DNA Photodamage, Repair, Gene Induction and Genotoxicity Following Exposures to 254 nm UV and 8-Methoxypsoralen Plus UVA in a Eukaryotic Cell System

Essential Oils as Multicomponent Mixtures and Their Potential for Human Health and Well-Being

Essential oils (EOs) and their individual volatile organic constituents have been an inherent part of our civilization for thousands of years. They are widely used as fragrances in perfumes and cosmetics and contribute to a healthy diet, but also act as active ingredients of pharmaceutical products. Their antibacterial, antiviral, and anti-inflammatory properties have qualified EOs early on for both, the causal and symptomatic therapy of a number of diseases, but also for prevention. Obtained from natural, mostly plant materials, EOs constitute a typical example of a multicomponent mixture (more than one constituent substances, MOCS) with up to several hundreds of individual compounds, which in a sophisticated composition make up the property of a particular complete EO. The integrative use of EOs as MOCS will play a major role in human and veterinary medicine now and in the future and is already widely used in some cases, e.g., in aromatherapy for the treatment of psychosomatic complaints, for inhalation in the treatment of respiratory diseases, or topically administered to manage adverse skin diseases. The diversity of molecules with different functionalities exhibits a broad range of multiple physical and chemical properties, which are the base of their multi-target activity as opposed to single isolated compounds. Whether and how such a broad-spectrum effect is reflected in natural mixtures and which kind of pharmacological potential they provide will be considered in the context of ONE Health in more detail in this review.

Applications of Essential Oils as Antibacterial Agents in Minimally Processed Fruits and Vegetables—A Review

Microbial foodborne diseases are a major health concern. In this regard, one of the major risk factors is related to consumer preferences for “ready-to-eat” or minimally processed (MP) fruits and vegetables. Essential oil (EO) is a viable alternative used to reduce pathogenic bacteria and increase the shelf-life of MP foods, due to the health risks associated with food chlorine. Indeed, there has been increased interest in using EO in fresh produce. However, more information about EO applications in MP foods is necessary. For instance, although in vitro tests have defined EO as a valuable antimicrobial agent, its practical use in MP foods can be hampered by unrealistic concentrations, as most studies focus on growth reductions instead of bactericidal activity, which, in the case of MP foods, is of utmost importance. The present review focuses on the effects of EO in MP food pathogens, including the more realistic applications. Overall, due to this type of information, EO could be better regarded as an “added value” to the food industry.

Hrq1, a homolog of the human RecQ4 helicase, acts catalytically and structurally to promote genome integrity

Human RecQ4 (hRecQ4) affects cancer and aging but is difficult to study because it is a fusion between a helicase and an essential replication factor. Budding yeast Hrq1 is homologous to the disease-linked helicase domain of RecQ4 and, like hRecQ4, is a robust 3'-5' helicase. Additionally, Hrq1 has the unusual property of forming heptameric rings. Cells lacking Hrq1 exhibited two DNA damage phenotypes: hypersensitivity to DNA interstrand crosslinks (ICLs) and telomere addition to DNA breaks. Both activities are rare; their coexistence in a single protein is unprecedented. Resistance to ICLs requires helicase activity, but suppression of telomere addition does not. Hrq1 also affects telomere length by a noncatalytic mechanism, as well as telomerase-independent telomere maintenance. Because Hrq1 binds telomeres in vivo, it probably affects them directly. Thus, the tumor-suppressing activity of RecQ4 could be due to a role in ICL repair and/or suppression of de novo telomere addition.

