Ionizing radiation‐induced chromosomal rearrangements occur in transcriptionally active regions of the genome

PURPOSE

The mechanism by which ionizing radiation induces chromosomal rearrangements in mammalian cells has for long been a subject of debate. In order to dissect these events at a molecular level, we have studied the sequences involved in gamma irradiation-induced rearrangements.

MATERIALS AND METHODS

An inverse polymerase chain reaction (PCR)-based methodology was used to amplify rearrangements that had occurred between one of four target regions (in or neighbouring the avian myelocytomatosis viral oncogene homologue (c-MYC), cyclin-dependent kinase inhibitor 1A (CDKN1A), fibroblast growth factor receptor 2 (FGFR2), or retinoblastoma 1 (RB1) genes) and sequences elsewhere in the genome, following gamma irradiation and subsequent incubation at 37 degrees C of normal human IMR-90 fibroblasts.

RESULTS

The sequences of 90 such rearrangements, including both inter- and intra-chromosomal events, have been analysed. Sequence motifs (including DNA topoisomerase recognition sites) were not found to be consistently present either at or near rearrangement breakpoint sites. Statistical analysis suggested that there was significantly more homology between the sites of DNA rearrangement breakpoints than would be expected to occur by chance, however, most DNA rearrangements showed little or no homology between the interacting sequences. The rearrangements were shown to predominantly involve transcriptionally active sequences, a finding that may have significant implications for our understanding of radiation-induced carcinogenesis.

CONCLUSION

The results obtained are difficult to reconcile with most models for ionizing radiation-induced chromosomal aberration formation, but are consistent with the Transcription-Based model.

Transformation and Radiosensitivity of Human Diploid Skin Fibroblasts Transfected with SV40 T-antigen Mutants Defective in RB and P53 Binding Domains

A series of human diploid fibroblast cell clones were developed by DNA transfection with either wild-type SV40 T-antigen (SV40 T) or T-antigen mutants defective in its various functional domains. Cell clones expressing the wild-type SV40 T were significantly radioresistant as compared with clones transfected with the neo gene only (D0 = 192 +/- 13 vs 127 +/- 19). This radioresistance persisted in post-crisis, immortalized cell lines. A series of mutants with point or deletion mutations within each functionally active domain of SV40 T were also examined for their ability to alter radiosensitivity and induce morphological transformation. Cell clones transfected with T-antigen mutants defective in nuclear localization or origin binding showed increased radioresistance similar to clones transfected with wild-type T-antigen, and expressed morphological changes characteristic of SV40 T-transfected cells. A retinoblastoma susceptibility gene (RB) binding defective mutant showed moderately increased radioresistance (D0 = 174 +/- 10). However, cell clones transfected with three different p53 binding defective mutants showed no change in radiosensitivity (D0 = 132 +/- 5) as compared with neo gene transfected controls. Transfection with T-antigen mutants defective in either the RB or p53 binding domain yielded no morphological alterations characteristic of transformation. These data suggest that the SV40 T/p53 complex may be of importance in the radioresistance phenotype.

Genotoxic stress and cellular stress alter the subcellular distribution of human T-cell leukemia virus type 1 tax through a CRM1-dependent mechanism

Human T-cell leukemia virus type 1 Tax is a predominantly nuclear viral oncoprotein that colocalizes with cellular proteins in nuclear foci known as Tax speckled structures (TSS). Tax is also diffusely distributed throughout the cytoplasm, where it interacts with and affects the functions of cytoplasmic cellular proteins. Mechanisms that regulate the distribution of Tax between the cytoplasm and nucleus remain to be identified. Since Tax has been shown to promote genome instability by perturbing cell cycle progression and DNA repair mechanisms following DNA damage, we examined the effect of genotoxic stress on the subcellular distribution and interacting partners of Tax. Tax localization was altered in response to various forms of cellular stress, resulting in an increase in cytoplasmic Tax and a decrease in Tax speckled structures. Concomitantly, colocalization of Tax with sc35 (a TSS protein) decreased following stress. Tax translocation required the CRM1 nuclear export pathway, and a transient interaction between Tax and CRM1 was observed following stress. These results suggest that the subcellular distribution of Tax and the interactions between Tax and cellular proteins respond dynamically to cellular stress. Changes in Tax distribution and interacting partners are likely to affect cellular processes that regulate cellular transformation.

[Retention of tumorigenicity in radioresistant progeny of cells surviving exposure to high doses of gamma irradiation]

The cell tumorigenic ability and the cell clonogenicity in semi-solid medium of highly radioresistant variant cell line, PIC-20 (the progeny of djungarian hamster fibroblast cell line DX-TK- surviving acute exposure to 20 Gy of gamma-irradiation), were examined. In the absence of additional radiation, no differences between tested features of non-irradiated PIC-20 cells and parental DX-TK- cells were observed. On the contrary, after gamma-irradiation with high doses the essential differences in the properties of the examined cell lines were revealed. After exposure to 10 Gy the surviving fraction of PIC-20 cells was 20 times higher than that of the parental cells. Both irradiated and non-irradiated PIC-20 cells produced colonies of similar size. It is revealed that even after irradiation with doses of 5, 10 or 15 Gy, the PIC-20 cells kept their tumorigenicity as high as non-irradiated ones. In all these cases the 90-100% of animals had the tumour, with the average latent period of tumour appearance after inoculation being the same both for irradiated and non-irradiated PIC-20 cells. After irradiation of parental DX-TK- cells with the highest dose of 15 Gy, the amount animals with tumour decreased by 70% and the average latent period of tumour appearance increased fivefold as compared with that for non-irradiated DX-TK- cells. The data obtained indicate that PIC-20 is highly radioresistant cells, which are able to proliferate both in semi-solid medium and in an animal organism even after radiation exposure to high doses.

