Regulation of TNF
production and release in human and mouse keratinocytes and mouse skin after UV-B irradiation
Authors: Yarosh D.1; Both D.1; Kibitel J.1; Anderson C.2; Elmets C.2; Brash D.3; Brown D.1
Source: Photodermatology Photoimmunology & Photomedicine, Volume 16, Number 6, 1 December 2000 , pp. 263-270(8)
Publisher: Blackwell Publishing
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Abstract:
TNF is a primary cytokine responsible for inflammatory and immunosuppressive responses in skin. After UV-B irradiation of cultured human keratinocytes, we found that TNF was released into the media, as monitored by ELISA, and was bound to cells, as observed by immunofluorescence microscopy. The release of TNF into cell culture supernatant during the 24 h after UV-B irradiation was augmented by the addition of IL-1 to the cells. Further, we found this secretion was unaffected by rapamycin, and therefore independent of FRAP DNA-protein kinase mediated signal transduction. However, UV-B also induced expression of membrane-bound TNF, and this was dependent on FRAP signaling. In wild type mice, TNF bound to skin increased immediately after irradiation, declined at 6 h, and then rose again at 12 h before falling by 24 h. This pattern of induction was confirmed by RT-PCR of TNF mRNA message in cultured epidermal cells. Induction of membrane-bound TNF was also found in c-fos gene knockout mice deficient in the AP-1 transcription factor, suggesting that, although AP-1 containing c-fos signaling is required for some UV responses, AP-1 containing c-fos is not required for this TNF activation. However, in homozygous p53 knockout mice the basal level of TNF bound to the epidermis was greatly elevated without UV irradiation. This level declined and remained constant following irradiation. This implies that p53 directly or indirectly represses TNF gene expression and that modification of p53 mRNA stability or phosphorylation of p53 protein after UV may be responsible for TNF induction in the membrane. Overexpression of the immunosuppressive cytokine TNF in this locale may contribute to the carcinogen-susceptibility of p53 knockout mice.
Keywords: c-fos; DNA damage; immunosuppression; skin cancer
Document Type: Original article
Affiliations: 1: Applied Genetics Inc. Dermatics, Freeport, New York 2: Department of Dermatology, Case Western Reserve University, Cleveland, Ohio 3: Department of Radiation Therapy, Yale University, New Haven, Connecticut, USA
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