Regulation and role of interleukin 6 in wounded human epithelial keratinocytes

Dermal wounding is accompanied by inflammation and the resulting proinflammatory cytokines, including interleukin (IL)-6, are thought to play an important role in the repair process. IL-6 is produced by normal human keratinocytes to various dermatological diseases and we have recently shown it is also required for normal wound repair. However, neither the events responsible for its induction nor its role in repair have been clearly identified. Using a recently developed in vitro wounding model, we demonstrate that IL-6 mRNA is expressed and immunoreactive IL-6 is released from cultures of human epidermal keratinocytes (NHEKs) following wounding. The transcription factors, NF kappa B and NF-IL-6 (C/EBP beta), which coordinately help regulate IL-6 expression, were activated following wounding and preceded the appearance of IL-6. Addition of IL-1 alpha to NHEK cultures increased IL-6 production and activated NF kappa B and C/EBP beta. Addition of the IL-1 alpha receptor antagonist inhibited both IL-6 mRNA expression and the transcription factors following wounding. Immunoreactive IL-1 alpha was detected in the medium following wounding in the absence of new message. Furthermore, addition of IL-6 to NHEK cultures decreased the expression of keratins 1 and 10, differentiation markers of keratinocytes, while proliferation was not affected. Taken together, these data indicate that constitutive keratinocyte-derived IL-1 alpha is a stimulus for IL-6 production in wounded epidermis, the response involves NF kappa B and C/EBP beta transcription factors, and IL-6 may be associated with modulation of keratinocyte differentiation rather than proliferation.