Epothilone A induces apoptosis in neuroblastoma cells with multiple mechanisms of drug resistance

Epothilone A, a novel macrolide antibiotic, is produced by the myxobacterium Sorangium cellulosum. Similarly to paclitaxel (Taxol), epothilone A inhibits cell proliferation and induces apoptosis by binding to tubulin and stabilizing of microtubuli. Like paclitaxel, epothilone A induced apoptosis in neuroblastoma cells which exhibit constitutive cytoplasmic sequestration of p53 and, hence, an impaired DNA-damage-dependent apoptosis. However, in contrast to paclitaxel, epothilone A was also effective against a constitutively Pgp-expressing, multidrug resistant neuroblastoma cell line (SK-N-SH). Moreover, the efficacy of epothilone A was not impaired even though the Pgp level was further increased during treatment with the drug.

Influenza A virus infection of mice induces nuclear accumulation of the tumorsuppressor protein p53 in the lung

To investigate whether the tumor suppressor p53 protein, an indicator of DNA damage and cell stress, accumulates in the course of influenza-virus-induced murine pneumonia at the site of inflammation, female BALB/c mice were infected each with 5 x 10(4) infectious units of influenza virus A, strain Puerto Rico (PR) 8, by instillation into the nose and the pharynx. Two days later the mice became sick. Three and 6 days after infection the lungs of sacrificed infected and uninfected mice were examined. We assessed the presence and localisation of inflammation, the expression of influenza viral and p53 protein, as well as of the WAF1/Cip1/SDI gene product p21. Further, the appearance of nitrotyrosine, as an indicator of the formation of peroxynitrite, and eventually of apoptotic cells was examined. No significant nuclear p53 accumulation was found in influenza virus-infected murine cells in vitro. The results show, that in the course of influenza A virus-mediated murine pneumonia inflammatory bystander cells may cause activation of the tumor suppressor protein p53, due to oxidative stress and DNA damage, with ensuing p53-dependent upregulation of p21. Apoptosis is then mainly due to these indirect processes, with possible involvement of p53.

Evidence that wild-type p53 in neuroblastoma cells is in a conformation refractory to integration into the transcriptional complex

Neuroblastoma (NB) cells reportedly accumulate wild-type p53 exclusively in the cytoplasm. However, immunofluorescence assays with five different antibodies showed that p53 accumulates in the nucleus of up to 10% of NB cells. PAb1801 detected cytoplasmic 'punctate structures' which were also found in p53-null cells, rendering this antibody unsuitable for p53 detection. A comparison of DO-1 and PAb1801 staining in NB tissue sections confirmed the results obtained with NB cells. Nuclear accumulation of p53 was induced in NB cells using substances which disturb p53's tertiary structure at its zinc finger motif, or by treatment with mitomycin C. Constitutive nuclear accumulation was observed in an SK-N-SH variant, AW-1, which has a point mutation in p53 at Cys176>Ser, disturbing the same motif. Even though p53 showed DNA-binding capability after mitomycin C treatment of NB cells, the target gene products MDM2 and p21(WAF1,CIP1,SDI1) were not synthesized and no p53 transactivating activity measured in a reporter gene assay. Therefore we suggest that p53 in NB cells might be predominantly in a conformation refractory to integration into the transcriptional complex, resulting in at least partial transcriptional inactivity, hyperactive nuclear export and resistance to degradation by exogenously expressed MDM2.

p53 in SV40-transformed DNA-damaged human cells binds to its cognate sequence but fails to transactivate target genes

Human SV40-transformed cells contain high levels of stabilized p53 of which only a fraction is complexed with the SV40 large tumor antigen (T-antigen). This raises the question whether the p53 which is not complexed with T-antigen retains some biological activity. Two human SV40-transformed cell lines, BEAS and SV80, were investigated. A significant level of constitutive cognate-sequence-specific DNA-binding of p53 was detected by electrophoretic mobility shift assay (EMSA) of cell extracts. Upon DNA damage by treatment with mitomycin C the DNA-binding activity was increased, as known for cells with wild-type p53. However, in both cell lines, before and after DNA damage, p53 was not able to transactivate a target gene as shown by reporter gene assay. Hence, the capability of p53 to bind its cognate sequence is a prerequisite but no proof of p53 transactivating activity. Nuclear p53 levels were not further increased after mitomycin C treatment, occasionally rather slightly decreased, often accompanied by an even larger decrease in amount of T-antigen. In conclusion, SV40-transformation of human cells has caused a loss of essential features of wild-type p53 activity, even in that fraction of p53 not in physical complex with SV40 T-antigen.

