T-oligos augment UV-induced protective responses in human skin

5-aminolaevulinic acid-based photodynamic therapy inhibits ultraviolet B-induced skin photodamage

To evaluate the photoprotective effect of 5-aminolaevulinic acid-based photodynamic therapy (ALA-PDT) on ultraviolet B (UVB)-induced skin photodamage. In vivo experiments, the dorsal skin of hairless mice were treated with ALA-PDT or saline-PDT, and then exposed to 180 mJ/m2 UVB. Results showed that the number of sunburn cells and apoptotic cells in the epidermis of ALA-PDT-treated groups at 24 h after UVB irradiation were significantly decreased compared with those in the UVB groups. And the removal rate of CPDs was obviously higher in ALA-PDT-treated groups. At 48 h, the number of Ki67 positive nuclei in ALA-PDT-UVB group was significantly fewer than that in UVB group. Further in vitro experiments, human keratinocyte cell line (HaCaT) cells of two groups (one treated with ALA-PDT, the other untreated), were exposed to 60 mJ/m2 UVB irradiation. We found 0.5 mmol/L of ALA and 3 J/cm2 of red light did not affect the vitality of cells, and could reduce UVB induced apoptosis, accelerate the clearance of CPDs, inhibit proliferation and activate p53. Thus, our data demonstrate that ALA-PDT pretreatment can induce a protective DNA damage response that protects skin cells from UVB-induced photodamages.

5-Aminolevulinic Acid-Based Photodynamic Therapy Pretreatment Mitigates Ultraviolet A-Induced Oxidative Photodamage

Aim

To determine whether 5-aminolevulinic acid-based photodynamic therapy (ALA-PDT) is effective in combating ultraviolet A- (UVA-) induced oxidative photodamage of hairless mice skin in vivo and human epidermal keratinocytes in vitro.

Methods

In in vitro experiments, the human keratinocyte cell line (HaCaT cells) was divided into two groups: the experimental group was treated with ALA-PDT and the control group was left untreated. Then, the experimental group and the control group of cells were exposed to 10 J/m² of UVA radiation. ROS, O₂⁻ species, and MMP were determined by fluorescence microscopy; p53, OGG1, and XPC were determined by Western blot analysis; apoptosis was determined by flow cytometry; and 8-oxo-dG was determined by immunofluorescence. Moreover, HaCaT cells were also treated with ALA-PDT. Then, SOD1 and SOD2 were examined by Western blot analysis. In in vivo experiments, the dorsal skin of hairless mice was treated with ALA-PDT or saline-PDT, and then, they were exposed to 20 J/m² UVA light. The compound 8-oxo-dG was detected by immunofluorescence.

Conclusion

In human epidermal keratinocytes and hairless mice skin, UVA-induced oxidative damage can be prevented effectively with ALA-PDT pretreatment.

Challenge and perspective: the relevance of ultraviolet (UV) radiation and the vitamin D endocrine system (VDES) for psoriasis and other inflammatory skin diseases

During evolution, the ability of many organisms to synthesize vitamin D photochemically represented, and still represents, a major driving factor for the development of life on earth. In humans because not more than 10-20% of the requirement of vitamin D can be satisfied by the diet (under most living conditions in the US and Europe), the remaining 80-90% need to be photochemically synthesized in the skin through the action of solar or artificial ultraviolet-B (UV-B) radiation. The skin is a key organ of the human body's vitamin D endocrine system (VDES), representing both the site of vitamin D synthesis and a target tissue for biologically active vitamin D metabolites. Human keratinocytes contain the enzymatic machinery (CYP27B1) for the synthesis of the biologically most active natural vitamin D metabolite 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃), representing an autonomous vitamin D₃ pathway. Cutaneous production of 1,25(OH)₂D₃ may mediate intracrine, autocrine and paracrine effects on keratinocytes and on neighboring cells. Many skin cells (including keratinocytes, sebocytes, fibroblasts, melanocytes, macrophages and other skin immune cells) express the vitamin D receptor (VDR), an absolute pre-requisite for exerting genomic effects of 1,25(OH)₂D₃ and analogs. The VDR is a member of the superfamily of trans-acting transcriptional regulatory factors, which also contains the steroid and thyroid hormone receptors as well as the retinoid-X receptors (RXR) and retinoic acid receptors (RAR). A large body of evidence, including cDNA microarray analyses of mRNAs, indicates that as many as 500-1000 genes may be controlled by VDR ligands that regulate a broad variety of cellular functions including growth, differentiation, and apoptosis. Clinical and laboratory investigations, including the observation that 1,25(OH)₂D₃ is very effective in inducing the terminal differentiation and in inhibiting the proliferation of cultured human keratinocytes have resulted in the use of 1,25(OH)₂D₃ and analogs for the treatment of psoriasis. Focussing on the UV-induced cutaneous synthesis of vitamin D, this review gives an update on the relevance of the VDES and of UV radiation for the management of psoriasis and other inflammatory skin diseases.

