Transcriptional regulation of tumor necrosis factor‐α in keratinocytes mediated by interleukin‐1β and tumor necrosis factor‐α

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.