SV40 large T antigen targets multiple cellular pathways to elicit cellular transformation

Synthesis and structure–activity relationships of small molecule inhibitors of the simian virus 40 T antigen oncoprotein, an anti-polyomaviral target

Polyomavirus infections are common and relatively benign in the general human population but can become pathogenic in immunosuppressed patients. Because most treatments for polyomavirusassociated diseases nonspecifically target DNA replication, existing treatments for polyomavirus infection possess undesirable side effects. However, all polyomaviruses express Large Tumor Antigen (T Ag), which is unique to this virus family and may serve as a therapeutic target. Previous screening of pyrimidinone–peptoid hybrid compounds identified MAL2-11B and a MAL2-11B tetrazole derivative as inhibitors of viral replication and T Ag ATPase activity (IC50 of ~20-50 μM. To improve upon this scaffold and to develop a structure–activity relationship for this new class of antiviral agents, several iterative series of MAL2-11B derivatives were synthesized. The replacement of a flexible methylene chain linker with a benzyl group or, alternatively, the addition of an ortho-methyl substituent on the biphenyl side chain in MAL2-11B yielded an IC50 of 50 μM, which retained antiviral activity. After combining both structural motifs, a new lead compound was identified that inhibited T Ag ATPase activity with an IC50 of 50 μM. We suggest that the knowledge gained from the structure–activity relationship and a further refinement cycle of the MAL2-11B scaffold will provide a specific, novel therapeutic treatment option for polyomavirus infections and their associated diseases.

A novel strategy for targeted killing of tumor cells: Induction of multipolar acentrosomal mitotic spindles with a quinazolinone derivative mdivi-1

Traditional antimitotic drugs for cancer chemotherapy often have undesired toxicities to healthy tissues, limiting their clinical application. Developing novel agents that specifically target tumor cell mitosis is needed to minimize the toxicity and improve the efficacy of this class of anticancer drugs. We discovered that mdivi-1 (mitochondrial division inhibitor-1), which was originally reported as an inhibitor of mitochondrial fission protein Drp1, specifically disrupts M phase cell cycle progression only in human tumor cells, but not in non-transformed fibroblasts or epithelial cells. The antimitotic effect of mdivi-1 is Drp1 independent, as mdivi-1 induces M phase abnormalities in both Drp1 wild-type and Drp1 knockout SV40-immortalized/transformed MEF cells. We also identified that the tumor transformation process required for the antimitotic effect of mdivi-1 is downstream of SV40 large T and small t antigens, but not hTERT-mediated immortalization. Mdivi-1 induces multipolar mitotic spindles in tumor cells regardless of their centrosome numbers. Acentrosomal spindle poles, which do not contain the bona-fide centrosome components γ-tubulin and centrin-2, were found to contribute to the spindle multipolarity induced by mdivi-1. Gene expression profiling revealed that the genes involved in oocyte meiosis and assembly of acentrosomal microtubules are highly expressed in tumor cells. We further identified that tumor cells have enhanced activity in the nucleation and assembly of acentrosomal kinetochore-attaching microtubules. Mdivi-1 inhibited the integration of acentrosomal microtubule-organizing centers into centrosomal asters, resulting in the development of acentrosomal mitotic spindles preferentially in tumor cells. The formation of multipolar acentrosomal spindles leads to gross genome instability and Bax/Bak-dependent apoptosis. Taken together, our studies indicate that inducing multipolar spindles composing of acentrosomal poles in mitosis could achieve tumor-specific antimitotic effect, and mdivi-1 thus represents a novel class of compounds as acentrosomal spindle inducers (ASI).

The landscape of somatic chromosomal copy number aberrations in GEM models of prostate carcinoma

Human prostate cancer is known to harbor recurrent genomic aberrations consisting of chromosomal losses, gains, rearrangements, and mutations that involve oncogenes and tumor suppressors. Genetically engineered mouse (GEM) models have been constructed to assess the causal role of these putative oncogenic events and provide molecular insight into disease pathogenesis. While GEM models generally initiate neoplasia by manipulating a single gene, expression profiles of GEM tumors typically comprise hundreds of transcript alterations. It is unclear whether these transcriptional changes represent the pleiotropic effects of single oncogenes, and/or cooperating genomic or epigenomic events. Therefore, it was determined whether structural chromosomal alterations occur in GEM models of prostate cancer and whether the changes are concordant with human carcinomas. Whole genome array-based comparative genomic hybridization (CGH) was used to identify somatic chromosomal copy number aberrations (SCNA) in the widely used TRAMP, Hi-Myc, Pten-null, and LADY GEM models. Interestingly, very few SCNAs were identified and the genomic architecture of Hi-Myc, Pten-null, and LADY tumors were essentially identical to the germline. TRAMP neuroendocrine carcinomas contained SCNAs, which comprised three recurrent aberrations including a single copy loss of chromosome 19 (encoding Pten). In contrast, cell lines derived from the TRAMP, Hi-Myc, and Pten-null tumors were notable for numerous SCNAs that included copy gains of chromosome 15 (encoding Myc) and losses of chromosome 11 (encoding p53).

IMPLICATIONS

Chromosomal alterations are not a prerequisite for tumor formation in GEM prostate cancer models and cooperating events do not naturally occur by mechanisms that recapitulate changes in genomic integrity as observed in human prostate cancer.

Homologous recombination is a primary pathway to repair DNA double-strand breaks generated during DNA rereplication

Re-initiation of DNA replication at origins within a given cell cycle would result in DNA rereplication, which can lead to genome instability and tumorigenesis. DNA rereplication can be induced by loss of licensing control at cellular replication origins, or by viral protein-driven multiple rounds of replication initiation at viral origins. DNA double-strand breaks (DSBs) are generated during rereplication, but the mechanisms of how these DSBs are repaired to maintain genome stability and cell viability are poorly understood in mammalian cells. We generated novel EGFP-based DSB repair substrates, which specifically monitor the repair of rereplication-associated DSBs. We demonstrated that homologous recombination (HR) is an important mechanism to repair rereplication-associated DSBs, and sister chromatids are used as templates for such HR-mediated DSB repair. Micro-homology-mediated non-homologous end joining (MMEJ) can also be used but to a lesser extent compared to HR, whereas Ku-dependent classical non-homologous end joining (C-NHEJ) has a minimal role to repair rereplication-associated DSBs. In addition, loss of HR activity leads to severe cell death when rereplication is induced. Therefore, our studies identify HR, the most conservative repair pathway, as the primary mechanism to repair DSBs upon rereplication.

Phosphodiesterase 4D inhibitors limit prostate cancer growth potential

Phosphodiesterase 4D (PDE4D) has recently been implicated as a proliferation-promoting factor in prostate cancer and is overexpressed in human prostate carcinoma. However, the effects of PDE4D inhibition using pharmacologic inhibitors have not been examined in prostate cancer. These studies examined the effects of selective PDE4D inhibitors, NVP-ABE171 and cilomilast, as anti-prostate cancer therapies in both in vitro and in vivo models. The effects of PDE4D inhibitors on pathways that are critical in prostate cancer and/or downstream of cyclic AMP (cAMP) were examined. Both NVP-ABE171 and cilomilast decreased cell growth. In vitro, PDE4D inhibitors lead to decreased signaling of the sonic hedgehog (SHH), androgen receptor (AR), and MAPK pathways, but growth inhibition was best correlated to the SHH pathway. PDE4D inhibition also reduced proliferation of epithelial cells induced by paracrine signaling from cocultured stromal cells that had activated hedgehog signaling. In addition, PDE4D inhibitors decreased the weight of the prostate in wild-type mice. Prostate cancer xenografts grown in nude mice that were treated with cilomilast or NVP-ABE171 had decreased wet weight and increased apoptosis compared with vehicle-treated controls. These studies suggest the pharmacologic inhibition of PDE4D using small-molecule inhibitors is an effective option for prostate cancer therapy.

