Pharmacological and genetic approaches have shown that prostaglandins (PGs) synthesized by cyclooxygenase-2 (COX-2) have tumor promoting/progression activity in murine skin. To determine whether the EP4 receptor for PGE2 contributes to this tumor promoting/progression activity, EP4 over-expressing mice (BK5.EP4) were generated and subjected to several carcinogenesis protocols. A two-stage 7,12-dimethylbenz[a]anthracene (DMBA)-12-O-tetradecanoylphorbol- 13-acetate (TPA) protocol resulted in 25-fold more squamous cell carcinomas (SCCs) in the BK5.EP4 mice than wild type (WT) mice. A similar increase in SCCs was observed following treatment with DMBA alone (no TPA) and following UV irradiation. DMBA caused a cytotoxicity in BK5.EP4, but not WT mice, that was characterized by increased apoptosis, increased metalloproteinase(MMP)-9 and MMP-7 expression, and sloughing of the interfollicular epidermis, followed by regeneration and SCC development. An analysis of cytochrome P450 levels, wound healing time and keratinocyte stem cells showed no difference between BK5.EP4 and WT mice. 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, including interleukin-20 (IL-20), which was verified at the protein level, supporting a pro-tumorigenic role for the EP4 receptor.

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Chronic inflammation has recently been suggested to be involved in cancer development, and cyclooxygenase-2 (COX-2), a key mediator of the inflammatory response, is known to be upregulated in several cancers. COX-2 is responsible for the production of prostaglandins, and prostaglandin E2 (PGE2) is the major prostaglandin involved in inflammation. PGE2 binds to four receptors (EP1-EP4), and the EP4 receptor has recently been shown to be important in carcinogenesis depending on the tissue in which it is expressed. To determine the role of EP4 in skin carcinogenesis, transgenic mice were generated that overexpress EP4 in the basal layer of the skin under the control of the bovine keratin 5 promoter (BK5.EP4). Using a two-stage chemical carcinogenesis protocol, the BK5.EP4 mice were shown to develop both papillomas and squamous cell carcinomas earlier than wild type (WT) mice. However, a tumor observed before 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment on one BK5.EP4 mouse suggested that TPA was not necessary for the promotion of the tumors. Therefore a 7,12-dimethylbenz[a]anthracene (DMBA)-only carcinogenesis protocol was performed, and by 30 weeks, the BK5.EP4 mice again developed more carcinomas compared to none on the WT mice. Immunohistochemistry performed on DMBA-treated mice demonstrated that the BK5.EP4 epidermis began to detach 48 hours after treatment with total detachment occurring 5 days after treatment, while WT mice had only increased epidermal thickening. By 7 to 10 days after DMBA treatment, patches were observed on the BK5.EP4 skin where it appeared the hair and epidermis were detaching, which were not seen on the WT mice. MMP-9, MMP-7, and E-cadherin expression also were upregulated in the BK5.EP4 mice at the same time detachment of the epidermis was occurring. However, no differences in proliferation, stem cell numbers, or CYP1A1 and CYP1B1 expression have been observed. These data suggest that overexpression of EP4 in the mouse skin can increase tumorigenesis, possibly through the wounding of the skin and the subsequent inflammation and epidermal regeneration acting as a tumor promoter. Supported by CA100140. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2462.

Chronic inflammation has recently been suggested to be involved in cancer development, and cyclooxygenase-2 (COX-2), a key mediator of the inflammatory response, is known to be upregulated in several cancers. COX-2 is responsible for the production of prostaglandins, and prostaglandin E2 (PGE2) is the major prostaglandin involved in inflammation. PGE2 binds to four receptors (EP1-EP4), and the EP4 receptor has recently been shown to be important in carcinogenesis, depending on the tissue in which it is expressed. To determine the role of EP4 in skin carcinogenesis, transgenic mice were generated that overexpress EP4 in the basal layer of the epidermis under the control of the bovine keratin 5 promoter (BK5.EP4 Tg). Using a two-stage chemical carcinogenesis protocol, the BK5.EP4 Tg mice were shown to develop both papillomas and squamous cell carcinomas earlier than wild type (WT) mice. However, a tumor observed before 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment on one BK5.EP4 Tg mouse suggested that TPA was not necessary for the promotion of the tumors. Therefore a 7,12-dimethylbenz[a]anthracene (DMBA)-only carcinogenesis protocol was performed, and by 30 weeks, the BK5.EP4 Tg mice developed more carcinomas compared to none on the WT mice. Immunohistochemistry performed on DMBA-treated mice demonstrated that the BK5.EP4 Tg epidermis began to detach 48 hours after treatment with total detachment occurring 5 days after treatment, while WT mice had only increased epidermal thickening. Caspase-3, MMP-9, and MMP-7 expression also were upregulated in the BK5.EP4 Tg mice at the same time detachment of the epidermis was occurring. Ki67 analysis showed an initial increase in proliferation in WT mice that slowly declined back to normal levels, while the BK5.EP4 Tg mice instead had a sustained increase in proliferation, which occurred during reepithelialization of the epidermis. These data suggest that overexpression of EP4 in the mouse skin can increase tumorigenesis, possibly through the wounding of the skin and the subsequent epidermal regeneration acting as a tumor promoter. Supported by CA100140. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 912. doi:10.1158/1538-7445.AM2011-912