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

Sepsis reveals compartment-specific responses in intestinal proliferation and apoptosis in transgenic mice whose enterocytes re-enter the cell cycle

Cell production and death are tightly regulated in the rapidly renewing gut epithelium, with proliferation confined to crypts and apoptosis occurring in villi and crypts. This study sought to determine how stress alters these compartmentalized processes. Wild-type mice made septic via cecal ligation and puncture had decreased crypt proliferation and increased crypt and villus apoptosis. Fabpi-TAg mice expressing large T-antigen solely in villi had ectopic enterocyte proliferation with increased villus apoptosis in unmanipulated animals. Septic fabpi-TAg mice had an unexpected increase in villus proliferation compared with unmanipulated littermates, whereas crypt proliferation was decreased. Cell cycle regulators cyclin D1 and cyclin D2 were decreased in jejunal tissue in septic transgenic mice. In contrast, villus and crypt apoptosis were increased in septic fabpi-TAg mice. To examine the relationship between apoptosis and proliferation in a compartment-specific manner, fabpi-TAg mice were crossed with fabpl-Bcl-2 mice, resulting in expression of both genes in the villus but Bcl-2 alone in the crypt. Septic bi-transgenic animals had decreased crypt apoptosis but had a paradoxical increase in villus apoptosis compared with septic fabpi-TAg mice, associated with decreased proliferation in both compartments. Thus, sepsis unmasks compartment-specific proliferative and apoptotic regulation that is not present under homeostatic conditions.-Lyons, J. D., Klingensmith, N. J., Otani, S., Mittal, R., Liang, Z., Ford, M. L., Coopersmith, C. M. Sepsis reveals compartment-specific responses in intestinal proliferation and apoptosis in transgenic mice whose enterocytes re-enter the cell cycle.

SV40 Large T Antigen Disrupts Embryogenesis of Canine and Porcine Somatic Cell Nuclear Transfer Embryo

Background

Somatic cell nuclear transfer (SCNT) is a useful biotechnological tool for transgenic animal production using genetically modified somatic cells (GMSCs). However, there are several limitations preventing successful transgenic animal generation by SCNT, such as obtaining proper somatic donor cells with a sufficiently long life span and proliferative capacity for generating GMSCs. Here, we established simian virus 40 large T antigen (SV40LT)-mediated lifespan-extended canine fibroblast cells (SV40LT-K9 cells) and evaluated their potential as nuclei donors for SCNT, based on cellular integrity and SCNT embryo development.

Results

SV40LT did not cause canine cell transformation, based on cell morphology and proliferation rate. No anchorage-independent growth in vitro and tumorigenicity in vivo were observed. After SCNT with SV40LT-K9 cells, embryos were transferred into surrogate dogs. All dogs failed to become pregnant. Most embryos did not proceed past the 8-cell stage and only one surrogate showed an implantation trace in its oviduct, indicating that the cells rarely developed into blastocysts. Because of the absence of an in vitro maturation method for canine embryos, we performed identical experiments using porcine fibroblast cells. Similarly, SV40LT did not transform porcine fibroblast cells (SV40LT-Pig cells). During in vitro development of SV40LT-Pig cell-driven SCNT embryos, their blastocyst formation rate was clearly lower than those of normal cells. Karyotyping analysis revealed that both SV40LT-K9 and SV40LT-Pig cells had aberrant chromosomal statuses.

Conclusions

Although lifespan-extended canine and porcine cells via SV40LT exhibit no apparent transforming changes, they are inappropriate for use as nuclei donors for SCNT because of their aneuploidy.

Conditionally Immortal Slc4a11-/- Mouse Corneal Endothelial Cell Line Recapitulates Disrupted Glutaminolysis Seen in Slc4a11-/- Mouse Model

Purpose

To establish conditionally immortal mouse corneal endothelial cell lines with genetically matched Slc4a11+/+ and Slc4a11-/- mice as a model for investigating pathology and therapies for SLC4A11 associated congenital hereditary endothelial dystrophy (CHED) and Fuchs' endothelial corneal dystrophy.

Methods

We intercrossed H-2Kb-tsA58 mice (Immortomouse) expressing an IFN-γ dependent and temperature-sensitive mutant of the SV40 large T antigen (tsTAg) with Slc4a11+/+ and Slc4a11-/- C57BL/6 mice. The growth characteristics of the cell lines was assessed by doubling time. Ion transport activities (Na+/H+ exchange, bicarbonate, lactate, and Slc4a11 ammonia transport) were analyzed by intracellular pH measurement. The metabolic status of the cell lines was assessed by analyzing TCA cycle intermediates via gas chromatography mass spectrometry (GC-MS).

Results

The immortalized Slc4a11+/+ and Slc4a11-/- mouse corneal endothelial cells (MCECs) remained proliferative through passage 49 and maintained similar active ion transport activity. As expected, proliferation was temperature sensitive and IFN-γ dependent. Slc4a11-/- MCECs exhibited decreased proliferative capacity, reduced NH3:H+ transport, altered expression of glutaminolysis enzymes similar to the Slc4a11-/- mouse, and reduced proportion of TCA cycle intermediates derived from glutamine with compensatory increases in glucose flux compared with Slc4a11+/+ MCECs.

Conclusions

This is the first report of the immortalization of MCECs. Ion transport of the immortalized endothelial cells remains active, except for NH3:H+ transporter activity in Slc4a11-/- MCECs. Furthermore, Slc4a11-/- MCECs recapitulate the glutaminolysis defects observed in Slc4a11-/- mouse corneal endothelium, providing an excellent tool to study the pathogenesis of SLC4A11 mutations associated with corneal endothelial dystrophies and to screen potential therapeutic agents.

P53 deregulation in Epstein-Barr virus-associated gastric cancer

TP53 is a tumour suppressor gene frequently mutated in human cancers; nevertheless, in EBV-associated malignancies mutations are uncommon despite frequent deregulation of the p53 pathway. In this study, we aimed to investigate p53 expression, TP53 mRNA levels and TP53 mutations in EBV-associated gastric carcinoma (EBVaGC). A case-control study was performed using 46 patients: 15 EBVaGC and 31 EBV-negative GC (EBVnGC) cases. p53 expression was detected by immunohistochemistry (IHC), the evaluation of p53 mRNA levels was performed by RT-qPCR and TP53 mutations were investigated only in EBVaGC cases using the DNA sanger sequencing method. p53 expression was found in 97.8% (45/46) of all gastric cancer cases (including EBVaGC and EBVnGC groups). Despite the high frequency of p53 expression in both groups, the percentages of cells are significantly higher among EBVaGC cases (p = 0.027). Regarding the mRNA levels, we found a significantly increased expression of p53 mRNA in EBVnGC (2^-ΔΔCt = 13.4 ± 2.4; p = 0.0029) when compared with EBVaGC. Furthermore, the sequencing analysis of TP53 gene revealed that only one of the 15 EBVaGC cases presented a missense mutation. Our results demonstrated that EBV-associated gastric carcinomas are characterized by a significant decrease of TP53 mRNA levels with a strong p53 expression and rare TP53 mutations when compared with EBV-negative cancers. Considering these results, EBV seems to induce a stabilization of p53 in the EBVaGC independently of the presence of mutations, which remains to be explained.