IMPLICATIONS

PDE4D inhibitors decrease the growth of prostate cancer cells in vivo and in vitro, and PDE4D inhibition has therapeutic potential in prostate cancer.

Effects of transforming growth factor-β1 on the proliferation and invasion of the HTR-8/SVneo cell line

Transforming growth factor-β1 (TGF-β1) is involved in the regulation of trophoblast cell proliferation and invasion. However, the mechanism underlying this process remains unknown, which is predominantly due to the difficulty in obtaining and maintaining primary trophoblast cells in culture over a long period of time. The HTR-8/SVneo cell line is an immortalized trophoblast cell line, which has been reported to exhibit a number of similar characteristics to those of parental trophoblast cells. Therefore, the cell line has been a useful tool for the investigation of placental function and tumor progression. In the present study, the HTR-8/SVneo cell line was used as a model to investigate the TGF-β1/SMAD signaling pathway in the proliferation and invasion of trophoblast cells. The proliferation and invasion ability of HTR-8/SVneo cells was determined using the MTT and Transwell assays, respectively. In addition, reverse transcription polymerase chain reactions were performed to detect the mRNA expression of a panel of known downstream mediators of TGF-β1, including TGF-β receptor I (TβRI), SMAD4, SMAD3, SMAD7 and tissue inhibitor of metalloproteinases-1 (TIMP-1). The results indicated that TGF-β1 promotes the proliferation and invasion of the HTR-8/SVneo cell line at passage 90. Furthermore, the expression of TβRI, SMAD3 and SMAD4 were reduced following treatment with TGF-β1, while the expression of SMAD7 was increased and the expression of TIMP-1 remained unchanged following TGF-β1 treatment. These observations indicated that the effects of TGF-β1 on the proliferation and invasion of the HTR-8/SVneo cell line at passage 90 were different from those of parental trophoblasts, which is in contrast to the results of previous studies. It was concluded that the HTR-8/SVneo cell lines, which have been grown for over 90 passages, do not accurately represent parental trophoblast cells in studies of the TGF-β/SMAD signaling pathway.

Sexually dimorphic RB inactivation underlies mesenchymal glioblastoma prevalence in males

The prevalence of brain tumors in males is common but unexplained. While sex differences in disease are typically mediated through acute sex hormone actions, sex-specific differences in brain tumor rates are comparable at all ages, suggesting that factors other than sex hormones underlie this discrepancy. We found that mesenchymal glioblastoma (Mes-GBM) affects more males as the result of cell-intrinsic sexual dimorphism in astrocyte transformation. We used astrocytes from neurofibromin-deficient (Nf1(-/-)) mice expressing a dominant-negative form of the tumor suppressor p53 (DNp53) and treated them with EGF as a Mes-GBM model. Male Mes-GBM astrocytes exhibited greater growth and colony formation compared with female Mes-GBM astrocytes. Moreover, male Mes-GBM astrocytes underwent greater tumorigenesis in vivo, regardless of recipient mouse sex. Male Mes-GBM astrocytes exhibited greater inactivation of the tumor suppressor RB, higher proliferation rates, and greater induction of a clonogenic, stem-like cell population compared with female Mes-GBM astrocytes. Furthermore, complete inactivation of RB and p53 in Mes-GBM astrocytes resulted in equivalent male and female tumorigenic transformation, indicating that intrinsic differences in RB activation are responsible for the predominance of tumorigenic transformation in male astrocytes. Together, these results indicate that cell-intrinsic sex differences in RB regulation and stem-like cell function may underlie the predominance of GBM in males.

Oncogenic ras-driven cancer cell vesiculation leads to emission of double-stranded DNA capable of interacting with target cells

Cell free DNA is often regarded as a source of genetic cancer biomarkers, but the related mechanisms of DNA release, composition and biological activity remain unclear. Here we show that rat epithelial cell transformation by the human H-ras oncogene leads to an increase in production of small, exosomal-like extracellular vesicles by viable cancer cells. These EVs contain chromatin-associated double-stranded DNA fragments covering the entire host genome, including full-length H-ras. Oncogenic N-ras and SV40LT sequences were also found in EVs emitted from spontaneous mouse brain tumor cells. Disruption of acidic sphingomyelinase and the p53/Rb pathway did not block emission of EV-related oncogenic DNA. Exposure of non-transformed RAT-1 cells to EVs containing mutant H-ras DNA led to the uptake and retention of this material for an extended (30days) but transient period of time, and stimulated cell proliferation. Thus, our study suggests that H-ras-mediated transformation stimulates vesicular emission of this histone-bound oncogene, which may interact with non-transformed cells.

Phosphorylation of large T antigen regulates merkel cell polyomavirus replication

Merkel Cell Polyomavirus (MCPyV) was recently discovered as a novel human polyomavirus that is associated with ~80% of Merkel Cell Carcinomas. The Large Tumor antigen (LT) is an early viral protein which has a variety of functions, including manipulation of the cell cycle and initiating viral DNA replication. Phosphorylation plays a critical regulatory role for polyomavirus LT proteins, but no investigation of MCPyV LT phosphorylation has been performed to date. In this report mass spectrometry analysis reveals three unique phosphorylation sites: T271, T297 and T299. In vivo replication assays confirm that phosphorylation of T271 does not play a role in viral replication, while modification at T297 and T299 have dramatic and opposing effects on LT’s ability to initiate replication from the viral origin. We test these mutants for their ability to bind, unwind, and act as a functional helicase at the viral origin. These studies provide a framework for understanding how phosphorylation of LT may dynamically regulate viral replication. Although the natural host cell of MCPyV has not yet been established, this work provides a foundation for understanding how LT activity is regulated and provides tools for better exploring this regulation in both natural host cells and Merkel cells.

Comparison of oxygen consumption rates in minimally transformed BALB/3T3 and virus-transformed 3T3B-SV40 cells

In the recent years, bioenergetics of tumor cells and particularly cell respiration have been attracting great attention because of the involvement of mitochondria in apoptosis and growing evidence of the possibility to diagnose and treat cancer by affecting the system of oxidative phosphorylation in mitochondria. In the present work, a comparative study of oxygen consumption in 3T3B-SV40 cells transformed with oncovirus SV40 and parental BALB/3T3 cells was conducted. Such fractions of oxygen consumption as "phosphorylating" respiration coupled to ATP synthesis, "free" respiration not coupled to ATP synthesis, and "reserve" or hidden respiration observed in the presence of protonophore were determined. Maximal respiration was shown to be only slightly decreased in 3T3B-SV40 cells as compared to BALB/3T3. However, in the case of certain fractions of cellular respiration, the changes were significant. "Phosphorylating" respiration was found to be reduced to 54% and "reserve" respiration, on the contrary, increased up to 160% in virus-transformed 3T3B-SV40 cells. The low rate of "phosphorylating" respiration and high "reserve" respiration indicate that under normal incubation conditions the larger part of mitochondrial respiratory chains of the virus-transformed cells is in the resting state (i.e. there is no electron transfer to oxygen). The high "reserve" respiration is suggested to play an important role in preventing apoptosis of 3T3B-SV40 cells.

