Altered expression of the p53-regulated proteins, p21Waf1/Cip1, MDM2, and Bax in ultraviolet-irradiated human skin

Bioactive substances in the stratum corneum of the epidermis found as indicators of skin damage due to sun exposure

Background/Purpose

Although an inflammatory response upon acute injury caused by ultraviolet radiation (UV) can be observed immediately, the influence of long‐term, repetitive low‐dose UV exposure on the skin cannot be precisely perceived, making early detection of chronic damage difficult. This study investigated bioactive substances in the stratum corneum as a potential early and sensitive indicator of the influence of sun exposure on the skin using receiver operating characteristic (ROC) analysis.

Methods

Receiver operating characteristic analysis was performed to assess the responsiveness of cytokines [interleukin (IL)‐1α, IL‐1 receptor antagonist (IL‐1ra), IL‐10, tumor necrosis factor (TNF)‐α], BCL2‐associated protein X (Bax), Toll‐like receptor (TLR)3, and TLR4 in the stratum corneum of healthy people exposed (dorsum of the hand) and unexposed (inner arm) to UV. Sunscreen was applied to patients with photodermatosis for 4 weeks to evaluate changes in IL‐1ra/IL‐1α, TNF‐α, Bax, and TLR3 levels after sunscreen application, as these molecules exhibited high responsiveness to sun exposure according to ROC analysis. In addition, IL‐1ra, IL‐1α, and IL‐10 levels were quantified by enzyme‐linked immunosorbent assay, and TNF‐α, Bax, TLR3, and TLR4 levels were semi‐quantitatively assessed by immunocytochemistry.

Results

Receiver operating characteristic analysis identified IL‐1ra/IL‐1α, TNF‐α, Bax, and TLR3 in the stratum corneum as highly responsive to sun exposure. Moreover, in participants, including patients with photodermatosis, IL‐1ra/IL‐1α, TNF‐α, and Bax levels decreased significantly after sunscreen application.

Conclusion

The results revealed that IL‐1ra/IL‐1α, TNF‐α, and Bax in the stratum corneum represent sensitive indicators of the influence of sun exposure on the skin.

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.

Variable Bax antigenicity is linked to keratinocyte position within epidermal strata and UV-induced apoptosis

Pro- and anti-apoptotic members of the Bcl-2 family are fundamental in the control of apoptosis. Among them, Bax plays a key role in apoptosis induction by mediating the release of apoptogenic factors from mitochondria to the cytosol. In this report, we investigated, by immunohistofluorescence, the in vivo distribution of Bax in normal human epidermis before and 24 h after exposure to solar-simulated radiation. Bax expression was evaluated with three different, Western blot pretested, anti-Bax antibodies (Ab) and correlated with markers of keratinocyte differentiation and apoptosis using anti-beta(1) integrin and anti-active caspase-3 Abs respectively. Using anti-Bax N20 and A-3533 polyclonal Ab, we found that, whereas undifferentiated keratinocytes of the basal proliferative compartment contained Bax in the cytosol, the differentiated suprabasal cells had Bax mainly in the nucleus. This immunoreactivity pattern was not modified by skin irradiation. Interestingly, the well known apoptosis-related Bax redistribution to mitochondria in response to a cell death signal, could be detected only with yet another, the 2D2 monoclonal Ab. This relocalization occurred specifically in apoptotic, active caspase-3 positive cells of irradiated epidermis. Our data highlight the differentiation- and apoptosis-associated changes in the pattern of Bax subcellular and cellular distribution as uncovered by different anti-Bax Abs and suggest that Bax undergoes successive activation that progresses in parallel with keratinocyte differentiation and apoptosis.

The effect of ultra violet B (TL-01) phototherapy on epidermal expression of p53 protein in psoriatic plaques

BACKGROUND

Psoriasis is a genetically determined inflammatory skin disease. It is now recognized that narrow band TL-01 phototherapy is an effective treatment for psoriasis. However, ultraviolet (UV) exposure induces p53 mutations in keratinocytes and repeated exposure of skin to UV radiation results in clonal expansion of these initiated p53-mutant cells within the epidermis.

AIM

The present study aims to examine epidermal p53 expression in the skin of psoriatic patients at different time points following TL-01 phototherapy.

METHODS

Skin samples from patients suffering from plaque-type psoriasis, collected before, during and at the final stages of TL-01 phototherapy were examined for p53 expression by immunohistochemistry.