The rise and fall of photomutagenesis

UV is the most abundant human carcinogen, and protection from extensive exposure to it is a widespread human health issue. The use of chemicals (sunscreens) for protection is intuitive and efficacious. However, these chemicals may become activated to reactive intermediates when absorbing energy from UV, thus producing damage themselves, which may manifest itself in phototoxic, photoallergenic or photocarcinogenic reactions in humans. The development of safe sunscreens for humans is of high interest. Similar issues have been observed for some therapeutically used principles such as PUVA therapy for psoriasis or porphyrins for phototherapy of human cancers. Photoactivation has also been reported as a side effect of various pharmaceuticals such as the antibacterial fluoroquinolones. In this context, the authors have been involved over more than 20 years in the development and refinement of assays to test for photomutagenicity as an unwanted side effect of UV-mediated activation of such chemicals for cosmetic or pharmaceutical use. The initial years of great hopes for simple mammalian cell-based assays for photomutagenicity to screen out substances of concern for human use were followed by many years of collaborative trials to achieve standardization. However, it is now realized that this topic, albeit of human safety relevance, is highly complex and subject to many artificial modifiers, especially in vitro in mammalian cell culture. Thus, it is not really suitable for being engineered into a general testing framework within cosmetic or pharmaceutical testing guidelines. Much knowledge has been generated over the years to arrive at the conclusion that yes, photomutagenicity does exist with the use of chemicals, but how to best test for it will require a sophisticated case-by-case approach. Moreover, in comparison to the properties and risks of exposure to UV itself, it remains a comparatively minor human safety risk to address. In considering risks and benefits, we should also acknowledge beneficial effects of UV on human health, including an essential role in the production of Vitamin D. Thus, the interrelationships between UV, chemicals and human health remain a fascinating topic of research.

The antimicrobial activity of thyme essential oil against multidrug resistant clinical bacterial strains

AIM

The aim of this work was to investigate the antimicrobial activity of thyme essential oil against clinical multidrug resistant strains of Staphylococcus, Enterococcus, Escherichia, and Pseudomonas genus.

MATERIALS

The antibacterial activity of oil was tested against standard strains of bacteria and 120 clinical strains isolated from patients with infections of the oral cavity, abdominal cavity, respiratory and genitourinary tracts, skin, and from the hospital environment.

METHODS

Agar diffusion was used to determine the microbial growth inhibition of bacterial growth at various concentrations of oil from Thymus vulgaris. Susceptibility testing to antibiotics was carried out using disk diffusion.

RESULTS

Thyme essential oil strongly inhibited the growth of the clinical strains of bacteria tested.

CONCLUSIONS

The use of phytopharmaceuticals based on an investigated essential oil from thyme in the prevention and treatment of various human infections may be reasonable.

Effects of xanthotoxin treatment on trichothecene production in Fusarium sporotrichioides

There are 4 P450 oxygenases involved in the biosynthesis of T-2 toxin in Fusarium sporotrichioides. Exactly how these enzymes react to antimicrobial plant defense compounds is unknown. Xanthotoxin (8-methoxypsoralen) is a phototoxic furanocoumarin that acts as a P450 oxygenase inhibitor. The current study shows that the addition of concentrations of 1.0 mmol/L or less of xanthotoxin to liquid cultures of F. sporotrichioides NRRL3299 can effectively block T-2 toxin production and cause an increase in accumulation of trichodiene, the hydrocarbon precursor of trichothecenes. The addition of xanthotoxin to liquid cultures of a trichodiene-accumulating F. sporotrichioides Tri4- mutant caused a 3- to 10-fold increase in trichodiene accumulation, suggesting that xanthotoxin not only blocks trichothecene oxygenation reactions, but may in some way also promote the synthesis of trichodiene. Feeding studies showed that 2 of the 4 P450 oxygenases, TRI4 and TRI1, were more sensitive to xanthotoxin, while oxygenases TRI11 and TRI13 were unaffected. Quantitative reverse-transcriptase PCR indicated that several of the genes in the toxin biosynthetic pathway were upregulated by xanthotoxin, with Tri4 showing the highest increase in expression. These results indicate that while xanthotoxin inhibits specific P450 oxygenase activity, it also has an effect on gene expression.