Reflections on the use of 10 IARC carcinogenic characteristics for an objective approach to identifying and organizing results from certain mechanistic studies

To find a scientifically based method for evaluating mechanistic data related to risks to human beings, a new protocol for identifying, organizing, and summarizing mechanistic data for decision-making on cancer hazard identification was proposed by the International Agency for Research on Cancer and by an international working group of multidisciplinary experts. This Commentary examined the 10 key carcinogens’ characteristics proposed in the context of several paradigms assumed in the using of these 10 characteristics. These characteristics were assumed to represent a “carcinogen’s” mechanism of action but what was ignored were characteristics of the mechanisms of the “initiation,” “promotion,” and “progression” carcinogenic process. Challenges were made to the interpretation of genotoxicity data as well as from concepts and findings related to the promotion phase and the role of adult human stem cells. Reliance of interpretation of “genotoxicity” data (molecular-DNA lesions in DNA; induction of free radicals/oxidative stress markers; phenotypic surrogates of gene mutations), as well as from lesions in genomic versus mitochondrial DNA, or in the target cells for the carcinogenic process in either in vitro cultures or in vivo tissues, makes this “objective” use of the data questionable. A challenge to the “dedifferentiation” hypothesis of cancer was made. Because of an agent being misclassified as “genotoxic”—rather than an “epigenetic”—agent (which works by threshold levels; can be blocked; and must be present at critical times during development and at regular, sustained chronic exposures) could lead to unwise policy decisions.

Cell lines generated from a chronic lymphocytic leukemia mouse model exhibit constitutive Btk and Akt signaling

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of mature CD5⁺ B cells in blood. Spontaneous apoptosis of CLL cells in vitro has hampered in-depth investigation of CLL pathogenesis. Here we describe the generation of three monoclonal mouse cell lines, EMC2, EMC4 and EMC6, from the IgH.TEμ CLL mouse model based on sporadic expression of SV40 large T antigen. The cell lines exhibit a stable CD5⁺CD43⁺IgM⁺CD19⁺ CLL phenotype in culture and can be adoptively transferred into Rag1^−/− mice. RNA-seq analysis revealed only minor differences between the cell lines and their primary tumors and suggested that NF-κB and mTOR signaling pathways were involved in cell line outgrowth. In vitro survival and proliferation was dependent on constitutive phosphorylation of Bruton's tyrosine kinase (Btk) at Y551/Y223, and Akt(S473). Treatment of the cell lines with small molecule inhibitors specific for Btk (ibrutinib) or PI3K (idelalisib), which is upstream of Akt, resulted in reduced viability, proliferation and fibronectin-dependent cell adhesion. Treatment of cell line-engrafted Rag1^−/− mice with ibrutinib was associated with transient lymphocytosis, reduced splenomegaly and increased overall survival. Thus, by generating stable cell lines we established a novel platform for in vitro and in vivo investigation of CLL signal transduction and treatment modalities.

Study of SV40 large T antigen nucleotide specificity for DNA unwinding

Background

Simian Virus 40 (SV40) Large Tumor Antigen (LT) is an essential enzyme that plays a vital role in viral DNA replication in mammalian cells. As a replicative helicase and initiator, LT assembles as a double-hexamer at the SV40 origin to initiate genomic replication. In this process, LT converts the chemical energy from ATP binding and hydrolysis into the mechanical work required for unwinding replication forks. It has been demonstrated that even though LT primarily utilizes ATP to unwind DNA, other NTPs can also support low DNA helicase activity. Despite previous studies on specific LT residues involved in ATP hydrolysis, no systematic study has been done to elucidate the residues participating in the selective usage of different nucleotides by LT. In this study, we performed a systematic mutational analysis around the nucleotide pocket and identified residues regulating the specificity for ATP, TTP and UTP in LT DNA unwinding.

Methods

We performed site-directed mutagenesis to generate 16 LT nucleotide pocket mutants and characterized each mutant’s ability to unwind double-stranded DNA, oligomerize, and bind different nucleotides using helicase assays, size-exclusion chromatography, and isothermal titration calorimetry, respectively.

Results

We identified four residues in the nucleotide pocket of LT, cS430, tK419, cW393 and cL557 that selectively displayed more profound impact on using certain nucleotides for LT DNA helicase activity.

Conclusion

Little is known regarding the mechanisms of nucleotide specificity in SV40 LT DNA unwinding despite the abundance of information available for understanding LT nucleotide hydrolysis. The systematic residue analysis performed in this report provides significant insight into the selective usage of different nucleotides in LT helicase activity, increasing our understanding of how LT may structurally prefer different energy sources for its various targeted cellular activities.

Engineered Exosomes as Vehicles for Biologically Active Proteins

Exosomes represent an attractive vehicle for the delivery of biomolecules. However, mechanisms for loading functional molecules into exosomes are relatively unexplored. Here we report the use of the evolutionarily conserved late-domain (L-domain) pathway as a mechanism for loading exogenous proteins into exosomes. We demonstrate that labeling of a target protein, Cre recombinase, with a WW tag leads to recognition by the L-domain-containing protein Ndfip1, resulting in ubiquitination and loading into exosomes. Our results show that Ndfip1 expression acts as a molecular switch for exosomal packaging of WW-Cre that can be suppressed using the exosome inhibitor GW4869. When taken up by floxed reporter cells, exosomes containing WW-Cre were capable of inducing DNA recombination, indicating functional delivery of the protein to recipient cells. Engineered exosomes were administered to the brain of transgenic reporter mice using the nasal route to test for intracellular protein delivery in vivo. This resulted in the transport of engineered exosomes predominantly to recipient neurons in a number of brain regions, including the olfactory bulb, cortex, striatum, hippocampus, and cerebellum. The ability to engineer exosomes to deliver biologically active proteins across the blood-brain barrier represents an important step for the development of therapeutics to treat brain diseases.

Animal models as a tool in hepatocellular carcinoma research: A Review

Cancer is the first cause of death in developed countries and the second in developing countries. Concerning the most frequent worldwide-diagnosed cancer, primary liver cancer represents approximately 4% of all new cancer cases diagnosed globally. However, among primary liver cancer, hepatocellular carcinoma is by far the most common histological subtype. Notwithstanding the health promotion and disease prevention campaigns, more than half a million new hepatocellular carcinoma cases are reported yearly, being estimated to growth continuously until 2020. Taking this scenario under consideration and the fact that some aspects concerning hepatocellular carcinoma evolution and metastasize process are still unknown, animal models assume a crucial role to understand this disease. The animal models have also provided the opportunity to screen new therapeutic strategies. The present review was supported on research and review papers aiming the complexity and often neglected chemically induced animal models in hepatocarcinogenesis research. Despite the ongoing debate, chemically induced animal models, namely, mice and rat, can provide unique valuable information on the biotransformation mechanisms against xenobiotics and apprehend the deleterious effects on DNA and cell proteins leading to carcinogenic development. In addition, taking under consideration that no model achieves all hepatocellular carcinoma research purposes, criteria to define the " ideal" animal model, depending on the researchers' approach, are also discussed in this review.

P53/Rb inhibition induces metastatic adrenocortical carcinomas in a preclinical transgenic model

Adrenocortical carcinoma (ACC) is a rare cancer with poor prognosis. Pan-genomic analyses identified p53/Rb and WNT/β-catenin signaling pathways as main contributors to the disease. However, isolated β-catenin constitutive activation failed to induce malignant progression in mouse adrenocortical tumors. Therefore, there still was a need for a relevant animal model to study ACC pathogenesis and to test new therapeutic approaches. Here, we have developed a transgenic mice model with adrenocortical specific expression of SV40 large T-antigen (AdTAg mice), to test the oncogenic potential of p53/Rb inhibition in the adrenal gland. All AdTAg mice develop large adrenal carcinomas that eventually metastasize to the liver and lungs, resulting in decreased overall survival. Consistent with ACC in patients, adrenal tumors in AdTAg mice autonomously produce large amounts of glucocorticoids and spontaneously activate WNT/β-catenin signaling pathway during malignant progression. We show that this activation is associated with downregulation of secreted frizzled related proteins (Sfrp) and Znrf3 that act as inhibitors of the WNT signaling. We also show that mTORC1 pathway activation is an early event during neoplasia expansion and further demonstrate that mTORC1 pathway is activated in ACC patients. Preclinical inhibition of mTORC1 activity induces a marked reduction in tumor size, associated with induction of apoptosis and inhibition of proliferation that results in normalization of corticosterone plasma levels in AdTAg mice. Altogether, these data establish AdTAg mice as the first preclinical model for metastatic ACC.