RESULTS/CONCLUSION

Our results showed an increase in p53 expressing keratinocytes following TL-01 phototherapy. Some of these cells were arranged spatially, as conical clones arising from putative stem cell compartments, suggesting that the chronic TL-01 treatment might have triggered cell growth and clonal expansion, an important step in initiating skin carcinogenesis.

Modulation of Gene Expression Induced in Human Epidermis by Environmental Stress In Vivo

Environmental insults on the skin induce biologic responses through the modulation of expression of genes implicated in different cell functions. The aim of this study was to investigate the modulation of gene expression profile in human epidermis in vivo following different stresses. We determined the modulations of gene expression using cDNA macroarray in the epidermis of 28 healthy volunteers, following mild and physiologic insults, including: (1), tape stripping; (2) application of 10% sodium dodecyl sulfate; (3) daily application of vaseline; and (4), exposure to one minimal erythema dose of solar-simulated radiation. The analysis was performed 19 h after treatment. The reverse transcription-polymerase chain reaction method was used to confirm our results. We showed that: (1) the intensity of gene modulation was variable among the volunteers following the same skin stress; (2) the nature and intensity of skin treatment modified the pattern of gene expression; and (3) some genes were modulated only by specific stress, some others are modulated irrespective of the stress. GADD45, Bax, SAS, and granulocyte chemotactic protein-2 were overexpressed exclusively following solar-simulated radiation, whereas tape stripping led to the modulation of genes implicated in different pathways (inflammation, cell proliferation, cell differentiation, detoxification, etc.). Concerning common gene modulation, MRP8 and MRP14 were highly upregulated in human skin epidermis after solar-simulated radiation, vaseline application or tape stripping, and to a lower extent after sodium dodecyl sulfate. Such upregulation of the MRP 8/14 genes was confirmed at the protein level in an ex-vivo skin culture model following tape stripping and solar-simulated radiation. Together, these results suggest that MRP8 and MRP14 may be general, yet highly sensitive, markers for a great variety of skin stresses and that they are implicated in several epidermal repair pathways.

Differential expression of proliferation- and apoptosis-related markers in lentigo maligna and solar keratosis keratinocytes

Keratinocytes influence the number, morphology, and proliferation of melanocytes. An interference in the melanocyte-keratinocyte relationship may contribute to melanoma development. This study examined the expression of apoptotic and proliferative markers in keratinocytes in lentigo maligna to characterize the epidermis permissive to these lesions. Formalin-fixed and paraffin-embedded tissues from 25 samples of lentigo maligna, 20 samples of solar keratoses, and 5 samples each of normal sun-exposed and non-sun-exposed skin (controls) were immunostained with antibodies directed against the proapoptotic markers bax and p53, the antiapoptotic marker bcl-2, and the proliferation marker ki-67. Eight percent of the lentigo maligna samples were positive for keratinocyte expression of bcl-2, 24% were positive for p53, and 76% were positive for bax; respective findings for solar keratoses were 35%, 85%, and 90%. Comparison with normal sun-exposed skin yielded lower rates of keratinocyte proliferation in 56% of the lentigo maligna samples, similar rates in 36%, and higher rates in 8%; for solar keratoses, proliferation was higher than controls in 60% of samples, similar in 35%, and lower in 5%. All these differences were statistically significant. These findings indicate that there are variable patterns of epidermal reaction to chronic sun exposure. The epidermis in lentigo maligna shows overall low proliferation and an apparently low apoptotic tendency. The dysfunctional epidermis may be permissive to aberrant melanocyte proliferation in the early stages of melanoma development.

Comparison of the expression of p53, p21, Bax and the induction of apoptosis between patients with basal cell carcinoma and normal controls in response to ultraviolet irradiation

AIM

Ultraviolet light (UV) is known to cause DNA damage in the epidermis. The damaged DNA is repaired or deleted by apoptosis to prevent the generation of cancer. It has been suggested that a deficient apoptotic mechanism may predispose individuals to skin cancer. Therefore, the response of normal controls and patients with basal cell carcinoma (BCC) to UV irradiation was investigated.

METHODS

The buttock skin from normal volunteers and patients with BCC was irradiated using solar simulated radiation (SSR). SSR mimics the effect of natural sunlight. Skin biopsies were excised and examined for p53, p21, and Bax protein expression and for the induction of apoptosis.

