A distinct first replication cycle of DNA introduced in mammalian cells

Many mutation events in microsatellite DNA sequences were traced to the first embryonic divisions. It was not known what makes the first replication cycles of embryonic DNA different from subsequent replication cycles. Here we demonstrate that an unusual replication mode is involved in the first cycle of replication of DNA introduced in mammalian cells. This alternative replication starts at random positions, and occurs before the chromatin is fully assembled. It is detected in various cell lines and primary cells. The presence of single-stranded regions increases the efficiency of this alternative replication mode. The alternative replication cannot progress through the A/T-rich FRA16B fragile site, while the regular replication mode is not affected by it. A/T-rich microsatellites are associated with the majority of chromosomal breakpoints in cancer. We suggest that the alternative replication mode may be initiated at the regions with immature chromatin structure in embryonic and cancer cells resulting in increased genomic instability. This work demonstrates, for the first time, differences in the replication progression during the first and subsequent replication cycles in mammalian cells.

Shp2 suppresses PyMT-induced transformation in mouse fibroblasts by inhibiting Stat3 activity

We have examined the effect of expression of the protein tyrosine phosphatase Shp2 on transformation by the mouse polyoma virus middle T antigen (PyMT). Gain-of-function mutations in Shp2 indicate that it may serve as an oncogene in several types of human leukemia. Paradoxically, however, some catalytically dominant-negative mutations of Shp2 have also been identified in leukemia and neuroblastomas. In this study, we show that Shp2 suppresses transformation induced by PyMT, the major polyoma viral oncoprotein known to act through binding and activation of pp60(c-src). Over-expression of a catalytically inactive Shp2 mutant in NIH3T3 cells significantly enhanced PyMT-induced transformation. Conversely, re-introduction of Shp2 into Shp2-deficient cells strongly inhibited PyMT-induced transformation and tumorigenesis. Short hairpin RNA (shRNA)-mediated Shp2 knockdown potentiated PyMT-induced transformation. Finally, we present evidence that the transformation-suppressive effects of Shp2 are mediated at least partially through the inhibition of signal transducers and activators of transcription 3.

A specific docking site for DNA polymerase {alpha}-primase on the SV40 helicase is required for viral primosome activity, but helicase activity is dispensable

Replication of simian virus 40 (SV40) DNA, a model for eukaryotic chromosomal replication, can be reconstituted in vitro using the viral helicase (large tumor antigen, or Tag) and purified human proteins. Tag interacts physically with two cellular proteins, replication protein A and DNA polymerase α-primase (pol-prim), constituting the viral primosome. Like the well characterized primosomes of phages T7 and T4, this trio of proteins coordinates parental DNA unwinding with primer synthesis to initiate the leading strand at the viral origin and each Okazaki fragment on the lagging strand template. We recently determined the structure of a previously unrecognized pol-prim domain (p68N) that docks on Tag, identified the p68N surface that contacts Tag, and demonstrated its vital role in primosome function. Here, we identify the p68N-docking site on Tag by using structure-guided mutagenesis of the Tag helicase surface. A charge reverse substitution in Tag disrupted both p68N-binding and primosome activity but did not affect docking with other pol-prim subunits. Unexpectedly, the substitution also disrupted Tag ATPase and helicase activity, suggesting a potential link between p68N docking and ATPase activity. To assess this possibility, we examined the primosome activity of Tag with a single residue substitution in the Walker B motif. Although this substitution abolished ATPase and helicase activity as expected, it did not reduce pol-prim docking on Tag or primosome activity on single-stranded DNA, indicating that Tag ATPase is dispensable for primosome activity in vitro.

Culture, immortalization, and characterization of human meibomian gland epithelial cells

PURPOSE

Meibomian gland epithelial cells are essential in maintaining the health and integrity of the ocular surface. However, very little is known about their physiological regulation. In this study, the cellular control mechanisms were explored, first to establish a defined culture system for the maintenance of primary epithelial cells from human meibomian glands and, second, to immortalize these cells, thereby developing a preclinical model that could be used to identify factors that regulate cell activity.

