Expression profiling of cancer-related genes in human keratinocytes following non-lethal ultraviolet B irradiation

Desmosomes as Signaling Hubs in the Regulation of Cell Behavior

Desmosomes are intercellular junctions, which preserve tissue integrity during homeostatic and stress conditions. These functions rely on their unique structural properties, which enable them to respond to context-dependent signals and transmit them to change cell behavior. Desmosome composition and size vary depending on tissue specific expression and differentiation state. Their constituent proteins are highly regulated by posttranslational modifications that control their function in the desmosome itself and in addition regulate a multitude of desmosome-independent functions. This review will summarize our current knowledge how signaling pathways that control epithelial shape, polarity and function regulate desmosomes and how desmosomal proteins transduce these signals to modulate cell behavior.

Protective effects of sunscreen (50+) and octatrienoic acid 0.1% in actinic keratosis and UV damages

Actinic keratosis is a form of dysplastic epidermal lesion resulting from chronic and excessive UV exposure with a certain risk of becoming cancerous. Current guidelines advocated the use of sunscreens to prevent photodamage. An efficient photoprotection must involve both primary protective factors such as UV filters and secondary factors (eg, antioxidants) able to disrupt the photochemical and genetic cascade triggered by UVs. An in vitro model of human skin (Phenion FT) was used to assess the photoprotective potential of a sunscreen containing inorganic sun-filters (50+ SPF) and 0.1% octatrienoic acid (KERA’+) after UVA (10 J/cm²) and UVB (25 mJ/cm²) by means of evaluation of the number of sunburn cells (SBCs) and apoptotic keratinocytes. Also resulting alterations in the gene expression of markers involved in apoptosis (Tumor protein 53), inflammation/immunosuppression (IL-6 and IL-8), oxidative stress (oxidative stress response enzyme heme oxygenase 1), remodeling (metalloproteinase 1) and cell-cell adhesion (E-cadherin) were investigated. Gene expression was investigated using quantitative real-time PCR. This work demonstrated that the sunscreen preparations under study (with and without 0.1% octatrienoic acid, respectively) can be distinguished about their ability to prevent UVs-induced damage. Synergism between the inorganic filters and 0.1% octatrienoic acid was found (KERA’+) on all end points analyzed and this effect was found to be statistically significant (p<0.05). Our data revealed that topical application of a sunscreen containing inorganic filters (50+SPF) and 0.1% octatrienoic acid can protect from SBC formation, reduce the number of apoptotic keratinocytes and protect from the main molecular alterations caused by UV radiations.

Cancer Stem Cells, Quo Vadis? The Notch Signaling Pathway in Tumor Initiation and Progression

The Notch signaling pathway regulates cell proliferation, cytodifferentiation and cell fate decisions in both embryonic and adult life. Several aspects of stem cell maintenance are dependent from the functionality and fine tuning of the Notch pathway. In cancer, Notch is specifically involved in preserving self-renewal and amplification of cancer stem cells, supporting the formation, spread and recurrence of the tumor. As the function of Notch signaling is context dependent, we here provide an overview of its activity in a variety of tumors, focusing mostly on its role in the maintenance of the undifferentiated subset of cancer cells. Finally, we analyze the potential of molecules of the Notch pathway as diagnostic and therapeutic tools against the various cancers.

Identification of differentially expressed genes in actinic keratosis samples treated with ingenol mebutate gel

Actinic keratosis is a common skin disease that may progress to invasive squamous cell carcinoma if left untreated. Ingenol mebutate has demonstrated efficacy in field treatment of actinic keratosis. However, molecular mechanisms on ingenol mebutate response are not yet fully understood. In this study, we evaluated the gene expression profiles of actinic keratosis lesions before and after treatment with ingenol mebutate using microarray technology. Actinic keratoses on face/scalp of 15 immunocompetent patients were identified and evaluated after treatment with topical ingenol mebutate gel 0.015%, applied once daily for 3 consecutive days. Diagnostic and clearance of lesions was determined by clinical, dermoscopic, and reflectance confocal microscopy criteria. Lesional and non-lesional skin biopsies were subjected to gene expression analysis profiled by Affymetrix microarray. Differentially expressed genes were identified, and enrichment analyses were performed using STRING database. At 8 weeks post-treatment, 60% of patients responded to ingenol mebutate therapy, achieving complete clearance in 40% of cases. A total of 128 differentially expressed genes were identified following treatment, and downregulated genes (114 of 128) revealed changes in pathways important to epidermal development, keratinocyte differentiation and cornification. In responder patients, 388 downregulated genes (of 450 differentially expressed genes) were also involved in development/differentiation of the epidermis, and immune system-related pathways, such as cytokine and interleukin signaling. Cluster analysis revealed two relevant clusters showing upregulated profile patterns in pre-treatment actinic keratoses of responders, as compared to non-responders. Again, differentially expressed genes were mainly associated with cornification, keratinization and keratinocyte differentiation. Overall, the present study provides insight into the gene expression profile of actinic keratoses after treatment with ingenol mebutate, as well as identification of genetic signatures that could predict treatment response.

Deciphering UV-induced DNA Damage Responses to Prevent and Treat Skin Cancer

Ultraviolet (UV) radiation is among the most prevalent environmental factors that influence human health and disease. Even 1 h of UV irradiation extensively damages the genome. To cope with resulting deleterious DNA lesions, cells activate a multitude of DNA damage response pathways, including DNA repair. Strikingly, UV-induced DNA damage formation and repair are affected by chromatin state. When cells enter S phase with these lesions, a distinct mutation signature is created via error-prone translesion synthesis. Chronic UV exposure leads to high mutation burden in skin and consequently the development of skin cancer, the most common cancer in the United States. Intriguingly, UV-induced oxidative stress has opposing effects on carcinogenesis. Elucidating the molecular mechanisms of UV-induced DNA damage responses will be useful for preventing and treating skin cancer with greater precision. Excitingly, recent studies have uncovered substantial depth of novel findings regarding the molecular and cellular consequences of UV irradiation. In this review, we will discuss updated mechanisms of UV-induced DNA damage responses including the ATR pathway, which maintains genome integrity following UV irradiation. We will also present current strategies for preventing and treating nonmelanoma skin cancer, including ATR pathway inhibition for prevention and photodynamic therapy for treatment.