RESULTS

At 33 hours after UV irradiation, the induction of apoptosis was significantly higher (p = 0.04) in patients with BCC than in normal volunteers (Mann Whitney test). A trend towards higher p21 expression was found at 33 hours in patients with BCC (mean, 18.69 positive cells/field) than in normal volunteers (mean, 9.89), although this difference was not significant (p = 0.05 positive cells/field).

CONCLUSION

These results may imply that patients with BCC have enhanced sensitivity to UV irradiation or that there is some defect in the cell arrest or repair pathways, which results in damaged cells been pushed into apoptosis rather than repair.

The expression of p53, p21, Bax and induction of apoptosis in normal volunteers in response to different doses of ultraviolet radiation

BACKGROUND

Ultraviolet radiation (UVR) damages keratinocytes. Direct DNA damage may undergo enzymatic repair followed by resumption of the normal cell cycle. Cells may also be eliminated without inflammation by the error-free process of programmed cell death or apoptosis. Necrosis of cells can occur after overwhelming damage. Failure of apoptosis leads to retention of cells with persistent mutations.

OBJECTIVES

This study investigates p53-dependent apoptotic responses in normal skin following solar-simulated radiation (SSR).

METHODS

Sun-protected buttock skin from normal volunteers with no history or clinical evidence of skin cancer was exposed to graded doses of SSR, 0.5, 1, 2 and 3 times the minimal erythema dose (MED). Biopsies taken at a range of time points (4.5, 9, 24, 33, 48 and 72 h) after UVR, quantified the time course and dose-response of apoptosis and the expression of the relevant proteins, p53, p21waf1/Cip1 and Bax, by single and double labelling techniques.

RESULTS

Apoptosis was upregulated in a dose-dependent manner as was the expression of p53, p21waf1/Cip1 and Bax in response to SSR. Following exposure to 3 MEDs it was found that: (i) the maximum number of apoptotic cells occurred at 48 h; (ii) p53 protein expression was upregulated from 4 to 72 h preceding peak p21waf1/Cip1 protein expression (9-48 h) and peak Bax protein expression (33 h).

CONCLUSIONS

These results suggest that, following SSR, normal human skin induces apoptosis by the p53, p21waf1/Cip1, Bax pathway in vivo. In addition, induction of apoptosis and expression of p53, p21waf1/Cip1 and Bax occurs in a dose-dependent manner.

Demonstration of apoptosis in human skin injuries as an indicator of vital reaction

Demonstrating the vital character of an injury and estimation of the age are routine tasks in forensic pathology and although many different techniques have been applied to this problem none have been found to be completely satisfactory. Apoptosis, an active genetically controlled process, is the major mechanism by which homeostasis of a number of physiological systems in the body is regulated and changes in the rate following different kinds of stimuli have prompted us to test it as an indicator of vitality. We used an in situ end-labelling technique (Apop-Tag) in 30 human surgical skin injuries with age since injury ranging from 3 min to 8 h and found that apoptotic keratinocytes are found in over 50% of the cases with a post-infliction interval of at least 120 min. Apoptosis was not seen in injuries less than 120 min old or in normal skin, which was used as an external control. These results suggest that apoptosis could be a useful indicator for the intravital occurrence of injuries and could help to estimate the date of the skin injuries in some cases. The importance of strict technical control is stressed and the necessity of a complementary technique to confirm apoptosis is discussed.

Altered p53 expression in benign and malignant skin lesions from renal transplant recipients and immunocompetent patients with skin cancer: correlation with human papillomaviruses?

