Induction of p53 expression in skin by radiotherapy and UV radiation: a randomized study

Q-switched 1064 nm Nd: YAG laser restores skin photoageing by activating autophagy by TGFβ1 and ITGB1

Excessive ultraviolet B ray (UVB) exposure to sunlight results in skin photoageing. Our previous research showed that a Q-switched 1064 nm Nd: YAG laser can alleviate skin barrier damage through miR-24-3p. However, the role of autophagy in the laser treatment of skin photoageing is still unclear. This study aims to investigate whether autophagy is involved in the mechanism of Q-switched 1064 nm Nd: YAG in the treatment of skin ageing. In vitro, primary human dermal fibroblast (HDF) cells were irradiated with different doses of UVB to establish a cell model of skin photoageing. In vivo, SKH-1 hairless mice were irradiated with UVB to establish a skin photoageing mouse model and irradiated with laser. The oxidative stress and autophagy levels were detected by western blot, immunofluorescence and flow cytometer. String was used to predict the interaction protein of TGF-β1, and CO-IP and GST-pull down were used to detect the binding relationship between TGFβ1 and ITGB1. In vitro, UVB irradiation reduced HDF cell viability, arrested cell cycle, induced cell senescence and oxidative stress compared with the control group. Laser treatment reversed cell viability, senescence and oxidative stress induced by UVB irradiation and activated autophagy. Autophagy agonists or inhibitors can enhance or attenuate the changes induced by laser treatment, respectively. In vivo, UVB irradiation caused hyperkeratosis, dermis destruction, collagen fibres reduction, increased cellular senescence and activation of oxidative stress in hairless mice. Laser treatment thinned the stratum corneum of skin tissue, increased collagen synthesis and autophagy in the dermis, and decreased the level of oxidative stress. Autophagy agonist rapamycin and autophagy inhibitor 3-methyladenine (3-MA) can enhance or attenuate the effects of laser treatment on the skin, respectively. Also, we identified a direct interaction between TGFB1 and ITGB1 and participated in laser irradiation-activated autophagy, thereby inhibiting UVB-mediated oxidative stress further reducing skin ageing. Q-switched 1064 nm Nd: YAG laser treatment inhibited UVB-induced oxidative stress and restored skin photoageing by activating autophagy, and TGFβ1 and ITGB1 directly incorporated and participated in this process.

Association of Merkel Cell Polyomavirus Status With p53, RB1, and PD-L1 Expression and Patient Prognosis in Merkel Cell Carcinomas: Clinical, Morphologic, and Immunohistochemical Evaluation of 17 Cases

BACKGROUND

Merkel cell carcinoma (MCC) is a rare, aggressive, primary neuroendocrine carcinoma of the skin whose main risk factors are immunosuppression, UV radiation exposure, and Merkel cell polyomavirus. Programmed death-1/programmed death ligand-1 (PD-L1)-based immunotherapy is currently the first choice for treating patients with metastatic MCC.

METHODS

MCC biopsies (17) were evaluated for their nucleus and cytoplasm characteristics and growth patterns, as well as for intratumor lymphocytes, mitotic number, and lymphovascular invasion. Paraffin-embedded tissue samples of the biopsies were stained with MCPyV large T-antigen (LTag), RB1, p53, and PD-L1.

RESULTS

We observed MCPyV LTag expression in 9 out of the 17 tumors, and all 9 cases were positive for RB1 (P<0.000). p53 staining was not significantly correlated with MCPyV LTag. We observed no relationship between p53 expression and any other parameters, and PD-L1 expression was low in the MCC samples. We evaluated PD-L1 using both the combined positive score and tumor proportion score (TPS), and found that TPS was correlated with MCPyV LTag expression (P=0.016). Tumors with tumor-infiltrating lymphocytes showed a better prognosis than those without these lymphocytes (P=0.006).

DISCUSSION

Our data demonstrated that RB1 was effective for immunohistochemically investigating the MCPyV status of tumors. TPS was superior to the combined positive score in evaluating PD-L1 in MCC. Tumor-infiltrating lymphocytes were the only parameters that were associated with survival. Further studies with larger series are required to confirm these results.

The Benefit of Reactivating p53 under MAPK Inhibition on the Efficacy of Radiotherapy in Melanoma

Radiotherapy (RT) in patients with melanoma historically showed suboptimal results, because the disease is often radioresistant due to various mechanisms such as scavenging free radicals by thiols, pigmentary machinery, or enhanced DNA repair. However, radiotherapy has been utilized as adjuvant therapy after the complete excision of primary melanoma and lymph nodes to reduce the rate of nodal recurrences in high-risk patients. The resistance of melanoma cells to radiotherapy may also be in relation with the constitutive activation of the MAPK pathway and/or with the inactivation of p53 observed in about 90% of melanomas. In this study, we aimed to assess the potential benefit of adding RT to BRAF-mutated melanoma cells under a combined p53 reactivation and MAPK inhibition in vitro and in a preclinical animal model. We found that the combination of BRAF inhibition (vemurafenib, which completely shuts down the MAPK pathway), together with p53 reactivation (PRIMA-1Met) significantly enhanced the radiosensitivity of BRAF-mutant melanoma cells. This was accompanied by an increase in both p53 expression and activity. Of note, we found that radiation alone markedly promoted both ERK and AKT phosphorylation, thus contributing to radioresistance. The combination of vemurafenib and PRIMA-1Met caused the inactivation of both MAPK kinase and PI3K/AKT pathways. Furthermore, when combined with radiotherapy, it was able to significantly enhance melanoma cell radiosensitivity. Interestingly, in nude mice bearing melanoma xenografts, the latter triple combination had not only a synergistic effect on tumor growth inhibition, but also a potent control on tumor regrowth in all animals after finishing the triple combination therapy. RT alone had only a weak effect. In conclusion, we provide a basis for a strategy that may overcome the radioresistance of BRAF-mutated melanoma cells to radiotherapy. Whether this will translate into a rational to use radiotherapy in the curative setting in BRAF-mutated melanoma patients deserves consideration.

