Effects of UVB on E prostanoid receptor expression in murine skin

Diversified Stimuli-Induced Inflammatory Pathways Cause Skin Pigmentation

The production of melanin pigments by melanocytes and their quantity, quality, and distribution play a decisive role in determining human skin, eye, and hair color, and protect the skin from adverse effects of ultraviolet radiation (UVR) and oxidative stress from various environmental pollutants. Melanocytes reside in the basal layer of the interfollicular epidermis and are compensated by melanocyte stem cells in the follicular bulge area. Various stimuli such as eczema, microbial infection, ultraviolet light exposure, mechanical injury, and aging provoke skin inflammation. These acute or chronic inflammatory responses cause inflammatory cytokine production from epidermal keratinocytes as well as dermal fibroblasts and other cells, which in turn stimulate melanocytes, often resulting in skin pigmentation. It is confirmed by some recent studies that several interleukins (ILs) and other inflammatory mediators modulate the proliferation and differentiation of human epidermal melanocytes and also promote or inhibit expression of melanogenesis-related gene expression directly or indirectly, thereby participating in regulation of skin pigmentation. Understanding of mechanisms of skin pigmentation due to inflammation helps to elucidate the relationship between inflammation and skin pigmentation regulation and can guide development of new therapeutic pathways for treating pigmented dermatosis. This review covers the mechanistic aspects of skin pigmentation caused by inflammation.

Expression of prostaglandin E2 receptor 3 in the eyelid epidermis of patients with Stevens-Johnson syndrome/toxic epidermal necrolysis

Background/aims

In a previous genome-wide association study of Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN) patients we reported the association between SJS/TEN and the prostaglandin E receptor 3 (PTGER3) gene, and that its protein PGE2 receptor 3 (EP3) was markedly downregulated in the conjunctival epithelium of SJS/TEN patients. Here we examined EP3 expression of the eyelid epidermis in SJS/TEN patients with severe ocular complications and investigated the function of EP3.

Methods

For the immunohistochemical study, we obtained eyelid samples from five SJS/TEN patients and five patients without SJS/TEN (control subjects) who were undergoing surgery to treat trichiasis, and investigated the expression of EP3 protein in the epidermis of those samples. To investigate the EP3 function in the human epidermal keratinocytes, we performed ELISA and quantitative reverse transcription polymerase chain reaction, since it is reported that PGE2 suppresses cytokine production via EP3 in human conjunctival epithelium.

Results

The results of the immunohistochemical study revealed that EP3 expression in the eyelid epidermis of the SJS/TEN patients was the same as that in the controls. PGE2 and a selective EP3 agonist suppressed cytokine production and expression induced by polyinosine-polycytidylic acid stimulation, such as chemokine ligand 5 and chemokine motif ligand 10.

Conclusion

Our findings revealed that in chronic-phase SJS/TEN, EP3 protein was expressed in the eyelid epidermis and was not downregulated, unlike in conjunctival epithelium, and that PGE2 could suppress cytokine production via EP3 in human epidermal keratinocytes. Thus, EP3 expression in the epidermis might contribute to a silencing of skin inflammation in chronic-phase SJS/TEN.

Role of PGE-2 and Other Inflammatory Mediators in Skin Aging and Their Inhibition by Topical Natural Anti-Inflammatories

Human skin aging is due to two types of aging processes, “intrinsic” (chronological) aging and “extrinsic” (external factor mediated) aging. While inflammatory events, triggered mainly by sun exposure, but also by pollutants, smoking and stress, are the principle cause of rapid extrinsic aging, inflammation also plays a key role in intrinsic aging. Inflammatory events in the skin lead to a reduction in collagen gene activity but an increase in activity of the genes for matrix metalloproteinases. Inflammation also alters proliferation rates of cells in all skin layers, causes thinning of the epidermis, a flattening of the dermo-epidermal junction, an increase in irregular pigment production, and, finally, an increased incidence of skin cancer. While a large number of inflammatory mediators, including IL-1, TNF-alpha and PGE-2, are responsible for many of these damaging effects, this review will focus primarily on the role of PGE-2 in aging. Levels of this hormone-like mediator increase quickly when skin is exposed to ultraviolet radiation (UVR), causing changes in genes needed for normal skin structure and function. Further, PGE-2 levels in the skin gradually increase with age, regardless of whether or not the skin is protected from UVR, and this smoldering inflammation causes continuous damage to the dermal matrix. Finally, and perhaps most importantly, PGE-2 is strongly linked to skin cancer. This review will focus on: (1) the role of inflammation, and particularly the role of PGE-2, in accelerating skin aging, and (2) current research on natural compounds that inhibit PGE-2 production and how these can be developed into topical products to retard or even reverse the aging process, and to prevent skin cancer.