Cross-reactivity of the monoclonal antibody 9E10 with murine c-MYC

The C-terminal regions of the human and the murine c-MYC consist of a common conserved sequence, the amino acids (a.a.) 418-439 with one terminal exchange (C438G). The pre-C-terminal region of both proteins, a.a. 408-417, exhibit four exchanges. A commercially available monoclonal antibody, 9E10, raised against the C-terminal a. a. 408-439 of human c-MYC, is declared to recognize specifically and exclusively human c-MYC. However, in an immunofluorescence assay we observed, in addition to the reaction with a human cell line (SV80), reactivity with the murine cell line L929. In analogy, a rabbit polyclonal antiserum raised against a peptide which corresponds to the murine pre-C-terminus of c-MYC, a.a. 408-417, showed also cross-reactivity in immunofluorescence. The immunostaining with both anti-bodies in the human and the murine cell line was competed by the peptide, corresponding to the murine pre-C-terminal a.a. 408-417, whereas the staining of both cell lines with an antiserum raised against the conserved N-terminal region of c-MYC was not competed by this peptide. The cross-reactivity of 9E10 with murine c-MYC was confirmed by Western blot using two additional cell lines. In conclusion, our findings indicate that 9E10 which is generally regarded as specific for human c-MYC cross-reacts with denaturated murine c-MYC.

Cell cycle arrest in ovarian cancer cell lines does not depend on p53 status upon treatment with cytostatic drugs

Human ovarian cancer cell lines with different p53 status were investigated for p53-dependency of cell cycle arrest upon treatment with cytostatic drugs. For this purpose commonly used anti-cancer drugs and a novel anti-cancer drug, gemcitabine, were applied. Cell cycle arrest was dependent on the drug dose used, as observed for all anti-cancer drugs applied, but not related to functional p53. With the exception of the etoposide-effected G2/M arrest at high concentrations, which seems to depend on functional p53, since it did not occur in cells with inactive p53. Only in cells with wt p53 and quasi-wild-type, p53 accumulated in the nucleus upon drug treatment with all anti-cancer agents applied. The level of accumulation was drug dose-dependent for each drug tested. The accumulated p53 was biochemically active, as measured in a transient transfection assay upon treatment with gemcitabine, cisplatin, etoposide, and Taxol. Activity was dependent on the drug dose applied and proportional to the level of accumulated p53, except for Taxol-induced p53 accumulation which correlated inversely with p53 biochemical activity. Apoptosis was estimated by in situ end labeling by biotinylated dUTP with the terminal deoxyribonucleotidyl transferase assay. Apoptosis occured after arrest at the various phases of the cell cycle in all cell lines tested, depending on the drug and the drug dose used. Nevertheless, cells with wt p53 exhibited the highest fraction of apoptotic cells.

Protection of mice against SV40 tumours by Pam3Cys, MTP-PE and Pam3Cys conjugated with the SV40 T antigen-derived peptide, K(698)-T(708)

The intraperitoneal injection of Balb/c mice with synthetic analogues of adjuvants S-[2,3-bis(palmitoyloxy)-(2-RS)-propyl]-N-palmitoyl-R-cysteine (Pam3Cys) or muramyltripeptide phosphatidylethanolamine (MTP-PE) inhibited the tumourigenic growth of subcutaneously injected VLM cells, a syngeneic simian virus 40 (SV40)-transformed cell line. Furthermore, the Pam3Cys conjugate of K698-T708 (KT), which represents the C-terminal undecapeptide of the SV40 large tumour (T) antigen, was tumour-protective. Also syngeneic spleen cells, preincubated in vitro with this Pam3Cys-KT derivative, which anchores spontaneously at the cell membrane, were, through SV40 tumour mimicry, tumour-protective. The protection was impaired by treatment of the mice with either anti-CD4, anti-CD8 IgG, anti asialo GM1 antiserum or dextrane sulfate, which deplete the CD4+, CD8+ and NK cells or the macrophages, respectively. In summary, SV40 tumour transplantation resistance can be experimentally elicited by a tumour-epitope-specific vaccine. In the absence of an immunogenic epitope protection was obtained by administration of biological response modifiers. Protection is effected by SV40-T-antigen-specific cytotoxic lymphocytes in cooperation with NK cells and macrophages.