An Unexpected Surge in Plasma BKPyV Viral Load Heralds the Development of BKPyV-Associated Metastatic Bladder Cancer in a Lung Transplant Recipient With BKPyV Nephropathy

We report a lung transplant recipient who developed BK polyoma virus (BKPyV) DNAemia and BKPyV nephropathy. With careful management of his immunosuppression he achieved significant reduction in BKPyV DNAemia and stabilization of his kidney function. He later developed a high-grade bladder cancer and shortly thereafter he experienced a major upsurge in the level of BKPyV DNAemia that coincided with the discovery of hepatic metastasis. Retrospectively, the bladder cancer and the hepatic secondary tumor stained uniformly for SV40 large T antigen, and the BKPyV DNA sequences identified in plasma corresponded to BKPyV DNA within hepatic tissue, indicating that the spike in BKPyV load was likely derived from the circulating tumor cells or cell-free tumor DNA following metastases of a BKV-associated cancer. To the best of our knowledge, this is the first description of a surge in BKPyV load in a patient with controlled BKPyVN that heralded the appearance of a metastatic urothelial malignancy. This report discusses the literature on BKPyV-associated malignancies and the possibility that unexplained increases in BKPyV DNAemia may be a biomarker for metastatic BKPyV-related urothelial cancer.

Low p16INK4a Expression in Early Passage Human Prostate Basal Epithelial Cells Enables Immortalization by Telomerase Expression Alone

BACKGROUND

There are two principal senescence barriers that must be overcome to successfully immortalize primary human epithelial cells in culture, stress-induced senescence, and replicative senescence. The p16^INK4a /retinoblastoma protein (p16/Rb) pathway mediates stress-induced senescence, and is generally upregulated by primary epithelial cells in response to the artificial conditions from tissue culture. Replicative senescence is associated with telomere loss. Following each round of cell division, telomeres progressively shorten. Once telomeres shorten to a critical length, the DNA damage response pathway is activated, and the tumor suppressor p53 pathway triggers replicative senescence. Exogenous expression of telomerase in normal human epithelial cells extends the replicative capacity of cells, and in some cases, immortalizes cells. However reliable immortalization of epithelial cells usually requires telomerase activity coupled with inactivation of the p16/Rb pathway.

METHODS

A lentiviral vector, pLOX-TERT-iresTK (Addgene #12245), containing a CMV promoter upstream of a bicistronic coding cassette that includes loxP sites flanking the catalytic subunit of human telomerase gene (TERT) and herpes simplex virus type-1 thymidine kinase gene (HSV1-tk) was used to transduce normal prostate basal epithelial cells (PrECs) initiated in cell culture from prostate cancer patients undergoing radical prostatectomies.

RESULTS

Transduction of early (i.e., <7) passage PrECs with TERT led to successful immortalization. However, attempts to immortalize late (i.e., >7) passage PrECs were unsuccessful. Late passage PrECs, which acquired elevated p16, were unable to overcome the senescence barrier. Immortalized PrECs (TERT-PrECs) retained a normal male karyotype and low p16 expression. Additionally, TERT-PrECs were non-tumorigenic when inoculated into intact male immunodeficient NSG mice.

CONCLUSIONS

The present studies document that early passage human PrECs have sufficiently low p16 to permit immortalization by TERT expression alone. TERT-PrECs developed using this transduction approach provides an appropriate and experimentally facile model for clarifying the molecular mechanism(s) involved in both immortalization of human PrECs, as well as identifying genetic/epigenetic "drivers" for conversion of these immortalized non-tumorigenic cells into fully lethal prostate cancers. Notably, loxP sites flank the exogenous TERT gene in the TERT-PrECs. Cre recombinase can be used to excise TERT, and resolve whether TERT expression is required for these cells to be fully transformed into lethal cancer. Prostate 77: 374-384, 2017. © 2016 Wiley Periodicals, Inc.

Autophagy regulates UBC9 levels during viral-mediated tumorigenesis

UBC9, the sole E2-conjugating enzyme required for SUMOylation, is a key regulator of essential cellular functions and, as such, is frequently altered in cancers. Along these lines, we recently reported that its expression gradually increases during early stages of human papillomavirus (HPV)-mediated cervical lesions transformation. However, a better understanding of how UBC9 is exploited by transforming viral oncoproteins is still needed. In the present study, we show that in human samples HPV drives UBC9 up-regulation also in very early steps of head and neck tumorigenesis, pointing to the important role for UBC9 in the HPV-mediated carcinogenic program. Moreover, using HPV-infected pre-cancerous tissues and primary human keratinocytes as the natural host of the virus, we investigate the pathological meaning and the cellular mechanisms responsible for UBC9 de-regulation in an oncoviral context. Our results show that UBC9 overexpression is promoted by transforming viral proteins to increase host cells' resistance to apoptosis. In addition, ultrastuctural, pharmacological and genetic approaches crucially unveil that UBC9 is physiologically targeted by autophagy in human cells. However, the presence of HPV E6/E7 oncoproteins negatively impacts the autophagic process through selective inhibition of autophagosome-lysosome fusion, finally leading to p53 dependent UBC9 accumulation during viral-induced cellular transformation. Therefore, our study elucidates how UBC9 is manipulated by HPV oncoproteins, details the physiological mechanism by which UBC9 is degraded in cells, and identifies how HPV E6/E7 impact on autophagy. These findings point to UBC9 and autophagy as novel hallmarks of HPV oncogenesis, and open innovative avenues towards the treatment of HPV-related malignancies.

What roles do colon stem cells and gap junctions play in the left and right location of origin of colorectal cancers?

This "Commentary" examines an important clinical observation that right-sided colorectal cancers appear less treatable than the left-sided cancers. The concepts of (a) the "initiation/promotion/progression" process, (b) the stem cell hypothesis, (c) the role gap junctional intercellular communication, (d) cancer cells lacking GJIC either because of the non-expression of connexin genes or of non-functional gap junction proteins, and (e) the role of the microbiome in promoting initiated colon stem cells to divide symmetrically or asymmetrically are examined to find an explanation. It has been speculated that "embryonic-like" lesions in the ascending colon are initiated stem cells, promoted via symmetrical cell division, while the polyp-type lesions in the descending colon are initiated stem cells stimulated to divide asymmetrically. To test this hypothesis, experiments could be designed to examine if right-sided lesions might express Oct4A and ABCG2 genes but not any connexin genes, whereas the left-sided lesions might express a connexin gene, but not Oct4A or the ABCG2 genes. Treatment of the right sided lesions might include transcriptional regulators, whereas the left-sided lesions would need to restore the posttranslational status of the connexin proteins.

HOP expression is regulated by p53 and RAS and characteristic of a cancer gene signature

The Hsp70/Hsp90 organising protein (HOP) is a co-chaperone essential for client protein transfer from Hsp70 to Hsp90 within the Hsp90 chaperone machine. Although HOP is upregulated in various cancers, there is limited information from in vitro studies on how HOP expression is regulated in cancer. The main objective of this study was to identify the HOP promoter and investigate its activity in cancerous cells. Bioinformatic analysis of the -2500 to +16 bp region of the HOP gene identified a large CpG island and a range of putative cis-elements. Many of the cis-elements were potentially bound by transcription factors which are activated by oncogenic pathways. Luciferase reporter assays demonstrated that the upstream region of the HOP gene contains an active promoter in vitro. Truncation of this region suggested that the core HOP promoter region was -855 to +16 bp. HOP promoter activity was highest in Hs578T, HEK293T and SV40- transformed MEF1 cell lines which expressed mutant or inactive p53. In a mutant p53 background, expression of wild-type p53 led to a reduction in promoter activity, while inhibition of wild-type p53 in HeLa cells increased HOP promoter activity. Additionally, in Hs578T and HEK293T cell lines containing inactive p53, expression of HRAS increased HOP promoter activity. However, HRAS activation of the HOP promoter was inhibited by p53 overexpression. These findings suggest for the first time that HOP expression in cancer may be regulated by both RAS activation and p53 inhibition. Taken together, these data suggest that HOP may be part of the cancer gene signature induced by a combination of mutant p53 and mutated RAS that is associated with cellular transformation.

