A Low UVB Dose, with the Potential to Trigger a Protective p53-Dependent Gene Program, Increases the Resilience of Keratinocytes against Future UVB Insults

Insulin-like Growth Factor-1 Impacts p53 Target Gene Induction in UVB-irradiated Keratinocytes and Human Skin

The tumor suppressor protein p53 limits mutagenesis in response to ultraviolet-B (UVB) light exposure by activating the transcription of genes that mitigate the damaging effects of UVB radiation on DNA. Because most nonmelanoma skin cancers (NMSCs) occur in older individuals, it is important to understand the process of mutagenesis in the geriatric skin microenvironment. Based on previous studies demonstrating that geriatric skin expresses lower levels of the growth factor insulin-like growth factor-1 (IGF-1) than young adult skin, a role for IGF-1 in the regulation of p53 target genes was investigated in both human keratinocytes in vitro and human skin explants ex vivo. The products of the p53 target genes p21 and DNA polymerase eta (pol η) were found to be increased by UVB exposure in both experimental systems, and this induction was observed to be partially abrogated by depriving keratinocytes of IGF-1 in vitro or by the treatment of keratinocytes in vitro and human skin explants with an IGF-1 receptor antagonist. Because p21 and pol η function to limit mutagenic DNA replication following UVB exposure, these results suggest that NMSC risk in geriatric populations may be due to age-dependent decreases in IGF-1 signaling that disrupt p53 function in the skin.

Ultraviolet Exposure Scenarios: Balancing Risks of Erythema and Benefits of Cutaneous Vitamin D Synthesis

Exposure to sunlight is a major source of vitamin D for most people. Yet public health advice has focused overwhelmingly on avoiding exposure of unprotected skin because of the risks of erythema and skin cancer. Given that there are also health risks associated with low vitamin D status, we explore the possibilities of achieving a range of targets associated with vitamin D and the accompanying erythema risk. We have calculated the exposure required to gain a number of proposed oral-equivalent doses of vitamin D, as functions of latitude, season, skin type and skin area exposed, together with the associated risk of erythema, expressed in minimum erythema doses. The model results show that a recommended daily intake of 400 IU is readily achievable through casual sun exposure in the midday lunch hour, with no risk of erythema, for all latitudes some of the year, and for all the year at some (low) latitudes. We also show that such daily, sub-erythemal doses at lunchtime during the summer months is sufficient to avoid winter-time vitamin D deficiency for the UK all-weather climate, provided that lower arms and legs are exposed in the warmer months. At the higher proposed vitamin D dose of 1000 IU, lunchtime sun exposure is still a viable route to the vitamin but requires the commitment to expose greater areas of skin and is effective for a shorter period of the year. The highest vitamin D requirement considered was 4000 IU per day. For much of the globe and much of the year, this is not achievable in a lunchtime hour and where it is possible large areas of skin must be exposed to prevent erythema. When the only variable considered was skin type, latitudinal and seasonal limits on adequate vitamin D production were more restrictive for skin type 5 than skin type 2.

Mechanisms of and variables affecting UVR photoadaptation in human skin

Humans have been exposed to solar UV radiation since their appearance on Earth and evolution has enabled most individuals to adapt to this exposure, to some degree. UV radiation produces several deleterious effects in human skin and light-skinned individuals are at greatest risk for both acute and long-term negative effects such as DNA damage, sunburn, immune suppression and skin cancer. The benefits of photoadaptation, which leads to a decreased response after acclimatization, are that humans who have skin that is capable of photoadaptation can work and play in the sun with reduced fear of painful sunburn. However, the effects of photoadaptation on DNA damage and development of skin cancer are quite complex and less well-understood. In this article, we have reviewed the current state of knowledge of UVR photoadaptation in human skin. However, more studies are needed to explore the use of UVR photoadaptation to protect against critical endpoints, such as skin cancer.

Infrared and skin: Friend or foe

In the last decade, it has been proposed that the sun's IR-A wavelengths might be deleterious to human skin and that sunscreens, in addition to their desired effect to protect against UV-B and UV-A, should also protect against IR-A (and perhaps even visible light). Several studies showed that NIR may damage skin collagen content via an increase inMMP-1 activity in the same manner as is known for UVR. Unfortunately, the artificial NIR light sources used in such studies were not representative of the solar irradiance. Yet, little has been said about the other side of the coin. This article will focus on key information suggesting that IR-A may be more beneficial than deleterious when the skin is exposed to the appropriate irradiance/dose of IR-A radiation similar to daily sun exposure received by people in real life.IR-A might even precondition the skin--a process called photo prevention--from an evolutionary standpoint since exposure to early morning IR-A wavelengths in sunlight may ready the skin for the coming mid-day deleterious UVR. Consequently IR-A appears to be the solution, not the problem. It does more good than bad for the skin. It is essentially a question of intensity and how we can learn from the sun. © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Loss of protein phosphatase 6 in mouse keratinocytes increases susceptibility to ultraviolet-B-induced carcinogenesis