Biological effects of essential oils--a review

Since the middle ages, essential oils have been widely used for bactericidal, virucidal, fungicidal, antiparasitical, insecticidal, medicinal and cosmetic applications, especially nowadays in pharmaceutical, sanitary, cosmetic, agricultural and food industries. Because of the mode of extraction, mostly by distillation from aromatic plants, they contain a variety of volatile molecules such as terpenes and terpenoids, phenol-derived aromatic components and aliphatic components. In vitro physicochemical assays characterise most of them as antioxidants. However, recent work shows that in eukaryotic cells, essential oils can act as prooxidants affecting inner cell membranes and organelles such as mitochondria. Depending on type and concentration, they exhibit cytotoxic effects on living cells but are usually non-genotoxic. In some cases, changes in intracellular redox potential and mitochondrial dysfunction induced by essential oils can be associated with their capacity to exert antigenotoxic effects. These findings suggest that, at least in part, the encountered beneficial effects of essential oils are due to prooxidant effects on the cellular level.

Antioxidant activity of diphenyl diselenide prevents the genotoxicity of several mutagens in Chinese hamster V79 cells

Diphenyl diselenide (DPDS) is an electrophilic reagent used in the synthesis of a variety of pharmacologically active organic selenium compounds. Studies have shown its antioxidant, hepatoprotective, neuroprotective, anti-inflammatory, and antinociceptive effects. We recently showed the antioxidant effect of DPDS in V79 cells, and established the beneficial and toxic doses of this compound in this cell line. Here, we report the antigenotoxic and antimutagenic properties of DPDS, investigated by using a permanent lung fibroblast cell line derived from Chinese hamsters. We determined the cytotoxicity by clonal survival assay, and evaluated DNA damage in response to several mutagens by comet assay and micronucleus test in binucleated cells. In the clonal survival assay, at concentrations ranging from 1.62 to 12.5microM, DPDS was not cytotoxic, while at concentrations up to 25microM, it significantly decreased survival. The treatment with this organoselenium compound at non-cytotoxic dose range increased cell survival after challenge with hydrogen peroxide, methyl-methanesulphonate, and UVC radiation, but did not protect against 8-methoxypsoralen plus UVA-induced cytotoxicity. In addition, the treatment prevented induced DNA damage, as verified in the comet assay. The mutagenic effect of these genotoxins, as measured by the micronucleus test, similarly attenuated or prevented cytotoxicity and DNA damage. Treatment with DPDS also decreased lipid peroxidation levels after exposure to hydrogen peroxide MMS, and UVC radiation, and increased glutathione peroxidase activity in the extracts. Our results clearly demonstrate that DPDS at low concentrations presents antimutagenic properties, which are most probably due to its antioxidant properties.

Repair of genome destabilizing lesions

Living organisms are constantly exposed to detrimental agents both from the environment (e.g. ionizing radiation, ultraviolet light, natural and synthetic chemicals) and from endogenous metabolic processes (e.g. oxidative and hydrolytic reactions), resulting in modifications of proteins, lipids and DNA. Proteins and lipids are degraded and resynthesized, but the DNA is replicated only during cell division, when DNA damage may result in mutation fixation. Thus the DNA damage generated has the potential to lead to carcinogenesis, cell death, or other genetic disorders in the absence of efficient error-free repair. Because modifications in DNA sequence or structure may be incompatible with its essential role in preservation and transmission of genetic information from generation to generation, exquisitely sensitive DNA repair pathways have evolved to maintain genomic stability and cell viability. This review focuses on the repair and processing of genome destabilizing lesions and helical distortions that differ significantly from the canonical B-form DNA in mammalian cells. In particular, we discuss the introduction and processing of site-specific lesions in mammalian cells with an emphasis on psoralen interstrand crosslinks.