Single-chromosome Gains Commonly Function as Tumor Suppressors

Aneuploidy is a hallmark of cancer, although its effects on tumorigenesis are unclear. Here, we investigated the relationship between aneuploidy and cancer development using cells engineered to harbor single extra chromosomes. We found that nearly all trisomic cell lines grew poorly in vitro and as xenografts, relative to genetically matched euploid cells. Moreover, the activation of several oncogenic pathways failed to alleviate the fitness defect induced by aneuploidy. However, following prolonged growth, trisomic cells acquired additional chromosomal alterations that were largely absent from their euploid counterparts and that correlated with improved fitness. Thus, while single-chromosome gains can suppress transformation, the genome-destabilizing effects of aneuploidy confer an evolutionary flexibility that may contribute to the aggressive growth of advanced malignancies with complex karyotypes.

Affinity Purification of the RNA Degradation Complex, the Exosome, from HEK-293 Cells

The RNA exosome complex plays a central role in RNA processing and regulated turnover. Present both in cytoplasm and nucleus, the exosome functions through associations with ribonucleases and various adapter proteins (reviewed in [Kilchert et al., 2016]). The following protocol describes an approach to purify RNA exosome complexes from HEK-293 cells, making use of inducible ectopic expression, affinity capture, and rate-zonal centrifugation. The obtained RNA exosomes have been used successfully for proteomic, structural, and enzymatic studies (Domanski et al., 2016).

Immortalized Mouse Achilles Tenocytes Demonstrate Long-Term Proliferative Capacity While Retaining Tenogenic Properties

Investigating the cellular processes underlying tendon healing can allow researchers to improve long-term outcomes after injury. However, conducting meaningful studies to uncover the injury healing mechanism at cellular and molecular levels remains challenging. This is due to the inherent difficulty in isolating, culturing, and expanding sufficient primary tenocytes, due to their limited proliferative capacity and short lifespan. In this study, we sought to establish a novel line of immortalized mouse Achilles tenocytes (iMATs) with primary tenocyte properties, but increased proliferative capacity suitable for extensive in vitro experimentation. We show that isolated primary mouse Achilles tenocytes (pMATs) can be effectively immortalized using a piggyBac transposon expressing SV40 large T antigen flanked by FLP recombination target site (FRT). The resulting iMATs exhibit markedly greater proliferation and survival, which can be reversed with FLP recombinase. Furthermore, iMATs express the same set of tendon-specific markers as that of primary cells, although in lower levels, and respond similarly to exogenous stimulation with bone morphogenetic protein 13 (BMP13) as has been previously reported with pMATs. Taken together, our results suggest that iMATs acquire long-term proliferative capacity while maintaining tenogenic properties. We believe that iMATs are a suitable model for studying not only the native cellular processes involved in injury and healing, but also potential therapeutic agents that may augment the stability of tendon repair.

A diverse virome in kidney transplant patients contains multiple viral subtypes with distinct polymorphisms

Recent studies have established that the human urine contains a complex microbiome, including a virome about which little is known. Following immunosuppression in kidney transplant patients, BK polyomavirus (BKV) has been shown to induce nephropathy (BKVN), decreasing graft survival. In this study we investigated the urine virome profile of BKV+ and BKV- kidney transplant recipients. Virus-like particles were stained to confirm the presence of VLP in the urine samples. Metagenomic DNA was purified, and the virome profile was analyzed using metagenomic shotgun sequencing. While the BK virus was predominant in the BKV+ group, it was also found in the BKV- group patients. Additional viruses were also detected in all patients, notably including JC virus (JCV) and Torque teno virus (TTV) and interestingly, we detected multiple subtypes of the BKV, JCV and TTV. Analysis of the BKV subtypes showed that nucleotide polymorphisms were detected in the VP1, VP2 and Large T Antigen proteins, suggesting potential functional effects for enhanced pathogenicity. Our results demonstrate a complex urinary virome in kidney transplant patients with multiple viruses with several distinct subtypes warranting further analysis of virus subtypes in immunosuppressed hosts.

Generation and Characterization of Eptesicus fuscus (Big brown bat) kidney cell lines immortalized using the Myotis polyomavirus large T-antigen

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Eptesicus fuscus kidney cells immortalized using Myotis polyomavirus T-antigen.

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E. fuscus interferon competent kidney cell line supports the growth of vesicular stomatitis virus, porcine epidemic diarrhea virus, herpes simplex virus and Middle-East respiratory syndrome coronavirus.

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All cell lines exhibit a marker for fibroblasts (vimentin), some also exhibit an epithelial marker (cytokeratin).

It is speculated that bats are important reservoir hosts for numerous viruses, with 27 viral families reportedly detected in bats. Majority of these viruses have not been isolated and there is little information regarding their biology in bats. Establishing a well-characterized bat cell line supporting the replication of bat-borne viruses would facilitate the analysis of virus-host interactions in an in vitro model. Currently, few bat cell lines have been developed and only Tb1-Lu, derived from Tadarida brasiliensis is commercially available. Here we describe a method to establish and immortalize big brown bat (Eptesicus fuscus) kidney (Efk3) cells using the Myotis polyomavirus T-antigen. Subclones of this cell line expressed both epithelial and fibroblast markers to varying extents. Cell clones expressed interferon beta in response to poly(I:C) stimulation and supported the replication of four different viruses, namely, vesicular stomatitis virus (VSV), porcine epidemic diarrhea coronavirus (PED-CoV), Middle-East respiratory syndrome coronavirus (MERS-CoV) and herpes simplex virus (HSV). To our knowledge, this is the first bat cell line from a northern latitude insectivorous bat developed using a novel technology. The cell line has the potential to be used for isolation of bat viruses and for studying virus-bat interactions in culture.

SV40 T-Antigen Amino Acid Changes that Disrupt Cul-7 or Bub-1 Binding Do Not Globally Distort the T-Common Region

BACKGROUND

Amino acids 1-107 of the SV40 T antigen constitute a functionally important and complex region. Cellular proteins, Hsc70, Bub-1, Cul-7, and Rb, each of which is involved in cell growth control or genomic stability, bind within this portion of the T antigen. Mutational analysis has mapped the J domain/Hsc70, Bub-1, and the Rb binding motifs. Two regions of the T antigen have been implicated in Cul-7 binding. Mutation of F98A diminished Cul-7 binding, and deletion of amino acids 68-83 abolished it. The authors suggest, based on T-antigen structure, that F98 is inaccessible and that the F98A change altered the configuration of the upstream region, preventing Cul-7 binding. Our objective was to determine, by using monoclonal T-antigen antibodies, whether F98 is accessible and whether F98A substitution globally distorted the T-common region.

METHODS

Cell-expressing T antigens, immunoprecipitation, and immunoblot were used to determine the accessibility of amino acids.

CONCLUSION

Full-length T-antigen and N-terminal fragments containing F98A were immunoprecipitated by monoclonal antibody PAb902, which recognizes a conformation-dependent epitope within the first 82 amino acids. Therefore, this alteration does not globally distort the entire T-common region. Additionally, PAb416, which displaces Cul-7 from the T antigen and immunoprecipitates bound pRb peptides, depends on F98 for binding, implying that amino acid 98 is part of the epitope and accessible in the native T antigen.