METHODS

Human meibomian glands were removed from lid segments after surgery, enzymatically digested, and dissociated. Isolated epithelial cells were cultured in media with or without serum and/or 3T3 feeder layers. To attempt immortalization, the cells were exposed to retroviral human telomerase reverse transcriptase (hTERT) and/or SV40 large T antigen cDNA vectors, and antibiotic-resistant cells were selected, expanded, and subcultured. Analyses for possible biomarkers, cell proliferation and differentiation, lipid-related enzyme gene expression, and the cellular response to androgen were performed with biochemical, histologic, and molecular biological techniques.

RESULTS

It was possible to isolate viable human meibomian gland epithelial cells and to culture them in serum-free medium. These cells proliferated, survived through at least the fifth passage, and contained neutral lipids. Infection with hTERT immortalized these cells, which accumulated neutral lipids during differentiation, expressed multiple genes for lipogenic enzymes, responded to androgen, and continued to proliferate.

CONCLUSIONS

The results show that human meibomian gland epithelial cells may be isolated, cultured, and immortalized.

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

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

A computational analysis of ATP binding of SV40 large tumor antigen helicase motor

Simian Virus 40 Large Tumor Antigen (LTag) is an efficient helicase motor that unwinds and translocates DNA. The DNA unwinding and translocation of LTag is powered by ATP binding and hydrolysis at the nucleotide pocket between two adjacent subunits of an LTag hexamer. Based on the set of high-resolution hexameric structures of LTag helicase in different nucleotide binding states, we simulated a conformational transition pathway of the ATP binding process using the targeted molecular dynamics method and calculated the corresponding energy profile using the linear response approximation (LRA) version of the semi-macroscopic Protein Dipoles Langevin Dipoles method (PDLD/S). The simulation results suggest a three-step process for the ATP binding from the initial interaction to the final tight binding at the nucleotide pocket, in which ATP is eventually “locked” by three pairs of charge-charge interactions across the pocket. Such a “cross-locking” ATP binding process is similar to the binding zipper model reported for the F1-ATPase hexameric motor. The simulation also shows a transition mechanism of Mg²⁺ coordination to form the Mg-ATP complex during ATP binding, which is accompanied by the large conformational changes of LTag. This simulation study of the ATP binding process to an LTag and the accompanying conformational changes in the context of a hexamer leads to a refined cooperative iris model that has been proposed previously.

The Large Tumor antigen (LTag) encoded by Simian Virus 40 (SV40) is a marvelous molecule that is not only a viral oncogene, but also an efficient molecular machine as a helicase that unwinds double helix DNA for genome replication, an essential process in all living organisms. LTag hexameric helicase uses the energy of ATP to power its conformational switch for DNA unwinding. Understanding how the LTag conformational switch is coupled to the energy from ATP usage by LTag to do the mechanical work of unwinding DNA is of great interest to biologists, and yet remains to be established. Based on our previous high-resolution structures of LTag helicase in different conformational states, we simulated an LTag conformational transition pathway in the ATP binding process using the targeted molecular dynamics method. Our simulation results suggest a three-step process for the ATP binding to the nucleotide pocket, in which ATP is eventually “locked” into the pocket by three pairs of “locker” interactions. We have also quantitatively evaluated the energy profile of ATP binding using a special computational simulation technique. Additionally, our simulation study of ATP binding by LTag and the accompanying conformational switches in the context of a hexamer leads to a refined cooperative iris model that may be used for DNA unwinding.

Cell cycle-related cyclin b1 quantification

Background

To obtain non-relative measures of cell proteins, purified preparations of the same proteins are used as standards in Western blots. We have previously quantified SV40 large T antigen expressed over a several fold range in different cell lines and correlated the average number of molecules to average fluorescence obtained by cytometry and determined cell cycle phase related expression by calculation from multi-parametric cytometry data. Using a modified approach, we report quantification of endogenous cyclin B1 and generation of the cell cycle time related expression profile.