The application of transcriptional benchmark dose modeling for deriving thresholds of effects associated with solar-simulated ultraviolet radiation exposure

Considerable data has been generated to elucidate the transcriptional response of cells to ultraviolet radiation (UVR) exposure providing a mechanistic understanding of UVR-induced cellular responses. However, using these data to support standards development has been challenging. In this study, we apply benchmark dose (BMD) modeling of transcriptional data to derive thresholds of gene responsiveness following exposure to solar-simulated UVR. Human epidermal keratinocytes were exposed to three doses (10, 20, 150 kJ/m² ) of solar simulated UVR and assessed for gene expression changes 6 and 24 hr postexposure. The dose-response curves for genes with p-fit values (≥ 0.1) were used to derive BMD values for genes and pathways. Gene BMDs were bi-modally distributed, with a peak at ∼16 kJ/m² and ∼108 kJ/m² UVR exposure. Genes/pathways within Mode 1 were involved in cell signaling and DNA damage response, while genes/pathways in the higher Mode 2 were associated with immune response and cancer development. The median value of each Mode coincides with the current human exposure limits for UVR and for the minimal erythemal dose, respectively. Such concordance implies that the use of transcriptional BMD data may represent a promising new approach for deriving thresholds of actinic effects. Environ. Mol. Mutagen. 59:502-515, 2018. © 2018 The Authors Environmental and Molecular Mutagenesis published by Wiley Periodicals, Inc. on behalf of Environmental Mutagen Society.

Alternative activation of hedgehog pathway induced by ultraviolet B radiation: preliminary study

BACKGROUND

There is still much ambiguity in studies of Sonic hedgehog (Shh) pathways and its dysregulation. Some studies concerning the role of the Shh pathway in basal cell carcinoma (BCC) have been conducted, but there is a lack of studies about Shh pathway dysregulation under the influence of ultraviolet (UV)B radiation.

AIM

To evaluate skin expression of Shh, Ptch1, Ptch2, Smo and Gli1 proteins in BCCs with and without the influence of UVB radiation.

METHODS

In total, 34 healthy controls (HCs) and 42 patients with nodular BCC were recruited into the study. Patients were divided into five groups (A-E), depending on UVB dose received and BCC status. In all skin specimens, expression of Shh, Ptch1, Ptch2, Smo and Gli1 protein was evaluated.

RESULTS

Comparing the BCC group with the HC group, there was significantly higher expression of Shh, Ptch1, Ptch2, Smo and Gli1 proteins. Expression of Ptch2, Smo and Gli1 was increased in response to UVB doses of 3 MED (minimal erythema dose), whereas expression of Ptch1 and Shh was unaffected.

CONCLUSION

The lack of change in expression of Shh and Ptch1 after exposure to UVB suggests that the Shh pathway may be activated through a noncanonical pathway under the influence of strong UVB doses.

Mitotic genes are transcriptionally upregulated in the fibroblast irradiated with very low doses of UV-C

Ultraviolet (UV) radiation induces a variety of biological effects, including DNA damage response and cell signaling pathways. We performed transcriptome analysis using microarray in human primary cultured fibroblasts irradiated with UV-C (0.5 or 5 J/m²) and harvested at 4 or 12 h following UV exposure. All transcript data were analyzed by comparison with the corresponding results in non-irradiated (control) cells. The number of genes with significantly altered expression (≥2-fold difference relative to the control) is higher in the sample irradiated with high dose of UV, suggesting that gene expression was UV dose-dependent. Pathway analysis on the upregulated genes at 12 h indicates that the expression of some cell cycle-related genes was predominantly induced irrespective of UV-dose. Interestingly, almost all the genes with significant altered expression were cell cycle-related genes designated as ‘Mitotic Genes’, which function in the spindle assembly checkpoint. Therefore, even a low dose of UV could affect the transcriptional profile.

Pathophysiological Functions of Rnd3/RhoE

Rnd3, also known as RhoE, belongs to the Rnd subclass of the Rho family of small guanosine triphosphate (GTP)-binding proteins. Rnd proteins are unique due to their inability to switch from a GTP-bound to GDP-bound conformation. Even though studies of the biological function of Rnd3 are far from being concluded, information is available regarding its expression pattern, cellular localization, and its activity, which can be altered depending on the conditions. The compiled data from these studies implies that Rnd3 may not be a traditional small GTPase. The basic role of Rnd3 is to report as an endogenous antagonist of RhoA signaling-mediated actin cytoskeleton dynamics, which specifically contributes to cell migration and neuron polarity. In addition, Rnd3 also plays a critical role in arresting cell cycle distribution, inhibiting cell growth, and inducing apoptosis and differentiation. Increasing data have shown that aberrant Rnd3 expression may be the leading cause of some systemic diseases; particularly highlighted in apoptotic cardiomyopathy, developmental arrhythmogenesis and heart failure, hydrocephalus, as well as tumor metastasis and chemotherapy resistance. Therefore, a better understanding of the function of Rnd3 under different physiological and pathological conditions, through the use of suitable models, would provide a novel insight into the origin and treatment of multiple human diseases.

Identification of Cyclobutane Pyrimidine Dimer-Responsive Genes Using UVB-Irradiated Human Keratinocytes Transfected with In Vitro-Synthesized Photolyase mRNA

Major biological effects of UVB are attributed to cyclobutane pyrimidine dimers (CPDs), the most common photolesions formed on DNA. To investigate the contribution of CPDs to UVB-induced changes of gene expression, a model system was established by transfecting keratinocytes with pseudouridine-modified mRNA (Ψ-mRNA) encoding CPD-photolyase. Microarray analyses of this model system demonstrated that more than 50% of the gene expression altered by UVB was mediated by CPD photolesions. Functional classification of the gene targets revealed strong effects of CPDs on the regulation of the cell cycle and transcriptional machineries. To confirm the microarray data, cell cycle-regulatory genes, CCNE1 and CDKN2B that were induced exclusively by CPDs were selected for further investigation. Following UVB irradiation, expression of these genes increased significantly at both mRNA and protein levels, but not in cells transfected with CPD-photolyase Ψ-mRNA and exposed to photoreactivating light. Treatment of cells with inhibitors of c-Jun N-terminal kinase (JNK) blocked the UVB-dependent upregulation of both genes suggesting a role for JNK in relaying the signal of UVB-induced CPDs into transcriptional responses. Thus, photolyase mRNA-based experimental platform demonstrates CPD-dependent and -independent events of UVB-induced cellular responses, and, as such, has the potential to identify novel molecular targets for treatment of UVB-mediated skin diseases.

Desmosomes: regulators of cellular signaling and adhesion in epidermal health and disease

Desmosomes are intercellular junctions that mediate cell-cell adhesion and anchor the intermediate filament network to the plasma membrane, providing mechanical resilience to tissues such as the epidermis and heart. In addition to their critical roles in adhesion, desmosomal proteins are emerging as mediators of cell signaling important for proper cell and tissue functions. In this review we highlight what is known about desmosomal proteins regulating adhesion and signaling in healthy skin-in morphogenesis, differentiation and homeostasis, wound healing, and protection against environmental damage. We also discuss how human diseases that target desmosome molecules directly or interfere indirectly with these mechanical and signaling functions to contribute to pathogenesis.