We previously reported that deficiency in the gene encoding the catalytic subunit of protein phosphatase 6 (Ppp6c) predisposes mouse skin tissue to papilloma formation initiated by DMBA. Here, we demonstrate that Ppp6c loss acts as a tumor promoter in UVB-induced squamous cell carcinogenesis. Following UVB irradiation, mice with Ppp6c-deficient keratinocytes showed a higher incidence of skin squamous cell carcinoma than did control mice. Time course experiments showed that following UVB irradiation, Ppp6c-deficient keratinocytes upregulated expression of p53, PUMA, BAX, and cleaved caspase-3 proteins. UVB-induced tumors in Ppp6c-deficient keratinocytes exhibited a high frequency of both p53- and γH2AX-positive cells, suggestive of DNA damage. Epidemiological and molecular data strongly suggest that UVB from sunlight induces p53 gene mutations in keratinocytes and is the primary causative agent of human skin cancers. Our analysis suggests that PP6 deficiency underlies molecular events that drive outgrowth of initiated keratinocytes harboring UVB-induced mutated p53. Understanding PP6 function in preventing UV-induced tumorigenesis could suggest strategies to prevent and treat this condition.

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.

Increased levels of p53 and PARP-1 in EL-4 cells probably related with the immune adaptive response induced by low dose ionizing radiation in vitro

OBJECTIVE

This paper is to explore the DNA repair mechanism of immune adaptive response (AR) induced by low dose radiation (LDR), the changes of mRNA levels and protein expressions of p53, ATM, DNA-PK catalytic subunit (DNA-PKcs) and PARP-1 genes in the LDR-induced AR in EL-4 cells.

METHODS

The apoptosis and cell cycle progression of EL-4 cells were detected by flow cytometry in 12 h after the cells received the pre-exposure of 0.075 Gy X-rays (inductive dose, D1) and the succeeding high dose irradiation (challenge dose, D2; 1.0, 1.5, and 2.0 Gy X-rays, respectively) with or without wortmannin (inhibitor of ATM and DNA-PK) and 3-aminobenzamid (inhibitor of PARP-1). And the protein expressions and mRNA levels related to these genes were detected with flow cytometry and reverse transcription-polymerase chain reaction in 12 h after irradiation with D2.

RESULTS

The mRNA and protein expressions of p53 and PARP-1 in EL-4 cells in the D1 + D2 groups were much lower than those in the D2 groups, and those of PARP-1 in the 3-AB + D2 and the 3-AB + D1 + D2 groups were much lower than those in the D2 and the D1 + D2 groups. The percentage of apoptotic EL-4 cells in the 3-AB + D1 + D2 groups was much higher than that in the D1 + D2 groups, that in the G₀/G₁ and the G₂ + M phases was much higher, and that in the S phase were much lower. Although the ATM and DNA-PKcs mRNA and protein expressions in wortmannin + D1 + D2 groups were much lower than those in the D1 + D2 groups, there were no significant changes in the apoptosis and cell cycle progression between the wortmannin + D1 + D2 and the D1 + D2 groups.

CONCLUSION

PARP-1 and p53 might play important roles in AR induced by LDR.

Photoprotective effects of nicotinamide

Sun protective measures can reduce numbers of both precancerous actinic keratoses and cutaneous squamous cell carcinomas within relatively short periods of time even in high-risk populations. Sunscreens, which tend to provide greater protection against shortwave UVB than against longer wavelength UVA radiation, can however provide only partial protection from the mutagenic and immune suppressive effects of sunlight. In large part, this reflects poor compliance with proper sunscreen application and reapplication. Skin cancer is by far the most common malignancy in Caucasian populations, and additional strategies to reduce the morbidity and economic burden of this disease are now urgently needed. Nicotinamide, the amide form of vitamin B3, is an inexpensive agent which is used for a variety of dermatological applications with little or no toxicity even at high doses. Nicotinamide has photoprotective effects against carcinogenesis and immune suppression in mice, and is photoimmunoprotective in humans when used as a lotion or orally. UV irradiation depletes keratinocytes of cellular energy and nicotinamide, which is a precursor of nicotinamide adenine dinucleotide, may act at least in part by providing energy repletion to irradiated cells.

Proteomic profiling of human keratinocytes undergoing UVB-induced alternative differentiation reveals TRIpartite Motif Protein 29 as a survival factor

Background

Repeated exposures to UVB of human keratinocytes lacking functional p16^INK-4a and able to differentiate induce an alternative state of differentiation rather than stress-induced premature senescence.