Effective blue light photodynamic therapy does not affect cutaneous langerhans cell number or oxidatively damage DNA

BACKGROUND

Photodynamic therapy (PDT) using aminolevulinic acid (ALA) with blue light or red light is effective for treating actinic keratoses (AKs). However, immunosuppression follows red light PDT, raising the spectre of skin cancer promotion in treated skin.

OBJECTIVE

To determine whether broad-area short incubation (BASI)-ALA-PDT using blue light immunosuppression immunosuppresses treated skin.

METHODS

Patients were evaluated clinically and by standardized facial biopsies of non-AK skin before, 24 hours and 1 month after customary blue light BASI-ALA-PDT. All biopsies were stained for markers of epidermal atypia and Langerhans cells (LCs); and at 24 hours to detect oxidative DNA damage.

RESULTS

Patients had an 81% reduction in AKs and slight improvement in clinical and histologic signs of photoaging after 1 month. The biopsied chronically photodamaged skin without clinically detectable AKs showed no effect of PDT on the LC number, distribution, or morphology; and no oxidative DNA damage, in contrast to the changes reported after customary red light PDT.

CONCLUSION

Customary blue light BASI-ALA-PDT does not affect the LC number or produce oxidative DNA damage, the sequelae of red light PDT responsible for immunosuppression in treated skin.

A tissue graft model of DNA damage response in the normal and malignant human prostate

PURPOSE

DNA damage responses are relevant to prostate cancer initiation, progression and treatment. Few models of the normal and malignant human prostate that maintain stromal-epithelial interactions in vivo exist in which to study DNA damage responses. We evaluated the feasibility of maintaining tissue slice grafts at subcutaneous vs subrenal capsular sites in RAG2(-/-)γC(-/-) mice to study the DNA damage responses of normal and malignant glands.

MATERIALS AND METHODS

We compared the take rate and histology of tissue slice grafts from fresh, precision cut surgical specimens that were maintained for 1 to 4 weeks in subcutaneous vs subrenal capsular sites. Induction of γH2AX, p53, ATM and apoptosis was evaluated as a measure of the DNA damage response after irradiation.

RESULTS

The take rate of subcutaneous tissue slice grafts was higher than typically reported but lower than at the subrenal capsular site. Subcutaneous tissue slice grafts frequently showed basal cell hyperplasia, squamous metaplasia and cystic atrophy, and cancer did not survive. In contrast, normal and malignant histology was well maintained in subrenal capsular tissue slice grafts. Regardless of implantation site the induction of γH2AX and ATM occurred in tissue slice graft epithelium 1 hour after irradiation and decreased to basal level by 24 hours, indicating DNA damage recognition and repair. As observed previously in prostatic ex vivo models, p53 was not activated. Notably, tumor but not normal cells responded to irradiation by undergoing apoptosis.

CONCLUSIONS

To our knowledge this is the first study of DNA damage responses in a patient derived prostate tissue graft model. The subrenal capsular site of RAG2(-/-)γC(-/-) mice optimally maintains normal and malignant histology and function, permitting novel studies of DNA damage responses in a physiological context.

Dose-dependent onset of regenerative program in neutron irradiated mouse skin

Background

Tissue response to irradiation is not easily recapitulated by cell culture studies. The objective of this investigation was to characterize, the transcriptional response and the onset of regenerative processes in mouse skin irradiated with different doses of fast neutrons.

Methodology/Principal Findings

To monitor general response to irradiation and individual animal to animal variation, we performed gene and protein expression analysis with both pooled and individual mouse samples. A high-throughput gene expression analysis, by DNA oligonucleotide microarray was done with three months old C57Bl/6 mice irradiated with 0.2 and 1 Gy of mono-energetic 14 MeV neutron compared to sham irradiated controls. The results on 440 irradiation modulated genes, partially validated by quantitative real time RT-PCR, showed a dose-dependent up-regulation of a sub-class of keratin and keratin associated proteins, and members of the S100 family of Ca²⁺-binding proteins. Immunohistochemistry confirmed mRNA expression data enabled mapping of protein expression. Interestingly, proteins up-regulated in thickening epidermis: keratin 6 and S100A8 showed the most significant up-regulation and the least mouse-to-mouse variation following 0.2 Gy irradiation, in a concerted effort toward skin tissue regeneration. Conversely, mice irradiated at 1 Gy showed most evidence of apoptosis (Caspase-3 and TUNEL staining) and most 8-oxo-G accumulation at 24 h post-irradiation. Moreover, no cell proliferation accompanied 1 Gy exposure as shown by Ki67 immunohistochemistry.

Conclusions/Significance

The dose-dependent differential gene expression at the tissue level following in vivo exposure to neutron radiation is reminiscent of the onset of re-epithelialization and wound healing and depends on the proportion of cells carrying multiple chromosomal lesions in the entire tissue. Thus, this study presents in vivo evidence of a skin regenerative program exerted independently from DNA repair-associated pathways.

