deficiency and the generation of chromosomal translocations, a common characteristic of cancer cells. Telomerase deficiency increased the rate of formation of spontaneous translocations by homologous recombination involving telomere proximal sequences during crisis. However, telomerase deficiency also decreased the frequency of translocation formation following multiple HO-endonuclease catalyzed DNA double-strand breaks at telomere proximal or distal sequences before, during and after crisis. This decrease correlated with a sequestration of the central homologous recombination factor, Rad52, to telomeres determined by chromatin immuno-precipitation. This suggests that telomerase deficiency results in the sequestration of Rad52 to telomeres, limiting the capacity of the cell to repair double-strand breaks throughout the genome. Increased spontaneous translocation formation in telomerase-deficient yeast cells undergoing crisis is consistent with the increased incidence of cancer in elderly humans, as the majority of our cells lack telomerase. Decreased translocation formation by recombinational repair of double-strand breaks in telomerase-deficient yeast suggests that the reemergence of telomerase expression observed in many human tumors may further stimulate genome rearrangement. Thus, telomerase may exert a substantial effect on global genome stability, which may bear significantly on the appearance and progression of cancer in humans.

Telomere dysfunction and tumour suppression: the senescence connection

Long-lived organisms such as humans have evolved several intrinsic tumour suppressor mechanisms to combat the slew of oncogenic somatic mutations that constantly arise in proliferating stem-cell compartments. One of these anticancer barriers is the telomere, a specialized nucleoprotein complex that caps the ends of eukaryotic chromosome. Impaired telomere function activates the canonical DNA damage response pathway that engages p53 to initiate apoptosis or replicative senescence. Here, we discuss how p53-dependent senescence induced by dysfunctional telomeres may be as potent as apoptosis in suppressing tumorigenesis in vivo.

Dual roles of telomere dysfunction in initiation and suppression of tumorigenesis

Human carcinomas arise through the acquisition of genetic changes that endow precursor cancer cells with a critical threshold of cancer-relevant genetic lesions. This complex genomic alterations confer upon precursor cancer cells the ability to grow indefinitely and to metastasize to distant sites. One important mechanism underlying a cell's tumorigenic potential is the status of its telomere. Telomeres are G-rich simple repeat sequences that serve to prevent chromosomal ends from being recognized as DNA double-strand breaks (DSBs). Dysfunctional telomeres resemble DSBs, leading to the formation of dicentric chromosomes that fuel high degrees of genomic instability. In the setting of an intact p53 pathway, this instability promotes cellular senescence, a potent tumor suppressor mechanism. However, rare cells that stochastically lose p53 function emerge from this sea of genomic instability and progress towards cancer. In this review, we describe the use of mouse models to probe the impact of dysfunctional telomeres on tumor initiation and suppression.

Low telomerase activity: possible role in the progression of human medullary thyroid carcinoma

Maintenance of telomere length has been reported to be an absolute requirement for unlimited growth of human tumour cells and in about 85% of cases, this is achieved by reactivation of telomerase, the enzyme that elongates telomeres. Only in rare cases, like in human medullary thyroid carcinomas (MTC), telomerase activity (TA) is low or undetectable; however, this does not limit tumours to become clinically significant. Here, we report that very low TA (below 5% of HEK293) observed in MTC cell strains derived from different patients, although not sufficient for immortalising the cells, is necessary for prolonging their replicative life span. Telomere erosion led to induction of a crisis period after long-term in vitro cultivation, which was reached earlier when treating the cells with MST-312, a telomerase inhibitor at non-toxic concentrations. Crisis was bypassed either by ectopic hTERT introduction or by infrequent spontaneous immortalisation, the latter of which was always associated with telomerase reactivation and changes of the cellular phenotype. While confirming the high importance of telomerase for tumour development, these data draw attention to the relevance of low TA: although insufficient for telomere stabilisation, it allows MTC cells to reach more population doublings, increasing both cell numbers as well as the risk of accumulating mutations and thus might support the development of clinically significant MTC.

