Regulation of TNF alpha production and release in human and mouse keratinocytes and mouse skin after UV-B irradiation

TNF alpha is a primary cytokine responsible for inflammatory and immunosupp ressive responses in skin. After UV-B irradiation of cultured human keratin ocytes, we found that TNF alpha was released into the media, as monitored b y ELISA, and was bound to cells, as observed by immunofluorescence microsco py. The release of TNF alpha: into cell culture supernatant during the 24 h after UV-B irradiation was augmented by the addition of IL-1 alpha to the cells. Further, we found this secretion was unaffected by rapamycin, and th erefore independent of FRAP DNA-protein kinase mediated signal transduction , However, UV-B also induced expression of membrane-bound TNF alpha, and th is was dependent on FRAP signaling. In wild type mice, TNFa bound to skin i ncreased immediately after irradiation, declined at 6 h, and then pose agai n at 12 h before falling by 24 h, This pattern of induction was confirmed b y RT-PCR of TNF alpha mRNA message in cultured epidermal cells. Induction o f membrane-hound TNF alpha was also found in c-fos gene knockout mice defic ient in the AP-1 transcription factor, suggesting that, although AP-1 conta ining c-fos signaling is required for some UV responses, AP-1 containing c- fos is not required for this TNF alpha activation. However, in homozygous p 53 knockout mice the basal level of TNF alpha bound to the epidermis was gr eatly elevated without UV irradiation, This level declined and remained con stant following irradiation, This implies that p53 directly or indirectly r epresses TNF alpha gene expression and that modification of p53 mRNA stabil ity or phosphorylation of p53 protein after UV may be responsible for TNF a lpha induction in the membrane. Overexpression of the immunosuppressive cyt okine TNF alpha in this locale may contribute to the carcinogen-susceptibil ity of p53 knockout mice.