Cytotoxicity and gene induction by some essential oils in the yeast Saccharomyces cerevisiae

In order to get an insight into the possible genotoxicity of essential oils (EOs) used in traditional pharmacological applications we tested five different oils extracted from the medicinal plants Origanum compactum, Coriandrum sativum, Artemisia herba alba, Cinnamomum camphora (Ravintsara aromatica) and Helichrysum italicum (Calendula officinalis) for genotoxic effects using the yeast Saccharomyces cerevisiae. Clear cytotoxic effects were observed in the diploid yeast strain D7, with the cells being more sensitive to EOs in exponential than in stationary growth phase. The cytotoxicity decreased in the following order: Origanum compactum>Coriandrum sativum>Artemisia herba alba>Cinnamomum camphora>Helichrysum italicum. In the same order, all EOs, except that derived from Helichrysum italicum, clearly induced cytoplasmic petite mutations indicating damage to mitochondrial DNA. However, no nuclear genetic events such as point mutations or mitotic intragenic or intergenic recombination were induced. The capacity of EOs to induce nuclear DNA damage-responsive genes was tested using suitable Lac-Z fusion strains for RNR3 and RAD51, which are genes involved in DNA metabolism and DNA repair, respectively. At equitoxic doses, all EOs demonstrated significant gene induction, approximately the same as that caused by hydrogen peroxide, but much lower than that caused by methyl methanesulfonate (MMS). EOs affect mitochondrial structure and function and can stimulate the transcriptional expression of DNA damage-responsive genes. The induction of mitochondrial damage by EOs appears to be closely linked to overall cellular cytotoxicity and appears to mask the occurrence of nuclear genetic events. EO-induced cytotoxicity involves oxidative stress, as is evident from the protection observed in the presence of ROS inhibitors such as glutathione, catalase or the iron-chelating agent deferoxamine.

DNA repair defects channel interstrand DNA cross-links into alternate recombinational and error-prone repair pathways

The repair of psoralen interstrand cross-links in the yeast Saccharomyces cerevisiae involves the DNA repair groups nucleotide excision repair (NER), homologous recombination (HR), and post-replication repair (PRR). In repair-proficient yeast cells cross-links induce double-strand breaks, in an NER-dependent process; the double-strand breaks are then repaired by HR. An alternate error-prone repair pathway generates mutations at cross-link sites. We have characterized the repair of plasmid molecules carrying a single psoralen cross-link, psoralen monoadduct, or double-strand break in yeast cells with deficiencies in NER, HR, or PRR genes, measuring the repair efficiencies and the levels of gene conversions, crossing over, and mutations. Strains with deficiencies in the NER genes RAD1, RAD3, RAD4, and RAD10 had low levels of cross-link-induced recombination but higher mutation frequencies than repair-proficient cells. Deletion of the HR genes RAD51, RAD52, RAD54, RAD55, and RAD57 also decreased induced recombination and increased mutation frequencies above those of NER-deficient yeast. Strains lacking the PRR genes RAD5, RAD6, and RAD18 did not have any cross-link-induced mutations but showed increased levels of recombination; rad5 and rad6 cells also had altered patterns of cross-link-induced gene conversion in comparison with repair-proficient yeast. Our observations suggest that psoralen cross-links can be repaired by three pathways: an error-free recombinational pathway requiring NER and HR and two PRR-dependent error-prone pathways, one NER-dependent and one NER-independent.

Mutation induction in haploid yeast after split-dose radiation exposure. II. Combination of UV-irradiation and X-rays

Split-dose protocols can be used to investigate the kinetics of recovery from radiation damage and to elucidate the mechanisms of cell inactivation and mutation induction. In this study, a haploid strain of the yeast, Saccharomyces cerevisiae, wild-type with regard to radiation sensitivity, was irradiated with 254-nm ultraviolet (UV) light and then exposed to X-rays after incubation for 0-6 hr. The cells were incubated either on nutrient medium or salt agar between the treatments. Loss of reproductive ability and mutation to canavanine resistance were measured. When the X-ray exposure immediately followed UV-irradiation, the X-ray survival curves had the same slope irrespective of the pretreatment, while the X-ray mutation induction curves were changed from linear to linear quadratic with increasing UV fluence. Incubations up to about 3 hr on nutrient medium between the treatments led to synergism with respect to cell inactivation and antagonism with respect to mutation, but after 4-6 hr the two treatments acted independently. Incubation on salt agar did not cause any change in the survival curves, but there was a strong suppression of X-ray-induced mutation with increasing UV fluence. On the basis of these results, we suggest that mutation after combined UV and X-ray exposure is affected not only by the induction and suppression of DNA repair processes, but also by radiation-induced modifications of cell-cycle progression and changes in the expression of the mutant phenotype.