DNA-damage-inducible p53 activity in SV40-transformed cells

The biological state of the tumour suppressor proteins Rb and p53 is altered in papillomavirus- and SV40-transformed cells, due to interaction with the DNA tumour virus oncogene proteins E6/E7 and the tumour (T) antigen. Thus, the DNA damage response function of p53, a crucial feature of the tumour suppressor p53, might be considered as inactive. To investigate this subject, C57SV and VLM, two SV40-transformed murine cell lines enharboring constitutively high nuclear p53 and SV40 large T antigen levels, were treated with mitomycin C. Mitomycin C is known for its activity to elicit DNA damage, followed by nuclear accumulation of biologically active p53. Surprisingly, the nuclear p53 level significantly increased in mitomycin-C-treated C57SV cells and to a lesser degree in VLM cells. In addition, expression of p21WAF1 protein was induced in C57SV and VLM cells. This indicates a possible DNA-damage-elicited p53 activation. Finally, nuclear extracts of mitomycin-C-treated C57SV and VLM cells, but not of untreated cells, exhibited PAb421-enhanced specific DNA-binding activity of p53, as proven by gel shift analysis. Thus, DNA damage induced essential biological functions typical for wild-type p53 in the SV40-transformed cell lines examined so far.

Butyrate modulates DNA-damage-induced p53 response by induction of p53-independent differentiation and apoptosis

Butyrate, a physiologically occurring agent, has been reported to decrease constitutively high expressed p53 levels in transformed cells. To elucidate whether butyrate also inhibits DNA-damage-induced p53 response we investigated the effects of butyrate and the anticancer drug mitomycin C in normal C3H10T1/2 cells harbouring wild-type p53. In comparison with p53-deficient fibroblasts we examined p53 protein level, cell cycle arrest, differentiation, and apoptosis. Butyrate induced G1 phase arrest, differentiation, and p53-independent increase in p21(waf1/cip1) protein. Moreover, butyrate induced p53-independent apoptosis, which was, as well as p53-mediated apoptosis, associated with a dose-dependent increase in Bax and c-Myc protein. Pretreatment with butyrate repressed dose-dependently mitomycin-C-induced p53 accumulation and interfered with p53-dependent cell cycle arrest. Butyrate further partially inhibited p53-mediated apoptosis, but low doses of butyrate were more effective than higher concentrations. This was reflected in an enhanced decrease in c-Myc and Bax protein in response to mitomycin C with low concentrations of butyrate. Our data indicate that the differentiation stimulus of butyrate, in association with p21(waf1/cip1) induction, and apoptosis, may explain antineoplastic effects of butyrate. Co-carcinogenic features of butyrate may result from inhibition of p53-mediated DNA damage response.

DNA damage by filtered, tar- and aerosol-free cigarette smoke in rodent cells: a novel evaluation

Nuclear accumulation of the tumorsuppressor protein p53 indicates the occurrence of chromatin injury (J. Cancer Res. Clin. Oncol. 1991, 117, 30; Oncogene 1993, 8, 307) and may be used as an analytical tool to detect genotoxic agents. This mechanism was used to evaluate the DNA-damaging potency (clastogenicity) of the tar- and aerosol-free, gaseous phase of cigarette smoke which is obtained by filtration through Cambridge glass fiber filters. This condensate-free gas phase was absorbed by phosphate-buffered saline and immediately thereafter poured onto monolayers of the murine cell line L929 for 10 min. Eighteen hours later the nuclear accumulation of p53, an indicator for DNA damage, was determined. The elicited level of p53 was similar to that obtained by direct incubation with the gas phase of filtered cigarette smoke for 2 min or with several micrograms of mitomycin C per ml. Previous exhaustive filtration obviously does not inhibit the clastogenic property of tobacco smoke to exert severe DNA damage.

