A TGF-ß- and p63-Responsive Enhancer Regulates IFN-κ Expression in Human Keratinocytes.

Type I IFNs have antiviral and immune-modulating activities. IFN-α/-ß have very low basal expression levels but are strongly induced upon activation of pattern recognition receptors. In contrast, IFN-κ is constitutively expressed in uninfected keratinocytes and responds only weakly to pattern recognition receptor activation. IFN-κ expression has been implicated in the pathogenesis of inflammatory skin diseases and in limiting human papillomavirus replication in human keratinocytes. We have identified an enhancer ∼5 kb upstream of the IFNK gene driving its expression in keratinocytes. The enhancer consists of binding sites for the transcription factors jun-B, SMAD3/4, AP-2α/γ, and p63, of which the latter two are key regulators of keratinocyte biology. The jun-B and SMAD3/4 elements confer activation by the TGF-ß pathway. Furthermore, inhibition of ERK1/2 kinases activates IFN-κ expression. Our study provides a framework for the cell type-specific, constitutive expression of IFN-κ and its modulation by signal transduction pathways in human keratinocytes.

Interferon Kappa Inhibits Human Papillomavirus 31 Transcription by Inducing Sp100 Proteins.

UNLABELLED: High-risk human papillomaviruses (hr-HPV) establish persistent infections in keratinocytes, which can lead to cancer of the anogenital tract. Interferons (IFNs) are a family of secreted cytokines that induce IFN-stimulated genes (ISGs), many of which display antiviral activities. Transcriptome studies have indicated that established hr-HPV-positive cell lines display a reduced expression of ISGs, which correlates with decreased levels of interferon kappa (IFN-κ), a type I IFN constitutively expressed in keratinocytes. Prior studies have also suggested that IFN-ß has anti-hr-HPV activity but the underlying mechanisms are not well understood. The downregulation of IFN-κ by hr-HPV raises the possibility that IFN-κ has anti-HPV activity. Using doxycycline-inducible IFN-κ expression in CIN612-9E cells, which maintain extrachromosomally replicating HPV31 genomes, we demonstrated that IFN-κ inhibits the growth of these cells and reduces viral transcription and replication. Interestingly, the initiation of viral early transcription was already inhibited at 4 to 6 h after IFN-κ expression. This was also observed with recombinant IFN-ß, suggesting a common mechanism of IFNs. Transcriptome sequencing (RNA-seq) analysis identified 1,367 IFN-κ-regulated genes, of which 221 were modulated >2-fold. The majority of those (71%) matched known ISGs, confirming that IFN-κ acts as a bona fide type I IFN in hr-HPV-positive keratinocytes. RNA interference (RNAi) and cotransfection experiments indicated that the inhibition of viral transcription is mainly due to the induction of Sp100 proteins by IFN-κ. Consistent with published data showing that Sp100 acts as a restriction factor for HPV18 infection, our results suggest that hr-HPV target IFN-κ to prevent Sp100 expression and identify Sp100 as an ISG with anti-HPV activity. IMPORTANCE: High-risk HPV can establish persistent infections which may progress to anogenital cancers. hr-HPV interfere with the expression of interferon (IFN)-stimulated genes (ISGs), which is due to reduced levels of IFN-κ, an IFN that is constitutively expressed in human keratinocytes. This study reveals that IFN-κ rapidly inhibits HPV transcription and that this is due to the induction of Sp100 proteins. Thus, Sp100 represents an ISG for hr-HPV.