The NF-κB, p38 MAPK and STAT1 pathways differentially regulate the dsRNA-mediated innate immune responses of epidermal keratinocytes

The epidermis is the primary boundary between the body and the environment, and it serves as the first line of defense against microbial pathogens. Production of chemokines and cytokines is an important step in the initiation of innate immune responses to viral infections. Epidermal keratinocytes produce IFN-alpha, -beta and macrophage inflammatory protein (MIP)-1 alpha in response to double-stranded RNA (dsRNA) or viral infections. We showed that human keratinocytes produced cytokines [tumor necrosis factor (TNF)-alpha, IL-1 beta and IL-15] and chemokines [MIP-1 beta, RANTES and liver and activation-regulated chemokine (LARC)] in response to dsRNA, with activation of the nuclear factor kappa B (NF-kappa B), p38 mitogen-activated protein kinase (MAPK) and signal transducers and activators of transcription 1 (STAT1) pathways. To study the roles of these pathways in their production, we transfected keratinocytes with adenoviral vectors (Ax) carrying a dominant-negative form of inhibitor kappa B alpha (I kappa B alpha) (I kappa B alpha M), a dominant-negative mutant form of STAT1 (STAT1F) or suppressors of cytokine signaling 1 (SOCS1). Transfection with AxI kappa B alpha M or addition of a p38 inhibitor (SB203580) significantly decreased the dsRNA-mediated production of TNF-alpha, IL-1 beta and MIP-1 alpha, but not of IFN-beta, IL-15, MIP-1 beta, RANTES or LARC. Transfection with AxSTAT1F or AxSOCS1 inhibited the dsRNA-mediated production of TNF-alpha, IL-15, MIP-1 alpha, MIP-1 beta, RANTES and LARC, but not IFN-beta or IL-1 beta. In conclusion, the NF-kappa B, p38 MAPK and STAT1 pathways differentially regulate dsRNA-mediated innate immune responses in epidermal keratinocytes.