Preventive effect of Dioscorea japonica on squamous cell carcinoma of mouse skin involving down-regulation of prostaglandin E2 synthetic pathway

Hyperproduced prostaglandin E₂ by cyclooxygenase-2 and microsomal prostaglandin E synthase-1 evokes several pathophysiological responses such as inflammation and carcinogenesis. Our recent study demonstrated that Dioscorea japonica extract suppressed the expression of cyclooxygenase-2 and microsomal prostaglandin E synthase-1 and induced apoptosis in lung carcinoma A549 cells. In the present study, we investigated the effects of Dioscorea japonica on squamous cell carcinoma of mouse skin. Dioscorea japonica feeding and Dioscorea japonica extract topical application suppressed the expression of cyclooxygenase-2, microsomal prostaglandin E synthase-1, interleukin-1β and interleukin-6 and inhibited tumor formation, hyperplasia and inflammatory cell infiltration. Immunohistochemical analyses showed the immunoreactivities of cyclooxygenase-2 and microsomal prostaglandin E synthase-1 in tumor keratinocytes and stronger immunoreactivities of cyclooxygenase-2 and hematopoietic prostaglandin D synthase in epidermal dendritic cells (Langerhans cells). Treatment with Dioscorea japonica decreased the immunoreactivity of cyclooxygenase-2 and microsomal prostaglandin E synthase-1. These results indicate that Dioscorea japonica may have inhibitory effects on inflammation and carcinogenesis via suppression of the prostaglandin E₂ synthetic pathway.

Loss of INK4a/Arf gene enhances ultraviolet radiation-induced cutaneous tumor development

The CDKN2A locus encodes for tumor suppressor genes p16^INK4a and p14^Arf which are frequently inactivated in human skin tumors. The purpose of this study was to determine the relationship between loss of INK4a/Arf activity and inflammation in the development of ultraviolet (UV) radiation-induced skin tumors. Panels of INK4a/Arf^-/- mice and wild-type (WT) mice were treated with a single dose of UVB (200 mJ/cm² ). For long-term studies, these mice were irradiated with UVB (200 mJ/cm² ) three times weekly for 30 weeks. At the end of the experiment, tissues were harvested from mice and assayed for inflammatory biomarkers and cytokines. A single dose of UVB resulted in a significant increase in reactive oxygen species (ROS) and 8-dihydroxyguanosine (8-oxo-dG) lesions in INK4a/Arf^-/- mice compared to WT mice. When subjected to chronic UVB, we found that 100% of INK4a/Arf^-/- mice had tumors, whereas there were no tumors in WT controls after 24 weeks of UVB exposure. The increase in tumor development correlated with a significant increase in nuclear factor (NF)-κB, cyclooxygenase-2 (COX-2), prostaglandin E₂ (PGE₂ ) and its receptors both in UVB-exposed skin and in the tumors. A significant increase was seen in inflammatory cytokines in skin samples of INK4a/Arf^-/- mice following treatment with chronic UVB radiation. Furthermore, significantly more CD11b⁺ Gr1⁺ myeloid cells were present in UVB-exposed INK4a/Arf^-/- mice compared to WT mice. Our data indicate that by targeting UVB-induced inflammation, it may be possible to prevent UVB-induced skin tumors in individuals that carry CDKN2A mutation.