Mutation induction in human cells after low dose X ray exposure

Mutations induced after low dose ionising radiation exposure have been intensively analysed not only for radiation risk estimation but also for basic understanding of cellular responses. Human lymphoblastoid TK6-20C cells were irradiated with 100 mGy of X rays and mutation at the heterozygous thymidine kinase (TK) locus was selected by trifluorothymidine (TFT) resistance. Although the mutation frequency at the TK locus increased from 5.6 x 10(-6) to 7.4 x 10(-6), this increase was not statistically significant. However, molecular analysis of TK mutants exhibiting loss of heterozygocity (LOH) demonstrated a clear effect of such low dose IR exposure. Exposure to 100 mGy X ray increased the fraction of hemizygous-LOH from 10% to 42%. In previous experiments, a similar tendency in the increase of hemizygous-LOH was also observed in TK6 cells after exposure to a 2 Gy dose of X rays. This type of LOH can be considered as a result of end-joining repair of DNA double strand breaks.

Localization of tumor suppressor gene candidates by cytogenetic and short tandem repeat analyses in tumorigenic human bronchial epithelial cells

Radon exposure is associated with increased risk for bronchogenic carcinoma. Mutagenesis analyses have revealed that radon induces mostly multi-locus chromosome deletions. Based on these findings, it was hypothesized that deletion analysis of multiple radon-induced malignant transformants would reveal common mutations in chromosomal regions containing tumor suppressor genes responsible for malignant transformation. This hypothesis was supported by a previous study in which tumorigenic derivatives of the human papillomavirus 18-immortalized human bronchial epithelial cell line BEP2D were established following irradiation with 30 cGy of high linear energy transfer radon-simulated alpha-particles. Herein, we describe the analyses of 10 additional tumorigenic derivative cell lines resulting from the irradiation of five additional independent BEP2D populations. The new transformants have common cytogenetic changes, including the loss of chromosome (ch)Y, one of three copies of ch8, one of two copies of ch11p15-pter and one of three copies of ch14. These changes are the same as those reported previously. Analysis of PCR-amplified short tandem repeats of informative loci confirmed the loss of heterozygosity (LOH) at 12 loci spanning the length of ch8 in cell lines from four of the total of eight irradiation treatments to date and the loss of chY in all cell lines (8 of 8). LOH analysis with a total of 17 informative loci confirmed loss on ch14 in transformants from seven of eight irradiation treatments and indicated a 0.5-1.7 cM region of common involvement centered around locus D14S306. No LOH was detected at any of the informative loci on ch11. The overall results support our stated hypothesis. Further studies are currently in progress to determine whether the ch8 and ch14 regions contain genes with tumor suppressor function in bronchial epithelial cells.

Radiation-enhanced expression of E6/E7 transforming oncogenes of human papillomavirus-16 in human cervical carcinoma

BACKGROUND

Human papillomavirus (HPV) infection represents the most important risk factor for cervical carcinoma. Levels of expression of E6 and E7 transforming oncoproteins of high risk HPV genotypes (i.e., HPV-16 and HPV-18) have been linked specifically to the mitotic activity of cervical carcinoma and appear to be necessary for maintaining the malignant phenotype. However, E6/E7 viral proteins recently have been reported to be effective tumor rejection antigens in animal models and humans. Radiation treatment represents a standardized and effective modality for contemporary cervical carcinoma therapy. However, although the physiologic and cellular changes associated with high doses of irradiation have been well documented it has been shown only recently that an increased synthesis of specific cellular proteins is observed after irradiation. In this study, the authors analyzed the effects of high doses of gamma irradiation on the expression of E6/E7 oncoproteins in HPV-16-infected cervical carcinoma cell lines. In addition, the effects of radiation on major histocompatibility complex (MHC) restriction elements also were studied.

METHODS

The effect of high doses of gamma irradiation (i.e., 1250, 2500, 5000, and 10,000 centigray [cGy]) on the kinetics of E6/E7 oncoprotein expression in two HPV-16 positive cervical carcinoma cell lines (i.e., CaSki and SiHa) was evaluated by Northern blot analysis. In addition, the effect of radiation on the expression of MHC molecules also was studied by Northern blot and fluorescence activator cell sorter (FACS) analysis.

RESULTS

Dose ranging from 1250 (sublethal) to 10,000 (lethal) cGy significantly increased the expression of E6/E7 oncoproteins as well as MHC Class I molecules in CaSki and SiHa cell lines when compared with untreated tumor cells. Both cell lines showed increased mRNA expression for MHC Class I molecules in a dose-dependent manner. E6/E7 oncoproteins also were up-regulated in a dose-dependent manner in the CaSki cell line, whereas in the SiHa cell line their expression plateau at 5000 cGy. When the kinetics of radiation-induced up-regulation of E6/E7 were studied, persistent up-regulation of the viral oncoproteins was noted for all doses of irradiation, with the lower and sublethal doses (i.e., 1250-2500 cGy) inducing the most significant enhancement.

CONCLUSIONS

High doses of irradiation can induce a significant and long-lasting up-regulation of E6/E7 oncogenes and MHC Class I restriction elements on HPV positive cervical carcinoma cell lines. These effects by themselves suggest that irradiation could enhance local tumor immunogenicity in patients receiving radiation therapy. However, in contrast to this possible beneficial effect, sublethal tumor irradiation (up-regulating E6/E7 transforming oncoproteins) also could confer a significant growth advantage to radiation-resistant tumor cells. These findings, combined with the previously reported acquisition of a radiation-induced drug resistance, could provide a biologic basis for the poor prognosis of patients with cervical carcinoma recurrence after radiation therapy.

