Localization of prostaglandin H synthase isoenzymes in murine epidermal tumors: Suppression of skin tumor promotion by inhibition of prostaglandin H synthase-2

Abstract

The growth factor- and phorbol ester-inducible prostaglandin H synthase (PGHS)-2 has been found to be constitutively overexpressed in epidermal tumors generated by the initiation-promotion protocol in murine skin, whereas the expression of PGHS-1 does not change under these conditions. In this paper we report the intra-tumor distribution of the aberrantly expressed PGHS-2 and the cancer chemopreventive activity of a specific PGHS-2 inhibitor. By immunohistochemical methods using isoenzyme-specific antibodies, we found that the PGHS-1 protein was expressed in keratinocytes and Langerhans cells dispersed throughout the epithelial part of papillomas and squamous cell carcinomas and in inflammatory infiltrates occasionally seen in these tumors. A uniform pattern of PGHS-2 expression was observed in the basal keratinocytes of papillomas and in the follicular keratinocytes of carcinomas. In addition, Langerhans cells as well as tumor-associated inflammatory infiltrates exhibited PGHS-2-specific immunoreactivity. PGHS-2-catalyzed prostaglandin synthesis stimulated by the phorbol ester 12-O-tetradecanoylphorbol-13 acetate (TPA) in mouse epidermis in vivo was dose-dependently suppressed by topical administration of SC-58125, a specific PGHS-2 inhibitor. TPA-induced edema formation, epidermal DNA synthesis, and mitotic activity were not impaired by SC-58125 applied at a dose that inhibited TPA-induced prostaglandin E2 synthesis. However, the repetitive epicutaneous administration of SC-58125 substantially and significantly suppressed papilloma development. Malignant progression of papillomas was slightly retarded by the drug. These results indicate that aberrant expression of PGHS-2 in epidermal tumors may be a relevant target for prevention of epidermal cancer development in experimental animals and that the PGHS-2-specific inhibitor SC-58125, which is a potent inhibitor of tumor promotion in mouse skin, may be important for cancer chemoprevention in humans as well.

UVB light upregulates prostaglandin synthases and prostaglandin receptors in mouse keratinocytes

“…Increased expression of this enzyme has been directly associated with many UVB-induced skin inflammatory reactions including edema, erythema, keratinocyte proliferation and epidermal hyperplasia (Rodriguez-Burford et al, 2005). Changes in COX-2 expression have also been linked to the accumulation of DNA damage and mutations, as well as the development of premalignant lesions and skin cancer (Muller-Decker et al, 1998;Fischer et al, 2007). We found that COX-2 mRNA and protein were increased in mouse keratinocytes following UVB exposure.…”

Abnormal differentiation of epidermis in transgenic mice constitutively expressing cyclooxygenase-2 in skin

“…In fact, there is ample evidence that pharmacological (12,15,17) or genetic (44) inactivation of COX-2 may result in a strong inhibition of mouse skin carcinogenesis, pointing to a causal relationship between COX-2 expression and the development of squamous cell carcinomas in skin.…”

“…Using the experimental protocol of multistage carcinogenesis in mouse skin (9), we found aberrant COX-2 expression to be associated with the promotion stage (12,15), where initiated keratinocytes harboring a Ha-ras mutation clonally expand into preneoplastic papillomas, some of which subsequently develop into carcinomas. The close interrelation between COX-2 expression and inflammation (16), wounding (7), and skin carcinogenesis (14,15,17) prompted us to analyze the possible consequences of an aberrant overexpression of COX-2 in epidermal tissue in vivo.…”

“…Immunoprecipitation of COX-2 and COX-1 as well as immunoblot analysis were carried out by using isoenzyme-specific antisera as described (6,15).…”

“…Epidermal thickness was determined at regular intervals of H&E-stained sections by means of the AXIOVISION 2.05 software (Zeiss). COX isozymes were immunodetected by using 5-m cryosections (6,15). K i -67, keratin 10, loricrin, and CD31 stainings were performed according to the same protocol, except that 1% ELISA-BSA in PBS was used as blocking solution and sections were fixed in acetone for 10 min.…”