Regulation of Rad51 promoter

The DNA double-strand break repair and homologous recombination protein Rad51 is overexpressed in the majority of human cancers. This correlates with therapy resistance and decreased patient survival. We previously showed that constructs containing Rad51 promoter fused to a reporter gene are, on average, 850-fold more active in cancer cells than in normal cells. It is not well understood what factors and sequences regulate the Rad51 promoter and cause its high activity in cancerous cells. Here we characterized regulatory regions and examined genetic requirements for oncogenic stimulation of the Rad51 promoter. We identified specific regions responsible for up- and downregulation of the Rad51 promoter in cancerous cells. Furthermore, we show that Rad51 expression is positively regulated by EGR1 transcription factor. We then modeled the malignant transformation process by expressing a set of oncoproteins in normal human fibroblasts. Expression of different combinations of SV40 large T antigen, oncogenic Ras and SV40 small T antigen resulted in step-wise increase in Rad51 promoter activity, with all the 3 oncoproteins together leading to a 47-fold increase in expression. Cumulatively, these results suggest that Rad51 promoter is regulated by multiple factors, and that its expression is gradually activated as cells progress toward malignancy.

The human fetal glial cell line SVG p12 contains infectious BK polyomavirus

The human fetal glial cell line SVG was generated in 1985 by transfecting primary fetal brain cells with a plasmid containing an origin-defective mutant of simian virus 40 (SV40). The cells, which express SV40 large T-antigen, support the replication of human JC polyomavirus (JCPyV) and have been used for JCPyV studies but also for other studies in which cells of neural origin were desirable. We intended to use the SVG p12 cells from ATCC for antiviral drug studies with JCPyV. However, during initial experiments, immunofluorescence microscopy controls unexpectedly revealed cells expressing the late viral proteins VP1, VP2/VP3, and agno. This was confirmed by Western blotting. Since our agnoprotein antiserum is specific for BKPyV agnoprotein, infection with BKPyV was suspected. Indeed, specific BKPyV PCR of SVG p12 supernatants revealed a viral load of >1 × 10(10) genomic equivalents/ml. Negative-staining electron microscopy showed characteristic polyomavirus virions, and infectious BKPyV was transmitted from SVG p12 supernatant to other cells. Long-range PCR covering the viral genome, followed by DNA sequencing, identified BKPyV strain UT as well as deletion derivatives. This was confirmed by next-generation sequencing. JCPyV (MAD-4) was found to infect apparently uninfected and BKPyV-infected SVG p12 cells. In total, 4 vials from 2 different ATCC lots of SVG p12 cells dating back to 2006 contained BKPyV, whereas the subclone SVG-A was negative. In conclusion, SVG p12 cells from ATCC contain infectious BKPyV. This may have affected results and interpretations of previous studies, and caution should be taken in future experiments.

IMPORTANCE

This work reveals that one of the most frequently used cell lines for JC polyomavirus (JCPyV) research, the SV40-immortalized human fetal glial cell line SVG p12 obtained directly from ATCC, contains infectious BK polyomavirus (BKPyV) of strain UT and a spectrum of defective mutants. Strain UT has been previously found in urine and in tumors of different patients but is also frequently used for research. It is therefore not clear if BKPyV was present in the brain tissue used to generate the cell line or if this is a contamination. Although productive JCPyV infection of SVG cells was not dependent on prior BKPyV infection, the unnoticed presence of BKPyV may have influenced the results of studies using these cells. The interpretation of past results should therefore be reconsidered and cells tested for BKPyV before new studies are initiated. The frequently used subclone SVG-A did not contain BKPyV and could be a useful substitute.

Both decreased and increased SRPK1 levels promote cancer by interfering with PHLPP-mediated dephosphorylation of Akt

Akt activation is a hallmark of human cancers. Here, we report a critical mechanism for regulation of Akt activity by the splicing kinase SRPK1, a downstream Akt target for transducing growth signals to regulate splicing. Surprisingly, we find that SRPK1 has a tumor suppressor function because ablation of SRPK1 in mouse embryonic fibroblasts induces cell transformation. We link the phenotype to constitutive Akt activation from genome-wide phosphoproteomics analysis and discover that downregulated SRPK1 impairs the recruitment of the Akt phosphatase PHLPP1 (pleckstrin homology (PH) domain leucine-rich repeat protein phosphatase) to Akt. Interestingly, SRPK1 overexpression is also tumorigenic because excess SRPK1 squelches PHLPP1. Thus, aberrant SRPK1 expression in either direction induces constitutive Akt activation, providing a mechanistic basis for previous observations that SRPK1 is downregulated in some cancer contexts and upregulated in others.

Viral microRNA effects on pathogenesis of polyomavirus SV40 infections in syrian golden hamsters

Effects of polyomavirus SV40 microRNA on pathogenesis of viral infections in vivo are not known. Syrian golden hamsters are the small animal model for studies of SV40. We report here effects of SV40 microRNA and influence of the structure of the regulatory region on dynamics of SV40 DNA levels in vivo. Outbred young adult hamsters were inoculated by the intracardiac route with 1×10⁷ plaque-forming units of four different variants of SV40. Infected animals were sacrificed from 3 to 270 days postinfection and viral DNA loads in different tissues determined by quantitative real-time polymerase chain reaction assays. All SV40 strains displayed frequent establishment of persistent infections and slow viral clearance. SV40 had a broad tissue tropism, with infected tissues including liver, kidney, spleen, lung, and brain. Liver and kidney contained higher viral DNA loads than other tissues; kidneys were the preferred site for long-term persistent infection although detectable virus was also retained in livers. Expression of SV40 microRNA was demonstrated in wild-type SV40-infected tissues. MicroRNA-negative mutant viruses consistently produced higher viral DNA loads than wild-type SV40 in both liver and kidney. Viruses with complex regulatory regions displayed modestly higher viral DNA loads in the kidney than those with simple regulatory regions. Early viral transcripts were detected at higher levels than late transcripts in liver and kidney. Infectious virus was detected infrequently. There was limited evidence of increased clearance of microRNA-deficient viruses. Wild-type and microRNA-negative mutants of SV40 showed similar rates of transformation of mouse cells in vitro and tumor induction in weanling hamsters in vivo. This report identified broad tissue tropism for SV40 in vivo in hamsters and provides the first evidence of expression and function of SV40 microRNA in vivo. Viral microRNA dampened viral DNA levels in tissues infected by SV40 strains with simple or complex regulatory regions.

The recent discovery of virally encoded microRNAs (miRNAs) raises the possibility of additional regulatory processes being involved in viral replication, immune recognition, and host cell survival. In this study, we sought to characterize the effect of SV40-encoded miRNAs and the structure of the viral regulatory region on infections in outbred Syrian golden hamsters. Results revealed that SV40 has a wide tissue tropism, including liver, kidney, spleen, lung, and brain, with kidney the preferred site for long-term persistent infection. Significant increases in tissue-associated viral DNA loads were observed with miRNA-negative mutant strains, whereas the presence of SV40 miRNAs had no effect on tumor induction and little effect on viral clearance. Our results provide the first evidence for SV40 miRNA expression and function in an in vivo animal model and highlight the complexity of regulation of SV40 viral replication and persistent infections.

Oncogenes induce a vimentin filament collapse mediated by HDAC6 that is linked to cell stiffness

Oncogenes deregulate fundamental cellular functions, which can lead to development of tumors, tumor-cell invasion, and metastasis. As the mechanical properties of cells govern cell motility, we hypothesized that oncogenes promote cell invasion by inducing cytoskeletal changes that increase cellular stiffness. We show that the oncogenes simian virus 40 large T antigen, c-Myc, and cyclin E induce spatial reorganization of the vimentin intermediate filament network in cells. At the cellular level, this reorganization manifests as increased width of vimentin fibers and the collapse of the vimentin network. At nanoscale resolution, the organization of vimentin fibers in these oncogene-expressing cells was more entangled, with increased width of the fibers compared with control cells. Expression of these oncogenes also resulted in up-regulation of the tubulin deacetylase histone deacetylase 6 (HDAC6) and altered spatial distribution of acetylated microtubules. This oncogene expression also induced increases in cellular stiffness and promoted the invasive capacity of the cells. Importantly, HDAC6 was required and sufficient for the structural collapse of the vimentin filament network, and was required for increased cellular stiffness of the oncogene-expressing cells. Taken together, these data are consistent with the possibility that oncogenes can induce cellular stiffness via an HDAC6-induced reorganization of the vimentin intermediate filament network.