[The isolation and analysis of lymphoblastoid cell lines from patients with xeroderma pigmentosum and progeria]

Lymphoblastoid cell lines from patients with xeroderma pigmentosum (2 forms) and progeria (unusual form) were established using transformation of peripheral blood lymphocytes by Epstein--Barr virus. The influence of different UV doses on cell vitality, proliferation and cell cycle progression was studied by means of flow cytometry. The cell vitality was determined after incubation of cells with etidium bromide and FDA. We used cytograms with two logarithmic signals (log green/log red) to discriminate the cell cycle status. Cell cultures were used with density of 500,000 cells per 1 ml, previously synchronized at G-phase by the incubation in a medium with low serum content. The effect of UV irradiation was followed during 72 h. Among four analysed cell lines only line XP2SP demonstrated enhanced UV sensitivity, expressed by decreasing of the amount of living cells after the UV dose of 2.5 J/m2 and higher. The cell cycle studies showed that cells were blocked in S-phase and simultaneously the amount of apoptotic cells with both reduced DNA content and ability to bind FDA was seen increased. Similar events were observed in the control line only after the dose of 20 J/m2 and higher.

Analysis of oncogenic progression in a radiation leukemia virus model

The mechanism by which non-oncogene-bearing, slowly transforming retroviruses induce leukemia is not well understood, but appears to represent a multi-step process. Cell lines have been isolated following in vitro infection of lymphoid cells with radiation leukemia virus (RadLV) and they have been used to develop a two-step model for leukemia development. Thymic tumors were induced when one of the cell lines, C1-V13D, was inoculated into CBA/H mouse thymus. Upon reisolation of C1-V13D cells after one, two and three passages through thymus, individual cloned cell lines displayed increased tumorigenic potential compared with the non-tumorigenic parental line. Southern analysis has been used to track any genetic changes occurring while cells undergo further transformation and become increasingly tumorigenic. Specifically, retrovirus integration has been monitored in clones derived from C1-V13D at the primary, secondary and tertiary passage through thymus using probes specific for long terminal repeat (LTR), gag, pol and env genes of RadLV. The data indicate multiple ecotropic retrovirus integration sites in C1-V13D cells. Primary thymic tumors also showed the integration of a new recombinant or defective virus. There was no evidence that new ecotropic retrovirus integration had occurred during subsequent passage of primary tumors through the thymus, i.e. during the progression to oncogenesis. All data indicate an important role for the thymic environment in the development of a fully transformed cell.

A human gene that restores the DNA-repair defect in SCID mice is located on 8p11.1-->q11.1

In order to map the gene that is responsible for the DNA-repair defect in severe combined immune deficient (SCID) mice, a mixture of microcells independently isolated from mouse A9 cells containing pSV2neo-tagged human chromosomes 5, 7, 8, 9, 11, 15, 18 or 20 were fused with SCID fibroblast cell lines SCVA2 and SCVA4, which were originally established from lung tissue of the C.B.17-scid/scid mouse by SV40 virus transfection. After irradiation with 60Co gamma-rays and selection with antibiotic G418, 12 independent clones were obtained, of which 4 contained an intact chromosome 8, 3 clones contained a deleted chromosome 8 [del(8)q22-->qter or del(8)q23--> qter] and remaining 5 had no detectable or specific human chromosome. We further independently transferred a single human chromosome 8 or 11 into the SCVA cells via microcell fusion, and examined the radiation sensitivity of the microcell hybrids. Complementation of the radiation sensitivity was correlated with the presence of human chromosome 8 in microcell hybrids, whereas no correlation was observed in clones following the transfer of human chromosome 11. Thus, the results indicate that human chromosome 8 restored high sensitivity to ionizing radiation. A number of subclones that were radiation resistant or sensitive were isolated from the microcell hybrids. The concordance of the radiation sensitivity with the presence or absence of specific DNA fragments on chromosome 8 indicates that the human gene is located on the centromeric region of chromosome 8, i.e., 8p11.1--> q11.1.

Chicken embryo fibroblasts exposed to weak, time-varying magnetic fields share cell proliferation, adenosine deaminase activity, and membrane characteristics of transformed cells

Chicken embryo fibroblasts (CEF) exposed to a sinusoidally varying magnetic field (SVMF) (100 Hz, 700 microT, for 24 h) showed a remarkable rise of segmental rotational relaxation rate of adenosine deaminase (ADA, EC 3.5.4.4) as determined by multifrequency phase fluorometry. Pyrene-labeled, small subunit ADA was applied to cultured (normal) CEF, which have available and abundant ADA complexing protein (ADCP) on their plasma membranes. Sine-wave-modulated fluorometry of the pyrene yielded a profile of phase angle vs. modulation frequency. In SVMF-treated cells and in Rous-sarcoma-virus (RSV) transformed cells the differential phase values at low modulation frequencies of the excitation are remarkably reduced. This effect is magnetic rather than thermal, because the temperature was carefully controlled and monitored; nevertheless to further check this matter we studied CEF, infected by the RSV-Ts68 temperature-sensitive mutant (36 degrees C transformed, 41 degrees C "revertant"). When grown at 36 degrees C in the SVMF, cells did not show the slightest trend towards reversion, as would be expected had there been local heating. Concomitant with the increased segmental rotational relaxation rate of ADA, there was a decrease in fluorescence lifetime and a slight, yet significant, increase in membrane lipid "microfluidity." These biophysical observations prompted us to examine the effect of SVMF on cell proliferation and ADA activity (a malignancy marker): higher rates of cell proliferation and reduced specific activity of ADA were observed.

Autonomous growth of human T-lymphotropic virus type I infected human lymphocytes treated with N-methyl-N'-nitro-N-nitrosoguanidine and ultraviolet rays

Human T-cell cultures infected with human T-lymphotropic virus type I (HTLV-I) and interleukin-2 (IL-2)-dependent for their continuous growth were treated with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and then maintained in the medium containing phorbol 12-myristate 13-acetate (TPA). Cells achieved independence from IL-2 but became TPA-dependent for continuous growth. Multiple ultraviolet (UV) irradiations of TPA-dependent cells resulted in their autonomous growth. G-band karyotype analysis revealed multiple chromosomal abnormalities that were seen in cells before and after MNNG treatment and UV irradiations, and those that were only seen in autonomously growing cells. Viral expression was found to be transiently enhanced in association with emergence of certain chromosomal changes. Exposure of HTLV-I infected cells to certain mutagens may promote the occurrence of the specific rearrangement of cellular genes responsible for regulation of cellular and viral replication and may lead these cells to neoplastic transformation.

