Gene expression analysis of pancreatic cystic neoplasm in SV40Tag transgenic mice model

AIM: To study the gene expression changes in pancreatic cystic neoplasm in SV40Tag transgenic mice model and to provide information about the prevention, clinical diagnosis and therapy of pancreatic cancer.

METHODS: Using the pBC-SV40Tag transgenic mice model of pancreatic cystic neoplasm, we studied the gene expression changes by applying high-density microarrays. Validation of part gene expression profiling data was performed using real-time PCR.

RESULTS: By using high-density oligonucleotide microarray, of 14 113 genes, 453 were increased and 760 decreased in pancreatic cystic neoplasm, including oncogenes, cell-cycle-related genes, signal transduction-related genes, skeleton-related genes and metabolism-related genes. Among these, we confirmed the changes in Igf, Shh and Wnt signal pathways with real-time PCR. The results of real-time PCR showed similar expression changes in gene chip.

CONCLUSION: all the altered expression genes are associated with cell cycle, DNA damage and repair, signal pathway, and metabolism. SV40Tag may cooperate with several proteins in promoting tumorigenesis.

The p110alpha isoform of phosphatidylinositol 3-kinase is essential for polyomavirus middle T antigen-mediated transformation

Middle T antigen (MT) of polyomavirus is known to play an important role in virus-mediated cellular transformation. While MT has been extensively examined in spontaneously immortalized rodent fibroblasts, its interactions with cells of other types and species are less well understood. We have undertaken a cross-species and cross-cell-type comparison of MT-induced transformation in cells with genetically defined backgrounds. We tested the transforming abilities of a panel of MT mutants, Y250F, Y315F, and Y322F, that are selectively mutated in the binding sites for the principal effectors of MT--Src homology 2 domain-containing transforming protein, phosphatidylinositol 3-kinase (PI3K), and phospholipase C-gamma, respectively--in fibroblasts and epithelial cells of murine or human origin. We found that the Y315F mutation disabled the ability of MT to induce transformation in all cell types and species tested. While Y315F also failed to activate the PI3K pathway in these cells, genetic evidence has indicated Y315 may make other contributions to transformation. To confirm the role of PI3K, the PIK3CA gene, encoding p110alpha, the prime effector of PI3K signaling downstream from activated growth factor receptors, was genetically ablated. This abolished the transforming activity of MT, demonstrating the essential role for this PI3K isoform in MT-mediated transformation. The Y250F mutant was able to transform the human, but not the murine, cells that were examined. Interestingly, this mutant fully activates the PI3K pathway in human cells but activated PI3K signaling poorly in the murine cells used in the study. This again points to the importance of PI3K activation for transformation and suggests that the mechanism by which MT activates the PI3K pathway differs in different species.

Polyomavirus small T antigen transactivates genes by its ability to provoke the synthesis and the stabilization of MYC

DNA tumor viruses are capable of driving quiescent cells into the cell cycle. In case of polyomaviridae, two viral proteins, the large and the small (ST) T antigens are responsible for this outcome. ST interacts with the protein phosphatase PP2A and with chaperons of the dnaK type and leads to the transactivation of several genes, which play a role in S-phase induction. One of these is the transcription factor myelocytomatosis (MYC), which by itself is an important regulator of growth. Microarray analysis has revealed several ST-induced genes, which are also targets of MYC; hence, ST may induce these genes via MYC. Experiments shown here are in line with this assumption. MYC-regulated genes are induced by ST at later times than MYC and a MYC responsive promoter is stimulated by ST. Regulation of MYC occurs through signal transduction pathways, which are co-ordinated by PP2A suggesting that they may be targets of ST. Here, we show that this is the case as important kinases involved in these pathways appear in the active phosphorylated form in the presence of ST. Inhibition of these kinases interferes with MYC induction and inhibition of MYC activity blocks ST-mediated transactivation.