PGE2 synthesis and signaling in malignant transformation and progression of human hepatocellular carcinoma

Prostaglandin E 2 (PGE₂), which is the most abundant prostaglandin produced in hepatocellular carcinoma (HCC), may be involved in hepatocarcinogenesis. Here, the amount of PGE₂ was significantly increased in HCC tissue and adjacent noncancerous tissues relative to normal liver tissue (P<.001). In addition, the expression of EP2 receptor was considerably upregulated in HCC tissue compared with the expression of EP1 (P<.05), EP3 (P<.01), and EP4 (P<.01) receptor. The expression of EP2 receptor was positively correlated with the level of PGE₂ in HCC tissue (P<.001). Furthermore, PGE₂ significantly increased proliferation and invasion potential of human HCC cells. However, antagonism of EP2 signaling suppressed PGE₂-induced growth and invasion in human HCC cells. Taken together, upregulation of PGE₂ level was associated with proliferation and invasion potential of HCC, and EP2 receptor predominately mediated the function of PGE₂ in the transformation and progression of HCC.

Therapeutic effects of human gingiva-derived mesenchymal stromal cells on murine contact hypersensitivity via prostaglandin E2-EP3 signaling

BACKGROUND

The immunomodulatory and anti-inflammatory functions of human gingiva-derived mesenchymal stromal cells (GMSCs) have been demonstrated in contact hypersensitivity (CHS) models; however, their therapeutic effect during the late phase of CHS has been poor.

METHODS

The murine CHS model was induced by applying oxazolone to the ears of mice. Mesenchymal stromal cells were applied via two methods (intravenous or local injection) at three time points: 1 day before sensitization, 1 day before challenge, or 1 h after challenge. Prostaglandin E2 (PGE2) and sulprostone were administered subcutaneously 1 h after challenge.

RESULTS

The application of GMSCs, bone marrow mesenchymal stem cells, and adipose-derived stem cells all effectively suppressed CHS; however, GMSC treatment exhibited the greatest efficacy. Local injection of GMSCs led to a more marked attenuation of CHS compared with intravenous injection, especially during the late phase of CHS, and this manifested as decreased infiltration of inflammatory cells, suppression of the levels of various proinflammatory cytokines, reconstruction of the disrupted Th1/Th2 balance, and upregulation of regulatory T cells in the allergen contact areas. Pretreatment with indomethacin significantly abrogated the GMSC-mediated immunosuppressive effects, while PGE2 application reversed the effects of indomethacin pretreatment of GMSCs. Moreover, GMSC administration promoted the expression of EP3, a prostaglandin E receptor, and the application of sulprostone, an agonist of EP3, significantly attenuated CHS to a similar degree as that of GMSC administration.

CONCLUSIONS

GMSCs have reproducible and powerful immunomodulatory functions. Local injection of GMSCs is the superior mode for therapeutic application. PGE2-EP3 signaling plays an important role in the immunomodulatory functions of GMSCs in murine CHS.

Distribution of EP4 receptor in different Atlantic salmon (Salmo salar L.) tissues

Prostaglandin E2 (PGE2) is an important lipid mediator that plays diverse functions in mammals. Four receptor subtypes of PGE2, designated EP1-4, have been identified to mediate its signaling pathways. Extensive studies of PGE2 and its receptors have been carried out in mammals, but little is known in fish, including Atlantic salmon. In the current study, the distribution of Atlantic salmon EP4 receptor in different tissues was investigated using RT- and real-time PCR. A custom made antibody was used to investigate the distribution of this receptor in different tissues. Quantitative analysis by real-time PCR revealed that the expression was more abundant in the spleen followed by head kidney, skin and fin while it was least expressed in heart, muscles and brain. The staining intensity obtained by immunohistochemistry correlated with the RT-PCR results. EP4 expression was strongly associated with the immune cells in different tissues. To our knowledge, this is the first study to describe the distribution of EP4 receptor in Atlantic salmon tissues. Our findings suggest that EP4 may play a role in mediating immune responses as observed in mammals.

The tumor promoting activity of the EP4 receptor for prostaglandin E2 in murine skin

To determine whether the EP4 receptor for prostaglandin E2 (PGE2) contributes to the tumor promoting activity of PGs in murine skin, EP4 over-expressing mice (BK5.EP4) were generated and subjected carcinogenesis protocols. An initiation/promotion protocol resulted in 25-fold more squamous cell carcinomas (SCCs) in the BK5.EP4 mice than wild type (WT) mice. An increase in SCCs also occurred following treatment with initiator alone or UV irradiation. The initiator dimethylbenz[a]anthracene caused cytotoxicity in BK5.EP4, but not WT mice, characterized by sloughing of the interfollicular epidermis, regeneration and subsequent SCC development. A comparison of transcriptomes between BK5.EP4 and WT mice treated with PGE2 showed a significant upregulation of a number of genes known to be associated with tumor development, supporting a pro-tumorigenic role for the EP4 receptor.