Enhancement of adenovirus transformation of cloned rat embryo fibroblast cells by gamma irradiation

We have analyzed the effect of gamma irradiation on the induction of morphological transformation of cloned rat embryo fibroblast (CREF) cells by the host-range cold-sensitive type 5 adenovirus mutant, H5hr1. Treatment of CREF cells with 1-6 Gy of gamma irradiation immediately prior to viral infection resulted in dose-dependent decrease in cell survival and concomitant increase in viral transformation frequency. Exposure of CREF cells to 1-6 Gy of gamma radiation alone resulted in a similar dose-dependent inhibition in cell survival but without any subsequent morphological transformation. The effect of gamma irradiation on viral transformation was greatest when cells were irradiated directly before viral infection. The reduction in the enhancement of transformation was both dose and time dependent. The ability of gamma irradiation to enhance viral transformation was substantially reduced if CREF cells were treated with inhibitors of RNA (actinomycin D) and protein (cycloheximide) synthesis. Employing a single-cell colony transfer assay and in situ hybridization with a 32P-labeled Ad5 DNA probe, we found that gamma irradiation of CREF cells prior to infection with H5hr1 resulted, 10 and 17 d after infection and replating, in an increase in the percentage of surviving CREF colonies that contain Ad5 DNA. Analysis of viral DNA integration by DNA-filter hybridization (Southern blot analysis) in H5hr1-transformed CREF clones isolated from untreated and gamma-irradiated cultures indicates that gamma irradiation caused increases in both the number of copies of Ad5 E1A DNA sequences integrated into cellular DNA and the number of unique Ad5 E1A DNA integration sites in transformed cells. These results indicate that gamma irradiation enhancement of adenovirus transformation was a consequence of radiation-induced cellular factors with finite life spans that are mediators of enhanced viral transformation. Potentially important components of the radiation enhancement process appear to involve an alteration in both the retention of free Ad5 DNA in surviving cells and an alteration in the profile of viral-DNA integration in gamma-irradiated cells.

Antinuclear antibodies in the sera of patients with nasopharyngeal carcinoma

We studied the production of heterophile antinuclear antibodies (ANAs) in the sera of 50 patients, 20 with nasopharyngeal carcinoma (NPC) and 30 with other head and neck cancers (laryngeal cancer and maxillary cancer), before and after radiation therapy. A higher incidence of ANAs was found in the sera of patients with NPC and ANA production in these patients was higher after radiation therapy. We therefore performed in vitro experiments to explore the mechanisms of ANA production in the serum of postirradiated NPC patients. X-ray-irradiated NPC-derived cells (NPC-KT) produced a large amount of Epstein-Barr virus (NPC EBV) compared with non-irradiated NPC-KT cells. Nasopharyngeal carcinoma EBV-infected lymphocytes produced high levels of ANAs. These data suggest that lymphocytes infected by EBV from NPC cells may produce ANAs in the sera of NPC patients.

An attempt to select pseudonormal revertants of Friend erythroleukaemia cells using cytochalasin B

Treatment of Friend erythroleukaemia cells with cytochalasin B (CB) resulted in multinucleation and loss of viability characteristic of a virus-transformed cell line. In an attempt to isolate pseudonormal revertants of this cell line mutagenized cultures were exposed to CB and surviving clones isolated. Many of these were found to be mutants resistant to the growth inhibitory effects of CB. The proportion of such mutants was reduced by simultaneous selection in CB and cytosine arabinoside. Of 699 clones examined none consistently exhibited reduced levels of multinucleation in the presence of CB. The inability of CB to select for revertants displaying a phenotype closer to normal cells is discussed.

DNA damage stimulates human cell transformation by integrative but not episomal Epstein-Barr virus-derived plasmid

Previous work has demonstrated that ultraviolet (UV) irradiation of SV40-based plasmids can strikingly enhance the frequency of stable transformation of human cells. In this study we compared the effect of UV-induced DNA damage on transformation mediated by integrative versus autonomously replicating plasmids derived from human Epstein-Barr virus (EBV). We report that transfection of human fibroblasts with UV-irradiated integrative EBV-based plasmid results in enhanced transformation. However, transfection of UV-damaged episomal EBV-based constructs into the same human cell line does not enhance transformation; in fact, the extrachromosomal status of the plasmid is maintained irrespective of the UV dose to the plasmid. We conclude that enhanced transformation of human cells by damaged DNA requires its chromosomal integration.

Delayed expression of enhanced reactivation and decreased mutagenesis of UV-irradiated adenovirus in UV-irradiated ataxia telangiectasia fibroblasts

Fibroblasts from patients with ataxia telangiectasia (AT) are hypersensitive to the lethal effects but hyposensitive to the mutagenic effects of ionizing radiation, suggesting that AT cells may be defective in some process which modifies damage to DNA. In this study we have examined the UV-enhanced reactivation (UVER) and UV-enhanced mutagenesis (UVEM) of UV-irradiated adenovirus in AT fibroblasts. UVER was examined using both V antigen expression as well as progeny production from infected cell cultures. Viral mutagenesis was studied by examining the induction of phenotypically wild-type revertants among the progeny obtained from fibroblasts infected with a temperature-sensitive early mutant of adenovirus (Ad5ts36). UVER factors for Ad V antigen expression were significantly less than normal in the AT strains tested when infection occurred immediately after UV-irradiation of cells. However, UVER factors were greater than 1 and similar to those found for normal strains when cells were infected 24 h after UV-irradiation, indicating a delay in the expression of UVER for Ad V antigen in AT cells. UV-irradiation of both normal and AT cells 24 h prior to infection also resulted in a significant increase in progeny survival for UV-irradiated Ad. In normal cells, this progeny UVER was concomitant with a significant increase in the mutation frequency for UV-irradiated virus (increase in targeted mutagenesis) suggesting the existence of an inducible error-prone DNA repair mode in normal human cells. In contrast, pre-UV-irradiation of AT cells resulted in a significant decrease in the mutation frequency for UV-irradiated virus. These results suggest that AT cells lack an inducible error-prone DNA mode and that the delayed expression of UVER in AT cells results from a relatively error-free mechanism.