Micrometastasis expressing insulin arise in lung and spleen at advanced stage of rip1-tag2 transgenic mice

Rip1-Tag2 mice is one overt pancreatic β-cell tumor model, which is widely used for studying pancreas tumor angiogenesis and tumor development. However, tumor metastasis in Rip1-Tag2 mice had rarely been reported, in this present study, we find some micrometastasis in lung and spleen of the Rip1-Tag2 mice at advanced stage, which is important for uncovering metastasis cell characteristics and exploring how to survive in cancer microenvironment. To study the micrometastasis of Rip1-Tag2 mice in advanced pancreatic cancer, we first observed the pathology process of β cell tumor in Rip1-Tag2 mice through HE staining, then we performed immunohistochemistry with insulin antibody, T-antigen antibodies and C-petide antibody on lung and spleen tissues sections from advanced stage, comparing with background wild-type C57BL/6 mice sections. The results indicated that micrometastasis expressing insulin was found in the Rip1-Tag2 mice lung, and spleen. Further evidences demonstrate pathology structure of lung and spleen are damaged. Interestingly and importantly, the expression of T antigen and insulin antibodies are all decreased in advanced stage of primary β cell tumor, which suggest that the at least partly micrometastasis is derived from the early stage or from advanced stage of β cell tumor then return to undifferentiated state like cancer stem cell. The findings contributed to the study of cancer metastasis and cancer stem cell.

Altered mitochondria morphology and cell metabolism in Apaf1-deficient cells

Background

Apaf1 (apoptotic protease activating factor 1) is the central component of the apoptosome, a multiprotein complex that activates procaspase-9 after cytochrome c release from the mitochondria in the intrinsic pathway of apoptosis. Other cellular roles, including a pro-survival role, have also been described for Apaf1, while the relative contribution of each function to cell death, but also to cell homeostatic conditions, remain to be clarified.

Methodology and Principal Findings

Here we examined the response to apoptosis induction of available embryonic fibroblasts from Apaf1 knockout mice (MEFS KO Apaf1). In the absence of Apaf1, cells showed mitochondria with an altered morphology that affects cytochrome c release and basal metabolic status.

Conclusions

We analysed mitochondrial features and cell death response to etoposide and ABT-737 in two different Apaf1-deficient MEFS, which differ in the immortalisation protocol. Unexpectedly, MEFS KO Apaf1 immortalised with the SV40 antigen (SV40IM-MEFS Apaf1) and those which spontaneously immortalised (SIM-MEFS Apaf1) respond differently to apoptotic stimuli, but both presented relevant differences at the mitochondria when compared to MEFS WT, indicating a role for Apaf1 at the mitochondria.

Immortalization of neuronal progenitors using SV40 large T antigen and differentiation towards dopaminergic neurons

Transplantation is common in clinical practice where there is availability of the tissue and organ. In the case of neurodegenerative disease such as Parkinson's disease (PD), transplantation is not possible as a result of the non-availability of tissue or organ and therefore, cell therapy is an innovation in clinical practice. However, the availability of neuronal cells for transplantation is very limited. Alternatively, immortalized neuronal progenitors could be used in treating PD. The neuronal progenitor cells can be differentiated into dopaminergic phenotype. Here in this article, the current understanding of the molecular mechanisms involved in the differentiation of dopaminergic phenotype from the neuronal progenitors immortalized with SV40 LT antigen is discussed. In addition, the methods of generating dopaminergic neurons from progenitor cells and the factors that govern their differentiation are elaborated. Recent advances in cell-therapy based transplantation in PD patients and future prospects are discussed.

Genetically engineered mice as experimental tools to dissect the critical events in breast cancer

Elucidating the mechanism of pathogenesis of breast cancer has greatly benefited from breakthrough advances in both genetically engineered mouse (GEM) models and xenograft transplantation technologies. The vast array of breast cancer mouse models currently available is testimony to the complexity of mammary tumorigenesis and attempts by investigators to accurately portray the heterogeneity and intricacies of this disease. Distinct molecular changes that drive various aspects of tumorigenesis, such as alterations in tumor cell proliferation and apoptosis, invasion and metastasis, angiogenesis, and drug resistance have been evaluated using the currently available GEM breast cancer models. GEM breast cancer models are also being exploited to evaluate and validate the efficacy of novel therapeutics, vaccines, and imaging modalities for potential use in the clinic. This review provides a synopsis of the various GEM models that are expanding our knowledge of the nuances of breast cancer development and progression and can be instrumental in the development of novel prevention and therapeutic approaches for this disease.

High-affinity Rb binding, p53 inhibition, subcellular localization, and transformation by wild-type or tumor-derived shortened Merkel cell polyomavirus large T antigens

Interference with tumor suppressor pathways by polyomavirus-encoded tumor antigens (T-Ags) can result in transformation. Consequently, it is thought that T-Ags encoded by Merkel cell polyomavirus (MCPyV), a virus integrated in ∼90% of all Merkel cell carcinoma (MCC) cases, are major contributors to tumorigenesis. The MCPyV large T-Ag (LT-Ag) has preserved the key functional domains present in all family members but has also acquired unique regions that flank the LxCxE motif. As these regions may mediate unique functions, or may modulate those shared with T-Ags of other polyomaviruses, functional studies of MCPyV T-Ags are required. Here, we have performed a comparative study of full-length or MCC-derived truncated LT-Ags with regard to their biochemical characteristics, their ability to bind to retinoblastoma (Rb) and p53 proteins, and their transforming potential. We provide evidence that full-length MCPyV LT-Ag may not directly bind to p53 but nevertheless can significantly reduce p53-dependent transcription in reporter assays. Although early region expression constructs harboring either full-length or MCC-derived truncated LT-Ag genes can transform primary baby rat kidney cells, truncated LT-Ags do not bind to p53 or reduce p53-dependent transcription. Interestingly, shortened LT-Ags exhibit a very high binding affinity for Rb, as shown by coimmunoprecipitation and in vitro binding studies. Additionally, we show that truncated MCPyV LT-Ag proteins are expressed at higher levels than those for the wild-type protein and are able to partially relocalize Rb to the cytoplasm, indicating that truncated LT proteins may have gained additional features that distinguish them from the full-length protein.

IMPORTANCE

MCPyV is one of the 12 known polyomaviruses that naturally infect humans. Among these, it is of particular interest since it is the only human polyomavirus known to be involved in tumorigenesis. MCPyV is thought to be causally linked to MCC, a rare skin tumor. In these tumors, viral DNA is monoclonally integrated into the genome of the tumor cells in up to 90% of all MCC cases, and the integrated MCV genomes, furthermore, harbor signature mutations in the so-called early region that selectively abrogate viral replication while preserving cell cycle deregulating functions of the virus. This study describes comparative studies of early region T-Ag protein characteristics, their ability to bind to Rb and p53, and their transforming potential.