Differential contextual responses of normal human breast epithelium to ionizing radiation in a mouse xenograft model

Radiotherapy is a key treatment option for breast cancer, yet the molecular responses of normal human breast epithelial cells to ionizing radiation are unclear. A murine subcutaneous xenograft model was developed in which nonneoplastic human breast tissue was maintained with the preservation of normal tissue architecture, allowing us to study for the first time the radiation response of normal human breast tissue in situ. Ionizing radiation induced dose-dependent p53 stabilization and p53 phosphorylation, together with the induction of p21(CDKN1A) and apoptosis of normal breast epithelium. Although p53 was stabilized in both luminal and basal cells, induction of Ser392-phosphorylated p53 and p21 was higher in basal cells and varied along the length of the ductal system. Basal breast epithelial cells expressed ΔNp63, which was unchanged on irradiation. Although stromal responses themselves were minimal, the response of normal breast epithelium to ionizing radiation differed according to the stromal setting. We also demonstrated a dose-dependent induction of γ-H2AX foci in epithelial cells that was similarly dependent on the stromal environment and differed between basal and luminal epithelial cells. The intrinsic differences between human mammary cell types in response to in vivo irradiation are consistent with clinical observation that therapeutic ionizing radiation is associated with the development of basal-type breast carcinomas. Furthermore, there may be clinically important stromal-epithelial interactions that influence DNA damage responses in the normal breast. These findings demonstrate highly complex responses of normal human breast epithelium following ionizing radiation exposure and emphasize the importance of studying whole-tissue effects rather than single-cell systems.

Immunohistochemical analysis of P53 protein in odontogenic cysts

The p53 is a well-known tumor suppressor gene, the mutations of which are closely related to the decreased differentiation of cells. Findings of studies on immunohistochemical P53 expression in odontogenic cysts are controversial. The present study was carried-out to investigate the immunohistochemical expression of P53 protein in odontogenic cysts. Thirty paraffin blocks of diagnosed odontogenic cysts were processed to determine the immunohistochemical expression of P53 protein. Nine of the 11 odontogenic keratocysts (81.8%) expressed P53, one of three dentigerous cyst cases expressed P53, while none of the 16 radicular cysts expressed P53 protein. The findings of the present work supported the reclassification of OKC as keratocystic odontogenic tumor.

Differential gene expression in primary human skin keratinocytes and fibroblasts in response to ionizing radiation

Although skin is usually exposed during human exposures to ionizing radiation, there have been no thorough examinations of the transcriptional response of skin fibroblasts and keratinocytes to radiation. The transcriptional response of quiescent primary fibroblasts and keratinocytes exposed to from 10 cGy to 5 Gy and collected 4 h after treatment was examined. RNA was isolated and examined by microarray analysis for changes in the levels of gene expression. Exposure to ionizing radiation altered the expression of 279 genes across both cell types. Changes in RNA expression could be arranged into three main categories: (1) changes in keratinocytes but not in fibroblasts, (2) changes in fibroblasts but not in keratinocytes, and (3) changes in both. All of these changes were primarily of p53 target genes. Similar radiation-induced changes were induced in immortalized fibroblasts or keratinocytes. In separate experiments, protein was collected and analyzed by Western blotting for expression of proteins observed in microarray experiments to be overexpressed at the mRNA level. Both Q-PCR and Western blot analysis experiments validated these transcription changes. Our results are consistent with changes in the expression of p53 target genes as indicating the magnitude of cell responses to ionizing radiation.

Cellular and sub-cellular responses to UVA in relation to carcinogenesis

PURPOSE

UVA radiation (315-400 nm) contributes to skin aging and carcinogenesis. The aim of this review is to consider the mechanisms that underlie UVA-induced cellular damage, how this damage may be prevented or repaired and the signal transduction processes that are elicited in response to it.

RESULTS

Exposure to ultraviolet (UV) light is well-established as the causative factor in skin cancer. Until recently, most work on the mechanisms that underlie skin carcinogenesis focused on shorter wavelength UVB radiation (280-315 nm), however in recent years there has been increased interest in the contribution made by UVA. UVA is able to cause a range of damage to cellular biomolecules including lipid peroxidation, oxidized protein and DNA damage, such as 8-oxoguanine and cyclobutane pyrimidine dimers. Such damage is strongly implicated in both cell death and malignant transformation and cells have a number of mechanisms in place to mitigate the effects of UVA exposure, including antioxidants, DNA repair, and stress signalling pathways.

CONCLUSIONS

The past decade has seen a surge of interest in the biological effects of UVA exposure as its significance to the process of photo-carcinogenesis has become increasingly evident. However, unpicking the unique complexity of the cellular response to UVA, which is only now becoming apparent, will be a major challenge for the field of photobiology in the 21st century.

Association between TP53 codon 72 single-nucleotide polymorphism and radiation sensitivity of human fibroblasts

Inherent radiosensitivity varies widely between individuals. We hypothesized that amino acid substitution variants in two highly radiation-responsive proteins, TP53 (p53) and CDKN1A (p21, Waf1, Cip1), are associated with and could explain individual variations in radiosensitivity. The two non-synonymous single-nucleotide polymorphisms (SNPs) TP53 codon 72 Arg/Pro G>C and CDKN1A codon 31 Ser/Arg C>A were genotyped in 92 normal fibroblast cell strains of different radiosensitivity. The clonogenic surviving fraction at 2 Gy (SF2) ranged between 0.15 and 0.50 (mean = 0.34, SD = 0.08). The mean SF2 was used to divide the cell strains into radiosensitive (45) and normal groups (47). A significant association was observed between SF2 and the TP53 codon 72 haplotype (C compared to G, P = 0.01). No association was observed between CDKN1A codon 31 haplotype and radiosensitivity (P = 0.86). The variant TP53 Arg72 allele was associated with a decrease in radiosensitivity, presumably due to suboptimal function leading to less stringent control of cell division. We conclude that certain SNPs in susceptible genes can influence cellular radiation response. Such risk alleles could ultimately be used as predictive markers for radiosensitivity to help stratifying individuals during assessment of risk of radiation exposure.