Methodology

Recombinant cyclin B1 was purified from a baculovirus lysate using an antibody affinity column and concentrated. We created fixed cell preparations from nocodazole-treated (high cyclin B1) and serum starved (low cyclin B1) PC3 cells that were either lyophilized (for preservation) or solubilized. The lysates and purified cyclin B1 were subjected to Western blotting; the cell preparations were subjected to cytometry, and fluorescence was correlated to molecules. Three untreated cell lines (K562, HeLa, and RKO) were prepared for cytometry without lyophilization and also prepared for Western blotting. These were quantified by Western blotting and by cytometry using the standard cell preparations.

Results

The standard cell preparations had 1.5×10⁵ to 2.5×10⁶ molecules of cyclin B1 per cell on average (i.e., 16-fold range). The average coefficient of variation was 24%. Fluorescence varied 12-fold. The relationship between molecules/cell (Western blot) and immunofluorescence (cytometry) was linear (r² = 0.87). Average cyclin B1 levels for the three untreated cell lines determined by Western blotting and cytometry agreed within a factor of 2. The non-linear rise in cyclin B1 in S phase was quantified from correlated plots of cyclin B1 and DNA content. The peak levels achieved in G2 were similar despite differences in lineage, growth conditions, and rates of increase through the cell cycle (range: 1.6–2.2×10⁶ molecules per cell).

Conclusions

Net cyclin B1 expression begins in G1 in human somatic cells lines; increases non-linearly with variation in rates of accumulation, but peaks at similar peak values in different cell lines growing under different conditions. This suggests tight quantitative end point control.

Activation of PyMT in beta cells induces irreversible hyperplasia, but oncogene-dependent acinar cell carcinomas when activated in pancreatic progenitors

It is unclear whether the cellular origin of various forms of pancreatic cancer involves transformation or transdifferentiation of different target cells or whether tumors arise from common precursors, with tumor types determined by the specific genetic alterations. Previous studies suggested that pancreatic ductal carcinomas might be induced by polyoma middle T antigen (PyMT) expressed in non-ductal cells. To ask whether PyMT transforms and transdifferentiates endocrine cells toward exocrine tumor phenotypes, we generated transgenic mice that carry tetracycline-inducible PyMT and a linked luciferase reporter. Induction of PyMT in β cells causes β-cell hyperplastic lesions that do not progress to malignant neoplasms. When PyMT is de-induced, β cell proliferation and growth cease; however, regression does not occur, suggesting that continued production of PyMT is not required to maintain the viable expanded β cell population. In contrast, induction of PyMT in early pancreatic progenitor cells under the control of Pdx1 produces acinar cell carcinomas and β-cell hyperplasia. The survival of acinar tumor cells is dependent on continued expression of PyMT. Our findings indicate that PyMT can induce exocrine tumors from pancreatic progenitor cells, but cells in the β cell lineage are not transdifferentiated toward exocrine cell types by PyMT; instead, they undergo oncogene-dependent hyperplastic growth, but do not require PyMT for survival.

Lessons in signaling and tumorigenesis from polyomavirus middle T antigen

The small DNA tumor viruses have provided a very long-lived source of insights into many aspects of the life cycle of eukaryotic cells. In recent years, the emphasis has been on cancer-related signaling. Here we review murine polyomavirus middle T antigen, its mechanisms, and its downstream pathways of transformation. We concentrate on the MMTV-PyMT transgenic mouse, one of the most studied models of breast cancer, which permits the examination of in situ tumor progression from hyperplasia to metastasis.

Modulation of nucleocytoplasmic trafficking by retention in cytoplasm or nucleus

Nuclear protein transport processes have largely been studied using in vitro semi-intact cell systems where high concentrations of nuclear localizing substrates are used, and cytoplasmic components such as the microtubule (MT) network, are either absent or damaged. Here we use the fluorescence recovery after photobleaching (FRAP) technique to analyze the nucleocytoplasmic flux of distinct fluorescently tagged proteins over time in living cultured cells. FRAP was performed in different parts of the cell to analyze the kinetics of nucleocytoplasmic trafficking and intranuclear/cytoplasmic mobility of the tumor suppressor Rb protein and a SV40 large tumor antigen (T-ag) derivative containing the nuclear localization sequence (NLS), both fused to green fluorescent protein (GFP). The results indicate that proteins carrying the T-ag NLS are highly mobile in the nucleus and cytoplasm. Rb, in contrast, is largely immobile in both cellular compartments, with similar nuclear import and export kinetics. Rb nuclear export was CRM-1-mediated, with its reduced mobility in the cytoplasm in part due to association with MTs. Overall our results show that nuclear and cytoplasm retention modulates the rates of nuclear protein import and export in intact cells.