Renal transplant recipients are prone to numerous benign and malignant skin lesions. Previous work in the authors' laboratory has determined that the human papillomavirus may be the viral aetiology of these skin lesions. The p53 tumor-suppressor gene is the most frequently mutated gene in a wide range of human cancers. Here the authors describe an immunohistochemical study to evaluate the expression of p53 in benign and malignant skin lesions from renal transplant recipients and immunocompetent patients with skin cancer. The effect of p53 mutations on the expression patterns observed were examined by polymerase chain reaction-single strand conformation polymorphism analysis and direct cycle sequencing. The expression of the p53-regulated cyclin-dependant kinase inhibitor p21Waf1/Cip1 and Mdm2 was also examined in p53-positive cells. The expression of p53 in benign and malignant lesions was found to be markedly different. p53 was expressed in only 40% (6/15) of viral warts analyzed. The expression was confined to the basal layer both in the lesion and in adjacent normal skin, and the level of expression was low and only in a small number of cells (<10%). Of the cutaneous squamous cell carcinomas analyzed, 60% (9/15) showed p53 expression. Two different patterns of expression were observed. Basal layer expression in both the invasive tumor and adjacent normal skin was observed in 50% of the p53-positive squamous cell carcinomas; in the remaining 50%, p53 was expressed diffusely throughout the invasive tumor and in the basal layer of adjacent normal skin. The level of expression was high and in a large number of cells. Polymerase chain reaction-single strand conformation polymorphism analysis revealed that only one of the squamous cell carcinomas expressing p53 harbored a p53 mutation and that the accumulated p53 in the remaining tumors was wild type. No Mdm2 or p21Waf1/Cip1 expression was detected in the p53-positive squamous cell carcinomas, indicating that although the accumulated p53 is stable, it does not function effectively as a transcriptional activator. This represents a novel p53 phenotype in cutaneous squamous cell carcinoma. In addition, no correlation was seen between the presence and absence of human papillomavirus and p53 expression.

Activation of p53 by roscovitine-mediated suppression of MDM2 expression

The p53 tumor suppressor is regulated by the MDM2 oncoprotein. Overexpression of MDM2 maintains p53 at low levels and contributes to the functional inactivation of p53 in a subset of tumors. We found that treatment with roscovitine and olomoucin, which were originally developed as cyclin-dependent kinase (CDK) inhibitors, can efficiently stabilize and activate nuclear p53 in tumor cells with MDM2 amplification or cytoplasmic p53. These inhibitors block the degradation of p53 without affecting p53-MDM2 binding and the nuclear shuttling function of p53 and MDM2. Roscovitine also induces stabilization of the p53 Ala-315 mutant, indicating that it does not act by regulating the CDK phosphorylation of serine 315. Roscovitine induces down-regulation of MDM2 expression at both protein and mRNA levels. Ectopic expression of MDM2 can abrogate the ability of roscovitine to induce p53 stabilization. Low concentrations of roscovitine cooperate with the DNA-damaging agent camptothecin to activate p53 in a synergistic fashion. These results show that the small molecule CDK inhibitors can be used to activate p53 through their potent inhibitory effect on MDM2 expression and may be useful as sensitizing agents for other DNA-damaging drugs.

Distribution of Bcl-2 and Bax in embryonic and fetal human skin: antiapoptotic and proapoptotic proteins are differentially expressed in developing skin

The Bcl-2 protein is involved in the regulation of apoptosis. Bax has an antagonistic effect and enhances cell death. We report that in early gestation, Bcl-2 and Bax colocalize to the epidermal portion of the hair follicle. In the more advanced stages, Bax is located in the compartments where a hair canal is excavated and keratinization and holocrine secretion are initiated, in contrast to Bcl-2, which is expressed in the follicular papilla, preventing apoptosis and underscoring its role as a permanent and stable population of specialized fibroblasts. Scattered dendritic cells located in the basal and immediate suprabasal interfollicular epidermis as well as in the outer root sheath of the developing hair follicle, including the bulge, strongly express Bcl-2 and label for HMB-45, identifying them as melanocytes. The spatial and temporal expression pattern of Bcl-2 and Bax during human hair follicle development underscores their importance for hair biology and most likely is disturbed in the evolution of follicular tumors.

Expression and modulation of apoptosis regulatory molecules in human melanocytes: significance in vitiligo

Although the aetiology of the hypopigmentary disorder vitiligo is ill understood, it is clear that pigment producing cells are absent from vitiliginous lesional skin. The present study was designed to investigate the possible role of melanocyte-expressed apoptosis regulatory molecules in melanocyte disappearance. Flow cytometric evaluation of p53, p21, Bcl-2 and Bax revealed no differences in in vitro expression levels between normal control and non-lesional melanocytes. Moreover, no in situ immunohistological differences were observed in melanocytes present in control, non-lesional and perilesional skin. However, an enhanced number of p53+ nuclei, in the absence of detectable p21 expression, was detected in involved areas. The observed p53 expression pattern did not involve melanocytes and could be the result of ultraviolet (UV) A irradiation. Further, we showed that UVB is capable of modulating melanocyte-expressed apoptosis regulatory molecules. Consequently, a lethal dose of UVB was given to two groups of cultured normal control and non-lesional melanocytes. No significant differences were found when comparing the percentages and kinetics of UVB-induced apoptosis in these groups. In conclusion, our results indicate that the relative apoptosis susceptibility of melanocytes in vitiligo is comparable with that of normal control cells. It is therefore unlikely that vitiligo is causally related to dysregulation of apoptosis regulatory molecules.