Parafibromin tumor suppressor enhances cell growth in the cells expressing SV40 large T antigen

Parafibromin (PF) is a 531-amino acid protein encoded by HRPT2, a putative tumor suppressor gene recently implicated in the autosomal-dominant hyperparathyroidism-jaw tumor familial cancer syndrome and sporadic parathyroid carcinoma. To investigate effects of PF's overexpression on cell proliferation, we performed assays in four different cell lines. The transient overexpression of PF inhibited cell growth in HEK293 and NIH3T3 cells, but enhanced cell growth in the SV40 large T antigen-expressing cell lines such as 293FT and COS7 cells. In 293FT cells, PF was found to interact with SV40 large T antigen and its overexpression promoted entry into the S phase, implying that the interaction enhanced progression through the cell cycle. The tumor suppressor protein PF acts as a positive regulator of cell growth similar to an oncoprotein in the presence of SV40 large T antigen.

Serum from postmenopausal women directs differentiation of human clonal osteoprogenitor cells from an osteoblastic toward an adipocytic phenotype

A consistent observation in osteoporosis is bone volume reduction accompanied by increased marrow adipose tissue. No single cause linking the two phenomena has yet been identified. In a human progenitor cell clone (hOP 7) derived from bone marrow, however, we have demonstrated that rabbit serum can direct differentiation away from an osteoblast lineage to one of adipocytes. We now report on whether human serum has a similar effect. Serum was collected from 10 pre- and 10 postmenopausal women and from the 10 postmenopausal women before and following 6-week hormone replacement therapy (HRT). hOP 7 cells were cultured with the various sera, and after 7-14 days adipocytogenesis was determined by oil red O staining and lipoprotein lipase (LPL) and glycerol 3-phosphate dehydrogenase (G3PDH) expression. Incubation with 10% premenopausal serum led to labeling of 10.9% of cells (P < 0.05) with oil red O, whereas application of 10% postmenopausal serum led to a much larger effect, 43.5% labeling (P < 0.001 with respect to premenopausal serum). Oil red O positivity was accompanied by loss of type I collagen expression and increased LPL and G3PDH expression. HRT did not reverse the adipocytogenic effect of postmenopausal serum. In conclusion, serum from postmenopausal women contains factors that steer hOP 7 bone progenitor cells toward an adipocytic phenotype, irrespective of HRT. The study suggests a role for serum factors in the development of fatty marrow in postmenopausal osteoporosis.

Diversity of escape variant mutations in Simian virus 40 large tumor antigen (SV40 Tag) epitopes selected by cytotoxic T lymphocyte (CTL) clones

To better understand the relationship between epitope variation and tumor escape from immune surveillance, SV40 T antigen-transformed B6/K-0 cells were subjected to selection with individual CTL clones specific for the SV40 T antigen H-2D(b)-restricted epitopes I or V. CTL-resistant populations were isolated from a majority of the selection cultures and substituted epitope sequences were identified within most of the resistant populations. Tag sequences deleted of all or portions of the selection-targeted epitope were identified, but in lower numbers compared to epitope sequences bearing single residue substitutions. Relatively few flanking residue substitutions were identified, and only in epitope I-targeted selections. The diversity (numbers and epitope residue locations) of substituted epitope residue positions varied between selections. These findings suggest that the scope of spontaneously occurring mutations that could allow for escape from individual CD8+ T cell clones is large.

Repression of intestinal drug metabolizing enzymes by the SV40 large T antigen

Toxic compounds such as carcinogens are removed from the body by the action of a series of detoxifying enzymes and transporters expressed in the liver and the small intestine. We have found that intestinal epithelial cells expressing the SV40 large T antigen (TAg) contain significantly lower levels of mRNAs, encoding several drug metabolizing/detoxifying enzymes and transporters compared to their non-transgenic littermates. In addition, TAg blocks the induction of these mRNAs by xenobiotics. The repression depends on an intact LXCXE motif in TAg, suggesting that inactivation of the retinoblastoma (Rb) family of tumor suppressors plays a role in the process. These results imply that a functional Rb pathway in the intestine is necessary for the expression of the detoxification system used to clear carcinogens, and suggest that loss of this tumor suppressor might alter susceptibility to chemical injury. In addition, the effect of TAg on the detoxification pathway appears to be tissue-specific, as its ectopic expression in the liver failed to suppress the P450 enzymes. The TAg-mediated suppression of drug metabolizing/detoxifying enzymes may have broad implications in the metabolism and mechanism of action of both carcinogens and prescription drugs.

