Transcriptional regulation of tumor necrosis factor-alpha in keratinocytes mediated by interleukin-1beta and tumor necrosis factor-alpha.

Irritant contact dermatitis (ICD) is an inflammatory skin reaction in which cytokines are thought to play a crucial role. In particular, tumor necrosis factor-alpha (TNF-alpha) has been implicated in the mechanism of this reaction. We report that interleukin-1beta (IL-1beta) that has been reported up-regulated in many inflammatory skin conditions is capable of increasing TNF-alpha mRNA and protein expression in murine keratinocytes. Furthermore, we show that TNF-alpha is capable of up-regulating itself in keratinocytes most likely in an autocrine manner. The signalling mechanisms involved in both IL-1beta- and TNF-alpha-mediated regulation of TNF-alpha are critically dependent upon protein kinase C (PKC), as demonstrated by blocking studies using protein kinase inhibitors. Furthermore, the increase in TNF-alpha mRNA expression seen after stimulation with rTNF-alpha and rIL-1beta involved increased transcription of TNF-alpha mRNA. This was demonstrated in a chloramphenicol acetyltransferase (CAT) assay using a CAT-construct containing the full-length TNF-alpha promoter. These observations support the notion of keratinocytes functioning as an amplifier of pro-inflammatory cytokine generation in the epidermis during ICD and other inflammatory skin conditions.