Effect of APE1 T2197G (Asp148Glu) polymorphism on APE1, XRCC1, PARP1 and OGG1 expression in patients with colorectal cancer

It has been hypothesized that genetic variation in base excision repair (BER) might modify colorectal adenoma risk. Thus, we evaluated the influence of APE1 T2197G (Asp148Glu) polymorphism on APE1, XRCC1, PARP1 and OGG1 expression in normal and tumor samples from patients with colorectal cancer. The results indicate a downregulation of OGG1 and an upregulation of XRCC1 expression in tumor tissue. Regarding the anatomical location of APE1, OGG1 and PARP-1, a decrease in gene expression was observed among patients with cancer in the rectum. In patients with or without some degree of tumor invasion, a significant downregulation in OGG1 was observed in tumor tissue. Interestingly, when taking into account the tumor stage, patients with more advanced grades (III and IV) showed a significant repression for APE1, OGG1 and PARP-1. XRCC1 expression levels were significantly enhanced in tumor samples and were correlated with all clinical and histopathological data. Concerning the polymorphism T2197G, GG genotype carriers exhibited a significantly reduced expression of genes of the BER repair system (APE1, XRCC1 and PARP1). In summary, our data show that patients with colorectal cancer present expression changes in several BER genes, suggesting a role for APE1, XRCC1, PARP1 and OGG1 and APE1 polymorphism in colorectal carcinogenesis.

UVB-dependent changes in the expression of fast-responding early genes is modulated by huCOP1 in keratinocytes

Ultraviolet (UV) B is the most prominent physical carcinogen in the environment leading to the development of various skin cancers. We have previously demonstrated that the human ortholog of the Arabidopsis thaliana constitutive photomorphogenesis 1 (COP1) protein, huCOP1, is expressed in keratinocytes in a UVB-regulated manner and is a negative regulator of p53 as a posttranslational modifier. However, it was not known whether huCOP1 plays a role in mediating the UVB-induced early transcriptional responses of human keratinocytes. In this study, we report that stable siRNA-mediated silencing of huCOP1 affects the UVB response of several genes within 2 h of irradiation, indicating that altered huCOP1 expression sensitizes the cells toward UVB. Pathway analysis identified a molecular network in which 13 of the 30 examined UVB-regulated genes were organized around three central proteins. Since the expression of the investigated genes was upregulated by UVB in the siCOP1 cell line, we hypothesize that huCOP1 is a repressor of the identified pathway. Several members of the network have been implicated previously in the pathogenesis of non-melanoma skin cancers; therefore, clarifying the role of huCOP1 in these skin diseases may have clinical relevance in the future.

The desmosomal protein desmoglein 1 aids recovery of epidermal differentiation after acute UV light exposure

Epidermal structure is damaged by exposure to UV light, but the molecular mechanisms governing structural repair are largely unknown. UVB (290-320 nm wavelengths) exposure before induction of differentiation reduced expression of differentiation-associated proteins, including desmoglein 1 (Dsg1), desmocollin 1 (Dsc1), and keratins 1 and 10 (K1/K10), in a dose-dependent manner in normal human epidermal keratinocytes (NHEKs). The UVB-induced reduction in both Dsg1 transcript and protein was associated with reduced binding of the p63 transcription factor to previously unreported enhancer regulatory regions of the Dsg1 gene. As Dsg1 promotes epidermal differentiation in addition to participating in cell-cell adhesion, the role of Dsg1 in aiding differentiation after UVB damage was tested. Compared with controls, depleting Dsg1 via short hairpin RNA resulted in further reduction of Dsc1 and K1/K10 expression in monolayer NHEK cultures and in abnormal epidermal architecture in organotypic skin models recovering from UVB exposure. Ectopic expression of Dsg1 in keratinocyte monolayers rescued the UVB-induced differentiation defect. Treatment of UVB-exposed monolayer or organotypic cultures with trichostatin A, a histone deacetylase inhibitor, partially restored differentiation marker expression, suggesting a potential therapeutic strategy for reversing UV-induced impairment of epidermal differentiation after acute sun exposure.

GENE PROFILING: IMPLICATIONS IN DERMATOLOGY

DNA microarrays are capable of following the level of expression of, virtually, all genes in a human tissue. This has been employed to determine the aberrant gene expression profiles in many skin diseases, including ultraviolet light damage, inflammatory processes and cancers. Because of its accessibility, skin also served as one of the initial targets of basic research using DNA microarrays. Both the epidermis and dermis have been extensively investigated. Development of bed-side uses of DNA arrays, and the concomitant price reduction of the materials and methods of microarray analyses, holds great promise for improved diagnosis, treatment and prevention of dermatologic disorders.

Analysis and meta-analysis of transcriptional profiling in human epidermis

Because of its accessibility, skin has been among the first organs analyzed using DNA microarrays; psoriasis, melanomas, carcinomas, chronic wounds, and responses of epidermal keratinocytes in culture have been intensely investigated. Skin has everything: stem cells, differentiation, signaling, inflammation, hereditary diseases, etc. Here we provide step-by-step instructions for bioinformatics analysis of transcriptional profiling of skin. We also present methods for meta-analysis of transcription profiles from multiple contributors, available in public data repositories. Specifically, we describe the use of GCOS and RMAExpress programs for initial normalization and selection of differentially expressed genes and RankProd for meta-analysis of multiple related studies. We also describe DAVID and Lists2Networks programs for annotation of genes, and for statistically relevant identification of over- and underrepresented functional and biological categories in identified gene sets, as well as oPOSSUM for analysis of transcription factor binding sites in the promoter regions of gene sets. This work can serve as a primer for researchers embarking on skinomics, the comprehensive analysis of transcriptional changes in skin.

Smad4 loss in mouse keratinocytes leads to increased susceptibility to UV carcinogenesis with reduced Ercc1-mediated DNA repair

Smad4 loss occurs frequently in human skin squamous cell carcinoma (SCC), but it is unknown if this loss increases ultraviolet-induced (UV) carcinogenesis, a major etiological factor in skin cancer. In the present study, mice with keratinocyte-specific Smad4 deletion (K14.Smad4^−/−) and wildtype (WT) littermates were chronically UV-irradiated. Compared to WT, K14.Smad4^−/− mice exhibited increased DNA damage and increased susceptibility to UV-induced skin cancer. Among genes involved in repairing UV-induced DNA damage, Excision repair cross-complementation group1 (Ercc1) mRNA was significantly reduced in UV treated K14.Smad4^−/− skin compared to WT skin. Further analysis revealed that Smad4 loss confers reduced Snail binding to the Ercc1 regulatory elements, resulting in reduced Ercc1 transcription. Consistently, transient transfection of Snai1 into Smad4^−/− keratinocytes led to increased repair of UV-induced DNA lesions. Transfection of Ercc1 into Smad4^−/− keratinocytes restored repair of UV-induced DNA damage. Further, immunostaining revealed that the presence of Smad4 protein is associated with the presence of Snail and Ercc1 proteins in human skin SCC and precancerous actinic keratoses (AK). Collectively, Smad4 loss associated Snail reduction compromises Ercc1-mediated DNA repair, contributing to increased UV-induced skin carcinogenesis. Thus we identified a role for Snail in UV-induced DNA repair.