Ability to acquire drug resistance arises early during the tumorigenesis process

Resistance to chemotherapy is one of the principal causes of cancer mortality and is generally considered a late event in tumor progression. Although cellular models of drug resistance have been useful in identifying the molecules responsible for conferring drug resistance, most of these cellular models are derived from cell lines isolated from patients at a late stage in cancer progression. To ask at which stage in the tumorigenic progression does the cell gain the ability to acquire drug resistance, we generated a series of pre-tumorigenic and tumorigenic cells from human embryonic skin fibroblasts by introducing, sequentially, the catalytic subunit of telomerase, SV40 large T and small T oncoproteins, and an oncogenic form of ras. We show that the ability to acquire multidrug resistance (MDR) can arise before the malignant transformation stage. The minimal set of changes necessary to obtain pre-tumorigenic drug-resistant cells is expression of telomerase and inactivation of p53 and pRb. Thus, the pathways inactivated during tumorigenesis also confer the ability to acquire drug resistance. Microarray and functional studies of drug-resistant pre-tumorigenic cells indicate that the drug efflux pump P-glycoprotein is responsible for the MDR phenotype in this pre-tumorigenic cell model.

The immortalized cell lines with differentiation potentials: their establishment and possible application

Approximately 200 types of the cells are qualified as differentiated cells in the human body. If these different types of cells can be separated from each other (or cloned) and obtained in sufficient quantity, it will be beneficial for studying development, morphogenesis, tissue maintenance, cancer and aging, and for reconstructing functional tissues in vitro for regenerative medicine. We produced the transgenic mouse and rat harboring SV40 T-antigen gene to make the immortalized cell lines in the primary tissue culture and succeeded in establishing many functionally active cell lines from various tissues. Many immortalized cell lines from various tissues are shown to exhibit the unique characteristics of tissue functions and they should be useful as an in vitro model of various tissues for physiological and pharmacological investigations. Future application of these cells to drug screening is discussed.

Growth mechanism of satellite cells in human urethral rhabdosphincter

AIMS

To examine the presence of satellite cells in human urethral rhabdosphincter (RS) and to clarify the growth mechanism of these cells.

METHODS

Human RS was obtained from patients undergoing radical prostatectomy for prostate cancer. Primary cells were selectively cultured by magnetic affinity cell sorting (MACS) using an anti-neural cell adhesion molecule (NCAM) antibody. Selectively cultured cells, transfected with simian virus-40 T antigen to extend their lifespan, were used for the following experiments: (1) determination of the effects of hepatocyte growth factor (HGF), insulin-like growth factor-1 (IGF-1), and basic fibroblast growth factor (b-FGF); (2) clarification of the signal transduction pathways used by these growth factors; and (3) examination of the autocrine actions in these cells.

RESULTS

Selectively cultured cells expressed striated muscle markers and could differentiate into myotubes. HGF and IGF-1 stimulated the growth of these cells in a dose-dependent fashion. Regarding signal transduction, HGF phosphorylated ERK1/2 for 120 min while only transiently modifying Akt. In contrast, IGF-1 phosphorylated Akt but not ERK1/2. Furthermore, these cells produced transcripts and proteins for both HGF and IGF-1, and anti-HGF and anti-IGF-1 antibodies suppressed cell proliferation.

CONCLUSIONS

Satellite cells are present in human RS. The proliferation of these cells is primarily enhanced through both the endogenous and exogenous actions of HGF and IGF-I via ERK1/2 and Akt. These findings may be useful in the development of a novel technique for the regeneration of human RS to treat urinary incontinence.

