Mechanism of the antimutagenic action of dibunol

In experiments with cultured V-79 Chinese hamster cells a study was made of the influence of dibunol on the level of gamma-radiation-induced micronuclei and sedimentation properties of cell nucleoids during ultracentrifugation in a neutral sucrose gradient. Protection of DNA molecule against the effects of both primary and secondary damages was found to be involved in the mechanism of the protective action of dibunol.     

Mechanism of the antimutagenic effect of interferon in human fibroblasts based on induced protein analysis]

Proteins induced in human fibroblasts after treatment of some antimutagens (interferon, p-aminobenzoic acid, heating and vaccinia virus infection) were identified by means of polyacrylamide gel electrophoresis (10-15%) followed by fluorography of the gel. Influenza virus proteins (A/WSN/33) were used as markers to determine the molecular weights of the new proteins. The results obtained suggest that interferon, p-aminobenzoic acid, heating and vaccinia virus infection induced proteins with mol. weights of 24 and 18 kD except the protein with 76 kD observed only after heating insult.     

An approach for determining the capacity of human cells to repair gamma-induced DNA damage using interferon

The method of ultracentrifugation of a nucleoid in a neutral sucrose gradient in the presence of ethidium bromide was used to detect gamma radiation-induced DNA breaks and their resynthesis in human HEp-2 cells and fibroblasts taken from a skin biopsy of patients with homocystinuria (HCN). In HEp-2 cells pretreated with interferon the nucleoid sedimentation rate after gamma irradiation did not differ from that in intact cells, that is, interferon exerted its protective effect whereas in HCN cells interferon was ineffective. After incubation with interferon, the resynthesis of the induced breaks was enhanced in these cells as well.     

The interrelation of the antimutagenic action of mannitol to its effect on cellular metabolic processes]

The mannitol influence on mutagenesis of ionizing radiation and cyclophosphate has been studied in albino mongrel rats using the methods of genetic and biochemical analysis. N correlation is determined between antimutagenic action of this preparation and a decrease of malondialdehyde content in cells and free fractions of matrix lysosomes (beta-galactosidase; N-acetyl-beta-D-glucosaminidase) and firmly membrane-structurized microsomal (glucose-6-phosphatase) enzymes, whose level increases under the influence of mutagens. It is shown that, one of the way of antimutagenic actions of mannitol is connected with mutagenesis correction at the stage of origin of mutagenic products and their transport to chromosome DNA.     

Supervision of cellular response to radiation by human interferon

Human interferon (HuIFN) conferred human RSa cells to increased resistance to ultraviolet light, 4-nitroquinoline-1-oxide and X-ray in association with enhancement of DNA-repair capacity. The HuIFN actions were summarized by the supervision of cellular response, possibly via plasminogen activator-like protease induction.     

Decreased DNA repair capacity of UV-irradiated cells following interferon treatment

The aim of this study was to examine the effect of interferons (IFNs) on the recovery of UV-damaged cells by means of measuring cell viability rates. The influence of the recombinant human interferons IFN-alpha, IFN-beta and IFN-gamma on the repair capacity of the UV-irradiated human cell lines WISH and HeLa was studied. The ability of cells to repair UV-induced damage was determined by the comet assay and both short- and long-term survival assays in proliferating cell cultures. We found that INFs negatively regulated DNA repair in cells damaged by UV light. One day after treatment, in both cell lines tested, IFN-alpha had a stronger inhibitory effect than IFN-gamma. Combined treatment with different IFNs exhibited a stronger inhibitory effect on cell recovery than treatment with each of them. The protein kinase inhibitor wortmanin further aggravated the effect of IFNs on cell survival.     

Effects of human interferon on cellular response to UV in UV-sensitive human cell strains

Cells of a human RSa cell line, with high sensitivity to UV killing and low capacity for DNA repair, when pretreated with 1-100 units/ml of human interferon (HuIFN) preparations for more than 12 h before irradiation, acquired an enhancement of UV-induced DNA-repair replication synthesis in association with recovery from inhibition of total cellular DNA synthesis and UV survival. Prompt and transient induction of plasminogen activator activities was also found within 5 min after UV irradiation in the cells pretreated with HuIFN but not in the cells non-pretreated with HuIFN. The enhancement and induction effects of HuIFN were observed, irrespective of the kind of HuIFN preparation used (alpha, beta or gamma, and natural or recombinant) and in other UV-sensitive fibroblast cells which were derived from Cockayne syndrome and xeroderma pigmentosum fibroblasts (XP1KY). However, all of the enhancement of DNA-repair synthesis and the induction of plasminogen activator activities by HuIFN was suppressed by treatment with cycloheximide immediately after UV irradiation.     