Mechanism of Action of G-Quadruplex-Forming Oligonucleotide Homologous to the Telomere Overhang in Melanoma

T-oligo, a guanine-rich oligonucleotide homologous to the 3'-telomeric overhang of telomeres, elicits potent DNA-damage responses in melanoma cells; however, its mechanism of action is largely unknown. Guanine-rich oligonucleotides can form G-quadruplexes (G4), which are stabilized by the hydrogen bonding of guanine residues. In this study, we confirmed the G4-forming capabilities of T-oligo using nondenaturing PAGE, nuclear magnetic resonance, and immunofluorescence. Using an anti-G-quadruplex antibody, we showed that T-oligo can form G4 in the nuclei of melanoma cells. Furthermore, using DNase I in a nuclease degradation assay, G4-T-oligo was found to be more stable than single-stranded T-oligo. G4-T-oligo had decreased antiproliferative effects compared with single-stranded T-oligo. However, G4-T-oligo has similar cellular uptake as single-stranded T-oligo, as shown by FACS analysis. Inhibition of JNK, which causes DNA damage-induced apoptosis, partially reversed the antiproliferative activity of T-oligo. T-oligo also inhibited mRNA expression of human telomerase reverse transcriptase, a catalytic subunit of telomerase that was reversed by JNK inhibition. Furthermore, two shelterin complex proteins TRF2/POT1 were found to be up-regulated and bound by T-oligo, suggesting that T-oligo may mediate dissociation of these proteins from the telomere overhang. These studies show that T-oligo can form a G-quadruplex and that the antitumor effects of T-oligo may be mediated through POT1/TRF2 and via human telomerase reverse transcriptase inhibition through JNK activation.

UV signaling pathways within the skin

The effects of UVR on the skin include tanning, carcinogenesis, immunomodulation, and synthesis of vitamin D, among others. Melanocortin 1 receptor polymorphisms correlate with skin pigmentation, UV sensitivity, and skin cancer risk. This article reviews pathways through which UVR induces cutaneous stress and the pigmentation response. Modulators of the UV tanning pathway include sunscreen agents, MC1R activators, adenylate cyclase activators, phosphodiesterase 4D3 inhibitors, T oligos, and MITF regulators such as histone deacetylase (HDAC)-inhibitors. UVR, as one of the most ubiquitous carcinogens, represents both a challenge and enormous opportunity in skin cancer prevention.

Imiquimod-induced TLR7 signaling enhances repair of DNA damage induced by ultraviolet light in bone marrow-derived cells