Anticancer activity of an adenoviral vector expressing short hairpin RNA against BK virus T-ag

The human polyomavirus BK (BKV) is oncogenic in rodents and induces malignant transformation of rodent cells in vitro. Although its role in human tumorigenesis is still debated, BKV represents an excellent model to evaluate molecularly targeted antineoplastic approaches. Here, we have tested whether stable suppression of the T antigen (T-ag) oncogene expression could inhibit the in vitro and in vivo malignant phenotype of BKV-transformed mouse cells. An adenovirus vector system that expresses small hairpin RNAs (shRNAs), which are converted into active small interfering RNAs (siRNA) molecules against the BKV T-ag, was developed. This vector was able to inhibit the expression of BKV T-ag through a highly efficient in vitro and in vivo delivery of the siRNA molecule. In addition, it allowed a stable expression of siRNA for a period of time sufficient to elicit a biological effect. Inhibition of T-ag expression results in reduction of the in vitro growth rate of BKV-transformed cells, which is, at least in part, caused by restoration of p53 activity and induction of apoptosis. In vivo studies proved that adenovirus vectors expressing anti-T-ag siRNA were able to suppress tumorigenicity of BKV-transformed cells. Moreover, adenovirus vector direct treatment of growing tumors resulted in a significant reduction of tumor growth. This study indicates that siRNAs delivery via a viral vector have a potential usefulness as in vivo anticancer tool against viral and cellular oncogenes.

Protein encoded by HSV-1 stimulation-related gene 1 (HSRG1) interacts with and inhibits SV40 large T antigen

Herpes simplex virus (HSV)-1 stimulation-related gene 1 (HSRG1) protein expression is induced in HSV-1 infected cells. We found that HSRG1 interacts with SV40 large T antigen (LT) in yeast two-hybrid assay and bimolecular fluorescence complementation (BiFC) assay. This interaction alters LT's regulation of the SV40 promoter and its ability to influence the cell cycle. Choramphenicol acetyl-transferase (CAT) assays revealed that initiation of gene transcription by LT is changed by HSRG1 expression. HSRG1 inhibits the ability of LT to activate SV40 late gene transcription. Further data indicate that the ability of LT protein to stimulate S-phase entry is also inhibited by the expression of HSRG1. The results of a colony-forming assay suggested that expression of HSRG1 in cells transfected by LT gene decreased the rate of colony formation. Yeast two-hybrid beta-galactosidase assay revealed that amino acid residues 132-450 in LT bind HSRG1.

Establishment and characterization of SV40 large T antigen-immortalized cell lines derived from fetal bovine brain tissues after prolonged cryopreservation

Bovine brain cell lines with specific characteristics are useful in vitro experimental systems for molecular and cellular investigation of the interactions between bovine specific neuropathogenic agents and the host. Here, we established two novel cell lines from cultures of cryopreserved fetal bovine brain tissue by the transfection of SV40 large T antigen. Both cell lines showed cobblestone morphology in DMEM/F12 medium supplemented with 10% fetal bovine serum, epidermal growth factor and basic fibroblast growth factor. They were immunostained with endothelial marker, Von Willebrand Factor. Endothelial properties, such as capillary-like tube formation on matrigel and the incorporation of DiI-AcLDL were confirmed with these cells. Removal of growth factors increased the number of cells expressing alpha-smooth muscle actin, suggesting the potential of these cell lines to differentiate into smooth muscle cells. This study suggests an efficient protocol to immortalize brain endothelial cell lines from fetal bovine brain tissue culture.

Characterization of the functional and growth properties of cell lines established from ileal and rectal carcinoid tumors

Carcinoids of the intestine are the most common gastrointestinal carcinoid tumors. Therapeutic options to treat patients with these tumors are limited. There are very few ileal carcinoid cell lines available for in vitro studies to analyze new drugs that could be effective in treating patients with metastatic tumors. A replication defective recombinant adenovirus with an SV40 early T-antigen insert was used to infect two intestinal carcinoid tumors to create carcinoid cell lines. The cell lines were studied by cell culture, reverse transcription polymerase chain reaction, Western blotting, and immunohistochemistry. Both cell lines expressed SV40 large T antigen and receptors for TGFbeta1, TGFbeta2, EGFR, and somatostatin receptors. Treatment with TGFbeta1 led to growth inhibition and increased apoptosis in the cultured cells. Octreotide inhibited cell growth of both cell lines while stimulating apoptosis. Treatment of the HC45 cells with gefitinib also inhibited cell growth in a concentration-dependent manner. TGFbeta treatment stimulated chromogranin A expression while expression of two other granins, chromogranin B and 7B2, did not change significantly. RNA profiling of cells treated with TGFbeta1 showed increased expression of vitamin D3 receptor. This finding was validated by real-time quantitative polymerase chain reaction, Western blotting, and immunohistochemistry. These results indicate that these carcinoid cell lines can be used to study the proliferative and apoptotic mechanisms involved in intestinal carcinoid tumor growth regulation.