Protein kinases and transcription factors activation in response to UV-radiation of skin: implications for carcinogenesis

Solar ultraviolet (UV) radiation is an important environmental factor that leads to immune suppression, inflammation, photoaging, and skin carcinogenesis. Here, we reviewed the specific signal transduction pathways and transcription factors involved in the cellular response to UV-irradiation. Increasing experimental data supporting a role for p38, MAPK, JNK, ERK1/2, and ATM kinases in the response network to UV exposure is discussed. We also reviewed the participation of NF-κB, AP-1, and NRF2 transcription factors in the control of gene expression after UV-irradiation. In addition, we discussed the promising chemotherapeutic intervention of transcription factors signaling by natural compounds. Finally, we focused on the review of data emerging from the use of DNA microarray technology to determine changes in global gene expression in keratinocytes and melanocytes in response to UV treatment. Efforts to obtain a comprehensive portrait of the transcriptional events regulating photodamage of intact human epidermis after UV exposure reveals the existence of novel factors participating in UV-induced cell death. Progress in understanding the multitude of mechanisms induced by UV-irradiation could lead to the potential use of protein kinases and novel proteins as specific targets for the prevention and control of skin cancer.

Comprehensive transcriptional profiling of human epidermis, reconstituted epidermal equivalents, and cultured keratinocytes using DNA microarray chips

Because of its accessibility, skin has been among the first organs analyzed using DNA microarrays; psoriasis, melanomas, carcinomas, chronic wound biopsies, and epidermal keratinocytes in culture have been intensely investigated. Skin has everything: stem cells, differentiation, signaling, inflammation, diseases, cancer, etc. Here we provide step-by-step instructions for bioinformatics analysis of transcriptional profiling of skin. Specifically, we describe the use of GCOS and RMA programs for initial normalization and selection of differentially expressed genes, DAVID and LOLA programs for annotation of genes, and statistically relevant identification of over- and under-represented functional and biological categories in identified gene sets, L2L and Venn diagrams for comparing multiple lists of genes, and oPOSSUM for identification of statistically over-represented transcription factor binding sites in the promoter regions of gene sets. The work can be a primer for researchers embarking on skinomics, the comprehensive analysis of transcriptional changes in the skin.

Ultraviolet radiation-induced transcription is associated with gene-specific histone acetylation

UVR is an important environmental carcinogen and a powerful modulator of the cutaneous immune system. Exposure to UVR activates many signaling pathways leading to changes in the expression of several hundred genes. While the covalent modification of histones has been shown to play a central role in regulating gene expression, the impact of UVR on histone modifications and the contribution of histone acetyltransferases (HATs) and histone deacetylases (HDACs) to the UVR-induced transcriptional response have not been completely characterized. In this report, we have examined the impact of UVR on histone H3 K9/14 acetylation. The potential role of UVR-induced histone acetylation in the UVR transcriptional response was also explored using the HAT inhibitor curcumin and HDAC inhibitor trichostatin A (TSA). We found that UVR caused an increase in histone H3 acetylation within the promoter regions of ATF3, COX2, IL-8, MKP1 and MnSOD. In most of the regions examined, histone H3 acetylation peaked 24 h after UVR and then returned to baseline levels by 72 h. The induction of ATF3, COX2 and MKP1 was blocked in the presence of curcumin at doses that decrease in vivo histone H3 acetylation but not at lower doses that do not affect acetylation levels. We also provide evidence that for ATF3, a transcriptional superinduction occurs after repeat exposures to UVR that can be recapitulated when the second UVR exposure is replaced with TSA treatment. Thus, UVR can alter histone acetylation within human keratinocytes and these changes may contribute to the UVR-transcriptional response.

Evaluating the cytotoxic doses of narrowband and broadband UVB in human keratinocytes, melanocytes, and fibroblasts

BACKGROUND

No comparative and simultaneous in vitro studies have been performed to determine the cytotoxic dose of narrowband UVB (NBUVB) and broadband UVB (BBUVB) for keratinocytes, melanocytes, and fibroblasts. Culture medium was often replaced with phosphate-buffered saline (PBS) before UV irradiation; however, its amount differed across studies. We determined the cytotoxic doses of NBUVB and BBUVB and tested for changes in viability according to the amount of PBS.

METHODS

We exposed cultured human keratinocytes, melanocytes, and fibroblasts to ultraviolet light in the range 12.5-1000 mJ/cm(2) for NBUVB and 1.25-100 mJ/cm(2) for BBUVB. The viability was assessed after 24 h. We also determined changes in viability at cytotoxic doses according to the amount of PBS (40, 80, and 120 microl/well in a 96-well plate).

RESULTS

Cytotoxicity was observed at doses of 100, 200, and 400 mJ/cm(2) for NBUVB and 5, 10, and 25 mJ/cm(2) for BBUVB in keratinocytes, melanocytes, and fibroblasts, respectively. At cytotoxic doses, there was no change in viability according to the amount of PBS.

CONCLUSIONS

Fibroblasts are more resistant to UVB irradiation, irrespective of the amount of NBUVB and BBUVB, than keratinocytes and melanocytes. The amount of PBS during irradiation had no effect on viability.

Photoexposition discriminates Notch 1 expression in human cutaneous squamous cell carcinoma

The Notch signaling pathway may play opposing roles in cancer. It can be oncosuppressive or protumoral, depending on the cellular and tissue context. In skin cancer, Notch 1 expression is downregulated, thus supporting the hypothesis of an oncosuppressive role in cutaneous carcinomas. However, as members of the Notch family undergo downregulation upon exposure to UV irradiation, we wondered whether Notch 1 expression in skin carcinomas may be governed by additional factors, including UV exposure. We investigated the expression of Notch 1 and its ligands, Jagged 1, Jagged 2 and Delta-like 1, by immunohistochemistry in a series of premalignant and invasive cutaneous carcinomas, including 4 solar keratoses, 5 Bowen's disease, 5 squamous cell carcinomas on sun-exposed skin, 6 squamous cell carcinomas on sun-protected genital skin and 14 basal cell carcinomas of different histotypes (nodular, superficial type, sclerodermiform/infiltrating and baso-squamous). Expression of Notch 1 was decreased in solar keratoses and invasive squamous cell carcinomas localized on sun-exposed skin. In contrast, marked Notch 1 staining was observed in extragenital Bowen's disease as well as in genital (penile) human papilloma virus-related in situ and invasive squamous cell carcinomas. A diffuse Notch 1 staining was detected in nodular and superficial basal cell carcinomas while sclerodermiform/infiltrating and baso-squamous basal cell carcinomas showed a low to absent Notch 1 expression. Jagged 1, Jagged 2 and Delta-like 1 proteins were expressed in all tissues examined. Present findings show divergent expression of Notch 1 in skin cancer, depending on anatomical site and tumor histotype. Thus, whereas in UV-related squamous cell photocarcinogenesis Notch 1 downregulation could mirror a tumor suppressor function of the receptor, in sun-protected squamous cell carcinomas Notch 1 was upregulated. Furthermore, Notch 1 expression was minimal in basal cell carcinoma subtypes correlated with risk of recurrence (sclerodermiform/infiltrating and baso-squamous) in comparison with nodular and superficial types.