Preclinical models for interrogating drug action in human cancers using Stable Isotope Resolved Metabolomics (SIRM)

AIMS

In this review we compare the advantages and disadvantages of different model biological systems for determining the metabolic functions of cells in complex environments, how they may change in different disease states, and respond to therapeutic interventions.

BACKGROUND

All preclinical drug-testing models have advantages and drawbacks. We compare and contrast established cell, organoid and animal models with ex vivo organ or tissue culture and in vivo human experiments in the context of metabolic readout of drug efficacy. As metabolism reports directly on the biochemical state of cells and tissues, it can be very sensitive to drugs and/or other environmental changes. This is especially so when metabolic activities are probed by stable isotope tracing methods, which can also provide detailed mechanistic information on drug action. We have developed and been applying Stable Isotope-Resolved Metabolomics (SIRM) to examine metabolic reprogramming of human lung cancer cells in monoculture, in mouse xenograft/explant models, and in lung cancer patients in situ (Lane et al. 2011; T. W. Fan et al. 2011; T. W-M. Fan et al. 2012; T. W. Fan et al. 2012; Xie et al. 2014b; Ren et al. 2014a; Sellers et al. 2015b). We are able to determine the influence of the tumor microenvironment using these models. We have now extended the range of models to fresh human tissue slices, similar to those originally described by O. Warburg (Warburg 1923), which retain the native tissue architecture and heterogeneity with a paired benign versus cancer design under defined cell culture conditions. This platform offers an unprecedented human tissue model for preclinical studies on metabolic reprogramming of human cancer cells in their tissue context, and response to drug treatment (Xie et al. 2014a). As the microenvironment of the target human tissue is retained and individual patient's response to drugs is obtained, this platform promises to transcend current limitations of drug selection for clinical trials or treatments.

CONCLUSIONS AND FUTURE WORK

Development of ex vivo human tissue and animal models with humanized organs including bone marrow and liver show considerable promise for analyzing drug responses that are more relevant to humans. Similarly using stable isotope tracer methods with these improved models in advanced stages of the drug development pipeline, in conjunction with tissue biopsy is expected significantly to reduce the high failure rate of experimental drugs in Phase II and III clinical trials.

The DNA Structure-Specific Endonuclease MUS81 Mediates DNA Sensor STING-Dependent Host Rejection of Prostate Cancer Cells

Self-DNA is present in the cytosol of many cancer cells and can promote effective immune rejection of tumor cells, but the mechanisms leading to the presence of cytosolic DNA are unknown. Here, we report that the cleavage of genomic DNA by DNA structure-specific endonuclease MUS81 and PARP-dependent DNA repair pathways leads to the accumulation of cytosolic DNA in prostate cancer cells. The number of nuclear MUS81 foci and the amount of cytosolic dsDNA increased in tandem from hyperplasia to clinical stage II prostate cancers and decreased at stage III. Cytosolic DNA generated by MUS81 stimulated DNA sensor STING-dependent type I interferon (IFN) expression and promoted phagocytic and T cell responses, resulting in type I and II IFN-mediated rejection of prostate tumor cells via mechanisms that partly depended on macrophages. Our results demonstrate that the tumor suppressor MUS81 alerts the immune system to the presence of transformed host cells.

FGFR3b Extracellular Loop Mutation Lacks Tumorigenicity In Vivo but Collaborates with p53/pRB Deficiency to Induce High-grade Papillary Urothelial Carcinoma

Missense mutations of fibroblast growth factor receptor 3 (FGFR3) occur in up to 80% of low-grade papillary urothelial carcinoma of the bladder (LGP-UCB) suggesting that these mutations are tumor drivers, although direct experimental evidence is lacking. Here we show that forced expression of FGFR3b-S249C, the most prevalent FGFR3 mutation in human LGP-UCB, in cultured urothelial cells resulted in slightly reduced surface translocation than wild-type FGFR3b, but nearly twice as much proliferation. When we expressed a mouse equivalent of this mutant (FGFR3b-S243C) in urothelia of adult transgenic mice in a tissue-specific and inducible manner, we observed significant activation of AKT and MAPK pathways. This was, however, not accompanied by urothelial proliferation or tumorigenesis over 12 months, due to compensatory tumor barriers in p16-pRB and p19-p53-p21 axes. Indeed, expressing FGFR3b-S249C in cultured human urothelial cells expressing SV40T, which functionally inactivates pRB/p53, markedly accelerated proliferation and cell-cycle progression. Furthermore, expressing FGFR3b-S243C in transgenic mouse urothelium expressing SV40T converted carcinoma-in-situ to high-grade papillary urothelial carcinoma. Together, our study provides new experimental evidence indicating that the FGFR3 mutations have very limited urothelial tumorigenicity and that these mutations must collaborate with other genetic events to drive urothelial tumorigenesis.

High-throughput Functional Genomics Identifies Regulators of Primary Human Beta Cell Proliferation

The expansion of cells for regenerative therapy will require the genetic dissection of complex regulatory mechanisms governing the proliferation of non-transformed human cells. Here, we report the development of a high-throughput RNAi screening strategy specifically for use in primary cells and demonstrate that silencing the cell cycle-dependent kinase inhibitors CDKN2C/p18 or CDKN1A/p21 facilitates cell cycle entry of quiescent adult human pancreatic beta cells. This work identifies p18 and p21 as novel targets for promoting proliferation of human beta cells and demonstrates the promise of functional genetic screens for dissecting therapeutically relevant state changes in primary human cells.

Rad54 and Mus81 cooperation promotes DNA damage repair and restrains chromosome missegregation

Rad54 and Mus81 mammalian proteins physically interact and are important for the homologous recombination DNA repair pathway; however, their functional interactions in vivo are poorly defined. Here, we show that combinatorial loss of Rad54 and Mus81 results in hypersensitivity to DNA-damaging agents, defects on both the homologous recombination and non-homologous DNA end joining repair pathways and reduced fertility. We also observed that while Mus81 deficiency diminished the cleavage of common fragile sites, very strikingly, Rad54 loss impaired this cleavage to even a greater extent. The inefficient repair of DNA double-strand breaks (DSBs) in Rad54(-/-)Mus81(-/-) cells was accompanied by elevated levels of chromosome missegregation and cell death. Perhaps as a consequence, tumor incidence in Rad54(-/-)Mus81(-/-) mice remained comparable to that in Mus81(-/-) mice. Our study highlights the importance of the cooperation between Rad54 and Mus81 for mediating DNA DSB repair and restraining chromosome missegregation.

Development of a clonal equine myoblast cell line capable of terminal differentiation into mature myotubes in vitro

OBJECTIVE

To produce a clonal equine myoblast cell line that retains the ability to divide for multiple passages and differentiate into multinucleated myotubes during specific conditions.

SAMPLE

Cultured primary equine skeletal muscle-derived cells from a healthy Thoroughbred.

PROCEDURES

Cell cultures were transfected by electroporation with a plasmid (pNIT) that expresses the temperature-sensitive simian vacuolating virus 40 large T antigen (TAg), which can be controlled by a doxycycline-responsive promoter. Cells that stably integrated the TAg were selected and expanded to passage 25. For each passage, differentiation and fusion properties of the cells were determined and immunocytochemical analyses were performed to evaluate expression of TAg and other muscle-specific proteins. Optimum conditions that led to cell differentiation into myotubes were also determined.