Inhibition of estrogen-independent mammary carcinogenesis by disruption of growth hormone signaling

Clinical trials and laboratory-based studies indicate that the growth hormone/insulin-like growth factor-I axis may affect the development of breast cancer. The purpose of the present investigation was to develop a genetic model of mammary cancer to test the hypothesis that downregulation of GH signaling can substantially retard mammary cancer progression. We crossed the Laron mouse, in which the gene for the GH receptor/binding protein has been disrupted, with the C3(1)/TAg mouse, which develops estrogen receptor alpha negative mammary cancers. All mice used in our experiments were heterozygous for the large T antigen (TAg) and either homozygous wild-type for GHR (Ghr+/+) or null for GHR (Ghr-/-). Compared with the TAg/Ghr+/+ mice, the TAg/Ghr-/- mice showed delayed mammary cancer latency with significantly decreased multiplicity (9.8 +/- 1.4 versus 3.2 +/- 1.2) and volume (776.1 +/- 284.4 versus 50.5 +/- 8.9 mm3). Furthermore, the frequency of mammary hyperplasias was significantly reduced in the TAg/Ghr-/- mice (15.0 +/- 1.7 versus 6.8 +/- 1.7). To establish that these mammary cancers were estrogen-independent, 12-week-old TAg/Ghr+/+ mice, which lack visible hyperplasia, were either ovariectomized (ovx) or sham operated (sham). Compared with the sham group, ovariectomy resulted in no difference in the frequency of mammary hyperplasia, mammary tumor latency, incidence, multiplicity or tumor size. Together, these data demonstrate that the disruption of GH signaling significantly retards TAg-driven mammary carcinogenesis, and suggest that disrupting GH signaling may be an effective strategy to inhibit the progression of estrogen-independent breast cancer.

Homogeneity of mesothelial cells with lymphatic endothelium: expression of lymphatic endothelial markers by mesothelial cells

BACKGROUND

Mesothelial cell monolayers cover the serous cavities and internal organs, and provide a protective low-friction interface between apposed organs and tissues. The mesothelium also regulates inflammation, fluid and cell exchange, and tissue repair in these compartments and possibly tumor metastasis. In the present study, a stable pleural mesothelial cell line (MIM) was isolated and characterized, and the expression of several lymphatic specific markers by these cells examined.

METHODS AND RESULTS

MIM were isolated from mice stably expressing a temperature-sensitive SV40 large T antigen ('Immortomouse', strain: H-2K(b)-tsA58). These cells were compared with lymphatic endothelial cells (LEC) derived from the mesenteric adventitia of the Immortomouse. MIM and LEC expression of lymphatic-specific markers (Flt-4, LYVE-1, and Prox-1) was examined, and the tight junction protein (ZO-1) was studied by immunofluorescence and immunoblotting in these cells.

RESULTS

LYVE-1, Prox-1, and Flt-4 were detected in both MIM and LEC, with Prox-1 and LYVE-1 more strongly expressed on LEC than MIM. Conversely, Flt-4 was more densely expressed on MIM than on LEC. Spatially, ZO-1 was prominent at MIM junctions, but was less well organized in LEC.

CONCLUSION

MIM and LEC share several characteristic markers usually associated with lymphatic endothelium. MIM might be useful for studying the biology and pathology of mesothelial cells in vitro and help in the development of therapies for mesothelial-related diseases, such as mesothelioma and pleural effusion.