DNA damaging activity of ellagic acid derivatives

A strain of yeast rendered repair deficient by the conditional expression of the RAD52 locus was used to search for natural products capable of damaging DNA. Four ellagic acid derivatives, namely 3,3'-dimethyl-4'-O-beta-D-glucopyranosyl ellagic acid (1), 3,3',4-trimethyl-4'-O-beta-D-glucopyranosyl ellagic acid (2), 3'-methyl-3,4-O,O-methylidene ellagic acid (3) and 3'-methyl-3,4-O,O-methylidene-4'-O-beta-D-glucopyranosyl ellagic acid (4), were identified by this assay as DNA damaging natural principles from several plants, including Alangium javanicum, Anisophyllea apetala, Crypteronia paniculata, Mouririi sp. and Scholtzia parviflora. Although none of the isolated principles mediated frank strand scission of DNA in vitro, all of them potently inhibited the growth of yeast in the absence of expression of RAD52.

Decreased survival of UV-irradiated Staphylococcus aureus in the presence of 8-methoxypsoralen in the post-irradiation plating medium

For Staphylococcus aureus, the presence of 8-methoxypsoralen (8-MOP) in the post-irradiation plating medium increased the lethal effect of far-UV light (FUV; approximately 254 nm) and of 8-MOP plus near-UV light (8-MOP+NUV; approximately 365 nm), an effect similar to that caused by acriflavine which inhibits DNA repair. In the repair-proficient strain, the presence of 8-MOP in the plating medium was almost as effective in inhibiting the repair of damage caused by FUV as that caused by 8-MOP photoadditions. Survival data obtained with Rec(-)-like and Uvr(-)-like strains suggest that 8-MOP in the plating medium, although possibly inhibiting recombination repair, was much more effective in inhibiting excision repair of FUV damage. Regarding 8-MOP+NUV treatment, 8-MOP in the plating medium had a lesser effect in the repair-deficient strains, differing from that observed after FUV treatment, which is consistent with the notion that different types of damage are caused by the two treatments.

Preclinical safety of a nucleic acid-targeted Helinx compound: a clinical perspective

Helinx technology (Cerus Corp, Concord, CA) uses amotosalen HCl (S-59) and ultraviolet A (UVA) light in an ex vivo photochemical treatment (PCT) to inactivate viruses, bacteria, and leukocytes in platelet concentrates while preserving therapeutic function. A comprehensive preclinical safety program was conducted, which included carcinogenicity, single-dose and multiple-dose (up to 13 weeks' duration) toxicity, safety pharmacology (central nervous system [CNS], renal, and cardiovascular), reproductive toxicity, genotoxicity, vein irritation, phototoxicity, and toxicokinetic testing. The results of the toxicokinetic analyses indicated that the test articles provided large multiples of the clinical exposure to S-59, whether the comparison was based on dose, maximum plasma concentration, or area under the concentration-time curve. No specific target organ toxicity, reproductive toxicity, or carcinogenicity was observed. S-59 and/or PCT formulations demonstrated CNS toxicity, electrocardiographic (ECG) effects, and phototoxicity at supraclinical doses. On the basis of the extremely large safety margins, the CNS and ECG observations (at >30,000-fold the expected clinical exposure) as well as the results of genotoxicity and phototoxicity studies are not considered to be of toxicological relevance. The results of an extensive series of studies have thus demonstrated no toxicologically relevant effects of platelets treated with Helinx technology.