Radiosensitivity of Human Fibroblasts is Associated With Amino Acid Substitution Variants in Susceptible Genes And Correlates With The Number of Risk Alleles

PURPOSE

Genetic predictive markers of radiosensitivity are being sought for stratifying radiotherapy for cancer patients and risk assessment of radiation exposure. We hypothesized that single nucleotide polymorphisms in susceptible genes are associated with, and the number of risk alleles has incremental effect on, individual radiosensitivity.

METHODS AND MATERIALS

Six amino acid substitution variants (ATM 1853 Asp/Asn G>A, p53 72 Arg/Pro G>C, p21 31 Ser/Arg C>A, XRCC1 399 Arg/Gln G>A, XRCC3 241 Thr/Met C>T, and TGFbeta1 10 Leu/Pro T>C) were genotyped by direct sequencing in 54 fibroblast strains of different radiosensitivity.

RESULTS

The clonogenic survival fraction at 2 Gy range was 0.15-0.50 (mean, 0.34, standard deviation, 0.08). The mean survival fraction at 2 Gy divided the cell strains into radiosensitive (26 cases) and normal (28 controls). A significant association was observed between the survival fraction at 2 Gy and ATM 1853 Asn, XRCC3 241 Met, and TGFbeta1 10 Leu alleles (p = 0.05, p = 0.02, and p = 0.02, respectively). The p53 72 Arg allele showed a borderline association (p = 0.07). The number of risk alleles increased with increasing radiosensitivity, and the group comparison showed a statistically significant difference between the radiosensitive and control groups (p < or = 0.001).

CONCLUSION

The results of our study have shown that single nucleotide polymorphisms in susceptible genes influence cellular radiation response and that the number of risk alleles has a combined effect on radiosensitivity. Individuals with multiple risk alleles could be more susceptible to radiation effects than those with fewer risk alleles. These results may have implications in predicting normal tissue reactions to radiotherapy and risk assessment of radiation exposure.

Evidence that Individual Variations in TP53 and CDKN1A Protein Responsiveness are Related to Inherent Radiation Sensitivity

We tested the hypothesis that individual variations in the induction of the TP53 tumor suppressor protein by radiation are related to inherent radiosensitivity. Thirty-two fibroblast cell strains were examined. Radiosensitivity was measured by a clonogenic survival assay. The induction of TP53 and its transcriptionally activated CDKN1A (p21) protein were studied by Western blotting 3 h after a single dose of 5 Gy. The relative cell culture age, as determined by the colony size distribution, was studied as a confounding factor. Survival curves showed wide range of radiosensitivity. The surviving fraction at 2 Gy (SF2) ranged between 0.02 and 0.49 (mean = 0.29, SD = 0.13). TP53 induction ranged between 1.28 and 2.34 (mean = 1.80, SD = 0.31). CDKN1A showed a wider induction (1.09-4.05, mean = 2.33, SD = 0.78). Positive correlations were observed between SF2 and TP53 induction (R(2) = 0.62, P < 0.001) and CDKN1A (R(2) = 0.64, P < 0.001). No correlation with the colony size distribution was observed. In conclusion, these results suggest that the individual variations in radiosensitivity and in the level of induction of TP53 (and consequently CDKN1A) are congruent, irrespective of the genetic background of these nontransformed fibroblasts. It is postulated that underlying mechanisms culminating in a stronger TP53 induction lead to higher survival, presumably due to more efficient repair of radiation-induced damage.

Ophthalmic and adnexal complications of radiotherapy

The role of radiotherapy in ophthalmic practice continues to grow. This growth has seen an expansion of indications for radiotherapy, a refinement of the modalities that can be used and a reduction in the ocular and adnexal complications that result from this form of therapy. The compendium of indications for radiotherapy in ophthalmology continues to grow and now includes many conditions such as the treatment of lid and adnexal disease, ocular surface disorders and both benign and malignant disease of the posterior segment and optic pathways. The radiotherapeutic modalities employed to manage these conditions are numerous and include both radioactive plaques (brachytherapy) and external beam radiation techniques. New techniques such as stereotactic radiosurgery are delivering benefits in the management of conditions such as optic nerve sheath meningioma, where the treatment of this blinding and occasionally life-threatening intracranial neoplasm now results in fewer adverse affects. The purpose of this review is to give a brief overview of the indications and treatment modalities, and a more in-depth discussion of the potential side-effects when radiotherapy is used for ocular and periorbital disease.

Radiation-induced cutaneous carcinoma of the head and neck: is there an early role for p53 mutations?

BACKGROUND

Little is known about the molecular mechanisms underlying ionizing radiation-induced carcinogenesis of the skin.

AIMS

To investigate the possible role of p53 in radiodermatitis and in the development of radiation-induced cutaneous carcinomas.