Role of hypoxia-inducible factor 1, α subunit and cAMP-response element binding protein 1 in synergistic release of interleukin 8 by prostaglandin E2 and nickel in lung fibroblasts

Numerous epidemiological studies have linked exposure to particulate matter (PM) air pollution with acute respiratory infection and chronic respiratory and cardiovascular diseases. We have previously shown that soluble nickel (Ni), a common component of PM, alters the release of CXC chemokines from cultured human lung fibroblasts (HLF) in response to microbial stimuli via a pathway dependent on disrupted prostaglandin (PG)E2 signaling. The current study sought to identify the molecular events underlying Ni-induced alterations in PGE2 signaling and its effects on IL-8 production. PGE2 synergistically enhances Ni-induced IL-8 release from HLF in a concentration-dependent manner. The effects of PGE2 were mimicked by butaprost and PGE1-alcohol and inhibited with antagonists AH6809 and L-161,982, indicating PGE2 signals via PGE2 receptors 2 and 4. PGE2 and forskolin stimulated cAMP, but it was only in the presence of Ni-induced hypoxia-inducible factor 1, α subunit (HIF1A) that these agents stimulated IL-8 release. The Ni-induced HIF1A DNA binding was enhanced by PGE2 and mediated, in part, by activation of p38 MAPK. Negation of cAMP-response element binding protein 1 or HIF1A using short interfering RNA blocked the synergistic interactions between Ni and PGE2. The results of the current study provide novel information on the ability of atmospheric hypoxia-mimetic metals to disrupt the release of immune-modulating chemokines by HLF in response to PGE2. Moreover, in the presence of HIF1A, cAMP-mediated signaling pathways may be altered to exacerbate inflammatory-like processes in lung tissue, imparting a susceptibility of PM-exposed populations to adverse respiratory health effects.

The role of the EP receptors for prostaglandin E2 in skin and skin cancer

One of the most common features of exposure of skin to ultraviolet (UV) light is the induction of inflammation, a contributor to tumorigenesis, which is characterized by the synthesis of cytokines, growth factors and arachidonic acid metabolites, including the prostaglandins (PGs). Studies on the role of the PGs in non-melanoma skin cancer (NMSC) have shown that the cyclooxygenase-2 (COX-2) isoform of the cyclooxygenases is responsible for the majority of the pathological effects of PGE₂. In mouse skin models, COX-2 deficiency significantly protects against chemical carcinogen- or UV-induced NMSC while overexpression confers endogenous tumor promoting activity. Current studies are focused on identifying which of the G protein-coupled EP receptors mediate the tumor promotion/progression activities of PGE₂ and the signaling pathways involved. As reviewed here, the EP1, EP2, and EP4 receptors, but not the EP3 receptor, contribute to NMSC development, albeit through different signaling pathways and with somewhat different outcomes. The signaling pathways activated by the specific EP receptors are context specific and likely depend on the level of PGE₂ synthesis, the differential levels of expression of the different EP receptors, as well as the levels of expression of other interacting receptors. Understanding the role and mechanisms of action of the EP receptors potentially offers new targets for the prevention or therapy of NMSCs.

The EP1 receptor for prostaglandin E2 promotes the development and progression of malignant murine skin tumors

High levels of prostaglandin E2 (PGE2) synthesis resulting from the up-regulation of cyclooxygenase (COX)-2 has been shown to be critical for the development of non-melanoma skin tumors. This effect of PGE2 is likely mediated by one or more of its 4 G-protein coupled membrane receptors, EP1-4. A previous study showed that BK5.EP1 transgenic mice produced more carcinomas than wild type (WT) mice using initiation/promotion protocols, although the tumor response was dependent on the type of tumor promoter used. In this study, a single topical application of either 7,12-dimethylbenz[a]anthracene (DMBA) or benzo[a]pyrene (B[a]P), alone, was found to elicit squamous cell carcinomas (SCCs) in the BK5.EP1 transgenic mice, but not in WT mice. While the epidermis of both WT and transgenic mice was hyperplastic several days after DMBA, this effect regressed in the WT mice while proliferation continued in the transgenic mice. Several parameters associated with carcinogen initiation were measured and were found to be similar between genotypes, including CYP1B1 and aromatase expression, B[a]P adduct formation, Ras activity, and keratinocyte stem cell numbers. However, EP1 transgene expression elevated COX-2 levels in the epidermis and SCC could be completely prevented in DMBA-treated BK5.EP1 mice either by feeding the selective COX-2 inhibitor celecoxib in their diet or by crossing them onto a COX-2 null background. These data suggest that the tumor promoting/progressing effects of EP1 require the PGE2 synthesized by COX-2.