A novel SV40 TAg transgenic model of asbestos-induced mesothelioma: malignant transformation is dose dependent

Although it has been clear for >40 years that mesothelioma can be caused by asbestos, not all patients with this disease have a history of asbestos exposure. Other factors, including non-asbestos fibers and ionizing radiation, are known to cause malignant transformation of mesothelial cells. In addition, it is likely that genetics will play some role in susceptibility. Recently, it has been suggested that SV40 viral oncogenes could contribute to the carcinogenicity of asbestos. To better understand the role of SV40, we used the mesothelin promoter to construct MexTAg mice that express SV40 large T antigen (TAg) in the mesothelial compartment. We generated four MexTAg lines that carry high, intermediate, and low copy numbers of the transgene. All of these mice show a relatively low level of spontaneous tumor development. High-copy, 299h mice rapidly developed mesotheliomas when exposed to asbestos, and these tumors were faster growing and more invasive than those developing in wild-type and single-copy (266s) mice. In addition, we found a direct relationship between transgene copy number and survival after exposure to asbestos. A single copy of TAg was sufficient to immortalize mesothelial cells in vitro, but these cells did not show evidence of malignant transformation. In contrast, cell lines developed from mesothelial cells of animals carrying multiple copies of TAg were growth factor independent and could be cloned at limiting dilution in soft agar. These data provide the first in vivo demonstration of co-carcinogenicity between SV40 and asbestos.

Chemotherapy resistance of mouse WAP-SVT/t breast cancer cells is mediated by osteopontin, inhibiting apoptosis downstream of caspase-3

Impairment of the complex regulatory network of cell death and survival is frequently the reason for therapy resistance of breast cancer cells and a major cause of tumor progression. We established two independent cell lines from a fast growing mouse breast tumor (WAP-SVT/t transgenic animal). Cells from one line (ME-A cells) are sensitive to apoptotic stimuli such as growth factor depletion or treatment with antitumor agents (e.g. doxorubicin). Cells from the second line (ME-C cells), which carry a missense mutation at the p53 codon 242, are very insensitive to apoptotic stimuli. Co-cultivation experiments revealed that the ME-C cells mediate cell death resistance to the ME-A cells. Microarray and Western blot analysis showed that osteopontin (OPN) is selectively overexpressed by the ME-C cells. This glycoprotein is the most abundant protein secreted by the ME-C cells and we obtained strong indications that OPN is the main antiapoptotic factor. However, the OPN containing ME-C cell medium does not alter the expression level of pro- or antiapoptotic genes or known inhibitors of apoptosis (IAPs). Its signaling involves mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase (MEK)1/2 as the kinase inhibitor PD98059 restores apoptosis but not the Akt inhibitor. In the ME-A cells, mitochondrial cytochrome c release occurs with and without external apoptotic stimuli. OPN containing ME-C cell medium does not prevent the mitochondrial cytochrome c release and caspase-9 processing. In serum starved ME-A cells, the OPN containing ME-C cell medium prevents caspase-3 activation. However, in doxorubicin-treated cells, although apoptosis is blocked, it does not inhibit caspase-3. This indicates that the ME-A cells distinguish between the initial apoptotic stimuli and that the cells possess a further uncharacterized control element acting downstream from caspase-3.

Polyoma and SV40 proteins differentially regulate PP2A to activate distinct cellular signaling pathways involved in growth control

Binding of Src family kinases to membrane-associated polyoma virus middle T-antigen (PyMT) can result in the phosphorylation of PyMT tyrosine 250, which serves as a docking site for the binding of Shc and subsequent activation of the Raf-MEK-ERK (MAP) kinase cascade. In a screen for PyMT variants that could not activate the ARF tumor suppressor, we isolated a cytoplasmic nontransforming mutant (MTA) that encoded a C-terminal truncated form of the PyMT protein. Surprisingly, MTA was able to strongly activate the MAP kinase pathway in the absence of Src family kinase and Shc binding. Interestingly, the polyoma small T-antigen (PyST), which shares with MTA both partial amino acid sequence homology and cellular location, also activates the MAP kinase cascade. Activation of the MAP kinase cascade by both MTA and PyST has been demonstrated to be PP2A-dependent. Neither MTA nor PyST activate the phosphorylation of AKT. The SV40 small T-antigen, which is similar to PyST in containing a J domain and in binding to the PP2A AC dimer, does not activate the MAP kinase cascade, but does stimulate phosphorylation of AKT in a PP2A-dependent manner. These findings highlight a novel role of PP2A in stimulating the MAP kinase cascade and indicate that the similar polyoma and SV40 small T-antigens influence PP2A to activate discrete cellular signaling pathways involved in growth control.