METHODS

The study group comprised six patients affected by cutaneous carcinomas arising in radiodermatitis (one squamous cell carcinoma and five basal cell carcinomas), and seven patients presenting only chronic radiodermatitis. Skin specimens were evaluated for p53 immunohistochemical expression. Using laser-assisted microdissection, areas with different p53 immunoreactivity were separately submitted to DNA isolation and p53 gene analysis.

RESULTS

In the majority of cases (9/12, 75%), p53 immunoreactivity was detected in radiation-damaged epidermis. In carcinomas p53 oncoprotein was expressed by several neoplastic cells in one case (16.7%%), or by nearly all neoplastic cells in four (66.7%). SSCP band shifts were detected in 9/25 samples (36%) microdissected from irradiated epidermis and in 3/6 (50%) carcinomas. DNA sequencing demonstrated two repeatedly found mutations: a G deletion at codon 244 and an A-->G transition at codon 205, as well as hallmarks of ultraviolet mutagenic action, including a C-->T transition occurring at a dipyrimidine site and a CC-->TT tandem double-base transition.

CONCLUSION

Our data indicate that irradiation induces significant p53 alterations that may be relevant in the modification of epithelial maturation processes and may be responsible for the high risk for development of carcinomas in radiodermatitis.

Radiation-induced effects on gene expression: an in vivo study on breast cancer

BACKGROUND AND PURPOSE

Breast cancer is diagnosed worldwide in approximately one million women annually and radiation therapy is an integral part of treatment. The purpose of this study was to investigate the molecular basis underlying response to radiotherapy in breast cancer tissue.

MATERIAL AND METHODS

Tumour biopsies were sampled before radiation and after 10 treatments (of 2 Gray (Gy) each) from 19 patients with breast cancer receiving radiation therapy. Gene expression microarray analyses were performed to identify in vivo radiation-responsive genes in tumours from patients diagnosed with breast cancer. The mutation status of the TP53 gene was determined by using direct sequencing.

RESULTS AND CONCLUSION

Several genes involved in cell cycle regulation and DNA repair were found to be significantly induced by radiation treatment. Mutations were found in the TP53 gene in 39% of the tumours and the gene expression profiles observed seemed to be influenced by the TP53 mutation status.

Interleukin 1beta (IL1B) signaling is a critical component of radiation-induced skin fibrosis

Interleukin 1 beta (IL1B), a potent pro-inflammatory cytokine, is directly up-regulated by radiation and is known to regulate other inflammation-related molecules, such as the matrix metalloproteinases (MMPs) and their endogenous inhibitors (TIMPs). However, the nature of the interaction of IL1B with MMPs and TIMPs in radiation-induced skin fibrosis is unknown. We examined the response of primary dermal keratinocytes, fibroblasts and endothelial cells to single-fraction radiation (10 Gy) and compared the results to a temporal sequence of histology from irradiated C57BL/6 and IL1R1 knockout mice. These studies showed that keratinocytes are the major IL1-producing cells in vitro and that radiation induces an immediate and chronic elevation in the expression of IL1B mRNA in the skin of C57BL/6 mice. This elevation was principally early and was less pronounced in the IL1R1 knockout strain, which also demonstrated reduced late radiation fibrosis. Radiation also increased expression of MMP mRNA in C57BL/6 mice. Finally, exogenous IL1B protein induced robust endogenous IL1B mRNA expression, along with a brisk increase in MMPs and collagen III, but only in the C57BL/6 mice. In conclusion, these data suggest that IL1B plays a critical role in radiation-induced fibrosis and that the increased MMPs fail to block the IL1-related collagen accumulation.

Accumulation, activation and interindividual variation of the epidermal TP53 protein in response to ionizing radiation in organ cultured human skin

In this study, we examined effects of low-dose ionizing radiation on organ cultured human foreskin and, in particular, on the epidermis. Diagnostic, therapeutic, natural environmental and incidental exposures to moderate to low doses of radiation are inevitable and, although information on cultured cells continues to accumulate, little is known about the effects of low-dose radiation on human tissues. Our hypothesis is that ex vivo organ cultured foreskin is a simple and reliable model to study the biochemical effects of low-dose radiation exposure on skin. A model such as this will aid in the identification and quantification of low-dose radiation-induced changes in proteins in human skin and may be useful in the development of a precise, non-invasive, and reliable assay of exposure. In this work, several aspects of skin responses to culture conditions and radiation were examined. The responses of epidermal TP53 from organ cultured skin irradiated in medium with and without serum were found to be similar. TP53 levels in organ cultured neonatal foreskin epidermis were then examined for baseline TP53 expression. After an initial increase at 4 h, the TP53 D01 signal returned to low steady-state levels for at least 72 h. Irradiated skin samples from different individuals revealed variations in the TP53 D01 signal. The dose and temporal response of dermis and epidermis to radiation were examined by Western blotting from 0 to 24 h after exposure. After irradiation and incubation, the epidermis was removed and assayed by Western blotting and was found to have increases in the TP53 D01 epitope and the TP53 phosphoserine 15 (TP53-S15p) epitope that reached a maximum at about 3 h. In the epidermis, doses of 1-5 cGy of radiation were detectable with the TP53 D01, and CDKN1A antibodies and doses greater than 10 cGy were detectable with the TP53-S15p antibody. When the dermis was compared to epidermis, it was found that dermis had a smaller response to radiation and more phosphorylated TP53.