Imiquimod is a TLR7/8 agonist that has anticancer therapeutic efficacy in the treatment of precancerous skin lesions and certain nonmelanoma skin cancers. To test our hypothesis that imiquimod enhances DNA repair as a mechanism for its anticancer activity, the nucleotide excision repair genes were studied in bone marrow-derived cells. Imiquimod enhanced the expression of xeroderma pigmentosum (XP) A and other DNA repair genes (quantitative real-time PCR analysis) and resulted in an increased nuclear localization of the DNA repair enzyme XPA. This was dependent on MyD88, as bone marrow-derived cells from MyD88(-/-) mice did not increase XPA gene expression and did not enhance the survival of MyD88(-/-)-derived bone marrow-derived cells after UV B exposure as was observed in bone marrow-derived cells from MyD88(+/+) mice. Imiquimod also enhanced DNA repair of UV light (UVL)-irradiated gene expression constructs and accelerated the resolution of cyclobutane pyrimidine dimers after UVL exposures in P388 and XS52. Lastly, topical treatment of mouse skin with 5% imiquimod cream prior to UVL irradiation resulted in a decrease in the number of cyclobutane pyridimine dimer-positive APC that were found in local lymph nodes 24 h after UVL irradiation in both wild-type and IL-12 gene-targeted mice. In total, these data support the idea that TLR7 agonists such as imiquimod enhance DNA repair in bone marrow-derived cells. This property is likely to be an important mechanism for its anticancer effects because it protects cutaneous APC from the deleterious effects of UVL.

Chloroform extract from Moricandia arvensis inhibits growth of B16-F0 melanoma cells and promotes differentiation in vitro

OBJECTIVES

Poor therapeutic results have been reported for treatment of malignant melanoma; therefore in this study we have investigated inhibitory capacity of ethyl acetate, chloroform (Chl) and methanol extracts from Moricandia arvensis on mouse melanoma (B16-F0) and human keratinocyte (HaCaT) cell proliferation. Influence of Chl extract on percentage distribution in cell cycle phases and melanogenesis was also studied.

MATERIAL AND METHODS

Cell viability was determined at various periods using the MTT assay, and flow cytometry was used to analyse effects of Chl extract on progression through the cell cycle and apoptosis. In addition, amounts of melanin and tyrosinase were measured spectrophotometrically at 475 nm.

RESULTS

Chl extract exhibited significant anti-proliferative activity after incubation with the two types of tumour skin cells. Morphological changes in B16-F0 cells, accompanied by increase of tyrosinase activity, and of melanin synthesis were observed, which are markers of differentiation of malignant melanoma cells. Furthermore, cell cycle analysis revealed that B16-F0 cells treated with Chl extract were arrested predominantly in G(1) phase.

CONCLUSION

Chl extract had the ability to reverse malignant melanoma cells from proliferative to differentiated state, thus providing a new perspective in developing novel strategies for prevention and treatment of malignant melanoma, possibly through consumption of the extract in an appropriate cancer prevention diet. Moreover, there is scope for the extract being introduced into cosmetic products as a natural tanning agent.

Inhibition of melanoma angiogenesis by telomere homolog oligonucleotides

Telomere homolog oligonucleotides (T-oligos) activate an innate telomere-based program that leads to multiple anticancer effects. T-oligos act at telomeres to initiate signaling through the Werner protein and ATM kinase. We wanted to determine if T-oligos have antiangiogenic effects. We found that T-oligo-treated human melanoma (MM-AN) cells had decreased expression of vascular endothelial growth factor (VEGF), VEGF receptor 2, angiopoeitin-1 and -2 and decreased VEGF secretion. T-oligos activated the transcription factor E2F1 and inhibited the activity of the angiogenic transcription factor, HIF-1α. T-oligos inhibited EC tubulogenesis and total tumor microvascular density matrix invasion by MM-AN cells and ECs in vitro. In melanoma SCID xenografts, two systemic T-oligo injections decreased by 60% (P < .004) total tumor microvascular density and the functional vessels density by 80% (P < .002). These findings suggest that restriction of tumor angiogenesis is among the host's innate telomere-based anticancer responses and provide further evidence that T-oligos may offer a powerful new approach for melanoma treatment.

[Skin aging]

Like the entire human organism, the skin is subject to an intrinsic unpreventable aging process. But exogenous factors also influence skin aging. Ultraviolet radiation in particular results in premature skin aging, also referred to as extrinsic skin aging or photo aging, causing in large part aging-associated changes in sun-exposed areas. Intrinsic and extrinsic aging share several molecular similarities despite morphological and pathophysiological differences. The formation of reactive oxygen species and the induction of metalloproteinases reflect central aspects of skin aging. Accumulation of fragmented collagen fibrils prevents neocollagenesis and accounts for further degradation of extracellular matrix by means of positive feedback regulation. The importance of extrinsic factors in skin aging and the detection of its mechanisms has given rise to development of various therapeutic and preventive strategies.

