Enhancement of viral and DNA mediated transformation of cloned rat embryo fibroblast cells by 3-aminobenzamide

Low dose ionizing radiation strongly stimulates insertional mutagenesis in a γH2AX dependent manner

Extrachromosomal DNA can integrate into the genome with no sequence specificity producing an insertional mutation. This process, which is referred to as random integration (RI), requires a double stranded break (DSB) in the genome. Inducing DSBs by various means, including ionizing radiation, increases the frequency of integration. Here we report that non-lethal physiologically relevant doses of ionizing radiation (10-100 mGy), within the range produced by medical imaging equipment, stimulate RI of transfected and viral episomal DNA in human and mouse cells with an extremely high efficiency. Genetic analysis of the stimulated RI (S-RI) revealed that it is distinct from the background RI, requires histone H2AX S139 phosphorylation (γH2AX) and is not reduced by DNA polymerase θ (Polq) inactivation. S-RI efficiency was unaffected by the main DSB repair pathway (homologous recombination and non-homologous end joining) disruptions, but double deficiency in MDC1 and 53BP1 phenocopies γH2AX inactivation. The robust responsiveness of S-RI to physiological amounts of DSBs can be exploited for extremely sensitive, macroscopic and direct detection of DSB-induced mutations, and warrants further exploration in vivo to determine if the phenomenon has implications for radiation risk assessment.

PEA3 sites within the progression elevated gene-3 (PEG-3) promoter and mitogen-activated protein kinase contribute to differential PEG-3 expression in Ha-ras and v-raf oncogene transformed rat embryo cells

Transformation of normal cloned rat embryo fibroblast (CREF) cells with cellular oncogenes results in acquisition of anchorage-independent growth and oncogenic potential in nude mice. These cellular changes correlate with an induction in the expression of a cancer progression-promoting gene, progression elevated gene-3 (PEG-3). To define the mechanism of activation of PEG-3 as a function of transformation by the Ha-ras and v-raf oncogenes, evaluations of the signaling and transcriptional regulation of the approximately 2.0 kb promoter region of the PEG-3 gene, PEG-Prom, was undertaken. The full-length and various mutated regions of the PEG-Prom were linked to a luciferase reporter construct and tested for promoter activity in CREF and oncogene-transformed CREF cells. An analysis was also performed using CREF cells doubly transformed with Ha-ras and the Ha-ras specific suppressor gene Krev-1, which inhibits the transformed phenotype in vitro. These assays document an association between expression of the transcription regulator PEA3 and PEG-3. The levels of PEA3 and PEG-3 RNA and proteins are elevated in the oncogenically transformed CREF cells, and reduced in transformation and tumorigenic suppressed Ha-ras/Krev-1 doubly transformed CREF cells. Enhanced tumorigenic behavior, PEG-3 promoter function and PEG-3 expression in Ha-ras transformed cells were all dependent upon increased activity within the mitogen-activated protein kinase (MAPK) pathway. Electrophoretic mobility shift assays and DNase I footprinting experiments indicate that PEA3 binds to sites within the PEG-Prom in transformed rodent cells in an area adjacent to the TATA box in a MAPK-dependent fashion. These findings demonstrate an association between Ha-ras and v-raf transformation of CREF cells with elevated PEA3 and PEG-3 expression, and they implicate MAPK signaling via PEA3 as a signaling cascade involved in activation of the PEG-Prom.

Ionizing radiation greatly improves gene transfer efficiency in mammalian cells

The vast majority of clinical protocols involving gene therapy today rely on viral vectors for gene transduction. The primary reason that plasmid vectors have not been widely used for gene therapy trials is their relatively low rate of stable gene transfer. We show here that ionizing radiation can improve plasmid transfection efficiency in both normal and neoplastic human and mouse cells. As high as 1,400-fold improvement in transfection efficiency can be seen in primary human fibroblasts treated with 9 Gy. Radiation improves transfection efficiency in a dose-dependent manner of only linearized plasmid DNA in transformed or immortalized cells, but of both linearized and supercoiled plasmid in normal human fibroblasts. The gene transfer dose-response curves are linear for neoplastic cell lines and exponential for primary cell lines. This suggests that radiation can improve gene integration by at least two mechanisms, one that may require free DNA ends and one that does not. The 2-hr delay described here, from the time of irradiation to the beginning of enhanced gene integration, suggests an inducible process that becomes active after the bulk of the radiation damage has been repaired. Our data further suggest that radiation may be useful to target human gene therapy using plasmid vectors.