Untargeted viral mutagenesis is not found in X-irradiated monkey cells

The existence of untargeted viral mutagenesis in X-irradiated cells was investigated in a mammalian virus/cell system, where a low level of such viral mutagenesis can be demonstrated in UV-irradiated cells. In the positive control experiment UV-elicited mutagenesis was shown with cell exposures of 5, 10 and 15 J/m2 and a delay of 24 h between cell irradiation and infection with unirradiated herpes simplex virus. Although X-ray doses of 1, 3 and 10 Gy elicit enhanced reactivation of UV-irradiated virus, no untargeted mutagenesis for any X-ray dose at post-irradiation infection times of 0, 24 or 72 h was observed in this study. Thus untargeted mutagenesis of herpes simplex virus was not demonstrated in X-irradiated monkey cells, under conditions where X-ray-enhanced reactivation occurs and where untargeted mutagenesis in UV-irradiated cells occurs.

Characterization of the transformation properties of Shope fibroma virus

To investigate if Shope fibroma virus (SFV), a leporipoxvirus that induces benign tumors in adult rabbits, can trigger the second step of carcinogenesis in vitro or malignant transformation, an already immortalized rabbit cell line (SIRC) was inoculated with ultraviolet-irradiated virus. The resulting cell transformants displayed the characteristic properties of the malignant phenotype: lack of infectious particles, low serum requirement, high efficiency of cloning, resistance to superinfection, presence of viral DNA sequences in the nucleus, expression of viral proteins and induction of tumors in rabbits. However, this transformation was not stable since in all cell lines studied, a loss of the malignant phenotype was recorded close to the 50th passage. To assess the oncogenic potential of SFV, NIH 3T3 cells were transfected with SFV DNA. The results of these experiments indicate that SFV DNA can induce the formation of foci in certain NIH 3T3 cell lines. Taken together these results support the notion that SFV can elicit the transformation of cells in vitro.

Failla Memorial lecture. The future of heavy-ion science in biology and medicine

Interplanetary space contains fluxes of fast moving atomic nuclei. The distribution of these reflects the atomic composition of the universe, and such particles may pose limitations for space flight and for life in space. Over the past 50 years, since the invention of Ernest Lawrence's cyclotron, advances in accelerator technology have permitted the acceleration of charged nuclei to very high velocities. Currently, beams of any stable isotope species up to uranium are available at kinetic energies of several hundred MeV/nucleon at the Berkeley Bevalac. Recently, new areas of particle physics research relating to the mechanisms of spallation and fission have opened up for investigation, and it is now realistic to search for nuclear super-dense states that might be produced in heavy nuclear collisions. The heavy ions hold interest for a broad spectrum of research because of their effectiveness in producing a series of major lesions in DNA along single particle tracks and because of the Bragg depth ionization properties that allow the precise deposition of highly localized doses deep in the human body. Individual heavy ions can also interrupt the continuity of membraneous regions in cells. Heavy ions, when compared to low-LET radiation, have increased effectiveness for mammalian cell lethality, chromosome mutations, and cell transformation. The molecular mechanisms are not completely understood but appear to involve fragmentation and reintegration of DNA. Cells attempt to repair these lesions, and many of the deleterious effects are due to misrepair or misrejoining of DNA. Heavy ions do not require the presence of oxygen for producing their effects, and hypoxic cells in necrotic regions have nearly the same sensitivity as cells in well-oxygenated tissues. Heavy ions are effective in delaying or blocking the cell division process. Heavy ions are also strong enhancers of viral-induced cell transformation, a process that requires integration of foreign DNA. Some cell lines, known to be radioresistant to X rays, have exhibited greater sensitivity to heavy ions. These radiobiological properties, combined with the ability to deliver highly localized internal doses, make accelerated heavy ions potentially important radiotherapeutic tools. Other novel approaches include the utilization of radioactive heavy beams as instant tracers. Heavy-ion radiography and microscopy respond to delicate changes in tissue electron density. Dose localization with helium ions has achieved excellent results for pituitary tumors, tumors adjacent to the spinal cord, and ocular melanomas. We are working on adapting silicon- and neon-ion beams for controlled therapy studies.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of cyclosporin-A (CsA) on the ability of T lymphocyte subsets to inhibit the proliferation of autologous EBV-transformed B cells

We have analyzed the effect of Cyclosporin-A (CsA) on the in vitro suppression of Epstein-Barr virus (EBV)-induced B-cell proliferations separated on the basis of cell density. CsA abolished the growth-inhibitory capacity of high-density T cells but influenced only marginally the activity of low-density lymphocytes; this suggested that different mechanisms mediate suppression in the two subsets. Stimulation with irradiated EBV-transformed cells had a different impact on the activity of low- and high-density lymphocytes. Proliferative and cytotoxic responses were inversely correlated, i.e. high-density cells proliferated but exerted low cytotoxicity, while the lytic activity of the low-density subset was stronger in the absence of significant cell proliferation. Proliferation and generation of cytotoxicity were abrogated by CsA in both subsets. The activities could be restored by addition of exogenous IL-2, suggesting that the drug may interfere with the cascade of lymphokine--cell interactions which leads to activation of immune responses. From the analysis of athe CsA effects on the two subsets it seems that the high-density one contains specific memory T cells which are activated and proliferate upon encounter with EBV-infected cells. On the other hand, low-density lymphocytes are induced to release soluble factors with antiproliferative activity. The secretory function was resistant to the suppressive effect of CsA.