Chemoprevention of chemically induced skin tumorigenesis by ligand activation of peroxisome proliferator-activated receptor-beta/delta and inhibition of cyclooxygenase 2

Ligand activation of peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) and inhibition of cyclooxygenase-2 (COX2) activity by nonsteroidal anti-inflammatory drugs (NSAID) can both attenuate skin tumorigenesis. The present study examined the hypothesis that combining ligand activation of PPARβ/δ with inhibition of COX2 activity will increase the efficacy of chemoprevention of chemically induced skin tumorigenesis over that observed with either approach alone. To test this hypothesis, wild-type and Pparβ/δ-null mice were initiated with 7,12-dimethylbenz[a]anthracene (DMBA), topically treated with 12-O-tetradecanoylphorbol-13-acetate to promote tumorigenesis, and then immediately treated with topical application of the PPARβ/δ ligand GW0742, dietary administration of the COX2 inhibitor nimesulide, or both GW0742 and nimesulide. Ligand activation of PPARβ/δ with GW0742 caused a PPARβ/δ-dependent delay in the onset of tumor formation. Nimesulide also delayed the onset of tumor formation and caused inhibition of tumor multiplicity (46%) in wild-type mice but not in Pparβ/δ-null mice. Combining ligand activation of PPARβ/δ with dietary nimesulide resulted in a further decrease of tumor multiplicity (58%) in wild-type mice but not in Pparβ/δ-null mice. Biochemical and molecular analysis of skin and tumor samples show that these effects were due to the modulation of terminal differentiation, attenuation of inflammatory signaling, and induction of apoptosis through both PPARβ/δ-dependent and PPARβ/δ-independent mechanisms. Increased levels and activity of PPARβ/δ by nimesulide were also observed. These studies support the hypothesis that combining ligand activation of PPARβ/δ with inhibition of COX2 activity increases the efficacy of preventing chemically induced skin tumorigenesis as compared with either approach alone.

PGE(2) is a UVR-inducible autocrine factor for human melanocytes that stimulates tyrosinase activation

Prostaglandins activate signalling pathways involved in growth, differentiation and apoptosis. Prostaglandin E(2) (PGE(2)) is released by keratinocytes following ultraviolet irradiation (UVR) and stimulates the formation of dendrites in melanocytes. We show that multiple irradiations of human melanocytes with UVR-activated cPLA(2), the rate-limiting enzyme in eicosanoid synthesis and stimulated PGE(2) secretion. PGE(2) increased cAMP production, tyrosinase activity and proliferation in melanocytes. PGE(2) binds to four distinct G-protein coupled receptors (EP(1-4)). We show that PGE(2) stimulates EP(4) receptor signalling in melanocytes, resulting in cAMP production. Conversely, PGE(2) also stimulated the EP(3) receptor in melanocytes, resulting in lowered basal cAMP levels. These data suggest that relative levels or activity of these receptors controls effects of PGE(2) on cAMP in melanocytes. The data are the first to identify PGE(2) as an UVR-inducible autocrine factor for melanocytes. These data also show that PGE(2) activates EP(3) and EP(4) receptor signalling, resulting in opposing effects on cAMP production, a critical signalling pathway that regulates proliferation and melanogenesis in melanocytes.