Immortality, but not oncogenic transformation, of primary human cells leads to epigenetic reprogramming of DNA methylation and gene expression

Tumourigenic transformation of normal cells into cancer typically involves several steps resulting in acquisition of unlimited growth potential, evasion of apoptosis and non-responsiveness to growth inhibitory signals. Both genetic and epigenetic changes can contribute to cancer development and progression. Given the vast genetic heterogeneity of human cancers and difficulty to monitor cancer-initiating events in vivo, the precise relationship between acquisition of genetic mutations and the temporal progression of epigenetic alterations in transformed cells is largely unclear. Here, we use an in vitro model system to investigate the contribution of cellular immortality and oncogenic transformation of primary human cells to epigenetic reprogramming of DNA methylation and gene expression. Our data demonstrate that extension of replicative life span of the cells is sufficient to induce accumulation of DNA methylation at gene promoters and large-scale changes in gene expression in a time-dependent manner. In contrast, continuous expression of cooperating oncogenes in immortalized cells, although essential for anchorage-independent growth and evasion of apoptosis, does not affect de novo DNA methylation at promoters and induces subtle expression changes. Taken together, these observations imply that cellular immortality promotes epigenetic adaptation to highly proliferative state, whereas transforming oncogenes confer additional properties to transformed human cells.

Gene expression profiling of lens tumors, liver and spleen in α-crystallin/SV40 T antigen transgenic mice treated with Juzen-taiho-to

The autogenic lens tumors induced by the Simian vacuolating virus 40 (SV40) T antigen in α-crystallin/SV40 T antigen transgenic (TG) mice, provide a tool to screen anti-tumor reagents in vivo and to clarify the underlying mechanisms. Juzen-taiho-to, a Chinese medicine composed of 10 herbs, was frequently used as an alternative medicine for cancer patients by clinicians and occasionally it was demonstrated to have beneficial effects on the prognosis and general condition of cancer patients. However, it was not scientifically verified. In the present study, the anti-tumor effects and underlying mechanisms of Juzen-taiho-to in the TG mice model was examined using cDNA microarray analysis and the results were confirmed by real-time PCR. The TG mice demonstrated a higher cumulative survival rate after treatment with the drug compared with the control group (P<0.05). Gene chip profiles demonstrated that cell functions involving the membrane, glycoprotein, cell membrane, signal and ionic channel for the lens tumor, the cell cycle, DNA replication, homeobox, mitosis and cell division for the spleen and the acetylation, mitochondrion, ribosomal protein, ribonucleoprotein for the liver, were altered by the administration of Juzen‑taiho-to. The important canonical pathways were those of the mitogen-activated protein kinase (MAPK), the cell cycle and the ribosome for the altered genes of the lens tumor, spleen and liver after drug administration, respectively. From real-time PCR, in the eyeball, epidermal growth factor receptor (Egfr), Rasgrf1 and heat shock protein 1B (Hspa1b) mRNAs were found to be significantly lower in treated lenses than in those not exposed to the drug, while Rps25 mRNA demonstrated the opposite association in the liver. It was suggested that Juzen-taiho-to may prolong the survival time of SV40 T antigen TG mice by improving their nutritional condition, inhibiting the MAPK pathway and strengthening the immune system without causing hepatic toxicity.

Apocynin, an NADPH oxidase inhibitor, suppresses rat prostate carcinogenesis

Recent evidence suggests that oxidative stress contributes to the pathogenesis of prostate cancer. The present study focused on the effect of apocynin, an inhibitor of NADPH oxidase, on prostate carcinogenesis using the transgenic rat for adenocarcinoma of prostate (TRAP) model. There were no toxic effects with apocynin treatment. The percentages and numbers of carcinomas in both the ventral and lateral prostate were significantly reduced by apocynin treatment, with dose dependence. Reduction of reactive oxygen species by apocynin was confirmed by immunohistochemistry of 8-OHdG and dihydroethidium staining. Positivity of Ki67 was significantly reduced by apocynin treatment, and downregulation of clusterin expression, as well as inactivation of the MEK-ERK1/2 pathway, was a feature of the apocynin treated groups. In human prostate cancer cell line LNCaP, apocynin also inhibited reactive oxygen species production and blocked cell growth by inducing G0/G1 arrest with downregulation of clusterin and cyclin D1. These data suggest that apocynin possesses chemopreventive potential against prostate cancer.

The adenovirus 55 residue E1A protein is a transcriptional activator and binds the unliganded thyroid hormone receptor

The early region 1A (E1A) of human adenovirus types 2 and 5 is differentially spliced to yield five distinct mRNAs that encode different proteins. The smallest E1A RNA transcript encodes a 55 residue (55R) protein that shares only 28 amino acid residues with the other E1A proteins. Even though it is the most abundant E1A transcript at late times post-infection, little is known about the functions of this E1A isoform. In this study, we show that the E1A 55R protein interacts with, and modulates the activity of the unliganded thyroid hormone receptor (TR). We demonstrate that E1A 55R contains a signature motif known as the CoRNR box that confers interaction with the unliganded TR; this motif was originally identified in cellular corepressors. Using a system reconstituted in the yeast Saccharomyces cerevisiae, which lack endogenous TR and TR coregulators, we show that E1A 55R nonetheless differs from cellular corepressors as it functions as a strong co-activator of TR-dependent transcription and that it possesses an intrinsic transcriptional activation domain. These data indicate that the E1A 55R protein functions as a transcriptional regulator.

The transcription factor FOXM1 (Forkhead box M1): proliferation-specific expression, transcription factor function, target genes, mouse models, and normal biological roles

FOXM1 (Forkhead box M1) is a typical proliferation-associated transcription factor, which stimulates cell proliferation and exhibits a proliferation-specific expression pattern. Accordingly, both the expression and the transcriptional activity of FOXM1 are increased by proliferation signals, but decreased by antiproliferation signals, including the positive and negative regulation by protooncoproteins or tumor suppressors, respectively. FOXM1 stimulates cell cycle progression by promoting the entry into S-phase and M-phase. Moreover, FOXM1 is required for proper execution of mitosis. Accordingly, FOXM1 regulates the expression of genes, whose products control G1/S-transition, S-phase progression, G2/M-transition, and M-phase progression. Additionally, FOXM1 target genes encode proteins with functions in the execution of DNA replication and mitosis. FOXM1 is a transcriptional activator with a forkhead domain as DNA binding domain and with a very strong acidic transactivation domain. However, wild-type FOXM1 is (almost) inactive because the transactivation domain is repressed by three inhibitory domains. Inactive FOXM1 can be converted into a very potent transactivator by activating signals, which release the transactivation domain from its inhibition by the inhibitory domains. FOXM1 is essential for embryonic development and the foxm1 knockout is embryonically lethal. In adults, FOXM1 is important for tissue repair after injury. FOXM1 prevents premature senescence and interferes with contact inhibition. FOXM1 plays a role for maintenance of stem cell pluripotency and for self-renewal capacity of stem cells. The functions of FOXM1 in prevention of polyploidy and aneuploidy and in homologous recombination repair of DNA-double-strand breaks suggest an importance of FOXM1 for the maintenance of genomic stability and chromosomal integrity.

Two independent regions of simian virus 40 T antigen increase CBP/p300 levels, alter patterns of cellular histone acetylation, and immortalize primary cells

Simian virus 40 (SV40) large T antigen (SVT) interferes with normal cell regulation and thus has been used to identify cellular components controlling proliferation and homeostasis. We have previously shown that SVT-mediated transformation requires interaction with the histone acetyltransferases (HATs) CBP/p300 and now report that the ectopic expression of SVT in several cell types in vivo and in vitro results in a significant increase in the steady-state levels of CBP/p300. Furthermore, SVT-expressing cells contain higher levels of acetylated CBP/p300, a modification that has been linked to increased HAT activity. Concomitantly, the acetylation levels of histone residues H3K56 and H4K12 are markedly increased in SVT-expressing cells. Other polyomavirus-encoded large T antigens also increase the levels of CBP/p300 and sustain a rise in the acetylation levels of H3K56 and H4K12. SVT does not affect the transcription of CBP/p300, but rather, alters their overall levels through increasing the loading of CBP/p300 mRNAs onto polysomes. Two distinct regions within SVT, one located in the amino terminus and one in the carboxy terminus, can independently alter both the levels of CBP/p300 and the loading of CBP/p300 transcripts onto polysomes. Within the amino-terminal fragment, a functional J domain is necessary for increasing CBP/p300 and specific histone acetylation levels, as well as for immortalizing primary cells. These studies uncover the action of polyomavirus T antigens on cellular CBP/p300 and suggest that additional mechanisms are used by T antigens to induce cell immortalization and transformation.