RESULTS

Compared with nontransfected control cells, myogenic, desmin-positive cells expressed the TAg when incubated at 33°C and could be maintained in culture for numerous passages. Reduced expression of TAg was identified in cells incubated at 37°C or when incubated with doxycycline at 33°C. Expression of TAg was not detected when cells were incubated with doxycycline at 37°C, and when serum was withdrawn from the culture medium, those clones differentiated into a pure population of multinucleated myotubes.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that production of an immortalized clonal equine skeletal muscle cell line was possible. A clonal equine skeletal muscle cell line will be a valuable in vitro tool for use in equine physiology and disease research.

Chronic DNA Replication Stress Reduces Replicative Lifespan of Cells by TRP53-Dependent, microRNA-Assisted MCM2-7 Downregulation

Circumstances that compromise efficient DNA replication, such as disruptions to replication fork progression, cause a state known as DNA replication stress (RS). Whereas normally proliferating cells experience low levels of RS, excessive RS from intrinsic or extrinsic sources can trigger cell cycle arrest and senescence. Here, we report that a key driver of RS-induced senescence is active downregulation of the Minichromosome Maintenance 2–7 (MCM2-7) factors that are essential for replication origin licensing and which constitute the replicative helicase core. Proliferating cells produce high levels of MCM2-7 that enable formation of dormant origins that can be activated in response to acute, experimentally-induced RS. However, little is known about how physiological RS levels impact MCM2-7 regulation. We found that chronic exposure of primary mouse embryonic fibroblasts (MEFs) to either genetically-encoded or environmentally-induced RS triggered gradual MCM2-7 repression, followed by inhibition of replication and senescence that could be accelerated by MCM hemizygosity. The MCM2-7 reduction in response to RS is TRP53-dependent, and involves a group of Trp53-dependent miRNAs, including the miR-34 family, that repress MCM expression in replication-stressed cells before they undergo terminal cell cycle arrest. miR-34 ablation partially rescued MCM2-7 downregulation and genomic instability in mice with endogenous RS. Together, these data demonstrate that active MCM2-7 repression is a physiologically important mechanism for RS-induced cell cycle arrest and genome maintenance on an organismal level.

Duplication of the genome by DNA replication is essential for cell proliferation. DNA replication is initiated from many sites (“origins”) along chromosomes that are bound by replication licensing proteins, including MCM2-7. They are also core components of the replication helicase complex that unwinds double stranded DNA to expose single stranded DNA that is the template for DNA polymerase. Eukaryotic DNA replication machinery faces many challenges to duplicate the complex and massive genome. Circumstances that inhibit progression of the replication machinery cause “replication stress” (RS). Cells can counteract RS by utilizing “dormant” or “backup” origins. Abundant MCM2-7 expression sufficiently licenses dormant origins, but reducing MCMs compromises cellular responses to RS. We show that MCM2-7 expression is downregulated in cells experiencing chronic RS, and this depends on the TRP53 tumor suppressor and microRNAs it regulates. Extended RS eventually reduces MCMs to a point that terminal cell cycle arrest occurs. We propose that this mechanism is a crucial protection against neoplasia.

Effects of pyrrolidine dithiocarbamate on proliferation and nuclear factor-κB activity in autosomal dominant polycystic kidney disease cells

BACKGROUND

Pyrrolidine dithiocarbamate (PDTC) reduces renal cyst growth in a rodent model of polycystic kidney disease (PKD) but the mechanism of action is not clear. Here, we investigated the hypothesis that PDTC reduces the proliferation of cystic epithelial cells in vitro in a nuclear factor (NF)-κB-dependent manner.

METHODS

Immortalized autosomal dominant PKD (ADPKD) cells that are heterozygous (WT9-7) and homozygous (WT-9-12) for a truncating Pkd1 mutation, and immortalized normal human tubular cells (HK-2), were exposed to NF-κB-inducing agents with or without PDTC. Cell proliferation and apoptosis were assessed by bromodeoxyuridine assay and Annexin V flow cytometry, respectively. NF-κB activity was assessed by luciferase reporter assay and western blotting for nuclear p65, p50, and RelB subunits and cytoplasmic phosphorylated-IκBα.

RESULTS

Serum-induced proliferation was similar in all cell lines over 72 h. PDTC demonstrated anti-proliferative effects that were delayed in ADPKD cells compared to HK-2. Basal NF-κB-dependent luciferase reporter activity was lower in ADPKD cells compared to normal cells. Classical NF-κB stimulants, lipopolysaccharide (LPS) and tumor necrosis factor (TNF)-α, increased NF-κB luciferase activity in HK-2, whereas in PKD cell lines, NF-κB activity was only induced by TNF-α. However, neither stimulant altered proliferation in any cell line. PDTC reduced TNF-α-stimulated NF-κB activity in HK-2 only.

CONCLUSIONS

PDTC reduced proliferation in ADPKD cells but did not consistently alter NF-κB activation, suggesting that other signalling pathways are likely to be involved in its ability to attenuate renal cyst growth in vivo.

Activation loop phosphorylation regulates B-Raf in vivo and transformation by B-Raf mutants

Despite being mutated in cancer and RASopathies, the role of the activation segment (AS) has not been addressed for B-Raf signaling in vivo. Here, we generated a conditional knock-in mouse allowing the expression of the B-Raf(AVKA) mutant in which the AS phosphoacceptor sites T599 and S602 are replaced by alanine residues. Surprisingly, despite producing a kinase-impaired protein, the Braf(AVKA) allele does not phenocopy the lethality of Braf-knockout or paradoxically acting knock-in alleles. However, Braf(AVKA) mice display abnormalities in the hematopoietic system, a distinct facial morphology, reduced ERK pathway activity in the brain, and an abnormal gait. This phenotype suggests that maximum B-Raf activity is required for the proper development, function, and maintenance of certain cell populations. By establishing conditional murine embryonic fibroblast cultures, we further show that MEK/ERK phosphorylation and the immediate early gene response toward growth factors are impaired in the presence of B-Raf(AVKA). Importantly, alanine substitution of T599/S602 impairs the transformation potential of oncogenic non-V600E B-Raf mutants and a fusion protein, suggesting that blocking their phosphorylation could represent an alternative strategy to ATP-competitive inhibitors.

The oncogenic potential of BK-polyomavirus is linked to viral integration into the human genome

It has been suggested that BK-polyomavirus is linked to oncogenesis via high expression levels of large T-antigen in some urothelial neoplasms arising following kidney transplantation. However, a causal association between BK-polyomavirus, large T-antigen expression and oncogenesis has never been demonstrated in humans. Here we describe an investigation using high-throughput sequencing of tumour DNA obtained from an urothelial carcinoma arising in a renal allograft. We show that a novel BK-polyomavirus strain, named CH-1, is integrated into exon 26 of the myosin-binding protein C1 gene (MYBPC1) on chromosome 12 in tumour cells but not in normal renal cells. Integration of the BK-polyomavirus results in a number of discrete alterations in viral gene expression, including: (a) disruption of VP1 protein expression and robust expression of large T-antigen; (b) preclusion of viral replication; and (c) deletions in the non-coding control region (NCCR), with presumed alterations in promoter feedback loops. Viral integration disrupts one MYBPC1 gene copy and likely alters its expression. Circular episomal BK-polyomavirus gene sequences are not found, and the renal allograft shows no productive polyomavirus infection or polyomavirus nephropathy. These findings support the hypothesis that integration of polyomaviruses is essential to tumourigenesis. It is likely that dysregulation of large T-antigen, with persistent over-expression in non-lytic cells, promotes cell growth, genetic instability and neoplastic transformation.