Ultraviolet radiation and immunosuppression

Ultraviolet (UV) radiation is a complete carcinogen. The effects of UV radiation are mediated via direct damage to cellular DNA in the skin and suppression of image surveillance mechanisms. In the context of organ transplantation, addiction of drugs which suppress the immune system add greatly to the carcinogenicity of UV radiation. This review considers the mechanisms of such effects.

Stepping up melanocytes to the challenge of UV exposure

Exposure to solar ultraviolet radiation (UV) is the main etiological factor for skin cancer, including melanoma. Cutaneous pigmentation, particularly eumelanin, afforded by melanocytes is the main photoprotective mechanism, as it prevents UV-induced DNA damage in the epidermis. Therefore, maintaining genomic stability of melanocytes is crucial for prevention of melanoma, as well as keratinocyte-derived basal and squamous cell carcinoma. A critical independent factor for preventing melanoma is DNA repair capacity. The response of melanocytes to UV is mediated mainly by a network of paracrine factors that not only activate melanogenesis, but also DNA repair, anti-oxidant, and survival pathways that are pivotal for maintenance of genomic stability and prevention of malignant transformation or apoptosis. However, little is known about the stress response of melanocytes to UV and the regulation of DNA repair pathways in melanocytes. Unraveling these mechanisms might lead to strategies to prevent melanoma, as well as non-melanoma skin cancer.

Mimetics of hormetic agents: stress-resistance triggers

Mimetics of hormetic agents offer a novel approach to adjust dose to minimize the risk of toxic response, and maximize the benefit of induction of at least partial physiological conditioning. Nature selected and preserved those organisms and triggers that promote tolerance to stress. The induced tolerance can serve to resist that challenge and can repair previous age, disease, and trauma damage as well to provide a more youthful response to other stresses. The associated physiological conditioning may include youthful restoration of DNA repair, resistance to oxidizing pollutants, protein structure and function repair, improved immunity, tissue remodeling, adjustments in central and peripheral nervous systems, and altered metabolism. By elucidating common pathways activated by hormetic agent's mimetics, new strategies for intervention in aging, disease, and trauma emerge. Intervention potential in cancer, diabetes, age-related diseases, infectious diseases, cardiovascular diseases, and Alzheimer's disease are possible. Some hormetic mimetics exist in pathways in primitive organisms and are active or latent in humans. Peptides, oligonucleotides, and hormones are among the mimetics that activate latent resistance to radiation, physical endurance, strength, and immunity to physiological condition tolerance to stress. Co-activators may be required for expression of the desired physiological conditioning health and rejuvenation benefits.

Telomeric DNA induces p53-dependent reactive oxygen species and protects against oxidative damage

BACKGROUND

Reactive oxygen species (ROS) are generated by cellular metabolism as well as by exogenous agents. While ROS can promote cellular senescence, they can also act as signaling molecules for processes that do not lead to senescence. Telomere homolog oligonucleotides (T-oligos) induce adaptive DNA damage responses including increased DNA repair capacity and these effects are mediated, at least in part, through p53.

OBJECTIVE

Studies were undertaken to determine whether such p53-mediated protective responses include enhanced antioxidant defenses.

METHODS

Normal human fibroblasts as well as R2F fibroblasts expressing wild type or dominant negative p53 were treated with an 11-base T-oligo, a complementary control oligo or diluents alone and then examined by western blot analysis, immunofluorescence microscopy and various biochemical assays.

RESULTS

We now report that T-oligo increases the level of the antioxidant enzymes superoxide dismutase 1 and 2 and protects cells from oxidative damage; and that telomere-based gammaH2AX (DNA damage) foci that form in response to T-oligos contain phosphorylated ATM and Chk2, proteins known to activate p53 and to mediate cell cycle arrest in response to oxidative stress. Further, T-oligo increases cellular ROS levels via a p53-dependent pathway, and these increases are abrogated by the NAD(P)H oxidase inhibitor diphenyliodonium chloride.