Replication stress and mitotic dysfunction in cells expressing simian virus 40 large T antigen

We previously demonstrated that simian virus 40 (SV40) large T antigen (LT) binds to the Bub1 kinase, a key regulator of the spindle checkpoint and chromosome segregation. Bub1 mutations or altered expression patterns are linked to chromosome missegregation and are considered to be a driving force in some human cancers. Here we report that LT, dependent on Bub1 binding, causes micronuclei, lagging chromatin, and anaphase bridges, which are hallmarks of chromosomal instability (CIN) and Bub1 insufficiency. Using time-lapse microscopy, we demonstrate that LT imposes a Bub1 binding-dependent delay in the metaphase-to-anaphase transition. Kinetochore fibers reveal that LT, via Bub1 binding, causes aberrant kinetochore (KT)-microtubule (MT) attachments and a shortened interkinetochore distance, consistent with a lack of tension. Previously, we showed that LT also induces the DNA damage response (DDR) via Bub1 binding. Using inducible LT cell lines, we show that an activated DDR was observed before the appearance of anaphase bridges and micronuclei. Furthermore, LT induction in serum-starved cells demonstrated γ-H2AX accumulation in cells that had not yet entered mitosis. Thus, DDR activation can occur independently of chromosome segregation defects. Replication stress pathways may be responsible, because signatures of replication stress were observed, which were attenuated by exogenous supplementation with nucleosides. Our observations allow us to propose a model that explains and integrates the diverse manifestations of genomic instability induced by LT.

Comparative transcriptome profiling of an SV40-transformed human fibroblast (MRC5CVI) and its untransformed counterpart (MRC-5) in response to UVB irradiation

Simian virus 40 (SV40) transforms cells through the suppression of tumor-suppressive responses by large T and small t antigens; studies on the effects of these two oncoproteins have greatly improved our knowledge of tumorigenesis. Large T antigen promotes cellular transformation by binding and inactivating p53 and pRb tumor suppressor proteins. Previous studies have shown that not all of the tumor-suppressive responses were inactivated in SV40-transformed cells; however, the underlying cause is not fully studied. In this study, we investigated the UVB-responsive transcriptome of an SV40-transformed fibroblast (MRC5CVI) and that of its untransformed counterpart (MRC-5). We found that, in response to UVB irradiation, MRC-5 and MRC5CVI commonly up-regulated the expression of oxidative phosphorylation genes. MRC-5 up-regulated the expressions of chromosome condensation, DNA repair, cell cycle arrest, and apoptotic genes, but MRC5CVI did not. Further cell death assays indicated that MRC5CVI was more sensitive than MRC-5 to UVB-induced cell death with increased caspase-3 activation; combining with the transcriptomic results suggested that MRC5CVI may undergo UVB-induced cell death through mechanisms other than transcriptional regulation. Our study provides a further understanding of the effects of SV40 transformation on cellular stress responses, and emphasizes the value of SV40-transformed cells in the researches of sensitizing neoplastic cells to radiations.

Generation of mouse small intestinal epithelial cell lines that allow the analysis of specific innate immune functions

Cell lines derived from the small intestine that reflect authentic properties of the originating intestinal epithelium are of high value for studies on mucosal immunology and host microbial homeostasis. A novel immortalization procedure was applied to generate continuously proliferating cell lines from murine E19 embryonic small intestinal tissue. The obtained cell lines form a tight and polarized epithelial cell layer, display characteristic tight junction, microvilli and surface protein expression and generate increasing transepithelial electrical resistance during in vitro culture. Significant up-regulation of Cxcl2 and Cxcl5 chemokine expression upon exposure to defined microbial innate immune stimuli and endogenous cytokines is observed. Cell lines were also generated from a transgenic interferon reporter (Mx2-Luciferase) mouse, allowing reporter technology-based quantification of the cellular response to type I and III interferon. Thus, the newly created cell lines mimic properties of the natural epithelium and can be used for diverse studies including testing of the absorption of drug candidates. The reproducibility of the method to create such cell lines from wild type and transgenic mice provides a new tool to study molecular and cellular processes of the epithelial barrier.

p53-stabilizing agent CP-31398 prevents growth and invasion of urothelial cancer of the bladder in transgenic UPII-SV40T mice

The high prevalence of bladder cancer and its recurrence make it an important target for chemoprevention. About half of invasive urothelial tumors have mutations in p53. We determined the chemopreventive efficacy of a p53-stabilizing agent, CP-31398, in a transgenic UPII-SV40T mouse model of bladder transitional cell carcinoma (TCC) that strongly resembles human TCC. After genotyping, six-week-old UPII-SV40T mice (n = 30/group) were fed control (AIN-76A) or experimental diets containing 150 or 300 ppm of CP-31398 for 34 weeks. Progression of bladder cancer growth was monitored by magnetic resonance imaging. At 40 weeks of age, all mice were killed; urinary bladders were collected to determine weights, tumor incidence, and histopathology. There was a significant increase in bladder weights of transgenic versus wild-type mice (male: 140.2 mg vs 27.3 mg, P < .0001; female: 34.2 mg vs 14.8 mg, P < .0001). A significant decrease in the bladder tumor weights (by 68.6-80.2%, P < .0001 in males and by 36.9-55.3%, P < .0001 in females) was observed in CP-31398-treated mice. Invasive papillary TCC incidence was 100% in transgenic mice fed control diet. Both male and female mice exposed to CP-31398 showed inhibition of invasive TCC. CP-31398 (300 ppm) completely blocked invasion in female mice. Molecular analysis of the bladder tumors showed an increase in apoptosis markers (p53, p21, Bax, and Annexin V) with a decrease in vascular endothelial growth factor in transgenic mice fed CP-31398. These results suggest that p53-modulating agents can serve as potential chemopreventive agents for bladder TCC.

A simple, robust and highly efficient transient expression system for producing antibodies

Transient expression systems in mammalian cells have become the method of choice for producing research quantities of antibodies. Both the speed and yield of the available transient systems and the natural posttranslational modifications favor these systems above expression in lower eukaryotes, prokaryotes or stable cell lines. We describe an optimized mammalian transient expression system, capable of producing up to 400mg/L of native secreted antibodies in less than a week. The system is composed of commercially available components and is based on expression in the fast growing suspension cell line, FreeStyle™ 293-F (HEK-293F). The method depends on an optimal combination of a gene transfer method, an expression vector and cotransfection with expression enhancing plasmids, encoding the large T antigen of the SV40 virus and the cell cycle inhibitors p21 and p27. Optimization of all components of the expression system, by experimental design techniques, yielded maximal expression levels (including antibody isotypes IgG1, 2, 3, 4 and Fab fragments of various species). Expression volumes were scalable from 0.1 ml up to 1.2L in a simple shaker flask system in animal component free, low protein medium, enabling consistent production of relatively high amounts of a large number of native antibodies.