Identification of Two Novel Members of the Tentative Genus Wukipolyomavirus in Wild Rodents

Two novel polyomaviruses (PyVs) were identified in kidney and chest-cavity fluid samples of wild bank voles (Myodes glareolus) and common voles (Microtus arvalis) collected in Germany. All cloned and sequenced genomes had the typical PyV genome organization, including putative open reading frames for early regulatory proteins large T antigen and small T antigen on one strand and for structural late proteins (VP1, VP2 and VP3) on the other strand. Virus-like particles (VLPs) were generated by yeast expression of the VP1 protein of both PyVs. VLP-based ELISA and large T-antigen sequence-targeted polymerase-chain reaction investigations demonstrated signs of infection of these novel PyVs in about 42% of bank voles and 18% of common voles. In most cases only viral DNA, but not VP1-specific antibodies were detected. In additional animals exclusively VP1-specific antibodies, but no viral DNA was detected, indicative for virus clearance. Phylogenetic and clustering analysis including all known PyV genomes placed novel bank vole and common vole PyVs amongst members of the tentative Wukipolymavirus genus. The other known four rodent PyVs, Murine PyV and Hamster PyV, and Murine pneumotropic virus and Mastomys PyV belong to different phylogenetic clades, tentatively named Orthopolyomavirus I and Orthopolyomavirus II, respectively. In conclusion, the finding of novel vole-borne PyVs may suggest an evolutionary origin of ancient wukipolyomaviruses in rodents and may offer the possibility to develop a vole-based animal model for human wukipolyomaviruses.

Defective heat shock factor 1 inhibits the growth of fibrosarcoma derived from simian virus 40/T antigen‑transformed MEF cells

Heat shock factor 1 (Hsf1) serves an important role in regulating the proliferation of human tumor cell lines in vitro and tissue specific tumorigenesis in certain mouse models. However, its role in viral‑oncogenesis remains to be fully elucidated. In the current study, the role of Hsf1 in fibroblastoma derived from simian virus 40/T antigen (SV40/TAG)‑transformed mouse embryonic fibroblast (MEF) cell lines was investigated. Knockout of Hsf1 inhibited MEF cell proliferation in vitro and fibroblastoma growth and metastasis to the lungs in vivo in nude mice. Knockout of Hsf1 increased the protein expression levels of p53 and phosphorylated retinoblastoma protein (pRb), however reduced the expression of heat shock protein 25 (Hsp25) in addition to the expression of the angiogenesis markers vascular endothelial growth factor, cluster of differentiation 34 and factor VIII related antigen. Furthermore, immunoprecipitation indicated that knockout of Hsf1 inhibited the association between SV40/TAG and p53 or pRb. These data suggest that Hsf1 is involved in the regulation of SV40/TAG‑derived fibroblastoma growth and metastasis by modulating the association between SV40/TAG and tumor suppressor p53 and pRb. The current study provides further evidence that Hsf1 may be a novel therapeutic target in the treatment of cancer.

Regulation mechanism of Fbxw7-related signaling pathways (Review)

F-box and WD repeat domain-containing 7 (Fbxw7), the substrate-recognition component of SCFFbxw7 complex, is thought to be a tumor suppressor involved in cell growth, proliferation, differentiation and survival. Although an increasing number of ubiquitin substrates of Fbxw7 have been identified, the best characterized substrates are cyclin E and c-Myc. Fbxw7/cyclin E and Fbxw7/c-Myc pathways are tightly regulated by multiple regulators. Fbxw7 has been identified as a tumor suppressor in hepatocellular carcinoma. This review focused on the regulation of Fbxw7/cyclin E and Fbxw7/c-Myc pathways and discussed findings to gain a better understanding of the role of Fbxw7 in hepatocellular carcinoma.

A porcine model system of BRCA1 driven breast cancer

BRCA1 is a breast and ovarian tumor suppressor. Hereditary mutations in BRCA1 result in a predisposition to breast cancer, and BRCA1 expression is down-regulated in ~30% of sporadic cases. The function of BRCA1 remains poorly understood, but it appears to play an important role in DNA repair and the maintenance of genetic stability. Mouse models of BRCA1 deficiency have been developed in an attempt to understand the role of the gene in vivo. However, the subtle nature of BRCA1 function and the well-known discrepancies between human and murine breast cancer biology and genetics may limit the utility of mouse systems in defining the function of BRCA1 in cancer and validating the development of novel therapeutics for breast cancer. In contrast to mice, pig biological systems, and cancer genetics appear to more closely resemble their human counterparts. To determine if BRCA1 inactivation in pig cells promotes their transformation and may serve as a model for the human disease, we developed an immortalized porcine breast cell line and stably inactivated BRCA1 using miRNA. The cell line developed characteristics of breast cancer stem cells and exhibited a transformed phenotype. These results validate the concept of using pigs as a model to study BRCA1 defects in breast cancer and establish the first porcine breast tumor cell line.

Conditional immortalization of primary adipocyte precursor cells

The production of new adipocytes requires the differentiation of adipocyte precursor (AP) cells residing within the adipose tissue stromal-vascular compartment. The objective was to obtain an immortalized primary adipogenic cell line derived from FACS isolated committed APs using the conditional expression of SV40 T antigen. Adipocyte precursors were isolated from white adipose tissue (WAT) using FACS to remove non-adipogenic cell populations from mice expressing a conditionally regulated SV40 T antigen. APs were maintained by continuous culture and induced to undergo adipogenic differentiation. Adipogenesis, determined by Oil Red O staining, was assessed with each passage and compared to wildtype controls. Adipogenic capability was rapidly lost with increased passage number in committed APs with concurrent reduction in cell proliferation and expression of essential late adipogenic genes, including Pparγ and C/ebpα. Thus, FACS purified committed APs have limited capability to undergo expansion and subsequent adipogenic differentiation in vitro even if they are immortalized with the SV40 T antigen.

Mouse models of prostate cancer: picking the best model for the question

When the National Institutes of Health Mouse Models of Human Cancer Consortium initiated the Prostate Steering Committee 15 years ago, there were no genetically engineered mouse (GEM) models of prostate cancer (PCa). Today, a PubMed search for "prostate cancer mouse model" yields 3,200 publications and this list continues to grow. The first generation of GEM utilized the newly discovered and characterized probasin promoter driving viral oncogenes such as Simian virus 40 large T antigen to yield the LADY and TRAMP models. As the PCa research field has matured, the second generation of models has incorporated the single and multiple molecular changes observed in human disease, such as loss of PTEN and overexpression of Myc. Application of these models has revealed that mice are particularly resistant to developing invasive PCa, and once they achieve invasive disease, the PCa rarely resembles human disease. Nevertheless, these models and their application have provided vital information on human PCa progression. The aim of this review is to provide a brief primer on mouse and human prostate histology and pathology, provide descriptions of mouse models, as well as attempt to answer the age old question: Which GEM model of PCa is the best for my research question?

Cellular transformation of mouse embryo fibroblasts in the absence of activator E2Fs

The E2F family of transcription factors, broadly divided into activator and repressor E2Fs, regulates cell cycle genes. Current models indicate that activator E2Fs are necessary for cell cycle progression and tumorigenesis and are also required to mediate transformation induced by DNA tumor viruses. E2Fs are negatively regulated by the retinoblastoma (RB) family of tumor suppressor proteins, and virus-encoded oncogenes disrupt the RB-E2F repressor complexes. This results in the release of activator E2Fs and induction of E2F-dependent genes. In agreement, expression of large tumor T antigens (TAg) encoded by polyomaviruses in mammalian cells results in increased transcriptional levels of E2F target genes. In addition, tumorigenesis induced by transgenic expression of simian virus 40 (SV40) TAg in choroid plexus or intestinal villi requires at least one activator E2F. In contrast, we show that SV40 TAg-induced transformation in mouse embryonic fibroblasts is independent of activator E2Fs. This work, coupled with recent studies showing that proliferation in stem and progenitor cells is independent of activator E2Fs, suggests the presence of parallel pathways governing cell proliferation and tumorigenesis.