Methodology/Principal Findings

A 2D-DIGE proteomic profiling of this alternative state of differentiation was performed herein at various times after the exposures to UVB. Sixty-nine differentially abundant protein species were identified by mass spectrometry, many of which are involved in keratinocyte differentiation and survival. Among these protein species was TRIpartite Motif Protein 29 (TRIM29). Increased abundance of TRIM29 following UVB exposures was validated by Western blot using specific antibody and was also further analysed by immunochemistry and by RT-PCR. TRIM29 was found very abundant in keratinocytes and reconstructed epidermis. Knocking down the expression of TRIM29 by short-hairpin RNA interference decreased the viability of keratinocytes after UVB exposure. The abundance of involucrin mRNA, a marker of late differentiation, increased concomitantly. In TRIM29-knocked down reconstructed epidermis, the presence of picnotic cells revealed cell injury. Increased abundance of TRIM29 was also observed upon exposure to DNA damaging agents and PKC activation. The UVB-induced increase of TRIM29 abundance was dependent on a PKC signaling pathway, likely PKCδ.

Conclusions/Significance

These findings suggest that TRIM29 allows keratinocytes to enter a protective alternative differentiation process rather than die massively after stress.

Nuclear factor kappaB- and specificity protein 1-dependent p53-mediated bi-directional regulation of the human manganese superoxide dismutase gene

Tumor suppressor p53 is known to activate certain sets of genes while suppressing others. However, whether p53 can both activate and suppress the same gene is unclear. To address this question, concentration-dependent p53 effect on the manganese superoxide dismutase (MnSOD) gene was investigated. By transfecting p53 in PC-3 cells, we demonstrate that low concentrations of p53 increase while high concentrations suppress MnSOD expression. The physiological relevance of this effect was determined in vitro and in vivo using combined UVB-mediated activation and small interference RNA-mediated suppression of p53. Results were consistent with the bi-directional effect of p53 on MnSOD expression. MnSOD-promoter/enhancer analysis demonstrates that p53 is suppressive to the promoter activity regardless of the presence or absence of putative p53 binding sites. However, a low level of p53 increases MnSOD gene transcription in the presence of the intronic-enhancer element, and this effect is dependent on nuclear-factor kappaB (NF-kappaB) binding sites. Expression of p53 enhances nuclear levels of p65 with corresponding increase in the DNA-binding activity of NF-kappaB as detected by electrophoretic mobility shift and chromatin immunoprecipitation assays. Transfection of p65 small interference RNA reduces the positive effect of p53 on MnSOD gene transcription. These data suggest that p65 can overcome the negative effect of p53 on MnSOD expression. However, when the level of p53 was further increased, the suppressive effect of p53 outweighed the positive effect of p65 and led to the suppression of MnSOD gene transcription. These results demonstrated that p53 can both suppress and induce MnSOD expression depending on the balance of promoter and enhancer binding transcription factors.

COP1 contributes to UVB-induced signaling in human keratinocytes

UVB irradiation has been shown to trigger a broad range of changes in gene expression in human skin; however, factors governing these events are still not well understood. In this study, we show that human constitutive photomorphogenic protein-1 (huCOP1), an E3 ligase, contributes to the orchestration of UVB response of keratinocytes. Accordingly, our data show that (i) huCOP1 protein is expressed both in the nucleus and in the cytoplasm of cultured keratinocytes, (ii) UVB reduces the levels of the huCOP1 mRNA and protein, and (iii) induces changes in the subcellular localization of huCOP1. Finally, we show that gene-specific silencing of huCOP1 induces the accumulation of the tumor suppressor p53 protein, which is further increased after UVB irradiation.

Quantification of Inducible SOS-Like Photoprotective Responses in Human Skin

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

Ribonucleotide reductase subunits M2 and p53R2 are potential biomarkers for metastasis of colon cancer

BACKGROUND

Ribonucleoside diphosphate reductase plays a key role in converting ribonucleoside diphosphate to 2'-deoxyribonucleoside diphosphate, which is necessary for DNA repair and replication. To determine if human ribonucleotide reductase small subunit M2 (hRRM2) and p53-dependent human ribonucleotide reductase small subunit R2 (p53R2) play roles on invasion ability of cancer cells, the gene transferring technique was used to construct stable hRRM2 and p53R2 overexpression transfectants. Increase of hRRM2 dramatically enhanced the cell migration in KB and PC-3 cells, but p53R2 overexpression reduced cellular invasion potential to 50% and 40% in KB and PC-3 cells, respectively. Furthermore, hRRM2 enhanced cancer cells to induce the cell migration of Human Umbilical Vein Endothelial Cells, but p53R2 reduced this ability in transfectants.