Flavonoids activate wild-type p53

Flavonoids are diphenyl propanoids widely distributed in edible plants. They play a dual role in mutagenesis and carcinogenesis. Some of them act as anticarcinogens or inhibit the growth of tumour cells, whereas others act as cocarcinogens, are mutagenic or able to induce DNA damage. To further elucidate this dual role, we investigated the influence of apigenin, luteolin and quercetin on the tumour suppressor protein p53, regarding p53 accumulation, cell cycle arrest, apoptosis, and biological activity. We found that incubation of the non-tumour cell line C3H10T1/2CL8 with these flavonoids resulted in induction of p53 accumulation and apoptosis. Apoptosis occurred out of the G2/M phase of the cell cycle. The G2/M arrest seems to be p53-dependent as it did not occur in p53 knockout fibroblasts which further supports the recent finding that p53 is involved in the G2/M checkpoint control. Differences between the flavonoids tested concerned p53 accumulation kinetics as well as the biological activity of accumulated p53 and might be due to different modes of flavonoid action. These data suggest that both aspects of flavonoid effects, i.e. inhibition of tumour growth through cell cycle arrest and induction of apoptosis, are functionally related to p53.

Enhanced p53 activity and accumulation in response to DNA damage upon DNA transfection

In response to DNA damage the wild-type tumor suppressor protein p53 accumulates in the nucleus of rodent and primate cells. To investigate the minimal requirement for this reaction the cellular DNA was restricted by two alternative ways: (i) by calicheamicin gamma 1, an enediyne, which causes direct, sequence-specific DNA damage, as shown by fluorimetric analysis of DNA unwinding and by poly(ADP-ribose) polymerase activation. The dose-dependent DNA damage correlated with the nuclear p53 accumulation. In addition, restriction was generated (ii) by the intracellular introduction of the restriction enzyme PvuII, which generates blunt-ended DNA breaks, applying a mild hypotonic shock (pellet method). Previous transfection of linear or circular, single- or ds, DNA, followed by mitomycin C-treatment, lead to a dramatic increase in nuclear p53 accumulation and p53 activity according to electrophoretic mobility shift analysis. The nature of transfected DNA was irrelevant for enhanced accumulation. The data suggest, that the cellular p53 response to DNA damage is sensitized by uptake of exogenous DNA.

Quantitative cytofluorimetric determination of cell membrane-associated large tumor antigen on SV40-transformed cells

The aim of this study was to quantitate the number of cell membrane-located SV40 large tumor antigen (large T) molecules of SV40-transformed cell lines by cytofluorimetric analysis. Five different SV40-transformed cell lines were labelled by either a biotin- or a fluorescein-conjugated monoclonal antibody, PAb1605, which is specific for the large T carboxyterminus. The conjugated-antibody fluorescence signals of the stained large T molecules of transformed cells were measured via cytofluorimetry. Comparison of the fluorescence signals of calibrated beads bearing a known number of fluorescein molecules to the signals of conjugated PAb1605 antibodies bound on microbeads to a defined number of IgG binding sites made it possible to determine the number of antibody-accessible large T molecules per SV40-transformed cell. The numbers (x10(-4)) found per cell were 1.0 (ELONA, hamster), 3.0 (VLM, mouse), 3.5 (mKSA, mouse), 11 (C57SV, mouse), and 5.5 (SV80, human), respectively. Thus, the technique described allows a precise quantitation of surface-exposed, antibody-accessible viral antigen expression.

Monospecific polyclonal anti-anti-idiotypic antibodies to the carboxyterminal undecapeptide of the SV40 large tumour antigen

The murine monoclonal antibody PAb1605 defines an epitope, peptide Lys(698)-Thr(708) (KT), on the carboxyterminus of the tumour(T)antigen of SV40-transformed cells. In vivo and in vitro experiments had shown that this sequence represents an epitope for both humoral and cellular immune responses. When injected into rabbits PAb1605 induces anti-idiotypic antibodies (Ab-2). Ab-2 beta (internal image type) was purified by adsorption chromatography and characterized by the ability of KT to compete with the binding of ab-2 with ab-1. Murine anti-anti-idiotypic antibodies (ab-3) were obtained by immunization of mice with ab-2 beta. Both ab-1 and ab-3 JgG showed affinities to immunoprecipitated SV40 T antigen by immunoblot analysis and to nuclear SV40 T antigen by the immunofluorescence assay. The binding of ab-3 to SV40 T antigen was completely inhibited by competition with KT. We conclude that the polyclonal ab-3 is of the ab-3 subtype and specific for only one epitope which is represented by KT and defined by ab-1. The results demonstrate that the specificity for a defined peptide epitope of an antibody was conserved even after two consecutive steps of anti-idiotypic-antibody formation in two host species. Since this postulate of network theory could be verified for a sequence of a tumour-associated antigen which represents a B- and T cell epitope, this model is of great interest for further tumour immunological studies.