Procoagulant activity of mouse and human cultured cells following various types of transformation

The presence of fibrin deposits in the microenvironment of tumor cells has been reported repeatedly and considered to play an important role in tumor biology. Among the mechanisms by which fibrin may be deposited in tumors, procoagulant activities (PCA) of different types have been described in cancer cells. The present study was aimed at establishing whether the nature of cellular PCA was a characteristic associated with malignant transformation. PCA of normal and transformed cells was investigated on pairs of murine and human origin. The transformed counterparts were obtained after treatment with low-dose radiation, chemical carcinogen, viral infection or after in vitro spontaneous immortalization. Both before and after any type of transformation cell PCA was of the tissue thromboplastin type, identified on the basis of biological criteria: requirement of factor VII for its expression and lack of inhibition by the serine protease inhibitor diisopropylfluorophosphate (DFP). Transformed cells of murine origin showed significantly lower activity than their normal counterparts, whereas all the transformed human cell lines expressed significantly higher activity than normal. An inverse correlation between the levels of PCA and the cell density in culture was observed in all but one of the lines tested. These findings suggest that the factor X activating property described in some tumors or in transformed cells cannot be considered as a general marker of transformation.

Factor determining the antigenic type of interferons produced in human lymphoblastoid cell lines

The factor that determines the antigenic type of IFN produced in human lymphoblastoid cell lines was examined using live Sendai virus, ultraviolet (UV)-irradiated virus, HANA spikes exposed on L cells persistently infected with Sendai virus (L-HVJ) and poly-inosinic acid poly-cytidylic acid (poly I: C). When Sendai virus was irradiated with UV-light for 300 sec, its abilities to infect chicken eggs and induce IFN were diminished, but its HA activity was unaffected. HANA spikes exposed on L-HVJ could not induce IFN in human lymphoblastoid cell lines, although they induced IFN in mouse spleen cells. These results suggest that the induction of IFN in human lymphoblastoid cells is closely related to viral nucleic acid. Poly I: C also induced IFN in some human lymphoblastoid cell lines in which IFN production is induced by Sendai virus. The antigenic types of IFN induced by poly I: C were the same as those induced by Sendai virus. These results suggest that the antigenic type of IFN produced depends on the nature of the IFN producer cells rather than on the kind of IFN inducer.

UV Irradiation induces an activity which stimulates Simian virus 40 rescue upon cell fusion

UV irradiation of African green monkey cells greatly stimulated efficiency of simian virus 40 induction from simian virus 40-transformed Syrian hamster cells after cell fusion. The maximum inducing activity was observed at 15 to 20 h after irradiation but remained only transiently. The addition of cycloheximide after UV irradiation eliminated the stimulation of the activity.

U.v.-enhanced reactivation of u.v.-irradiated herpes virus by primary cultures of rat hepatocytes

Carcinogen treatment of cultured mammalian cells prior to infection with u.v.-irradiated virus results in enhanced virus survival and mutagenesis suggesting the induction of SOS-type processes. In this paper, we report the development of a primary rat hepatocyte culture system to investigate cellular responses to DNA damage which may be relevant to hepatocarcinogenesis in vivo. We have obtained data demonstrating that enhanced reactivation of u.v.-irradiated Herpes simplex virus type 1 (HSV-1) occurs in hepatocytes irradiated with u.v. Cultured hepatocytes were pretreated with u.v. at the time of enhanced DNA synthesis. These treatments caused an inhibition followed by a recovery of DNA synthesis. At various times after pretreatment, the hepatocytes were infected with control or u.v.-irradiated HSV-1 at low multiplicity, and virus survival was measured by direct plaque assay. U.v.-irradiated HSV-1 exhibited the expected two-component survival curve in control or u.v. pretreated hepatocytes. The magnitude of enhanced reactivation of HSV-1 was dependent on the u.v. dose to the hepatocytes, the time of infection following u.v. pretreatment, and the level of DNA synthesis at the time of pretreatment. These results suggest that u.v. treatment of rat hepatocytes causes the induction of SOS-type functions that may have a role in the initiation of hepatocarcinogenesis.

Involvement of DNA polymerase alpha in host cell reactivation of UV-irradiated herpes simplex virus

Aphidicolin is a potent inhibitor of both host cell DNA polymerase alpha and herpes simplex virus (HSV)-induced DNA polymerase but has no effect on DNA polymerases beta and gamma of host cells. By using an aphidicolin-resistant mutant (Aphr) of HSV, a possible involvement of DNA polymerase alpha in host cell reactivation of UV-damaged HSV was studied. Plaque formation by UV-irradiated Aphr was markedly inhibited by 1 microgram of aphidicolin per ml, which did not affect the plating efficiency of nonirradiated Aphr. Aphidicolin added before 12 h postinfection inhibited plaque formation by irradiated Aphr, which became aphidicolin insensitive after 36 h postinfection. The results strongly suggest that host cell DNA polymerase alpha is involved in the repair of UV-irradiated HSV DNA.

Increased sensitivity of cultured fibroblasts from colon cancer-prone rats to cytotoxicity of carcinogens and to viral transformation: a comparison with fibroblasts from patients with adenomatosis coli

Lethal effects of mitomycin C (MMC), 4-nitroquinoline 1-oxide (4NQO) and ultraviolet light (UV) on fibroblast cell lines derived from a colon cancer-prone substrain of Wistar-Furth rats (WF/OSAKA rats) were measured in terms of the cellular colony-forming ability, and compared with the sensitivity to these agents of human fibroblasts from patients with adenomatosis coli and rectum (ACR). All 6 fibroblast strains from the cancer-prone WF/OSAKA rats were significantly more sensitive (though to various extents) to MMC as well as 4NQO than normal rat fibroblasts derived from the parental WF Hiroshima rats. These WF/OSAKA cell strains were slightly more sensitive to UV than normal rat cell strains. Similarly, 5 out of 6 fibroblast strains derived from ACR patients were hypersensitive to both MMC and 4NQO. Further, the WF/OSAKA cell strains were more susceptible to morphological transformation induced by Kirsten murine sarcoma virus than normal rat strains. The observed higher sensitivity to chemical agents and to viral transformation suggests a close similarity in cellular terms between the colon cancer-prone WF/OSAKA rats and human individuals affected with ACR.