Role of telomeres and telomerase in genomic instability, senescence and cancer

Telomeres are ribonucleoprotein structures that protect the end of linear chromosomes from recognition as DNA double-stranded breaks and activation of a DNA damage response. Telomere-associated proteins also regulate telomerase, the protein responsible for maintaining telomere length. Loss of telomere function results from either alteration in the capping function at telomeres, or from progressive loss of telomeric repeats necessary to maintain proper telomeric structure. Dysfunctional telomeres activate p53 to initiate cellular senescence or apoptosis to suppress tumorigenesis. However, in the absence of p53, telomere dysfunction is an important mechanism to generate chromosomal instability commonly found in human carcinomas. Telomerase is expressed in the majority of human cancers, making it an attractive therapeutic target. Emerging anti-telomerase therapies that are currently in clinical trials might prove useful against some forms of human cancers.

Cellular senescence: when bad things happen to good cells

Cells continually experience stress and damage from exogenous and endogenous sources, and their responses range from complete recovery to cell death. Proliferating cells can initiate an additional response by adopting a state of permanent cell-cycle arrest that is termed cellular senescence. Understanding the causes and consequences of cellular senescence has provided novel insights into how cells react to stress, especially genotoxic stress, and how this cellular response can affect complex organismal processes such as the development of cancer and ageing.

Hallmarks of telomeres in ageing research

Telomeres are repetitive DNA sequences at the ends of linear chromosomes. Telomerase, a cellular reverse transcriptase, helps maintain telomere length in human stem cells, reproductive cells and cancer cells by adding TTAGGG repeats onto the telomeres. However, most normal human cells do not express telomerase and thus each time a cell divides some telomeric sequences are lost. When telomeres in a subset of cells become short (unprotected), cells enter an irreversible growth arrest state called replicative senescence. Cells in senescence produce a different constellation of proteins compared to normal quiescent cells. This may lead to a change in the homeostatic environment in a tissue-specific manner. In most instances cells become senescent before they can become cancerous; thus, the initial growth arrest induced by short telomeres may be thought of as a potent anti-cancer protection mechanism. When cells can be adequately cultured until they reach telomere-based replicative senescence, introduction of the telomerase catalytic protein component (hTERT) into telomerase-silent cells is sufficient to restore telomerase activity and extend cellular lifespan. Cells with introduced telomerase are not cancer cells, since they have not accumulated the other changes needed to become cancerous. This indicates that telomerase-induced telomere length manipulations may have utility for tissue engineering and for dissecting the molecular mechanisms underlying genetic diseases, including cancer.

The induction of growth arrest in fibroblasts by SV40 T antigen

DNA tumor viruses such as SV40, Ras and papillomaviruses are the most commonly used agents in immortalization of non-hematopoietic cells, but the results are quite different. Some of them even lead instead to a senescence-like state. To verify the potential of SV40 T antigen-mediated immortalization or properties and functions of it to regulate cell growth, human dermal fibroblasts were cultured and then transfected with eukaryotic expressing plasmid psv3-neo which containing SV40 T DNA. We found that expression of oncogenic SV40 T in human dermal fibroblasts resulted in growth, arrest, earlier than the occurrence of control cell senescence, although telomerase was positive and cells grew faster than control ones in early stage following transfection. These observations suggest that SV40 T antigen can activate growth arrest in human dermal fibroblasts under normal growth condition instead of always prolonging the lifespan of fibroblasts. Moreover, high rate of cell division in early stage after transfection may be associated with the expression of telomerase activity.

[Senescence: a telomeric limit to immortality or a cellular response to physiologic stresses?]

Cells entering a state of senescence undergo a irreversible cell cycle arrest, associated by a set of functional and morphological changes. Senescence occurs following telomeres shortening (replicative senescence) or exposure to other acute or chronic physiologic stress signals (a phenomenon termed stasis: stress or aberrant signaling-induced senescence). In this review, I discuss the pathways of cellular senescence, the mechanisms involved and the role that these pathways have in regulating the initiation and progression of cancer. Telomere-initiated senescence or loss of telomere function trigger focal recruitement of protein sensors of the DNA double-strand breaks leading to the activation of the DNA damage checkpoint responses and the tumour suppressor gene product, p53, which in turn induces the cell-cycle inhibitor, p21(WAF1). Loss of p53 and pRb function allows continued cell division despite increasing telomere dysfunction and eventually entry into telomere crisis. Immortalisation is an essential prerequisite for the formation of a tumour cell. Therefore, a developing tumour cell must circumvent at least two proliferative barriers--cellular senescence and crisis--to achieve neoplastic transformation. These barriers are regulated by telomere shortening and by the p16(INK4a)/Rb and p53 tumour suppressor pathways. Elucidation of the genes and emerging knowledge about the regulatory mechanisms that lead to senescence and determine the pattern of gene expression in senescent cells may lead to more effective treatments for cancer.