Pharmacokinetic and toxicology assessment of INTERCEPT (S-59 and UVA treated) platelets

The pathogen inactivation process developed by Cerus and Baxter Healthcare Corporations uses the psoralen, S-59 (amotosalen) in an ex vivo photochemical treatment (PCT) process to inactivate viruses, bacteria, protozoans, and leukocytes in platelet concentrates and plasma. Studies were performed by intravenous infusion of S-59 PCT formulations +/- compound adsorption device (CAD) treatment and with non-UVA illuminated S-59, using doses that were multiples of potential clinical exposures. The studies comprised full pharmacokinetic, single- and repeated-dose (up to 13 weeks duration) toxicity, safety pharmacology (CNS, renal, and cardiovascular), reproductive toxicity, genotoxicity, carcinogenicity testing in the p53(+/-) mouse, vein irritation, and phototoxicity. No specific target organ toxicity (clinical or histopathological), reproductive toxicity, or carcinogenicity was observed. S-59 and/or PCT formulations demonstrated CNS, ECG, and phototoxicity only at supraclinical doses. Based on the extremely large safety margins (>30,000-fold expected clinical exposures), the CNS and ECG observations are not considered to have any toxicological relevance. Additionally, after a complete assessment, mutagenicity and phototoxicity results are not considered relevant for the proposed use of INTERCEPT platelets. Thus, the results of an extensive series of in vitro and in vivo studies have not demonstrated any toxicologically relevant effects of platelet concentrates prepared by the INTERCEPT system.

Cytolethal distending toxin demonstrates genotoxic activity in a yeast model

Cytolethal distending toxins (CDTs) are multisubunit proteins produced by a variety of bacterial pathogens that cause enlargement, cell cycle arrest, and apoptosis in mammalian cells. While their function remains uncertain, recent studies suggest that they can act as intracellular DNases in mammalian cells. Here we establish a novel yeast model for understanding CDT-associated disease. Expression of the CdtB subunit in yeast causes a G2/M arrest, as seen in mammalian cells. CdtB toxicity is not circumvented in yeast genetically altered to lack DNA damage checkpoint control or that constitutively promote cell cycle progression via mutant Cdk1, because CdtB causes a permanent type of damage that results in loss of viability. Finally, we establish that CDTs are likely to be potent genotoxins, as indicated by in vivo degradation of chromosomal DNA associated with expression of CdtB-suggesting that the varied distribution of CDT in bacteria implicates many human pathogens as possessors of genotoxic activity.

Recombinational and mutagenic repair of psoralen interstrand cross-links in Saccharomyces cerevisiae

Psoralen photoreacts with DNA to form interstrand cross-links, which can be repaired by both nonmutagenic nucleotide excision repair and recombinational repair pathways and by mutagenic pathways. In the yeast Saccharomyces cerevisiae, psoralen cross-links are processed by nucleotide excision repair to form double-strand breaks (DSBs). In yeast, DSBs are repaired primarily by homologous recombination, predicting that cross-link and DSB repair should induce similar recombination end points. We compared psoralen cross-link, psoralen monoadduct, and DSB repair using plasmid substrates with site-specific lesions and measured the patterns of gene conversion, crossing over, and targeted mutation. Psoralen cross-links induced both recombination and mutations, whereas DSBs induced only recombination, and monoadducts were neither recombinogenic nor mutagenic. Although the cross-link- and DSB-induced patterns of plasmid integration and gene conversion were similar in most respects, they showed opposite asymmetries in their unidirectional conversion tracts: primarily upstream from the damage site for cross-links but downstream for DSBs. Cross-links induced targeted mutations in 5% of the repaired plasmids; all were base substitutions, primarily T --> C transitions. The major pathway of psoralen cross-link repair in yeast is error-free and involves the formation of DSB intermediates followed by homologous recombination. A fraction of the cross-links enter an error-prone pathway, resulting in mutations at the damage site.

