Glucocorticoid hormones are very potent inhibitors of physiological DNA synthesis in keratinocytes in vivo. These hormones are also very effective in preventing carcinogen- and tumor promoter-induced skin hyperplasia, inflamination, and mouse skin tumor formation when applied to skin together with a carcinogen or a tumor promoter. We and others have shown, however, that glucocorticoids do not affect the growth of either established papillomas, squamous ceil carcinomas (SCC), or transformed keratinocytes in vitro. In addition, we recently found that glucocorticoids do net affect glucocorticoid-responsive genes in transformed keratinocytes both;in vitro/and in vivo. The glucocorticoid control of cellular functions is mediated by the glucocorticoid receptor (GR), a well-known transcription factor. We have found that NF-KB transcription factor is constitutively activated in mouse skin tumors which appears to alter some of GR functions. We have also found that this activation of NF-KB is primarily due to up-regulation of SCFmHOS ubiquitin ligase. We have generated skin-targeted transgenic mice over-expressing GR under the control of keratin 5 (K5) promoter. These adult transgenic mice have impaired proliferative and inflammatory responses to skin tumor promoters. Our initial studies showed that K5.GR transgenic animals are resistant to /-as-induced tumorigenesis. The constitutively nuclear overexpression and activation of GR in the epidermis dramatically inhibited skin tumor development in K5.GR/ras+ double transgenic mice in terms of number of animals that develop tumors, number of tumors per animal, and tumor size. We propose to prove the hypothesis that GR functions as a tumor suppressor in mouse skin carcinogenesis. Pursuant to this goal, the specific aims are: 1) To develop animals deficient in the expression of GR in skin, and analyze their sensitivity to skin carcinogenesis. 2) To determine whether transrepression activities of GR are sufficient to suppress tumorigenic properties of mouse skin papilloma and carcinoma cell lines. 3) To determine the stage(s) of carcinogenesis where GR plays a role of tumor suppressor a) develop transgenic animals with the conditional expression of GR in skin (TRE.GR X K5.Tet-On). b) analyze the sensitivity of these mice to skin carcinogenesis, when over-expression of GR induced at different stages of tumor development. 4) To analyze the effects of dissociated glucocorticoids on skin inflammation, keratinocyte proliferation, and on skin tumor development.