Establishment and partial characterization of an ovine synovial membrane cell line obtained by transformation with Simian Virus 40 T antigen

The small ruminant lentiviruses, namely caprine arthritis encephalitis virus (CAEV) and Maedi Visna virus (MVV) are grown currently in secondary synovial membrane cells. Primary and secondary cell cultures are sometimes difficult to obtain and support a low number of passages and, therefore, permissive cell lines are needed. A transformed cell line was obtained by transfection of ovine synovial membrane secondary cell culture with a plasmid containing the SV40 large T antigen gene. The transformed cell culture described in this paper showed a higher growth rate and a more homogenous population of fibroblast-like cells when compared to the original ovine synovial membrane secondary cell cultures. Karyotype analysis has indicated the induction of many random chromosome changes, leading to a decrease in chromosome number. The SV40 DNA was detected in the nucleus and in the cytoplasm of transformed cells. The putative expression of large T antigen was presumed by the detection of the corresponding mRNA by PCR. Finally, the transformed ovine synovial membrane cells were shown to be permissive to small ruminant lentiviruses, and these are suggested as a cell line for in vitro isolation and propagation of these viruses.

Modeling aging and cancer in the telomerase knockout mouse

The telomerase deficient mouse has been invaluable in providing insights into basic questions pertaining to consequences of telomere dysfunction during aging and cancer in the context of the mammalian organism. Studies using this mouse model have demonstrated that cellular responses to telomere dysfunction are fundamentally conserved in both humans and mice, and that the tight regulation of telomere length and telomerase activity in somatic cells may be important in mediating the balance between aging and cancer. Here, I discuss the use of the telomerase null mouse for understanding the contrasting roles of telomeres and telomerase in organismal aging and cancer.

Amplification and overexpression of aurora kinase A (AURKA) in immortalized human ovarian epithelial (HOSE) cells

Immortalization is an early and essential step of human carcinogenesis. Amplification of chromosome 20q has been shown to be a common event in immortalized cells and cancers. We have previously reported that gain and amplification of chromosome 20q is a non-random and common event in immortalized human ovarian surface epithelial (HOSE) cells. The chromosome 20q harbors genes including TGIF2 (20q11.2-q12), AIB1 (20q12), PTPN1 (20q13.1), ZNF217 (20q13.2), and AURKA (20q13.2-q13.3), which were previously reported to be amplified and overexpressed in ovarian cancers. Some of these genes may be involved in immortalization of HOSE cells and represent crucial premalignant changes in ovarian surface epithelium. Investigation of the involvement of these genes was examined in four pairs of pre-crisis (preimmortalized) and post-crisis (immortalized) HOSE cells. Overexpression of AURKA (Aurora kinase A), also known as BTAK and STK15, by both real time-quantitative polymerase chain reaction (RT-QPCR) and Western blotting was detected in all the four immortalized HOSE cells examined while overexpression of AIB1 and ZNF217 was observed in two of four immortalized HOSE cells examined. Overexpression of TGIF2 and PTPN1 was not significant in our immortalized HOSE cell systems. The degree of overexpression of AURKA was shown to be closely associated with the amplification of chromosome 20q in immortalized HOSE cells. Fluorescence in situ hybridization (FISH) with labeled P1 artificial clone (PAC) confirmed the amplification of the chromosomal region (20q13.2-13.3) where AURKA resides. DNA amplification of AURKA was also confirmed using semi-quantitative PCR. Our study showed that amplification and overexpression of AURKA is a common and significant event during immortalization of HOSE cells and may represent an important premalignant change in ovarian carcinogenesis.