Betulinic acid reduces ultraviolet-C-induced DNA breakage in congenital melanocytic naeval cells: evidence for a potential role as a chemopreventive agent

Melanoma transformation progresses in a multistep fashion from precursor lesions such as congenital naevi. Exposure to ultraviolet (UV) light promotes this process. Betulinic acid (BA) was identified by our group as a selective inhibitor of melanoma that functions by inducing apoptosis. The present study was designed to investigate the effect of BA and UV-C (254 nm) on cultured congenital melanocytic naevi (CMN) cells, using the single-cell gel electrophoresis (comet) assay to detect DNA damage. Exposure to UV light induced a 1.7-fold increase in CMN cells (P = 0.008) when compared with controls. When a p53 genetic suppressor element that encodes a dominant negative polypeptide (termed GSE56) was introduced into the CMN cells, the transfected cells were more sensitive to UV-induced DNA breakage. This suggests that p53 can protect against UV-induced DNA damage and subsequent melanoma transformation. Pretreatment with BA (3 microm) for 48 h resulted in a 25.5% reduction in UV-induced DNA breakage in the CMN cells (P = 0.023), but no changes were observed in the transfected cells. However, Western blot analysis revealed no changes in the p53 or p21 levels in BA-treated cells, suggesting that BA might mediate its action via a non-p53 pathway. These data indicate that BA may have an application as a chemopreventive agent in patients with congenital naevi.

Damage-induced recombination in the yeast Saccharomyces cerevisiae

Prokaryotic and eukaryotic cells have developed a network of DNA repair systems that restore genomic integrity following DNA damage from endogenous and exogenous genotoxic sources. One of the mechanisms used to repair damaged chromosomes is genetic recombination, in which information present as a second chromosomal copy is used to repair a damaged region of the genome. In this review, I summarized what is known about the molecular and cellular mechanisms by which various DNA-damaging agents induce recombination in yeast. The yeast Saccharomyces cerevisiae has served as an excellent model organism to study the induction of recombination. It has helped to define the basic phenomenology and to isolate the genes involved in the process. Given the evolutionary conservation of the various DNA repair systems in eukaryotes, it is likely that the knowledge gathered about induced recombination in yeast is applicable to mammalian cells and thus to humans. Many carcinogens are known to induce recombination and to cause chromosomal rearrangements. An understanding of the mechanisms, by which genotoxic agents cause increased levels of recombination will have important consequences for the treatment of cancer, and for the assessment of risks arising from exposure to genotoxic agents in humans.

Activation of p70 ribosomal protein S6 kinase is an essential step in the DNA damage-dependent signaling pathway responsible for the ultraviolet B-mediated increase in interstitial collagenase (MMP-1) and stromelysin-1 (MMP-3) protein levels in human dermal fibroblasts

Ultraviolet B (UVB) irradiation has been shown to stimulate the expression of matrix-degrading metalloproteinases via generation of DNA damage and/or reactive oxygen species. Matrix-degrading metalloproteinases promote UVB-triggered detrimental long term effects like cancer formation and premature skin aging. Here, we were interested in identifying components of the signal transduction pathway that causally link UVB-mediated DNA damage and induction of matrix-degrading metalloproteinase (MMP)-1/interstitial collagenase and MMP-3/stromelysin-1 in human dermal fibroblasts in vitro. The activity of p70 ribosomal S6 kinase, a downstream target of the FK506-binding protein-12/rapamycin-associated protein kinase (FRAP) kinase (RAFT1, mTOR), was identified to be 4.8 +/- 0.8-fold, and MMP-1 and MMP-3 protein levels 2.4- and 11.5-fold increased upon UVB irradiation compared with mock-irradiated controls. The FRAP kinase inhibitor rapamycin and the DNA repair inhibitor aphidicolin significantly suppressed the UVB-mediated increase in p70 ribosomal S6 kinase activity by 50-65% and MMP-1 and MMP-3 protein levels by 34-68% and 42-88% compared with UVB-irradiated fibroblasts. By contrast, the interleukin-1beta-mediated increase in MMP-1 and MMP-3 protein levels could not be suppressed by rapamycin. Collectively, our data suggest that the FRAP-controlled p70 ribosomal S6 kinase is an essential component of a DNA damage-dependent, but not of the interleukin-1/cell membrane receptor-dependent signaling.