Sphingosylphosphorylcholine down-regulates filaggrin gene transcription through NOX5-based NADPH oxidase and cyclooxygenase-2 in human keratinocytes

Sphingosylphosphorylcholine (SPC) mediates various inflammatory and behavioral responses in atopic dermatitis. Recent studies have shown that dysfunction of the epidermal permeability barrier itself plays a primary role in the etiology of atopic dermatitis. However, the effects of SPC on major proteins essential to the development of the epidermal permeability barrier such as filaggrin, loricrin, involucrin, keratin 1, keratin 10 and small proline-rich proteins are still unclear. In this study, we demonstrated that SPC significantly reduces filaggrin gene transcription, implying that SPC plays a pivotal role in impairment of the epidermal permeability barrier in atopic dermatitis lesional skin. In cultured normal human keratinocytes (NHKs), SPC increases the intracellular level of reactive oxygen species (ROS) and up-regulates NADPH oxidase 5 (NOX5) gene transcription. SPC also stimulates prostaglandin (PG) E(2) production by increasing cyclooxygenase (COX)-2 expression in NHK. The effects of the prostanoid EP receptor agonists, limaprost, butaprost, and sulprostone on filaggrin gene expression in NHK suggest that the prostanoid EP2 receptor plays a significant role in the PGE(2)-mediated filaggrin down-regulation. In contrast, limaprost and butaprost do not affect NOX5 expression in NHK, implying that the NOX5-regulated ROS pathway stimulated by SPC may be upstream of the COX-2 pathway. We propose that the increase in SPC levels further aggravates dermatological symptoms of atopic dermatitis through SPC-induced down-regulation of filaggrin in NHK.

The EP1 subtype of prostaglandin E2 receptor: role in keratinocyte differentiation and expression in non-melanoma skin cancer

We have previously demonstrated that the EP1 subtype of PGE2 receptor is expressed in the differentiated compartment of normal human epidermis and is coupled to intracellular calcium mobilization. We therefore hypothesized that the EP1 receptor is coupled to keratinocyte differentiation. In in vitro studies, radioligand binding, RT-PCR, immunoblot and receptor agonist-induced second messenger studies demonstrate that the EP1 receptor is up-regulated by high cell density in human keratinocytes and this up-regulation precedes corneocyte formation. Moreover, two different EP1 receptor antagonists, SC51322 and AH6809, both inhibited corneocyte formation. SC51322 also inhibited the induction of differentiation-specific proteins, cytokeratin K10 and epidermal transglutaminase. We next examined the immunolocalization of the EP1 receptor in non-melanoma skin cancer in humans. Well-differentiated SCCs exhibited significantly greater membrane staining, while spindle cell carcinomas and BCCs had significantly decreased membrane staining compared with normal epidermis. This data supports a role for the EP1 receptor in regulating keratinocyte differentiation.

Prostaglandin E(2)-EP(3) signaling suppresses skin inflammation in murine contact hypersensitivity

BACKGROUND

Prostaglandin (PG) E(2) exerts a variety of actions through 4 G protein-coupled receptors designated as EP(1), EP(2), EP(3), and EP(4). We have reported that PGE(2) acts on EP(3) in airway epithelial cells and exerts anti-inflammatory actions in ovalbumin-induced murine allergic asthma. Although EP(3) is also expressed in skin and PGE(2) is produced abundantly during skin allergic inflammation, the role of PGE(2)-EP(3) signaling in skin allergic inflammation remains unknown.

OBJECTIVE

We sought to investigate whether PGE(2)-EP(3) signaling exerts anti-inflammatory actions in skin allergic inflammation.

METHODS

We used a murine contact hypersensitivity (CHS) model and examined the role of EP(3) by using an EP(3)-selective agonist, ONO-AE-248 (AE248), and EP(3)-deficient mice. The inflammation was evaluated by the thickness and histology of the hapten-challenged ear. Inflammation-associated changes in gene expression and effects of AE248 were examined by means of microarray analysis of the skin. Localization of EP(3) was examined by staining for beta-galactosidase knocked in at the EP(3) locus in EP(3)-deficient mice. EP(3) action was also examined in cultured keratinocytes.

RESULTS

Administration of AE248 during the elicitation phase significantly suppressed CHS compared with that seen in vehicle-treated mice. Microarray analysis revealed that administration of AE248 inhibited the gene expression of neutrophil-recruiting chemokines, including CXCL1, at the elicitation site. X-gal staining in EP(3)-deficient mice revealed EP(3) expression in keratinocytes, which was further confirmed by anti-EP(3) antibody in wild-type mice. In cultured keratinocytes AE248 suppressed CXCL1 production induced by TNF-alpha.