CONCLUSION

These results suggest the existence of innate telomere-based protective responses that act to reduce oxidative damage to cells. T-oligo treatment induces the same responses and offers a new model for studying intracellular ROS signaling and the relationships between DNA damage, ROS, oxidative stress, and cellular defense mechanisms.

Telomere-mediated effects on melanogenesis and skin aging

UV-induced melanogenesis (tanning) and "premature aging" or photoaging result in large part from DNA damage. This article reviews data tying both phenomena to telomere-based DNA damage signaling and develops a conceptual framework in which both responses may be understood as cancer-avoidance protective mechanisms.Journal of Investigative Dermatology Symposium Proceedings (2009) 14, 25-31; doi:10.1038/jidsymp.2009.9.

DNA repair and cytokine responses

As sunscreens do not provide complete protection against solar/UV radiation, alternative protective strategies are necessary to cope with the increasing incidence of skin cancer. These strategies include the reduction of UVR-induced DNA damage by the topical application of bacterial DNA repair enzymes. Recent evidence suggests that nucleotide excision repair, the physiological repair system that is mostly responsible for the removal of UVR-mediated DNA damage, can be modulated by cytokines, including IL-12, IL-18, and alpha-melanocyte-stimulating hormone. The mechanisms involved and the biological as well as the potential therapeutic implications of these findings are discussed.Journal of Investigative Dermatology Symposium Proceedings (2009) 14, 63-66; doi:10.1038/jidsymp.2009.3.

New insights into pigmentary pathways and skin cancer

The ability of cells to respond to and to mitigate environmental stress is crucial for their survival. Constitutive and facultative pigmentation have evolved in order for human skin to contend with high levels of terrestrial ultraviolet radiation (UVR). When this melanin 'shield' is compromised, individuals are exposed to increased skin cancer risk. The purpose of this review is to discuss new insights into the genetic basis of phenotypic risk factors for skin cancer, their connection to pigmentation and tanning, the precise molecular connections linking UVR to the tanning response, and potential methods of modulating pigmentation that avoid genotoxic damage. Highly translational implications of this research include a scientific basis on which to counsel patients regarding the carcinogenicity of UVR exposure related to tanning and potential new tanning agents that may actually protect against skin cancer by circumventing the need for UVR exposure.

The benefits and risks of ultraviolet tanning and its alternatives: the role of prudent sun exposure

Sunlight- and indoor ultraviolet (UV)-induced tanning is a common behavior, especially among adolescents, young adults, and individuals who have lighter skin. Excessive sun exposure is associated with several health risks, including the acceleration of skin aging and the promotion of skin cancers. Several health benefits of UV exposure include vitamin D production and improved mood. This article analyzes these health risks and benefits and discusses pertinent issues surrounding indoor tanning, the role of sunless tanning products, and prudent sun exposure.

Ultraviolet A within sunlight induces mutations in the epidermal basal layer of engineered human skin

The ultraviolet B (UVB) waveband within sunlight is an important carcinogen; however, UVA is also likely to be involved. By ascribing mutations to being either UVB or UVA induced, we have previously shown that human skin cancers contain similar numbers of UVB- and UVA-induced mutations, and, importantly, the UVA mutations were at the base of the epidermis of the tumors. To determine whether these mutations occurred in response to UV, we exposed engineered human skin (EHS) to UVA, UVB, or a mixture that resembled sunlight, and then detected mutations by both denaturing high-performance liquid chromatography and DNA sequencing. EHS resembles human skin, modeling differential waveband penetration to the basal, dividing keratinocytes. We administered only four low doses of UV exposure. Both UVA and UVB induced p53 mutations in irradiated EHS, suggesting that sunlight doses that are achievable during normal daily activities are mutagenic. UVA- but not UVB-induced mutations predominated in the basal epidermis that contains dividing keratinocytes and are thought to give rise to skin tumors. These studies indicate that both UVA and UVB at physiological doses are mutagenic to keratinocytes in EHS.