The atypical Rho GTPase Wrch1 collaborates with the nonreceptor tyrosine kinases Pyk2 and Src in regulating cytoskeletal dynamics

The Cdc42-like GTPase Wnt responsive Cdc42 homolog 1 (Wrch1) has several atypical features; it has an N-terminal proline-rich extension that confers binding to SH3 domains, and it harbors an extremely high intrinsic nucleotide exchange activity, which overrides the normal GTPase activity. As a result, Wrch1 resides mainly in the active, GTP-loaded conformation under normal cellular conditions. We have previously shown that ectopic expression of Wrch1 in fibroblasts resulted in an altered cell morphology visible as a formation of filopodia, a loss of stress fibers, and a reduction in focal adhesions. Here, we show that Wrch1 binds to the nonreceptor tyrosine kinase Pyk2. The interaction required Wrch1 to be in a GTP conformation and also required an intact N-terminal proline-rich extension as well as an intact effector loop. Wrch1 requires Pyk2 in imposing the cytoskeletal effects, seen as the formation of filopodia, since treatment of cells with a Pyk2-specific small interfering RNA abrogated this response. Interestingly, we found that the presence and activity of Src were needed for the formation of a Wrch1-Pyk2 complex as well as for the Wrch1-induced formation of filopodia. We propose a model in which Pyk2 and Src function to coordinate the Wrch1-dependent effects on cytoskeletal dynamics.

Topical dorsal skin immersion in seawater induces apoptosis and proliferation in hairless mice

Recreational and occupational exposure to seawater (SW), have increased but the effect of SW on skin has not been elucidated. The purpose of present study was to assess the effects of SW immersion on the dorsal skin in hairless mice. Adult hairless mice were individually immersed in SW for 3 h, 6 h and 12 h; then, full-thickness dorsal skin of 2 cm diameter was excised for pathological examination (light microscope), apoptosis detection (terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate nick end labeling [TUNEL]) and proliferation index evaluation (immunohistochemistry). Normal and normal saline (NS)-immersed skin were used as controls. Histological examination revealed that there were randomly distributed cell deaths, presenting cell shrinkage, condensation of nuclear chromatin and eosinophilic cytoplasm in the epidermis, and neutrophil infiltration in the dermis, after SW immersion. Moreover, TUNEL showed low levels of apoptosis in normal (9.07 +/- 0.70%) and NS-immersed skin (9.99 +/- 1.22%). There was an apparent increase in the 6-h and 12-h SW immersed groups (29.90 +/- 6.85%, P < 0.01; 45.46 +/- 6.12%, P < 0.01, respectively). Ki-67 antigen was located in the basal layer of the epidermis and hair follicles, the rates of Ki-67-positive cells were 7.90 +/- 1.45% and 7.76 +/- 1.52% in normal and NS-immersed skin, respectively, and in the 12-h SW immersed group, the rate of Ki-67-positive cells reached 23.85 +/- 4.21% (threefold, P < 0.01). In each group, the rate of apoptosis was higher than that of proliferation. We conclude that SW immersion can cause time-dependent apoptosis and proliferation in the epidermis, and the overall effect of SW immersion is injury to the epidermis.

Primer on the human genome

The study of the expression patterns of many genes, or even the entire genome, is now routinely possible. Such powerful tools have enabled hypothesis-generating research at a scale never before possible. Moreover, spatially or temporally linked gene and protein expression, implying co-regulation and functional relatedness, has led to the identification of particular clusters of genes important for fundamental biologic processes, such as development and cancer. Not only is this expected to yield further mechanistic insights into disease processes, but perhaps most exciting, it will likely establish the foundation of predictive medicine, in which understanding of individual genomic signatures leads to the use of appropriately targeted therapy.

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should be able to understand the fundamental tenets of molecular biology as they relate to the field of genomics.

High doses of ultraviolet-C irradiation increases vasoactive intestinal contractor/endothelin-2 expression in keratinocytes of the newborn mouse epidermis

We examined the expression profiles of vasoactive intestinal contractor/endothelin-2 (VIC/ET-2) at both gene and peptide level in skin irradiated with different ultraviolet wavelengths. We found that VIC/ET-2 gene expression is sensitive only to ultraviolet-C (UVC) irradiation and has an immediate response. These results provide direct evidence that high doses of UVC irradiation induce an increase in gene expression and protein production of VIC/ET-2 and endothelin (ET) receptors in a dose-dependent manner in epidermal keratinocytes. We suggest that VIC/ET-2 can play an essential role in the maintenance, protection and hyperpigmentation of the epidermis exposed to UVC irradiation from artificial or natural sources.

Endothelin-2/vasoactive Intestinal Contractor via ROCK regulates transglutaminase 1 on differentiation of mouse keratinocytes

We previously found that endothelin-2/vasoactive intestinal contractor (ET-2/VIC) greatly increased in mouse epidermis after birth. In the present study, we evaluated whether ET-2/VIC expression was associated with the calcium-induced differentiation of cultured mouse keratinocytes. The differentiation induction was revealed by morphological change, cornified envelope (CE) formation, and involucrin and transglutaminase 1 (TG 1) expressions. ET-2/VIC gene expression and peptide production subsequently increased in the induction of the differentiation. We also found that Y-27632, a Rho-associated coiled-coil forming protein serine/threonine kinase (ROCK) inhibitor, suppressed up-regulation of ET-2/VIC gene expression, the induction of morphological change, the CE formation, and TG 1 expression, but not involucrin expression. These results indicate new three findings, (1) ET-2/VIC expression increases and has potential as a differentiation marker, (2) ET-2/VIC expression is mediated by ROCK, and (3) the ROCK regulated TG 1 expression, on the calcium-induced differentiation of mouse keratinocytes.