BK Polyomavirus in Renal Transplants: Role of Electron Microscopy and Immunostaining in Detecting Early Infection

Reactivation of BK polyomavirus (BKV) is increasingly recognized as a cause of failure of renal allografts. Since no specific treatment is available for this infection, early diagnosis is important, as it allows for early intervention and possible recovery of renal function. Forty-four consecutive renal transplant biopsies performed over a 2-year period were included in the study. In addition to evaluation of renal biopsy tissue sections using routine histochemical stains, CD3, CD20, BK virus immunostains using the specific BK virus and the SV40 antibodies and electron microscopy studies were performed. None of the transplant cases but one exhibited classical histologic viral changes. Viral particles were seen by EM in 19%, and BK-virus positivity was identified in only 43% of these cases. CD20-rich inflammatory infiltrates predominated in cases in which either positive BK stain and/or viral particles were identified ultrastructurally. A combined approach using electron microscopic and immunohistochemical evaluation can be utilized effectively to identify BK virus-associated nephropathy at an early phase facilitating early clinical intervention.

The simultaneous induction of tumorigenesis and Cre-loxP recombination in mice

To investigate the role of Rac1 for tumorigenesis, we generated inducible transgenic (Tg) mice that simultaneously express polyomavirus middle T antigen (mT) and Cre recombinase under the control of mouse mammary tumor virus long terminal repeat (MMTV-LTR) promoter (MMTV-LTR-tTA/mT-TRE-cre Tg). MMTV-LTR-tTA/mT- TRE-cre Tg mice formed tumors in the subcutaneous tissue and developed lung metastasis. We examined tumor latency and types in rac1 deficient (rac1(flox/-)) and control (rac1(+/+), rac1(+/-) or rac1(flox/+)) MMTV-LTR-tTA/mT-TRE-cre Tg mice and found that formation of cutaneous appendage tumor was suppressed although tumor latency in these mice was not affected by loss of Rac1. These results suggested that Rac1 may play a pivotal role in induction and growth of the mT-mediated epithelial tumors. MMTV-LTR-tTA/mT-TRE-cre Tg mice would provide a versatile animal model to investigate genetic interaction in the tumorigenesis.

An anti-apoptotic peptide improves survival in lethal total body irradiation

Cell penetrating peptides (CPPs) have been used to deliver the anti-apoptotic Bcl-xL-derived BH4 peptide to prevent injury-induced apoptosis both in vitro and in vivo. Here we demonstrate that the nuclear localization sequence (NLS) from the SV40 large T antigen has favorable properties for BH4 domain delivery to lymphocytes compared to sequences based on the HIV-1 TAT sequence. While both TAT-BH4 and NLS-BH4 protected primary human mononuclear cells from radiation-induced apoptotic cell death, TAT-BH4 caused persistent membrane damage and even cell death at the highest concentrations tested (5-10 microM) and correlated with in vivo toxicity as intravenous administration of TAT-BH4 caused rapid death. The NLS-BH4 peptide has significantly attenuated toxicity compared to TAT-BH4 and we established a dosing regimen of NLS-BH4 that conferred a significant survival advantage in a post-exposure treatment model of LD90 total body irradiation.

Establishment of vascular endothelial cell lines from the aortas of wild Japanese serows (Capricornis crispus)

Endothelial cell lines were established from the aortas of wild Japanese serows (Capricornis crispus) by transfection of a simian virus 40 (SV40) large T antigen gene. The cloned cell lines, designed SeET (Japanese serow endothelial-SV40T) cells, express SV40T antigen and retain cobblestone-like morphology. Although von Willbrand Factor (vWF) is expressed in the cells, the expression rate and the quantity are lower than in serow primary endothelial cells. The SeET cells exhibit positive uptake of acetylated low density lipoprotein and dose-dependent cell proliferation upon exposure to vascular endothelial growth factor. These results suggest that these SeET cells have preserved endothelial phenotypes and able to function with decreased expression of vWF. The SeET cell line will be a valuable tool for in vitro studies on the physiological properties of endothelial cells and for the propagation of viruses and parasites of Japanese serows.