The cell-binding carboxyterminal undecapeptide of SV40 tumour antigen provides protective cell-dependent immunity

This paper describes the use of the synthetic carboxyterminal undecapeptide of large SV40 tumour antigen, lys698-thr708 (KT) to protect Balb/c mice against growth of subcutaneously transplanted tumorigenic SV40-transformed cells (VLM). The vaccine was prepared by conjugation of KT with 3-(2-pyridyldithio)propionic acid N-hydroxysuccinimide (SPDP). Addition of the SPDP-derivative of KT to syngeneic spleen cells rendered KT covalently linked to free thiol-groups of the cell membranes by the formation of -S-S-CH2-CH2-CO-epsilon-NH-lys698 bonds. Vaccination with KT-conjugated cells was intraperitoneal. Alternatively, KT-conjugated cells were generated in the peritoneum by injection of PDP-KT ((2-pyridyldithio)propionic acid-KT). As a control 60Co-irradiated VLM cells were used. In five experiments all VLM-vaccinated and the majority of the PDP-KT-(or KT-spleen cell)-vaccinated mice were protected against tumour growth. However, mice pretreated with saline, unconjugated spleen cells, free KT, KT conjugated to bovine serum albumin, or KT with incomplete Freund's adjuvant developed tumours. Treatment of PDP-KT-vaccinated mice with anti-CD4 or anti-CD8 immunoglobulin abolished tumour immunity completely. Thus, covalent binding of the carboxyterminal undecapeptide of SV40 tumour antigen to viable, untransformed cells yielded a vaccine which protects Balb/c mice against SV40 tumours.

Nuclear accumulation of p53 in response to treatment with DNA-damaging agents

A number of agents which damage DNA also trigger the nuclear accumulation of the tumor suppressor protein p53. Here we show the correlation with different p53 detection methods. As an example we investigated the effects of the cancer therapy drug mitomycin C on different mammalian cell lines. Our findings demonstrate that either the immunofluorescence techniques (indirect immunofluorescence staining or flow cytometric analysis) or ELISA or immunoblot assays are useful methods in detecting p53 accumulation. Simultaneously we measured DNA damage with the terminal deoxynucleotidyl transferase assay. Compatible data were obtained. Thus p53 accumulation may be used as indicator of DNA injury.

Covalent immunochemical membrane labeling of viable cells with K698-T708, a simian virus 40 tumor antigen-derived peptide

The process of covalent immunochemical linking of viable cell membranes with a Simian Virus 40 (SV40) tumor antigen-derived undecapeptide, K(698)PPTPPPEPET(708) (KT), is described. The principle applied was the reaction of the lysine residue, K 698, of the undecapeptide with the succinimidyl moiety of a heterobifunctional linker molecule, N-succinimidyl-3-(2-pyridyldithio)propionate (SPDP) or sulfosuccinimidyl(4-iodo-acetyl)aminobenzoate (sulfo-SIAB). Thereby, upon release of N-hydroxy-succinimide, the rest of the linker molecule reacts covalently with the epsilon-NH2 group of lysine. Upon release of pyridyl-2-thion or hydrogen iodide, respectively, the second reactive moiety of the linker is then ready to form a covalent bond with SH-groups of cell membrane compounds. As a result, KT is covalently linked onto the cell membrane by an -SS- or an -S-bond, respectively. Binding is prevented by treatment of the candidate cells with iodoacetamide, an SH-reactive compound. This artificial cell membrane epitope can be demonstrated by surface immunofluorescence and by binding to immunomagnetic beads loaded with PAb1605, a KT-specific monoclonal antibody. Quantitation by cytofluorimetry shows some 10(4) KT molecules bound per cell, a number that is in the range of the number of SV40 tumor antigen molecules of genuine SV40-transformed mammalian cells.