CONCLUSION

PGE(2)-EP(3) signaling inhibits keratinocytes activation and exerts anti-inflammatory actions in murine CHS.

Chromosomal aberrations in UVB-induced tumors of immunosuppressed mice

In immunocompromised individuals, such as organ transplant recipients, the risk of cutaneous squamous cell carcinoma (SCC) is increased 60-250 fold, and there is an increased likelihood to develop aggressive, metastatic SCC. An understanding of the genes involved in SCC tumorigenesis is critical to prevent SCC-associated morbidity and mortality. Mouse models show that different immunosuppressive drugs lead to SCCs varying in size, number, and malignant potential. In this study, we used mouse models that mimic adult transplant recipients to study the effect of immunosuppressive drugs and UV light on SCC development. UV-induced tumors from six treatment groups, control, tacrolimus (Tac), rapamycin (Rap), cyclosporin (CsA), mycophenolate mofetil (MMF), and Rap plus CsA, were evaluated by array comparative genomic hybridization. Mouse SCCs appear to show similar genomic aberrations as those reported in human SCCs and offer the ability to identify genomic changes associated with specific and combinatorial effects of drugs. Fewer aberrations were seen in tumors of mice treated with MMF or Rap. Tumors from Tac-treated animals showed the highest number of changes. Calcineurin inhibitors (Tac and CsA) did not cluster together by their genomic aberrations, indicating their contribution to UV mediated carcinogenesis may be through different pathways. The combination treatment (Rap plus CsA) did not cluster with either treatment individually, suggesting it may influence SCC tumorigenesis via a different mechanism. Future studies will identify specific genes mapping to regions of aberration that are different between treatment groups to identify target pathways that may be affected by these drugs.

UVB light upregulates prostaglandin synthases and prostaglandin receptors in mouse keratinocytes

Prostaglandins belong to a class of cyclic lipid-derived mediators synthesized from arachidonic acid via COX-1, COX-2 and various prostaglandin synthases. Members of this family include prostaglandins such as PGE(2), PGF(2alpha), PGD(2) and PGI(2) (prostacyclin) as well as thromboxane. In the present studies we analyzed the effects of UVB on prostaglandin production and prostaglandin synthase expression in primary cultures of undifferentiated and calcium-differentiated mouse keratinocytes. Both cell types were found to constitutively synthesize PGE(2), PGD(2) and the PGD(2) metabolite PGJ(2). Twenty-four hours after treatment with UVB (25 mJ/cm(2)), production of PGE(2) and PGJ(2) increased, while PGD(2) production decreased. This was associated with increased expression of COX-2 mRNA and protein. UVB (2.5-25 mJ/cm(2)) also caused marked increases in mRNA expression for the prostanoid synthases PGDS, mPGES-1, mPGES-2, PGFS and PGIS, as well as expression of receptors for PGE(2) (EP1 and EP2), PGD(2) (DP and CRTH2) and prostacyclin (IP). UVB was more effective in inducing COX-2 and DP in differentiated cells and EP1 and IP in undifferentiated cells. UVB readily activated keratinocyte PI-3-kinase (PI3K)/Akt, JNK and p38 MAP signaling pathways which are known to regulate COX-2 expression. While inhibition of PI3K suppressed UVB-induced mPGES-1 and CRTH2 expression, JNK inhibition suppressed mPGES-1, PGIS, EP2 and CRTH2, and p38 kinase inhibition only suppressed EP1 and EP2. These data indicate that UVB modulates expression of prostaglandin synthases and receptors by distinct mechanisms. Moreover, both the capacity of keratinocytes to generate prostaglandins and their ability to respond to these lipid mediators are stimulated by exposure to UVB.

Prostaglandin E2 regulates melanocyte dendrite formation through activation of PKCzeta