DNA microarrays in dermatology and skin biology

Because of its accessibility, skin has been among the first organs analyzed using DNA microarrays. Skin cancers, melanomas, and basal and squamous cell carcinomas have been intensely investigated because they are very frequent and can be fatal. Psoriasis, one of the most common human inflammatory diseases, has been studied comprehensively using DNA microarrays. In addition, epidermal keratinocytes have been the target of many studies because they respond to a rich variety of inflammatory and immunomodulating cytokines, hormones, vitamins, ultraviolet (UV) light, toxins, and physical injury. Because of the ethical considerations, the effects of harmful or dangerous agents on skin have been studied using artificial skin substitutes. Transcriptional mechanisms that regulate epidermal differentiation and cornification have begun to yield their mysteries, and very exciting recent studies identified the genes specifically expressed in epidermal stem cells. Thus, skin has everything: stem cells, differentiation, signaling, inflammation, diseases, and cancer. All these exciting facets of skin have been explored using DNA microarrays. Researchers in skin biology and dermatology were among the first to implement this technology and we expect that they will continue to generate exciting and useful new knowledge.

Erbb2 regulates inflammation and proliferation in the skin after ultraviolet irradiation

Exposure to ultraviolet (UV) irradiation is the major cause of nonmelanoma skin cancer, the most common form of cancer in the United States. UV irradiation has a variety of effects on the skin associated with carcinogenesis, including DNA damage and effects on signal transduction. The alterations in signaling caused by UV regulate inflammation, cell proliferation, and apoptosis. UV also activates the orphan receptor tyrosine kinase and proto-oncogene Erbb2 (HER2/neu). In this study, we demonstrate that the UV-induced activation of Erbb2 regulates the response of the skin to UV. Inhibition or knockdown of Erbb2 before UV irradiation suppressed cell proliferation, cell survival, and inflammation after UV. In addition, Erbb2 was necessary for the UV-induced expression of numerous proinflammatory genes that are regulated by the transcription factors nuclear factor-kappaB and Comp1, including interleukin-1beta, prostaglandin-endoperoxidase synthase 2 (Cyclooxygenase-2), and multiple chemokines. These results reveal the influence of Erbb2 on the UV response and suggest a role for Erbb2 in UV-induced pathologies such as skin cancer.

DNA Repair Pathway Profiling and Microsatellite Instability in Colorectal Cancer

BACKGROUND

The ability to maintain DNA integrity is a critical cellular function. DNA repair is conducted by distinct pathways of genes, many of which are thought to be altered in colorectal cancer. However, there has been little characterization of these pathways in colorectal cancer.

METHOD

By using the TaqMan real-time quantitative PCR, RNA expression profiling of 20 DNA repair pathway genes was done in matched tumor and normal tissues from 52 patients with Dukes' C colorectal cancer.

RESULTS

The relative mRNA expression level across the 20 DNA repair pathway genes varied considerably, and the individual variability was also quite large, with an 85.4 median fold change in the tumor tissue genes and a 127.2 median fold change in the normal tissue genes. Tumor-normal differential expression was found in 13 of 20 DNA repair pathway genes (only XPA had a lower RNA level in the tumor samples; the other 12 genes had significantly higher tumor levels, all P<0.01). Coordinated expression of ERCC6, HMG1, MSH2, and POLB (RS>or=0.60) was observed in the tumor tissues (all P<0.001). Apoptosis index was not correlated with expression of the 20 DNA repair pathway genes. MLH1 and XRCC1 RNA expression was correlated with microsatellite instability status (P=0.045 and 0.020, respectively). An inverse correlation was found between tumor MLH1 RNA expression and MLH1 DNA methylation (P=0.003).

CONCLUSION

Our study provides an initial characterization of the DNA repair pathways for understanding the cellular DNA damage/repair system in human colorectal cancer.

The UVB-induced gene expression profile of human epidermis in vivo is different from that of cultured keratinocytes

In order to obtain a comprehensive picture of the molecular events regulating cutaneous photodamage of intact human epidermis, suction blister roofs obtained after a single dose of in vivo ultraviolet (UV)B exposure were used for microarray profiling. We found a changed expression of 619 genes. Half of the UVB-regulated genes had returned to pre-exposure baseline levels at 72 h, underscoring the transient character of the molecular cutaneous UVB response. Of special interest was our finding that several of the central p53 target genes remained unaffected following UVB exposure in spite of p53 protein accumulation. We next compared the in vivo expression profiles of epidermal sheets to that of cultured human epidermal keratinocytes exposed to UVB in vitro. We found 1931 genes that differed in their expression profiles between the two groups. The expression profile in intact epidemis was geared mainly towards DNA repair, whereas cultured keratinocytes responded predominantly by activating genes associated with cell-cycle arrest and apoptosis. These differences in expression profiles might reflect differences between mature differentiating keratinocytes in the suprabasal epidermal layers versus exponentially proliferating keratinocytes in cell culture. Our findings show that extreme care should be taken when extrapolating from findings based on keratinocyte cultures to changes in intact epidermis.

An intronic polymorphism associated with increased XRCC1 expression, reduced apoptosis and familial breast cancer

XRCC1 coordinates the activities of DNA polymerase-beta and DNA ligase for base excision repair of oxidative DNA damage. In addition, there is some evidence that XRCC1 is a negative regulator of apoptosis. Single nucleotide polymorphisms in XRCC1 have been inconsistently associated with breast cancer risk. We evaluated XRCC1 gene expression in breast cancer cell lines and carcinogen-induced apoptosis in benign breast epithelial cells in relation to XRCC1 genotypes. XRCC1 IVS10+141G>A was associated with increased expression of XRCC1 mRNA and protein, and reduced apoptosis in response to benzo-[a]-pyrene or ionizing radiation, but XRCC1 R399Q was not. These genotypes were also assessed in a clinic-based sample that included 190 breast cancer patients with a family history of breast cancer and 95 controls with no family history of breast cancer. Heterozygous XRCC1 IVS10+141G>A was associated with an increased breast cancer risk (O.R. = 1.7, 95% C.I. 1.016-2.827, P = 0.04) as was homozygous XRCC1 IVS10+141G>A (O.R. = 4.7, 95% C.I. 1.028-21.444, P = 0.03). XRCC1 R399Q was not associated with breast cancer (O.R. 1.00, 95% C.I. 0.61-1.64). The XRCC1 IVS10+141G>A locus is centered in a sequence that is nearly identical to the consensus binding site for the PLAG1 transcription factor. XRCC1 IVS10+141G>A is an intronic polymorphism that is associated with XRCC1 expression, apoptosis and familial breast cancer. It may occur within an intronic regulatory sequence.

Function and regulation of Rnd proteins

The Rnd proteins, which form a distinct sub-group of the Rho family of small GTP-binding proteins, have been shown to regulate the organization of the actin cytoskeleton in several tissues. In the brain, they participate in neurite extension, whereas in smooth muscle, they modulate contractility. Recent evidence has shown that Rnd3 (RhoE) is also involved in the regulation of cell-cycle progression and transformation, indicating that these proteins might have other, as yet unexplored roles.