Functional expression of human poly(ADP-ribose) polymerase in Schizosaccharomyces pombe results in mitotic delay at G1, increased mutation rate, and sensitization to radiation

The activity of poly(ADP-ribose) polymerase (PADPRP), a chromatin-associated enzyme present in most eukaryotic cells, is stimulated by DNA strand breaks, suggesting a role for the enzyme in the cellular response to DNA damage. However, the primary function of PADPRP remains unknown. We have selected Schizosaccharomyces pombe as a simple eukaryotic system in which to study PADPRP function because this fission yeast shares with mammalian cells important cellular features possibly associated with poly-(ADP-ribos)ylation pathways. We investigated the existence of an endogenous yeast PADPRP by DNA and RNA hybridization to mammalian probes under low-stringency conditions and by PADPRP activity assays. Our data indicate that fission yeasts are naturally devoid of PADPRP. We therefore isolated S. pombe strains expressing PADPRP by transformation with a human full-length PADPRP cDNA under the control of the SV40 early promoter. The human PADPRP construct was transcribed and translated in S. pombe, generating a major transcript of the same size (3.7 kb) as that detected in mammalian cells and a 113-kDa polypeptide, identical in size to the native human PADPRP protein. Yeast recombinant PADPRP was enzymatically active and was recognized by antibodies to human PADPRP. S. pombe cells expressing PADPRP (SPT strains) showed a stable phenotype that was characterized by: (i) cell cycle retardation as a result of a specific delay at the G1 phase, (ii) decreased cell viability in stationary cultures, (iii) enhanced rates of spontaneous and radiation-induced ade6-ade7 mutations, and (iv) increased sensitivity to radiation. SPT strains may prove efficient tools with which to investigate PADPRP functions in eukaryotic cells.

Genetic analysis of carcinogen enhancement of type 5 adenovirus transformation of cloned Fischer rat embryo fibroblast cells

Pretreatment of CREF cells with methyl methanesulfonate (MMS) before infection with the host-range cold-sensitive type 5 adenovirus (Ad5) mutant H5hr1 results in a dose-dependent carcinogen enhancement of viral transformation (CET). The properties of CET observed with H5hr1, which include both an MMS dose-dependent enhancement in the number of transformed foci and an increase in transformation frequency after correction for cell toxicity, are not observed in carcinogen-pretreated wild-type (wt) Ad5 (H5wt)-infected CREF cells. This study was conducted to determine the role of the viral E1A and E1B transforming genes of H5hr1 in mediating the unique CET phenotype of H5hr1. Coinfection of MMS-pretreated CREF cells with H5wt or H5sub309 (which displays a wt Ad5 phenotype) and H5hr1 resulted in a suppression of the unique CET phenotype that was directly related to the multiplicity of infection with wt Ad5. Suppression of the unique H5hr1 CET phenotype was also apparent in MMS-pretreated CREF cells coinfected with H5hr1 and an Ad5 mutant expressing either a wt 13S E1A-encoded 289 amino-acid (aa) protein and an intact wt E1B gene or a wt 13S E1A-encoded 289-aa protein and a 22S E1B-encoded 495-aa protein. In contrast, the unique H5hr1 CET phenotype was not suppressed in MMS-pretreated CREF cells coinfected with H5hr1 and Ad5 or Ad2 mutants expressing either a wt 12S E1A-encoded 243-aa protein and both wt E1B gene products or an intact wt E1A gene and a wt E1B 13S-encoded 175-aa protein. That genetic changes in both the E1A and E1B viral regions of H5hr1 were required to induce the unique CET phenotype was also indicated by the inability of a recombinant Ad5 containing the 0-4.5 map-unit region of H5hr1 and the 4.5-100 map-unit region of H5sub309 to display the H5hr1 unique CET phenotype. Direct confirmation of the requirement for both gene regions of H5hr1 to mediate its unique CET was obtained by generating CREF cells stably expressing a wt Ad5 E1A 13S-encoded 289-aa protein and a wt E1B 22S-encoded 495-aa protein. In these CREF transformants (which displayed a CREF-like morphology), transformation by H5hr1 was not reduced, but the unique CET phenotype after MMS pretreatment was eliminated. These results suggest that alterations in both the 13S-encoded E1A and 22S-encoded E1B gene products of H5hr1 contribute to its unique CET.

Poly(ADP-ribose) polymerase activity in mononuclear leukocytes of 13 mammalian species correlates with species-specific life span