Mutant p53 potentiates protein kinase C induction of vascular endothelial growth factor expression

Many tumor cells produce vascular endothelial growth factor (VEGF), which is thought to be a pivotal mediator of tumor neoangiogenesis. Expression of the VEGF gene can be induced by tumor promoting phorbol esters, such as 12-O-tetradecanoylphorbol-13-acetate (TPA), which activate protein kinase C (PKC). Here we show that in transient transfection assays a mutated form of the murine p53 tumor suppressor gene (ala135-->val) induces expression of VEGF mRNA and potentiates TPA stimulated VEGF mRNA expression. In NIH 3T3 cells which stably overexpress the temperature sensitive p53 (ala135-->val), displaying mutant phenotype at 37 degrees C and wildtype phenotype at 32.5 degrees C, induction of VEGF mRNA and protein by activated PKC is strongly synergistic with mutant, but not wildtype p53. Mutant p53 specifically increases TPA induction of VEGF without affecting the expression of other TPA inducible genes. TPA dependent VEGF expression is also enhanced by human p53 mutated at amino acid 175. Thus, our data link PKC and p53, the gene most frequently altered in human tumors, with the regulation of tumor angiogenesis.

PAb1614, a monoclonal antibody reactive with the tumor antigens of SV40, JC, BK, and polyoma virus, and other JC virus tumor antigen cross-reactive antibodies of the PAb1601-1636 panel

PAb1614, an SV40-specific monoclonal antibody of the panel PAb1601-1636 reacts with large and small tumor antigens of SV40, BK and JC virus, and with polyoma virus large and middle tumor antigens, but not with the large tumor antigen of the lymphotropic papova virus. Using immunofluorescence and immunoblot competition assays and ELISA with synthetic peptides, it is shown that the epitope is represented by the SV40 tumor antigen undecapeptide, K39-E49. This peptide comprises the tumor antigen consensus sequence, H42-G47, of the polyoma viruses. However, the epitope of PAb1614 probably does not exactly coincide with this hexapeptide. This explains why some cross-reactions are less strong, or absent, as in the case of the lymphotropic papova virus. Further antibodies of the PAb1601-1636 panel that cross-react with the JC virus large tumor antigen are PAb1602, 1604, 1606, 1618, 1621, 1622, 1623, 1624, 1626, 1629, and 1633.

Induction of nuclear accumulation of the tumor-suppressor protein p53 by DNA-damaging agents

Cancer therapy drugs, such as diamminedichloroplatinum (cisplatin), mitomycin C, etoposide and a number of other compounds, as well as energy-rich radiation, are known to act on cellular DNA. These agents are shown to induce nuclear accumulation of the so-called tumor-suppressor protein p53 in fibroblastoid cells, as well as in epithelioid normal and immortalized cells of murine, simian, and human origin. p53 accumulation starts a few hours after treatment and can remain detectable in surviving cells for at least 20 days. Accumulation occurs because of increased p53 protein stability and depends on ongoing translation. It is not the result of enhanced gene expression. A number of cell cycle inhibitors do not affect p53 protein accumulation, suggesting that the process may start from several points in the cell cycle. Since the increase in the nuclear p53 protein levels occurs within a few hours in most of the treated normal diploid cells, it is unlikely that the accumulated p53 protein is derived from a mutated p53 gene. The results obtained are in accordance with the view that the DNA damage-induced p53 accumulation may either inhibit cell growth, allowing DNA repair processes, or, in the case of severe damage, initiate apoptosis.

Interferon inhibits herpes simplex virus-specific translation: a reinvestigation

Reports on the arrest of herpes simplex virus type 1 (HSV-1) replication by interferon (IFN) are inconsistent. By the use of immunofluorescence and immunoblot assays with monoclonal and polyclonal antibodies, effective arrest of viral translation by human IFN-alpha in human fibroblasts was detected for the HSV-1 strains KOS and McIntyre. In HeLa cells which are less sensitive to IFN inhibition and in 444 cells, a HeLa-fibroblast hybrid cell line, the inhibition was less pronounced. These results confirm earlier observations that IFN or polyinosinic.polycytidylic acid block the replication of HSV-1 in human, monkey and mouse cells no later than the immediate early phase of infection.