Transformation of human diploid cells by adenovirus type 4 irradiated with ultraviolet light

Inoculation of ultraviolet (UV)-irradiated adenovirus type 4 (Ad4) led to in vitro transformation of human diploid cells (HDC). Two transformed cell lines could be established: cell line H 1418, from HDC inoculated with the 10(-3) dilution of Ad4 UV-irradiated for 20 min at a distance of 20 cm, co-cultivated with uninfected HDC, and cell line H 1557, from HDC inoculated with the 10(-2) dilution of Ad4 irradiated at the same distance for 12 min. Both transformed cell lines were resistant to superinfection with homologous virus. Virus-specific antigen could be made evident by the indirect immunofluorescence technique in the nuclei of both H 1418 and H 1557 cells.

SV40-induced transformation and T-antigen production is enhanced in normal and repair-deficient human fibroblasts after pretreatment of cells with UV light

Human fibroblasts irradiated with UV light were infected with simian virus 40 and tested either for transformation or T-antigen production. At UV doses that allowed approximately 5-10% of the irradiated cells to survive, the number of surviving transformed colonies increased. This result was confirmed by testing for T-antigen 96 h post infection by means of indirect immunofluorescence. Since these results were obtained for a normal cell line as well as for two UV excision repair-deficient ones (XP groups A and D), it was concluded that excision repair functions cannot play a decisive role in the events leading to increased transformation and T-antigen production. It is proposed that the relative increase of transformation and T-antigen production is the expression of host functions which are induced by DNA damage threatening cell survival.

Lack of enhanced mutation of UV- and gamma-irradiated herpes virus in UV-irradiated CV-1 monkey cells

The frequency of forward mutation of unirradiated, UV-irradiated or gamma-irradiated herpes virus was determined after infecting UV-irradiated or unirradiated CV-1 monkey kidney cells, to investigate the correlation between UV-enhanced reactivation (UVER) and mutagenesis. UV-irradiation to cells had no effect on mutation frequency of irradiated virus even in the conditions in which UVER was maximally expressed for the survival of UV-irradiated virus.

Genital condyloma virus infection following pelvic radiation therapy: report of seven cases

Six women who underwent radiation therapy for gynecologic malignancies demonstrated cytologic evidence of condyloma virus infection 2 or more years following radiation. Histologic confirmation was obtained in two of the cases. A seventh patient developed in situ and invasive squamous cell carcinoma in a vulvar condyloma acuminatum following radiation therapy for Hodgkin's disease. This venereal infection is found most frequently in sexually active younger women (average age, 27 years). It is felt that depressed cell-mediated immunity consequent to the radiation therapy allowed the development of this infection in the older patients described in this report. The evolution of invasive squamous cell carcinoma in the condyloma acuminatum may indicate a possible oncogenic or cocarcinogenic effect of the virus. The immunologic responses to infection caused by the human papillomavirus group are discussed, as well as its potential for malignant transformation.

Further evidence that ultraviolet radiation-enhanced reactivation of simian virus 40 in monkey kidney cells is not accompanied by mutagenesis

Can simian virus 40 (SV40) be used to detect mutagenic DNA repair in cultured mammalian cells? The published evidence from different laboratories are in direct conflict. In order to decide between the conflicting evidence, we conducted experiments in two separate laboratories using experimental protocols similar to those previously used to investigate mutagenic repair with viral probes. Mutagenesis in SV40 virus stocks obtained by infecting ultraviolet (UV)-irradiated or unirradiated CV-1 monkey kidney cells with UV-irradiated or unirradiated temperature-sensitive SV40 mutant tsB201 was investigated. The frequency of reversion of the ts mutant to phenotypically wild-type virus was determined by assaying the virus stocks at permissive (33 degrees) and non-permissive (39 degrees) temperatures. These data show that (a) the reversion frequency for unirradiated virus propagated in irradiated cells was more than that in unirradiated cells; (b) irradiated virus gave more reversion than unirradiated virus in unirradiated and irradiated cells; and (c) irradiated virus had a lower reversion frequency in irradiated cells than in unirradiated cells. Reactivation experiments carried out in parallel; with the mutagenesis showed enhanced reactivation in UV-irradiated SV40 in UV-irradiated CV-1 cells. We conclude that enhanced reactivation of UV-irradiated SV40 was not mutagenic in monkey kidney cells.

Action spectrum for the in vitro induction of simian virus 40 by ultraviolet radiation

A line of simian virus 40-transformed hamster kidney cells was exposed to ultraviolet radiation at eleven different wavelengths in the region 238-302 nm. An action spectrum derived from the resulting exposure-response curves for the induction of simian virus 40 from these cells exhibits a broad peak in the region 260-270 nm suggesting DNA as the major chromophore for this response. This conclusion is consistent with results obtained by other investigators who have noted viral induction by a number of DNA-damaging agents.

Effect of caffeine on induction of endogenous type C virus in mouse cells in vitro

The effect of caffeine on the expression of murine endogenous virus in mouse cells induced by radiation and chemicals was studied. Postirradiation treatment of K-BALB cells with caffeine enhanced cell killing as well as the induction of xenotropic virus after ultraviolet light irradiation. The degree of enhancement for the virus induction was comparable to that for cell killing. On the other hand, colony-forming ability and the expression of xenotropic virus of K-BALB cells after X-irradiation were unaffected by caffeine. These data suggest a linear relationship between the degree of endogenous virus expression and the amount of lethal damages after irradiation. For induction by halogenated pyrimidines, a 24-hr incubation of AKR2B cells with caffeine after 5-iodo-2'-deoxyuridine treatment resulted in marked suppression of the expression of ecotropic virus. On the contrary, in K-BALB cells, caffeine exerted only a small effect on 5-iodo-2'-deoxyuridine-induced expression of ecotropic and xenotropic viruses. These results indicate that, although using the same inducing agent, the pathway of endogenous virus induction may be different for AKR2B cells and for K-BALB cells.