Characterization of the nuclear import pathways of galectin-3

Galectin-3 (Gal-3), a pleiotropic beta-galactoside-binding protein, was shown to be involved in several nuclear-dependent functions, including up-regulation of transcriptional factors, RNA processing, and cell cycle regulation. Gal-3 compartmentalization in the nucleus versus the cytoplasm affects, in part, the malignant phenotype of various cancers. However, to date, the mechanism by which Gal-3 translocates into the nucleus remains debatable. Thus, we have constructed and expressed a variety of fusion proteins containing deletion mutants of Gal-3 fused with monomers, dimers, and trimers of enhanced green fluorescent protein and searched for the Gal-3 sequence motifs essential for its nuclear localization in vivo. In addition, a digitonin-permeabilized, cell-free transport in vitro assay was used to directly examine the mechanism of Gal-3 nuclear import. Partial deletions of the COOH-terminal region (114-250) of the human Gal-3 significantly decreases its nuclear translocation, whereas a peptide (1-115) was transported to the nuclei. The in vitro nuclear import assay revealed that there are at least two independent nuclear pathways for shuttling Gal-3 into the nucleus: a passive diffusion and an active transport. This is the first article providing direct evidence for the nuclear import mechanisms of Gal-3 and suggests that Gal-3 nuclear translocation is governed by dual pathways, whereas the cytoplasmic/nuclear distribution may be regulated by multiple processes, including cytoplasmic anchorage, nuclear retention, and or nuclear export. These results may lead to the development of a therapeutic modality aiming at abrogating Gal-3 translocation into the nucleus and thus hampering its activity during cancer progression and metastasis.

Crystal structure of SV40 large T-antigen bound to p53: interplay between a viral oncoprotein and a cellular tumor suppressor

The transformation potential of Simian Virus 40 depends on the activities of large T-antigen (LTag), which interacts with several cellular tumor suppressors including the important "guardian" of the genome, p53. Inhibition of p53 function by LTag is necessary for both efficient viral replication and cellular transformation. We determined the crystal structure of LTag in complex with p53. The structure reveals an unexpected hexameric complex of LTag binding six p53 monomers. Structure-guided mutagenesis of LTag and p53 residues supported the p53-LTag interface defined by the complex structure. The structure also shows that LTag binding induces dramatic conformational changes at the DNA-binding area of p53, which is achieved partially through an unusual "methionine switch" within p53. In the complex structure, LTag occupies the whole p53 DNA-binding surface and likely interferes with formation of a functional p53 tetramer. In addition, we showed that p53 inhibited LTag helicase function through direct complex formation.

Aquaporin expression and cell volume regulation in the SV40 immortalized rat submandibular acinar cell line

The amount of aquaporins present and the cellular ability to perform regulatory volume changes are likely to be important for fluid secretions from exocrine glands. In this work these phenomena were studied in an SV40 immortalized rat submandibular acinar cell line. The regulatory cell volume characteristics have not previously been determined in these cells. Cell volume regulation following hyposmotic exposure and aquaporin induction was examined with Coulter counter methodology, radioactive efflux studies, fura-2 fluorescence, and polymerase chain reaction and Western blot techniques. Cell volume regulation was inhibited by the K(+) channel antagonists quinine and BaCl(2) and the Cl(-) channel blocker 5-nitro-2-(3-phenypropylamino)benzoic acid. A concomitant increase in cellular (3)H-taurine release and Ca(2+) concentration was also observed. Chelation of both intra- and extracellular Ca(2+) with EGTA and the Ca(2+) ionophore A23187 did not, however, affect cell volume regulation. Aquaporin 5 (AQP5) mRNA and protein levels were upregulated in hyperosmotic conditions and downregulated upon return to isosmotic solutions, but were reduced by the mitogen-activated ERK-activating kinase (MEK) inhibitor U0126. A 24-h MEK inhibition also diminished hyposmotically induced cell swelling and cell volume regulation. In conclusion, it was determined that regulatory volume changes in this immortalized cell line are due to KCl and taurine efflux. In conditions that increased AQP5 levels, the cells showed a faster cell swelling and a more complete volume recovery following hyposmotic exposure. This response could be overturned by MEK inhibition.