PATIENTS AND METHODS

To further determine the role of human ribonucleotide reductase subunits on cancer metastasis, a tissue array, including 59 primary and 49 metastatic colon adenocarcinoma samples, was used. Immunohistochemistry was used to evaluate the relationship between human ribonucleotide reductase subunits and metastasis.

RESULTS

Univariate and multivariate analysis revealed that p53R2 is negatively related to the metastasis of colon adenocarcinoma samples (odds ratio, 0.23; P < 0.05); hRRM2 increases the risk of metastasis in colon cancer, but did not show significantly. Thus, opposing regulation of hRRM2 and p53R2 in invasion potential might play a critical role in determining the invasion and metastasis phenotype in cancer cells.

CONCLUSION

The expression level of ribonucleotide reductase small subunits could serve as biomarkers to predict the malignancy potential of human cancers in the future.

New strategies of photoprotection

Adequate photoprotection is essential to control UV-related disorders, including sunburn, photoaging and photocarcinogenisis. Sun avoidance, protection of skin with clothing, and sunscreens are presently the best way of photoprotection, assuming that they are used properly. However, new strategies, which are based on or make use of the endogenous protective response to UV light, may further improve currently used photoprotective means. The addition of repair enzymes and/or antioxidants has a positive effect on skin's recovery from UV-induced DNA-damage. Several botanical agents, mainly vitamins and polyphenols, have shown to influence signal transduction pathways leading to photoprotective effects. Also stimulation of endogenous UV-response pathways via irradiation with a low UV dose or via simulation of UV-induced DNA-damage results in photoprotective effects. Future research in this field and combination of different photoprotective strategies will hopefully lead to improved photoprotection.

The protective role of a small GTPase RhoE against UVB-induced DNA damage in keratinocytes

RhoE, a p53 target gene, was identified as a critical factor for the survival of human keratinocytes in response to UVB. The Rho family of GTPases regulates many aspects of cellular behavior through alterations to the actin cytoskeleton, acting as molecular switches cycling between the active, GTP-bound and the inactive, GDP-bound conformations. Unlike typical Rho family proteins, RhoE (also known as Rnd3) is GTPase-deficient and thus expected to be constitutively active. In this study, we investigated the response of cultured human keratinocyte cells to UVB irradiation. RhoE protein levels increase upon exposure to UVB, and ablation of RhoE induction through small interfering RNA resulted in a significant increase in apoptosis and a reduction in the levels of the pro-survival targets p21, Cox-2, and cyclin D1, as well as an increase of reactive oxygen species levels when compared with control cells. These data indicate that RhoE is a pro-survival factor acting upstream of p38, JNK, p21, and cyclin D1. HaCat cells expressing small interfering RNA to p53 indicate that RhoE functions independently of its known associates, p53 and Rho-associated kinase I (ROCK I). Targeted expression of RhoE in epidermis using skin-specific transgenic mouse model resulted in a significant reduction in the number of apoptotic cells following UVB irradiation. Thus, RhoE induction counteracts UVB-induced apoptosis and may serve as a novel target for the prevention of UVB-induced photodamage regardless of p53 status.

Metastasis-suppressing potential of ribonucleotide reductase small subunit p53R2 in human cancer cells

PURPOSE

Previous gene transfection studies have shown that the accumulation of human ribonucleotide reductase small subunit M2 (hRRM2) enhances cellular transformation, tumorigenesis, and malignancy potential. The latest identified small subunit p53R2 has 80% homology to hRRM2. Here, we investigate the role of p53R2 in cancer invasion and metastasis.

EXPERIMENTAL DESIGN

The immunohistochemistry was conducted on a tissue array including 49 primary and 59 metastatic colon adenocarcinoma samples to determine the relationship between p53R2 expression and metastasis. A Matrigel invasive chamber was used to sort the highly invasive cells and to evaluate the invasion potential of p53R2.

RESULTS

Univariate and multivariate analyses revealed that p53R2 is negatively related to the metastasis of colon adenocarcinoma samples (odds ratio, 0.23; P<0.05). The decrease of p53R2 is associated with cell invasion potential, which was observed in both p53 wild-type (KB) and mutant (PC-3 and Mia PaCa-2) cell lines. An increase in p53R2 expression by gene transfection significantly reduced the cellular invasion potential to 54% and 30% in KB and PC-3 cells, respectively, whereas inhibition of p53R2 by short interfering RNA resulted in a 3-fold increase in cell migration.

CONCLUSIONS

Opposite regulation of hRRM2 and p53R2 in invasion potential might play a critical role in determining the invasion and metastasis phenotype in cancer cells. The expression level of ribonucleotide reductase small subunits may serve as a biomarker to predict the malignancy potential of human cancers in the future.