Tumor Necrosis Factor α-Mediated Induction of Interleukin 17C in Human Keratinocytes Is Controlled by Nuclear Factor κB

IL-17C is a member of the IL-17 family of cytokines. The expression of IL-17C has been demonstrated to be strongly induced by TNF alpha in human keratinocytes, and recently the level of IL-17C was found to be increased in the inflammatory skin disease psoriasis. However, little is known about the molecular mechanisms involved in the regulation of IL-17C. Here, we show that pretreatment of cultured human keratinocytes with the inhibitor of kappa B kinase 2 inhibitor, SC-514, resulted in a significant reduction in both IL-17C mRNA and protein expression, indicating the significance of this pathway in the regulation of IL-17C. NF-kappa B binding sites were identified upstream from the IL-17C gene, and by electrophoretic mobility shift assay NF-kappa B was shown to bind to all three identified binding sites. Moreover, NF-kappa B binding to these sites was inducible by TNF alpha Supershift analysis revealed binding of the NF-kappa B subunits p65 and p50 to all three NF-kappa B binding sites. To determine the contribution of NF-kappa B in IL-17C expression, we conducted luciferase gene reporter experiments and demonstrated that a 3204-bp promoter fragment of IL-17C containing three putative NF-kappa B binding sites was strongly activated by TNF alpha. Interestingly, mutations of the three NF-kappa B binding sites revealed that one specific NF-kappa B binding site was crucial for the TNF alpha-mediated IL-17C induction because mutation of this specific site completely abolished TNF alpha-induced IL-17C promoter activation. We conclude that the activation of NF-kappa B (p65/p50) is crucial for the TNF alpha-induced stimulation of IL-17C expression in human keratinocytes.