Poly(ADP-ribosyl)ation is a eukaryotic posttranslational modification of proteins that is strongly induced by the presence of DNA strand breaks and plays a role in DNA repair and the recovery of cells from DNA damage. We compared poly(ADP-ribose) polymerase (PARP; EC 2.4.2.30) activities in Percoll gradient-purified, permeabilized mononuclear leukocytes from mammalian species of different maximal life span. Saturating concentrations of a double-stranded octameric oligonucleotide were applied to provide a direct and maximal stimulation of PARP. Our results on 132 individuals from 13 different species yield a strong positive correlation between PARP activity and life span (r = 0.84; P << 0.001), with human cells displaying approximately 5 times the activity of rat cells. Intraspecies comparisons with both rat and human cells from donors of all age groups revealed some decline of PARP activity with advancing age, but it was only weakly correlated. No significant polymer degradation was detectable under our assay conditions, ruling out any interference by poly(ADP-ribose) glycohydrolase activity. By Western blot analysis of mononuclear leukocytes from 11 species, using a crossreactive antiserum directed against the extremely well-conserved NAD-binding domain, no correlation between the amount of PARP protein and the species' life spans was found, suggesting a greater specific enzyme activity in longer-lived species. We propose that a higher poly(ADP-ribosyl)ation capacity in cells from long-lived species might contribute to the efficient maintenance of genome integrity and stability over their longer life span.

Suppression of adenovirus type 5 E1A-mediated transformation and expression of the transformed phenotype by caffeic acid phenethyl ester (CAPE)

Viral transformation and DNA-transfection assays were employed to investigate the differential toxic effect of caffeic acid phenethyl ester (CAPE), an extract of the honeybee hive product propolis, on adenovirus type 5 (Ad5)-transformed cloned rat embryo fibroblast (CREF) cells. CAPE inhibited, in a dose-dependent manner, both de novo and carcinogen-enhanced transformation of CREF cells by H5hr1, the cold-sensitive (cs) host-range mutant of Ad5. CAPE had a selective inhibitory effect on Ad5-induced transformation when a wild-type (wt) Ad5 E1A gene or a cs Ad5 E1A gene (at 37 degrees C, but not at 32 degrees C) was cotransfected into CREF cells with a dominant-acting bacterial hygromycin-resistance gene. A requirement for the expression of Ad5 E1A-encoded mRNAs and transforming proteins and sensitivity to CAPE was demonstrated using CREF cells stably transformed by a cs Ad5 E1A gene and an Ad5 E1A gene under the transcriptional control of a mouse mammary tumor virus promoter. To distinguish between the effects of the two Ad5 E1A-encoded proteins of 289 amino acids (aa) and 243 aa, CREF cells were stably transformed with cDNAs encoding either the 13S or the 12S E1A mRNA. CREF cells expressing the 13S E1A-encoded 289-aa protein were more sensitive to the growth-suppressing effect of CAPE than cells producing only the 12S E1A-encoded 243-aa protein. However, the growth-suppressing and toxic effects of CAPE were greatest in cells expressing both E1A-encoded transforming proteins. Analysis of the effect of CAPE on E1A and beta-actin gene expression in wt and cs E1A and H5hr1-transformed CREF cells indicated that low levels of CAPE, which were growth suppressive, did not selectively suppress E1A expression. These results demonstrated that cellular changes induced in CREF cells by the 13S E1A-encoded 289-aa protein of Ad5, when expressed alone or in combination with the 12S E1A-encoded 243-aa protein, rendered transformed cells sensitive to the growth-suppressing and toxic effects of CAPE.

Low-level beta 1 protein kinase C expression in cloned rat embryo fibroblast cells enhances transformation induced by the adenovirus type 5 E1A gene

Expression of the E1A gene of adenovirus type 5 (Ad5) in a cloned rat embryo fibroblast (CREF) cell line results in morphological transformation. The efficiency of E1A-mediated transformation of CREF cells is increased if a wild-type Ad5 E1A gene is cotransfected with a rat beta 1 protein kinase C (beta 1 PKC) gene. A direct demonstration of complementation between a functional-transforming Ad5 E1A gene and beta 1 PK in inducing transformation was demonstrated using Ad5 E1A cold-sensitive mutant (E1Acs) genes. The E1Acs gene enhanced transformation only at the transformation-permissive temperature of 37 degrees C and not at the nonpermissive transforming temperature of 32 degrees C. CREF cells constitutively expressing low levels of beta 1 PKC mRNA were transformed at a higher frequency than parental CREF cells after transfection with an Ad5 E1A gene or infection with wild-type Ad5 or the Ad5 host-range cold-sensitive mutant H5hr1. There was no enhancement of transformation in low-level beta 1 PKC-expressing CREF cells when cultures were grown continuously in the presence of the PKC-inhibitor 1-(5-isoquinolynsulfonyl)-2-methylpiperazine dihydrochloride. Transfected CREF cells expressing low levels of beta 1 PKC mRNA displayed CREF-like morphology and did not form colonies when grown in agar. In contrast, retroviral vector-transformed CREF cells expressing high levels of beta 1 PKC mRNA and beta 1 PKC enzyme activity were morphologically transformed and grew efficiently in agar. These findings indicate that the beta 1 PKC gene, when expressed at low levels, can cooperate with the Ad5 E1A gene in the initiation of viral oncogene-mediated transformation.