Background/Purpose: Cutaneous lupus erythematosus (CLE) affects up to 70% of patients with systemic lupus erythematosus (SLE), and type I interferons (IFNs) are important promoters of SLE and CLE. Our previous work identified IFN-kappa (IFNκ), a keratinocyte-produced type I IFN, as upregulated in non-lesional and lesional lupus skin and a critical regulator for enhanced UVB-mediated cell death in SLE keratinocytes. Importantly, the molecular mechanisms governing regulation of IFNκ expression have been relatively unexplored. Thus, this study sought to identify critical regulators of IFNκ and identified a novel role for IFN beta (IFNβ).

Methods: Human N/TERT keratinocytes were treated with the RNA mimic poly (I:C) or 50 mJ/cm² ultraviolet B (UVB), followed by mRNA expression quantification by RT-qPCR in the presence or absence of the JAK1 inhibitor baricitinib (BARI) or a neutralizing antibody to the type I IFN receptor (IFNAR). IFNB, MYD88, IFNK, STAT1, and TMEM173 knockout (KO) keratinocytes were generated using CRISPR/Cas9.

Results: Time courses of poly-IC and UVB treatment revealed a differential expression of IFN genes: IFNβ was upregulated between 3-6 hours and IFNκ was upregulated 24 hours after stimulation. Intriguingly, while the upregulation of IFNβ and IFNκ was inhibited by baricitinib, only IFNκ expression was substantially abrogated by neutralizing antibodies to IFNAR, suggesting that only IFNκ upregulation required type I IFN signaling for induction. This was confirmed using STAT1 KO keratinocytes which exhibited normal upregulation of IFNB but no upregulation of IFNK after poly-IC and UVB. The sequential nature of transcription, specifically IFNB followed by IFNK upregulation with both poly-IC and UVB treatment suggests that IFNβ1 may play a role in regulation of IFNk induction in KC. Indeed, IFNB1 KO keratinocytes abrogated IFNK induction and the downstream IFN-stimulated gene MX1 expression in response to either PolyIC or UVB, suggesting that robust IFN-κ production is dependent on an initial upregulation of IFNB.

Conclusion: Collectively, our work describes a novel mechanistic paradigm in keratinocytes in which initial IFNK induction in response to PolyIC and UVB is IFNβ1-dependent. Loss of this regulatory dependence in SLE keratinocytes could be an explanation as to why IFNκ is increased in SLE skin. Further experiments to determine if this mechanism is intact or skewed in SLE keratinocytes are ongoing.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/a-novel-requirement-for-ifn%ce%b21-signaling-for-ifn%ce%ba-induction-in-keratinocytes/