Synthetic oligopeptides define epitopes at the amino- and carboxy-terminus of simian virus 40 large tumor antigen which are recognized by monoclonal antibodies

Synthetic oligopeptides were used to define the epitopes recognized by monoclonal antibodies directed against the SV40 large tumor (T) antigen. The two monoclonal antibodies PAb 1622 and PAb 1626 reacted with the N-terminal undecapeptide Met(1)-Leu(11) as detected by inhibition of nuclear SV40 T antigen immunofluorescence. Antibody PAb 1605 recognized the hexapeptide Thr(701)-Pro(706) at the carboxy-terminus of the SV40 T antigen as detected by inhibition of an enzyme-linked immunosorbent assay. The specificities of these monoclonal antibodies differ from those of antibodies previously raised against the respective synthetic oligopeptides.

Transformation-related cellular protein p53: increased level in untransformed rat cells following treatment with the tumorpromoter, tetradecanoylphorbol-acetate

12-O-Tetradecanoylphorbol-13-acetate (TPA, 100 ng ml-1), a tumor promoting phorbol ester, is able to induce enhanced levels of the transformation-associated cellular antigen p53 in normal rat 2 cells which had not been previously initiated by a carcinogen. p53 was estimated in ethanol-fixed treated cells on microtiter plates with ELISA using the monoclonal antibody Pab 1620 [EMBO J. 7, 1485, (1984)]. Induction of p53 was confirmed by immunoblotting. This effect of TPA is an additional phenotypic characteristic of tumor cells which can be induced by TPA in untransformed rodent cells.

Monoclonal antibodies against simian virus 40 nuclear large T tumour antigen: epitope mapping, papova virus cross-reaction and cell surface staining

Thirty six cloned hybridomas have been isolated which produce monoclonal antibodies directed against simian virus 40 (SV40) large T tumour antigen. They have been shown to recognize at least six different epitopes along the T antigen polypeptide according to their reaction with the various truncated forms of T antigen expressed by adenovirus-SV 40 hybrid viruses. Sixteen antibodies cross-react with cells infected by the closely related human BK virus. Only two antibodies, PAb1604 and PAb1614, directed against different epitopes of the SV40 T antigen, cross-react with polyoma large T tumour antigen which has a more limited amino acid sequence homology. This cross-reaction is rarely seen with polyclonal antibodies. Monoclonal antibody PAb1620 gave nuclear immunofluorescence only with murine cells transformed by SV40 and was found to react with a complex of T-antigen and 53 000-dalton host-coded protein. All the monoclonal antibodies react with nuclear T antigen and all but four antibodies stained the surface of SV40-transformed cells. These were four of the five antibodies directed against the central third of the T antigen. Thus the monoclonal antibodies show that cell surface T antigen differs from nuclear T antigen, either in accessibility or structure.

Incidence of radiation lymphomas in C57BL/6 mice is not promoted after intraperitoneal treatment with the phorbol ester tetradecanoylphorbol acetate

Female C57BL/6 mice, given 4 X-ray irradiations each with 1.7 Gy, according to H.S. Kaplan and M.S. Brown (J. Natl. Cancer Inst., 13 (1952) 185-192) developed lethal lymphomas in more than 90%, 270 days after irradiation. Intraperitoneal application of tetradecanoylphorbol acetate (TPA), 30 ng/g, twice weekly for 240 days had no influence on survival of the animals and incidence of the malignant lymphomas.

Diverse effects: augmentation, inhibition, and non-efficacy of 12-O-tetradecanoylphorbol-13-acetate (TPA) on retrovirus genome expression in vivo and in vitro

The action of 12-O-tetradecanoylphorbol-13-acetate (TPA) on several retrovirus-related functions was investigated in four virus-host cell systems. The following effects were recorded: (i) in STU-mice, infected with the Friend virus complex (Friend) murine leukaemia virus/Friend spleen focus forming virus) and treated with TPA (50 ng/g) for one week prior to infection, the number of spleen foci increased 5-fold over the control. (ii) Addition of TPA (0.04 to 40 ng/ml) to virus-producing cell systems resulted in a 2-fold increase of extracellular reverse transcriptase activity. The maximum response was observed in Friend leukemia virus-producing mouse cells at 0.1 to 0.4 ng TPA/ml and in simian sarcoma virus-producing rat cells at 4 ng/ml. (iii) The efficiency of transformation of BalbC 3T3 cells by Moloney murine sarcoma virus, tested in a focus formation assay, was slightly enhanced by TPA. (iv) TPA inhibited the induction of endogenous virus formation in B cell mitogen-stimulated spleen cell cultures from BalbC mice.