Mechanism of action of interferon is linked to its ability to protect the cell from interstrand cross-linking of DNA, induced by 8-methoxypsoralen, activated by long-wave UV-light

Treatment of human lymphocytes in the G1 phase of mitotic cycle with human lymphoblastoid interferon (Ly-IFN) decreased the frequencies of chromosome aberrations induced by 8-methoxy-psoralen-induced interstrand cross-links. Anticlastogenic effect of Ly-IFN was accompanied by stimulation of unscheduled synthesis of DNA in the G2 phase of mitotic cycle, as shown by increased percent of labeled cells registered by 3H-thymidine autoradiography. The data obtained seem to indicate that the mechanism of Ly-IFN protection is connected with stimulation of postreplicative repair.     

A defense mechanism of human cells in the radioadaptive response and antimutagenic activity of interferon has common paths

The radioadaptive response was assessed by the chromosome aberration test in lymphocytes of humans with hereditary diseases of connective tissue, which were earlier characterized as repair-deficient: Marfan syndrome (SM), Elers-Danlos syndrome (E-D), and homocystinurea (HCU). The radioadaptive response was observed in cells of patients with Marfan syndrome and Elers-Danlos syndrome but not in cells of patients with homocystinurea. Parameters of cell protection against gamma-irradiation at radioadaptive response were similar to those obtained in cells pretreated with interferon. These data indicate, first, the possibility that repair pathways and the radioadaptive response are independent and second, that there are common pathways of protection upon radioadaptive response and the antimutagenic action of interferon.     

Sendai virus C proteins must interact directly with cellular components to interfere with interferon action

Sendai virus (SeV) infection of interferon (IFN)-competent cells is one of the most efficient ways of inducing IFN production. Virus replication is nevertheless largely unaffected, since SeV infection also interfers with IFN action, a prerequisite for the establishment of an antiviral state. This property has been mapped by reverse genetics to the viral C gene, which is also known to act as a promoter-specific inhibitor of viral RNA synthesis. Using luciferase reporter plasmids containing IFN-responsive promoters, we have found that all four C proteins effectively interdict IFN signaling when expressed independently of SeV infection. The C proteins must therefore interact directly with cellular components to carry this out. The C gene in the context of an SeV infection was also found to induce STAT1 instability in some cells, whereas in other cells it apparently acts to prevent the synthesis of STAT1 in response to the virus infection or IFN treatment. The SeV C proteins appear to act in at least two ways to counteract the IFN induced by SeV infection.     

Pleotrophic action of interferon gamma in human orbital fibroblasts

Analysis of the two-dimensional electrophoretic patterns of total radiolabeled cellular proteins derived from human orbital fibroblast cultures revealed that interferon gamma (100 U/ml) elicited significant quantitative changes in 42% of 86 randomly-selected proteins relative to untreated cultures. The most substantial up-regulation involved a protein with pI/mw map coordinates of 5.9/54,000 and a heterogenous 5 isoform protein cluster (pIs = 6.1–5.6) of approximately 47- to 50-kDa. These proteins were identified as the previously described 54-kDa protein inducible in interferon gamma-sensitive cell types and type-1 plasminogen activator inhibitor (PAI-1), respectively. Definition of PAI-1 as an interferon gamma-responsive protein in orbital fibroblasts was confirmed by immunoprecipitation using PAI-1-specific antibodies. Induction of PAI-1 and the 54-kDa protein in orbital fibroblasts, moreover, was relatively specific for interferon gamma since interferon alpha failed to initiate a similar inductive response. The synthesis of a 170 kDa protein, tentatively identified as a collagen, was decreased by approximately 80%. Analysis of the labeled proteins secreted into the culture medium revealed that interferon gamma increased the medium content of fibronectin and decreased the secretion of collagen. It would appear from these data that the inflammatory cytokine can exert regulatory effects on the synthesis of many specific proteins in orbital fibroblasts.