Inhibition of cellular DNA synthesis by vesicular stomatitis virus

DNA synthesis in mouse myeloma (MPC-11) cells and L cells was rapidly and progressively inhibited by infection with vesicular stomatitis virus (VSV). No significant difference in cellular DNA synthesis inhibition was noted between synchronized and unsynchronized cells, nor did synchronized cells vary in their susceptibility to VSV infection after release from successive thymidine and hydroxyurea blocks. Cellular RNA synthesis was inhibited to about the same extent as DNA synthesis, but cellular protein synthesis was less affected by VSV at the same multiplicity of infection. The effect of VSV on cellular DNA synthesis could not be attributed to degradation of existing DNA or to decreased uptake of deoxynucleoside triphosphates, nor were DNA polymerase and thymidine kinase activities significantly different in VSV-infected and uninfected cell extracts. Analysis by alkaline sucrose gradients of DNA in pulse-labeled uninfected and VSV-infected cells indicated that VSV infection did not appear to influence DNA chain elongation. Cellular DNA synthesis was not significantly inhibited by infection with the VSV polymerase mutant tsG114(I) at the restrictive temperature or by infection with defective-interfering VSV DI-011 (5' end of the genome), but DI-HR-LT (3' end of genome) exhibited initially rapid but not prolonged inhibition of MPC-11 cell DNA synthesis. DNA synthesis inhibitory activity of wild-type VSV was only slowly and partially inactivated by very large doses of UV irradiation. These data suggest that, as in the effect of VSV on cellular RNA synthesis (Weck et al., J. Virol. 30:746-753, 1979), inhibition of cellular DNA synthesis by VSV requires transcription of a small segment of the viral genome.

Transformation of ultraviolet-irradiated human fibroblasts by simian virus 40 is enhanced by cellular DNA repair functions

Human fibroblasts irradiated with ultraviolet light were either tested for survival (colony formation) or infected with simian virus 40 and examined for transformation (foci formation). For normal cell cultures, the fractions of surviving colonies which were also transformed increased with increasing irradiation dose. In contrast, little increase in the transformation of ultraviolet-irradiated repair-deficient (xeroderma pigmentosum and xeroderma pigmentosum variant) cells was observed. Similar experiments with xeroderma pigmentosum variant cells treated with caffeine following irradiation indicated that, under these conditions, the deficient cells produced more transformants among the survivors of ultraviolet irradiation than did unirradiated cells. These results suggest (1) that DNA repair functions, not DNA damage per se, are required for enhanced viral transformation in normal cells; (2) that functions involved in excision repair and functions needed for replication of ultraviolet-damaged DNA appear necessary for this stimulation; and (3) that blocking DNA replication in ultraviolet-irradiated xeroderma pigmentosum variant cells by caffeine enhances viral transformation.

Enhancement of host cell reactivation of ultraviolet-irradiated Herpes simplex virus by caffeine, hydroxyurea and 5-bromodeoxyuridine

Enhancement of host cell reactivation (HCR) of ultraviolet (UV)-irradiated herpes simplex virus (HSV) was demonstrated in cell cultures pretreated with caffeine, hydroxyurea, or 5-bromodeoxyuridine (BrdUrd). The effect of caffeine on HCR was shown to depend on the time of drug treatment with respect to infection. In cultures treated with caffeine during the course of virus replication, the infectivity of irradiated HSV was reduced about nine-fold, while cultures pretreated with the drug before infection showed an increase in infectivity. The extent of HCR enhancement depended on the time interval between treatment with caffeine and infection, drug concentration, and the UV irradiation dose to which HSV was exposed. Magnitude of enhancement of HCR by caffeine differed in various cell species. The results suggest that enhanced HCR of UV-irradiated HSV by DNA antimetabolities is associated with DNA repair activated in consequence of cell DNA damage.

The effect of 8-methoxypsoralen-plus ultraviolet light on cell-virus interaction: the transforming infection; effect of PUVA on the transformation of baby hamster kidney cells by polyoma virus

Pre-treatment of baby hamster kidney (BHK) cells with 8-methoxypsoralen (8-MOP) plus ultraviolet (UV) light enhances the frequency of their transformation by polyoma (Py) virus. Of the doses tested, 0.5 microgram/ml 8-MOP plus 0.3 J/cm2 UV-light results in maximal (30-fold) stimulation of viral transformation. 8-MOP alone does not affect viral transformation and UV-light alone causes only a slight increase in the transformation frequency. Thus the drug and light act synergistically in promoting the effect. Treatment of BHK cells with drug plus light without Py infection does not lead to a transformed morphology. A drug-light combination (0.01 microgram/ml 8-MOP plus 1.2 J/cm2 UV) that inhibits cellular DNA synthesis to 75% of control at 28 hr after treatment results in a 6-fold stimulation of the transformation frequency.

Biochemical transformation of deoxythymidine kinase-deficient mouse cells with UV-irradiated equine herpesvirus type 1

A line of 3T3 mouse cells lacking deoxythymidine kinase (dTK-) was stably transformed to the dTK+ phenotype after exposure to UV-irradiated equine herpesvirus type 1 (EHV-1). Biochemical transformants were isolated in a system selective for the dTK+ phenotype (Eagle minimal essential medium containing 10(-4) M hypoxanthine, 6 X 10(-7) M aminopterin, and 2 X 10(-5) M deoxythymidine). Transformation was accompanied by the acquisition of a dTK activity with immunological, electrophoretic, and biochemical characteristics identical to those of the dTK induced by EHV-1 during productive infection. The transformed cells have been maintained in selective culture medium for more than 50 passages and have retained the capacity to express EHV-1--specific antigens. Spontaneous release of infectious virus has not been detected in the transformed lines, and the the cells were not oncogenic for athymic nude mice. In contrast to normal dTk+ 3T3 cells, EHV-1 transformants were unable to grow in the presence of arabinosylthymine, a drug selectively phosphorylated by herpesvirus-coded dTK's. These results indicate that a portion of the EHV-1 genome is able to persist in the transformed cells for many generations and be expressed as an enzymatically active viral gene product.