Stabilization of isometric DNA viruses against thermoinactivation by lowered ionic strength

The thermostability of isometric DNA viruses increases, if the ionic strength is diminished before heating. When unpurified virus material from cell cultures is heated under conditions (temperature, time) which lead to a reduction in infectivity by 3 to 4 log10, this loss in titer is 1 to 3 log10 less, if the ionic strength is decreased by diluting the material in dist. water (1:100) before heating. A dilution in Eagle's MEM (1:100) or a previous dialysis against water does not have the same effect. This property was found in the following members of 4 DNA virus families: adenovirus 5, herpesvirus 1, SV 40 and bovine parvovirus 1. In contrast, members of pox- (vaccinia) and picornaviruses (polio 2, coxsackie B5) were found to be less thermostable under conditions of low ionic strength. Reovirus 3 showed no difference in inactivation. The observed effect may be of practical importance for heat disinfection of viruses and for their persistence in the environment.

Simulation and prevention of retrovirus--specific reactions by mycoplasmas

From human mycosis fungoides tumor-derived cell lines, Mycoplasma hyorhinis was isolated. This mycoplasma shared the following characteristics with retroviruses: uptake of 3H-uridine, but not of 3H-thymidine in cell culture; banding at 1.16 g/ml sucrose density and partial shift to retrovirus core density position (approximately equal to 1.24 g/ml) after detergent treatment; incorporation of 3H-TMP into high molecular weight material in standard reverse transcriptase assays with the template-primer poly (A) . (dT)12. On the other hand, the specific reverse transcriptase reaction of retroviruses with poly(A) . (dT)12 and poly(C) . (dG) approximately 16 was almost completely abolished in the presence of the mycoplasma. Thus, M. hyorhinis may interfere with identification and isolation procedures for retroviruses.

African green monkey fibroblast actin morphology during SV40 infection

Monkey skin fibroblasts were infected with simian virus 40. Cells that exhibited the viral tumor antigen were found to retain the normal morphology of actin filaments up to six days after infection. However when cells were transformed in terms of focus formation they had lost the normal actin morphology.

Isolation of simian virus 40 from a newborn child

Rubella virus and simina virus 40 (SV40) were isolated from a newborn child suffering from neurological and anatomical anomalies. The SV40 isolate was very similar to SV40 strain 777 by electron microscopic, biological, and immunological criteria.

Loading of human red blood cells with DNA and RNA

Human erythrocytes were suspended in Hank's solution containing mammalian or viral DNA or RNA. After dialysis at 0 degrees C first against water and subsequently against Hank's solution, and a further incubation at 37 degrees C, the erythrocytes were found to be loaded with the nucleic acids. The nucleic acid trapped in the erythrocytes exhibited up to 35 per cent of the external concentration.

Estimation by reassociation assay of viral DNA copies in three polyoma virus transformed cell lines

The number of polyomavirus genome equivalents in three transformed hamster cell lines were shown by DNA reassociation assay to be 1.3, 1.9 and 2.5 per cell.

Cytosine arabinoside- and interferon-mediated control of polyoma and SV40 genome expression

By metabolic DNA inhibitors such as araC, viral as well as host DNA replication is suppressed in polyoma- and SV40-infected cells. The interruption of the current viral DNA replication has no effect on the current transcription of the late viral genes. The persistence of the late transcription indicates that the onset, but not the persistence, of the viral DNA replication is a prerequisite for the persistence of the late polyoma and SV40 genome transcription. Pretreatment of monkey kidney cells with poly(I):-poly(C) nearly completely inhibits the SV40 T antigen formation; the early SV40 RNA formation is suppressed far less. This type of SV40 genome control favors the concept of a primary action of poly(I):poly(C)-mediated interference on SV40 translation.