Mechanism of plasmid delivery by hydrodynamic tail vein injection. I. Hepatocyte uptake of various molecules

BACKGROUND

The hydrodynamic tail vein (HTV) injection of naked plasmid DNA is a simple yet effective in vivo gene delivery method into hepatocytes. It is increasingly being used as a research tool to elucidate mechanisms of gene expression and the role of genes and their cognate proteins in the pathogenesis of disease in animal models. A greater understanding of its mechanism will aid these efforts and has relevance to macromolecular and nucleic acid delivery in general.

METHODS

In an attempt to explore how naked DNA enters hepatocytes the fate of a variety of molecules and particles was followed over a 24-h time frame using fluorescence microscopy. The uptake of some of these compounds was correlated with marker gene expression from a co-injected plasmid DNA. In addition, the uptake of the injected compounds was correlated with the histologic appearance of hepatocytes.

RESULTS

Out of the large number of nucleic acids, peptides, proteins, inert polymers and small molecules that we tested, most were efficiently delivered into hepatocytes independently of their size and charge. Even T7 phage and highly charged DNA/protein complexes of 60-100 nm in size were able to enter the cytoplasm. In animals co-injected with an enhanced yellow fluorescent protein (EYFP) expression vector and fluorescently labeled immunoglobulin (IgG), hepatocytes flooded with large amounts of IgG appeared permanently damaged and did not express EYFP-Nuc. Hepatocytes expressing EYFP had only slight IgG uptake. In contrast, when an EYFP expression vector was co-injected with a fluorescently labeled 200-bp linear DNA fragment, both were mostly (in 91% of the observed cells) co-localized to the same hepatocytes 24 h later.

CONCLUSIONS

The appearance of permanently damaged cells with increased uptake of some molecules such as endogenous IgG raised the possibility that a molecule could be present in a hepatocyte but its transport would not be indicative of the transport process that can lead to foreign gene expression. The HTV procedure enables the uptake of a variety of molecules (as previous studies also found), but the uptake process for some of these molecules may be associated with a more disruptive process to the hepatocytes that is not compatible with successful gene delivery.

Oncogenic T-antigen of JC virus is present frequently in human gastric cancers

BACKGROUND

JC virus (JCV) is a polyomavirus that commonly infects humans and is the causative agent of progressive multifocal leukoencephalopathy in immune-compromised patients. An association between JCV and human cancers long has been suspected, because this virus induces brain tumors in several animal models. The oncogenic potential of JCV is mediated by a transforming protein, the T-antigen (T-Ag), which is a multifunctional protein that transforms cells through interactions with various growth-regulatory genes, including p53 and pRb, and by stabilizing beta-catenin. Previously, the laboratory at the authors' institution demonstrated that JCV is present frequently in the human gastrointestinal tract and may play a role in colorectal carcinogenesis. However, to date, no studies have determined whether JCV sequences are present specifically in gastric cancers. The current study was designed to investigate whether JCV sequences and expression are found in human gastric cancers.

METHODS

DNA was extracted from 23 paraffin embedded and 14 frozen gastric cancer specimens. For the detection of JCV gene sequences, polymerase chain reaction amplifications were performed using gene-specific primers for T-Ag, VP-1 (a JCV capsid gene), and the viral regulatory region (or transcriptional control region). Immunohistochemical staining was performed with an anti-T-Ag monoclonal antibody to detect protein expression.

RESULTS

Twenty-one of 37 gastric cancers (57%) harbored JCV T-Ag sequences, and 13 of 37 gastric cancers (30%) contained VP-1 sequences. T-Ag sequences also were found in adjacent nonneoplastic mucosa. In addition, JCV regulatory region sequences were present frequently in gastric cancers and adjacent nonneoplastic mucosa. T-Ag protein expression was found in 9 of 23 gastric cancers (39%), whereas no expression was observed in any of the nonneoplastic tissues.

CONCLUSIONS

To the authors' knowledge, this is the first demonstration of the presence of JCV T-Ag expression in human gastric cancers. These findings suggest a possible role for this polyomavirus in gastric carcinogenesis.

The induction of growth arrest in fibroblasts by SV40 T antigen

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