NICKEL AND SKIN IRRITANTS UP-REGULATE TUMOR-NECROSIS-FACTOR-ALPHA MESSENGER-RNA IN KERATINOCYTES BY DIFFERENT BUT POTENTIALLY SYNERGISTIC MECHANISMS

A critical role of tumor necrosis factor (TNF)-alpha in irritant conta ct dermatitis and in the challenge phase of allergic contact dermatiti s has recently been demonstrated in vivo, As in situ hybridization stu dies have indicated that keratinocytes were the cellular source of TNF -alpha in these reactions, we studied the mechanisms of TNF-alpha mRNA induction in keratinocytes by agents that induce contact dermatitis. Murine la(-)/CD3(-) epidermal cells were stimulated with phorbol myris tate acetate (PMA), dimethylsulfoxide (DMSO), sodium dodecyl sulfate ( SOS) and NiSO4, all of which up-regulated epidermal cell TNF-alpha mRN A production, In contrast, trinitrobenzenesulfonic acid and trinitroch lorobenzene did not significantly up-regulate TNF-alpha mRNA, These re sults were confirmed with murine keratinocyte cell lines, In keratinoc ytes transfected with a chloramphenicol acetyltransferase construct co ntaining the -1059 to +138 base pair TNF-alpha promoter, increased pro moter activity was observed upon stimulation with PMA and DMSO, In add ition, PMA stimulation did not affect the stability of TNF-alpha mRNA, The PMA- but also the DMSO- and SDS-induced up-regulation of TNF-alph a mRNA was abolished by an inhibitor of protein kinase C (PKC), In con trast, NiSO4 up-regulated TNF-alpha mRNA by a PKC-independent mechanis m, did not increase TNF-a promoter activity, but markedly increased th e stability of the TNF-alpha mRNA, Co-stimulation with PMA and NiSO4 i nduced a marked increase in TNF-alpha mRNA over that obtained with eac h agent alone, Thus, whereas PKC-dependent irritants act by up-regulat ing TNF-alpha promoter activity, nickel acts via post-transcriptional regulation. Our results also establish that some irritants and irritan t sensitizers directly induce TNF-alpha in keratinocytes without inter mediate Langerhans cell-derived signals.