Human keratinocyte radiosensitivity is linked to redox modulation

BACKGROUND

Ionising radiation-induced reactive oxygen species (ROS) overproduction induces keratinocyte alterations and constitutes one of the most common effects after therapeutic gamma-irradiation. ROS production is controlled by a complex enzymatic system.

OBJECTIVE

The aim of our study is to analyse the role of radiation-induced oxidative stress in keratinocytes death by apoptosis. We hypothesized that keratinocyte capacity to hamper radiation-induced ROS generation may control their radiosensitivity.

METHODS

For this purpose, an original human skin explant model was developed and two types of human epidermal cells were used: primary keratinocytes NHEK and spontaneous non-tumourigenic cell line HaCaT.

RESULTS

cDNA-arrays analysis was performed 24h after a 20Gy gamma-radiation and revealed down-regulation of genes involved in oxidative stress control and the apoptosis process. This was confirmed by alterations in catalase, GPx and SOD enzymatic activities. This redox modulation was concomitant to the down-regulation of anti-apoptotic genes and up-regulation of some pro-apoptotic genes (caspase 10, ubiquitin C). Interestingly TUNEL labelling revealed an increase in the number of apoptotic cells. We also demonstrated a differential inducibility of the cell antioxidant network in two keratinocyte lines, which results in a differential cellular level of ROS, explaining their different radiosensitivities.

CONCLUSION

Keratinocytes apoptosis is partly dependent on ROS production after exposure to gamma-rays. In addition, the differential radiosensitivity of keratinocytes is linked to different oxidative stress responses.

Ultraviolet radiation-induced apoptosis in keratinocytes: on the role of cytosolic factors

Epidemiological and experimental evidences have established solar ultraviolet (UV) radiation as the leading cause of skin cancers. Specifically, the frequency of non-melanoma skin cancer, one of the malignancies with the most rapidly increasing incidence, is directly related to the total exposure to solar UV light. As part of a general effort to elucidate the components of cellular signal transduction pathways, the mechanisms of cellular responses to UV radiation have received considerable attention over the last few years. These efforts were driven mainly by the conviction that understanding how normal cells respond to extracellular stimuli such as exposure to UV radiation will undoubtedly help in deciphering what goes wrong in a variety of clinical disorders including skin cancers and will assist in the development of novel therapeutic strategies. Studies over the last decade have established that UV radiation induces a bewildering array of signal transduction pathways, some of which could lead to apoptotic cell death. UV-induced cell death by apoptosis is considered to be a natural protective mechanism that removes damaged keratinocytes and circumvents the risk of malignant transformation. In this review, we summarize some of the most important findings regarding the response and role of mitogen-activated protein kinases in UVA and UVB radiation-induced signaling to apoptosis in keratinocytes. We will also briefly discuss what is known about the role of the BCL-2 family of proteins, the emerging role of lysosomal proteases and other important cytosolic signaling proteins in UV-induced apoptosis.

Cobalt chloride induces neurite outgrowth in rat pheochromocytoma PC-12 cells through regulation of endothelin-2/vasoactive intestinal contractor

We investigated whether endothelin-2/vasoactive intestinal contractor (ET-2/VIC) gene expression, upregulated by hypoxia in cancer cells, was associated with differentiation in neuronal cells. RT-PCR analysis, morphological observations, and immunostaining revealed that CoCl2, a hypoxic mimetic agent, at 200 microM increased expression of the ET-2/VIC gene, decreased expression of the ET-1 gene, and induced neurite outgrowth in PC-12 rat pheochromocytoma cells. These effects induced by 200 microM CoCl2 were completely inhibited by the antioxidant N-acetyl cysteine at 20 mM. In addition, CoCl2 increased the level of intracellular reactive oxygen species (ROS) at an early stage. Furthermore, interleukin (IL)-6 gene expression was upregulated upon the differentiation induced by CoCl2. These results suggest that expression of ET-2/VIC and ET-1 mediated by ROS may be associated with neuronal differentiation through the regulation of IL-6. When the cells were treated with 500 microM CoCl2 for 24 hr, however, ET-2/VIC gene expression disappeared, IL-6 gene expression was downregulated, and necrosis was subsequently induced in the PC-12 cells.

DNA microarrays: from structural genomics to functional genomics. The applications of gene chips in dermatology and dermatopathology

The human genome project was successful in sequencing the entire human genome and ended earlier than expected. The vast genetic information now available will have far-reaching consequences for medicine in the twenty-first century. The knowledge gained from the mapping and sequencing of human genes on a genome-wide scale--commonly referred to as structural genomics--is prerequisite for studies that focus on the functional aspects of genes. A recently invented technique, known as gene chip, or DNA microarray, technology, allows the study of the function of thousands of genes at once, thereby opening the door to the new field of functional genomics. At its core, the DNA microarray utilizes a unique feature of DNA known as complementary hybridization. As such, it is not different from Southern (DNA) blot or northern (RNA) blot hybridizations, or the polymerase chain reaction, with the exception that it allows expression profiling of the entire human genome in a single hybridization experiment. The article highlights the principles, technology, and applications of DNA microarrays as they pertain to the field of dermatology and dermatopathology. The most important applications are the gene expression profiling of skin cancer, especially of melanoma. Other potential applications include gene expression profiling of inflammatory skin diseases, the mutational analysis of genodermatoses, and polymorphism screening, as well as drug development and chemosensitivity prediction. cDNA microarrays will shape the diagnostic approach of the dermatology and the dermatopathology of the future and may lead to new therapeutic options.

Microarray analysis of UVB-regulated genes in keratinocytes: downregulation of angiogenesis inhibitor thrombospondin-1

BACKGROUND

Ultraviolet (UV) B light is an environmental mutagen that induces changes in cutaneous gene expression leading to immune suppression and carcinogenesis. Keratinocytes are a primary target for UVB.

OBJECTIVE

To further delineate UVB-induced gene expression changes in keratinocytes.

METHODS

cDNA microarray technology was utilized to examine gene expression in normal human KC (NHKC) following 20 mJcm(-2) UVB irradiation. Data was confirmed by semi-quantitative RT-PCR.

RESULTS

Microarray analysis revealed 57 genes were upregulated, and 27 genes were downregulated, by at least two-fold following UVB. One downregulated gene was the endogenous angiogenesis inhibitor thrombospondin-1 (TSP-1). Semi-quantitative RT-PCR confirmed persistent downregulation of TSP-1 up to 18h following UVB. Microarray analysis also revealed upregulation of platelet-derived endothelial cell growth factor (PD-ECGF)--an angiogenesis activator.