Abnormal differentiation, hyperplasia and embryonic/perinatal lethality in BK5-T/t transgenic mice

The cell-of-origin has a great impact on the types of tumors that develop and the stem/progenitor cells have long been considered main targets of malignant transformation. The SV40 (SV40-Simian Virus 40) large T and small t antigens (T/t), have been targeted to multiple-differentiated cellular compartments in transgenic mice. In most of these studies, transgenic animals develop tumors without apparent defects in animal development. In this study, we used the bovine keratin 5 (BK5) promoter to target the T/t antigens to stem/progenitor cell-containing cytokeratin 5 (CK5) cellular compartment. A transgene construct, BK5-T/t, was made and microinjected into the male pronucleus of FVB/N mouse oocytes. After implanting approximately 1700 embryos, only 7 transgenics were obtained, including 4 embryos (E9.5, E13, E15, and E20) and 3 postnatal animals, which died at P1, P2, and P18, respectively. Immunohistological analysis revealed aberrant differentiation and prominent hyperplasia in several transgenic CK5 tissues, especially the upper digestive organs (tongue, oral mucosa, esophagus, and forestomach) and epidermis, the latter of which also showed focal dysplasia. Altogether, these results indicate that constitutive expression of the T/t antigens in CK5 cellular compartment results in abnormal epithelial differentiation and leads to embryonic/perinatal animal lethality.

Fas-mediated T cell deletion potentiates tumor antigen-specific tolerance in a mouse model of prostate cancer

A pivotal obstacle to cancer immunotherapy is peripheral T cell tolerance to tumor-associated antigens (TAAs). Tolerance induction among mature T cells in the periphery operates through a variety of mechanisms, including anergy and apoptosis. Although Fas-FasL-mediated apoptosis is a well-defined tolerance inducing mechanism, direct evidence of its interference with TAA-specific immunity in vivo is still lacking. In this report, we used the TRAMP mouse, which expresses SV40 large T antigen (Tag) preferentially in the prostate and develops prostate tumors, as a model system to address the role of Fas-mediated apoptosis in regulating peripheral T cell tolerance. Using RT-PCR and tetramer staining to quantify TAA-specific TCR-expressing cytolytic T lymphocytes (CTLs), we have shown the presence of TAA-specific CTLs at higher levels in TRAMP mice than in syngeneic C57Bl/6 mice. Tag-specific immunization led to the expansion of Tag-specific CTLs in C57Bl/6 mice, and to their elimination in TRAMP mice. Interestingly, in TRAMP mice with deficient Fas (Hybrid TRAMP-lpr/lpr), Tag-specific CTL elimination in response to Tag immunization did not take place. The results of cytolytic-function assays were consistent with induction and elimination patterns of TAA-specific CTLs and those of RT-PCR and tetramer staining. In conclusion, our data show that Fas-mediated TAA-specific CTL apoptosis contributes to T cell tolerance and suggest that such tolerance could be potentiated following TAA-specific immunization.

Signal transduction in transgenic mouse models of human breast cancer--implications for human breast cancer

The advent of genetically engineered mouse models (GEMs) of human breast cancer, have provided important insight into molecular basis or human breast cancer. This review will focus on two of the most extensively studied mouse models for human breast cancer involving mammary gland specific expression of the polyoma middle T (PyV MT) antigen and of the ErbB2. In addition, this review will discuss past and recent advances in understanding relative contribution of the signaling pathways in tumor induction and metastasis by these potent mammary oncogenes.