Ultraviolet Irradiation Represses PATCHED Gene Transcription in Human Epidermal Keratinocytes through an Activator Protein-1-Dependent Process

Basal cell carcinoma (BCC) is one of the major types of skin cancer arising from keratinocytes. The SONIC HEDGEHOG pathway is deregulated in 100% of sporadic BCCs, as indicated by the overexpression of PATCHED, whose product encodes the receptor of SONIC HEDGEHOG, in 100% of analyzed BCCs. Reverse transcription-PCR analysis revealed that exposure to UVB irradiation, which is a risk factor known to contribute to BCC development, induces a strong and sharp decrease of PATCHED mRNA level both in vitro and ex vivo. Transcription of a reporter gene driven by the 4.4-kb 5'-regulatory region of the human PATCHED gene was shown to be down-regulated after UVB irradiation. Furthermore, overexpression of c-JUN, a member of the activator protein (AP)-1 family, induced repression of the PATCHED promoter. The role of AP-1 in UVB-induced PATCHED repression was confirmed in mouse embryonic fibroblasts knocked out for c-JUN NH(2)-terminal protein kinase. This study thus provides the first evidence of UV-induced down-regulation at the transcriptional level of the BCC-associated tumor suppressor PATCHED relying on activation of the AP-1 oncogenic pathway.

Solar ultraviolet radiation as a trigger of cell signal transduction

Ultraviolet light radiation in sunlight is known to cause major alterations in growth and differentiation patterns of exposed human tissues. The specific effects depend on the wavelengths and doses of the light, and the nature of the exposed tissue. Both growth inhibition and proliferation are observed, as well as inflammation and immune suppression. Whereas in the clinical setting, these responses may be beneficial, for example, in the treatment of psoriasis and atopic dermatitis, as an environmental toxicant, ultraviolet light can induce significant tissue damage. Thus, in the eye, ultraviolet light causes cataracts, while in the skin, it induces premature aging and the development of cancer. Although ultraviolet light can damage many tissue components including membrane phospholipids, proteins, and nucleic acids, it is now recognized that many of its cellular effects are due to alterations in growth factor- and cytokine-mediated signal transduction pathways leading to aberrant gene expression. It is generally thought that reactive oxygen intermediates are mediators of some of the damage induced by ultraviolet light. Generated when ultraviolet light is absorbed by endogenous photosensitizers in the presence of molecular oxygen, reactive oxygen intermediates and their metabolites induce damage by reacting with cellular electrophiles, some of which can directly initiate cell signaling processes. In an additional layer of complexity, ultraviolet light-damaged nucleic acids initiate signaling during the activation of repair processes. Thus, mechanisms by which solar ultraviolet radiation triggers cell signal transduction are multifactorial. The present review summarizes some of the mechanisms by which ultraviolet light alters signaling pathways as well as the genes important in the beneficial and toxic effects of ultraviolet light.

Resistance to UV-induced apoptosis in human keratinocytes during accelerated senescence is associated with functional inactivation of p53

Compared to proliferating keratinocytes (KCs), growth-arrested KCs are relatively resistant to UV-light induced apoptosis. When KCs undergo confluency, or following exposure to anti-proliferative agents such as IFN-gamma plus a phorbol ester-12-O-tetradecanoylyphorbol-13-acetate (TPA), they convert from a proliferative to a nonproliferative state resembling senescence. Since p53 regulates UV-induced apoptosis of KCs, this report further characterizes p53 half-life, post-translational modifications, and transcriptional activity using cultured human KCs and living epidermal equivalents. The half-life of p53 in KCs was longer than fibroblasts (greater than approximately 3 h vs. 30 min). Exposure of proliferating KCs to UV-light induces post-translational modifications of p53 including acetylation of lysine-382 residues. By contrast, KCs undergoing irreversible growth arrest following confluency, or exposure to IFN-gamma plus TPA, were resistant to UV-induced apoptosis, and failed to undergo the acetylation modification of p53. Exposure of KCs to IFN-gamma plus TPA reduced total cellular p53 levels and reduced the transcriptional activity of p53. Addition of Trichostatin A (TSA), an inhibitor of de-acetylation, increased acetylation of lysine-382 in confluent KCs, thereby enhancing susceptibility of confluent cultures to UV-induced apoptosis. Pre-treatment of epidermal equivalents with IFN-gamma plus TPA also blocked UV-light induced increase in p53 levels, and reduced apoptosis. In conclusion, these studies demonstrate that growth arrested KCs may resist UV-light induced apoptosis by inactivating the pro-apoptotic function of p53.

Chorionic gonadotropin regulates the transcript level of VHL, p53, and HIF-2? in human granulosa lutein cells

The ovarian corpus luteum plays a critical role in reproduction being the primary source of circulating progesterone. After ovulation the corpus luteum is build by avascular granulosa lutein cells through rapid vascularization regulated by gonadotropic hormones. The present study was performed to investigate whether this process might be influenced by the human chorionic gonadotropin (hCG)-dependent expression of different tumor suppressor genes and hypoxia dependent transcription factors. RNA was isolated from cultured granulosa lutein cells, transcribed into cDNA, and the transcript level of following genes were determined: RB-1, VHL, NF-1, NF-2, Wt-1, p53, APC, and hypoxia inducible factor-1 (HIF-1), -2, and -3alpha. Additionally, the influence of hCG on the expression of VHL, p53, and HIf2alpha were investigated. We demonstrate that in human granulosa lutein cells the tumor suppressor genes RB-1, VHL, NF-1, NF-2, Wt-1, p53, and APC and the hypoxia dependent transcription factors HIF-1alpha, -2alpha, and -3alpha are expressed. In addition, we showed that hCG regulates the expression of p53, VHL, and HIF-2alpha. Our results indicate that hCG may determine the growth and development of the corpus luteum by mediating hypoxic and apoptotic pathways in human granulosa lutein cells.