The benefits and risks of ultraviolet tanning and its alternatives: the role of prudent sun exposure

Sunlight- and indoor ultraviolet (UV)-induced tanning is a common behavior, especially among adolescents, young adults, and individuals who have lighter skin. Excessive sun exposure is associated with several health risks, including the acceleration of skin aging and the promotion of skin cancers. Several health benefits of UV exposure include vitamin D production and improved mood. This article analyzes these health risks and benefits and discusses pertinent issues surrounding indoor tanning, the role of sunless tanning products, and prudent sun exposure.

Modifying skin pigmentation - approaches through intrinsic biochemistry and exogenous agents

Rates of skin cancer continue to increase despite the improved use of traditional sunscreens to minimize damage from ultraviolet radiation. The public perception of tanned skin as being healthy and desirable, combined with the rising demand for treatments to repair irregular skin pigmentation and the desire to increase or decrease constitutive skin pigmentation, arouses great interest pharmaceutically as well as cosmeceutically. This review discusses the intrinsic biochemistry of pigmentation, details mechanisms that lead to increased or decreased skin pigmentation, and summarizes established and potential hyper- and hypo-pigmenting agents and their modes of action.

Topical thymidine dinucleotide treatment reduces development of ultraviolet-induced basal cell carcinoma in Ptch-1+/- mice

Treatment with thymidine dinucleotide (pTT) has well documented DNA-protective effects and reduces development of squamous cell carcinoma in UV-irradiated mice. The preventive effect of pTT on basal cell carcinoma (BCC) was evaluated in UV-irradiated Ptch-1(+/-) mice, a model of the human disease Gorlin syndrome. Topical pTT treatment significantly reduced the number and size (P < 0.001) of BCCs in murine skin after 7 months of chronic irradiation. Skin biopsies collected 24 hours after the final UV exposure showed that pTT reduced the number of nuclei positive for cyclobutane pyrimidine dimers by 40% (P < 0.0002) and for 8-hydroxy-2'-deoxyguanosine by 61% (P < 0.01 compared with vehicle control). Immunostaining with an antibody specific for mutated p53 revealed 63% fewer positive patches in BCCs of pTT-treated mice compared with controls (P < 0.01), and the number of Ki-67-positive cells was decreased by 56% (P < 0.01) in pTT-treated tumor-free epidermis and by 76% (P < 0.001) in BCC tumor nests (P < 0.001). Terminal dUTP nick-end labeling staining revealed a 213% increase (P < 0.04) in the number of apoptotic cells in BCCs of pTT-treated mice. Cox-2 immunostaining was decreased by 80% in tumor-free epidermis of pTT-treated mice compared with controls (P < 0.01). We conclude that topical pTT treatment during a prolonged period of intermittent UV exposure decreases the number and size of UV-induced BCCs through several anti-cancer mechanisms.

The melanocortin 1 receptor and the UV response of human melanocytes--a shift in paradigm

Cutaneous pigmentation is the major photoprotective mechanism against the carcinogenic and aging effects of UV. Epidermal melanocytes synthesize the pigment melanin, in the form of eumelanin or pheomelanin. Synthesis of the photoprotective eumelanin by human melanocytes is regulated mainly by the melanocortins alpha-melanocortin (alpha-MSH) and adrenocorticotropic hormone (ACTH), which bind the melanocortin 1 receptor (MC1R) and activate the cAMP pathway that is required for UV-induced tanning. Melanocortins stimulate proliferation and melanogenesis and inhibit UV-induced apoptosis of human melanocytes. Importantly, melanocortins reduce the generation of hydrogen peroxide and enhance repair of DNA photoproducts, independently of pigmentation. MC1R is a major contributor to the diversity of human pigmentation and a melanoma susceptibility gene. Certain allelic variants of this gene, namely R151C, R160W and D294H, are strongly associated with red hair phenotype and increased melanoma susceptibility. Natural expression of two of these variants sensitizes melanocytes to the cytotoxic effect of UV, and increases the burden of DNA damage and oxidative stress. We are designing potent melanocortin analogs that mimic the effects of alpha-MSH as a strategy to prevent skin cancer, particularly in individuals who express MC1R genotypes that reduce but do not abolish MC1R function, or mutations in other melanoma susceptibility genes, such as p16.