Establishment and functional characterization of a tracheal epithelial cell line RTEC11 from transgenic rats harboring temperature-sensitive simian virus 40 large T-antigen

A tracheal epithelial cell line RTEC11 was established from transgenic rats harboring temperature-sensitive simian virus 40 large T-antigen. The cells grew continuously at a permissive temperature of 33 degrees C but not at a non-permissive temperature of 39 degrees C. Morphological and functional investigations demonstrated that the cells were polarized epithelial cells maintaining a regulated permeability barrier function. Interestingly, the expression levels of Muc1 (mucin 1) and Scgb1a1 (uteroglobin), non-ciliated secretory cell markers, and Tubb4 (tubulin beta 4), a ciliated cell marker, were significantly increased under the cell growth-restricted condition. Global gene expression and computational network analyses demonstrated a significant genetic network associated with cellular development and differentiation in cells cultured at the non-permissive temperature. The tracheal epithelial cell line RTEC11 with unique characteristics should be useful as an in vitro model for studies of the physiological functions and gene expression of tracheal epithelial cells.

Adenovirus small e1a alters global patterns of histone modification

Adenovirus small early region 1a (e1a) protein drives cells into S phase by binding RB family proteins and the closely related histone acetyl transferases p300 and CBP. The interaction with RB proteins displaces them from DNA-bound E2F transcription factors, reversing their repression of cell cycle genes. However, it has been unclear how the e1a interaction with p300 and CBP promotes passage through the cell cycle. We show that this interaction causes a threefold reduction in total cellular histone H3 lysine 18 acetylation (H3K18ac). CBP and p300 are required for acetylation at this site because their knockdown causes specific hypoacetylation at H3K18. SV40 T antigen also induces H3K18 hypoacetylation. Because global hypoacetylation at this site is observed in prostate carcinomas with poor prognosis, this suggests that processes resulting in global H3K18 hypoacetylation may be linked to oncogenic transformation.

[Expression of SV40Tag, Rb and IRS-1 in glioma detected by tissue microarray and their relation with tumorigenesis and progression of gliomas]

OBJECTIVE

To determine the expression of SV40Tag, Rb and IRS-1 in gliomas and to identify their function in gliomagenesis and progression.

METHODS

Tissue microarrays were constructed containing 118 samples including human glioma and meningioma, experimental glioma, and normal human brain tissue. The expression of SV40Tag, Rb, IRS-1, SV40Tag combined with Rb, and SV40Tag combined with IRS-1 were assayed by immunofluorescence or immunohistochemical techniques. The expression ratio and level were analyzed.

RESULTS

The expressions of SV40Tag, Rb and IRS-1 were detected in gliomas and benign brain tumors. Their positive expression rate in glioma was 65.9%, 64.6% and 48.8%, respectively, with a statistically non-significant difference between the malignant and benign brain tumors. The malignant degree was positively correlated with SV40Tag and IRS-1, but negatively correlated with Rb expression. The combined expression rate of SV40Tag and Rb was 51.2%, and the combined expression rate of SV40Tag and IRS-1 was 40.2%. In the normal human brain tissue only the expression of Rb (77.8%, 7/9) and IRS-1 (22.2%, 2/9) were detected, but expression of SV40Tag could not be observed.

CONCLUSION

Our findings that no expression of SV40Tag was observed in normal human brain tissue indicates that expression of SV40Tag may play an important role in the pathogenesis of glioma. It may be assumed that after SV40 virus invading human body, Rb disfunction and IRS-1 activation promote the malignant transformation of cells, which could be one of important factors in pathogenesis and procession of glioms.

Improved efficiency and pace of generating induced pluripotent stem cells from human adult and fetal fibroblasts