Human immunodeficiency virus type-1 Tat/co-activator acetyltransferase interactions inhibit p53Lys-320 acetylation and p53-responsive transcription

Patients with AIDS are at increased risk for developing various neoplasms, including Hodgkin's and non-Hodgkin's lymphomas, Kaposi's sarcomas, and anal-rectal carcinomas, suggestive that human immunodeficiency virus type-1 infection might promote establishment of AIDS-related cancers. Tat, the viral trans-activator, can be endocytosed by uninfected cells and has been shown to inhibit p53 functions, providing a candidate mechanism through which the human immunodeficiency virus type-1 might contribute to malignant transformation. Because Tat has been shown to interact with histone acetyltransferase domains of p300/cAMP-responsive element-binding protein (CREB)-binding protein and p300/CREB-binding protein-associated factor, we have investigated whether Tat might alter p53 acetylation and tumor suppressor-responsive transcription. Here, we demonstrate that both Tat and p53 co-localize with p300/CREB-binding protein-associated factor and p300 in nuclei of IMR-32 human neuroblastoma cells and in PC-12 pheochromocytoma cells. Further, p53 trans-activation of the 14-3-3varsigma promoter was markedly repressed by Tat-histone acetyltransferase interactions, and p53 acetylation by p300/CREB-binding protein-associated factor on residue Lys(320) was diminished as a result of Tat-histone acetyltransferase binding in vivo and in vitro. Tat also inhibited p53 acetylation by p300 in a dosage-dependent manner in vitro. Finally, HIV-1-infected Molt-4 cells displayed reduced p53 acetylation on lysines 320 and 373 in response to UV irradiation. Our results allude to a mechanism whereby the human immunodeficiency virus type-1 trans-activator might impair tumor suppressor functions in immune/neuronal-derived cells, thus favoring the establishment of neoplasia during AIDS.

TP53 mutations in workers exposed to occupational carcinogens

In some cases, evidence exists that exogenous carcinogenic exposures contribute to the mutation spectrum of the TP53 gene (p53) in human cancers. Although the clearest examples come from dietary and environmental sources, only a restricted number of papers have concentrated specifically on TP53 mutations in tumors from workers exposed to occupational carcinogens. In populations exposed to dietary aflatoxin B1 with liver cancer (AFB1) and ultraviolet (UV)-radiation with skin cancer, a single specific-looking TP53 mutation has been described in some of the tumors. Whether these fingerprints in the TP53 gene can be used to reveal an occupational etiology remains to be shown. In other cases, although differences in the TP53 mutation spectrum exist, they are more diffuse and difficult to interpret at this point. For instance, cigarette smoking seems to induce long-lasting molecular footprints in TP53. However, their use to rule out other occupational exposures as etiological factors in occupational cancers is still very questionable, especially due to the putative synergistic effects of cigarette smoke with other carcinogens. Although interesting implications of possible typical mutation spectra among cancers with other occupational etiologies exist, the data are scanty and await further development of TP53 mutation databases.

The mutagenic effect of ultraviolet-A1 on human skin demonstrated by sequencing the p53 gene in single keratinocytes

BACKGROUND

Sun exposure is accepted as the major risk factor for developing skin cancer, the most common cancer in the western world. Ultraviolet-B (UV-B) radiation is considered the causative agent, but recently several findings suggest a role also for ultraviolet-A (UV-A) radiation. Repeated suberythemal doses of ultraviolet-A1 (UV-A1) on healthy human skin induce an increase of p53 immunoreactive cells in epidermis, which may indicate cell cycle arrest and/or occurrence of p53 mutations.

METHODS

We have investigated the possible mutagenic effect of UV-A1 on skin by sequencing exons 4-11 and adjacent intron sequence of the p53 gene in immunoreactive single cells from three healthy individuals. Previously unexposed buttock skin was irradiated three times a week for 2 weeks with physiological fluences (40 J/cm2) of UV-A1. Punch biopsies were taken before and at different time-points after the exposure, and from these single p53 immunoreactive cells were isolated by using laser-assisted microdissection.

RESULTS

Three mutations--all being indicative of oxidative damage and most likely related to UV-A exposure--were found among the 37 single cells from exposed skin, whereas no mutations were found in the 22 single cells taken before exposure.

CONCLUSIONS

The findings indicate a mutagenic effect of low-dose UV-A1 on healthy human skin, which further demonstrates the importance of considering UV-A when taking protective measures against skin cancer.

UVB light suppresses nitric oxide production by murine keratinocytes and macrophages

Nitric oxide is an important mediator of excessive cell growth and inflammation associated with many epidermal proliferative disorders. It is a highly reactive oxidant generated in keratinocytes and macrophages via the inducible form of the enzyme nitric oxide synthase (NOS2). In the present studies, we examined the effects of ultraviolet light (UVB, 2.5-25mJ/cm(2)) on interferon-gamma (IFN-gamma)-induced expression of NOS2 in these cells. Transient transfection assays using wild-type and mutant NOS2 promoter/luciferase reporter constructs showed that DNA binding of the transcription factors Stat1 and NF-kappaB was essential for optimal expression of the NOS2 gene. Whereas NF-kappaB was constitutively expressed in both cell types, Stat1 phosphorylation and nuclear binding activity were dependent upon IFN-gamma. UVB light, which is used therapeutically to treat inflammatory dermatosis, was found to suppress IFN-gamma-induced expression of NOS2 mRNA and protein, and nitric oxide production in both keratinocytes and macrophages. In macrophages, this was associated with complete inhibition of NF-kappaB nuclear binding activity and partial (approximately 20-25%) reduction of Stat1 activity. In keratinocytes, both responses were partially reduced at the highest doses of UVB light (15-25mJ/cm(2)). Whereas in macrophages UVB light suppressed NOS2 wild-type promoter-luciferase reporter activity, this activity was stimulated in keratinocytes. These data suggest that UVB light functions to suppress NOS2 gene expression in macrophages by inhibiting the activity of key regulatory transcription factors. In contrast, in keratinocytes, inhibition occurs downstream of NOS2 promoter activity.