IMPORTANCE

The RB-E2F pathway is altered in many cancers and is also targeted by DNA tumor viruses. Viral oncoprotein action on RBs results in the release of activator E2Fs and upregulation of E2F target genes; thus, activator E2Fs are considered essential for normal and tumorigenic cell proliferation. However, we have observed that SV40 large T antigen can induce cell proliferation and transformation in the absence of activator E2Fs. Our results also suggest that TAg action on pRBs regulates both E2F-dependent and -independent pathways that govern proliferation. Thus, specific cell proliferation pathways affected by RB alterations in cancer may be a factor in tumor behavior and response to therapy.

Simian virus Large T antigen interacts with the N-terminal domain of the 70 kD subunit of Replication Protein A in the same mode as multiple DNA damage response factors

Simian virus 40 (SV40) serves as an important model organism for studying eukaryotic DNA replication. Its helicase, Large T-antigen (Tag), is a multi-functional protein that interacts with multiple host proteins, including the ubiquitous ssDNA binding protein Replication Protein A (RPA). Tag recruits RPA, actively loads it onto the unwound DNA, and together they promote priming of the template. Although interactions of Tag with RPA have been mapped, no interaction between Tag and the N-terminal protein interaction domain of the RPA 70kDa subunit (RPA70N) has been reported. Here we provide evidence of direct physical interaction of Tag with RPA70N and map the binding sites using a series of pull-down and mutational experiments. In addition, a monoclonal anti-Tag antibody, the epitope of which overlaps with the binding site, blocks the binding of Tag to RPA70N. We use NMR chemical shift perturbation analysis to show that Tag uses the same basic cleft in RPA70N as multiple of DNA damage response proteins. Mutations in the binding sites of both RPA70N and Tag demonstrate that specific charge reversal substitutions in either binding partner strongly diminish the interaction. These results expand the known repertoire of contacts between Tag and RPA, which mediate the many critical roles of Tag in viral replication.

KATs in cancer: functions and therapies

Post-translational acetylation of lysines is most extensively studied in histones, but this modification is also found in many other proteins and is implicated in a wide range of biological processes in both the cell nucleus and the cytoplasm. Like phosphorylation, acetylation patterns and levels are often altered in cancer, therefore small molecule inhibition of enzymes that regulate acetylation and deacetylation offers much potential for inhibiting cancer cell growth, as does disruption of interactions between acetylated residues and ‘reader’ proteins. For more than a decade now, histone deacetylase (HDAC) inhibitors have been investigated for their ability to increase acetylation and promote expression of tumor suppressor genes. However, emerging evidence suggests that acetylation can also promote cancer, in part by enhancing the functions of oncogenic transcription factors. In this review we focus on how acetylation of both histone and non-histone proteins may drive cancer, and we will discuss the implications of such changes on how patients are assigned to therapeutic agents. Finally, we will explore what the future holds in the design of small molecule inhibitors for modulation of levels or functions of acetylation states.

Models of neuroendocrine prostate cancer

Prostate cancer remains the second leading cause of cancer death in men in the USA and most western countries. Prostatic acinar adenocarcinoma is the most commonly diagnosed form of prostate cancer. Small-cell neuroendocrine carcinoma is less frequently identified at the time of initial diagnosis, but this highly aggressive form of prostate cancer is increasingly observed in patients who have failed first- and second-line hormone therapy. Thus, developing and exploring models of neuroendocrine prostate cancer (NePC) are of increasing importance. This review examines the relevant xenograft tumor and genetically engineered mouse models of NePC, with the aim of addressing salient features and clinical relevance.

Mechanisms of Barrett's oesophagus: intestinal differentiation, stem cells, and tissue models

Barrett's oesophagus (BE) is defined as any metaplastic columnar epithelium in the distal oesophagus which replaces normal squamous epithelium and which predisposes to cancer development. It is this second requirement, the predisposition to cancer, which makes this condition both clinically highly relevant and an important area for ongoing research. While BE has been defined pathologically since the 1950's (Allison and Johnstone, Thorax 1955), and identified as a risk factor for esophageal adenocarcinoma since the 1970's (Naef A.P., et al J Thorac Cardiovasc Surg. 1975), our understanding of the molecular events giving rise to this condition remains limited. Herein we will examine what is known about the intestinal features of BE and how well it recapitulates the intestinal epithelium, including stem identity and function. Finally, we will explore laboratory models of this condition presently in use and under development, to identify new insights they may provide into this important clinical condition.

Delineating the regulation of energy homeostasis using hypothalamic cell models

Attesting to its intimate peripheral connections, hypothalamic neurons integrate nutritional and hormonal cues to effectively manage energy homeostasis according to the overall status of the system. Extensive progress in the identification of essential transcriptional and post-translational mechanisms regulating the controlled expression and actions of hypothalamic neuropeptides has been identified through the use of animal and cell models. This review will introduce the basic techniques of hypothalamic investigation both in vivo and in vitro and will briefly highlight the key advantages and challenges of their use. Further emphasis will be place on the use of immortalized models of hypothalamic neurons for in vitro study of feeding regulation, with a particular focus on cell lines proving themselves most fruitful in deciphering fundamental basics of NPY/AgRP, Proglucagon, and POMC neuropeptide function.

Mechanism of subunit coordination of an AAA+ hexameric molecular nanomachine

Simian virus 40 large tumor antigen (LT) is both a potent oncogenic protein and an efficient hexameric nanomachine that harnesses the energy from ATP binding/hydrolysis to melt origin DNA and unwind replication forks. However, how the six subunits of the helicase motor coordinate during ATP hydrolysis and DNA unwinding/translocation is unresolved. Here we investigated the subunit coordination mechanisms "binomial distribution mutant doping" experiments in the presence of various DNA substrates. For ATP hydrolysis, we observed multiple coordination modes, ranging from random and semi-random, and semi-coordinated modes, depending on which type of DNA is present. For DNA unwinding, however, the results indicated a fully-coordinated mode for the natural origin-containing duplex DNA, but a semi-coordinated mode for a pre-existing fork-DNA, providing direct evidence for LT to use potentially different mechanisms to unwind the two types of substrates. The results of this study provide insights into DNA translocation and unwinding mechanisms for LT hexameric biomotor. From the clinical editor: The study describes the subunit coordination of simian virus 40 large tumor antigen (LT) showing that multiple mechanisms exist that handle the specific needs of different stages of DNA replication.

Novel expression vectors enabling induction of gene expression by small-interfering RNAs and microRNAs

Small-interfering RNAs and microRNAs are small ∼21-22 nucleotide long RNAs capable of posttranscriptional suppression of gene expression. The synthetic siRNAs are especially designed to target pre-specified genes and are common molecular biology tools. The miRNAs are endogenous regulators of gene expression found in a wide variety of eukaryotes. miRNAs are currently utilized for diagnostics applications. Therapeutically, various miRNA-antagonizing tools are being explored and miRNAs are also utilized for cell-specific inhibition of the expression of gene therapy vectors harboring target sites for specific miRNAs. Here we show, for the first time, that siRNAs and miRNAs can be harnessed to induce gene expression. We designed special expression vectors in which target sites for artificial siRNAs or endogenous miRNAs are located between the transgene and an Upstream Inhibitory Region (UIR). We hypothesized that cleavage of the mRNA by siRNAs or miRNAs will separate the transgene from the UIR and the resulting uncapped mRNA will be capable of being translated. A UIR composed of seven open reading frames was found to be the most efficient inhibitor of the translation of the downstream transgene. We show that under such a configuration both artificial siRNAs and endogenous miRNAs were capable of inducing transgene expression. We show that using the diphtheria toxin A-chain gene, in combination with target sites for highly expressed miRNAs, specific induction of cell-death can be achieved, setting the stage for application to cancer therapy.