The molecular basis for ethnic variation and histological subtype differences in prostate cancer

Prostate cancer is a common malignancy among men in Western countries. Recently the morbidity and mortality of prostate cancer increase dramatically in several oriental countries including China. Rapidly evolving technology in molecular biology such as high-throughput sequencing and integrative analysis of genomic and transcriptomic landscapes have enabled the identification of key oncogenic events for prostate cancer initiation, progression and resistance to hormonal therapy. These surging data of prostate cancer genome also provide insights on ethnic variation and the differences in histological subtype of this disease. In this review, differences in the incidence of prostate cancer and the prevalence of main genetic alterations between Asian and Western populations are discussed. We also review the recent findings on the mechanisms underlying neuroendocrine differentiation of prostate cancer and the development of small cell neuroendocrine carcinoma after androgen deprivation therapy.

Identification of an overprinting gene in Merkel cell polyomavirus provides evolutionary insight into the birth of viral genes

Many viruses use overprinting (alternate reading frame utilization) as a means to increase protein diversity in genomes severely constrained by size. However, the evolutionary steps that facilitate the de novo generation of a novel protein within an ancestral ORF have remained poorly characterized. Here, we describe the identification of an overprinting gene, expressed from an Alternate frame of the Large T Open reading frame (ALTO) in the early region of Merkel cell polyomavirus (MCPyV), the causative agent of most Merkel cell carcinomas. ALTO is expressed during, but not required for, replication of the MCPyV genome. Phylogenetic analysis reveals that ALTO is evolutionarily related to the middle T antigen of murine polyomavirus despite almost no sequence similarity. ALTO/MT arose de novo by overprinting of the second exon of T antigen in the common ancestor of a large clade of mammalian polyomaviruses. Taking advantage of the low evolutionary divergence and diverse sampling of polyomaviruses, we propose evolutionary transitions that likely gave birth to this protein. We suggest that two highly constrained regions of the large T antigen ORF provided a start codon and C-terminal hydrophobic motif necessary for cellular localization of ALTO. These two key features, together with stochastic erasure of intervening stop codons, resulted in a unique protein-coding capacity that has been preserved ever since its birth. Our study not only reveals a previously undefined protein encoded by several polyomaviruses including MCPyV, but also provides insight into de novo protein evolution.

Leger JA, Navarrete-Macias I, Nilson E, Sanchez-Leon M, Liang E, Seimon T, Jain K, Karesh W, Daszak P, Briese T, Lipkin WI. Identification of a novel cetacean polyomavirus from a common dolphin (Delphinus delphis) with Tracheobronchitis

A female short-beaked common dolphin calf was found stranded in San Diego, California in October 2010, presenting with multifocal ulcerative lesions in the trachea and bronchi. Viral particles suggestive of polyomavirus were detected by EM, and subsequently confirmed by PCR and sequencing. Full genome sequencing (Ion Torrent) revealed a circular dsDNA genome of 5,159 bp that was shown to form a distinct lineage within the genus Polyomavirus based on phylogenetic analysis of the early and late transcriptomes. Viral infection and distribution in laryngeal mucosa was characterised using in-situ hybridisation, and apoptosis observed in the virus-infected region. These results demonstrate that polyomaviruses can be associated with respiratory disease in cetaceans, and expand our knowledge of their diversity and clinical significance in marine mammals.

Merkel cell polyomavirus large T antigen disrupts host genomic integrity and inhibits cellular proliferation

Clonal integration of Merkel cell polyomavirus (MCV) DNA into the host genome has been observed in at least 80% of Merkel cell carcinoma (MCC). The integrated viral genome typically carries mutations that truncate the C-terminal DNA binding and helicase domains of the MCV large T antigen (LT), suggesting a selective pressure to remove this MCV LT region during tumor development. In this study, we show that MCV infection leads to the activation of host DNA damage responses (DDR). This activity was mapped to the C-terminal helicase-containing region of the MCV LT. The MCV LT-activated DNA damage kinases, in turn, led to enhanced p53 phosphorylation, upregulation of p53 downstream target genes, and cell cycle arrest. Compared to the N-terminal MCV LT fragment that is usually preserved in mutants isolated from MCC tumors, full-length MCV LT shows a decreased potential to support cellular proliferation, focus formation, and anchorage-independent cell growth. These apparently antitumorigenic effects can be reversed by a dominant-negative p53 inhibitor. Our results demonstrate that MCV LT-induced DDR activates p53 pathway, leading to the inhibition of cellular proliferation. This study reveals a key difference between MCV LT and simian vacuolating virus 40 LT, which activates a DDR but inhibits p53 function. This study also explains, in part, why truncation mutations that remove the MCV LT C-terminal region are necessary for the oncogenic progression of MCV-associated cancers.

Gastric carcinoids (neuroendocrine neoplasms)

Gastric neuroendocrine neoplasms of the stomach can be divided into the usually well-differentiated, hypergastrinemia-dependent type I and II lesions and the more aggressively behaving gastrin-independent type III lesions. Studying menin and its complex interrelationship with gastrin may provide insight into tumor biology at the clinical level and in terms of basic cell biology (eg, the role of the epigenome in neuroendocrine cell proliferation), and lead to potential consideration of other targets that are known candidates for molecular-based therapies in other adenocarcinomas.

Majority of differentially expressed genes are down-regulated during malignant transformation in a four-stage model

The transformation of normal cells to malignant, metastatic tumor cells is a multistep process caused by the sequential acquirement of genetic changes. To identify these changes, we compared the transcriptomes and levels and distribution of proteins in a four-stage cell model of isogenically matched normal, immortalized, transformed, and metastatic human cells, using deep transcriptome sequencing and immunofluorescence microscopy. The data show that ∼6% (n = 1,357) of the human protein-coding genes are differentially expressed across the stages in the model. Interestingly, the majority of these genes are down-regulated, linking malignant transformation to dedifferentiation. The up-regulated genes are mainly components that control cellular proliferation, whereas the down-regulated genes consist of proteins exposed on or secreted from the cell surface. As many of the identified gene products control basic cellular functions that are defective in cancers, the data provide candidates for follow-up studies to investigate their functional roles in tumor formation. When we further compared the expression levels of four of the identified proteins in clinical cancer cohorts, similar differences were observed between benign and cancer cells, as in the cell model. This shows that this comprehensive demonstration of the molecular changes underlying malignant transformation is a relevant model to study the process of tumor formation.

Extended lifespan of normal human B lymphocytes experimentally infected by SV40 or transfected by SV40 large T antigen expression vector

SV40 footprints were detected in different lymphoproliferative disorders and in blood specimens of healthy donors. However, little is known on the ability of SV40 to infect/transform normal human B-lymphocytes. In this in vitro study, experimental SV40 infection and SV40 Tag transfection of normal human B-lymphocytes from healthy blood donors were carried out. In SV40 infected/transfected purified B-cells, during the time course analyses, viral DNA sequences were detected by PCR, while Tag mRNA and protein were revealed by RT-PCR and immunocytochemistry, respectively. Trypan blue and Alamar blue assays showed an increase in number of cells and cell viability of infected/transfected B-cells up to day 50, then a drastic and constant cell number reduction was observed in cultures. Approximately 50% of both infected and transfected B-cells appeared morphologically transformed. SV40 viral progeny and its titer from infected B-cells was determined by plaque assay in permissive CV-1 cells. Our data indicate that human B-cells can be efficiently infected by SV40, release a viral progeny, while at the same time are transformed. SV40 infected/Tag transfected B-cells may represent an experimental model of study for investigating new biomarkers and targets for innovative therapeutic approaches in human B-cell malignancies.

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.

Theca-derived BMP4 and BMP7 down-regulate connexin43 expression and decrease gap junction intercellular communication activity in immortalized human granulosa cells

CONTEXT

Connexin43 (Cx43)-coupled gap junctions in granulosa cells play important roles in follicular and oocyte development and may be modulated by theca cell-derived bone morphogenic protein (BMP) 4 and BMP7.