Photoprotection in human skin--a multifaceted SOS response

Human skin has developed elaborate defense mechanisms for combating a wide variety of potentially damaging environmental factors; principal among these is UV light. Despite these defenses, short-term damage may include painful sunburn and long-term UV damage results in both accelerated skin aging and skin cancers such as basal cell carcinoma, squamous cell carcinoma and even malignant melanoma. While UV radiation damages many cellular constituents, its most lasting effects involve DNA alteration. The following sections briefly review UV-inducible protective responses in bacteria and in skin, thymidine dinucleotides (pTT) as a powerful probe of DNA damage responses, and potential means of harnessing these inducible responses therapeutically to reduce the now enormous burden of cutaneous photodamage in our society.

Green tea phenol extracts reduce UVB-induced DNA damage in human cells via interleukin-12

Green tea chemoprevention has been a focus of recent research, as a polyphenolic fraction from green tea (GTP) has been suggested to prevent UV radiation-induced skin cancer. Recently, it was demonstrated that GTP reduced the risk for skin cancer in a murine photocarcinogenesis model. This was accompanied by a reduction in UV-induced DNA damage. These effects appeared to be mediated via interleukin (IL)-12, which was previously shown to induce DNA repair. Therefore, we studied whether GTP induction of IL-12 and DNA repair could also be observed in human cells. KB cells and normal human keratinocytes were exposed to GTP 5 h before and after UVB. UVB-induced apoptosis was reduced in UVB-exposed cells treated with GTP. GTP induced the secretion of IL-12 in keratinocytes. The reduction in UV-induced cell death by GTP was almost completely reversed upon addition of an anti-IL-12-antibody, indicating that the reduction of UV-induced cell death by GTP is mediated via IL-12. The ability of IL-12 to reduce DNA damage and sunburn cells was confirmed in "human living skin equivalent" models. Hence the previously reported UV-protective effects of GTP appear to be mediated in human cells via IL-12, most likely through induction of DNA repair.

Quantification of Inducible SOS-Like Photoprotective Responses in Human Skin

To document and quantify inducible photoprotective effects in human skin, explant cultures were treated once with thymidine dinucleotide (pTT) or diluent alone or UV-irradiated. Both pTT and UV increased the melanogenic protein levels on days 1-5 and comparably increased melanocyte dendricity and epidermal melanin content. Explants treated with pTT or UV but not with diluent alone showed initial inhibition of epidermal proliferation followed by mild reactive hyperplasia; melanocyte proliferation was minimal. To determine whether pTT and UV provide comparable protection against subsequent UV-induced DNA damage, explants were pTT- or diluent-treated or UV-irradiated. All explants were then irradiated with the same UV dose 72 hours later. Compared to diluent alone, pTT or UV pretreatment decreased the number of epidermal cells positive for cyclobutane pyrimidine dimers (CPDs) 50% immediately post-irradiation. In pTT- and UV- versus diluent-pretreated explants, the rate of CPD removal was also more rapid, approximately 80 vs 45% of the initial burden within 72 hours. These data confirm and quantify comparable SOS-like responses in human skin after pTT or UV irradiation, attributable to both increased epidermal melanin and increased DNA repair rate, in the case of pTT in the absence of initial damage.