CONCLUSION

Our results suggest a gene expression mechanism by which UVB induces an angiogenic switch in keratinocytes. This may represent an important early event promoting neovascularization and growth of cutaneous neoplasms.

Gene expression profiling of in vivo UVB-irradiated human epidermis

BACKGROUND

Several recent studies have employed microarray profiling to study UVB-regulated gene expression in human skin. These studies are all based on UV-irradiated cultured cells that differ substantially from the intact tissues they are supposed to imitate. The purpose of the present study was to analyze the differential expression of UVB-regulated genes in intact human epidermis following in vivo UV irradiation.

METHODS

The forearms of human volunteers were exposed to 4 MED of UVB in vivo, followed by removal of epidermal samples from exposed and non-exposed areas after 24 h. RNA samples were analyzed using oligonucleotide microarray (Affymetrix) technology analyzing 12 500 genes simultaneously. Verification of selected genes was performed by semi-quantitative reverse transcriptase polymerase chain reaction.

RESULTS

Gene expression patterns clearly distinguished UV-exposed epidermis from unexposed skin. Classification of these genes into functional categories revealed that several biological processes are globally affected by UVB. Significant changes were seen in more than 800 genes.

CONCLUSION

Human intact epidermis responds to a single low dose of in vivo UVB irradiation by differential regulation of numerous genes. Our results illustrate the power of global gene expression analysis of human epidermis to identify molecular pathways involved in UV-induced photodamage.

RhoE inhibits cell cycle progression and Ras-induced transformation

Rho GTPases are major regulators of cytoskeletal dynamics, but they also affect cell proliferation, transformation, and oncogenesis. RhoE, a member of the Rnd subfamily that does not detectably hydrolyze GTP, inhibits RhoA/ROCK signaling to promote actin stress fiber and focal adhesion disassembly. We have generated fibroblasts with inducible RhoE expression to investigate the role of RhoE in cell proliferation. RhoE expression induced a loss of stress fibers and cell rounding, but these effects were only transient. RhoE induction inhibited cell proliferation and serum-induced S-phase entry. Neither ROCK nor RhoA inhibition accounted for this response. Consistent with its inhibitory effect on cell cycle progression, RhoE expression was induced by cisplatin, a DNA damage-inducing agent. RhoE-expressing cells failed to accumulate cyclin D1 or p21(cip1) protein or to activate E2F-regulated genes in response to serum, although ERK, PI3-K/Akt, FAK, Rac, and cyclin D1 transcription was activated normally. The expression of proteins that bypass the retinoblastoma (pRb) family cell cycle checkpoint, including human papillomavirus E7, adenovirus E1A, and cyclin E, rescued cell cycle progression in RhoE-expressing cells. RhoE also inhibited Ras- and Raf-induced fibroblast transformation. These results indicate that RhoE inhibits cell cycle progression upstream of the pRb checkpoint.

Portrait of transcriptional responses to ultraviolet and ionizing radiation in human cells

To understand the human response to DNA damage, we used microarrays to measure transcriptional responses of 10 000 genes to ionizing radiation (IR) and ultraviolet radiation (UV). To identify bona fide responses, we used cell lines from 15 individuals and a rigorous statistical method, Significance Analysis of Microarrays (SAM). By exploring how sample number affects SAM, we rendered a portrait of the human damage response with a degree of accuracy unmatched by previous studies. By showing how SAM can be used to estimate the total number of responsive genes, we discovered that 24% of all genes respond to IR and 32% respond to UV, although most responses were less than 2-fold. Many genes were involved in known damage-response pathways for cell cycling and proliferation, apoptosis, DNA repair or the stress response. However, the majority of genes were involved in unexpected pathways, with functions in signal transduction, RNA binding and editing, protein synthesis and degradation, energy metabolism, metabolism of macromolecular precursors, cell structure and adhesion, vesicle transport, or lysosomal metabolism. Although these functions were not previously associated with the damage response in mammals, many were conserved in yeast. These insights reveal new directions for studying the human response to DNA damage.

Small ISGs coming forward

Interferons (IFNs) were first characterized as antiviral proteins. Since then, IFNs have proved to be involved in malignant, angiogenic, inflammatory, immune, and fibrous diseases and, thus, possess a broad spectrum of pathophysiologic properties. IFNs activate a cascade of intracellular signaling pathways leading to upregulation of more than 1000 IFN-stimulated genes (ISGs) within the cell. The function of some of the IFN-induced proteins is well described, whereas that of many others remain poorly characterized. This review focuses on three families of small intracellular and intrinsically nonsecreted proteins (10-20 kDa) separated into groups according to their amino acid sequence similarity: the ISG12 group (6-16, ISG12, and ISG12-S), the 1-8 group (9-27/Leu13, 1-8U, and 1-8D), and the ISG15 group (ISG15/UCRP). These IFN-induced genes are abundantly and widely expressed and mainly induced by type I IFN. ISG15 is very well described and is a member of the ubiquitin-like group of proteins. 9-27/Leu-13 associates with CD81/TAPA-1 and plays a role in B cell development. The functions of 1-8U, 1-8D, 6-16, ISG12, and ISG12-S proteins are unknown at present.

Expression profiling of human keratinocyte response to ultraviolet A: implications in apoptosis

Ultraviolet A radiation from sunlight is a major human health concern, as it is not absorbed by the ozone layer and can deeply penetrate into the skin causing skin damage. To study the molecular mechanism involved in the ultraviolet A effect, human HaCaT keratinocytes were exposed to ultraviolet A at doses of 10 J per cm2 and 30 J per cm2. Ultraviolet A irradiation caused dose- and time-dependent apoptotic cell death, as evidenced by DNA fragmentation, flow cytometry, and the activation of caspase-3. To study the genes altered by ultraviolet A at an apoptosis-inducing dose (30 J per cm2), cells were harvested immediately after ultraviolet A treatment (0 h), and 6 h and 24 h after ultraviolet A exposure. Total RNA was extracted for microarray and real-time RT-PCR analysis, and cellular proteins were extracted for western blot analysis. Of the selected critical genes/proteins, the induction of c-Jun, c-myc, and p33ING1, and the repression of epidermal growth factor receptor, inhibitor of apoptosis protein, and survivin pathways, could be involved in ultraviolet-A-induced apoptosis. On the other hand, the late induction of cyclin D1 and cyclin-dependent kinase 4 was indicative of possible cell cycle recovery in surviving cells. Real-time RT-PCR analysis confirmed these results and a majority of the protein levels paralleled their corresponding RNA levels. In addition, ultraviolet A treatment altered the expression of genes involved in signal transduction, RNA processing, structural proteins, and metabolism in a time-dependent manner. This initial microarray analysis could advance our understanding of cellular responses to ultraviolet A exposure, and provide a platform from which to further study ultraviolet-A-induced apoptosis and carcinogenesis.