Interleukin IL-12 blocks a specific subset of the transcriptional profile responsive to UVB in epidermal keratinocytes

Interleukin-12 (IL-12) is a proinflammatory and immunomodulatory cytokine that plays a critical role it in innate and adaptive immunity by inducing production of interferon-γ and other cytokines. IL-12 was shown to block the ultraviolet light-induced immunosuppression, important in cancer immunosurveillance, cutaneous allergies and inflammation. To characterize the molecular effects of IL-12 in epidermis we used large DNA microarrays and defined the transcriptional changes in human epidermal keratinocytes 1 h, 4 h, 24 h, and 48 h after treatment with IL-12, as well as in cells treated with both IL-12 and UV light. In keratinocytes, IL-12 activates STAT3 and STAT4; surprisingly, despite activating these transcription factors, the transcriptional effects of IL-12 did not rise above background levels. However, pre-treatment of keratinocytes with IL-12 strongly modulated the transcriptional effects of UV. Pre-treatment with IL-12 enhanced the UV-mediated regulation of 20 and antagonized the regulation of 263 genes. IL-12 enhanced the induction of cytokines by UV. IL-12 antagonized the suppression of cytoskeletal, junctional, metabolic, mitochondrial, and extracellular matrix proteins, while antagonizing the induction of certain signaling proteins and RNA processing enzymes. We conclude that in the epidermis, IL-12 interferes with a specific subset of transcriptional effects of UV irradiation.