Similar UV responses are seen in a skin organ culture as in human skin in vivo

Ultraviolet radiation (UVR) plays an important role in the development of non-melanoma skin cancer. Most tumors develop in chronically sun-exposed skin, most often in cosmetically sensitive locations, where in vivo experiments may be difficult to perform. In this study, we describe a skin organ culture model with preserved normal morphology and intact response to UVR. Skin explants from chronically sun-exposed and non-sun-exposed skin were irradiated with artificial UVA+UVB with and without topical sunscreen. UV-induced DNA damage, epidermal p53 response and repair kinetics were analyzed using immunohistochemistry. Four hours after UV-irradiation epidermal keratinocytes showed a strong immunoreactivity for thymine-dimers. Gradual repair during an incubation time resulted in few residual thymine-dimers after 48 h. Repair appeared to be more efficient in chronically sun-exposed skin compared with non-sun-exposed skin. There was also an accumulation of p53 protein in epidermal keratinocytes, peaking at 4-24 h after irradiation. Large interindividual differences with respect to formation and repair of thymine-dimers as well as induction and duration of the p53 response were observed. Skin explants treated with topical sunscreen prior to UV-irradiation showed a clear reduction of thymine-dimers and p53 expression. The epidermal UV-responses and repair kinetics in organ-cultured skin were similar to what was found in vivo. Our data suggest that organ-cultured skin provides a valuable tool for studies of UV-induced epidermal responses in chronically sun-exposed skin.

Regulation of apoptosis by p53 in UV-irradiated human epidermis, psoriatic plaques and senescent keratinocytes

The carcinogenic effects of sunlight in human epidermis may be thwarted by either: transient growth arrest and repair of DNA photodamage in keratinocytes (KCs); elimination of KCs with damaged DNA via apoptosis; or by stimulating a senescence switch whereby KCs become irreversibly growth arrested. Using normal human skin organ cultures and living epidermal equivalents, we demonstrate that in the proliferative basal layer, removal of KCs via apoptosis had a rapid onset (beginning within 2 h) following UV-light exposure generating progressively greater numbers of KCs with thymine dimers as the dose of UV-light was increased; involved induction of Apaf-1, activation of caspase-3, and was dependent on p53 activation as addition of a p53 chemical inhibitor blocked the apoptotic response. Suprabasal layer KCs underwent apoptosis at much later time points (>8 h). KCs in the basal layer repaired DNA damage more rapidly than KCs in suprabasal layers. Steady state levels of p53 increased in irradiated cells, and the increase was accompanied by phosphorylation of serine 9 and serine 15, but not serine 6 residues. By contrast, cultured KCs undergoing spontaneous replicative senescence were resistant to UV-induced apoptosis. Senescent KCs constitutively contained low levels of p53, which were neither increased nor phosphorylated or acetylated after UV-exposure and possessed minimal DNA binding activity, indicative of functional inactivation. Furthermore, treatment of senescent KCs with DNA damaging agent adriamycin did not result in activation of latent p53 or apoptosis. When KCs within psoriatic plaques were examined, they resembled senescent KCs in that they expressed p53, which was not phosphorylated or acetylated. Thus, UV-light induces DNA damage in human epidermal KCs triggering p53 activation, and subsequent apoptosis involving distinct cell layers and kinetics. However, the lack of p53 activation as seen in senescent KCs and psoriatic plaques, is associated with a relative resistance of KCs to UV-induced apoptosis. In conclusion, the sensitivity and resistance of KCs to apoptosis depends not only on the location within various layers of epidermis and levels of p53, but may also involve p53 activation via post-translational modifications.

Persistent p53 mutations in single cells from normal human skin

Epidermal clones of p53-mutated keratinocytes are abundant in chronically sun-exposed skin and may play an important role in early development of skin cancer. Advanced laser capture microdissection enables genetic analysis of targeted cells from tissue sections without contamination from neighboring cells. In this study p53 gene mutations were characterized in single cells from normal, chronically sun-exposed skin. Biopsies were obtained from skin subjected to daily summer sun and skin totally protected from the sun by blue denim fabric. Using laser capture microdissection, 172 single-cell samples were retrieved from four biopsies and analyzed using single-cell polymerase chain reaction and direct DNA sequencing. A total of 14 different mutations were identified in 26 of 99 keratinocytes from which the p53 gene could be amplified. Mutations displayed a typical UV signature and were detected in both scattered keratinocytes and in a small cluster of p53-immunoreactive keratinocytes. This minute epidermal p53 clone had a diameter of 10 to 15 basal cells. Two missense mutations were found in all layers of epidermis within the p53 clone. The presented data show that p53 mutations are common in normal skin and that a clone of keratinocytes with a mutated p53 gene prevailed despite 2 months of total protection from ultraviolet light.