Prostaglandins are lipid signaling intermediates released by keratinocytes in response to ultraviolet irradiation (UVR) in the skin. The main prostaglandin released following UVR is PGE(2), a ligand for 4 related G-protein-coupled receptors (EP(1), EP(2), EP(3) and EP(4)). Our previous work established that PGE(2) stimulates melanocyte dendrite formation through activation of the EP(1) and EP(3) receptors. The purpose of the present report is to define the signaling intermediates involved in EP(1)- and EP(3)-dependent dendrite formation in human melanocytes. We recently showed that activation of the atypical PKCzeta isoform stimulates melanocyte dendricity in response to treatment with lysophosphatidylcholine. We therefore examined the potential contribution of PKCzeta activation on EP(1)- and EP(3)-dependent dendrite formation in melanocytes. Stimulation of the EP(1) and EP(3) receptors by selective agonists activated PKCzeta, and inhibition of PKCzeta activation abrogated EP(1)- and EP(3)-receptor-mediated melanocyte dendricity. Because of the importance of Rho-GTP binding proteins in the regulation of melanocyte dendricity, we also examined the effect of EP(1) and EP(3) receptor activation on Rac and Rho activity. Neither Rac nor Rho was activated upon treatment with EP(1,3)-receptor agonists. We show that melanocytes express only the EP(3A1) isoform, but not the EP(3B) receptor isoform, previously associated with Rho activation, consistent with a lack of Rho stimulation by EP(3) agonists. Our data suggest that PKCzeta activation plays a predominant role in regulation of PGE(2)-dependent melanocyte dendricity.

Cyclooxygenase-2 inhibits UVB-induced apoptosis in mouse skin by activating the prostaglandin E2 receptors, EP2 and EP4

Cyclooxygenase-2 (COX-2) is induced by UVB light and reduces UVB-induced epidermal apoptosis; however, the mechanism is unclear. Therefore, wild-type (WT) and COX-2-/- mice were acutely treated with UVB (5 kJ/m(2)), and apoptotic signaling pathways were compared. Following exposure, apoptosis was 2.5-fold higher in COX-2-/- compared with WT mice. Because prostaglandin E(2) (PGE(2)) is the major UV-induced prostaglandin and manifests its activity via four receptors, EP1 to EP4, possible differences in EP signaling were investigated in WT and COX-2-/- mice. Following UVB exposure, protein levels of EP1, EP2, and EP4 were elevated in WT mice, but EP2 and EP4 levels were 50% lower in COX-2-/- mice. Activated cyclic AMP-dependent protein kinase (PKA) and Akt are downstream in EP2 and EP4 signaling, and their levels were reduced in UVB-exposed COX-2-/- mice. Furthermore, p-Bad (Ser(136) and Ser(155)), antiapoptotic products of activated Akt and PKA, respectively, were significantly reduced in UVB-exposed COX-2-/- mice. To further study the roles of EP2 and EP4, UVB-exposed CD-1 mice were topically treated with indomethacin to block endogenous PGE(2) production, and PGE(2), the EP2 agonist (butaprost) or EP4 agonist (PGE(1) alcohol), was applied. Indomethacin reduced PKA and Akt activation by approximately 60%, but PGE(2) and the agonists restored their activities. Furthermore, both agonists decreased apoptosis in COX-2-/- mice by 50%. The data suggest that COX-2-generated PGE(2) has antiapoptotic roles in UVB-exposed mouse skin that involves EP2- and EP4-mediated signaling.

Possible cross-regulation of the E prostanoid receptors

Exposure to UVB induces an inflammatory response in the skin that results in high levels of cyclooxygenase-2 (COX-2) and its enzymatic product, prostaglandin E2 (PGE(2)). PGE(2) signals via one of four E prostanoid (EP) receptors, EP1-4, but the roles of each of these receptors in UVB-mediated inflammation and skin carcinogenesis have not been fully defined. Topical application of ONO-8713, an EP1 antagonist, reduced the acute inflammatory effects of UVB irradiation. This compound also reduced UVB-induced tumor formation by approximately 50%, suggesting that signaling of PGE(2) via the EP1 receptor may play a role in UVB-mediated inflammation and carcinogenesis. Our laboratory has demonstrated that the EP1 receptor localized to the suprabasal layers of the epidermis and the EP3 receptor was found in the basal keratinocytes of unirradiated murine skin. While UVB exposure induced no change in the localization of the EP1 receptor, the EP3 receptor was detected in all layers of the epidermis in response to UVB. In mice that were topically treated with ONO-8713, UVB-induced changes in EP3 localization were prevented. This alteration in EP3 receptor localization was not seen following topical application of the anti-inflammatory drug celecoxib, indicating that the effects of ONO-8713 were not because of its anti-inflammatory properties. These results suggest a previously undescribed interaction between the EP1 and EP3 receptors in the epidermis.