OBJECTIVE

The aim of this study was to examine the effects of BMP4 and BMP7 on Cx43 expression in human granulosa cells and its potential mediation by the Smad-dependent pathway.

DESIGN

An immortalized human granulosa (SVOG) cell was used to investigate Cx43 expression and gap junction intercellular communication (GJIC) activity after exposure to BMP4 and BMP7. A BMP type I inhibitor, dorsomorphin, and small interfering RNAs targeting Smad4 were used to verify the specificity of the effects.

SETTING

The study was conducted in an academic center.

MAIN OUTCOME MEASURES

Extracts were prepared from cultured cells, the Cx43 mRNA levels were examined using RT-quantitative real-time PCR, and the levels of Cx43 protein and phosphorylated Smad1/5/8 were assayed using Western blot analyses. GJIC activities between SVOG cells were evaluated using a scrape loading and dye transfer assay.

RESULTS

Treatment with BMP4 and BMP7 significantly decreased Cx43 mRNA and protein levels, as well as GJIC activities. These suppressive effects were attenuated by cotreatment with the BMP type I receptor inhibitor dorsomorphin. Furthermore, Smad4 knockdown reversed the effects of BMP4 and BMP7 on Cx43 expression.

CONCLUSION

Theca cell-derived BMP4 and BMP7 down-regulate Cx43 expression and decrease GJIC activity in human granulosa cells. Our findings indicate that this biological effect is most likely mediated by a Smad-dependent pathway.

False-positive TUNEL staining observed in SV40 based transgenic murine prostate cancer models

The TRAMP (Transgenic Adenocarcinoma of the Mouse Prostate) and LADY (Probasin-large T antigen transgenic mouse) mice are widely used autochthonous models of prostate cancer. Both models utilise probasin promoters to direct androgen-regulated expression of oncogenic SV40 specifically to epithelial cells of the mouse prostate. The oncogenic processes and phenotypes which result mimic many features of human prostate cancer, making these transgenic mouse models useful experimental systems. The terminal deoxynucleotidyl transferase (Tdt)-mediated dUTP in situ nick end labelling (TUNEL) assay is a commonly used method for the detection of cells undergoing apoptosis. In this study, we demonstrate false-positive TUNEL staining in frozen prostate tissue from TRAMP and LADY mice, which was not observed in non-transgenic control animals and is not due to non-specific binding of labelled-dUTP substrate. The false-positive signal co-localised with large SV40 T-antigen expression. False-positive signal was apparent using multiple commercial TUNEL kits with different detection systems. These results caution against the use of the TUNEL assay for detection of apoptosis in frozen prostate tissue of large T-antigen based autochthonous transgenic models of prostate cancer.

Immortality of cancers: a consequence of inherent karyotypic variations and selections for autonomy

Immortality is a common characteristic of cancers, but its origin and purpose are still unclear. Here we advance a karyotypic theory of immortality based on the theory that carcinogenesis is a form of speciation. Accordingly, cancers are generated from normal cells by random karyotypic rearrangements and selection for cancer-specific reproductive autonomy. Since such rearrangements unbalance long-established mitosis genes, cancer karyotypes vary spontaneously but are stabilized perpetually by clonal selections for autonomy. To test this theory we have analyzed neoplastic clones, presumably immortalized by transfection with overexpressed telomerase or with SV40 tumor virus, for the predicted clonal yet flexible karyotypes. The following results were obtained: (1) All immortal tumorigenic lines from cells transfected with overexpressed telomerase had clonal and flexible karyotypes; (2) Searching for the origin of such karyotypes, we found spontaneously increasing, random aneuploidy in human fibroblasts early after transfection with overexpressed telomerase; (3) Late after transfection, new immortal tumorigenic clones with new clonal and flexible karyotypes were found; (4) Testing immortality of one clone during 848 unselected generations showed the chromosome number was stable, but the copy numbers of 36% of chromosomes drifted ± 1; (5) Independent immortal tumorigenic clones with individual, flexible karyotypes arose after individual latencies; (6) Immortal tumorigenic clones with new flexible karyotypes also arose late from cells of a telomerase-deficient mouse rendered aneuploid by SV40 virus. Because immortality and tumorigenicity: (1) correlated exactly with individual clonal but flexible karyotypes; (2) originated simultaneously with such karyotypes; and (3) arose in the absence of telomerase, we conclude that clonal and flexible karyotypes generate the immortality of cancers.

Merkel cell polyomavirus: a newly discovered human virus with oncogenic potential

A marked escalation in the rate of discovery of new types of human polyomavirus has occurred over the last five years largely owing to recent technological advances in their detection. Among the newly discovered viruses, Merkel Cell Polyomavirus (MCPyV or MCV) has gained the most attention due to its link with a rare human cancer. Infection with MCPyV is common in the human population, and the virus is detected in several anatomical locations, but most frequently in skin. Study of MCPyV molecular virology has been complicated by the lack of straightforward cell culture models, but recent in vitro studies are making strides towards understanding the virus life cycle, its cellular tropism, and mode of transmission. While MCPyV shares several traditional traits with other human polyomaviruses, the burst of research since its discovery reveals insight into a virus with many unique genetic and mechanistic features. The evidence for a causal link between MCPyV and the rare neuroendocrine cancer, Merkel Cell Carcinoma (MCC), is compelling. A majority of MCCs contain clonally integrated viral DNA, express viral T antigen transcripts and protein, and exhibit an addiction to the viral large T and small t antigen oncoproteins. The MCPyV large T antigen contains MCC tumor-specific mutations that ablate its replication capacity but preserve its oncogenic functions, and the small t antigen promotes an environment favorable for cap-dependent translation. The mechanisms of MCPyV-induced transformation have not been fully elucidated, but the likely etiological role of this new polyomavirus in human cancer provides a strong opportunity to expand knowledge of virus-host interactions and viral oncology.

Large T antigens of polyomaviruses: amazing molecular machines

The large tumor antigen (T antigen) encoded by simian virus 40 is an amazing molecular machine because it orchestrates viral infection by modulating multiple fundamental viral and cellular processes. T antigen is required for viral DNA replication, transcription, and virion assembly. In addition, T antigen targets multiple cellular pathways, including those that regulate cell proliferation, cell death, and the inflammatory response. Ectopic T antigen expression results in the immortalization and transformation of many cell types in culture and T antigen induces neoplasia when expressed in rodents. The analysis of the mechanisms by which T antigen carries out its many functions has proved to be a powerful way of gaining insights into cell biology. The accelerating pace at which new polyomaviruses are being discovered provides a collection of novel T antigens that, like simian virus 40, can be used to discover and study key cellular regulatory systems.

Measurement of mouse cytomegalovirus-induced interferon-β with immortalized luciferase reporter cells

The production of cytokines is a crucial element of the host response to viral and bacterial infections. To follow these events in vivo, transgenic mice have become a valuable tool to study cytokine production through induction of reporter genes. We describe here the generation and immortalization of cells derived from transgenic reporter mice for development of a high-throughput assay system for virus- or bacteria-induced cytokine induction. As an example we describe mouse cytomegalovirus (MCMV) infection of immortalized fibroblasts derived from mice expressing the firefly luciferase reporter downstream of the IFN-β promoter. Common methods to determine IFN-β production, including ELISA, quantitative real-time PCR (qPCR), and transient reporter assays using plasmid-based reporter constructs, have disadvantages and limitations. Transient transfections influence type I IFN responses in most cell types, and IFN-β ELISA as well as qPCR are both laborious and expensive. The method presented here is highly sensitive as well as cost-effective, and allows monitoring of a robust and dose-dependent induction of IFN-β upon virus infection in cell lysates as well as living cells.