It was reported recently that human fibroblasts can be reprogrammed into a pluripotent state that resembles that of human embryonic stem (hES) cells. This was achieved by ectopic expression of four genes followed by culture on mouse embryonic fibroblast (MEF) feeders under a condition favoring hES cell growth. However, the efficiency of generating human induced pluripotent stem (iPS) cells is low, especially for postnatal human fibroblasts. We started supplementing with an additional gene or bioactive molecules to increase the efficiency of generating iPS cells from human adult as well as fetal fibroblasts. We report here that adding SV40 large T antigen (T) to either set of the four reprogramming genes previously used enhanced the efficiency by 23-70-fold from both human adult and fetal fibroblasts. Discernible hES-like colonies also emerged 1-2 weeks earlier if T was added. With the improved efficiency, we succeeded in replacing MEFs with immortalized human feeder cells that we previously established for optimal hES cell growth. We further characterized individually picked hES-like colonies after expansion (up to 24 passages). The majority of them expressed various undifferentiated hES markers. Some but not all the hES-like clones can be induced to differentiate into the derivatives of the three embryonic germ layers in both teratoma formation and embryoid body (EB) formation assays. These pluripotent clones also differentiated into trophoblasts after EB formation or bone morphogenetic protein 4 induction as classic hES cells. Using this improved approach, we also generated hES-like cells from homozygous fibroblasts containing the sickle cell anemia mutation Hemoglobin Sickle. Disclosure of potential conflicts of interest is found at the end of this article.

Split mCherry as a new red bimolecular fluorescence complementation system for visualizing protein-protein interactions in living cells

Bimolecular fluorescence complementation (BiFC) is a recently developed technique for detection of protein-protein interactions in living cells. In this study, a new red BiFC system was developed by splitting mCherry, a mutant monomeric red fluorescent protein, into two fragments between amino acids 159-160 and was verified using a pair of interacting proteins, SV40 large T antigen (LTag), and human p53 protein. By combined use of the mCherry-based red BiFC system with a Venus-based yellow BiFC system, the interaction between LTag and p53 as well as the interaction between sp100 and promyelocytic leukemia protein (PML), were detected simultaneously in Vero cells. The brilliant redness, short maturation time, and the long excitation and emission wavelengths (587/610 nm) of mCherry make the new BiFC system an excellent candidate for analyzing protein-protein interactions in living cells and for studying multiple protein-protein interactions when coupled with other BiFC systems.

Sheep stromal-epithelial cell interactions and ovarian tumor progression

Previous studies suggest that underlying ovarian stromal cues may regulate the ovarian surface epithelium. However, little is known about the interaction between ovarian stromal cells (OSC) and ovarian surface epithelial cells (OSE) under normal physiologic and pathologic conditions, largely because of the lack of a suitable model. In the current study, the OSC obtained from a sheep were immortalized with SV-40 T/t antigen (designated IOSC) and telomerase reverse transcriptase (designated IOSCH), followed by transfection with the oncogenic allele of the human H-Ras oncogene (designated IOSChR). IOSC cells transfected with H-Ras before immortalization with telomerase were designated IOSCRH. These sheep OSCs were used in both in vitro and in vivo model systems to evaluate mechanisms by which OSCs influence ovarian tumor progression. Normal sheep OSCs were found to inhibit the growth of SKOV3 and OVCAR3 human ovarian cancer cells, but not normal sheep OSE and human OSE cells (hOSE137 cells). In contrast, IOSChR and IOSCRH cells stimulated the growth of normal sheep and human OSE cells, as well as cancer cells. These findings were confirmed by in vivo studies. Our data provide compelling support for the importance of stromal-epithelial cell interactions during tumor progression, and show for the first time that immortalized and transformed OSCs promote growth of ovarian epithelial tumors.

Generation and characterization of islet cell tumor in pTet-on/pTRE-SV40Tag double-transgenic mice model

A line of double-transgenic mice that develop neoplasms arising primarily in the pancreas was established. In these mice, the oncogene SV40 T antigen (Tag) was detected in the pancreas with and without the control of Tet-on system. The transgenic mice that developed pancreatic tumors as early as 20 weeks of age showed hypoglycemia on a blood glucose test. Pathological and immunohistochemical characterizations demonstrated that the tumors belonged to neuroendocrine neoplasms arising from pancreatic islets. A change in IGFs/IGF-1R signaling pathway was detected using real-time PCR analysis. A potential association between the IGFs/IGF-1R system and SV40Tag was studied to further explain the cancerogenesis of the double-transgenic mice by Western blot analysis and immunoprecipitation experiments. The results suggest that a Tag transgenic mice model could be used to study the molecular mechanism of the tumorigenesis of islets.