Oligonucleotide treatment increases eumelanogenesis, hair pigmentation and melanocortin-1 receptor expression in the hair follicle

It was previously reported that telomere homologue oligonucleotides (T-oligos) can induce a variety of cellular responses in skin including increased melanogenesis. To assess the effects of T-oligos on hair pigmentation, we administered thymidine dinucleotide (pTT), one-third of the TTAGGG telomere repeat sequence, intradermally at distinct time points of the depilation-induced hair cycle in C3H/HeJ mice. Penetration of T-oligos into the hair follicle (HF) was monitored by using FITC-labelled pTT and confocal microscopy. pTT treatment on days 1-5 after depilation, during early anagen, did not significantly alter the number and proliferation of melanocytes (Trp-2-positive cells), compared with vehicle-treated controls. However, pTT treatment on days 5-12 after depilation, during mid- to late anagen, resulted in the formation of darker hairs, that showed a significantly increased eumelanin/total melanin ratio in their sub-apical agouti band region, compared with vehicle-treated controls (P < 0.05). By RT-PCR and western blot, full thickness skin of pTT-treated mice showed increases in Trp-1, Trp-2 and tyrosinase mRNA and protein levels, compared with control mice. Western blot analyses of two receptors that positively regulate eumelanogenesis, melanocortin type 1 receptor (MC-1R) and kit, showed increased expression of MC-1R protein in pTT-treated versus control skin, while the levels of c-kit receptor remained unchanged. These data demonstrate that pTT treatment increases eumelanogenesis in HFs, associated with increased tyrosinase, TRP-1 and MC-1R expression. These data also raise the possibility of using T-oligos to modulate hair pigmentation.

Targeting telomeres and telomerase

Telomeres and telomerase represent, at least in theory, an extremely attractive target for cancer therapy. The objective of this review is to present the latest view on the mechanism(s) of action of telomerase inhibitors, with an emphasis on a specific class of telomere ligands called G-quadruplex ligands, and to discuss their potential use in oncology.

Telomeric DNA induces apoptosis and senescence of human breast carcinoma cells

INTRODUCTION

Cancer is a leading cause of death in Americans. We have identified an inducible cancer avoidance mechanism in cells that reduces mutation rate, reduces and delays carcinogenesis after carcinogen exposure, and induces apoptosis and/or senescence of already transformed cells by simultaneously activating multiple overlapping and redundant DNA damage response pathways.

METHODS

The human breast carcinoma cell line MCF-7, the adriamycin-resistant MCF-7 (Adr/MCF-7) cell line, as well as normal human mammary epithelial (NME) cells were treated with DNA oligonucleotides homologous to the telomere 3' overhang (T-oligos). SCID mice received intravenous injections of MCF-7 cells followed by intravenous administration of T-oligos.

RESULTS

Acting through ataxia telangiectasia mutated (ATM) and its downstream effectors, T-oligos induced apoptosis and senescence of MCF-7 cells but not NME cells, in which these signaling pathways were induced to a far lesser extent. In MCF-7 cells, experimental telomere loop disruption caused identical responses, consistent with the hypothesis that T-oligos act by mimicking telomere overhang exposure. In vivo, T-oligos greatly prolonged survival of SCID mice following intravenous injection of human breast carcinoma cells.

CONCLUSION

By inducing DNA damage-like responses in MCF-7 cells, T-oligos provide insight into innate cancer avoidance mechanisms and may offer a novel approach to treatment of breast cancer and other malignancies.

The influence of folic acid depletion on the Nucleotide Excision Repair capacity of human dermal fibroblasts measured by a modified Host Cell Reactivation Assay

Animal and human studies have shown that low levels of folic acid are associated with an impaired DNA Repair Capacity (DRC) and an increased cancer risk. However, the molecular evidence that folic acid enhances the DRC of cultured human cells is still limited because of a paucity of in vitro studies. We investigated the effect of folic acid depletion in vitro on the DRC of human dermal fibroblasts derived from 17 donors of different ages. To assess the cellular Nucleotide Excision DRC, we used a modified Host Cell-Reactivation Assay (HCRA), adapted to the Fluorescence Activated Cell Sorting (FACS)-technology, which is highly sensitive in comparison to luminometer-technology and allows single cell based analysis. We used DsRed as a reporter (irradiated with UVC light) and pEGFP to control the performance of the transformations. Folic acid had a statistically significant effect on the DRC in all of the 17 donors, however, the levels varied considerably between individuals (2.0-19.6%). When the effect of folic acid substituted on the DRC was compared to donor age, we observed that there was less DNA repair in old donors compared to the younger donors, although this was only significant at lower levels.