Autocrine nerve growth factor in human keratinocytes

Biologically active nerve growth factor (NGF) is synthesised and released by proliferating normal human keratinocytes. NGF up-regulates the expression of NGF mRNA in keratinocytes. Keratinocytes express both the low (p75)- and the high-affinity (TrkA) NGF-receptors, which are located in the basal layer of the epidermis. K252, a specific inhibitor of trk phosphorylation, blocks NGF-induced keratinocyte proliferation, in absence of exogenous NGF. Normal keratinocytes over-expressing TrkA proliferate better than control transfectants, while the NGF mimicking anti-Trk antibody induces an increased keratinocyte proliferation in Trk over-expressing cells as compared to mock transfected keratinocytes. In addition, NGF over-expressing keratinocytes proliferate better than mock transfected cells. K252, by blocking TrkA phosphorylation, induces apoptosis in normal keratinocytes, but not in keratinocytes over-expressing bcl-2. Furthermore, NGF transfected keratinocytes are protected from UV-B-induced keratinocyte apoptosis, by maintaining constant levels of Bcl-2 and Bcl-xL . Taken together these results support the concept of an autocrine survival system sustained by NGF and its high-affinity receptor in human keratinocytes. Because NGF and Trk levels are highly expressed in psoriasis. one could speculate that NGF autocrine system plays a role in the mechanisms associated with this and other hyperproliferative skin conditions, including cancer.

The cellular response to p53: the decision between life and death

The p53 tumor suppressor protein plays a crucial role in regulating cell growth following exposure to various stress stimuli. p53 induces either growth arrest, which prevents the replication of damaged DNA, or programmed cell death (apoptosis), which is important for eliminating defective cells. Whether the cell enters growth arrest or undergoes apoptosis, depends on the final integration of incoming signals with antagonistic effects on cell growth. Many factors affect the cellular response to activated p53. These include the cell type, the oncogenic status of the cell with emphasis on the Rb/E2F balance, the extracellular growth and survival stimuli, the intensity of the stress signals, the level of p53 expression and the interaction of p53 with specific proteins. p53 is regulated both at the levels of protein stability and biochemical activities. This complex regulation is mediated by a range of viral and cellular proteins. This review discusses this intriguing complexity which affects the cell response to p53 activation.

UVA1 radiation triggers two different final apoptotic pathways

Because ultraviolet-A1 (UVA1; 340-400 nm) radiation is used therapeutically, this in vitro study addressed the question "how does it work?" To begin addressing this question, UVA1 radiation was first established to reduce the survival of transformed T and B lymphocytes in a linear dose-dependent manner using clonogenic reproductive assays, and that cell death occurs by apoptosis using transmission electron microscopy, Annexin V, and flow cytometry. The primary mechanism was determined to be immediate pre-programmed cell death, an apoptotic mechanism that does not require protein synthesis post-insult, by quantifying the apoptotic cells over time in the absence or presence of a translation inhibitor. To explore how UVA1 radiation induces immediate pre-programmed cell death apoptosis, reactive oxygen species and mitochondrial activity were altered during exposure using a variety of agents, while a specific fluorescent probe, 5,5',6,6'tetrachloro- 1,1',3,3'-tetraethylbenzimidazolcarbocyanine iodide, was used to examine mitochondrial transmembrane depolarization. To show that UVA1 mediates singlet-oxygen damage to the mitochondrial membranes, X-rays, UVB (290-320 nm), 8-methoxypsoralen and UVA, vitamin K3, anti-Fas antibody, and blocking antibody were the negative controls, while rose bengal or protoporphyrin IX with visible light were the positive controls. Cyclosporine A, which inhibits the mitochondrial megapore from opening, was used with singlet-oxygen and superoxide-anion generators to distinguish between the two final apoptotic pathways. The collective results show that UVA1 radiation primarily mediates singlet-oxygen damage triggering immediate pre-programmed cell death apoptosis (T < 20 min) by immediately opening the cyclosporine A-sensitive ("S" site) mitochondrial megapore, while superoxide anions initiate another cyclosporine A-insensitive ("P" site) final apoptotic pathway.